Theoretical and Experimental Verification of CVR Energy Savings for Refrigeration Loads

Abstract

This paper presents analytical and experimental studies on Conservation Voltage Reduction (CVR) for Refrigeration Loads (RLs) driven by single-phase and three-phase induction motors. It is shown that the increase in motor efficiency is the factor that determines the regions where CVR works for RL loads. The results of this paper dispel the belief that CVR cannot save energy from RLs because the output energy must be constant to keep the same temperature. A criterion is developed to assess the effectiveness of CVR for RL loads. It is shown theoretically and experimentally that CVR energy savings come from the reduction of iron-core losses. Traditionally, the iron core losses are represented by shunt resistances ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R_m</i> ) that are frequently neglected in the literature. However, they are essential for the proper evaluation of CVR. Induction machines of all ratings have a region where energy savings can be obtained. When operating near their rating smaller machines produce larger energy savings under reduced voltages than larger machines in proportion to their ratings. An additional benefit of CVR, when applied to motor loads, is that the power factor increases substantially.