Experimental comparison and seasonal performance evaluation of different scroll compressor capacity modulation methods in an R410A water to water system

Abstract

Rising cooling needs for the residential and commercial air conditioning sectors and the demand for higher SEER require HVAC&R to handle cooling loads below the design condition. Although several studies exist focusing on a particular capacity modulation strategy, there is no extensive study that explores all these available modulation strategies in the same experimental facility. This study experimentally compared a single speed, a two-stage compressor, tandem combinations of two single speed compressors, a single speed and two-stage compressor, and a variable speed compressor using the same R410A water ethylene glycol (WEG) system for cooling application. These modulation strategies were tested according to AHRI Standard 551/591 (2020), and their seasonal performance is given by Integrated Part Load Value (IPLV.SI). A two-stage compressor with lower LMTD at the heat exchangers and a single speed compressor with higher isentropic efficiency have the same performance at one of the part load conditions. Additionally, a single speed compressor with an improved compressor motor has a 3% higher IPLV.SI than a two-stage compressor with the baseline motor. Different methods of interpolation that are available when the capacity is in between two compressor stages of operation were discussed. The tandem combinations with different number of stages have the same seasonal performance, showing that not all the stages available might be useful. The variable speed compressor with the best IPLV.SI was selected to further study the performance under heating application using EU 14825 (2013) standard with constant and variable condenser outlet conditions. For heating application, variable speed compressor with a wider range of modulation is recommended when selecting the compressor for variable condenser outlet temperature conditions while it might not be the best option due to compressor operating envelope limitation when operating with constant condenser temperature outlet.