Drinking Water Hygiene. Water Supply Circulation Systems

Transcription

1 Drinking Water Hygiene Water Supply Circulation Systems

2 Preface to fourth edition Preface to fourth edition 2

3 This fourth edition of the Kemper Geberit Circulation Manual has been completely revised. The coming into force of the amended European Drinking Water Regulations and related plumbing codes and standards has given drinking water hygiene a new importance, particularly in relation to public buildings such as care homes and hospitals. In fulfilling its duty of care to the public, the operator is now responsible for ensuring the quality of drinking water in building supply systems meets these requirements. Particularly in medical facilities, the monitoring health authorities tend to demand a more extensive test regime, for legionellae or pseudomonads for example, and sometimes stipulate drastic measures where results are positive. The authors have therefore completely revised the entire "Hygiene" chapter of this technical manual in light of the latest findings. The "Circulation system hydraulics" section was written and extensively supplemented by Professor Rickmann. Aspects directly related to the design and installation of circulation systems are taken into account, and typical practical decontamination measures explained. The hygiene information is based on Council Directive 98/ 83/EC on the quality of water intended for human consumption and the amended Drinking Water Regulations brought into force on 1 January The design examples for circulation systems are based on the principles established in the DVGW codes of practice. Kemper, Geberit and the authors will gladly answer any questions or offer further advice. Kemper GmbH + Co. KG Geberit International AG Ullrich Petzolt Martin Ziegler Olpe, February

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5 Dr Werner Mathys (Lecturer) Universitätsklinikum Münster Institute of Hygiene, Department of Environmental Hygiene Professional development and experience: Read Biology and Chemistry at the Westfälische Wilhelms-Universität Münster 1975 Award of Doctorate by the WWU Münster From 1975 Member of staff of the Institute of Hygiene of the WWU Münster From 1976 Head of Water, Soil and Air Hygiene Laboratories 1990 Accredited as Specialist in Hospital Hygiene by the Federal Office of Health (now RKI) in Berlin 1994 Completion of requirements and award of postdoctoral lecturing qualification in "Hygiene" by the Medical Faculty of the WWU Münster Recognised by the German Accreditation Council as Expert Assessor for Accreditation of Medical Laboratories From 2001 Deputy Head of the Institute of Hygiene and Head of the Department of Hygiene Professor Bernd Rickmann Fachhochschule Münster Department of Energy and the Built Environment Professional development and experience: Apprenticeship as "Plumber and Fitter" Studied "Heating and Sanitary Engineering" at the Staatliche Ingenieurakademie für Bauwesen in Berlin, and "Energy and Process Engineering" at the Technische Universität Berlin Technical Manager of Sanitary and Heating Engineering business From 1980 Professorship at the Fachhochschule Münster. Specialisms: "Plumbing & Hospital Engineering" and "Computer Aided Design" Member of CEN, DIN, DVGW and VDI committees Member of VDI and other committees 5

6 Content 1 Hygiene in water systems - basic principles of microbiology of drinking water, health risks posed by pathogens, protection Biofilms Cold water Pseudomonas aeruginosa Basic design and installation rules Pressure test Commissioning Flushing system Operating water supply system Hot water Atypical mycobacteria Legionellae Diseases caused by legionellae (legionellosis) Channel of infection Sources of proliferation and exposure Hot water system as source of infection Mode of operation Practical consequences and concepts Legislation Frequently asked questions Determining pipe diameters for hot and cold water Available pressure differential Calculating flow rates Flow velocities Water company meters Equipment Switching pressure differential of group of water heaters Floor pressure drop Pressure drops in pipes Pressure gradient due to pipe friction Detailed calculations Simplified calculations Designing flow path producing worst hydraulic conditions Balancing calculations Circulation systems Design principles Main distribution systems Bottom distribution system, side feed Bottom distribution system, central feed Tichelmann distribution system Top circulation collection manifold Liner circulation in hot water risers Protection against ingress of non-drinking water Floor systems

7 litre rule Circulation to points of use Design methods for circulation systems Short method Simplified and detailed methods Circulation flow rate Temperature drop in circulation circuit Determining pipe diameter and pump pressure differential Sizing circulation liners in hot water risers Special features Determining circulation flow rates Minimum flow rate in riser Regulation k V -range required for circulation regulating valves Available regulation technology Static circulation regulating valves Multi-Fix riser regulating valve Presettable isolating valve Thermostatic circulation regulating valves Multi-Therm riser regulating valve Eta-Therm floor regulating valve Commissioning a circulation system Verifying regulation through numerical simulation Bottom distribution system, side feed Top distribution system, central feed Tichelmann distribution system Top circulation collection manifold Liner circulation in hot water risers Circulation to points of use System decontamination Eliminating pipes with stagnant water Disinfection Unregulated system System regulated with thermostatic circulation regulating valves Verification of disinfection temperatures Configuration supporting thermal disinfection Increasing temperature in existing hot water supply systems System survey Temperature measurements Flow rate measurements Pressure differential measurements Diagnostics Water heating system Switching off circulation pump Backflows, circulation failure

8 Inadequate circulation flow rate Circulation pumps Check valves Heat exchangers Undersized pipes Regulating valves Excessive circulation flow rate Follow-up tests Design example Hot water supply pipes Floor pressure drop Floor water meter Filter Available pressure differential p verf calculated using simplified method Determining pipe diameter and calculating pressure drop Circulation system Design assumptions Calculating circulation flow rates Calculating diameters of circulation pipes Circulation pump delivery pressure Designing circulation regulating valves Temperature drop in circulation circuit Tables, charts and forms Forms Glossary

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10 1 Hygiene in water systems - basic principles of microbiology of drinking water, health risks posed by pathogens, protection Dr Werner Mathys (Lecturer), Dr Elisabeth Junge-Mathys, MD, Institute of Hygiene of the Universitätsklinikum Münster 1Hygiene in water systems - basic principles of microbiology of drinking water, health risks posed by pathogens, protection Dr Werner Mathys (Lecturer), Dr Elisabeth Junge-Mathys, MD, Institute of Hygiene of the Universitätsklinikum Münster It is commonly assumed that drinking water poses no risk to health. People are completely unaware of the potential danger from pathogens in the water from a building's supply system. Continuous development and the growing complexity of water supply systems have given rise to new, previously largely unknown risks from microorganisms not originating from sewage. This is particularly the case where building (hospital, care home, hotel, etc) water supply systems take the form of involved networks. Pathogens of this type are sometimes not adequately detected by conventional techniques, and the public and even experts often seriously underestimate their importance. Recent investigations show the water supply system is important as a source of infection not only with legionellae, but also other microorganisms, particularly Pseudomonas aeruginosa. This means both hot and cold supply systems must be considered in this respect. Section 3 of the new Drinking Water Regulations (2001) now covers building water supply systems and imposes quality requirements. This has an impact on the duty of care of the operator, who is responsible in the event of waterborne diseases arising. Practical studies show that serious infringements of the basic rules of hygiene arising in the course of design, installation and operation can often lead to stubborn microbial contamination of the water supply system. The following should be mentioned as potential risk factors for contamination of the building's cold water and sometimes its hot water system: Inappropriate design (for example, oversizing of storage vessels and pipes) Irregularly used sections of pipework with stagnant water Defective, inexpert installation Use of unsuitable materials and components Operation in contravention of regulations Temperature is excess of 20 ºC in cold water system Conditions favouring biofilm formation Inappropriate leak testing prior to commissioning Inappropriate commissioning The presence and extent of biofilms have a particularly important effect on the microbiological quality of drinking water in supply systems. 1.1 Biofilms Biofilms consist of bacterial, fungal and/or algal cells and an intracellular matrix (mucuses) that facilitates a build-up of iron or limescale deposits. Biofilms colonise all interfaces on which microbial growth is possible, such as the walls of pipes, storage vessels and equipment. Under these conditions microorganisms arise as mixed rather than pure culture. Pathogens such as legionellae or pseudomonads can also be associated with the biofilm and use it as a shield against otherwise adverse living conditions. Insufficient chlorination, for example, only leads to deactivation of the surface layer, leaving deeper layers of the biofilm untouched. Bacteria can continually replenish themselves in these deeper zones as some become entrained in the flow of water. Conventional microbiological checks only detect these "planktonic" bacteria. However, they represent just a tiny fraction of microorganisms present in the biofilms. Biofilm growth is favoured by water stagnation, low flow rates and the nutrient content of the water. In order to have a lasting effect, decontamination concepts that endeavour to eliminate or reduce bacteria in water supply systems must always aim to shrink or even get rid of the biofilms. The occurrence of biofilms in the overall water supply system also reveals the fact that ad hoc measures often fail to achieve the required success, since they generally only affect the free-swimming organisms. Water systems must therefore be designed, installed, operated and maintained in such a way that they do not favour the growth or formation of biofilms or microorganisms (see also VDI 6023). This generally requires: Installation using materials that where possible do not release any exploitable nutrients The avoidance of water stagnation The avoidance of unnecessary storage of the water Appropriate draw-off rates in accordance with regulations and design assumptions 10

11 The avoidance of temperature ranges that promote the growth of bacteria in general and pathogens in particular The most important microorganisms that can multiply in water supply systems and contribute to microbial problems include legionellae and atypical mycobacteria in hot water, and pseudomonads and other heterotrophic bacteria in cold water. 1.2 Cold water In addition to faecal indicators such as Escherichia coli, coliform bacteria and enterococci, which can indicate ingress from non-drinking water systems, in cold water supplies unspecific contaminations (increase in the number of colony forming units - CFU) and contamination by pseudomonads are important Pseudomonas aeruginosa Pseudomonas aeruginosa is a ubiquitous bacterium capable of colonising any moist niche. It occurs regularly in sewage, surface waters, plants, fruits, food, damp soil, damp cleaning cloths and sponges, washbasin traps, gullies, even in disinfectant solutions. On a culture medium it grows and produces a green pigment. Pseudomonads are characterised by their extremely modest nutritional needs and ability to multiply even at temperatures below 15 C. These attributes enable them to contaminate any water including drinking water. The most common form of contamination is localised, for example of point-of-use fittings. These are easily colonised via splashes from contaminated traps. Even non-touch fittings can be identified as a source of pseudomonads. Pseudomonas aeruginosa is familiar outside hospitals as a cause of skin infections such as whirlpool dermatitis and folliculitis, and otitis externa (infection of the ear canal) associated with swimming pools. Extremely high doses of the bacterium generally never achieved in water supply systems are needed for these infections. There is virtually no risk of a person in normal health becoming infected with P. aeruginosa. In the medical sector, however, it is one of the most common causative organisms of often fatal wound, urinary tract and airway infections. In such cases these organisms are generally transferred by being drawn into sensitive equipment such as ventilators, etc. Even in their own homes patients with inherited cystic fibrosis (mucoviscidosis) are particularly susceptible to airway infections. Terminal, non-systematic contamination is the most common source of hospital-acquired infections. Practically all available reports relate to this type of infection source. Sampling is of paramount importance here. It must allow clear identification of the source and extent of the contamination (see Sampling below). Recently, contamination of entire water supply systems with Pseudomonas aeruginosa has been increasingly reported. The various causes can arise anywhere in the chain from design through installation to operation. Commissioning in particular is very important Basic design and installation rules Fig 1 Culture of Pseudomonas aeruginosa on a culture medium, showing formation of typical green pigment (pyocyanin) The following list of typical weak points makes no claims to completeness. All of the materials and processes that can provide a vehicle for ingress of the substance (such as soil, dirt, animals, dirty water or residues) containing bacteria into a water supply system must be considered as possible sources. Pipes, equipment and valves must be sized for the intended use 11

12 Hygiene in water systems - basic principles of microbiology of drinking water, health risks posed by pathogens, protection Only clean and dry installation materials may be used. Caps and plugs may only be removed (for example from pipes or point-of-use fittings) immediately prior to installation. After commissioning, points of use must be used regularly at adequate flow rates. This applies even if a building is not being or cannot be used. As far as possible heat transfer from hot water pipes to cold water pipes must be prevented. The aim must be to keep the cold water temperatures permanently below 25 C and preferably below 20 C. "Wet" fire mains connected to the drinking water supply system cannot be operated in such a way as to achieve reliable hygiene. This type of fire main may only be installed if expressly required by the fire authority (see also VDI 6023) Pressure test Leak tests with water to DIN 1988 Part 2, 11.1 may only be performed with completely hygienic filtered drinking water, and are only permitted provided it is ensured (see also proceedings of the Consensus Conference of 31 March 2004 in Bonn): that the building service connection has been flushed and approved for connection and operation, or the site water connection is hygienically suitable for filling the system and the microbiological requirements of the Drinking Water Regulations (2001) are met. In addition to the requirements of Annex 1 to these regulations the scope of testing should be extended to include Pseudomonas aeruginosa, at least in hospitals and care homes. that the pipe system is filled through completely hygienic components; the use of hoses must be avoided. that no more than 48 hours may elapse between leak test with drinking water and commissioning in accordance with the regulations. To ensure proper hygiene, testing with drinking water and subsequent isolation and draining is never permitted. Water supply systems that cannot be commissioned immediately (within 48 hours) after the pressure test must be tested in accordance with the safety requirements with unlubricated compressed air or nitrogen. The test may be carried out in sections (see also explanatory notes of the ZVSHK St. Augustin's Leak Testing of Water Supply Systems) Commissioning System commissioning must be timed to ensure continuous subsequent operation. The system must be handed over to the operator/user immediately afterwards. At the time of handover the representative of the operator/ user also takes over responsibility for completely hygienic operation. The manufacturer must record system installation details and produce operating instructions, and hand this documentation over to the operator at the time of commissioning Flushing system Only completely hygienic drinking water or compressed air may be used. The water used for flushing must be checked to ensure it is of drinking quality as defined in Annex 1 of the Drinking Water Regulations (2001). In large buildings the test spectrum must also include Pseudomonas aeruginosa. Flushing must be performed immediately prior to commissioning a new system, and when recommissioning an existing system or sections that for operational reasons have been out of use for a long time. In healthcare facilities the system must not be approved for use until a flawless microbiological hygiene test report (also confirming freedom from P. aeruginosa in 100 ml) is available. If disinfection of the water is necessary when filling for the first time, adequate disinfection capacity at a terminal point of use must be demonstrated. The microbiological condition of the water at terminal points must be checked in accordance with the Drinking Water Regulations (2001). It is advisable to also check for the presence of Pseudomonas aeruginosa Operating water supply system It is highly advisable to check the microbial condition of the entire water supply system before a building is handed over to the user. This necessitates carrying out an initial risk analysis, for example using the Hazard Analysis Critical Control Point (HACCP) concept tried and tested in the food industry. The approach could take the following form: 1 Comprehensive documentation of the water supply system 2 Specification of critical control points and aspects that could impair water quality: supply, equipment (such as softeners, metering systems, filters, storage vessels or distribution manifolds), transfer points (such as pressure boosting systems, peripheral buildings, fully demineralised water, wet/dry fire main or drinking water systems) 3 Specification of descriptive control points representative of the system (for example at risers, circulation returns, floor distribution systems, most remote areas, etc) 4 Installation of special valves allowing appropriate sampling at all control points 5 The building must be brought to life by using water! 12

13 Hygiene in water systems - basic principles of microbiology of drinking water, health risks posed by pathogens, protection 6 Microbiological testing of the water quality (inclusion of Pseudomonas aeruginosa recommended) at all control points. The frequently encountered practice of taking only 1 or 2 samples from the periphery is completely inadequate for large buildings such as hotels, hospitals and care homes. To enable an appropriate response the test regime should be capable of identifying a potential source of contamination when first applied. 7 Handover to operator only when perfect microbiological test results available. During the handover the operator in particular must arrange for regular and complete changing of the drinking water at all points of use until the system is operating in accordance with the regulations and as intended. This is one of the most important measures for maintaining good drinking water quality. Without adequate changing of the water even decontamination measures are generally unsuccessful. It is advisable to formulate a plan with clear instructions specifying exactly where and how often water must be drawn off. The Drinking Water Regulations (2001) (11) only allow materials notified by the German Federal Ministry of Health and Social Security in a list in the Federal Health Bulletin to be used for disinfection. All measures must be carefully documented. After necessary decontamination the standard of microbiological hygiene must be re-tested and documented. 1.3 Hot water Even if the cold water is in perfect microbiological condition, specific colonisations with "hot water bacteria" can arise in hot water within certain temperature ranges. For hot water as well it makes sense to establish an HACCP concept in the design phase and include suitable sampling points. sources of infection, effective preventive measures and the importance of atypical mycobacteria for the general public. Measures to reduce legionellae can also be expected to be effective in reducing mycobacteria Legionellae Legionellae are among the most important causes of environmental infections in all buildings, particularly in hospital facilities, and will therefore now be described in detail. As a result of their high mortality rate and epidemiological character, diseases caused by legionellae are often very spectacular and are therefore reported with newspaper headlines, such as Killer Bacteria Strike During Sale, Bacteria Lurking in the Shower or Killer Bacteria Visit the Queen, that create great uncertainty amongst the public. The first outbreak described took place in 1976 in the Bellevue Stratford Hotel in Philadelphia at the annual convention of the American Legion of Philadelphia. The 221 guests contracted a severe pneumonia. Despite inpatient treatment in the nearby hospitals 29 died and the event was characterised by anxiety and hysteria. As it was mainly veterans who were affected, the press and television dubbed this illness Legionnaires' or Veterans' disease. It was not until six months after this outbreak that McDade, a member of the staff of the Center for Disease Control (CDC) in Atlanta, managed after an intensive search to isolate a previously unknown bacterium. This bacterium was completely unrelated to microorganisms described in the past and cannot be detected with conventional microbiological methods. It was named Legionella pneumophila. More than 35 other species and 50 subgroups have now also been described Atypical mycobacteria Mycobacteria such as M. gordonae, M.kansasii, M. xenopi and M. marinum are counted among the facultative pathogens and often categorised as "nontubercular" or "atypical" mycobacteria. In addition to soil, the environment, and hot water in particular, seems to be the natural habitat of many mycobacteria. They are generally associated with biofilms, within which they can multiply. They are characterised by a relatively high resistance to chlorine. Some species have been shown to be transferred by drinking water, particularly endangering dialysis patients and the HIV positive. In industrialised countries a significant percentage of AIDS patients develops fatal infections caused by atypical mycobacteria; infection from the environment is regarded as unlikely. However, there are still many uncertainties involved in assessing relevant Fig 2 Growth of legionellae from contaminated sample of hot water on special medium (BYCE-a agar) 13

14 Hygiene in water systems - basic principles of microbiology of drinking water, health risks posed by pathogens, protection Fig 3 Rod-shaped Legionella bacteria under fluorescing microscope at magnification of about 1000x Pathogens Legionellae are widespread, rod-shaped to roundish aerobic water bacteria (Figs 2 and 3). Their natural habitat is warm water and they are regularly isolated from lakes, ponds, rivers, hot springs and tropical rainwater. Their frequent intracellular occurrence within unicellular organisms such as amoebae and ciliates, or in association with algae, enables them to withstand even adverse living conditions. From their natural reservoirs they are sporadically introduced into artificial biotopes created by people, in which given optimal conditions - preferable in the temperature range between 30 and 45 ºC - they can multiply rapidly. The majority of species, and especially Legionella pneumophila, serogroup 1, Pontiac strain, are significant in terms of human pathology. All of the representatives of the Legionella pneumophila species, and numerous nonpneumophilic species, are now counted among the most important pathogens of infectious diseases (= legionellosis) inside and outside hospitals Diseases caused by legionellae (legionellosis) 1 Legionnaires' disease (more accurately known as Legionella pneumonia): - severe, often fatal, atypical pneumonia % of sufferers require intensive therapy - Antibiotic therapy always needed - Incubation period: 2-10 days - Multiple risk factors favour contraction of the disease 2 Pontiac fever: - Highly feverous, spontaneous infection of the respiratory tract with spontaneous recovery (influenza-like illness) - High rate of infection - Does not require hospitalisation - Incubation period: 5-66 hours - No risk-increasing factors known One of the last outbreaks of Pontiac fever arose in May 2002 in a café in a shopping mall in Tennessee, affecting about 100 patrons. The cause was evidently a water misting system. The non-specific clinical progression means isolated cases of Pontiac fever are virtually never identified as such. Intensive investigations have shown that legionellosis occurs worldwide and is by no means a rare infectious disease. Classic examples of epidemic outbreaks originating from hospitals include that in the Wadsworth Medical Center in Los Angeles with 218 cases, the extremely dramatic epidemic in a hospital in Stafford with 39 deaths, one in the North Bavarian REHA-Klinik in 1990 affecting ten patients and resulting in three deaths, and the outbreak of Legionnaires' disease in a hospital in Frankfurt an der Oder in 2003 with at least two deaths. Much more frequent, even if generally undetected, are isolated non-epidemic cases of illness, where it is very much more difficult to determine the channel of infection. The number of cases of Legionella pneumonia in the USA is estimated at about 25,000, and in Germany between 400 and 500 cases have been reported to the RKI in recent years. However, it has to be assumed that "dark figure" is very high, and probably only 5-10% of cases are correctly diagnosed. Not every contact with legionellae leads to an infection. Only under specific conditions can the condition develop: Virulence of legionellae The Pontiac strain of Legionella pneumophila SG 1 is particularly aggressive. It is responsible for most epidemics (for example, Philadelphia and REHA-Klinik in Bavaria). Number of absorbed bacteria and mode of transmission As the number of legionellae absorbed by humans grows the risk of disease increases. However, an infectious dose cannot be specified at present, as it depends on many factors internal and external to the person involved. It is assumed that inhalation of legionellae inside unicellular organisms is more likely to lead to development of a pneumonia than to absorption of free-living bacteria. The transmission mode primarily discussed is inhalation of extremely fine aerosols. High-risk patients in hospitals can also contract infections through aspiration or even drinking contaminated water. Susceptibility of the infectee In an age in which people are living longer and can undergo increasingly complicated medical inventions, their immune status is particularly important. Multiple risk factors can dramatically increase the likelihood of contracting legionellosis. In addition to general risk factors for contracting legionellosis, such as age, being of the male sex, smoking, alcohol abuse and underlying diseases such as diabetes mellitus, autoimmune diseases, malignant lung tumours 14

