CO₂ Heat pump system for combined heating and cooling of non-residential buildings

CO₂ heat pumps installed in non-residential buildings will achieve a high COP as long as the heat is rejected over a large temperature range and the return temperature in the heat distribution system is relatively low. In European non-residential buildings high-temperature radiators are commonly used to cover the space heating demand, and a CO₂ heat pump rejecting heat to only radiators will achieve a low COP due to the high return temperature. However, in many non-residential buildings the demand for heating of ventilation air after the heat recovery unit constitutes a relatively large share of the total heating demand of the building. Consequently, by making a serial connection of the radiator system and the ventilation heater batteries it is possible to obtain a relatively low return temperature and with that favourable operating conditions for a CO₂ heat pump. Preheating and reheating of hot water will lead to a further increase in the COP for CO₂ the heat pump system. Computer simulations have demonstrated that a CO₂ heat pump system in non-residential buildings can achieve the same or higher seasonal performance factor (SPF) than heat pumps using conventional working fluids as long as the heat distribution system is designed for a low return temperature. The operational time of the ventilation system will have a major impact on the SPF of the CO₂ heat pump, since the return temperature in the heat distribution system is considerably lower when the ventilation system is switched on. The construction of a prototype CO₂ heat pump system for heating and cooling of a Norwegian non-residential building is now being planned. The nominal heating capacity of the CO₂ heat pump will be in about 150 kW, and it will be designed as a single-stage unit using an inverter controlled reciprocating compressor