Consider the design of a central chilled water cooling system for a clubhouse and

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1 EXAMPLE CD10-1 Consider the design of a central chilled water cooling system for a clubhouse and residential lodges for a prestigious golf club. The clubhouse is large with a 75 ton cooling load. It is single storey with a basement for storage and mechanical equipment. Four lodges with 8 suites and 2 common areas have a cooling load of 20 tons each located to one side of the clubhouse. The first lodge is about 250 ft away and the others are spaced about 100 ft apart farther on. The equipment room is located at the end of the basement closest to the first lodge. Each lodge has a basement for equipment. The golf course is located 70 miles from a city where qualified service personnel are available and there is no on site operating personnel. Layout a suitable central chilled water system for the complex, describe the main features of the system and considerations in arriving at the design. SOLUTION: Obviously whatever type system is designed should be reliable and simple as possible without going overboard due to lack of local trained operating and service personnel. A system similar to that shown in Figure of the text would be a good choice to ensure reliable operation and is reasonably simple because it requires a minimum of controls. This type system would be very responsive to the expected variable load. Schematicly the system would appear as shown in Figure CD10-1. The air handling units in the clubhouse and the fan coils in the lodges with piping for the tertiary circuits are not shown but would resemble Figure in the text with the required number of units laid out in a reverse-return manner. In this case it is not

2 practical to use reverse-return for the secondary circuit. However, the control of pump P L by the required pressure differential at lodge No. 4 will ensure circulation to all tertiary circuits. The total combined cooling load is 155 tons. Two chillers with capacity of 75 tons each are chosen. Each can unload in four steps which allows the capacity of the system to vary from about 20 to 150 tons. Actually two chillers of about 60 tons each would be adequate due to the diversity in load usually encountered in situations of this kind. However, due to location, if a chiller was to fail, the other 75 ton unit would provide reasonable cooling in most cases until the second unit could be put back in service. It is assumed that the system will operate with chilled water supplied at 45 F and returned at 55 F. Then the flow rate of water for each chiller is Where is in gallons per min (gpm). Then gpm and the total flow rate at full load is 360 gpm. Each of the lodge circuits will be sized for 48 gpm which corresponds to 20 tons although there is theoretically only 45 gpm available for each lodge. It is highly unlikely that all four lodges would be at full load simultaneously. Now, in order to size the pipe and compute the lost head for the various circuits so that the pumps may be specified, a realistic layout of the piping is necessary. Normally a CAD drawing of the piping showing all valves, fittings and accessories would be made to scale and

3 overlaid on a plan of the buildings. Since that is not possible here a single line layout with some of the details is shown in Figure CD10-2. Using the criteria recommended and discussed in the text, the various sections of the piping can now be sized using Figures or in the text or the program PIPE given on this CD. The flow rates and pipe sizes are shown on Figure CD10-2, except for the tertiary circuits. An analysis for the lost head is not given here due to lack of details available in Figure CD10-2. However, the pipe sizing and head loss calculation is usually done simultaneously using a program like PIPE. For this design an analysis would yield the results shown below in Table CD10-1. The tertiary circuits for the clubhouse and lodges are similar to that shown in Figure in the text with the necessary additional coils and piped in a reverse-return manner. It is obvious that considerable work is required to design a system of this kind. The effort required to select all the required valves and accessories is great. However, attention to all the details ensures a reliable, trouble free design. Table CD10-1 Approximate Pump Specifications Pump Speed Location Capacity Total Head rpm gpm ft P Chiller P Chiller P a Lodges P c 3500 Clubhouse VSD Circuit P L 3500 Secondary Circuit

4 VSD a Typical of all 4 Lodges

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