Seasonal Performance Evaluation Procedures for Domestic Electric Driven Heat Pumps and Air Conditioners

摘要

Virtually all of the residential and commercial heat pumps available in today's market operates on the same fundamental principles as do that of the vapor compression cycle. Also, virtually all of these systems use fluorocarbon compounds as a working fluid and have a constant speed positive displacement compressor with leaf spring valves. This concept has been continuously developed throughout this century and has served society well; however, it contains a couple of inherent limitations which cause any particular design to perform somewhat less than ideally. The first and most significant of these limitations is due to the fact that a refrigerant's density is proportional to its pressure. Therefore, when the evaporator temperature is required to be decreased, the saturation pressure must also be decreased with a corresponding reduction in the circulating refrigerant suction density, causing a loss in system capacity. This capacity loss is accented by the use of constant speed piston compressors whose valves operate on a differential pressure between the interior cylinder conditions and either the suction or discharge line pressures. If either the condenser or evaporator temperature conditions increase or decrease, respectively, less valve open time will exist per stroke and thus less refrigerant will be pumped; leading to an additional loss in capacity. This capacity reduction is particularly significant in the heat pump heating application for residences since it occurs simultaneously with an increase in building transmission (and thus heat pump) load. This overall decrease in refrigerant flow rate which causes the decrease in capacity also causes a decrease in compressor work.