Study concerning the influence of refrigerant injection on the efficiency of a heat pump

Heat pumps are today a viable alternative to conventional heating systems. Their main disadvantage is the strong dependence on ambient temperature. For high performance operation in the case of temperature lift increase, it is necessary to use a two-stage compression system. There is the possibility of using an alternative solution, namely refrigerant injection technology. Instead of using a two-stage compressor where two-phase refrigerant can be injected between the two stages in order to cool the suction gas before it enters the high pressure stage, it is also possible to inject refrigerant at an intermediate pressure during a single-stage compression process. This measure is only possible for a few special compressor types. Examples for such compressors are screw or scroll compressors. This paper presents a study on the possibilities of improving the performance of a pump by using refrigerant injection. Comparative analyses of different solutions (flash tank, economizer and liquid injection) are analysed. (paper)