# Simulation of Hybrid Photovoltaic Solar Assisted Loop Heat Pipe/Heat Pump System
## 5 Conclusions  
1. During the heating of 150 L of water from 15 \({}^{\circ}\)C to 50 \({}^{\circ}\)C under typical sunny days in spring or autumn, the overall photovoltaic/thermal efficiency of hybrid LHP/HP mode was 0.496 and 33.7% lower than that of the independent HP mode, while the power consumed in the heating process of hybrid LHP/HP mode was 0.853 kW.h, saving 40.6% of compressor power than independent HP mode. It can be seen that the LHP/HP mode should have top-priority to be utilized in spring or autumn with abundant solar radiation. While in winter, it was difficult to operate LHP mode persistently because of short sunshine duration and lower solar irradiation, therefore the independent HP mode is the best choice for winter.
2. Solar irradiation and ambient air temperature were the two main external factors influencing the operating performances of the hybrid LHP/HP mode. With an increase in solar irradiation and ambient temperature, the temperature of working medium in the PV/T evaporator was  
Figure 11: Monthly mean overall efficiency and switching water temperature for HP mode and LHP/HP mode.  
Figure 10: Monthly mean electricity consumption for HP mode and LHP/HP mode.  
much higher than that in the condenser, so LHP mode could be utilized for a longer heating time. Therefore, the water temperature when switching LHP mode to HP mode was higher, so HP mode was utilized for a shorter heating time, resulting in less compressor power.
3. When using HP mode, the monthly mean photovoltaic/thermal efficiency varied from 0.697 to 0.776, which was higher in comparison to the LHP/HP mode, while the monthly mean power consumption of LHP/HP mode was apparently 13.9% less than that of HP mode. From March to November, hybrid LHP/HP mode should be prioritized to save energy. This hybrid mode could rely on LHP mode alone to make hot water without any power consumption especially in July and August.  
The research has been supported by the National Science & Technology Pillar Program of China during the Twelfth Five-year Plan Period (Projects 2014 BAJ01B05) and the Industry-Academy-Research Forward-Looking Program of Jiangsu province (Projects BY2015070-14).  
[PERSON], [PERSON], [PERSON], and [PERSON] conceived and designed the main analysis; [PERSON] performed the numerical simulations and wrote the paper.  
The authors declare no conflict of interest.  
\begin{tabular}{l l} \(A\) & area, m\({}^{2}\) \\ \(C_{p,2v}\) & specific heat of water, J/(kg\(\cdot\)K) \\ \(d\) & diameter of evaporator tube, m \\ \(E_{s}\) & solar irradiation, W/m\({}^{2}\) \\ \(h\) & heat transfer coefficient, W/(m\({}^{2}\cdot\)K) \\ \(lr\) & refrigerant enthalpy, J/kg \\ \(k_{m}\) & thermal conductivity of condensing tube, W/(m\(\cdot\)k) \\ \(m_{r}\) & mass flow rate, kg/s \\ \(M_{uv}\) & total mass of water, kg \\ \(N_{com}\) & power consumption of compressor, W \\ \(P_{pv}\) & power output of PV cells, W \\ \(Pr\) & Planck number \\ \(q_{w}\) & unit refrigerating capacity, J/kg \\ \(Q\) & heat energy, W \\ \(Q_{solar}\) & monthly total global solar radiation, MJ/m\({}^{2}\) \\ \(r\) & rotational speed of compressor, r/min \\ \(R\) & contact heat transfer resistance, (m\({}^{2}\cdot\)K)/W \\ \(Re\) & Reynolds number \\ \(t\) & time, s \\ \(t\)/\(T\) & temperature, \({}^{\circ}\)C/K \\ \(u_{w}\) & wind velocity, m/s \\ \(U_{L}\) & total heat loss coefficient between PV cells and environment, W/(m\({}^{2}\cdot\)K) \\ \(v\) & specific volume, m\({}^{3}\)/kg \\ \(V_{h}\) & theoretic displacement of compressor, m\({}^{3}\)/h \\ \(w_{p}\) & unit theoretic work of compressor, J/kg \\ \(Xtt\) & Martinelli number \\ \end{tabular}