OPTIMUM TRADE - OFF BETWEEN CHILLER POWER AND PUMP POWER FOR A CHILLER PLANT SERVING A COMMERCIAL BUILDING

This paper explains how to enhance the energy performance of a chiller plant designed with chillers ofequal size or unequal size and having superior coefficient of performance (COP) at part load operation.A simulation study was carried out on an air-cooled centrifugal chiller plant serving an office building.Four design options with respect to the number and nominal capacity of chillers were investigated(OP1: 6 x 1124kW; OP2: 8 x 810kW; OP3: 4 x 1213kW + 2 x 810kW; OP4: 2 x 1350kW + 2 x 1107kW +2 x 801kW). For each design option, the annual electricity consumption of chillers and pumps wasassessed using a chiller model capable of determining how the chiller COP changes at variousoperating conditions. It is found that prolonging the full load operation of chillers helps reduce thepumping energy, but fails to minimize the energy use of chillers having maximum COP at a part loadratio of around 0.8. An annual electricity saving of 5.2% can be achieved by using the design optionOP2 with which each of the chillers operate frequently with maximum COP at their optimum loadingpoints. This highlights the need to ascertain at what loading point the trade-off between the chillerenergy and pumping energy can be optimized to minimize the overall energy consumption of a chillerplant. The results of this paper will give engineers and researchers a better idea about how to select theright size and combination of chillers and how chiller part load performance curves can be used toevaluate improvements in the performance of a chiller plant with alternative designs.