15 Hygiene in water systems - basic principles of microbiology of drinking water, health risks posed by pathogens, protection and malignant haematological diseases, immunocompromised patients, undergoing, for example immunosuppression or steroid therapy, or recovering from surgical intervention, run a particularly high risk. Organ and bone marrow transplant patients are at extremely high risk Channel of infection Inhalation of aerosols containing bacteria, or aspiration of legionellae or protozoa containing them from water in the built environment, is probably the only potential cause of infection by legionellae worth considering. Person-toperson transmission is unknown. In the initial phase after transplantation, however, obviously any contact with legionellae can lead to a disease being triggered Sources of proliferation and exposure The epidemics of legionellosis from described below are intended as examples that reveal the source of importance for an infection, and the fact that infections involving a high proportion of deaths are still arising worldwide. Bovenkarspel, the Netherlands, whirlpool bath, 192 cases, more than 20 deaths, March cases of Legionnaires' disease with a high mortality rate were confirmed by the Dutch health authorities. All of those infected had visited the Flora flower show in Bovenkarspel am Ijsselmeer. Intensive investigations lead to identification of an exhibition whirlpool bath as the source of infection. This exhibit, which was filled with water and heated, but not disinfected, produced aerosols that could be inhaled by the visitors to the exhibition hall. It caused the biggest epidemic in Europe to date. In the Netherlands the shock of this outbreak triggered extensive legislation and regulations intended to prevent the growth of legionellae in water systems. Germany, prison, four cases, September 1999 Four inmates of a prison contracted legionellosis. High concentrations of L. pneumophila SG1 were analysed in water from the showers and other parts of the water system. Two of the contaminated showers had been used by those suffering from the disease. New shower facilities had been installed only three months beforehand. Belgium, hotel, four cases, one death, June 1999 Two patients in a Dutch hospital were diagnosed as having Legionnaires' disease. Both had stayed in the same hotel in South Belgium during an event. Two other cases of Legionnaires' disease could be traced back to a stay in the same hotel. Testing of the hot water system revealed massive colonisation with legionellae of the same species discovered in the infected guests. The temperature of the hot water was between 42 and 46 C. The system was hyperchlorinated (approximately 50 mg of chlorine per litre) and all outlets flushed with chlorine. The storage vessels were drained and cleaned and deposits removed. However, samples taken after these measures still showed a high level of contamination with legionellae. The entire system was then heated up to 70 C and each outlet flushed with hot water at 70 C for five minutes. Tests for legionellae were then negative. All of the guests who had stayed at the hotel within the relevant time period and all doctors were informed. Japan, public swimming pool, 14 cases, one fatality, June people aged between 58 and 85 showed symptoms of Legionnaires' disease, a 73-year-old man died. All of them had visited the pool a short time before it had been closed because of the outbreak. South Wales, UK, five cases, two deaths, February 2000 Five guests of a hotel in South Wales contracted Legionnaires' disease between July 1999 and February 2000, two died. The investigations conducted covered the hotel's swimming pool, the whirlpool facility, the water supply system and a water mister for food on display. This mister, which sprayed extremely fine droplets over cooled salads and vegetables to keep them looking attractive, was identified as the source of infection. Denmark, two cases in the same apartment building, Spring 2000 Two people living in the same apartment block and supplied by the same hot water system fell ill with Legionnaires' disease. Legionellae were isolated in both apartments and in the overall circulation system of the building, and identified as the cause. The water temperatures were raised to 60 C. A month later legionellae were still being isolated from the water, but in lower concentrations. The water system was then disinfected with chlorine. It is not known whether this decontamination measure was successful. Paris, new hospital, four deaths, December 2000 At least four patients in a newly built hospital in Paris died of Legionnaires' disease. The ultramodern 750-bed facility had been only been opened six months beforehand and was only partially occupied. The official assumption was that stagnant water in unused parts of the supply system was the source of the contamination. Murcia, Spain, 800 cases, two deaths, July 2001 The cause of this, the world's biggest epidemic, was apparently a contaminated cooling tower in the inner city. Early detection and efficient health management evidently made it possible to prevent further deaths. 15

16 Hygiene in water systems - basic principles of microbiology of drinking water, health risks posed by pathogens, protection Hospital in Paris, twelve cases, five deaths, July 2001 In the Pompidou Hospital in Paris nine cases of Legionnaires' disease, three of which resulted in deaths, arose in the period between November 2000 and January Changes were made to the hot water system. Despite these measures three further cases occurred in July, two of which resulted in deaths. Additional measures were taken in relation to the hot water system. Barrow-in-Furness, UK, 131 cases, four deaths, July 2002 The air conditioning system (open cooling tower) of a public building in Barrow-in-Furness in Cumbria was identified as the source of 131 cases of Legionella pneumonia and at least four deaths. More than 300 people with symptoms of Legionnaires' disease were given inpatient treatment. This was one of the biggest outbreaks in the UK. Japan, thermal springs, 252 presumed cases, six deaths, July 2002 A newly opened thermal bath in Southern Japan suffered 252 suspected cases of Legionnaires' disease and six deaths. All of those affected had bathed in the pool. The authorities closed the resort immediately. Koper, Slovenia, hotel, five cases, one death, August 2002 Five members of a party of 19 tourists from Saxony contracted Legionnaires' disease, one 73-year-old man died. The cause of the infection was identified as the hotel's hot water system, which was operated at only 43 ºC. Valencia, Spain, 25 cases, one death, June 2003 In Valencia in May and June 2003 there were two outbreaks, one involved an outpatient in Alcoy, and the other a hospital cancer ward inpatient. In addition to patients a number of visitors were affected. The source of the infection was the hospital's hot water system. The system was hyperchlorinated then the hot water temperatures increased. Germany, Klinikum Frankfurt-Oder, seven cases, at least two deaths, July 2003 Several patients were evidently infected via a contaminated water supply system. Both hot and cold systems were identified as a source of infection. The Public Prosecution Service brought a charge of causing death by negligence. New Jersey, July 2004, two cases, one death in a care home Both of those who contracted the disease (82-year-old man and 76-year-old woman) lived in the same unit. The cause was a contaminated hot water system. The authorities closed the home and had the system disinfected. Camping ground in Klagenfurt, Austria, June 2004, three cases, one death High numbers of L. pneumophila SG1 were detected in the water system. Thermal disinfection carried out did not achieve the required success and only hyperchlorination killed the legionellae. Further decontamination measures are required. These examples very vividly demonstrate the widespread nature of infection with legionellae, the severity of the potential commercial losses and how difficult it is to combat effectively. The most important sources are: Open cooling towers of air conditioning systems Building hot water systems operated at excessively low temperature (30-48 C) Heavily used whirlpool baths, hot tubs, hot spas, etc Equipment producing aerosols (misters, humidifiers, etc) A large number of cases of legionellosis are observed after holidays, for example in the Mediterranean. Pneumonias or bronchial illnesses that have been contracted after stays in hot countries and whose cause has not been clarified should therefore always be examined for the possibility of a Legionella infection. The European Working Group on Legionella Infection (EWGLI) documents centrally all reported of case of legionellosis contracted by tourists and all hotels in which infections have arisen Hot water system as source of infection The hot water system, particularly where operated at low temperatures (< 55 ºC) to prevent scalding or save energy, is particularly important as a source of infection. Ingress of extremely small amounts of bacteria from the municipal water supply or other sources (for example, construction, equipment installation and repairs) is unavoidable. At temperatures between 30 and 48 ºC massive proliferation can take place in the building water supply system within a few days. Primarily affected are large buildings, which frequently have kilometres of pipe carrying water that is often stagnant, and large quantities of stored hot water. More than 70% of the hot water of these buildings can be colonised with legionellae. However, the latest research by the Institute of Hygiene of the Universitätsklinikum Münster shows that even detached houses and houses divided into maisonettes with a common supply can have Legionella contaminations that can be quite comparable or even higher than those in large buildings. The crucial factor here was a temperature level that promotes growth and a central hot water supply. This means that, in order to ensure maximum protection of the public, every possible measure must be taken to reduce legionellae in private housing as well. Throughout the water supply system the temperature of hot water should always exceed 55 ºC and that of cold water should always be below 25 and preferably 20 ºC. A connection between the contamination of hot water systems and the occurrence of legionellosis has 16

17 Hygiene in water systems - basic principles of microbiology of drinking water, health risks posed by pathogens, protection been reported by numerous authors and is now regarded as confirmed. Since transmission is almost exclusively caused by direct or indirect contact with tap water, hygiene measures to reduce legionellae in water systems are extremely important. Potential critical points at which temperature ranges that promote growth can be achieved are shown in Fig 4: Temperature stratification in storage vessels Deposits in the storage vessel and distribution manifolds Sections of pipe carrying stagnant water (change in use, sections not directly isolated from the circulation system and installation of spare capacity) Inadequate water circulation Excessive heat losses in the circulation system Non-optimal regulation of hot water circulation systems Also to be taken into account is the possibility of heat being transferred from the hot to the cold water, so that legionellae arise in the heated cold water. The cold water problem is often overlooked. However, it must be allowed for in a risk assessment, particularly in large buildings. Points of use in Construction Phase B (showers, taps, etc) Points of use in Construction Phase A (showers, taps, etc) Riser Main return Circulation 2 return Circulation 1 return Hot water 1.4 Mode of operation The aim must always be to achieve operation that produces a stable situation in the supply system. When designing new systems and undertaking major modifications this can be achieved through consistent compliance with the relevant standards and codes of practice. With already contaminated systems the objective must be consistent, sustainably hygienic and safe management. Thermal or chemical disinfection of these systems is generally not effective, as such measures cannot eliminate the causes of the colonisation. System optimisation measures always paramount. System optimisation is always essential and cannot be replaced with other measures such as disinfection. In practice the common experience of failed attempts at decontamination can almost always be explained by a lack of proper system optimisation and remaining system weak points that inevitably lead to re-colonisation. One-off removal of the microbial growth is generally not sufficient, since there are numerous factors that can lead to regrowth. When contamination is detected the first priority is to keep calm, analyse the system and assess the risk! Plotting a temperature profile of the hot and cold supply systems is an easy way of obtaining initial indications of potential flaws. The technical and hygiene needs have to be coordinated to suit the system. There is no universal solution. Customised measures recognising the potential infection risk, limits of technical feasibility and cost effectiveness have to be applied. The success of each individual measure must always be checked. The aim must always be to come up with a stable, lasting solution. Simply comparing the level of colonisation with technical guide values is not an effective way of deriving decontamination measures. Additional measures in the sense of a multibarrier concept have to be taken to protect high-risk hospital patients, who are endangered by even extremely small counts of all Legionella species and subgroups. One important requirement for reducing infections of immunosuppressed or immunocompromised patients involves strict protection from any contact with hot or cold tap water. This can only be achieved through the use of sterile water (produced with, for example, a point-of-use sterile filter) that is completely free from bacteria for all purposes affecting the patients. Cold water Storage vessel Heater Fig 4 Schematic diagram of a hot water system, showing components that favour colonisation with legionellae: 1: Sediments containing iron; 2: Temperature stratification in the storage tank; 3: Sections of pipe carrying water that is stagnant (not constantly flowing); 4: Installation of spare capacity; 5: Unoptimised circulation resulting in low temperature zones 17

18 Hygiene in water systems - basic principles of microbiology of drinking water, health risks posed by pathogens, protection 1.5 Practical consequences and concepts The two-pronged approach of technical and, in hospitals, organisational measures is necessary to achieve the level of hygiene needed to reduce the incidence of legionellosis: 1 Technical measures to permanently reduce the number of legionellae in water and other technical systems by establishing stable management of a lean system. It particular cases installation of UV systems or continuous chemical disinfection with chlorine/ chlorine dioxide or hydrogen peroxide can be expedient. In each individual case the concept must be established and tested on site with an expert. 2 Additional organisational measures in hospitals: A special approach is needed on transplant wards, in intensive care units, Oncology and other departments treating immunocompromised or immunosuppressed patients. After successful decontamination of the water supply system, it is extremely important with high-risk patients to ensure strict compliance with clinical and care measures in conjunction with the Specialist in Hospital Hygiene. This can be summarised by recommending immunosuppressed patients be strictly protected from exposure to tap water. Only consistent adherence to the hygiene requirements can ensure safe operation of water supply and other water systems. The success of each individual measure must be checked and should ideally lead to complete elimination of Legionella infection. 1.6 Legislation When the legislation for preventing and combating human infectious diseases (IfSG), which superseded the earlier communicable diseases legislation, came into force on 1 January 2001, detection of legionellae as a cause of illness became notifiable ((7), Notifiable Detection of Pathogens, No 26 Legionella sp.) and therefore has to be reported to the responsible health authority. To clarify epidemiological relationships the Health Department is entitled to have assumed sources of infection investigated and to initiate other measures. Only non illness related detection of legionellae in water systems is not legally notifiable. With the introduction of the new Drinking Water Regulations (18) on 1 January 2003 the Health Department became responsible for monitoring the quality of drinking water in supply systems of public buildings, particularly in "schools, kindergartens, hospitals, restaurants and other communal facilities", in relation to compliance with the regulations through suitable testing. Under Scope of testing, (2), Periodic tests, the regulations state: "... Periodic testing also includes testing for legionellae in central heating systems of water supply systems in accordance with (3), No 2, c that are used to provide water for the public." This makes it mandatory to test for legionellae in virtually all public buildings. The Health Department and the operator of the system are obliged to carry out risk assessments, inform the public and immediately introduce suitable health protection measures. It therefore becomes absolutely essential to take effective measures against the growth of legionellae and if necessary keep documentary evidence that sufficient account has been taken in the design, installation and operation of the water supply system of all the hygiene-relevant standards and regulations. 1.7 Frequently asked questions I would like to have my water supply tested for the presence of legionellae. What do I have to do? The most important prerequisite is to obtain an accurate overview of the hot water system (get hold of any available plans and measurement data). Potential weak points of the system should be determined with the aid of the plans and in-situ testing. The most important instrument is temperature measurement at different points of the system. Are the required temperatures reached in all circuits? How long does it take to achieve the maximum temperature? Are certain sections of the building rarely or never used? Are there sections of pipe in which water does not flow? Is temperature stratification arising in the storage vessel? All zones in which temperatures below 50 ºC are measured are critical and may be colonised. Only when a clear overview of the system and its weak points has been obtained can an approved institute be commissioned to conduct the tests. What points of the system should I have checked to determine whether it is contaminated with legionellae? Basically all points identified as potential weak points in the preliminary check or specified as control points must be checked. Testing must fully clarify whether systematic contamination is taking place and whether the entire system or just certain parts are affected. A minimum test programme for hot water supplies is to be found in DVGW Code of Practice W 551. The outlet of the storage vessel, the individual returns (the main (collecting) return often leads or incorrect assessments) and samples from the periphery. The peripheral samples must be taken as far away from the central unit as possible and be representative of the individual circulation circuits. The cold water must also be included in the check, particularly if heat transfer to this system is to be feared or has already been detected. How is sampling to be carried out? Sampling must be conducted in such a way that systematic contamination can be detected. This is extremely important, particularly when checking for Pseudomonas 18

19 Hygiene in water systems - basic principles of microbiology of drinking water, health risks posed by pathogens, protection aeruginosa, otherwise incorrect conclusions can be reached and attempts at decontamination misdirected. It is also essential to eliminate all factors that could falsify the result (for example, shower hose, point-of-use fitting or reinforced hose). Unless there are special questions to be answered, rather than from showers the samples for initial testing must therefore be taken from special sampling valves that allow the water to be drawn off without being affected, and clearly related to the hot or cold supply. These special sampling valves must be installed at critical points (control points) throughout the system. The standard methods specified in DIN A3, -A14, -A19 and -A21 must be followed for all sampling, including that for legionellae. In practice it is unfortunately evident that there is a severe deficit of information about this aspect, even on the part of the health authorities. The necessity of sampling is clear, but how should it be done? The Drinking Water Regulations ((4), (14) and (19) in conjunction with Annex 4) prescribe annual testing of the drinking water in public buildings for legionellae. Operators that provide the public with drinking water are obliged to commission, for example, a local hygiene institute to test it. Exploratory, and possibly further and follow-up tests are required. DVGW Code of Practice W defines more closely the sampling points for determining whether a water supply system is contaminated with legionellae. In practice, however, there are generally no suitable sampling valves at these points. Sampling is therefore unnecessarily time-consuming and cannot always be carried out expertly. A more extensive, second sampling session is then often necessary, since the initial results do not show whether the microbiological contamination originates from the municipal water supply or the points of use. The narrowing down process is, however necessary to enable introduction of effectively targeted remedial measures. These multiple sampling sessions and temporary installation of 'makeshift sampling points' make the procedure more expensive. To avoid this it is advisable to provide suitable sampling points at the initial system design stage or to retrofit them. The following diagram shows the sampling locations defined in DVGW (CP) W 551 for the water supply system. They are divided into points for exploratory and further tests. 1. DVGW Code of Practice W 551, April 2004: "Water Supply Heating and Water Supply Pipes; Technical Measures for Reducing the Growth of Legionellae, Design, Installation, Operation and Decontamination of Water Supply Systems", Wirtschafts- und Verlagsgesellschaft Gas und Wasser GmbH, Bonn Schematic diagram of a system with sampling points to DVGW Code of Practice W 551 Sampling points (minimum number required) Exploratory testing as defined in DVGW W 551, 9.1: "Exploratory testing with a limited sampling plan is cost effective for systems free from legionellae. The limited scope of the sampling possible may make it impossible to introduce specific measures for decontaminating contaminated systems.... The number of samples required for the exploratory stage must be chosen so as to ensure that every pipe run is covered.... A sample must also be taken at the outlet of the supply heater (hot water pipe) and another at the inlet into the heater (circulation pipe)." The positioning of the sampling points on the risers and in the vicinity of the inlet and outlet of the heater must be specified by the operator and the sampler. The points must then be suitably identified on the key plan Water supply sampling points, for example as nodes with identification numbers. Further testing as defined in DVGW W 551, 9.2: "The number of samples required for further testing depends on the size, extent and complexity of the system. In addition to the sampling points for exploratory testing on each pipe run it is advisable to take additional samples in the individual pipes for the different floors (which offer information about potential contamination).... Samples must also be taken from sections of pipe that 19

20 Hygiene in water systems - basic principles of microbiology of drinking water, health risks posed by pathogens, protection carry stagnant water (for example, ventilation pipes for general protection, drain pipes, infrequently used points of use and diaphragm type expansion tanks).... If there are indications that cold water pipework is being heated samples must also be taken from cold water sampling points." According to DBGW W 551, for further testing sampling points must be installed at defined points of the hot water system to determine whether it is contaminated with legionellae. This also applies to cold water systems if there are indications that they are being heated. KEMPER sampling valve (Fig 187) on an isolating valve (Fig 173) Where can I have tests conducted? Can I carry them out myself? Only microbiological laboratories accredited to DIN EN ISO and listed by the German states in accordance with the Drinking Water Regulations (14) are entitled to conduct tests for legionellae that have been approved by the Public Health Officer. It is always advisable to ask the Health Department for details of reference laboratories. The test must be conducted in accordance with the applicable standards in order to obtain comparable and reproducible results. Sampling by the operator for exploratory tests is basically possible by agreement with the laboratory (see also Sampling). You can only conduct your own tests for legionellae with test kits in the event of extremely strong indications and after training. They never replace checking by an approved laboratory. Strict account must be taken of the sometimes considerable limitations on the significance of the tests. My hot water system contains legionellae. What should I do? In what order? An effective risk assessment must always be conducted in conjunction with an experienced laboratory, an engineer specialising in hygiene and possibly the Public Health Officer. An absolute prerequisite for the success of any decontamination measure is always a clear overview of the entire water distribution system including all equipment. Plotting of temperature profiles is an indispensable first step. There is no universal decontamination concept. Each case, each building requires individual analysis and a tailor-made package of measures. The primary objective must always be appropriate state of the art operation of the system. Safe water supply hygiene always takes priority over potential energy savings. A clean, lean system with adequate circulation in all sections and hot water temperatures above 55 ºC is crucial whatever the measures adopted. Design methods must be state of the art. Sections of pipe that are not required must always be isolated from the circulation system. The volumes of stored and transported water must always be minimised. The measures must always cover the entire system and be continuous. Checks must be carried out to verify the success of each individual measure. Do I have to notify the presence of legionellae in my hot water system? The IfSG only require notification of detection of legionellae related to illness. The legal position was significantly tightened with the introduction of the new Drinking Water Regulations in (3) of these regulations (which came into force on 1 January 2003) states: "The operator or holder of a building water supply system as defined in (3), 2, c who has become aware of facts indicating that the water in this system is being changed in such a way that it no longer meets the requirements of (5) to (7), where necessary must immediately have tests conducted to clarify the situation and take or initiate remedial measures and notify the Health Department accordingly." The criterion for such notification would be (5), 1: "Water for human consumption must not contain pathogens as defined in (2), 1 of the infection protection legislation in concentrations that could give rise to concerns about danger to human health." As there are no clear principles and guide values for such evaluation when legionellae arise in drinking water, this could basically lead to every positive result having to be reported to the Health Department, which would then have to carry out a risk assessment itself. 20

21 Hygiene in water systems - basic principles of microbiology of drinking water, health risks posed by pathogens, protection What do I do when a water system is contaminated with Pseudomonas aeruginosa? The following have been mentioned as relevant risk factors for sometimes chronic or recurrent contamination of cold water pipework with Pseudomonas aeruginosa (see also Consensus Conference in Bonn 2004): Inappropriate design (for example oversizing or long spur pipes) Contamination through central entrainment from water supply Inadequate, inexpert installation Use of unsuitable materials and components/ equipment Operation in contravention of regulations Temperature significantly above 20 ºC in cold water system Irregularly used sections of pipework with stagnant water Biofilm formation promoted by materials and operation Biofilm formation (for example, on organic components such as diaphragms) Inappropriate leak testing prior to commissioning Inappropriate commissioning This means that numerous water hygiene shortcomings can lead to colonisation with P. aeruginosa. The primary objective must therefore be to describe the extent and possible sources of contamination through systematic sampling and microbiological analyses. The reports on decontamination of water supply systems contaminated with Pseudomonas aeruginosa revealed different experiences. The decontamination measures included both chemical disinfection with chlorine and chorine dioxide, and thermal methods. Methods that could not be used continuously often did not lead to the desired success. One important - perhaps the most important - factor is deliberate consumption. Water must flow and must be changed. In some systems consumption is the only way of achieving a stable situation. One of the most serious mistakes is to shut down an affected system in which contamination has been detected. This often makes further attempts at decontamination impossible. Even when disinfectants are being used the top priority is consume, consume, consume. 21

