Proposal and performance evaluation of a solar hybrid heat pump with integrated air-source compression cycle

The solar-assisted air-source heat pump utilizes solar energy as heat source to achieve better thermodynamic performance than the air-source heat pump for space heating or hot water production, but it is difficult for the solar-assisted air-source heat pump to absorb solar energy and air thermal energy simultaneously owing to the absence of independent evaporating pressure in dual-source evaporators, so its performance improvement is very limited in comparison with the air-source heat pump. Based on the concept of temperature level matching energy grade, a solar hybrid heat pump with integrated air-source compression cycle is proposed in this paper. In the novel system, two in-parallel compressors coupled with two three-fluid heat exchangers are applied to form dual-source parallel-compression heat pump cycle, dual-source cascade heat pump cycle and air-source cascade heat pump cycle, so as to boost the contribution of low-grade energy to heating capacity. In order to assess the thermodynamic performance of the proposed system and then preliminarily evaluate its regional applicability, an office building located in typical cities in China (Zhengzhou, Beijing, Shenyang and Wuhan) is taken as the case study for heating, and the novel system acts as their heating source. The hourly heating load is simulated by the Designers Simulation Toolkit software, and the thermodynamic model is developed to evaluate energy consumption of the proposed system and explores the optimal operation control strategy aiming at the maximum utilization of solar energy, and comparisons of the heating performance, economic and environmental benefits with the air-source single compression heat pump are also discussed. The results indicate that the novel system has a good potential for energy saving and economy as well as a small environmental impact, and there is an optimal temperature difference between the collector inlet water and the ambient air to achieve the lowest seasonal power consumption. The proposed system has the seasonal performance factor of 3.45–4.24 in typical cities, and its power consumption is 14.3%—16.6% lower than that of the air-source single compression heat pump.