Cooling effectiveness of mist precooler for improving energy performance of air-cooled chiller

Mist is increasingly applied to precool outdoor air in heat rejection. This study investigates how the coefficient of performance of an air-cooled chiller varies with a mist precooler at different levels of cooling effectiveness. A multi-variate regression model was developed to simulate the operating variables of an air-cooled chiller with mist precooling. The model was validated with typical performance data of an air-cooled centrifugal chiller. The coefficient of performance would increase by up to 30%, depending on the cooling effectiveness and the wet bulb depression – the difference between the dry bulb and wet bulb temperatures of outdoor air. At a large wet bulb depression, the percentage increase of coefficient of performance tended to correlate linearly with the chiller capacity. Yet at a small wet bulb depression, the dynamic control of condensing temperature resulted in a non-linear relationship between the percentage change of coefficient of performance and the cooling effectiveness. Further experimental work is required to optimize cooling effectiveness for the maximum coefficient of performance.