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Direct-expansion solar assisted heat pump (DX-SAHP) is a promising technology for saving energy. In this paper, vapor injection (VI) cycle system to DX-SAHP system is studied. Thermodynamic comparative analyses of ideal VI cycle and ideal conventional vapor compression cycle was carried out for verifying the advantages by applying VI cycle into DX-SAHP. Additionally, photovoltaic/thermal (PVT) modules were used in the system to harvest thermal energy and electric power. A PVT based solar heat pump system employing VI cycle (PVT-VISHP) was proposed, fabricated and investigated experimentally. Performance of the experimental prototype was subsequently evaluated for seven days in winter. The system’s performance was evaluated based on the average ambient temperature of −1.13 °C and solar irradiation of 164.03 W/m2. Results showed that the total generated electricity, heat, and consumed power of the system were 0.51 kWh, 23.68 kWh, and 7.24 kWh, respectively. Moreover, average heating coefficient of performance (COPth) and advanced coefficient of performance (COPPVT) of the PVT-VISHP system were 3.27 and 3.45, respectively. In the study, the ambient-evaporating temperature difference ranged from 9.2 °C to 17.1 °C. Furthermore, variations of injected vapor’s pressure, mass flow rate, mass flow rate ratio, and subcooling effects were analyzed in detail. Performance of the PVT modules during a sunny day was tested. It was found that the PVT modules’ average thermal collecting and PV efficiencies were 49.9% and 7.51%, respectively.

Photovoltaic thermal (PVT) heat pump technology refers to the integration of photovoltaic and solar heat pump, representing the deep exploitation and utilization of solar energy. In this paper, roll-bond-PVT heat pump (RB-PVTHP) system with single stage compression is proposed and investigated experimentally. The roll-bond-PVT (RB-PVT) unit is introduced in detail which is combined with the photovoltaic module and single-sided roll-bond evaporation heat exchanger laminating together. The designed experimental system consists of 4 pieces of RB-PVT units, 1 HP heat pump unit and 150 L heat storage tank, which is also equipped with various monitoring sensors to explore the system operating characteristics. Then the performance evaluation method of the unit and system is proposed. The experimental investigation on the cogeneration performance of the system in northern China during summer is carried out simultaneously, in terms of the thermal efficiency, electrical efficiency, thermal-based overall efficiency of the unit and heating COP of the system. The operating characteristics monitoring results show that the system works in a long-term stable condition during the daytime with considerable cogeneration performance. The detailed performance parameters have been given in this paper. This study demonstrates that the RB-PVTHP system has the large-scale practically feasible application value in northern China.

This paper describes the development of a new type hybrid photovoltaic/thermal (PVT) solar collector. The test setup of the photovoltaic/thermal performance of the PVT solar collector filled with graphite was established to compare the conventional PV module and the PVT solar collector filled with graphite. The output power, backplane temperature, the inlet temperature, the outlet temperature and the tank temperature were tested in this study. The photovoltaic/thermal performance of the PVT solar collector filled with graphite was evaluated by the thermal efficiency, electrical efficiency and primary energy saving efficiency. The results show that the electrical efficiency of the PVT collector can be enhanced by cooling down to the backplane temperature. Lower inlet temperatures result in higher thermal efficiency. The inlet temperature increased with increased tank temperature. As the inlet temperature increased to some point, the outlet temperature gradually stabilized. The mean value of electrical efficiency of a PVT collector filled with graphite and conventional PV module were 6.46% and 5.15% between 8:00 a.m. and 4:00 p.m. The highest electrical efficiency of a PVT collector filled with graphite was 7.2%. The highest Primary Energy Saving efficiency of PVT collector filled with graphite was 48% at 10:35.

A gas–liquid separated solar collector system was developed. The operating temperatures are in the range between 100 and 150 °C. The boiling collector can be used for process heat supply in the industry and for solar cooling applications as well. This gas–liquid separated solar collector system can use flat-plate solar collector and heat pipe solar collector to generate mid-temperature steam. This system can reduce the usage of the heat pipe solar collector and heat the working medium to the saturated liquid by the flat-plate solar collector, which can reduce the cost of the system. R245fa, also known as 1,1,1,3,3-pentafluoropropane, was used as the high temperature working medium in this system. The simulation results show that this system can work normally. When the mass flow of working fluid was reduced by half of general condition, the collection time was cut by 25%. In contrast, when the mass flow of working fluid was kept the same and the collector area was doubled, the operation time was cut by 35%.

The heat transfer efficiency of solar collector tubes is a crucial factor for the application of solar heating and cooling systems (SHCS). How to enhance solar collector efficiency has become a hot topic. In this paper, a new type of collector tube – filled-type evacuated tube with U-tube (UFET), was presented to increase solar collector efficiency by eliminating the thermal resistance between the absorber tube and the copper fin of the conventional evacuated solar collector. First, a UFET heat transfer model was built with different U-tube structures and the universal UFET model in uniform boundary condition. Furthermore, the thermal performances of three types of UFET were compared theoretically and experimentally. The results show that the maximum solar collector efficiency of UFET with three U-tubes reaches 0.82 and is higher than other types with the same heat transfer surface area. In addition, the theoretical result is 4% higher than the experimental result, indicating that the developed model is validated by the experimental investigation in this study.