Evidence-based assessment of energy performance of two large centrifugal chillers over nine cooling seasons

The change over time of energy performance of large chillers used in commercial and institutional buildings is seldom presented in the literature. Most studies are based on measurements of small capacities of residential air-conditioners and heat pumps. Authors found in the literature only three papers on this topic. This paper presents the evidence-based assessment of long-term performance of two identical large capacity chillers that serve the cooling system of a university campus. The paper presents the estimation of uncertainty of direct and derived measurements by using as example measurements recorded at 15 min time intervals by the building automation system during the summer of 2016. First, the paper verifies the hypothesis that weekly values of coefficient of performance (COP) of these large chillers do not change significantly over the summer of 2016. Second, the t-test also verifies the hypothesis of no significant change of seasonal COP values from 2009 to 2017. Third, a linear correlation-based model shows a variation of COP values by 1-2% per year between 2009 and 2017. The results show that the seasonal variation of COP is not statistically significant.