Energetic, exergetic and exergoeconomic assessment of transcritical CO2 reversible system combined with dedicated mechanical subcooling (DMS) for residential heating and cooling

Abstract

A transcritical CO2 reversible heat pump-air conditioning system combined with dedicated mechanical subcooling (DMS) is proposed as an annual heating and cooling solution. A common residential building is selected as a scenario to assess the system annual performance from the viewpoint of energetic, exergetic, and exergoeconomic, and compare with traditional CO2 system (BASE). The influences of terminal type, climate condition, and energy-saving potential are discussed. The results indicate the annual performance factor (APF) of CO2 system is significantly improved by up to 6.23 ~ 22.90%. APF generally increases with the latitude, and it achieves the highest value of 3.41 by using small temperature difference fan-coil unit (STD-FCU) as terminal. The annual exergy efficiency (AEE) is promoted by 7.25 ~ 24.79%, and the throttling irreversibility can be significantly reduced by adopting DMS. From the perspective of thermoeconomic, introducing DMS to CO2 system is cost effective. The total cost, including non-exergy-related investment and cost of exergy destruction, is reduced by 16.96% for heating and 4.52% for cooling. The annual exergoeconomic factor increases with the improvement of building energy-saving potential while decreases with the compressor price reduction. To widen the application of CO2 system, it is suggested that the price of CO2 compressor should be reduced, such as with the help of government subsidies. Furthermore, the thermal insulation performance of the residential building should also be improved, especially for the severe cold and cold regions.