Experimental Comparison into the Effect of Oversized Heat Exchangers on Seasonal Performance Improvements of a Two-Stage and a Variable Speed Compressor in an R410A Chiller

There is an increased focus on improving the seasonal performance (SEER, IPLV.SI) of HVAC&R systems. Many studies suggest enhancing the efficiency and capacity modulation capabilities of the compressor to achieve higher seasonal performance. The improved compressor can better match the required cooling demand, undergo fewer cycling losses, and have lower power consumption in general. A larger heat exchanger improves the COP by lowering the operating pressure ratio and power consumption. This current paper focuses on the effect of using an oversized Brazed Plate Heat Exchanger (BPHX) as condenser on the seasonal performance of a similarly sized two-stage and a variable speed compressor in an R410A water ethylene glycol (WEG) chiller. The seasonal performance of this 8 kW-chiller is estimated using IPLV.SI according to AHRI 551/591. Experimental results indicate that a condenser having 70% more plates than the nominally sized condenser improves the COP by 18% for a two-stage compressor (with lower stages of capacity modulation) at the part load conditions while this is only 4% for the variable speed compressor. Additionally, the overall IPLV.SI improves by 18% for the two-stage compressor and by 12% for the variable speed compressor. These results show that the positive impact of condenser oversizing diminishes at part load conditions for variable speed compressors. Additionally, the effect of charge optimization is also explored.