A carbon dioxide domestic hot water heat pump with double wall plate heat exchanger gas cooler

A CO2 water-to-water heat pump for domestic hot water was built. The basic design includes a back pressure valve and a low pressure receiver; plate heat exchangers were adopted both as evaporator and gas cooler. The peculiarity of the heat pump lies in the use of a double wall plate heat exchanger as the gas cooler, which creates a failure-proof barrier between the domestic water and the refrigerant. The heat pump is to be coupled with a stratification tank and a variable speed pump which forces the cold water from the stratification tank to the gas cooler. The expansion valve and the variable speed pump are controlled by an original logic which optimises the high pressure value to meet the best COP, while maintaining the water temperature at the required level. The heat pump was laboratory tested and performances were recorded at different delivery temperatures of the tap water.