Experimental analysis into the effect of heat exchanger sizing on charge optimization in an R410A chiller with a dedicated subcooler

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There is an increased focus on the amount of refrigerant used in the HVAC&R systems due to the ongoing phase-down of high GWP refrigerants. In the current work, charge optimization is conducted with a variable speed compressor in an R410A chiller having a nominal cooling capacity of 8 kW, which is installed with a condenser, receiver and dedicated subcooler. This study also provides for the first time insights into how a receiver and a dedicated subcooler can be used to not only obtain optimum subcooling but also account for any potential refrigerant leaks by holding additional charge in the receiver. Results indicate that an ideal charge optimization curve can be achieved by sizing the condenser and subcooler to ensure only the optimum subcooling happens in the subcooler. The impact of dedicated subcooler and condenser sizing on charge optimization as well as the system, and seasonal performance is also studied. This analysis helps in understanding how these components should be sized and when the diminishing returns occur from oversizing. This work also shows that when the system is operating with enough refrigerant to fill the receiver with saturated liquid refrigerant, using a dedicated subcooler decouples the cooling capacity increment from power consumption increase typically observed with increasing subcooling. Results show that for the current system investigated increasing the dedicated subcooler area beyond 8 % of the total available heat rejection area will not yield any additional seasonal performance improvement.