CO2 heat pump for domestic hot water

This paper describes the development of a CO2 air/water heat pump, designed to meet the tap hot water requirement of a residential building located in the northern part of Italy. The basic design consists of a single-stage piston compressor, a coaxial type gas cooler, an electronic expansion valve, a finned tube evaporator and a low pressure receiver. The heat pump is combined with a storage tank designed to maintain internal water stratification . A new control method for the upper cycle pressure was developed to maximise the COP of the heat pump, while the water mass flow is adjusted to maintain the set water temperature at the gas cooler exit. Before commissioning, the heat pump was factory tested to verify its energy performance and to validate the high pressure control logic.