Performance Evaluation And Optimization Research Of Photovoltaic-thermal Combined Cooling,Heating And Power System

The environmental pollution and resource shortage caused by the utilization of fossil fuels are the main factors that constrain China’s sustainable development of economic,social,and environmental.Distributed solar energy system is one of the feasible methods to solve the problem.However,the randomness and volatility characteristics of solar energy bring challenges to the efficient,stable operation and real-time response of distributed energy system.Therefore,based on the energy demand of buildings,this study conducted the research on performance and optimization research of photovoltaic-thermal combined cooling/heating/power system to study the impact of building load characteristic on system performance and provide support for the design and application of distributed solar energy systems.First,the building model of student dormitory in Tianjin is established,and the structure,envelope parameters,internal disturbances and energy supply strategy are set,and simulation is performed in TRNBuild to obtain the load characteristics of dormitory.Secondly,the photovoltaic-thermal combined cooling/heating/power system consisting of photovoltaic-thermal(PV/T),low-temperature water source heat pump,high-temperature water source heat pump,bromide-lithium absorption chiller and heat storage water tank is proposed.Based on TRNS YS platform,the system analysis model and its performance evaluation indicators are studied.The performance is analyzed by energy,exergy,and economic.The results shows that the average energy efficiency is 32.70%,the exergy efficiency is 17.97%,the investment payback period is 6.66 years,unit product energy profit is 78.0 CNY/MWh,and unit product exergy cost is 119.27 CNY/MWh.In addition,solar radiation,PV/T area,and low-temperature water source heat pump rated capacity are selected for sensitivity analysis to study the impact on system operating performance.The results show that the increase of solar radiation intensity is beneficial to improving the heat pump COP,but it will lead to a decrease in heat pump exergy efficiency.The increase of PV/T area can promote the economic performance of system,but it is necessary to consider the limitations of building roof area on PV/T installed area in practical application.Moreover,the impact of rated capacity of low-temperature heat pump is relatively small compared to that of PV/T area.When the capacity reaches 60 kW,further increase of rated capacity have a slight downward trend in the payback period.Finally,the exergy efficiency and payback period of system are adopted as the objective functions,and PV/T area,rated capacity of low-temperature water source heat pump and direct heating set temperature are adopted as the decision variables for multiobjective optimization,and an beat operation point is selected from the Pareto frontier solution.In best operation condition,the PV/T area is 268 m2,the rated heat capacity of the low-temperature water source heat pump is 17 kW,the storage tank volume is 50 m3,and the direct heating set temperature is 47.9℃.The payback period is 6.83 years,and the system exergy efficiency is 19.90%.A comparative analysis with related studies revealed that the system exergy efficiency and payback period have further improvement.