Energy, exergy and exergoeconomic evaluation of the air source transcritical CO2 heat pump with internal heat exchanger for space heating

Abstract

• The system performance of CO 2 heat pump with internal heat exchanger is compared. • The system performance is evaluated with energy, exergy and exergoeconomic analysis. • The COP and exergy efficiency is significantly enhanced with the proposed system. • The cost per unit of exergy production is obviously reduced with the proposed system. • The internal heat exchanger effectiveness and sensitivity analysis are conducted. Currently, the air source heat pump is widely used for space heating. Although the CO 2 has great potential in the refrigeration system, the basic transcritical CO 2 heat pump performance is restricted by the huge throttling irreversibility caused by the higher gas cooler outlet temperature. The internal heat exchanger has been investigated extensively from the energetic perspective. However, little information is available about the exergy analysis, let alone the exergoeconomic analysis. In this paper, the transcritical CO 2 heat pump with/without the internal heat exchanger is studied with the energy, exergy, and exergoeconomic analysis. Results show that the optimal coefficient of performance can be increased to 2.96 and 2.17 in the different heating terminals. The enlarged internal heat exchanger effectiveness is also beneficial to reduce the optimal discharge pressure and increased the system coefficient of performance. The throttling valve irreversibility is decreased from 0.067 to 0.145 kW·kW −1 to 0.040–0.071 kW·kW −1 . With total irreversibility decrement, the exergy efficiency can be effectively improved, resulting in the 55.65%-73.42% reduction of the throttle valve cost rate. Considering the CO 2 compressor investment, its total exergy cost rate increment is reached up to 34.06%-50.21%, leading to the higher exergoeconomic factor. However, the sensitivity analysis results show that the cost per unit of exergy production is more sensitive to the electricity price. Moreover, the optimal cost per unit of exergy production reduction is declined by 58.71% with the return water temperature of 30 °C.