INTEGRATED CO2 HEAT PUMP SYSTEMS FOR SPACE HEATING AND HOT WATER HEATING IN LOW-ENERGY HOUSES AND PASSIVE HOUSES

Low-energy and passive houses are superinsulated and air-tight buildings where the space heating demand is considerably lower than that of buildings constructed in accordance with common buildings codes. Due to the low space heating demand, the annual heating demand for domestic hot water (DHW) typically consti-tutes 50 to 85 % of the total annual heating demand in the residence. A heat pump system can be used to cover the heating demands in low-energy houses and passive houses. The heat pump system can be designed as stand-alone systems, i.e. a heat pump water heater (HPWH) in combination with separate units for space heating, or be an integrated unit for combined space heating and hot water heating (IHPS). Due to compact design, the latter system is most likely to achieve the lowest investment and installation costs and with that the best profitability. Integrated residential heat pump systems using carbon dioxide (CO2, R744) as a working fluid can achieve high Coefficient of Performance (COP) due to the unique characteristics of the transcritical cycle with heat rejection in a gas cooler at a gliding CO2 temperature. Integrated CO2 heat pumps for space heating and hot water heating can be designed to utilize different heat sources such as bedrock, ground, exhaust ventilation air, ambient air or a combination of exhaust ventilation air and ambient air.