Energy and exergy analysis of a new direct-expansion solar assisted vapor injection heat pump cycle with subcooler for water heater

A new direct-expansion solar assisted vapor injection heat pump cycle with subcooler for water heater is proposed in this paper which aims to improve the performance of traditional subcooler vapor injection heat pump cycle by utilizing the solar energy. The new cycle has two working modes (SVIC mode and DX-SVIC mode) to be switched according to the solar radiation intensity. The performance enhancement potential of the new cycle is investigated by comparing with the traditional cycle through theoretical method. Under the considered conditions, the new cycle yields an average of 14.6% and 42.9% improvement in the heating coefficient of performance and heating capacity aspects compared with the traditional cycle, respectively. Both the new cycle and the traditional cycle have optimum injection pressures to obtain the maximum heating coefficient of performance. The simulation results indicate that the DX-SVIC mode outperforms the SVIC mode on most solar radiation condition, while the latter one is suitable for the extremely low and no solar radiation condition. The energy performance and heat exergy of the new cycle are improved with enhancing the solar radiation, while the variation of exergy efficiency shows contrary tendency. As increasing the injection pressure, the exergy input decreases more rapidly than the heat exergy, and thus the exergy efficiency is improved. The increase of the solar collector area always leads to the energy performance improvement of the new cycle.