Improving Vapor Compression Cycle Efficiencies in Support of Conventional Refrigerant Phaseouts

Abstract

Finding replacements for R-410A is paramount, and it primarily focuses on issues such as energy efficiency, GWP, flammability, toxicity, and safety. The study reported herein supports replacing R-410A by investigating reconfigurations to vapor-compression cycles and then determining performance improvements for these modified cycles. In addition, a comprehensive climate zone model was developed so that modified cycle performances could be evaluated and compared for the full range of a cooling-season weather conditions found throughout the U.S, which was necessary because cycle performances are dependent on outdoor temperatures and humidities. Using R-410A and other refrigerants, these evaluations and comparisons of modified vapor-compression cycles were first performed for outdoor air temperatures ranging from 26.7 to 35 ℃ and relative humidities ranging from 40% to 80% with assumed evaporator exit air temperatures of 7.2, 10, 12.8℃ and a typical compressor efficiency of 80%. The first set of modifications investigated are based on installing evaporative cooling at the condenser air inlet with external supply water sources being either producing COP highest improvements of 60% and internal water supplied by the evaporator condensate producing COP highest improvements 38%. The second set of modifications investigated are based on installing at the evaporator inlet HRV units with resulting COP improvements of 25% and ERV units with COP improvements reaching as high as 100%. The final two modifications both cool the refrigerant exiting the condenser and entering the evaporator by either using evaporator condensate water which resulted in COP improvement of less than 5%, or by transferring energy to the refrigerant exiting the evaporator and entering the compressor with the aid of an internal heat exchanger, which resulted in COP increase as high as 32%. As final step to determine the reconfiguration effectiveness for any modified cycle with any phaseout replacement refrigerant at any location were combined the two sets of models, namely the climate zone models and the refrigeration cycle models, to perform a comprehensive analysis over full cooling seasons, for each climate zone. The results show that the performance ranking of modification and refrigerant types vary considerably with location, as defined by climate zones, throughout the U.S.