The costs, energy efficiency and environmental impacts of district cooling (DC) are often compared to those of building-scale chiller systems. In such comparisons, the assumptions regarding the efficiency of building-scale systems have a significant impact on the comparative economic conclusions as well as the analysis of efficiency and the related environmental impacts. Generally, the assumptions for building systems are based on theoretical values or equipment ratings based on static laboratory conditions rather than “real world” data reflecting part load operations, weather variations, operator inputs and system depreciation. This may result in underestimation of the economic, efficiency and environmental benefits of DC.
This project set out to develop more realistic data on building-scale system efficiencies, by investigating the actual annual efficiency of building cooling systems and determining how this differs from the theoretical annual efficiency using values based on test conditions. Many variables affect the efficiency of building chiller systems, including type of chiller equipment, size of chillers and cooling towers relative to seasonal loads, condenser temperatures, chilled water supply temperatures, use of variable frequency drives (VFDs) and the age and maintenance history of the equipment.
Robert Thornton, International District Energy AssociationRobert Miller, FVB Energy Inc. Anis Robinson, BRE EnvironmentKen Gillespie, Pacific Gas & Electric
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