The a. in retrofit applications. Such a retrofit may come under. takes a look at. work, which could cause expensive down time.

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1 My purpose is to consider some practical engineering aspects when using alternative refrigerants especially in retrofit applications. Such a retrofit may come under the category of a drop in with little or no equipment change, or may require considerable more preparatory work, which could cause expensive down time. One alternative is to use HCFC-22. There can be complications with the change over to HCFCs. For example, conversion to HCFC-22 in existing CFC systems requires compressor and/or equipment change out or modification. As an option, the CFC may be retained and the system integrity maintained by using recycled refrigerant. Another option to avoid equipment change would be to use one of the blends available. The successful application of HCFC-22 for commercial refrigeration low and medium temperature is well documented. Whether the choice is to engineer the low temperature systems around a single stage screw, or to use one of the many good alternative options, an abundance of data and information-both theoretical and practical-is available. HFC-134a is the candidate which it is hoped will have the longest life. It has now become accepted as a leading replacement for CFC-12 in existing systems, in addition to being the only viable refrigerant for new wpment operating in the CFC-12 range. When there is no marked loss of performance from the use of HFC- 134a in place of a CFC or HCFC refrigerant in a new or existing system, its use should be encouraged. There are, however, some basic rules to be applied leading to a successful installation. Line sizing When the first HFC-134a test plant was designed, reliable data for line sizing wasnot readily available. The lines were therefore sized using well proven CFC- 12 data. There is now a good selection of line sizing data which has been proven to be valid in such installations. The procedure originally followed selected slightly higher velocity options, espedally for suction lines forming part of variable capacity circuits, where the n e f of fixtures per circuit was limited to four, all operating independently. The teat resuits obtained for these early trials were carefully checked against a rsslected computer-operated line sizing program, which produced compatible results. Materiai and component requirements The copper tube used for HFC-134a should be processed during manufacturing to remove all possible traces of lubricating grease used in the tube forming process. At all times-during storage, transportation to site, and during preparation for installation work on site-the tube ends should be capped. Similarly, when brazing is complete, any open ends should be capped. Inert gaspurgingis essentialandshouldbeusedfor allbrazed joints andconnections. It should be established from the manufacturer or supplier of the valves selected for the system that they are suitable for HFC-l34a, in particular the seats an8 gland material. The coating of valve parts with mineral oil during msembly can occur, and this should ideally be removed. Viton components must takes a look at By P. J. Cooper The a \r I 20/November 1993, RSC

