Heat Economic Analysis Of Flat-Plate Solar Collector With Double-Functions

In order to effectively promote the utilization of solar energy resources and strengthen the application of flat-plate solar collectors in Lanzhou,a flat-plate solar collector with double-functions is designed and the experiment and simulation are carried out in this paper.Considering the energy consumption of fan and water pump in the system,an evaluation method of thermal economy is proposed.Based on this method,the optimal air mass flow rate and water mass flow rate of the system can be analyzed.This study will make some contributions to the popularization and application of such solar collectors.Build the experimental platform and install the measuring apparatus.The heat collecting experiments are respectively carried out in air heating mode and water heating mode.Some data about environment and collector performance are collected.According to the analysis of experimental data,the average heat collection efficiency is 52.3%,and the maximum of that is62.7%in air heating mode.The average heat collection efficiency is 40.2%and the maximum of that is 65.2%in water heating mode.Calculating and analyzing the total heat loss coefficient,it is found that the variation range of the heat loss coefficient is large and the collector system have more heat loss.Analysis shows that the main causes of the heat loss are poor sealing of collector,the few glass cover layers and the long water flow path.Based on the physical prototype of the collector,the three-dimensional model and the numerical model are established.Select the solar irradiation intensity,inlet temperature measured from the experiment as the input conditions of the numerical model.Use Fluent 15.0to calculate the numerical model and output the simulation results.The numerical results can verify the correctness of the numerical model by comparing it with the experimental results.The results show that the maximum relative error of air outlet temperature at different time is7.6%and the average relative error of heat collection efficiency is only 2.6%in the air heating mode.The maximum relative error of water outlet temperature is only 0.3%while the average relative error of collector efficiency is 7.2%in water heating mode.The output data of the numerical model are in good agreement with the experimental data,so the simulation data is credible.The heat productivity of collector is simulated under different air mass flow rates or water mass flow rates.The outlet temperature,collector efficiency and the difference of heat productivity were analyzed.The recommended air and water mass flow rates were 0.06 kg·s^-1and 0.12 kg·s^-1,respectively.The energy consumption of fan and water pump under different flow rates is theoretically analyzed by the analogy principle of fluid mechanical.According to the law of conservation of energy,the heat productivity equation of the collector system considering the energy consumption of fan and water pump is established.The maximum productivity of the air collector system is 665.8W,and the maximum productivity of the water collector system is 669.14W.Considering the influence of energy grade,the relative coefficient of energy grade is defined which can get a deeper analysis about heat productivity and electricity consumption.The mass flow rates range that satisfies the optimal heat productivity of the system is obtained by analysis.The air mass flow rates is[0.016 kg·s^-1 to 0.019 kg·s^-1],and the water mass flow rates is[0.074 kg·s^-1 to 0.09 kg·s^-1].Finally,in order to analyze the application value of the collector system in the actual scene,the economic analysis of the collector system was carried out by selecting the winter residential heating and electricity prices of Qingdao,Lanzhou,Yinchuan and Urumqi in 2018.The results show that the application value of the collector strongly depends on local heat prices and electricity prices,so this type of collector are more adaptable to the application scene with high heat price and low electricity price.The output-input ratio can reach 10 only analyzing the heat productivity and power consumption,so the collector has a high development potential.