ASHRAE Journal - April 2009 - 33

ASHRAE 19 50 59–2009 YE A R S JOURNAL Central Chilled Water Distribution Systems Design By ERwiN G. HANSEN, P.E., FELLOw ASHRAE FEAtUREd iN ASHRAE JOURNAL, NOvEmBER 1974 new site. The criteria statement in essence read as follows: “Coil output in the building secondary circuit will be controlled by threeway valves maintaining constant flow in the circuit. The three-way valve linking the primary and secondary circuits will have a high resistance relative to the system pressure differential between buildings. It will maintain a constant 42°F temperature in the secondary circuit. Ten 4,000 ton refrigeration machines will be installed in the central plant. An equal number of pumps will supply 40°F chilled water in the primary circuit. Refrigeration machines and pumps will be started or stopped in direct relation to the load demand.” The second master plan concerned the expansion of a smaller campus type central chilled water system. It stated the following verbatim: “Several buildings are on the existing system and are designed for an 8°F differential. When the system differential is raised to 14°F, these building systems will be provided with secondary pumps and three-way temperature control valves to provide the same conditions of water temperature at the coils.” April 2009 I n hot water heating systems the behavior of any single element affecting the behavior of other elements is not generally critical since they are limited in size, serving mostly single buildings, and are usually very much over-designed. It is critical in high temperature water systems, but since they usually terminate in heat exchangers, serving low temperature steam or hot water building systems, rather than in the terminal equipment directly, the incompatibility can be more easily corrected. It is very critical in central chilled water systems, and there are many such systems in existence today which cannot attain design capacity, adequately supply the demands of all users, or operate efficiently, that is, without wasting energy unnecessarily. The causes for the insufficiency and energy wastage fall mostly into two categories: • Incompatibility of design concepts of the building systems with the central system due to lack of coordination or due to lack of understanding of the underlying principles. • Incorrect design of the interface. Recently I read the master plan reports for two campus-type central chilled water systems prepared by two of the most prestigious architect/engineer firms in this country. The first master plan concerned a Erwin G. HansEn, P.E., FEllow asHraE Erwin G. Hansen is former vice president of Syska and Hennessy inc. He served on tC 6.1, Hydronic and Steam Equipment and Systems, and wrote the high temperature water chapter in the 1966 ASHRAE Guide and data Book and the 1984 ASHRAE Handbook. He was involved in the planning, design and construction of numerous projects, including the U.S. Air Force Academy, Capitol Power Plant, Harvard University and King Saud University in Riyadh, Saudi Arabia. He has several patents, including a regenerative heating and cooling storage system. He died in 2005. 33 ASHRAE Journal a s h r a e. o rg

ASHRAE Journal - April 2009

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