Design Guidelines: CoolTools Chilled Water Plant
(2.7 MB PDF file)
Many large buildings, campuses, and other facilities have plants that make chilled water and distribute it to air handling units and other cooling equipment. The design operation and maintenance of these chilled water plants has a very large impact on building energy use and energy operating cost.
Not only do chilled water plants use very significant amounts of electricity (as well as gas in some cases), they also significantly contribute to the peak load of buildings. The utility grid in California, and in many other areas of the country, experiences its maximum peak on hot summer days. During this peak event, chilled water plants are often running at maximum capacity. When temperatures are moderate, chilled water plants are shut down or operated in stand-by mode. This variation in the rate of energy use is a major contributor to the peaks and valleys in energy demand, which is one of the problems that must be addressed by utility grid managers.
Most buildings and facilities that have chilled water plants have special utility rates where the cost of electricity depends on when it is used and the maximum rate of use. For instance, PG&E has five time charge periods: summer on-peak, summer mid-peak, summer off-peak, winter mid-peak and winter off-peak. The price of electricity is several times higher during the summer on-peak than it is during the off-peak periods. Not only does the cost of electricity vary, but most utility rates also have a monthly demand charge based on the maximum rate of electricity use for the billing period. Since chilled water plants operate more intensely during the summer peak period, efficiency gains and peak reductions can result in very large utility bill savings.
In addition to new construction, the chilled water plants of many existing buildings are being replaced or overhauled. Older chilled water plants have equipment that uses ozone-damaging refrigerants. International treaties, in particular the Montreal Protocol, call for ozone damaging chemicals (in particular CFCs) to be phased out of production. As the availability of CFCs is reduced, the price will skyrocket, creating pressure for chilled water plants to be overhauled or replaced.
The CoolTools Design Guide is written for mechanical engineers who design, redesign or retrofit chilled water plants. The guide provides engineering information on how to estimate plant loads; details on chillers, towers and other plant equipment; system piping arrangements and configurations; controls; design approaches; contract documents; and commissioning. While design engineers are the primary audience, the guide also provides useful information for operation and maintenance personnel, mechanical contractors, and building managers.
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