22 2 Determining pipe diameters for hot and cold water Professor Bernd Rickmann, Fachhochschule Münster, Department of Energy and the Built Environment 2Determining pipe diameters for hot and cold water Professor Bernd Rickmann, Fachhochschule Münster, Department of Energy and the Built Environment Against the backdrop depicted in Section 1, the extensive rules already contained in DIN 1988 Drinking Water Supply Systems have to be supplemented and modified in some respects. Such supplements to DIN 1988 are included in the DVGW's current publications. Reducing the Growth of Legionellae in Hot Water Systems (Codes of Practice W 551 and W 553) in particular will have a lasting effect on the design, installation and operation of building water supply systems. To prevent the possibility of supply systems getting contaminated, their water capacity must be minimised through design measures and pipe sizing. This ensures the area of internal surfaces is small and the water only remains in the system for a short time and is rapidly changed. Stagnant water and the heating of cold water in the supply system by its surroundings must always be avoided. Circulation systems or self-regulating trace heating systems must ensure that the temperature is not continuously below 55 ºC at any point of the supply system. Pipes for particular floors with a water capacity of less than 3 litres are exempt from the requirement. The sizing of water heating, distribution and circulation systems must take account of drinking water hygiene as a well as the purely functional and commercial aspects. The quality of the water depends not only on it being supplied in perfect condition by the water company, but also heavily on the following factors: Design Choice of pipe materials Standard of workmanship Sizes of the pipe system in the building If drinking water hygiene problems are discovered, the person responsible must expect to have to verify that the design, sizing and installation of the entire water supply system were in accordance with accepted practice at the time of installation. A quick look at the technical codes and regulations shows that the following design calculations are currently regarded as necessary in order to achieve drinking water of acceptable quality in the properly installed pipework of a supply system: Designing pipe system for hot and cold water to DIN taking account of VDI Guidelines Designing circulation pipes on the basis of DVGW Codes of Practice W and W Verification that the water capacity of sections of pipe where it does not circulate is less than the permissible value This manual aims to collate the most important rules for determining pipe diameters in water supply systems and provide practical comments. 2.1 Available pressure differential Hydraulic design calculations for a water supply system can only ever be performed along the flow paths. The individual paths start in the building service pipe and end at a particular point-of-use fitting. The first step in the DIN 1988 design method for hot and cold water supply pipes is to determine the worst flow path from the different ones available. The worst path is the one with the lowest permissible pressure drop per metre run of a straight pipe. The starting point for the hydraulic calculations can be found by considering the balance of pressure established along the associated flow paths. All pressure and pressure drop components throughout the system must be calculated for this state. This is expressed as follows: 2. DIN : "Drinking Water Supply Systems; - Pipe Sizing", Beuth Verlag, Berlin 3. VDI 6023 "Hygienic Aspects of the Planning, Design, Installation, Operation and Maintenance of Drinking Water Supply Systems", VDI- Gesellschaft Technische Gebäudeausrüstung. 4. DVGW Code of Practice W 551, April 2004: "Water Supply Heating and Water Supply Pipes; Technical Measures for Reducing the Growth of Legionellae, Design, Installation, Operation and Decontamination of Water Supply Systems", Wirtschafts- und Verlagsgesellschaft Gas und Wasser GmbH, Bonn 5. DVGW Code of Practice W 553, December 1998: "Designing Circulation Systems in Central Water Heating Systems", Wirtschafts- und Verlagsgesellschaft Gas und Wasser GmbH, Bonn 22

23 Equation 1 p minv p minfl p geod p wz p Ap Minimum static pressure at the point of connection to the municipal service pipe as specified by the responsible water company Required static pressure at the point of connection for a point-of-use fitting at its minimum flow rate (Fig 6) Geodetic pressure differential resulting from the difference in head between connecting pipe and point-of-use fitting Pressure drop across water meter Pressure drop across equipment such as filter p FIL, metering systems p DOS, softening systems p EH, etc p St Σ(l R + Z) Pressure drop in pipes for particular floors and individual spur pipes (only using simplified design calculations) Pressure drop from pipe friction and minor losses along flow path, starting in the building service pipe and ending at a particular point-of-use fitting or at the connection for a particular floor Fig 5 Definitions and notation for water supply systems 23

24 Determining pipe diameters for hot and cold water A positive (available) pressure differential verf must then remain to overcome pipe friction and minor losses Σ(l R + Z), and can therefore be used to size the pipes. This differential can be calculated as follows: this aspect in the standard should be regarded as maxima, manufacturers' data for specific models and detailed calculations generally lead to less conservative assumptions for designing the pipes. 2.2 Calculating flow rates Equation 2 Evenly "distributing" the available pressure differential p verf after subtracting the minor losses (a) along the entire length of the flow path (l ges ) gives an important design parameter for determining the pipe diameter, the pressure gradient available to cope with pipe friction R verf. This relative pressure gradient is a minimum for the worst flow path and a maximum for the best. Equation 3 p verf Pressure differential available for the pressure drop from pipe friction and minor losses a Estimated percentage contribution of the minor losses to the total pressure drop l ges Total length of the design flow path As the above equations show, the pressure gradient available to cope with pipe friction is mainly determined by the geodetic pressure differential p geod and the minimum flow pressure requirement of the point-of-use fitting p minfl. The quickest way of finding the worst point of use is to perform the calculations for the fittings with the highest flow pressure requirements on the top floor. Relatively large diameters must be chosen if R verf is small, and smaller diameters can be chosen if a relatively large pressure gradient is available. This available gradient therefore significantly affects not only the installation costs, but also the water capacity of the pipe system. In order to choose a suitable diameter for a particular section, in addition to the pressure gradient R verf available to cope with pipe friction, at least the flow rate for the particular design case - the peak flow rate V s must be known. The peak flow rate V s to be expected in a section is significantly influenced by the number and design of the pointof-use fittings to be supplied, the various design flow rates of these fittings VV R and the type of use of the fixture. A basic distinction is drawn between normal and continuous consumption. A point-of-use fitting is classified as a "continuous load" if the type of service means it is used for longer than 15 minutes. Typical continuous loads include point-of-use fittings used for sprinkler systems. If several continuous loads are to be supplied by one section, the extent to which they can be expected to be used simultaneously must be specified in conjunction with the user of the pipe system. However, the individual fitting is normally only used for a much shorter period of time than 15 minutes (normal consumption). If continuous consumption V D and peak flow rate from normal consumption V S,normal coincide, the two values must be added. Equation 4 The design flow rate of a point-of-use fitting V R is an average of the point-of-use flow rates at a maximum flow pressure (generally p ofl = 3.0 bar) and the minimum flow pressure (generally p minfi = 1.0 bar). Before starting to calculate the pressure drops a sufficiently large available gradient (R verf = mbar/m) must therefore be ensured along the worst flow path. The peak flow rate, minimum supply pressure, pipe lengths and geodetic heads are largely fixed and cannot be significantly changed for given system requirements. The designer of a pipe system can appreciably influence only the hydraulic data of the equipment ( p WZ, p FIL and p Ap ), the system for a particular floor p St, and that of the point-of-use fittings (p minfl ). As the specifications for 24

25 Determining pipe diameters for hot and cold water Fig 6 Definition of the design flow rate V R of a point-of-use fitting If the design flow rate V R, minimum flow pressure p minfl and maximum flow pressure p ofl of the fitting concerned are known, the minimum flow rate of a point-of-use fitting under standard conditions can be calculated using Equation 5. Equation 5 For example the minimum cold water or hot water flow rate of a bath mixer with the following data: V R = 0.15 l/s, p ofi = 3.0 bar, p minfi = 1.0 bar 25

26 Determining pipe diameters for hot and cold water Type of fitting p min FI Mixed water cold Mixed water hot cold or heated water only V R VV R V R mbar l/s l/s l/s Outlet valves without aerator DN Outlet valves without aerator DN Outlet valves without aerator DN Outlet valves with aerator DN Outlet valves with aerat DN WC push button flush system DN Urinal push button flush system DN Cistern to DIN DN Domestic dishwasher Domestic washing machine Mixer DN 15 for: Showers Baths Kitchen sinks Countertop basins Bidets Mixer DN Electric instant boiler water heater Table 1 Guide values for the design flow rate and the minimum flow pressure of common point-of-use fittings The total flow rate ΣV R is the sum of the design flow rates V R of all point-of-use fittings that can be supplied by a section. Point-of-use fittings within a utilisation unit beyond a certain standard of equipment 6 are not allowed for in determining the total flow rate. In flats the following, for example, may not be included: Bidets Additional washbasins or toilet facilities Shower in addition to bath, etc In other words in the calculations the peak flow rate for "luxury systems" can be reduced to the level actually required. For the example shown in Fig 7 the total flow rate of this system for an individual floor used to determine the nominal diameters of the basement distribution manifolds and risers can be reduced for cold water from ΣV R = 1.61 l/s to at least ΣV R =1.19l/s, and from ΣV R = 0.65 l/s to at least ΣVV R = 0.36 l/s for hot water. In the case of a larger installation unit (such as an owneroccupied dwelling) this purely computational measure based on DIN can lead to a notable reduction in the system costs and water capacity VDI 6023, 4.3 "Sizing and Routing of Pipework of Water Supply Systems" 7. Th Nyhuis and I Schmidt: "Effect of System for Individual Floor on the Diameter of Stainless Steel Pipes to DVGW W 541 for Water Supply Systems", dissertation1996, Fachhochschule Münster, unpublished 26

27 Determining pipe diameters for hot and cold water Fig 7 System for individual floor Up to a total flow rate of ΣV R = 20.0 l/s the peak flow rates to be expected also depend on the design of the point-ofuse fitting and its design flow rate. If the design flow rate of the individual fitting is greater than ΣV R = 0.5 l/s (for example in the case of WC push button flush systems) a higher peak flow rate must be expected for the same total flow rate in the section. For converting the total flow rate into the peak flow rate DIN 1988 categorises the use of the installation unit as a residential building, office/ administration building, hotel building, department store, hospital ward or school. The design equations are identified with letters. Ident. Range Equation Unit A ΣVV R > 1.0 1) V S = 1.7 [ΣV R ] l/s B 0.07 < ΣVV R 20 V S = [ΣVV R ] l/s C ΣVV R > 20 V S = 0.4 [ΣV R ] l/s D 1.0 < ΣV R 20 V S =[ΣV R ] l/s E 0.1 < ΣV R 20 V S = [ΣVV R ] l/s F ΣVV R > 20 V S = 1.08 [ΣV R ] l/s G ΣVV R > 20 V S = 4.3 [ΣV R ] l/s H ΣVV R > 20 V S = 0.25 [ΣVV R ] l/s I 1.5 < ΣV R 1.0 2) V S = 4.4 [ΣV R ] l/s K ΣVV R > 20 V S =-22.5 [ΣVV R ] l/s 1) Between ΣV R = 0.5 and 1.0 l/s: V S = ΣV R 2) for ΣVV R = 1.5: V S = ΣVV R Table 2 Design equations for converting the total flow rate into an anticipated peak flow rate 27

28 Determining pipe diameters for hot and cold water Fig 8 Peak flow rate for a total flow rate ΣV R < 20.0 l/s as a function of design flow rate of largest point-of-use fitting installed and type of use of building Fig 9 Peak flow rate at a total flow rate > 20.0 l/s depending on the use of the building 28

29 Determining pipe diameters for hot and cold water 2.3 Flow velocities In practice, instead of using the pressure gradient available to cope with pipe friction, pipes are often still sized by means of average flow velocities. Pipe diameters that appear to be reasonably appropriate can indeed be specified with this method, but no account is taken of the hydraulic relationships expressed in terms of the pressure gradient as described above. Mistakes are inevitable, as the method consistently leads to designs whose sections with poor hydraulic conditions are too small and those with better conditions too large. In addition to the purely commercial aspect, from the hygiene viewpoint a system designed in this way has an unnecessary large pipe volume with the potential dangers already described. It can basically be said that the level of error increases with the size of the pipe system - and therefore particularly in the case of the hospital and care home systems shown to be at risk. In the design methods stipulated by the standard flow velocities only have a limiting and not a design function. Pipe section Building service pipes Supply pipes with low-loss isolating valves ζ <2.5 Supply pipes with isolating valves ζ 2.5 Table 3 Permissible flow velocities in water supply systems 2.4 Water company meters Maximum permissible velocities for a flow duration of 15 minutes > 15 minutes 2.0 m/s 2.0 m/s 5.0 m/s 2.5 m/s 2.5 m/s 2.0 m/s drop in the pressure to below the minimum flow value at critical points of use, particularly on upper floors, leads to supply deficiencies. Unless otherwise specified by the water company, it is always advisable to size the meter for the peak flow rate as defined in DIN This is achieved by choosing the meter on the basis of: V S 3.6 V max in m 3 /h V g 3.6 V n in m 3 /h and the pressure drop calculated with Equation 6 p g V S V n V max Pressure differential determined by the manufacturer of the equipment at a given flow rate VVg in m 3 /h. For calculation of the pressure drop across the water meter V g =V max ; nd also in exceptional cases (continuous duty) VV g = V n. Peak flow rate in l/s Nominal flow rate in m 3 /h, corresponds to the permissible continuous load due to continuous consumption (V D ). Maximum permissible flow rate in m 3 /h, corresponds to the short-term permissible peak load of the water meter in m 3 /h. As well as covering the worst case this design approach provides the basis for economical design of the pipes. It must also be used if the water company is actually installing a smaller meter. Any malfunctions arising can then be readily and cost-effectively remedied by substituting the water meter for the design case. The water company specifies the size of the meter in accordance with the "General Water Supply Regulations" (AVB WasserV). Despite the fact that DIN 1988 specifies use of the seconds peak for designing water supply systems, the water meter supplied by some water companies is based on the five minute peak. This longer period results in the meter being designed for a different (lower) flow rate than the downstream pipe system. The method of determining the pressure drop across the water meter must therefore always be agreed with the responsible water company. If the peak load as defined in DIN 1988 arises, in marginal cases the different design basis can lead to the effective pressure drop across the meter exceeding the design value. The associated brief 29

30 Determining pipe diameters for hot and cold water Type of meter Connection to DIN ISO Nominal diameter flange p g V g = V n V g = V max bar m 3 /h m 3 /h Impeller G 1/2 B Impeller G1/2B Impeller G 3/4 B Impeller G1B Impeller G 1 1/4 B Impeller G11/2B Impeller G 2 B Woltmann ) Woltmann ) Woltmann ) Woltmann ) Woltmann ) Woltmann ) ) 600 mbar with vertical Woltmann water meters Table 4 Flow rate and pressure drop with water meters to DIN ISO Fig 10 Equipment pressure drops p Ap as a function of flow rate ratio V S / V g and the given pressure differential p g 30

31 Determining pipe diameters for hot and cold water 2.5 Equipment The generic term "equipment" covers filters, softeners, metering systems, demineralisation systems, heat exchangers, etc. The considerable impact of equipment pressure drops on the results of the hydraulic design means they must always be determined using the detailed method of calculation and the manufacturer's data (Equation 6). For a filter downstream of the water meter a pressure drop of p FIL = 200 mbar at the nominal flow rate can be used with sufficient accuracy when the system is new. 2.6 Switching pressure differential of group of water heaters When using hydraulically controlled groups of water heaters the generally very high switching pressure differential in the units must be taken into account. In this case as well, specific manufacturers' details give more reliable results than the guide values from Table 5. The specified values for p TE (water heater) generally must not be used in Equation 6. The pressure drop in central water heating systems (storage vessel system) is generally much smaller than in group water heaters and is taken into account in the calculations for the pipe system in the form of the storage vessel inflow and outflow losses (minor loss constants ζ from Table 23). Equipment type Electric instantaneous water heater (thermally regulated) Electric instantaneous water heater (hydraulically controlled) Electric or gas storage water heater (up to 80 litres) Gas instantaneous and combination heaters to DIN 3368 p TE bar Floor pressure drop When using the simplified method as defined in DIN the pressure drop for a particular floor can be taken from tables (see Table 13 on page 104). However, detailed design calculations for a simple floor system in residential buildings show that with the same floor pressure drop p St, in most cases pipe systems with smaller diameters than those worked out with the simplified method can be achieved (Table 12). The diameter of DN 20 often still encountered in systems for a particular floor is based on experience with older design rules (DVGW Code of Practice W 308) and in many cases is not hydraulically necessary. The additional or new rules for installing water supply systems in DVGW Codes of Practice W 551 to W 553 mean unnecessary generous sizing of such sections of pipe, particularly in the hot water system, should be a thing of the past. Comparative calculations show that in larger systems for commercial and hygiene reasons it is sensible to concentrate the total available pressure differential in the floor pipes and risers rather than in the basement distribution manifolds Pressure drops in pipes Flows in water supply pipe systems can be laminar or turbulent. Laminar flow is the orderly flow of fluid particles in layers or lamina that is to be expected primarily at low flow velocities. Friction considerably slows the particles close to the pipe wall, with the velocity increasing towards the centre of the pipe (Fig 11). In water supply systems this type of flow occasionally arises in circulation pipes in the design case. With turbulent flow complex motion normal to the centreline of the pipe is superimposed on the main flow. This decelerates higher velocity particles and accelerates lower velocity particles. The difference in velocity is therefore relatively small across the crosssection of the pipe (Fig 11). This type of flow is promoted by high velocities and predominates in almost all design cases covered by DIN Table 5 Guide values for switching pressure differentials of individual and group water heaters 8. Th Nyhuis and I Schmidt: "Effect of System for Individual Floor on the Diameter of Stainless Steel Pipes to DVGW W 541 for Water Supply Systems", dissertation1996, Fachhochschule Münster, unpublished 31

32 Determining pipe diameters for hot and cold water Equation 9 I R Z Pressure drop in a straight pipe of constant cross section Minor losses Pressure gradient due to pipe friction This gradient R is defined as follows: Equation 10 Fig 11 Velocity profile and average velocity v for laminar and turbulent flow The Reynolds number Re is defined as the ratio of the inertial and viscous forces. In plays an important role in dimensional analysis. Flows are hydraulically similar when the Reynolds number is the same. Equation 7 ν Kinematic viscosity (Fig 12) ν = 1.31 x 10-6 in m 2 /s at 10 C ν = 0.47 x 10-6 in m 2 /s at 60 C d i Inside diameter of pipe v Average flow velocity Equation 8 Tests have show that the transition from laminar to turbulent flow and vice versa occurs at a Reynolds number of approximately Re = For this reason calculation of the Reynolds number with Equation 7 can be used to ascertain whether the design case involves laminar (Re < 2320) or turbulent flow (Re 2320). DIN 1988 stipulates the use of Equation 9 to calculate the pressure drop p. It distinguishes between "detailed" and "simplified" (blanket) calculation of the pressure drop. With the detailed method the two components in Equation 9 are calculated separately. However, for normal applications the standard emphasises the simplified method, which enables the pressure drop for the given system requirements to be determined sufficiently accurately. With laminar flow (Re 2320), according to the Hagen- Poiseuille law the friction factor λ only depends on the Reynolds number. Equation 11 With turbulent flow (Re > 2320) the friction factor has to be determined using the Prandtl-Colebrook equation: Equation 12 ρ Density of water in kg/m 3 (Fig 12) ρ = kg/m 3 at 10 C ρ = kg/m 3 at 60 C d i Inside diameter of pipe k Natural inside wall roughness of pipe k = 0.15 Galvanised steel pipes k = Ductile cast iron pipes with cement mortar lining k = 0.1 Plastic pipes k = Copper pipes, stainless steel pipes k = Mepla pipe In the interest of simplification the pressure drop calculations in DIN assume a water temperature of 10 C for both hot and cold water pipes. The errors introduced by the different density and viscosity into the calculation of the R-value for flows in hot water pipes can generally be accepted, since they are on the safe side. 32

33 Determining pipe diameters for hot and cold water Because of the relatively high accuracy required for hydraulic balancing for circulation systems, in this case, however, the calculations according to DVGW Code of Practice W 553 must take account of a water temperature of 60 C. Fig 13 Detail from a pressure drop chart for stainless steel pipes at 60 ºC showing examples of values read off Example: Turbulent flow in cold water pipes Fig 12 Kinematic viscosity and density of water as function of temperature Example: Laminar flow in circulation pipes Given: To find: Circulation flow rate VV z =50l/h Stainless steel pipe, DN 20 (22 x 1.2) Water temperature 60 C The pressure gradient due to pipe friction R in mbar/m and the average flow velocity v Given: To find: Peak flow rate VV S = 1.0 l/s Stainless steel pipe, DN 25 (28 x 1.2), di = 25.6 mm Water temperature 10 C The pressure gradient due to pipe friction R in mbar/m and the average flow velocity v The flow velocity calculated with the continuity equation is With a flow velocity of The kinematic viscosity of ν = 1.31 x 10-6 in m 2 /s at a water temperature of 10 C gives a Reynolds number of: and a Reynolds number of The Hagen-Poiseuille law gives a friction factor of With turbulent flow the friction factor λ can be determined either by iteration using Equation 12, or graphically from the Moody diagram (Fig 14). With iteration an estimated value of λ must be changed until each side of the Prandtl- Colebrook equation works out to approximately the same value, λ = in this case (Table 6). If λ is known, the pressure gradient due to pipe friction R can be calculated with: 33

34 Determining pipe diameters for hot and cold water λ geschätzt (estimated) lg λ k di Re λ Table 6 Steps in iterative calculation of friction factor λ The Reynolds number and the relative roughness d i /k are needed in order to determine the friction factor from the Moody diagram: With these values Fig 14 gives a friction factor of λ = As a result of the relatively low absolute roughness k of the stainless steel pipe, the flow is approximately on the hydraulically smooth boundary curve (d i /k = 17067). If λ is known, the pressure gradient due to pipe friction R can be calculated. In both cases the computation is too complex for practical applications, so suitable pressure drop tables or charts are generally used to determine the flow velocities and the pressure gradient due to pipe friction (cf Fig 17 showing examples of values read off). Fig 14 Friction factor λ as a function of Reynolds number and relative roughness of pipe d i /k (Moody diagram), showing examples of values read off for laminar and turbulent flows 34

