| As renewable energy,solar energy has been widely used with the shortage of fossil energy.In particular,PVT heat pump,which integrates photovoltaic-thermal(PVT)technology with heat pump technology,has greatly improved the photoelectric conversion efficiency and heat collection efficiency.However,PVT heat pump only runs for short time in summer due to the abundance of light and heat resources and less heating demand,which cause a low system utilization.In order to improve the utilization of PVT heat pump and meet the huge cooling demand of building in summer,a new method of refrigeration utilizing PVT heat pump is proposed.From the perspective of refrigeration utilizing PVT heat pump,the following research contents have been carried out focused on experimental research,theoretical model research and application performance research.Firstly,the design of experimental system and the construction of experimental platform were completed.A new method of refrigeration using PVT heat pump,which can expressed as PVT heat pump combined cooling heating and power(CCHP)system,is proposed based on the current research progress.The system uses PVT unit as the condenser of heat pump system when refrigerating,which greatly enhances the heat dissipation of PVT unit.Based on the new system schematic diagram,system components were designed and manufactured and the construction of experimental platform were completed.Secondly,the refrigeration and cold storage performance of PVT heat pump in summer was tested and analyzed.The idea of utilizing PVT heat pump for refrigeration is feasible after a large number of experimental tests and analysis.The average COP of the system for making chilled water in the summer is 2.84,while the average COP for making ice is 2.29,and the refrigeration performance in clear sky night is better than cloudy sky night.PVT heat pump can also run the refrigerating mode in some cloudy daytime and rainy days.However,the refrigeration performance during cloudy daytime is poor and severely affected by solar radiation,so the system operation parameters is unstable.And the refrigeration performance of the system is significantly improved in rainy days.Thirdly,the theoretical model of PVT heat pump in refrigerating mode was established.Based on the experimental results,the steady-state model of the system was established,and a radiation heat transfer model for PVT unit was established especially.The accuracy of heat transfer model and system model was verified by experimental test results.Finally,analysis of influencing factors of refrigeration performance and application performance was performed based on the theoretical model.The influencing factors of system performance were studied.The results show that the system has better refrigeration performance in the environment with lower ambient temperature and higher wind speed.Increasing the number of PVT unit can improve refrigeration performance,while the unit installation angle has little impact on performance.The refrigeration performance during an entire cooling season in Dalian City was simulated.The results show that the refrigeration performance of system still has much improvement space under ideal heat exchange conditions.The concept of available hours for refrigeration was proposed.By comparing and analyzing the available hours and the cumulative refrigeration capacity in typical cities,it was found that utilizing PVT heat pump for refrigeration is more suitable in central regions.And using PVT heat pump to meet all cooling need of buildings is feasible from the perspective of cumulative refrigeration capacity. |
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