Applying condensing-temperature control in air-cooled reciprocating water chillers for energy efficiency

This paper reports on the modelling and findings of the energy performance of an air-cooled reciprocating multiple-chiller plant under the conventional head pressure control and the new condensing-temperature control in a subtropical climate. The simulation model was validated using the operating data of an existing chiller plant. As noted from this existing air-cooled reciprocating chiller plant, there was a substantial efficiency drop at part-load resulting from the head pressure control. If operating at variable lower condensing-temperatures based on the established operating mode of the condenser fans and compressors, it is shown that the chiller consumption can be maintained below 2 kW/refrigeration ton throughout the entire range of outdoor temperature and part-load conditions, giving an average efficiency of 1.08 kW/refrigeration ton. The energy imposition due to cycling on more condenser fans can be compensated by the reduced compressor consumption. Potential energy savings of 18.2 and 29% in the annual chiller consumption are achievable by applying the condensing-temperature control to two existing chiller plants studied. This supports the need to develop the condensing-temperature control as an improvement to the conventional head pressure control.