35 Determining pipe diameters for hot and cold water With the detailed method, in addition to the pressure drop in straight pipes (l R), significant minor losses (Z) such as Elbows and bends Tees Valves Reducers, etc can be determined with Equation 13. Equation 13 The dimensionless minor loss constants ζ for substitution in the equation are determined on the basis of pressure drop measurements on a test stand and/or examination of flow pulses. As the minor loss constant is heavily dependent on the form of the flow resistance, in detailed pressure drop calculations it is preferable to used the minor loss constants determined by the manufacturer for specific pipe fitting (Table 23) Detailed calculations Detailed calculations can only be carried out meaningfully if the type and exact location of each minor loss in the pipe system is known. Detailed working drawings for water supply systems that could provide this information are generally not available at the design stage. For this reason "detailed" pressure drop calculations for water supply systems as specified in DIN 1988 can only be performed in special cases. Such cases generally only arise when in borderline situations the necessity for a pressure boosting system has to be shown, the longest flow paths on a particular floor are more than m, the total flow rate of a system for a floor exceeds ΣV R = 2.0 l/s, the floor pressure drops p St for prefabricated elements, units or general installation standards, etc, have to be accurately determined and if for special systems for industry, agricultural sprinkler systems, etc, have to be designed. Fig 15 Isometric of system for particular floor from Fig 7 drawn in preparation for detailed calculation of the pressure drops on the particular floor Simplified calculations Simplified calculation of the pressure drop p as defined in DIN 1988 has the following important attributes: Pressure drop calculations in the true sense are only still carried out for sections of the basement distribution system and for the risers to the branch pipes for the different floors (Fig 5). A blanket allowance of a = 40 to 60% of the total pressure drop is made in these sections. The smaller value is to be used in more extensive, the smaller one in small branched pipe systems. As the correctness of the estimate made is not indicated in the subsequent calculations, the pressure drop calculations are limited to the straight sections of pipe. The relatively high pressure drops in the system for the floor p St can be determined from tables by detailed calculation. The blanket allowance for the floor pressure drop p St takes account of the following factors: The design flow rate V R of the largest point-of-use fitting installed The inside diameter of the floor pipes (permissible total length l St = 7.00 m) branching off from the riser. "Floor pipe" means all of the sections on the particular floor supplying more than one point-of-use fitting. The inside diameter of the spur pipe leading from the floor pipe to an individual point of use (permissible length l EZ = 3.00 m) 35

36 Determining pipe diameters for hot and cold water The system mainly associated with the floor and the spur pipe Cold water supply Central water heating system Group water heating system Design of the isolating valve (ζ-value) in the floor pipe The available pressure differential Fig 16 Definition of components of floor system 2.9 Designing flow path producing worst hydraulic conditions In choosing a suitable pipe diameter, the pressure gradient available to cope with pipe friction R verf must always be used as the characteristic parameter in addition to the peak flow rate V S. This gradient is more a guide than a precise quantity for calculation purposes. When a diameter is chosen from pressure drop tables or charts the value must necessarily fall below or exceed this guide, as there is always only a limited number of diameters available with a pipe series (Fig 17). It is important for the sum of all pressure drops Σ(I R + Z) along the entire flow path to be of approximately the same magnitude as the available pressure differential p verf. Example showing how values are read off: Given: Peak flow rate V S = 1.0 l/s Pressure gradient available to cope with pipe friction R verf = 10.0 mbar/m To find: Suitable nominal diameter (DN) R in mbar/m v in m/s. Results: See Table 7 and Fig 17 36

37 Determining pipe diameters for hot and cold water V DN 15 DN 20 DN 25 DN 32 DN 40 DN 50 18x1.0 22x1.2 28x1.2 35x1.5 42x1.5 54x1.5 R V R V R V R V R V R V l/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s Table 7 Example of figures read off for pressure drop tables The check specified above must then be repeated each time. It must also be ensured in the process that the maximum permissible flow velocities are not exceeded (Table 3). The pressure differential that remains "unused" in the calculation increases the flow pressure at the point of use. Hence even in the design case at peak flow rate there is a higher flow pressure than the required minimum p minfl available at almost all point-of-use fittings Balancing calculations Once the worst flow path has been designed, all of the other flow paths have at least one section whose diameter has already been specified. The pressure drops of the sections already calculated must be taken into designing the subsequent flow paths. The pressure available for the sections yet to be sized is then reduced by the sum Σ(I R+Z) TS of the pressure drops of the sections already designed. Equation 14 Fig 17 Example of figures read off for pressure drop charts This aspect of the flow calculations is generally called "balancing". It often allows sections yet to be designed in the vicinity of the building service pipe to be made smaller for the same peak flow rate. The design assumptions and results must be expressed in formulae for the individual flow paths (Step 0). When the diameters of all sections of the worst flow path have been specified, the total pressure drop Σ(I R + Z) must be determined. The result corresponds to the theoretical design assumption when Σ(I R+Z)= p verf. However, it is generally necessary to accept a result in which p verf is larger. Substantial positive or negative differences necessitate recalculation. This involves changing the diameters appropriately until an acceptable result is achieved. 37

38 3 Circulation systems Professor Bernd Rickmann, Fachhochschule Münster, Department of Energy and the Built Environment 3Circulation systems Professor Bernd Rickmann, Fachhochschule Münster, Department of Energy and the Built Environment To ensure drinking water hygiene requirements are met, the technical measures for reducing the growth of legionellae in water supply systems (DVGW Code of Practice W 551) place particular importance on the temperature of the hot water in the storage vessel and in the pipe system. For this reason a temperature of 60ºC must be maintained at the hot water outlet of the water heater. The temperature may only drop below this value for a matter of minutes and not consistently. Circulation systems or self-regulating trace heating systems must be used to ensure the temperature in the pipe system does not drop more than 5K below the storage vessel outlet temperature. Only floor or spur pipes with a water volume 3 litres may be installed without circulation pipes. As is known amongst experts, the design method in DIN for circulation pipes in large systems does not allow the temperatures required for drinking water hygiene to be maintained throughout the system! The incorrect results to be expected as a result of designing to DIN 1988 are largely attributable to the simplifying assumption that, depending on the volume of water circulating (V Zirk ), and the fact that it is circulated three times an hour, the circulation flow rate V St ) should be the same in each riser (Equations 15 and 16). These rules for determining the circulation flow rate apply irrespective of the extent and design details of the circulation system. With this method the nominal diameters for circulation pipes are essentially assigned depending on the diameter of the associated hot water pipe. Once the pipe diameters are known, the circulating volume of water for the entire circulation system (V Zirk ), the pump flow rate (V P ) and the rate at which water should flow through the risers (V St ), can be calculated. The requisite circulation pump pressure differential ( p P ) must be determined by calculating the pressure drop for the worst (longest) circulation circuit. This calculation must include checking that the maximum permissible flow velocity (v max = 0.5 m/s) is not exceeded in the circulation pipes. It may be necessary to choose a larger diameter than that predetermined. For hydraulic balancing DIN already requires installation of throttle valves in each riser. In practice, however, regulation is only carried out if the temperature in the circulation circuit of a water supply system drops below 45 ºC after a long period of time without any water being drawn off. In practice circulation systems designed and installed in accordance with DIN have almost always been commissioned without presetting the regulating valves. As a result of "hydraulic short circuits", in such systems the circulation flow rates through risers near the pump are high, whereas those further away from the pump are correspondingly lower. Numerical simulation for a block with 48 flats, with circulation diameters designed to DIN (Fig 18), shows the flow rate distribution to be expected. In riser ST 1 this simulation gave a flow rate in excess of 350 l/h, and in riser ST 12 it was just V Steig 5l/h. The low circulation flow rates in the risers distant from the pump make it possible for temperatures to drop below 45 C here. The temperature drop in an unregulated DIN 1988 crculation system can only maintained within the required 5 K range in the front half of the system (up to riser ST 5). Quite apart from the resultant hygiene risks, users regard hot water temperatures below 45 ºC, and corresponding delays before low-temperature water runs hot, as malfunctions of the hot water supply. Equation 15 Equation 16 38

39 Fig 18 Flow rate distribution and temperature profile in an (unregulated) circulation system designed to DIN (circulation pump (2)) Past attempts at decontamination in such cases tended to involve fitting of a more powerful pump rather than regulating the system. Fig 19 shows that in the example case this approach can increase the circulation flow rate in the system from 800 l/h to 1400 l/h. Although this slightly improves the flow through the risers with the worst hydraulic conditions, most of the circulation flow produced continues to pass through the "short circuit" sections in the front part of the system. The circulation flow rates needed to maintain the temperature (> 55 C) throughout the system can never be achieved by means of excessive pump capacity (Fig 20). Even if pumps with a suitable characteristic are available, or pumps can be connected in series to achieve sufficiently large pressure differentials, the conditions cannot be decisively improved. High flow velocities in the short circuit sections can cause noise and possibly erosion corrosion. 39

40 Circulation systems Fig 19 Pump and system characteristic for design examples shown in Figs 18 and 20. Operation with flow velocities significantly above v = 1.0 m/s, at least in systems with copper pipes, can markedly increase the risk of erosion corrosion. With large pump pressure differentials regulation creates additional problems, as in the circulation circuits near the pump corresponding pressure differentials have to be established across the circulation regulating valves at very low flow rates. Under such hydraulic conditions effective regulation can only still be achieved at great expense. Full regulation to achieve the circulation flow rates of the design case gives temperatures significantly above 45 ºC throughout the entire circulation system (Fig 21). The design example therefore confirms what has been found in practical experience, namely that the DIN 1988 method yields circulation systems that function adequately provided the only design objective is serviceability. At the same time, however, this example also makes it clear that the high temperatures (> 55 C) required in the DVGW codes of practice often cannot be achieved with this method, particularly in larger systems. Fig 20 Flow rate distribution and temperature profile in an unregulated circulation system designed to DIN with more powerful pump (3) 40

41 Circulation systems Fig 21 Flow rate distribution and temperature profile in a statically regulated circulation system designed to DIN Defined temperatures cannot necessarily be ensured in larger water supply systems with the method of designing circulation pipes described in Part 3 of DIN 1988! To maintain the temperature of the circulating water within the 5 K range much higher circulation flow rates than stipulated in DIN must be achieved in the circulation circuits further away from the pump (Fig 22). These relatively high circulation flow rates not only ensure the temperature is maintained in the last risers, but also make an important contribution to temperature maintenance in the circulation collection manifolds of the main distribution system. As a result of this flow rate distribution the new design rules also give correspondingly larger nominal diameters in the sections of the circulation system further away from the pump (Table 8). The new requirements for operating circulation pipe systems from DVGW Code of Practice W have led to the development of design methods based on thermodynamics (DVGW Code of Practice W ). The methods formulated in this publication aim to ensure energy efficient temperature maintenance in the circulation system. They have the following important features: Use of the pipe heat losses to determine the requisite circulation flow rates Stipulation of a temperature differential less than 5 K between water heater outlet and circulation connection Stipulation of flow velocities for designing the worst circulation circuit and determining the pump pressure differential Hydraulic balancing of better circulation circuits initially using pipe diameters alone, and taking account of the minimum inside diameter of DN 10 and maximum permissible flow velocity (v max = 1.0 m/s) Regulation using circulation regulating valves The DVGW design rules for circulation systems supersede the corresponding rules of DIN (TRWI) in Section 14 as generally accepted practice! 9. DVGW Code of Practice W 551, April 2004: "Water Supply Heating and Water Supply Pipes; Technical Measures for Reducing the Growth of Legionellae, Design, Installation, Operation and Decontamination of Water Supply Systems", Wirtschafts- und Verlagsgesellschaft Gas und Wasser GmbH, Bonn 10. DVGW Code of Practice W 553, December 1998; "Designing Circulation Systems in Central Water Heating Systems", Wirtschafts- und Verlagsgesellschaft Gas und Wasser GmbH, Bonn 41

42 Circulation systems Fig 22 Flow rate distribution and temperature profile in a statically regulated circulation system designed to DVGW Code of Practice W 553 TS TWW DIN TWZ W553 TWZ DIN / Z1 DN 50 DN 25 DN 25 5 / Z2 DN 50 DN 25 DN 25 6 / Z3 DN 40 DN 25 DN 20 7 / Z4 DN 40 DN 25 DN 20 8 / Z5 DN 40 DN 25 DN 20 9 / Z6 DN 40 DN 25 DN / Z7 DN 40 DN 20 DN / Z8 DN 40 DN 20 DN / Z9 DN 32 DN 20 DN / Z10 DN 32 DN 20 DN / Z11 DN 32 DN 15 DN / Z12 DN 25 DN 15 DN 12 Table 8 Circulation pipe diameters to DVGW Code of Practice W 553 and DIN for a block of 48 flats (reference example, see Fig 122 for dimensions) Small and medium-sized circulation systems designed using the DIN 1988 method can generally still be regulated to meet the new requirements of DVGW Code of Practice W 551 (Section 4). The higher network resistance of a DIN 1988 circulation system in the sections of the circulation system further away from the pump can lead in larger systems - even after regulation - to temperature maintenance problems, as the required circulation flow rates cannot be achieved at reasonable cost. In such cases the pipe system has to be modified (see ). 3.1 Design principles The actual pipework and use of the required regulation systems in its design predefine the critical characteristics for problem-free operation of the water circulation system. The accepted distribution principles for water supply systems will therefore be introduced and evaluated in the following sections. Important tips on effective and use of the regulation systems necessary for the particular distribution principle and installation location will also be given. The schematic diagrams of thermostatic valves include the basic temperature setting data. The regulation system diagrams use the following symbols: Isolating valve Thermostatic circulation regulating valve (Multi-Therm or Eta-Therm) Static circulation regulating valve (Multi- Fix or preset isolating valve) 42

43 Circulation systems The design of a circulation system must pursue the following objectives: Reduction of the area of surfaces losing heat, particularly in the riser ducts, in which hot and cold water pipes have to be laid in parallel. The differences in the lengths of the individual circulation circuits must be minimised. Hydraulic short circuits must be eliminated by using suitable regulation systems. Relatively large flow rates must be possible in risers with poor hydraulic conditions. In 3.5 an example with 12 risers and 48 flats shows the effects of the chosen distribution principle on the diameter of the circulation pipe, the circulation flow rate, the pressure differential of the circulation pump and the regulation system on the temperature level in the circulation circuits. This is described below as the "reference example". As the geometric configuration of the pipe system remains unchanged in these example calculations, they provide a quick overview of the advantages and disadvantages of each distribution principle Main distribution systems Bottom distribution system, side feed For construction reasons the points of use on the various floors are supplied with hot and cold water generally originating from basement distribution manifolds and risers on the "bottom distribution" principle (Fig 23). The lengths of the individual circulation circuits of distribution systems with side feed generally differ very considerably. The design of both the supply and the circulation pipes is based on the longest flow path (with worst hydraulic conditions). As with given pressure relationships the "pressure gradient available to cope with pipe friction" (see 2.9) reduces with the length of the flow path, the pipes of the main distribution system have to be made relatively large. Such a pipe configuration also leads to larger nominal diameters for the circulation system, a higher pump pressure differential and hence more difficult regulation conditions. These tendencies are unhelpful in terms of both cost and hygiene. Distribution principles with a more central feed are therefore to be preferred. In very large water supply systems the hot supply may only be configured with a central water heating system. Dividing this system up into several small units is a better solution. This is especially the case with distribution concepts that require high volumes of circulating water to maintain temperature, for example systems with circulation systems extending to the points of use. Fig 23 Circulation system with "bottom distribution" 43

44 Circulation systems Bottom distribution system, central feed If structurally feasible, a pipe configuration with approximately central feed (Fig 24) is to be preferred, since it achieves better hydraulic conditions than one with a side feed. Fig 24 Circulation system with "central feed" Tichelmann distribution system With a "Tichelmann distribution system" the aim is to make all of the circulation circuits the same length (Fig 25). This approach is based on the assumption that the pump has to overcome equal pressure differentials in circuits of about the same length. In heating circuits this can be regarded as being approximately the case. However, in the circulation systems of water supply systems the hydraulic conditions have to be evaluated differently, as the parallel flows and returns have different diameters, so this distribution principle also leads to a significant hydraulic imbalance here. The slight improvements in the hydraulic conditions are offset by higher pipework costs, larger water capacity and larger internal surface. In most specific design cases the disadvantages of this distribution principle predominate, so each individual case always has to be critically examined. As shown by the design example in 3.5, highly effective regulation is still indispensable even with a Tichelmann distribution system. With a Tichelmann distribution system in the circulation systems, it is initially surprising to find that the "worst" circulation circuit is the one including the riser next to the pump. This is because although this circuit has only a few large hot water pipe sections, it also has many smaller circulation sections. Unlike all of the other distribution principles discussed in this manual, with this principle a large circulation flow rate must be possible in the riser near the pump (see 3.5.3). 44

45 Circulation systems Fig 25 Circulation system based on Tichelmann principle Top circulation collection manifold With all of the circulation systems discussed above the circulation pipes are laid parallel to the hot water pipe. If water temperatures in excess of 55 ºC are maintained, in these cases a significant reduction in the stand-by heat losses for the central hot water supply can only be achieved through increased lagging or a reduction in the surface of the pipe system losing heat. The considerable extra expense involved in improving the lagging beyond the requirements of EnEV 11 means this seemingly obvious measure is not a suitable solution. Reduction of the pipe surface losing heat can however be achieved relatively simply by using different distribution principles. A "top distribution system" avoids, for example, the need to lay hot water and circulation pipes in parallel near the risers (Fig 26). This enables the cost of pipework and the water capacity of the supply system to be reduced. At the same time, however, heat losses in the riser ducts are also reduced by at least 40%. As hot and cold water pipes have to be installed in parallel in the confined space of these ducts, even when little cold water is being drawn off its temperature can be kept below 25 ºC for significantly longer (see Chapter 1). This distribution principle therefore meets the commercial and hygiene requirements for installing a circulation system very effectively. However, in most buildings there is not enough space to lay the hot water distribution manifold or the circulation collection manifold in the top or attic storey. 11. Energy Conservation Regulations (EnEV) of 16 November 2001 covering heat insulation and low-energy building services 45

46 Circulation systems Fig 26 Circulation system with "top distribution system" Liner circulation in hot water risers By way of departure from the standard systems described above, circulation systems whose pipes take the form of liners in the hot water risers have been installed in the tower blocks built in the new Federal German states since Like the "top distribution system" shown in Fig 26, this circulation principle reduces the surfaces losing heat in the riser ducts. Moreover, this system can be combined with a main distribution system laid in the basement, thereby also simplifying repairs and maintenance, as the isolation valves for the risers can be positioned centrally. In addition to this central advantage for maintaining the quality of the drinking water, liner circulation has other virtues that improve the cost effectiveness of central water heating and distribution systems: Lower heat losses thanks to reduced pipe surface Longer maintenance of cold water temperatures in riser ducts Smaller circulation pipes Reduced pipe support costs Less lagging Noise insulation and fire protection required for circulation pipe in slab no longer required Fig 27 Principle of liner circulation However, the apparent benefits of liner circulation are only reaped in installed systems if a modified method is used for designing the hot water risers and the circulation system (see 3.2). 46

47 Circulation systems Fig 28 Circulation system with liners in the hot water risers Protection against ingress of non-drinking water In the case of new systems the principle of individual protection as defined in DIN should always be used to protect against ingress of non-drinking water, foreign matter and pollutants (Fig 29). The general protection using riser ventilation valves conventionally employed in old systems causes unnecessarily high pipework costs, increases the pipe volume and significantly increases the proportion of stagnant water in the system. For these reasons of DVGW Code of Practice W also requires the following for decontamination of old systems: If the opening pressure of check valves in the circulation circuit has not been allowed for sufficiently or at all in the pump design, circulation may be prevented, as the pump can then no longer open the check valves. Hence in circulation systems only check valves with a low opening pressure may ever be used, for example the Kemper models shown in Figs 158/159 and 145/146 with p RV = 10 bar (Fig 29). Connecting pipes for ventilation valves for general protection must be removed. Fittings with individual protection must be installed. There is also a problem in that the check valve necessary in the riser with general protection generally develops a considerable flow resistance (opening pressure), which has to be overcome by the circulation pump during circulation. The opening pressure of normal combined check and isolation valves is general of the order of magnitude of the resistance of all of the pipes in the circulation system (Table 23) and therefore greatly increases the necessary circulation pump pressure differential. Fig 29 Configuration of a riser with individual or general protection as defined in DIN DIN "Drinking Water Supply Systems, Protection and Quality Control" 13. DVGW Code of Practice W 551, April 2004: "Water Supply Heating and Water Supply Pipes; Technical Measures for Reducing the Growth of Legionellae, Design, Installation, Operation and Decontamination of Water Supply Systems", Wirtschafts- und Verlagsgesellschaft Gas und Wasser GmbH, Bonn 47

48 Circulation systems Floor systems litre rule DIN 1988 permits a non-circulating volume of water along flow paths of floor and/or spur pipes of up to 3 litres. This volume relates to the individual flow path, calculated from the connection for the particular floor to the point of use, and not to the total water capacity of the floor system. Careful sizing of the pipe diameters in the floor systems using detailed calculations as defined in DIN not only improves the cost effectiveness of the entire water supply system, but also reduces the non-circulating volume in the hot water pipes, thereby improving the hygiene conditions (see also design example of a floor system in the appendix)! Fig 30 Floor system terminology and definitions Circulation to points of use If in a floor system the water capacity of the flow path is greater than 3 litres, a floor circulation system must be provided. It should be noted here that no circulation pipes may be connected downstream of the water meters for the individual flats, as this would lead to serious errors in estimating water and heating charges on the basis of consumption. With a floor circulation system the necessary flat water meters must be positioned downstream of the circulation connection, for example in the vicinity of the points of use. In high-risk systems (for example in hospitals, care homes, etc) for hygiene reasons circulation to each individual point of use is preferred. Although circulation pipes taken to the points of use improve the basic conditions for hygienic operation of the water supply system, they result in significantly higher pipework, regulation and operating costs (see 3.5.6). Such systems may therefore only be actually installed by agreement with the operator and the person responsible for hygiene, after taking into account all of the factors involved. In such cases specified circulation regulating valves (general Eta-Therm) must be installed in the floor circulation pipes. These valves must be able to adopt the regulating positions for the service conditions. The necessary throttling positions cannot be achieved with "presettable" concealed valves! Floor circulation systems must be designed so that the additional cost is justified by perfect system operation. Perfect operation of the floor circulation system can only be expected if only one additional circulation circuit is installed on the floor. Such a solution automatically results from installing on the particular floor a ring pipe system that starts at the riser connection for hot water and ends at the connection to the vertical circulation pipe. The always necessary regulation of the additional circuit with an effective valve should preferably be carried out in the vicinity of the floor isolation valves (bottom of Fig 32). The conditions for regulation become much less favourable if parallel connection of circulation pipes within the floor system produces hydraulically redundant circulation circuits (middle of Fig 32). In such systems it is generally not possible to keep the temperature above 55 ºC right to the point of use. Fig 31 Time taken for low-temperature water in a floor system to run hot at the point of use, using a fitting with a draw-off characteristic as shown in Fig 6 48

