Abstract
In this paper, energy performance of a loop-heat-pipe (LHP) type solar photovoltaic/thermal (PV/T) heat pump water heating system is studied to evaluate its feasibility in three different climatic regions. A mathematic model of this system in our former study is built and validated using outdoor test data. On the basis of this model, influences of main structural design parameters including the installation angle and the orientation of the PV/T collector/evaporator are discussed and main parameters are optimized to further improve system operation performance. Based on optimal design parameters, economic feasibility of the proposed system under different weather conditions is analyzed using the life cycle cost (LCC) method. The system is integrated with solar PV/T, loop heat pipe and solar assisted air source heat pump technologies. This combined approach is benefit for improving solar energy comprehensive application efficiency of conventional solar PV/T systems. Moreover, it enlarges the application region of traditional air source heat pump water heating systems. Depending on different solar radiation conditions, this system can operate in different modes including solar photovoltaic LHP mode, solar assisted air source heat pump mode and the only air source heat pump mode. In this study, Beijing, Shanghai and Guangzhou were selected as typical representative cities in cold area, hot summer and cold winter area, hot summer and warm winter area. Typical meteorological year (TMY) data of three cities were extracted from TRNSYS. Based on TMY data, annual operation performance of the proposed system is calculated through the validated dynamic mathematic model. Firstly, PV/T collector/evaporators of three systems are all fixed in the south direction and the same installation angle (35°) was chosen. In this case, annual net power consumptions and solar heating fractions of three systems are calculated and compared. Then installation angles and orientations are optimized to ensure maximum solar energy application. The investigation results show that, among three cities, the solar heating fraction in Guangzhou is the largest. And the least electricity is consumed in Guangzhou, which is decreased by 43.9% and 44.7% respectively compared with those in Beijing and Shanghai. The comprehensive photothermal efficiency in Guangzhou is 8.19%, 5.58% higher than those in Beijing and Shanghai. Therefore, from the view of solar energy comprehensive efficient utilization, the application of the system is most proposed in Guangzhou, and then followed by Shanghai and Beijing. Considering impacts of installation angles and orientations, the ideal installation inclination of the system in Beijing, Shanghai and Guangzhou are 35°, 25°, and 35°, and the optimal installation directions of Beijing and Shanghai are facing the south, while that of Guangzhou is 30°east to the south. With the optimal parameters, it is found that solar heating fractions in Beijing and Guangzhou (i.e. 57.42% and 58.45%) are slightly higher than that in Shanghai. It is concluded that influences of two structural parameters are different for such system in different climatic areas. To ensure maximal solar energy application, it was necessary to optimize these two parameters. For the life cycle cost analysis, a traditional air source heat pump hot water heating system is chosen as the base system. The analysis results indicate that the initial investment of the system increases significantly, which is 2.5 times of that of the base system. However, the annual power consumption of the system is about half of that of the traditional system. Besides, solar power supply fractions in Beijing, Shanghai and Guangzhou are 53%, 51% and 66% respectively. As a result, the total operation and maintenance fees in the life cycle drop significantly, which are reduced by 67.86%, 59.00%, and 62.21% in Beijing, Shanghai and Guangzhou. The life cycle cost is correspondingly reduced by 58.75%, 49.83% and 53.09% in three cities. In conclusion, the application of this system is feasible for considered weather conditions in terms of both the operating performance and economic benefits.
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