Part load efficiency of air-cooled multiple-chiller plants

This paper reports an analysis of the energy efficiency of air-cooled chiller plants in buildings and opportunity of improved part load efficiency. Load-frequency profile, weather-load profile and thermal performance lines obtained by simulation of typical office and hotel buildings in a subtropical climate are examined to address the methods of determining the plant size, identifying the loading characteristics, optimizing the combination of multiple-chillers and evaluating the energy saving alternatives in design or retrofit. It is shown that the percentage design load for office is best related to external temperature; for hotels the product of external temperature and humidity is more appropriate as a climatic index. The results indicate that for a particular value of percentage design load, the likely outdoor temperature can be determined statistically, and the consumption can be determined from a set of chiller efficiency curves as a function of chiller part load ratio and entering condenser air temperature. The opportunity for improving the operating efficiency of air-cooled multiple-chiller plants by lowering the condensing temperature at lower outdoor temperatures is discussed.