Advanced control of condensing temperature for enhancing the operating efficiencyof air-cooled chillers

Air-cooled chillers are commonlyused to provide cooling energyin commercial buildings in the subtropical climate. These chillers have long been considered inefficient because theyoperate under head pressure control where the condensing temperature is kept high in the refrigeration cycle. This paper considers a novel method to strategically lower the condensing temperature to enhance chiller efficiencyat anyoutdoor temperature. An experiment is carried out on an air-cooled reciprocating chiller to confirm that an electronic expansion valve enables refrigerant to be adequatelyfed into the evaporator in all operating conditions, even when the condensing temperature falls to around 20 1C. Byenhancing the heat rejection airflow of the condenser, both the condensing temperature and chiller power can decrease considerablywith less fluctuation. According to the algorithm of staging condenser fans, this enhancement corresponds to resetting the set point of the condensing temperature based on anyoutdoor temperature. The potential and benefits of implementing this reset strategyare discussed.