# Simulation of Hybrid Photovoltaic Solar Assisted Loop Heat Pipe/Heat Pump System
## 4 Simulation Results and Discussion
### Simulated All-Year Round Operating Performances of the PV-SALHP/HP System  
Nanjing has a typical summer-hot and winter-cold climate, requiring domestic hot water services all-year round. For different months, mean outdoor air temperature and mean total global solar radiation can range considerably. In order to study the all-year round performance of the system, monthly simulation was studied in this section. As shown in Table 4, the monthly mean outdoor air temperature, \(t_{a}\), can be as high as 28.6 \({}^{\circ}\)C in summer and as low as 2.2 \({}^{\circ}\)C in winter; the monthly mean total global solar radiation, \(Q_{solar}\), ranges from 229.0 MJ/m\({}^{2}\) (in December) to 485.0 MJ/m\({}^{2}\) (in August). In Nanjing, the yearly total sunshine duration exceeds 2000 h [11]. Using the meteorological data of Nanjing and the mathematical model developed above, the all-year round performances of PV-SALHP/HP system operating in independent HP mode and hybrid LHP/HP mode are reported in this section.  
Assuming that the system was operated at the monthly mean outdoor air temperature and the monthly mean solar irradiation on sunny days. Figures 10 and 11 show the simulated monthly operating performances of the PV-SALHP/HP system when generating electricity and heating 150 L of water from 15 \({}^{\circ}\)C to 50 \({}^{\circ}\)C. As shown in Figure 10, from March to November, using independent HP mode consumed the highest energy consumption of 1.65 kW-h in November and the least energy consumption of 1.11 kW-h in July and August. While using hybrid LHP/HP mode, the highest energy consumption was 1.42 kW-h in November, 13.9% lower than that of HP mode. During July and August, LHP/HP mode could rely on LHP mode alone without any power consumption when heating water up to the targeted temperature. From Figure 11, the switching water temperature is the highest in July and August. The varied tendency of monthly mean photovoltaic/thermal efficiency when using independent HP mode was similar to the varied tendency of monthly mean solar irradiation. The monthly photovoltaic/thermal efficiency of HP mode varied from 0.697 to 0.776, higher than that of the LHP/HP mode.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline
**Month** & **Jan.** & **Feb.** & **Max.** & **Apr.** & **May** & **June** & **July** & **Aug.** & **Sep.** & **Oct.** & **Nov.** & **Dec.** \\ \hline \(Q_{solar}\) (M/m\({}^{2}\)) & 232.4 & 222.0 & 387.6 & 405.3 & 465.6 & 480.3 & 484.3 & 485.0 & 381.8 & 318.8 & 261.3 & 229.0 \\ \(t_{a}\) (\({}^{\circ}\)C) & 2.2 & 4.5 & 8.9 & 15.7 & 20.6 & 24.8 & 28.6 & 27.7 & 23.5 & 16.9 & 10.5 & 4.9 \\ \hline \end{tabular}
\end{table}
Table 4: The simulated all-year-round operating characteristics of the system [26].  
Figure 9: Variations of compressor work and COP with weather conditions for LHP/HP mode.  
Through the above analysis and comparison, it was shown that on sunny days during March to November, hybrid LHP/HP mode should be prioritized as much as possible to save power consumption effectively. Especially in July and August, such a hybrid mode could rely on LHP mode alone to make hot water without any power consumption.