Experimental investigation on the influence of internal heat exchanger in a transcritical CO₂ heat pump water heater

In this paper, a transcritical CO₂ heat pump water heater prototype was experimentally investigated to research the influence of internal heat exchanger (IHX). In addition, the exergy analysis was carried out based on the experimental data. The results showed that the optimal discharge pressure reduced with the application of IHX, and this reduction could be amplified by the decrease of the ambient temperature, the increase of the water inlet temperature and the increase of the water outlet temperature. From the energy point of view, under the optimal discharge pressure, the coefficient of performance (COP) increased by up to 6.65% and the total power consumption decreased by up to 6.22% via using IHX. Then the influence of IHX on the heat pump cycle was discussed. The results of the exergy analysis showed that the exergy destruction of compressor, gas cooler and evaporator increased, and the exergy destruction of expansion valve decreased with the application of IHX. Furthermore, the product exergy and the total exergy destruction increased, and the exergy efficiency of system decreased in all working conditions. In conclusion, the application of IHX enhanced the energy performance and impaired the exergy efficiency in this research.