Performance assessment of an off-the-shelf R744 heat pump equipped with an ejector

This paper presents the experimental analysis of a prototype R744 water/water heat pump (5 kW heating power at 0°C evaporation temperature, 100 bar gas cooler pressure, 35°C gas cooler outlet temperature) which was equipped with a two-phase ejector. According to the traditional lay-out, the energy that was recovered from the expansion process inside the ejector improved the circulation of refrigerant through the evaporator. The same heat pump was also provided with a back-pressure valve as the expansion device, i.e. a direct comparison of the performance was possible between the heat pump systems, either equipped with the ejector or the expansion valve. Tests were performed to evaluate the performance when the heat pump produced hot tap water, i.e. heating water from the main waterworks temperature to storage temperature (~60°C). Additionally, an investigation took place to understand how the system performed when space heating was required, i.e. providing hot water with a limited temperature lift, however at relatively high inlet temperatures. Experiments demonstrated that the ejector is helpful to improve the heat pump performance, thus promoting the diffusion of R744 units also for domestic space heating and air conditioning. Technological issues related to lubricant recovery were faced.