Application of water mist pre-cooling on the air-cooled chillers

The operation of air-cooled chillers accounts for significant energy consumption in local commercial buildings, and low operational efficiency especially under partial load conditions and poor control are part of reasons for such huge energy consumption. Chiller efficiency can be improved by enhancing heat transfer rate in condensers. This paper considers how the chiller performance can be improved by using water mist to pre-cool ambient air entering the condensers to decrease compressor power. A simulation analysis on an air-cooled chiller equipped with a water mist pre-cooling system under head pressure control shows that applying water mist pre-cooling enables the coefficient of performance (COP) to increase. Variable condensing temperature control is superior to head pressure control, where condenser effectiveness is enhanced by staging all condenser fans to decrease the condensing temperature. When the chiller with a water mist pre-cooling system operates under condensing temperature control, the analysis indicates that the COP improvements would be more considerable. The cooling energy saving potential for a representative office building in Hong Kong will be assessed when water mist pre-cooling and variable condenser temperature control are applied to the air-cooled chiller plant.