Field Testing of an Economised Vapour Injection Heat pump

The purpose of this work was to evaluate the performance of an economised vapour injection (EVI) compressor utilised in an air source heat pump. It was to ascertain if such a unit is capable of economically heating a typical UK family home that was originally heated by a high temperature wet radiator system supplied with hot water from an oil boiler. The concerns were based around maintaining a sufficiently high seasonal coefficient of performance when utilising cold air as a heat source and delivering hot water to a heating circuit originally designed for temperatures of 60°C or more.The EVI compressor has the capability of overcoming some of the difficulties of high temperature lift operation (namely reduced capacity) by allowing liquid subcooling to maintain high evaporator capacity in order to provide adequate heating during cold ambient air periods. The laboratory tests (based on the EN14511 standard) carried out using air temperatures of -12°C to +15°C and water was delivered from 35°C to 65°C were found to have a superior performance to a compressor without EVI. The system was installed in a family home and its performance evaluated.