Comparative study on the energy performance of chiller system in an institutional building with stochastic frontier analysis

This study demonstrates how to compare the energy performance of an existing air-cooled chiller with and without mist precooling of condenser air, considering different operating conditions between the two situations. A comprehensive set of operating data was gathered for each situation for over 4 months. Using stochastic frontier analysis, technical efficiency (TE) for the coefficient of performance (COP) - output - was evaluated for each set of operating conditions - inputs - involving weather and controlled operating variables. TE had an average of 0.64 and a standard deviation of 0.14 under mist precooling, while the corresponding values were 0.56 and 0.18 in the absence of mist precooling. A positive correlation was identified between the COP and TE. Based on the frequency distribution of TE, mist precooling enabled the chiller to attain higher performance more frequently under standardized operating conditions. Pearson correlations among the variables ascertain that TE has the highest correlation with condensing temperature, followed by the temperature of supply chilled water, so their precise control would give performance enhancement. TE can provide a basis of benchmarking chiller performance at different operating conditions and help explain the extent of improvement brought from the weather responsive control.