49 Circulation systems Integration of numerous floor systems into a larger circulation system can result in unrealistic regulation settings (very large pressure differentials at extremely low circulation flow rates) of the floor regulating valves near the pump. This situation can be improved by a multistage regulation system consisting of a thermostatic valve in the floor system and further static regulating valves, for example at the bottom of the riser and/or on a central circulation collection manifold (bottom of Fig 32). With a multistage regulation system it must be ensured that only one thermostatically controlled valve is ever allowed in the circulation circuit. To maintain the valve authority the first valve in the circulation circuit must always be thermostatic. All other valves in the circuit may only have static restriction functions (Fig 33). Fig 32 Configuration of circulation system taken to points of use Fig 33 Circulation via floor system 3.2 Design methods for circulation systems 14. DVGW Code of Practice W 553, December 1998; "Designing Circulation Systems in Central Water Heating Systems", Wirtschafts- und Verlagsgesellschaft Gas und Wasser GmbH, Bonn DVGW Code of Practice W distinguishes between three design methods for circulation systems depending on the supply system requirements: The short method is intended for designing circulation pipes in smaller systems without thermal or hydraulic calculations. The simplified method can be used to provide preliminary or working designs of medium-sized systems. All sizes of system can basically be designed with the detailed method. This method should be used particularly for larger systems if the ambient temperatures in the basement differ significantly from 10 ºC (standard temperature assumed in simplified method), as can happen with, for example, continuously heated basement rooms. This ensures the design results are a better approximation of the actual service conditions. Because of the complexity of the individual calculation steps, detailed designs should always only be carried out with the aid of a computer program (Fig 56)! 49

50 Circulation systems Short method Fig 34 Limits of applicability of short method The short method can only be used if the system meets the following requirements: The water supply system may only have individually protected point-of-use fittings and hence no additional check valves. The pressure drop across a check valve (gravity) downstream of the pump must not exceed 30 mbar. The total length of all of the hot water pipes affected by the circulation Σ(I TWW ) in the water supply system must not exceed 30 m. The associated circulation pipes are not taken into account in determining the length. The total length of the circulation pipe in the longest circulation circuit must not exceed 20 m. The DN 15 circulation pump must be able to deliver a pump flow rate of at least V P 200 l/h at a pump pressure differential of p P =100mbar. If these conditions are met, the circulation pipe can be designed with d i 10 mm Simplified and detailed methods Circulation flow rate The circulation flow rate must be able to transport the quantity of heat lost via the surface of the pipe system at a given temperature. Only if this equilibrium can be ensured at every point of the circulation system can the desired temperature level be maintained in the pipe system. The heat loss via the surface of the pipe is directly related to the circulation flow rate needed to maintain the temperature and therefore forms the basis for calculating the flow rate. The heat loss from a section (ll q W ) is heavily dependent on the area of the surface of the lagged pipe, the thickness of the lagging, the thermal conductivity of the lagging and the average temperature differential between the water and ambient air (Equations 17 and 18). With a reasonable degree of accuracy all other factors relating to internal and external heat transfer can normally be regarded as constant or neglected. 50

51 Circulation systems Equation 17 q W k R ϑ Equation 18 λ D D d α a Specific heat loss of a lagged pipe in W/m Heat transmission coefficient of the pipe in W/(m K) Average positive temperature differential between the hot water in the pipe and the ambient air ϑ = 50 K at a basement air temperature of 10 C ϑ = 35 K at a basement air temperature of 25 C Thermal conductivity of the lagging (according to HeizAnlV λ D =0.035W/(m K) Outside diameter of the lagged pipe in m Outside diameter of the unlagged pipe in m External heat transfer coefficient (with normal environmental factors α a 10 W/(m 2 K) Example: Calculation of the heat loss from a stainless steel pipe laid in the basement and having a diameter of DN 40 (42 x 1.5) and full lagging (40 mm thick) to EnEV With a temperature differential of ϑ =50K: q W =k R ϑ = = 9.78 W/m (Fig 35 and Table 22) The heat losses of a circulation system can be calculated using the detailed method and hence Equation 17, or using the simplified method. As shown by the evaluations of calculations based on Equation 17, with thermal insulation to EnEV heat losses arise that are approximately the same for all pipe diameters. With sufficient accuracy this situation can be used as an initial design simplification, with the heat losses under normal conditions being regarded as constant whatever the diameter of the pipes: Exposed pipes in basement q W = 11 W/m (Fig 35) Laid in duct qq W = 7 W/m (Fig 36) Fig 35 Heat losses of insulated stainless steel pipes with different lagging thicknesses (λ D =0.035W/m K), with a temperature differential of ϑ =50K, giving an average of 11.0 W/m, fully lagged to EnEV 51

52 Circulation systems Fig 36 Heat losses of insulated stainless steel pipes with different lagging thicknesses (λ D = W/m K), with a temperature differential of ϑ =35K, giving an average of 7.0 W/m, fully lagged to EnEV However, if there are any deviations from the standard assumptions, for instance different ambient temperatures, or strong air currents are to be expected where the pipes are laid, the heat losses must be calculated using the detailed method and hence Equation 17. The normal approach of laying the hot water and circulation pipes in parallel in the basement and in the riser ducts gives approximately equal pipe lengths for the different sections (Fig 23). From the above description it can be concluded with sufficient accuracy that the temperature drop in the hot water pipes of a circulation circuit must then be as large as in the circulation pipes. With the simplified method the temperature drop ϑ W from the storage vessel to the start of the circulation pipe always corresponds to exactly half of the total temperature differential permitted in the circulation circuit (Fig 37). If the lengths of the hot water and circulation pipes are very different, as for example with a supply system with top distribution system (Fig 26), the permissible temperature drop in the hot water pipes ϑ W can be estimated with Equation 19. If this calculated temperature differential exceeds 3 K, Equations 23 and 24 must be used to verify that the total pressure differential of 5 K permitted by DVGW Code of Practice W 551 is not exceeded. Equation 19 Σ(I TWW ) Σ(I TWZ ) Total length of the hot water pipes in the worst circulation circuit Total length of the circulation pipes in the worst circulation circuit Account must also be taken of the fact that for continuity reasons the flow rates must be the same in the parallel hot water and circulation pipes. The circulation flow rate therefore only has to be worked out for the hot water pipes. Only when the heat losses are calculated using the "detailed" method does a certain level of error have to be tolerated as a result of this simplification, as the diameter of the circulation pipe is generally smaller than the associated diameter of the hot water pipe. As this can only result in a slightly smaller temperature differential between water heater outlet and circulation connection on the storage vessel than initially predicted by the calculation, the discrepancies to be expected are always on the safe side. This discrepancy therefore generally only has to be chekked by calculation in very large systems, or if, for example with a "top distribution system", the lengths of hot water and circulation pipes are very different. With the "simplified" method only the location in which the pipe is laid and the length of the section are required to 52

53 Circulation systems work out the heat loss. The sum of the heat losses that have to be covered from this section onwards in the flow direction can then be worked out from these details Σ(l qq W ). Fig 37 Circulation system notation (temperature relationships relate to the simplified method) Calculation of the flow rates starts with the first section downstream of the water heater. Here the circulation flow rate VV is identical to the pump flow rate V P (Equation 20). Q a = VV a ρ c ϑ and Q d = V d ρ c ϑ Equation 20 Σ[l q W ] ρ c ϑ W Sum of the heat losses over the surface of all hot water pipes in W Density of the water (ρ 1kg/l) Specific heat capacity of the water (c 1.2 Wh/(kg K)) Temperature drop permitted in the hot water pipes (TWW) between hot water heater (TWE) outlet and start of the circulation pipe, for example with the simplified method ϑ W =2.0K A relatively simple method of working out the required circulation flow rates in all other sections is provided by considering a branch point in a hot water (TWW) pipe system (Fig 38). For the branch heat flow (subscript a) at any separation point, and for the line heat flow (subscript d), the following initially completely generally expressions can be derived for pure circulation: Fig 38 Tee (branch point) notation As the temperature differential ϑ from any branch point to the water heater must always be the same along both flow paths, the following ratios can be equated: The flow continuity equation at the branch point V=V+VV d gives the basic equations for calculating the flow rates: Equation 21 53

54 Circulation systems Temperature drop in circulation circuit Equation 22 The flow rate in the section downstream of the water heater (TWE) corresponds to the pump flow rate (Equation 20): When determining the flow rates Equation 24 can be used to calculate the temperature drop at the end of each particular section. This step also gives the calculated temperature setting for the circulation regulating valve. Equation 23 If the pump flow rate is known, the branch (a) at the first tee and the line (d) circulation flow rates can subsequently also be calculated: Equation 24 ϑ TS I q W ϑ TWE Σ ϑ TS V ϑ W Temperature drop between beginning and end of a section Heat loss from the section being considered in W Storage vessel outlet temperature, e.g. 60 ºC Temperature drop to design point Flow rate in the section Temperature of the hot water at the end of the current section Hot water temperature at the end of the first section (Fig 39) downstream of the water heater (TWE). The temperature drop in section TS 4 is Fig 39 Example of calculation of circulation flow rate (see also design example in the appendix) and the hot water temperature at the calculation point, at the end of the section (Fig 40 and Table 21) Calculations of this complexity do not add to costs if the project is handled with a computer and a powerful design program for water supply systems, such as Geberit ProPlanner. The calculated temperature setting for the circulation regulating valve can be used to achieve more accurate regulation, particularly if thermostatically controlled valves are used. The temperature drop can also be used to calculate the circulation flow rate as an alternative to Equations 21 and 22 (Fig 40). 54

55 Circulation systems Fig 40 Temperature drop in the circulation circuits for risers ST 1 and ST 12 from Table 21 and resultant circulation flow rates (Fig 122) Determining pipe diameter and pump pressure differential The hydraulic calculations for a circulation system in a water supply system are carried out for steady-state service conditions with water no longer being drawn off. The basic equation (25) for designing such a circuit system can then be developed from a consideration of Bernoulli. It applies to any circulation circuit starting in the delivery connection of the pump and ending in its inlet connection. Equation 25 p P Σ(I R+Z TWW ) Σ(I R+Z TWZ ) Pump pressure differential Pressure drops in the hot water pipes (TWW) of the circulation circuit Pressure drops in the circulation pipes (TWZ) of the circulation circuit P RV Pressure drops across check valves, for example downstream of the pump (60 mbar) or across the protection combination for the riser (100 mbar). The manufacturer's details should preferably always be used here (Table 23). p TH Pressure drop across a fully open thermostatically controlled circulation regulating valve (Fig 60) p D Throttling pressure drop across circulation regulating valve p AP Pressure drop across any item of equipment, eg a heat exchanger in the circulation circuit In the hot water pipes sized for the peak load during use the relatively low circulation flow rate only causes a small pressure drop. When using the "simplified" method, therefore, the pressure drop in the hot water (TWW) pipe does not have to be checked by calculation. On similar lines to the design rules in DIN for hot and cold water pipes, the pressure drop calculations can also be carried out using either the "detailed" or the "simplified" method. Because of the low velocities in circulation systems the minor losses "a" make up a relatively small proportion of the total pressure drop. With the simplified method, according to DVGW Code of Practice W 6553 this contribution can be estimated as equivalent to adding 20 to 40% of the pressure drops for a straight pipe. Equation 26 When using the detailed method minor losses must be calculated using Equation 13 and the constants listed in Table 23. The circulation nominal diameters are specified for the circulation flow rate in the section, preferably taking account of a maximum flow velocity and not on the basis of a pressure gradient available to cope with pipe friction, as in the DIN 1988 calculations. Circulation nominal diameters must be chosen on the basis of the hydraulics in such a way that the flow velocities in the circulation circuit - towards the circulation pump - increase continuously. In sections near the pump the velocity can be up to v max =1.0m/s (Fig 41). In larger water supply systems in particular, sizing all circulation pipes in the vicinity of the maximum 55

56 Circulation systems permissible velocity leads to an extremely high pump pressure differential that results in uneconomic pipe operation. Fig 41 Desired velocity profile in the circulation pipes The pressure drop calculation for the worst circulation circuit defines the required pump pressure differential p P. Fig 42 Schematic diagram of a circulation system with names of important working parts By contrast with the provisions in Part 3 of DIN 1988, the next larger size of circulation pump must always be chosen. This means that the intersection of pump and pipe network characteristics (actual operating point) must always lie above the calculated operating point (Fig 43). 56

57 Circulation systems Fig 43 Pipe network and pump characteristics Sizing circulation liners in hot water risers Special features When liners are used for circulation only the annular gap between the outer pipe and the liner remains available for carrying the water to the load. The pressure drop calculations needed to size the outside pipe must therefore take account of the liner used rather than just being based on the inside diameter as though the full cross section were available. Using the otherwise identical design method of DIN , the liner generally leads to the outside pipe having to be one size larger than in conventional systems. The pressure drop calculations for the liner system are based on the ideal assumption of the liner being central in the outside pipe Determining circulation flow rates The aim in developing a method of designing liner circulation systems 15 was to adopt as many of the elements of the design rules for conventional systems from DVGW Code of Practice W 553 introduced in the meantime as possible. This also applies particularly to the method of calculating the required circulation flow rates. This is based on the heat lost via the surface of the insulated pipes. To allow for the absence of the heat losses from the external circulation pipe in the riser section, by analogy with the method according to DVGW Code of Practice W 553, only half the heat losses from the hot water riser are taken into account. Designing the liner system with a temperature drop of ϑ W = 2 K in the hot water pipes therefore leads to a temperature profile in the basement distribution manifolds that, as expected, is not critical (Fig 45). By comparison with the results from conventional systems it is striking that the circulation flow rates become extremely low in the risers near the pump and very high in the riser furthest away from the pump. Fig 44 Terminology for riser with circulation liner 15. Rickmann, Bernd "Circulation system with liners in hot water risers", TGA Fachplaner 6/24 57

58 Circulation systems Fig 45 Temperature profile in the basement distribution manifolds and flow rates in the risers calculated according to DVGW Code of Practice W 553 Equation 27 Equation 28 Key: Spalt Hüllrohr Luft Inliner = gap = outside pipe = air = liner Fig 46 Notation for a liner circulation system Unlike in a conventional circulation system, the temperature in liner circulation systems no longer drops continuously in the direction of flow in the riser section 16. Instead of the temperature of the outlet (ϑ Aus ) from the riser system as would be expected, the lowest temperature in the riser system is the head temperature (ϑ Kopf ) at the reversal in direction from the toroidal gap into the circulation liner (Fig 46). This temperature profile is caused by the fact that the flow in the toroidal gap loses heat both via the surface of the lagged pipe to the surrounding air and to the reverse circulation flow in the liner. The heat absorbed by the liner leads to an increase in temperature that reaches its maximum with the outlet temperature. 16. Anneken, Christoph / Knobloch, Sven "Design and Installation of a Test Facility for Examining the Problem of Internal Circulation Pipes", Degree dissertation, Fachhochschule Münster, 2002 An effective method of designing liner circulation systems cannot merely consider the inlet and outlet temperature of the riser system. It also has to check the temperature profile in the riser. The temperature profile in the "heat exchanger" to be considered can only be calculated step by step. The smaller the chosen increment the more accurate the result will be 17. If the temperature profile in risers 1 to 12 of the example is calculated with an increment of l = 10 cm, it becomes clear that with the circulation flow rates calculated according to W 553 the desired design temperature of 56 ºC cannot be maintained in the risers near the pump (Fig 47). Direct application of the W 553 design basis to liner circulation system is not permitted Meissner, Dorian / Wiebe, Jakob "Development of Algorithms for Designing Circulation Systems with Liners in Hot Water Risers", Degree dissertation, Fachhochschule Münster, Rudat, Klaus "Analytical Examination of Hot Water Distribution Systems with Runs with Internal Circulation Pipes", HLH, Vol 51,

59 Circulation systems Minimum flow rate in riser The method described initially of calculating the temperature profile in the riser is in any case so involved that it can only be incorporated in existing computer programs for designing water supply systems with considerable effort. It therefore seems sensible in the introductory phase of this technology to look for a simpler approach that ensures sufficiently high temperatures at the head of the riser. From the results of numerous detailed calculations it is possible to develop a simple numerical equation enabling calculation with the accuracy claimed for "simplified" calculations of a minimum flow rate for 35 x 11.5 or 28 x 1.4 outside pipes with 12 x 1.0 liners that leads to "head temperatures" > 56 ºC. Only the length of the riser and the inlet temperature ϑ E in the toroidal gap have to be known in order to apply this equation. Equation 29 V Z Minimum circulation flow rate in riser ϑ E Inlet temperature in hot water (TWW) riser in C l Length of riser Range of validity of equation Inlet temperature in riser: C Outside pipe = 35 x 1.5 Lagging in accordance with German Heating Regulations or EnEV Duct temperature 25 C Fig 47 Temperature profile in risers calculated according to DVGW Code of Practice W

60 Circulation systems Fig 48 Minimum flow rate for 28 x 1.5 / 12 x 1.0 and 35 x 1.5 / 12 x 1.0 liner risers as a function of inlet temperature in toroidal gap ϑ E and length, at an ambient temperature of 25 C and with lagging to EnEV In most cases the circulation flow rates via the risers resulting from calculation to DVGW Code of Practice W 553 are inadequate, and therefore have to be raised to the minimum flow rate (Fig 48) in the risers involved Regulation The pump pressure differential calculated for the worst circulation circuit is available in all other circulation circuits to overcome pressure drops. A "hydraulic balance" is only achieved when pump pressure and pressure drops are in equilibrium in each circulation circuit. The primary objective in sizing the circulation pipes must be set the "available" pressure differential of the pump against the pressure drops in pipes. A lower limit is set on the choice of suitable diameters for the circulation pipes to be sized by the available inside diameter of the chosen pipe series, and by the requirement in the design rules to observe minimum inside diameters (DN 10) and maximum velocities (v max = 1.0 m/s). In each circuit this results in differences between the pump pressure and the pressure drops with the design flow rate distribution in the pipe system. These deviations from the ideal situation of "hydraulic balance" are particularly large in the sections near the pump. Despite involved pipe system design calculations they lead to a completely different flow rate distribution being established in the pipe system that that planned (see 3.5). For this reason the pressure differential still lacking to achieve "hydraulic balance" must be set up at selected points with regulating valves. The differentials p D remaining in the pressure drop calculations between the available pump pressure p P and the pressure drops calculated in the circulation circuits must be reduced with circulation regulating valves (Equation 30). Equation 30 If "hydraulic balancing" is not performed, the design flow rates cannot be established in the installed system. The circulation flow rate must, however, be able to transport the quantity of heat lost via the surface of the pipe system. This means that a specified water temperature can only be achieved if the equilibrium described above is ensured at every point of the circulation system. Hydraulic balancing of a circulation system is therefore the basic prerequisite for reliable operation as defined in DVGW Code of Practice W 551. The Codes of Practice for Drinking Water Installations - TRWI (1988) already require the installation of throttle valves for balancing circulation systems. However, in this respect the regulation measures stipulated in DIN only aim to keep the circulation flow rates the same in all risers. This is intended to limit the temperature drop between the water heater (TWE) outlet and return inlet via the circulation system to about 7 to 10 K (Fig 21). As already mentioned in Chapter 3, these measures are no longer sufficient to meet the current requirements. 60

61 Circulation systems Fig 49 Condition for hydraulic balance in circulation systems As a result of the design rules for circulation systems having been made more precise in DVGW Code of Practice W 553, pipe system design gives settings (k V -values) that could not be achieved with the throttle valves available on the market at that time it was introduced 19. As the example calculations show, this applies particularly to the valves near the pump in larger circulation systems, as relatively large pressure differentials have to be established here at low flow rates (Fig 50). To meet the new requirements, in conjunction with the Plumbing and Sanitation Laboratory of the Fachhochschule Münster, valve manufacturer Gebr. Kemper based in Olpe has continued to develop its valve designs and extend its range of valves. The first step was to define on the basis of numerous example calculations for medium and large water supply systems the minimum boundary conditions a circulation regulating valve has to cover against the backdrop of the requirements of DVGW Code of Practice W 551. From these findings a reference system for residential buildings was then defined. This system consists of twelve risers, each serving four upper floors, ie a total of 48 flats with standard plumbing. On the basis of the results of the calculations for the reference system, a laboratory test stand was set up in which the hydraulic and thermal conditions for any two risers in this system could be simulated. The valve prototypes installed on the stand could be tested under realistic conditions 19. Ch. Saunus "Are Water Supply Systems Dying of Legionella?", Sanitär und Heizungstechnik, 4/5, 1993 (available in German only) even in the initial development stage The bar chart of the calculated throttling settings (circulation flow rate VV Z and pressure drop p D across the valve) for the circulation regulating valves (Fig 50) reveals that in the circulation circuits near the pump relatively large pressure differentials have to be built up at low circulation flow rates, whereas in the risers further away from the 20. B. Gertdenken "Designing Circulation Pipes to Part 3 of DIN Sources of Error and Suggestions for Improvement", Degree dissertation 1991, Fachhochschule Münster, unpublished (available in German only) 21. S. Rinsche "Designing a Water Supply System with Hygiene in Mind", Degree dissertation 1991, Fachhochschule Münster, unpublished (available in German only) 22. C. Batke, A. Tebroke "Designing a Circulation System for a Care Home According to the Rules of DVGW Code of Practice W 551, Using the Computer Programs AutoCad 12 and Dendrit 7.02", Degree dissertation 1991, Fachhochschule Münster, unpublished (available in German only) 23. M. Geesen "Computer Aided Design of a Water Supply System in a Care Home Using Dendrit 7.0", Degree dissertation 1995, Fachhochschule Münster, unpublished (available in German only) 24. G. Glasmeier, W. Hagemann, Ch. Teepe "Decontaminating Water Systems in a Meat Processing Facility", Degree dissertation 1995, Fachhochschule Münster, unpublished (available in German only) 25. B. von Höfen, R. Lünse "Designing a Water Supply System for a Care Home Using AutoCad 12 / Pit-Cup and Dendrit 7.0", Degree dissertation 1995, Fachhochschule Münster, unpublished (available in German only) 26. F. Schrapper "Hydraulic Characteristics of Thermally Controlled Regulating Valves - Design and Installation of a Test Stand", Degree dissertation 1995, Fachhochschule Münster, unpublished (available in German only) 27. A. Kleine-Hartlage "Enhancement of a Thermally Controlled Throttle Valve for Water Supply Circulation Systems", Degree dissertation 1995, Fachhochschule Münster, unpublished (available in German only) 28. J. Straube "Designing a Pilot Circulation System with Thermally Control Regulating Valves Using Windows Dendrit Preliminary Investigation of Measurement Aspects", Degree dissertation 1996, Fachhochschule Münster, unpublished (available in German only) 61

