Performance Analysis Of Solar Absorption Refrigeration System Based On PVT

Increasing the share of renewable energy in the energy structure is an effective way to solve current energy and environmental issues.Solar air conditioners are considered to have a broad prospect of applications and are receiving increasing attention.Solar photovoltaic thermal(PVT)technology is a new type of solar energy utilization technology that combines photovoltaic power generation and solar thermal utilization.Its overall energy efficiency is significantly higher than that of traditional photovoltaic cells or collectors.Therefore,PVT-based solar air conditioner is also expected to achieve higher efficiency of solar energy utilization.At present,most commercial photovoltaic cells have constrains on the operating temperature,which limits the quality of the thermal energy provided by PVT.This paper proposes a system that combines PVT collectors with two-stage lithium bromide absorption refrigeration cycle,using the low-grade thermal energy of PVT for refrigeration,to improve the cooling capacity of solar energy.This paper has conducted the following research on the system and the conclusions are drawn.A steady state model was.established on amorphous silicon PVT liquid collector with double glass covers.First the model was verified by the experimental results in the literature,and then the effects of solar radiation intensity,water mass flow rate,inlet water temperature and the series number of PVT modules on the thermal electrical performance and exergy efficiency were simulated and analyzed.The results showed that,the enhancement of the solar radiation could help to improve the thermal efficiency,but reduce the electric efficiency;the increase of water mass flow rate could help to improve the thermal efficiency and the electric efficiency,but its effect on thermal exergy efficiency and total exergy efficiency also depends on the inlet water temperature;the increase of inlet water temperature would reduce the thermal efficiency and the electric efficiency of the system,and there exists an optimum inlet water temperature that maximizes PVT total exergy efficiency;and the optimum inlet water temperature changes with the radiation intensity and the water mass flow rate;the change of the serial number of PVT modules is essentially to change the water mass flow rate per unit area of PVT,and thus its effect is similar to that of water mass flow rate.A steady state model of the two-stage lithium bromide absorption refrigeration cycle was established.The effects of heat source water inlet temperature,cooling water inlet temperature and chilled water outlet temperature on the cooling capacity,COP and exergy efficiency were simulated and analyzed.The results showed that,the increase of the temperatures of the heat source water and the chilled water,or the decrease of the cooling water temperature would enlarge the concentration difference between strong solution and weak solution,and reduce the share of heat for solution preheat in generator,leading to an increase in the cooling capacity and the COP;with the increase of the temperature of heat source water or chilled water,the exergy efficiency of refrigeration cycle first increases and then decreases;with the increase of the cooling water temperature,the exergy efficiency of refrigeration cycle decreases monotonically;the above changes in external conditions affects the proportion of exergy loss of each component and the proportion of exergy gained by the cooling water in the cycle.A solar refrigeration system based on PVT was established.The thermal energy of PVT is used to drive the two-stage lithium bromide absorption refrigeration cycle,and stratified water tank is used to link the PVT and refrigeration cycle.The steady state simulations were carried out.The effects of outlet water temperature of PVT collector on the performance of the whole system was analyzed,and the results showed that,there is an optimal outlet water temperature of PVT,which maximizes the total exergy efficiency of the system;if the electricity produced by PVT was also used for refrigeration,there is an optimum outlet water temperature of PVT which maximizes the SCOP of the system;with the conditions given in this paper,the optimum outlet water temperature of PVT is about 68 ?.The performance of the PVT solar absorption refrigeration system in a typical summer day in Fuzhou was analyzed,and the cooling area of the system was estimated based on the requirements of standard rooms;the overall cooling capacity of the system was compared with the refrigeration system driven by amorphous silicon photovoltaic cells and the single effect absorption refrigeration system driven by flat plate collector.The cooling capacity of the latter two systems is 60%and 71%of the PVT solar refrigeration system respectively,showing the great potential of PVT solar refrigeration system.