Experimental investigation into the influence of different system configurations on charge optimization in an R410A chiller with a dedicated subcooler

Abstract

The current study addresses the important issue of reducing the amount of refrigerant used in HVAC&R systems due to new regulations and the phase-down of high Global Warming Potential (GWP) refrigerants. Specifically, this research compares the optimal refrigerant charge for two distinct scroll compressors: a variable speed compressor and a single speed compressor, both operating within the same R410A chiller equipped with a condenser, receiver and dedicated subcooler. The nominal cooling capacity of this chiller is 8 kW. One novelty of this study lies in assessing the charge optimization not only at full load but also at part load conditions to determine if there is any effect of using continuous capacity modulation like a variable speed compressor on the optimum charge. The results reveal that the COP maximizing charge corresponds to when some part of the two-phase heat transfer happens in the dedicated subcooler and not when the receiver is partially filled with liquid refrigerant as expected. Interestingly, at part load conditions, the compressor lacking continuous capacity modulation demonstrates higher optimum subcooling and COP improvement potential compared to full load conditions. Moreover, the study also analyzes the impact of operating at peak COP charge on seasonal performance using a variable speed compressor. This seasonal performance investigation reveals that although cooling capacity obtained when the system is operating with COP maximizing charge is 6 % lower, the seasonal performance is 11 % higher when compared to typical operating charge. Notably, for the first time, charge optimization is conducted in the same experimental with different configurations of the condenser with/without receiver and with/without subcooler to understand the contribution of these components. This systematic comparison revealed the absence of abnormal COP peak in configurations without a dedicated subcooler.