62 Circulation systems pump relatively large flow rates are necessary to keep the temperature above 55 C. These high flow rates also lead to circulation pipes of larger diameter, which generally result in a circulation regulating valve with corresponding diameter (example in appendix). Fig 50 Required circulation flow rate via the riser and pressure differential across the regulating valves to ensure hydraulic balance Fig 51 k V -values and temperature settings for regulating valves in riser system (Table 20) Irrespective of whether "static" or "dynamic" regulation of a water circulation system is planned, the following valve data should be known for all regulating valves in the system through pipe system design: Flow rate V Z in the section (or through the valve) Pressure differential across the circulation regulating valve p D k V -value, calculated from V Z and p D (Equation 31) Temperature setting on valve in hydraulically balanced state Basically, it has to be said that the larger and more branched the circulation system the more important an accurate knowledge of these valve settings becomes. 62

63 Circulation systems k V -range required for circulation regulating valves Circulation regulating valves are generally sized and preset on the basis of what is termed the k V -value. This is defined as the flow rate in m 3 /h through the valve with a pressure drop of 1000 mbar. The k V -range of a regulating valve has to be determined by measurement and specified by the manufacturer of the valve in its technical documentation. The k V -value required for the circulation regulating valves can be calculated from the system values: circulation flow rate VV Z in l/h and pressure drop across the valve p D in mbar with Equation 31 (example calculation in Table 20). Equation 31 The numerical value obtained must be in the k V -range of the chosen circulation regulating valve to enable the pressure differentials required for hydraulic balancing to be built up. Example: Hydraulic design of a circulation system (Fig 122) gives the following valve data for a circulation circuit via the riser (ST 1 from Table 20): Circulation flow rate VV Z = 30 l/h Pressure differential across valve p D = 117 mbar These values give a k V -value of: 3.3 Available regulation technology Static circulation regulating valves Multi-Fix riser regulating valve If static circulation regulating valves are used, they are sized by means of the k V -value or the required valve data V Z and p D. With these data the required setting for a valve of a particular nominal diameter can be read off a diagram (Fig 42) or table (Table 9). Example: For a k V -value of 0.087m 3 /h Table 9 gives a valve setting of 1.7. The same value can be determined from Fig 52 using the circulation flow rate V Z = 30 l/h and the pressure differential p D = 117 mbar. Valve setting k V -value m 3 /h Table 9 Valve settings and k V -values for a circulation regulating valve (Multi-Fix, DN 15, Fig 150) 63

64 Circulation systems Fig 52 Valve settings for static circulation regulating valve (runs 1 to 12) Presettable isolating valve Fig 53 Presettable KEMPER isolating valve with Mapress press connection, Fig No characteristics are specified for presettable isolating valves. These valves should be positioned centrally, on circulation collection manifolds or in the delivery connection of the circulation pump (Fig 1), to make it possible to eliminate any pressure differentials still present between larger subsystems. Throttling can be carried out effectively on the basis of the temperature of the circulation return flow from the system. If, in an otherwise regulated circulation system, the temperature here is higher than the calculated design temperature (for example > 55 C), the flow rate via the last risers is larger than needed to maintain the temperature of the circulation collection manifold. Such a valve can be preset to throttle the flow in order to influence the pressure relationships (see 3.5.1). Fig 54 Applications of presettable isolating valve Key: TWZ = Circulation 64

65 Circulation systems Thermostatic circulation regulating valves Static regulation of a larger circulation system requires accurate pipe system design calculations that also yield the settings for the regulating valves. Any deviations of the installed circulation system from the original design have to be laboriously eliminated by manually readjusting the valves. As such deviations are routinely encountered on building sites in Germany, the obvious solution was to develop regulating valves that could eliminate such differences, which are likely to be slight, "automatically". In a manner similar to calculation of the required pressure drop across the circulation regulating valve for hydraulic balancing, the associated valve temperature can also be determined when carrying out the pipe system design calculations. The valve temperature in the hydraulically balanced state (temperature setting) depends on the system and differs for each regulating valve. In all systems to be operated with a storage vessel temperature of 60 C and a permissible temperature differential of 5 K, they lie within a tight range between about 56 and 58 ºC (Fig 51). More than a decade ago these facts prompted valve manufacturer Gebr. Kemper of Olpe in conjunction with the Fachhochschule Münster to develop thermostatically controlled circulation regulating valves that could automatically adopt suitable throttling positions depending on the valve temperature. These valves adopt a maximum throttling position when the temperature setting is reached. However, in this position they are still not completely closed (5.3 of DVGW Code of Practice W 553). As a result, the circulation flow rate needed in the pipe section involved is continuously available without the circulation flow being disrupted (Fig 57). The k V,min -value of the thermostatic valve used must correspond to the results of pipe system design calculations in accordance with DVGW Code of Practice W 553. Only in this case will the corresponding regulation or required temperature maintenance be achieved with minimal use of materials and energy. Because of the fundamental importance for proper circulation the DVGW has drawn up the requirements to be met for a test certificate to be issued for such valves Multi-Therm riser regulating valve Calculation and measurement has shown that it is generally sufficient for the DVGW-certified Multi-Therm regulating valves in the riser system to be set on an average temperature of 57 ºC. For this reason these valves are supplied with this setting as standard. This default should only be changed in larger systems if appropriately calculated (for instance with a computer program such as ProPlanner from Geberit (Fig 56)) specified temperature settings are known for the valves 30. Positioning the valves at a different point in the system may (slightly) alter the optimum temperature setting. Examples are to be found in the schematic diagrams in 3.1. If a storage vessel outlet temperature of 60 ºC cannot be ensured during operation, the temperature setting on the circulation regulating valve must be 3 K lower and the possible vessel outlet temperature. A thermostatically controlled circulation regulating valve is sized like the static valves using a throttling chart. In this case it also has to be checked whether the throttling positions required by the calculations lie within the characteristic of the chosen valve (Figs 59 or 60). If they do, fine operational regulation of the circulation system by the installed thermostatic valves depending on the temperature setting is carried out automatically. With otherwise balanced basic hydraulic conditions, deviations of the actual service from the design conditions can be automatically eliminated in this way without further manual intervention. However, more serious weaknesses in the hydraulics of the pipe system ( ) can no longer be eliminated by thermostatic circulation regulating valves, as these valves can only adopt throttling positions within tightly defined ranges and are not designed to be able to produce either reheating or pump pressure differentials! In designing thermostatic valves it must be ensured that the k V -value calculated as required does not exceed the actual k V -value of the chosen valve at 55 C (Fig 58 and ). The next larger valve may have to be chosen. Skilled use of thermostatic circulation regulating valves considerable reduces the complexity of both design and regulation of the installed system. As the free flow cross section in the valve must become very small at the maximum throttling positions, with static valves there is a danger of suspended matter being able to settle in the control cross section. With thermostatically controlled valves a resultant malfunction is rather unlikely, as reduction of the valve cross section during operation - and the associated drop in temperature - causes the valve to reopen automatically. However, all circulation regulating valves should be positioned in the system for ease of inspection and maintenance. By analogy with heating problems, in the circulation systems of water supply systems the effect of the thermostatic valves on the flow rate in the pipe system depends on the ratio of the pump pressure to the pressure drop in the control section (valve authority). System components 29. DVGW VP Provisional test guidelines "Thermostatic Circulation Regulating Valves for Hydraulic Balancing in Hot Water Supply Systems" 30. Mass, Tobias "Comparison of Technical Design Programs Based on ZVSHK Certification Procedure", Degree dissertation, Fachhochschule Münster,

66 Circulation systems that can impair the valve authorities, such as check valves, etc, must therefore be avoided through suitable design of the pipe systems (3.1.2). Fig 55 KEMPER isolating valve with Geberit Mepla connection, Fig , and KEMPER Multi-Therm circulation regulating valve with Geberit Mepla connection, Fig Fig 56 Geberit ProPlanner k V -values and temperature settings for circulation regulating valves in reference example, calculated for Mepla series of pipes Fig 57 Relationship between flow rate, pressure differential and temperature Multi-Therm circulation regulating valve, DN 15, temperature setting 57 ºC 66

67 Circulation systems Fig 58 Multi-Therm circulation regulating valve, DN 15 (temperature setting 57 C) k V -values as a function of valve temperature The valves can be chosen using charts (Figs 59 and 60) or automatically with a computer program (Fig 56). As the flow rates become higher a valve with larger nominal diameter must be used (Fig 60). This change in diameter is particularly important for proper circulation, as a high circulation flow rate - as for example in runs 11 and 12 - would produce substantial pressure drops p TH across the DN 15 valve (Fig 59). Incorrect valve design or positioning can lead to serious malfunctions in the circulation system ( ). Fig 59 Regulation range of the DN 15 Multi-Therm circulation regulating valve (temperature setting 57 ºC). The plotted points result from the settings calculated for the circulation regulating valves in runs 1 to 12 from Fig 122 and Table

68 Circulation systems Fig 60 Regulation range of the DN 20 Multi-Therm circulation regulating valve (temperature setting 57 ºC). The plotted points result from the settings calculated for the circulation regulating valves in runs 11 and 12 from Fig 122 and Table Eta-Therm floor regulating valve As the aim in high-risk systems is increasingly to ensure circulation to the points of use, a thermostatic circulation regulating valve has been developed that meets the hydraulic and design requirements for use in floor systems of limited extent (3.5.6). Fig 61 KEMPER Eta-Therm floor regulating valve, Fig (concealed with Mapress press connection) and Fig (installed exposed with Geberit Mepla),with k V,min = 0.05, for regulating circulation systems of floor systems, with temperature setting between 56 and 58 C 68

69 Circulation systems Fig 62 Eta-Therm circulation regulating valve, DN 15 (temperature setting 57 C), k V -values as a function of valve temperature 3.4 Commissioning a circulation system When a water supply system is commissioned measurements must be taken to check the temperatures in the circulation system. The results should be recorded and incorporated in the operating and maintenance documentation. The temperature measurements must be taken under service conditions corresponding to the design assumptions, ie static conditions. Such conditions are characterised by the fact that the temperatures in the system may no longer change with time. They are only established in the water supply circulation system after several hours without any water being drawn off. If the storage vessel temperature is regulated by means of a two-level controller, the switching differential of the vessel's thermostat must be taken into account when checking the temperatures. In "large systems" regulation of the storage vessel temperature is basically continuous and not by means of a two-level controller (DVGW Code of Practice W 551, 6.1). With a storage vessel outlet temperature of 60 C, temperatures approximating to the calculated values must be established in the circulation system automatically. Comparison of the actual temperature with the calculated temperature setting on the regulating valve yields not only simple conditions for checking during commissioning of a newly installed system, but also simplifies the necessary operational maintenance, checking and inspection. For this reason the Multi-Fix and Multi-Therm circulation regulating valves are provided with sensor (dial thermometer, "instantaneous" thermometer or remote monitoring sensor) connection points. To simplify monitoring and maintenance it is advisable to permanently note the valve data and temperature setting in the maintenance instructions and on the as-built drawings and associated valve name plates. VDI Guidelines stipulate that: "Water supply pipes, particularly hot water and circulation pipes, must be balanced as a complete system or in sections. Hydraulic regulation must be recorded." 3.5 Verifying regulation through numerical simulation The following section elucidates by means of numerical simulation the hydraulic and thermal relationships in unregulated and hydraulically balanced systems based on different distribution principles (see 3.1). All of the comments relate to a "reference example" with twelve risers and 48 flats. The hot water pipes (TWW) are sized on the basis of DIN and the circulation pipes on that of DVGW Code of Practice W 553. As the layout remains unchanged in these calculations, the examples give a quick overview of the effects of the circulation principle on circulation pipe diameters, circulation flow rate and circulation pump pressure differential, and of the effect of the regulation technology on the temperature level in the circulation circuits. 31. VDI 6023 "Hygienic Aspects of the Planning, Design, Installation, Operation and Maintenance of Drinking Water Supply Systems", VDI- Gesellschaft Technische Gebäudeausrüstung. 69

70 Circulation systems The numerical simulation carried out takes account of the following factors: changed storage vessel outlet temperatures, temperature drop in the pipe system due to heat losses calculated using detailed method for all hot water (TWW) and circulation (TWZ) pipes, changed pressure drops in the thermostatically controlled circulation regulating valves due to varying valve temperatures and resultant changes in flow rate in the circulation system with new network resistance and the new operating point on the pump characteristic Bottom distribution system, side feed Fig 63 Flow rates via risers, with temperature profile in basement distribution manifolds, unregulated, circulation pump (2) Fig 64 Flow rates via risers, with temperature profile in basement distribution manifolds, regulated with Multi-Therm circulation valve, DN 15 (temperature setting 57 ºC) 70

71 Circulation systems Fig 65 Flow rates via risers, with temperature profile in basement distribution manifolds, regulated with Multi-Therm circulation regulating valve, DN 15 (temperature setting 57 ºC), and centrally reregulated with a static valve Fig 66 Pipe network and pump characteristic with operating points for various service conditions plotted 71

72 Circulation systems Top distribution system, central feed Fig 67 Flow rates via risers, with temperature profile in the basement distribution manifolds, unregulated, circulation pump (1) Fig 68 Flow rates via risers, with temperature profile in basement distribution manifolds, regulated with Multi-Therm circulation valve, DN 15 (temperature setting 57 ºC) 72

73 Circulation systems Fig 69 Pipe network and pump characteristic with operating points for various service conditions plotted Tichelmann distribution system Fig 70 Flow rates via risers, with temperature profile in the basement distribution manifolds, unregulated, circulation pump (2) 73

74 Circulation systems Fig 71 Flow rates via risers, with temperature profile in basement distribution manifolds, regulated with Multi-Therm circulation regulating valve, DN 15 (temperature setting 57 ºC) Fig 72 Pipe network and pump characteristic with operating points for various service conditions plotted 74

75 Circulation systems Top circulation collection manifold Circulation systems with a top circulation collection manifold are particularly sensitive to hydraulic short circuits (Fig 73). In this case as well regulation must aim to produce a high flow rate in the worst riser. The ratio of the flow rate necessary to maintain the temperature in the first and second riser is particularly pronounced with this distribution principle. Fig 73 Flow rates via risers, with temperature profile in the basement distribution manifolds, unregulated, circulation pump (2) Fig 74 Flow rates via risers, with temperature profile in the basement distribution manifolds, regulated with Multi-Therm circulation regulating valve, DN 15 (temperature setting 57 ºC) 75

76 Circulation systems Fig 75 Pipe network and pump characteristic with operating points for various service conditions plotted Liner circulation in hot water risers When the aim is to regulate on the basis of temperature using thermostatically controlled valves, with liner circulation systems the circulation regulating valves must ideally be positioned at the points of lowest temperature, i.e. at the head of the riser. As for structural reasons valve systems generally cannot be installed here, in circulation systems with liners the regulating valves must be positioned in the region of the basement distribution manifolds. Fig 76 Flow rates via risers, with temperature profile in the basement distribution manifolds, unregulated, circulation pump (2) 76

77 Circulation systems Fig 77 Flow rates via risers, with temperature profile in basement distribution manifolds, regulated with Multi-Therm circulation valve, DN 15 (temperature setting 57 ºC) With a suitably designed and sized pipe system (3.2.3) circulation systems with liners in the hot water risers can be regulated with Multi-Therm circulation regulating valves, as the regulation characteristic of the valve can ensure that the temperatures at the head of the risers do not fall below the minimum design temperature (for example, 56 ºC) (Fig 79). Fig 78 Pipe network and pump characteristic with operating points for various service conditions plotted 77

78 Circulation systems Fig 79 Temperature profile in the risers after regulation with DN 15 Multi-Therm circulation valves Circulation to points of use Circulation to the points of use significantly enlarges the surface of the pipe system losing heat. To ensure in such a case that temperatures can be kept above 55 ºC throughout the circulation system, much higher circulation flow rates must be possible than in conventional systems. Fig 80 Flow rates via floor systems, with temperature profile in the basement distribution manifolds, unregulated, circulation pump (3) 78

79 Circulation systems Fig 81 Flow rates via floor systems, with temperature profile in basement distribution manifolds, regulated with Multi-Therm circulation regulating valves, DN 15 (temperature setting 57 ºC) Comparing the circulation flow rates of the reference system with "top distribution system, side feed" (V Z 700 l/h) with those of the system with "circulation to the points of use" (with optimum regulation with Eta- Therm circulation regulating valves) (V Z 1400 l/h) makes the proportions clear. With full circulation to the points of use it has to be assumed that even with the best possible regulation the necessary circulation flow rate has to be at least twice that in conventional circulation systems. If the floor systems are regulated with Multi-Therm circulation regulating valves the necessary circulation flow rate is even higher (Fig 84). This is because the minimal k V - value of this valve has been tailored to the regulation requirements of the riser system. As a result, even at the temperature setting with maximum throttling position the flow rates via the floor systems are still unnecessarily high (Fig 81). The fact that such conditions lead to uneconomic operation of larger systems for hospitals, care homes, etc, led to the development of the Eta-Therm valve. With this valve, even with circulation to the points of use the design principle of DVGW Code of Practice W 553 of keeping the temperature above 55 ºC with minimum energy can be maintained. 79

80 Circulation systems Fig 82 Flow rates via risers, with temperature profile in basement distribution manifolds, regulated with Eta-Therm circulation regulating valves, DN 15 (temperature setting 57 ºC) Fig 83 Flow rates via risers, with temperature profile in basement distribution manifolds, regulated with Eta-Therm circulation regulating valves, DN 15 (temperature setting 57 ºC), centrally reregulated 80

81 Circulation systems Fig 84 Pipe network and pump characteristic with operating points for various service conditions plotted 81

82 4 System decontamination Professor Bernd Rickmann, Fachhochschule Münster, Department of Energy and the Built Environment 4System decontamination Professor Bernd Rickmann, Fachhochschule Münster, Department of Energy and the Built Environment Decontamination has operational, reconfiguration and procedural aspects. In addition to the elimination of pipes with stagnant water, increasing the temperature in the hot water system is particularly important. To determine whether the hot water temperatures can be increased it is necessary to check the performance of the hot water heating system and existing circulation pump(s). The second important step is systematic use of regulation appropriate to the chosen hot water distribution principle. Basically regulating valves can only be effective in the pipe system where there are "hydraulic short circuits". The lack of flow resistance allows too much water to flow through these. Such circulation circuits are always found in the risers near the pump. They are characterised by high temperatures at the connected point-of-use fittings and a very small temperature differential between hot water pipe and associated circulation pipe. 4.1 Eliminating pipes with stagnant water Redundant pipes must be disconnected at the tee forming the branch. It must also be checked whether rarely used - centrally supplied - points of use can be isolated and supplied by individual or group water heating (TWE) systems. Isolating valves in drain pipes must be connected directly to the main pipe (Figs 85 and 86). Connection pipes for ventilation valves for general protection must be removed. Individually protected point-of-use fittings must then be fitted (Fig 29). Fig 86 Drain pipes in vicinity of distribution or collection manifolds 4.2 Disinfection As already mentioned in 1.6, the operator of a water supply system must immediately conduct tests and take remedial measures in the event of microbiological impairment of the drinking water. "In particular, systems that do not meet the requirements of DVGW Code of Practice W 551 are deemed to be potentially contaminated." If microbiological testing of a water supply system reveals contamination with legionellae, coordinated decontamination and/or disinfection measures become necessary. A relatively simple and quick possible way of disinfecting hot water supply systems is thermal disinfection with water temperatures in excess of 70 ºC. Legionellae are killed after even brief exposure to such temperatures. For these reasons a North Rhine-Westphalia Ministerial Gazette relating to environmentally friendly design and installation of water and sewage systems in property within the state 32 states: Fig 85 Drain pipes in vicinity of riser isolation valves with stagnant water 32. North Rhine-Westphalia Ministerial Gazette of 14 March 1997: "Environmentally Friendly Design and Installation of Water and Sewage Systems in the State of North Rhine-Westphalia" 82

83 It has to be assumed that water supply systems are always subject to contamination with legionellae. Periodic heating must be made possible for thermal disinfection of a system. The categorical nature of these statements means the option of thermal disinfection must be available in all systems - even those not covered by the gazette cited. Disinfection must cover the entire hot water system including the point-of-use fittings. Thermal disinfection is initiated by heating the water heater up to temperatures in excess of 70 ºC. During the disinfection the circulation pump must run continuously and water must not be drawn off Unregulated system With a temperature 70 C, measured at the circulation inlet of the storage vessel, it is generally assumed that the entire circulation system is also achieving disinfecting temperatures. However, the situation is deceptive, as shown by the following consideration: Thermal disinfection is primarily necessary if circulations are incapable of maintaining the temperatures in the pipe system above 55 ºC. This is always the case if circulation systems have not been regulated. If an attempt is made to produce disinfecting temperatures in an unregulated system, the hydraulic short circuits still present will lead to the temperatures in the storage vessel adopting valves in excess of 70 ºC, but the temperatures in the sections further from the pump still remaining in the critical ranges (Fig 87). Drawing off water from successive points to disinfect the connection pipes in accordance with of DVGW Code of Practice W 551 also only increases the temperatures in the hot water pipes involved to values in excess of 70 ºC. In this case as well it generally remains unnoticed that the associated circulation pipes cannot be brought up to disinfecting temperatures (Fig. 88). In the regions of the pipework where as a result of weak or non-existent circulation the temperature is not successfully increased, an effective concentration of disinfecting chemicals cannot be achieved even with chemical disinfection. This explains why experience shows that Thermal or chemical disinfection is generally not effective, as it cannot eliminate the cause of the colonisation (1.4). Fig 87 Disinfection: flow rates via risers with temperature profile in basement distribution manifolds, unregulated, circulation pump (2) 83