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3 be avoided. Ensure that any flexible hoses used are compatible with HFC- 134a. It may be necessary to examine the quality specifications for some manufactured components used in the system with a view to improving cleanliness. Contamination is possible from condenser coils, display case evaporators, built-in control components, and cold store evaporators. These should all be subjected to strict quality controls. It may be of interest to know that the oil, grease, and general debris which was removed from such components (especially the copper tube) during one test installation on HFC- 134a, was considerable. Contamination is undoubtedly always present in our systems, and should be a concern to all. How qany times has the TE valve blockaqk during commissioning proved t6 be a mystery? Perhaps we now know why. Procedures The importance of thoroughly evacuating all traces of HCFC refrigerant, if used during pressure testing, cannot be overemphasized. Remnants of chlorine-bearing refrigerant in a HFC-134a system will be evident from refrigerant and oil sample analysis. Also do not forget the non retum valve in the vacuum pump to prevent the wrong oil entering the system in the event of an unexpected power interruption. There is a view that CFC-12 and HFC-134a can be mixed and left to operate with mineral oil, subject to the proportions being very carefully controlled. This approach is not recomended by the writer and is not approved by many compressor manufacturers approached on the subject. Even withthe bestprocedures, the normal level of moisture present in thepolyolesrter oil (necessaryfor HFC- 134a systems) can be 50 ppm. This is dloaaetbing we must adjust to. This must be controlled by drier changes in the early period of operation ifproblems such as copper plating are to be avoided. Cumpefence Oil handling prior to and during charging into the system should always follow good practice. Procedures to inhibit the ingress of moisture-ladenair shouldbe observed, i.e., nitrogen purging. Oil pumps, dip tubes, hoses, and WnWers must be dedicated to the 2YNovember 1993, RSC Labels should be large and legble [as on this 134a chiller) andlocated where the type of oil and/or refrigerant may not be obvious. system. Additional care must be taken of the equipment when not in use. Storage should be arranged which will prevent contamination and misuse. Precisely the same advice holds for analyzer sets, pressure gauges, connecting hoses, etc. A new discipline is required by all who handle the new refrigerants. It is not acceptable for the technician to leave this equipment loose in the back of the van. The segregation of equipment dedicated to given refrigerants is essential if problems are to be avoided. Engineers must be made familiar with the different procedures to be followedinbuilding and servicing HFC systems, while emphasizing good refrigeration practice. One message is quite clear: Even the simple tasks will take longer and service wiu be more costly, a fact that some will find hard to accept but one that cannot be avoided. leak defecfion Leak detection now has a higher level of importance as HFC-134a will find its way to places other refrigerants will not reach. There is sufficient price incentive to prevent leakage, notwithstanding the legal and environmental issues. Automatic leak detection equipment provides additional insurance against undetected leakage, espe- cially from small leaks. The data that these systems provide is important. We can leam the pattern of leakage, the fluctuating leaks, the number that owing to size would have remained undetected, and the vulnerability of flared compression joints. When a leak is known to exist, the technician has to find it and then make it good. This process can be time consuming. With electronic leak detectors, take care to regularly change the sensing head and follow the manufacturer's instructions. And remember, that if in doubt, soap and water may still be the best method for leak detection. Installation, servicing, and maintenance manuals require examination to take account of the above factors. To assist those who may not be familiar with the operating conditions of HFC-l34a, a small pennanent pressurekemperature chart is of value, located adjacent to the control panel. Labels should belarge and legible and located where the type of oil and/or refrigerant may not be obvious. Change uuf of CFCs from existlng systems For those with the responsibility for the replacement of CFCs in existing installations, there are several basic questions which should be addressed: Is the oil change necessary? What refrigerant should be selected? What procedure should be followed? How long will the procedure take? How muchmoney should be allowed in the budget? Will there be a warranty and any ratings for the compressors? Will it be possible to recycle the selected refrigerant? Is the compressor in good condition?. Are there signs of leaking headgaskets? Do the valves hold on test? Procedure Central plant systems with long complex pipe routes require special attention when an oil change is necessary. The time taken to successfully eliminate the mineral oil, and the cost of the labor involved can be considerable. However, consider a typical well tried change-out procedure based on a small single compressor system operating in a small store. If the refrigerant selected was HFC-l34a, an oil -." v

4 change would be required on two occasions within a few hours, to be repeatedat regularintervals, until the mineral oil content has been reduced to a satisfactorily low level. A value of 1 % is frequently quoted as being the appropriate level although this is rarely achieved. Avalue of 5 to 10% is now widely accepted as being achievable and satisfactory for most applications. Beware of heat exchangers with enhanced tube surface. This can provide a trap for the remaining mineral oil, with obvious results. A level below 5% may be necessary in this instance. Oil sampling When the mineral oil is replaced by a POE prior to charging with HFC- 134a or a blend, oil samples have to be taken periodically from the syhtem to establish the percentage of mineral oil remaining. Testing kits are available for site use and should be available from wholesalers. Their use can save time. They have been found to be reasonably accurate. As a warning, it should be noted that the time taken for some oil suppli- It is not acceptable for the techrucian to leave this equipment loose in the back of the van. The segregation of equipment dedicated to given refngerants (as shown here) is essential if problems are to be avoided. ers to test the samples, has proved to be excessive. Some evaluations have taken up to two weeks. It is sound advice to involve your oil and compressor suppliers at the planning stage. Refrigeranf removal Prior to the removal of the existing refrigerant, a thorough leak check of the whole system is essential. This should include the increase of pressure above normal operating levels, especially if HFC-134a is to replace CFC-12. Bewareofvalveglands, compressor head joints, screwed sight glasses and, of course, flare joints. The pumping down and decanting of existing refrigerant can commence when the mineral oil content is acceptable. The recovery cylinders must be procured and made available on site to receive the used refrigerant. The time for pump down and decanting shouldnot beunderestimated. It may be reasonable for a small store installation. But consider, for example, a supermarket system. Time is measured in hours rather than minutes. The display cases must be emptied topreserve foodquality andtimemust be allowed for leak detection and any PUNovember 1993, RSC Circle 159 on Reader Action Card

