Non-condensable gas in the refrigerant of air-source heat pumps: Interactions between detection features, charge level, and temperature

Abstract

Non-condensable gas (NC) can be introduced into a vapor compression refrigeration cycle through improper installation or service, and decrease system efficiency, increase burden on the compressor, and reduce the compressor life span. Therefore, detecting this fault early can prevent energy waste and prolong the operating life of the system. However, diagnostic methods are not widely available, and neither are methods to quantify NC amounts based on easily measured variables. Therefore, an experimental test apparatus was built to provide data to improve understanding of NC-refrigerant interactions. Two NC fault intensities (50%, 100%), each at four charge levels (70%, 80%, 100%, 120%), were tested under five different ambient temperatures (0-40°C). Dry nitrogen gas was used for the NC. The results showed that the theoretical estimation method is inaccurate. The trends of the results from experimental tests are consistent with those from theoretical calculations, but the thresholds obtained from experimental tests are larger than those from theoretical calculations. This paper explains these differences, and provides a model to quantify the NC fault intensity using easily-measured variables. The specific model is applicable to typical residential air-conditioner and heat pump systems that use R410A refrigerant, but the general findings are applicable to other refrigerants.