84 System decontamination Fig 88 Disinfection with water being drawn off until it runs hot: flow rates via risers with temperature profile in basement distribution manifolds, unregulated, circulation pump (2) System regulated with thermostatic circulation regulating valves A temperature in excess of 70 ºC, measured at the circulation connection of the storage vessel, does not necessarily ensure that disinfecting temperatures are actually present throughout the circulating water system. In this case as well the necessary basis for successful disinfection is a circulation system that has been brought into hydraulic equilibrium by means of systematic regulation. This applies equally to new and old systems. For functional reasons circulation systems are now preferably (automatically) regulated by thermostatically controlled circulation regulating valves as a function of temperature. Regulating valves that close completely when the temperature setting of approximately C is reached, thereby interrupting the circulation (Fig 89), are no longer accepted practice (DVGW Code of Practice W 553, 5.3). In addition to having other important functional disadvantages, they make thermal disinfection virtually impossible, as the circulation pump has to work against closed valves during disinfection. This makes it impossible for disinfecting temperatures to be achieved in the circulation circuit! Even drawing off water can only improve the temperature conditions marginally, as the circulation pipes in particular cannot be heated beyond the temperature setting of the valves. 84

85 System decontamination Fig 89 Control characteristic of a valve that closes at the temperature setting and is therefore unsuitable for thermal disinfection To overcome this deficiency the Multi-Therm circulation regulating valve was designed so that in addition to providing ideal regulation it always allows thermal disinfection of the circulation system without manual intervention. A record of measurements taken on a valve test stand demonstrates the principle of operation (Fig 57). The valve is completely open up to a valve temperature of approximately 50 ºC. Between 50 ºC and the temperature setting (for example, 57 ºC) the throttling positions are a function of temperature. When the temperature setting is reached the valve is in its maximum possible throttling position. However, even in this position there is a small continuous circulation flow. If disinfection is initiated by heating the storage vessel to temperatures above 70 ºC, after a certain delay this also increases the valve temperature, with the maximum throttling position being maintained. From about 63 ºC the valve reopens and remains in a constant throttling position at a temperature of 70 ºC (Fig 57). The k V -values of these throttling positions are designed as a function of the nominal diameter so that even in larger systems disinfection temperatures can be established throughout the circulating system Verification of disinfection temperatures For the reference system numerical simulation exemplifies the fact that provided the design rules described in 3.1 are observed disinfecting temperatures above 70 ºC are established throughout the circulating system (Fig 90). The time it takes the water to flow out of the storage vessel outlet and re-enter it via the circulation system depends on the supply system. Calculating this time for the reference system shows that it takes about 15 to 20 minutes for the riser with the worst hydraulic conditions to reach disinfecting temperatures. It must be noted that during disinfection the increased temperature differential between water and surrounding air causes approximately 30% higher heat losses. To prevent the temperature drop exceeding 5 K even in this case, a correspondingly higher circulation flow rate must be possible in the circulation system. The circulation pump must have sufficient reserves for disinfection. In this situation these reserves must be called upon by increasing the pump speed or suspending the throttling setting of a regulating valve downstream of the circulation pump. When disinfection is complete the original state of regulation must be restored. In larger systems circulation pumps with flat characteristics and temperature-dependent speed control are to be preferred. 85

86 System decontamination Fig 90 Disinfection: flow rates via the risers with temperature profile in the basement distribution manifolds, regulated with Multi-Therm circulation regulating valve, circulation pump (2) Fig 91 Operating point of circulation pump during disinfection, after suspension of central throttling of circulation pump 86

87 System decontamination "It must be endeavoured to achieve circulation pipes with connections to the point of use that are as short as possible" 34 Logically configured circulation to the connections for the points of use avoids the need for laborious draw-off procedures in the event of thermal and/or disinfection becoming necessary. 4.3 Increasing temperature in existing hot water supply systems Fig 92 Storage vessel and pump operation during disinfection The DVGW codes of practice stipulate that, as in new systems, each operational and reconfiguration measure involved in decontamination must lead to the water temperature throughout the circulating system not falling below 55 ºC. Account must also be taken of the EnEV requirements here. The experience accumulated with decontamination measures aimed at increasing the temperature in existing hot water supply systems will now be summarised System survey Fig 93 Thermal disinfection of the floor system achieved by drawing off water at 70 ºC for at least three minutes When the storage vessel and circulating water are at disinfection temperature, the pipe sections not linked into the circulation system, such as floor and spur pipes, must be thermally disinfected step by step. DVGW Code of Practice W 551 stipulates that all points of use must be disinfected for at least three minutes - at least 70 ºC. It is essential to achieve this temperature for the specified time Configuration supporting thermal disinfection As drawing off water from a point-of-use fitting for even three minutes longer requires 15 to 40 litres of very hot water, it has to be assumed that such disinfection operations are very costly in terms of water and energy consumption. The obvious solution from viewpoint of both operation and hygiene is therefore to stipulate circulation to the connections for the point-of-use fittings. The relevant codes, standards and specifications therefore contain the following principles: "The circulation pipe must be routed as close as possible to the item connection" 33 Prior to reconfiguration measures a comprehensive system survey of the hot water system requiring decontamination must always be carried out. The DVGW codes stipulate that documentation should be based on any available as-built drawings, the system description, system data and maintenance and operating manuals. If this information is not available, drawings of the water supply system in conjunction with the layouts and sections through the building(s) must be prepared. These drawings must contain at least the following information: Water heating system - Heat exchanger - Storage vessel - Dimensions - Performance data Pipe system - Pipe routing - Pipe materials - Nominal diameters - Lagging material - Lagging thickness - Isolating valves, safety valves and regulating valves - Point-of-use fittings - Measuring equipment - Control systems and switchgear Water treatment systems 33. North Rhine-Westphalia Ministerial Gazette of 14 March 1997: "Environmentally Friendly Design and Installation of Water and Sewage Systems in the State of North Rhine-Westphalia 34. "Guidelines for Recognising, Preventing and Combating Hospitalacquired Infections", appendix to and

88 System decontamination The system survey must include measurement and documentation of the temperatures in the cold water, hot water and circulation systems. Flow meters must be fitted at suitable points to monitor the water consumption and determine the circulation flow rate. Existing pipe sections for monitoring purposes must be checked for deposits and signs of corrosion Temperature measurements Temperature measurements at the storage vessel and on the surface of the freely accessible valves in the circulation pipes are generally sufficient to describe the temperature distribution in the circulation system without having to remove the lagging. In particular, temperature measurements at the riser isolation valves of the circulation system are sufficient to enable reliable reporting of the functional weaknesses of the system to be decontaminated (Figs 94 and 96). They can be taken with simple instruments with a digital display suitable for measuring surface temperatures. Heat conductive paste must normally be used to ensure quality results and rule out the possibility of mismeasurement. As the measurements generally cannot be taken under ideal steady state conditions, the results must not be overinterpreted. Fig 94 Preferred temperature measuring points Fig 95 Digital temperature measuring instrument with surface probe Fig 96 Results of temperature measurement on circulation isolating valves in riser region Bothe, Torsten and Thesseling, Andreas "Decontamination of a Water Supply Circulation System in a Hospital in Accordance with DVGW Codes of Practice W W 553, Surveying current condition, devising decontamination measures and checking success", Degree dissertation, Fachhochschule Münster,

89 System decontamination Flow rate measurements Older systems generally do not have any meters for measuring the circulation flow rate. At best any water meters present in the cold water pipe to the water heater can be used to check the performance of the hot water heating system. However, they will not provide any information enabling evaluation the circulation system. Flow rate measurements in the circulating system are always expensive, as sensors have to be fitted in the pipe system. Ultrasonic flow rate measurement equipment is portable and avoids the need for built-in sensors. It can therefore be used without having to interfere with the pipe system, but is very expensive to buy and unsuitable for continuous operational monitoring. To avoid impairing the circulation, sensors permanently installed in the circulation circuit must not cause any significant pressure drop. This rules out simple methods of measuring flow rates that rely on orifices, nozzles or impellers. For this reason Kemper has developed an innovative, low-pressure-drop method of measuring flow rates, which although necessitating opening up the pipe system to install the sensors, overall represents an inexpensive and effective alternative to other methods, as installation can be done in combination with isolation and regulation systems, with measurement being displayed digitally on a small mobile computer for the purpose (Fig 98) Pressure differential measurements The pressure differential available in a circulation pipe system requiring decontamination can be measured with a differential gauge. In the simplest case the pressure take-off hose connections can be connected to existing drain valves. The pressure must be taken off the delivery and inlet side of the circulation pump. If the differential between the outgoing and incoming pipe is measured at a manifold bar, the pressure drop across the water heater is not included, only the pressure differential actually available to overcome network resistances is determined. The available pressure differential always has to be measured if several pumps are connected in series and/ or in parallel and it is therefore impossible to draw reliable conclusions about the operating point from a knowledge of the known characteristic of an individual pump. Particularly in old water supply systems, for example in hospitals, such system configurations tend to be the norm. When measuring account should also be taken of pressure fluctuations that indicate the switching on and off of pumps. Ideally the measurement data should be recorded on a data logger to ensure availability for further evaluation and documentation (Fig 100). Fig 99 Measurement of the pressure differential available for the circulation circuit and of the circulation flow rate Fig 97 Ultrasonic meter in use Fig 98 KEMPER Control flow meter (Fig 138) with mobile measuring computer in combination with Multi-Fix (Fig 150) Fig 100 Measuring pressure differential between hot water distribution manifold and circulation collection manifold with pressure sensor connected to existing drain valves 89

90 System decontamination Diagnostics Increasing the temperatures in a circulation system requiring decontamination to more than 55 ºC assumes the water heating system is capable of providing continuous temperatures of 60 ºC at the outlet from the storage vessel. Experience shows that such temperature stability is not necessarily achieved, particularly in old water heating systems, since heat exchangers may be scaled up and/or the hydraulic conditions necessary for heating up the water in the vessel degraded over the course of years of operation. Before decontamination the water heating system must be fully checked to verify that it is working properly Water heating system The functionality and performance of the water heating system can be evaluated most effectively by measuring and recording the storage vessel outlet temperatures and the cold water flow rate over an extended period (at least one day) (Fig 101). The measured data occasionally show that the storage vessel outlet temperatures are subject to noticeable fluctuations whose amplitude depends on the draw-off rate (Fig 102). Such results are particularly surprising when there is evidently plenty of storage capacity. The cause is often an excessively powerful heating pump, which prevents the demand being met at times of peak draw-off via the storage vessel. If the heat exchanger is no longer capable of heating the water drawn off directly as it flows through, the water temperatures drop below 60 ºC. In such cases throttling the flow with a valve directly upstream or downstream of the pump can activate the storage vessel to cover the peak draw-off rate. If it proves possible to appreciably reduce the consumption-dependent temperature fluctuations in this way, the heating pump must be replaced with a less powerful one, or a regulating valve fitted (Fig 100) that can be set to a reproducible and permanent throttling position. If decontamination is required, the first step must be to adopt "operational" and/or "reconfiguration" measures to ensure a constant storage vessel outlet temperature of 60 ºC (Fig 103). Fig 101 Measuring points for evaluating operation and effectiveness of a water heating system Fig 102 Plots of measurements of cold water flow rate and hot water outlet temperature from a (storage vessel) water heating system with marked temperature fluctuations 90

91 System decontamination Fig 103 Storage vessel system with constant outlet temperature Switching off circulation pump Circulation pumps may be switched off for up to 8 hours under perfect hygiene conditions only (DVGW W 551, 6.4). If decontamination is necessary the circulation pumps must run continuously. Fig 104 Temperature drop in a circulation system caused by switching off circulation pump overnight 91

92 System decontamination Backflows, circulation failure The flow rate and temperature measurements over an extended period as described above provide important information for effective decontamination of the hot water supply system. Figure 105, for example, reveals backflows via the storage vessel into the connecting pipe of the hot water heating system caused by a faulty check valve and an incorrectly installed circulation pump on the circulation collection manifold. Fig 105 Plots of measurements of cold water flow rate and hot water outlet temperature from a (storage vessel) water heating system, with backflows from storage vessel into connecting pipe of heating system Inadequate circulation flow rate Regulation will only be successful if the circulation pump(s) is (are) capable of achieving an adequate circulation flow rate against the network resistance. If in an unregulated circulation system with a constant storage vessel outlet temperature of 60 ºC the return circulation temperature from the system is not above the required 55 ºC, the circulation flow rate is inadequate (Fig 107). Fig 106 Measuring points for circulation flow rate and temperature of circulation on re-entry into water heating system 92

93 System decontamination Fig 107 Circulation flow rate and circulation temperature Before other measures can be taken the reason the cause of the inadequate circulation flow rate must be determined and eliminated Circulation pumps In checking the available pump capacity account must be taken of the fact that with circulation pumps of different sizes connected in series the smaller pumps often just act as flow resistances and therefore cannot help increase the circulation flow rate. Experience shows that decontamination based on increasing the temperature is more likely to succeed if more or less uncoordinated series and parallel pumps are removed and just one powerful circulation pump at a central point in the system remains operational (Fig 108). Fig 108 Arrangement of circulation pumps Key: TWZ = circulation A rough estimate of the necessary pressure differential and flow rate can be made in order to determine the size of a suitable circulation pump. In a circulation system without serious scaling the pressure drop in the pipes and minor losses of the longest circulation circuit can be estimated with sufficient accuracy with R m mbar/m. Control sections of pipe, which should be present in the system to meet the DVGW requirements, provide information about heavier scaling. A higher pressure drop per metre of pipe may have to be assumed and taken into account. 93

94 System decontamination Equation 32 p p R m l ges P RV p Ap In addition to the pressure differential the necessary circulation flow rate of the pump must be estimated. Equation 33 Estimated pump pressure differential in mbar Average pressure gradient due to pipe friction mbar/m Length of the worst (longest) circulation circuit in m Pressure drop across check valves in mbar Pressure drop across heat exchangers or other items of equipment in mbar Σ [l ges,z q W ] Sum of the heat losses over the surface of all pipes involved in circulation (hot water and circulation) in W ρ Density of water (ρ 1kg/l) c Specific heat capacity of water (c 1.2 Wh/(kg K)) ϑ W Permitted temperature drop between leaving and re-entering water heater ϑ W,max = 5 K If the "system survey" does not provide the data necessary for detailed calculation, or the data is not of the required quality, a rough estimate must be made in order to continue. To develop this initial idea of the magnitude of the heat losses at least the length of all of the pipes involved in the circulation system and an average heat loss per metre of pipe must also be known. An estimate of the average heat loss q W,m of between 10 and 15 W/m takes account of the worse case of lagging that does not meet EnEV requirements. If the necessary information is available, the above equation can now be used to calculate the flow rate needed to cover the total heat loss of the circulation system. The order or magnitude of all of the pump data needed for successful decontamination (pressure differential/pump flow rate) is then known. In the case of simple systems with just one pump the characteristic of the installed circulation pump is sufficient for evaluation purposes. If the calculated operating point is below the pump characteristic, the existing pump can continue to be used. Otherwise a larger pump must be used. A multistage circulation pump must then be used, which can be matched to the actual pipe system conditions, and still has reserve capacity for thermal disinfection (4.2). In more complex systems with several pumps in series the calculated operating point must be compared with the results of measurements to determine the actual operating point as described above. In order to work out the total heat loss from an existing system, as well as the pipe length the lagging material and its thickness have to be known. The "local survey" requirements of the DVGW codes of practice mean the data needed for the calculation must be known. As older systems generally do not meet EnEV requirements, the heat losses have to be calculated using the detailed method and the values for the particular system (Diagrams 1 to 3). Fig 109 Existing lagging on a system needing decontamination Dunker, Stefan "Decontamination of a Hospital Water Supply System Contaminated with Legionellae", Degree dissertation, Fachhochschule Münster,

95 System decontamination Fig 110 Checking pump capacity necessary for decontamination, with an estimate of the required operating point Example: Length of worst (longest) circulation circuit l ges =250m Total length of all of the sections involved in circulation l ges,z = 600 m After inspecting the system the average pressure gradient due to pipe friction Rm is estimated as being 1.5 mbar/m and the average heat loss per metre of pipe as 15 W/m. This gives the following circulation pump operating point for successful decontamination: p P = = 375 mbar Check valves If there is evidently sufficient pump capacity available, extraordinary flow resistances in the circulation system must be limiting the circulation flow rate 37. Such resistances can be caused by check valves in particular. Old spring-loaded check valves must be removed, as they always cause excessive pressure drops. If check valves are essential to the functioning of the system, they must be replaced with models with a low opening pressure (3.1.2). The existing isolating valves must be checked. These can also cause impermissible pressure drops arise through as a result of getting stuck, their discs coming loose, seats getting scaled, etc. Fig 111 shows that just removing superfluous check valves enabled the circulation flow rate in a system needing decontamination to be increased by a factor of Peters, Raimund and Pennekamp, Rainer "Decontamination of a Hospital Circulation System", Degree dissertation, Fachhochschule Münster, Peters, Raimund and Pennekamp, Rainer "Decontamination of a Hospital Circulation System", Degree dissertation, Fachhochschule Münster,

96 System decontamination Fig 111 Increasing circulation flow rate by removing several check valves connected in series Heat exchangers If the flow rate in circulation systems is too low, heat exchangers served by the circulation pump must be considered as a potential cause 39. Measuring the pressure differential between heat exchanger inlet and outlet sheds light on whether the undersizing or scaling of the heat exchanger is causing it to develop an excessive pressure drop (Fig 112). It may have to be cleaned or replaced with a larger model. 39. Dunker, Stefan "Decontamination of a Hospital Water Supply System Contaminated with Legionellae", Degree dissertation, Fachhochschule Münster,

97 System decontamination Fig 112 Measuring pressure differential across a heat exchanger (circulation) Fig 113 Doubling of circulation flow rate after installation of a larger heat exchanger with lower pressure drop Dunker, Stefan "Decontamination of a Hospital Water Supply System Contaminated with Legionellae", Degree dissertation, Fachhochschule Münster,

98 System decontamination Undersized pipes Older circulation systems can generally be decontaminated without major modifications to the pipe system. Old systems designed with the rule of thumb commonly used at the time: "Circulation pipe 1 or 2 sizes smaller than diameter of associated hot water pipe" are even less problematic to evaluate than circulation systems designed to DIN (3). Larger circulation systems are occasionally still designed without proper hydraulic calculations, just using the stipulations of DIN , Table 10 "Guide Values for Nominal Diameters of Circulation Collection Manifolds". Even when adopting conventional distribution principles, this approach is extraordinarily risky, and with "circulation to the points of use" it leads to catastrophic malfunctions. In such incorrectly designed circulation systems the circulation flow rates necessary to maintain the temperature (3.5.6) can only still be achieved by completely modifying the existing pipe system (for example Fig 114). Fig 114 Improving the hydraulic conditions by laying a circulation collection manifold in parallel Regulating valves The purpose of thermostatic circulation regulating valves is to establish pressure drops that depend on temperature. The available valve stroke is only a few millimetres. This small stroke means that when the valves are fully open (for example, measured with a deviation of 7 K), and the circulation flow rate is higher, they can produce a considerable pressure drop. As already repeatedly emphasised, the temperature can only be maintained in the circulation circuit if relatively high flow rates are possible in the risers further away from the pump. An incorrectly positioned or sized thermostatic valve in this area can lead to serious malfunctions! To make it possible to reliably avoid such errors, in larger circulation systems the circulation circuits with the worst hydraulic conditions must be equipped with regulating valves with minimum nominal diameters of DN 20. The installation locations that can be expected to be critical are marked for the different distribution principles (3.1 and 3.5). They can be avoided through careful design of the system! Diagnostics must include critical examination of the regulation technology already being used. The circulation flow rates must be expected to be impaired if Thermostatic valves of too small a nominal diameter have been arranged in circulation circuits with poor hydraulic conditions Several thermostatic valves are connected in series in the circulation circuits One thermostatic valve has been positioned centrally, for example on the circulation collection manifold In such cases the critical flow resistance can be temporarily eliminated by removing the thermostatic head from the circulation regulating valve (Fig 115). 98

99 System decontamination Fig 115 Multi-Therm circulation regulating valve with thermostatic head removed If this noticeably improves the temperature conditions, the valve must be removed and replaced with an isolating valve or possibly a static circulation regulating valve Excessive circulation flow rate Increasing the temperature by simply using oversized circulation pumps without examining the regulation technology always has serious disadvantages. This approach can ensure a temporary increase of the required magnitude in certain sections (Fig 116). Fig 116 After fitting a larger pump However, the excess flow rate in one section leads to insufficient flow elsewhere, or at the very least to uneconomic operation. DVGW Code of Practice W 551, 8.3.2, therefore also assumes that where decontamination is required the necessary temperatures can generally only be achieved by fitting regulating valves for hydraulic balancing. Not only the various calculations for the reference system but also measurements in existing circulation systems show that provided specialised regulation technology is used effective temperature maintenance is possible with approximately half the circulation flow rate of an unbalanced system (Fig 117). 99

100 System decontamination Fig 117 After regulation with Multi-Therm circulation regulating valves 4.4 Follow-up tests If a contaminated water supply system is successfully optimised, particularly by increasing the hot water temperatures to values in excess of 55 ºC, colonisation with legionellae can also be significantly reduced and in many cases actually eliminated (1.4). Final report on follow-up tests peripheral (station) points were continuously sampled and tested for legionellae. Sample volume: 100 ml; reported in colony forming units (CFU) For clarity the results were converted to 1 ml, hence values < 1 can arise, for example, 0.1 CFU/ml = 10 CFU/ 100 ml Test method: Detection of Legionellae in Drinking and Bathing Water, Federal Health Gazette : ; ISO 11731, : Water Quality - Detection and Enumeration of Legionella Test results (maximum and averages) 2000 to June 2001 (before decontamination): Maximum: 80 CFU/ml; average : 12 CFU/ml All of the sampling points were Legionella-positive in 100 ml Sampling on 26 September 2001 (after installation of pump): Maximum 8 CFU/ml; average : 0.8 CFU/ml 75 % of the samples were Legionella-positive in 100 ml Sampling on 28 November 2001 (after installation of valves) Maximum 2 CFU/ml; average : CFU/ml 50 % of the samples were Legionella-positive in 100 ml Sampling on 11 January 2002: Maximum 1 CFU/ml; average : 0.1 CFU/ml Only 1 of 10 samples was Legionella-positive Sampling on 20 March 2002: No legionellae were detected in 100 ml of water. Sampling on 10 May 2002: No legionellae were detected in 100 ml of water. Assessment: "The system could only to be described as heavily contaminated prior to decontamination. Installation of a new pump, and particularly the circulation regulating valves, substantially reduced the level of legionellae. After 4 months of operation legionellae were no longer detected, i.e. a resounding success! 41. Institute of Hygiene of the Universitätklinikum Münster 100

