Operational Performance Comparison of Variable and Fixed Speed Chillers at Duke University’s Chilled Water Plant No. 2

The objective of this study is to evaluate the performance of variable and fixed speed chillers in their current production environment using operational data sets from multiple chillers. The study seeks to determine the actual contribution to efficiency and conditions for efficiency of both variable and fixed speed chillers. The analysis also develops performance prediction models for both types of chillers under various operating conditions and in doing so demonstrates that variable speed chillers have significantly outperformed initial energy savings estimates. Lastly, the results demonstrate that chiller performance and potential energy savings are relatively predictable under most operating conditions, helping to verify operators’ current understanding of plant operation.