5 component change. Isolation valves in every display case may be essential to permit decanting during normal service. Replacement dehydrators, suction filters, sightglasses, and possibly thermostatic expansion valves should be fitted and the control and safety settings adjusted for the new refrigerant. Evacuation and charging Thorough evacuation of the system is particularly important and any temptation to shorten the process should be resisted. Large labels should now be fixed to every location where a technician could have access for service or maintenance. Where adjacent systems contain a different refrigerant, pipe lines and fixtures should also be clearly identified. The availability of the new refrigerant for any service purposes should be established at this stage, as consideration may have to be given to holding a stock locally. Refrigerant charging and system commissioning follow standard practice with due attention to the above comments. GETA TRANE WATER SOURCE HEAT PUMP BUILT TO ORDER IN JUSTTWE DAYS. Don t settle for a stock unit. We ll build a water source heat pump to most closely meet your needs. And we ll ship it in three days or less. Select one of our standard catalogued 1/2 to lo-ton horizontal units, or 1 1/2 to l@ton vertical units. Then together - we ll choose among our many piping and air discharge configurations and eledrical options. We ll even work with you to integrate controls with your current system. Test us. Call 1-80(1666-WSHP r your local Trane Commercial Sales Of6ce and see how fast we \ send product information and a price quote. OAmeicSn Standard Inc /November 1993, RSC THE Creating l%e Right Atmosphere Circle 173 on Reader Action Card Conclusions We wish to emphasize the importance of planning in detail the various activities involved in the change-out of oil and refrigerant and the recognition that some interruption to the system operation is inevitable. When considering compressor ratings, these may have to be estimated owing to the lack of alternative refrigerant application data for many of the older compressor models in the field. In the cases where HFC-134a has been used for applications at saturation suction temperature above -12 degrees C and with condensing temperature up to 43 degrees C, the CFC- 12 ratings were found to be reliable. But do not ignore the possibility of subcooling. Take care to study the condensing pressures and discharge temperatures when retrofitting in an existing system. If the system compressor is not new, there may in some instances be a reduction in capacity owing to wear, although it has probably been operating satisfactorily on a CFC prior to the change over. Cylinder head gasket anuorvalve plate change at this stage may provide good insurance against early operational or leakage problems. Inthe majority of installations, there should be no concern about the performance. There will, however, be some occasions when the compressor has to be changed. This should normally be identified during the site survey. The question of recycling presents no problems with HFC-l34a, but the same cannot be said of the blends. This is a topic that technicians would be advised to raise with their refrigerant supplier. When using blends, the refrigerant can only be added to the system as a liquid, unless the complete cylinder is charged. There is no doubt that this can be a limitation to those servicing small equipment, which is usually not equipped with a charging valve. There appears to be no doubt that the alternatives available in the market have a key role in the main issue of replacing CFCs and the eventual replacement of HCFCs. Consider the issues carefullybeforemakingthefirst move. But do not delay as surely the demand for CFCs will soon exceed the supply. EDITOR S NOTE: Peter J. Cooper is Director, Adtec Services Ltd., St. Albans, Hertfordshire, United Kingdom.

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