Developing a combined compressor expander heat pump-experimental evaluation of the compressor and expander

This study outlines the integration of a new rotary compressor-expander combined unit within a water-to-water heat pump to achieve higher coefficient of performance (COP) and heating capacity. This is particularly true when the heat pump operates as a retrofit unit operating at higher temperatures (>55°C) typically encountered in standard UK heating systems. In a refrigeration cycle, the expansion process is performed as an isenthalpic process which typically causes the refrigerant to enter the evaporator with approximate quality of 25% or more and this refrigerant is therefore unavailable for heat transfer in the evaporator. In this research, the aim is to improve the isentropic efficiency of expansion process by applying a rotary expander compressor which has an integrated turbine. A higher isentropic efficiency in expansion process leads to higher heating capacity by absorbing more heat in evaporator. Also the turbine can supply between 5-15% of compressor input power from the expansion process, so a higher COP will be achievable.