When it comes to providing hot water, heat pumps (HP) have long been recognized as a proficient substitute to conventional machines. The temperature change in the water used in this investigation (from 25°C to 50°C). Transcritical carbon dioxide HPs, on the one hand, are regarded to be one of the best solutions; however, the performance of a transcritical CO2 heat pump is strongly reliant on the temperature of the water inflow. Furthermore, performance is greatly dependent on the rejection pressure, which must be carefully managed in order to operate at its best in every circumstance. Sub cooling, on the other hand, appears to be crucial for HP performance while employed at large temperature rises in subcritical systems. As a result, systematic research of sub cooling that optimises COP should be required for the subcritical cycle. The purpose of this research is to evaluate the working and sub cooling functions of an air-to-water HP for hot water (HW) production when using heat recovery from an air source.