101 System decontamination Fig 118 Results of the microbiological tests as a function of decontamination measures and time Bothe, Torsten and Thesseling, Andreas "Decontamination of a Water Supply Circulation System in a Hospital in Accordance with DVGW Codes of Practice W W 553, Surveying current condition, devising decontamination measures and checking success", Degree dissertation, Fachhochschule Münster,

102 5 Design example 5Design example 5.1 Hot water supply pipes Floor pressure drop Fig 119 System for individual floor Number Point-of-use fitting Minimum Design flow rate flow pressure p minfl Cold water Hot water Mixed water Total flow rate in floor pipe Cold water Hot water V R V R VV R ΣVV R ΣV R mbar l/s l/s l/s l/s l/s 1 WC Kitchen sink Dishwasher Washbasin Bath Total flow rate for floor Table 10 Calculating total flow rate on floor 102

103 Minor loss DN Loss constant Number of components and sum of related minor losses Σζ for sections ζ Elbow, 90º Tee, counterflow from branch into line Reducer Tee, mainly through flow Concealed valve (make: Gebr. Kemper) Σζ in sections TS 1-3 (Fig 119) Table 11 Determining loss constants in sections TS 1-3 (Fig 119) TS Length ΣVV R V S DN R v I R Σζ Z (I R+Z) m l/s l/s mbar/m m/s mbar mbar mbar Σ (I R+Z) 180 Table 12 Floor pressure drop (hot water) calculated using detailed method, see Fig 119 for section designations 103

104 Design example Type of water heating Largest point-of-use fitting installed Type of pipe Nominal diameter of floor pipe Nominal diameter of spur pipe Concealed valve Length of flow path l ges Floor pressure drop Deductible pressure differential Floor pressure drop central < 0.5 l/s stainless steel DN 20 (22 x 1.0) DN 12 (15 x 1.0) straight seat valve 5.1 m 200 mbar ( ) * 5 = 25 mbar 175 mbar Total flow rate in building service pipe For each flat in the example a total flow rate of ΣV R,WOE = 0.86 l/s is worked out (Fig 119). From the total of 48 flats this results in the following value for the building service pipe ΣVV R = = l/s. Using Equation A the resultant peak flow rate can be calculated as V S = 3.02 l/s or read off Table 27. Chosen: G2B: Nominal flow rate VV n =10.0m 3 /h, V max = 20.0 m 3 /h at p G = 1000 mbar Filter Chosen: p max = 200 mbar, at V max = 20.0 m 3 /h Table 13 Floor pressure drop calculated using simplified method (Table 6 of DIN ) Comparing floor pressure drops calculated using the simplified and the detailed method makes it clear that with an approximately identical drop the detailed method gives smaller nominal diameters in each section (cf Chapter 2.7) Floor water meter Available pressure differential p verf calculated using simplified method The available pressure differential for sizing the pipes must be worked out on the basis of Equation 2. The mixer for the bath on the 4th floor - riser 12 (Fig 12) has been determined to be the worst point-of-use fitting in the flow paths of the hot water system. A G 1/2 B water meter for a flat with the following data was chosen from Table 4: Nominal flow rate V n =1.0m 3 /h and maximum flow rate of V max =2.0m 3 /h with a pressure drop of p G = 1000 mbar. The total flow rate in the floor connection pipe read off from Table 10 is ΣV R =0.29l/s, and the peak flow rate from Table 26 is V S = 0.25 l/s. Using Equation 6 gives a pressure drop across the floor water meter calculated using the detailed method of: Pressure drop across water company meter In order to work out the pressure drop across the water meter the peak flow rate in the building service pipe must first be known. 104

105 Design example No Name Symbol Units 1 Minimum supply pressure or outlet pressure after pressure reducing valve or pressure booster p minv mbar Pressure drop due to difference in geodetic head p geo mbar Pressure drop across items of equipment, for example: a) Water meter b) Filter c) Softening system d) Metering system e) Group water heater f) Other items of equipment p WZ p FIL p EH p DOS p TE p Ap mbar mbar mbar mbar mbar mbar Minimum flow pressure p minfl mbar Pressure drop of floor and spur pipes p St mbar Sum of the pressure drops from Nos 2 to 5 Σ p mbar Available for pressure drop from pipe friction and minor losses, values from No 1 minus value from No 6 p verf mbar Contribution estimated for minor losses...% 40 mbar 9 Available for pressure drops from pipe friction, value from No 7 minus value from No 8 mbar Pipe length I ges m Pressure gradient available to cope with pipe friction, value from No 9 divided by value from No 10 R verf mbar/m 5.1 Table 14 Determination of the pressure gradient available to cope with pipe friction R verf 105

106 Design example Determining pipe diameter and calculating pressure drop TS Length ΣVV R VV S DN R v I R m l/s l/s mbar/m m/s mbar I ges = Σ(I R) = Table 15 Calculation of pressure drop for worst flow path in hot water system The difference between the available pressure drop from Table 14, line 9 of 709 mbar and that of mbar calculated along the flow path (Table 15) is small, so does not have to be checked again. 106

107 Design example Fig 120 Design diagram of pipe runs for a four-storey block of 48 flats showing dimensions for determining the section lengths, section designations and nominal diameters from the hydraulic calculations (Table 15) 5.2 Circulation system Design assumptions Pipe diagram: see Fig 122 Type of pipe: Point-of-use fittings: stainless steel individually protected The hot and cold water supply pipes are designed according to DIN 1988 Part 3; see Table 15 and Fig 120 for nominal diameter, length and position of the hot water pipes. The following ambient temperatures are taken into account in the design example: Zone 1 (laid exposed in basement) ϑl =10 C (q W = 11 W/m from Fig 35) Zone 2 (laid in duct) ϑl = 25 C (qq W = 7 W/m from Fig 36) The heat flow for the various sections of the hot water pipes should be tabulated, giving the section number, section length, nominal diameter and temperature differential (Fig 122 and Table 16). 107

108 Design example TS Length Nominal diameter Temperature differential qq W l q W Σ[I q W ] Q m K K W/m W W W DN DN DN DN DN DN DN DN DN DN DN DN a 2.00 DN DN DN DN Table 16 Calculating the heat lost by the hot water pipes (TWW) Explanatory notes: Column 1: Section (TS) number, see Fig 120 Column 2: Section length, see Fig 120 Column 3: Nominal diameters of hot water pipes calculated according to DIN , see Table 15 Column 7 and Column 8: Column 9: Riser heat losses: TS 15a to TS W Heat flow in the section involved Calculating circulation flow rates The pump flow rate is calculated on the basis of Equation 20, from the sum of the heat losses of the hot water pipes (Table 16, column 9), with a temperature drop in the hot water pipes (TWW) of 2 K. Calculating component flow rates The flow rate for the branching (subscript: a) and line (subscript: d) sections is calculated on the basis of Equations 21 and 22, and should be documented as shown in Table 17. Example: Calculating flow rates for the branching (subscript: a) and line (subscript: d) section from section TS 4 (Figs 39 and 122). V d = V-V a = = 771 l/h 108

109 Design example TS QQ a Q d Q a + Q d VV V a V d W W W l/h l/h l/h Table 17 Calculating circulation flow rates Explanatory notes: Column 1: Section to branch, see Fig 122 for section numbers Column 2: Heat flow in branch, see Table 16 and Fig 122 Column 3: Heat flow in line, see Table 16 and Fig 122 Column 6: In the example the result in this column corresponds to the circulation flow rate that has to flow in risers ST 1 to ST 12 (Table 20, Column 3) Calculating diameters of circulation pipes The diameters of the circulation pipes are calculated using the simplified method of DVGW Code of Practice W 533. The percentage contribution of the minor losses should taken in account by adding 30% to the losses of the straight pipe (l R) (Table 19) Circulation pump delivery pressure The minimum circulation pump pressure differential necessary p P is calculated on the basis of Equation 25. Σ(I R+Z) TWW + TWZ = mbar See Table 19, Column 11 p RV = 10.0 mbar Check valve KEMPER, Fig 158 p TH =0.0 mbar No regulating valve should be fitted in the worst circulation circuit! p P = mbar See Equation 25 V p = l/h See Equation m 3 /h Chosen pump: Wilo Z 25 Table 18 Calculation of the necessary pump pressure differential 109

110 Design example The pipe network characteristic can be calculated from the data for the calculated operating point with Equation 34. Equation 34 Fig 121 Pipe network characteristic calculated from p =k V 2 and k = p P /V P 2, with operating point plotted for the circulation pump from Table

111 Design example TS Length V Z DN R v l R Z=0.3 l R I R+Z Σ(I R+Z) m l/h mbar/m m/s mbar mbar mbar mbar mbar ST DN Z DN Z DN Z DN Z DN Z DN Z DN Z DN Z DN Z DN Z DN Z DN Z DN Table 19 Calculating pipe diameters for the circulation pipes - simplified calculation of pressure drops for the worst circulation circuit (Fig 122) Explanatory notes: Column 1: Section numbers, see Fig 122 Column 2: Section length, see Fig 120 Column 3: Circulation flow rate (from Table 17, Columns 5 and 6) Column 4: Nominal diameters of hot water pipes (TWW) calculated according to DIN , Table 15 Column 5: Pressure gradient due to pipe friction for stainless steel pipe from the pressure drop chart or Table 31 Column 10: Sum of the pressure drops in the flow direction 111

112 Design example Designing circulation regulating valves Balance condition: p P = Σ(I R+Z) TWZ + Σ p RV + p D TS Length VV Z DN R v I R Z=0.3 l R I R+Z p TS Σ(I R+Z) p RV ϑ Ventil k V p D p P m l/h mbar/m m/s mbar mbar mbar mbar mbar mbar C m 3 /h mbar mbar ST No regulating valve 175 ST ST ST ST ST ST ST ST ST ST ST Table 20 Calculating diameters for the circulation pipes - simplified calculation of pressure drops for the worst circulation circuit (Fig 122) Explanatory notes: Column 3: Circulation flow rate from Table 17, Column 6 Column 10: Circulation circuit pressure drops already calculated (see also Table 19, Column 10) Column 12: Pressure drop across check valve downstream of pump (Kemper, Fig 158) Column 13: Calculated valve temperature settings (Fig 123) Column 14: k V -value of regulating valve, calculated with Equation 31 Column 15: Pressure differential necessary across regulating valve (Equation 30) Column 16: Available pump pressure differential (Fig 121 and Table 18) 112

113 Design example Fig 122 Pipe design diagram for four-storey block of 48 flats with nominal diameters, heat losses and settings for circulation regulating valves marked Fig 123 Pipe design diagram for four-storey block of 48 flats with calculated temperatures at end of each section (Table 21) 113

114 Design example Temperature drop in circulation circuit The temperature drop in the circulation circuit is calculated on the basis of Equation 23 or 24. TS V Z I q W ϑ TS Σ ϑ TS ϑ TWW/Z l/h W K K C a ST Z Z Z Z Z Z Z Z Z Z Z Z Table 21 Calculating the temperature drop in the worst circulation circuit (Fig 123). Note that the theoretical valve temperature is calculated as 57.8 ºC at the end of section ST

115 Design example 115

116 6 Tables, charts and forms Tables, charts and forms Chart 1 Heat losses from stainless steel pipes fully lagged to EnEV (λ D =0.035W/(m K)), as a function of temperature differential ϑ = ϑ W - ϑ L Key: Luft = air 116

117 DN d a in mm s in mm Lagging thickness to EnEV in mm D in mm ϑ W - ϑ L in K Heat loss from a pipe lagged to EnEV in W/m , Table 22 Heat loss from stainless steel pipes fully lagged to EnEV (ϑ D =0.035W/(m K)), as a function of temperature differential ϑ = ϑ W - ϑ L, calculated with Equation

118 Chart 2 Heat losses q in W/m from lagged pipes as a function of temperature differential between ambient air and water. Lagging thickness D = 30 mm, λ =0.040W/(m 2 K)) 118

119 Chart 3 Equivalent thicknesses in mm for lagging materials whose thermal conductivities differ from the minimum requirement of EnEV (λ = W/(m K)) Key: HeizAnlV = German Heating Regulations 119

120 No Minor loss Diagram Loss constant to DIN Tee, main flow from line into branch ζ 1.3 Loss constant (Kemper) (measured value) ζ Opening pressure mbar 2 Tee, main flow from branch into line Tee, mainly through flow, some line into branch 4 Tee, counterflow from line into branch Tee, counterflow from branch into line Tee, swept, main flow from line into branch Tee, swept, main flow from branch into line Tee, swept, mainly through flow, some line into branch 9 Tee, swept, mainly through flow, some branch into line Distribution manifold outlet Outlet from tank, storage vessel 0.5 to DIN Reg No Collection manifold inlet Tank inlet Change in direction produced by elbow or bend to DIN Reg No

121 No Minor loss Diagram Loss constant to DIN Reducer ζ 0.4 Loss constant (Kemper) (measured value) ζ Opening pressure mbar to DIN Reg No U-shaped expansion compensator Compensator 2.0 to DIN 2425 Part 1 18 Straight seat valve DN 15 DN 20 DN 25 DN 32 DN 40 DN 50 Figs: 180, 183, 184 Concealed valve DN 15 DN 18 DN 20 DN 25 DN 32 Concealed-plus valve DN 15 DN 20 DN 25 DN 32 Figs: , , , , , , , Figs: 520, 522, 523, 524, 525, 527, 560 Angle seat valve DN 15 DN 20 DN 25 DN 32 DN 40 DN 50 Figs: 073, 171, 172, 173, 174, 175, 176, 177, 178, 179, 190, 191 Flanged angle seat valve DN 15 DN 20 DN 25 DN 32 DN 40 DN 50 DN 65 DN

122 No Minor loss Diagram Loss constant to DIN Gate valve and piston valve Ball valve DN 10 - DN 15 DN 20 - DN 25 DN 32 - DN 150 ζ Loss constant (Kemper) (measured value) ζ Opening pressure mbar Figs: 200, 201, Diaphragm valve DN 15 DN 20 DN 25 DN 32 DN 40 DN 50 DN 65 DN 80 DN 100 DN 125 DN Angle valves DN 10 DN 15 DN 20 Fig: Figs: 140, 147, Check valves DN 15 - DN 20 DN 25 - DN 40 DN 50 DN 65 - DN Figs: 162, 163, 164, 195,

123 No Minor loss Diagram Loss constant to DIN Globe check valve DN 15 DN 20 DN 25 DN 32 DN 40 DN 50 Combined check DN 15 valve with angle seat DN 20 DN 25 DN 32 DN 40 DN 50 DN 65 DN 80 Figs: 158, 159 Figs: 060, 160, 161, 167, 168, 169, 170, Combined check DN valve with cartridge DN 20 DN 25 DN 32 DN DN 50 Figs: 145, Valve tapping clamp DN 25 - DN ζ Loss constant (Kemper) (measured value) ζ Opening pressure mbar Pressure reducing valve fully open 30.0 to DIN Reg No 594 Trap with double filter DN 6 DN 8 DN 10 DN 15 DN 20 DN 25 DN 32 DN 40 DN 50 Fig Table 23 Minor loss constants 123

124 Building use Individual fitting Equation Residential Office / administration Hotel Department store Hospital wards School V R < 0.5 V R 0.5 V R < 0.5 V R 0.5 V R < 0.5 V R 0.5 V R < 0.5 V R 0.5 V R < 0.5 V R 0.5 B A B A E D E D E D I Table 24 Choice of equation for calculating peak flow rate to DIN for ΣV R 20.0 l/s Building use Residential Office / administration Hotel Department store Hospital wards School Equation A C F G H K Table 25 Choice of equation for calculating peak flow to DIN for ΣV R > 20.0 l/s 124

125 A B C E I ΣV R V S VV S V S V S V S l/s l/s l/s l/s l/s l/s A B C E I ΣV R V S VV S V S V S V S l/s l/s l/s l/s l/s l/s

126 A B C E I ΣVV R V S V S VV S V S V S l/s l/s l/s l/s l/s l/s A B C E I ΣVV R V S V S VV S V S V S l/s l/s l/s l/s l/s l/s

127 A B C E I ΣV R V S VV S V S V S V S l/s l/s l/s l/s l/s l/s A B C E I ΣV R V S VV S V S V S V S l/s l/s l/s l/s l/s l/s Table 26 Calculating peak flow to DIN for ΣV R 20.0 l/s 127

128 A C F G H K ΣV R VV S V S V S V S V S VV S l/s l/s l/s l/s l/s l/s l/s A C F G H K ΣV R VV S VV S V S V S V S VV S l/s l/s l/s l/s l/s l/s l/s

129 A C F G H K ΣV R V S VV S VV S V S V S V S l/s l/s l/s l/s l/s l/s l/s A C F G H K ΣV R V S VV S VV S V S V S V S l/s l/s l/s l/s l/s l/s l/s

130 A C F G H K ΣV R VV S V S V S V S V S VV S l/s l/s l/s l/s l/s l/s l/s A C F G H K ΣV R VV S VV S V S V S V S VV S l/s l/s l/s l/s l/s l/s l/s Table 27 Calculating peak flow to DIN for ΣVV R > 20.0 l/s 130

131 Fig 124 Pressure drop chart for Mepla pipes at 10 C, k = mm 131

132 VV DN x 2.25 DN x 2.5 DN x 3.0 DN x 3.0 DN x 3.5 R v R v R v R v R v l/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s Table 28.1 Pressure drop tables for Mepla pipes at 10 C, k = mm 132

133 V DN x 2.5 DN x 3.0 DN x 3.0 DN x 3.5 DN x 4.0 R v R v R v R v R v l/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s Table 28.2 Pressure drop tables for Mepla pipes at 10 C, k = mm 133

134 VV DN x 3.0 DN x 3.5 DN x 4.0 DN x 4.5 DN x 4.65 R v R v R v R v R v l/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s Table 28.3 Pressure drop tables for Mepla pipes at 10 C, k = mm 134

135 Fig 125 Pressure drop chart for Mepla pipes at 60 ºC, k = mm 135

136 V DN x 2.25 DN x 2.5 Table 29.1 Pressure drop tables for Mepla pipes at 60 C, k = mm DN x 3.0 DN x 3.0 DN x 3.5 R v R v R v R v R v l/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s

137 VV DN x 3.0 DN x 3.5 Table 29.2 Pressure drop tables for Mepla pipes at 60 C, k = mm DN x 4.0 DN x 4.5 DN x 4.65 R v R v R v R v R v l/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s

138 Fig 126 Pressure drop chart for stainless steel pipes at 10 C 138

139 V DN x 1.0 DN x 1.0 Table 30.1 Pressure drop tables for stainless steel pipes at 10 C DN x 1.0 DN x 1.2 DN x 1.2 DN x 1.5 R v R v R v R v R v R v l/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s

140 V DN x 1.0 DN x 1.2 Table 30.2 Pressure drop tables for stainless steel pipes at 10 C DN x 1.2 DN x 1.5 DN x 1.5 DN x 1.5 R v R v R v R v R v R v l/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s

141 V DN x 1.5 DN x 1.5 Table 30.3 Pressure drop tables for stainless steel pipes at 10 C DN x 1.5 DN x 2.0 DN x 2.0 DN x 2.0 R v R v R v R v R v R v l/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s

142 Fig 127 Pressure drop chart for stainless steel pipes at 60 C 142

143 V DN x 1.0 DN x 1.0 Table 31.1 Pressure drop tables for stainless steel pipes at 60 C DN x 1.0 DN x 1.2 DN x 1.2 DN x 1.5 R v R v R v R v R v R v l/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s

144 V DN x 1.0 DN x 1.0 Table 31.2 Pressure drop tables for stainless steel pipes at 60 C DN x 1.2 DN x 1.2 DN x 1.5 DN x 1.5 R v R v R v R v R v R v l/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s

145 V DN x 1.2 DN x 1.2 Table 31.3 Pressure drop tables for stainless steel pipes at 60 C DN x 1.5 DN x 1.5 DN x 1.5 DN x 2.0 R v R v R v R v R v R v l/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s

146 Fig 128 Pressure drop chart for copper pipes at 10 C 146

147 V DN x 1.0 DN x 1.0 Table 32.1 Pressure drop tables for copper pipes at 10 C DN x 1.0 DN x 1.2 DN x 1.2 DN x 1.5 R v R v R v R v R v R v l/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s

148 V DN x 1.2 DN x 1.2 Table 32.2 Pressure drop tables for copper pipes at 10 C DN x 1.5 DN x 1.5 DN x 2.0 DN x 2.0 R v R v R v R v R v R v l/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s

149 V DN x 2.0 DN x 2.0 Table 32.3 Pressure drop tables for copper pipes at 10 C DN x 2.0 DN x 2.0 DN x 2.5 DN x 3.0 R v R v R v R v R v R v l/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s

150 V DN x 2.0 DN x 2.5 Table 32.4 Pressure drop tables for copper pipes at 10 C DN x 3.0 DN x 3.0 DN x 3.0 DN x 3.0 R v R v R v R v R v R v l/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s

151 Fig 129 Pressure drop chart for copper pipes at 60 C 151

152 V DN x 1.0 DN x 1.0 Table 33.1 Pressure drop tables for copper pipes at 60 C DN x 1.0 DN x 1.0 DN x 1.5 DN x 1.5 R v R v R v R v R v R v l/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s

153 V DN x 1.0 DN x 1.0 Table 33.2 Pressure drop tables for copper pipes at 60 C DN x 1.0 DN x 1.5 DN x 1.5 DN x 1.5 R v R v R v R v R v R v l/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s mbar/m m/s

154 Fig 130 Pressure drop chart for HDPE pipes to DIN at 10 C 154