Study On Heat Regulation Of Solar Energy-CO₂ Heat Pump And Combined Application Of Temperature Layered Water Tank

With the continuous progress of urbanization,the problem of energy shortage and environmental pollution has become increasingly prominent.According to the requirements of development strategy,the adoption of clean energy,multi-energy coordination,energy storage,multi-energy complementarity and integration is the current development trend.Both solar energy and air energy are ideal clean energy.To some extent,the application of solar hot water system and air source heat pump system alleviates the problem of energy shortage and environmental pollution.From the perspective of energy conservation and environmental protection,this paper conducts experimental research of the combined application of solar energy,CO₂ air source heat pump and temperature stratified water tank,aiming at improving the thermal performance of hot water system and thus improving the utilization rate of solar energy and air energy.Based on this,this paper first explored the influence of daily solar radiation and the initial temperature of the heat-collecting system on the thermal performance of the solar hot water system through experimental research,and explored the influence of the set outlet temperature of the heat pump,the inlet temperature of gas cooler on the thermal performance of the CO₂ air source heat pump system,and summarized the change rule of the system performance with the above parameters;Secondly it introduces the concept of temperature stratified water tank,through the numerical simulation to study the coil temperature stratification under the circumstance of different high to diameter ratio and presence of hot coil;Finally,the combined application of solar energy and CO₂ air source heat pump with different structure heat storage tank is studied through experiments.When the three were combined,the influence of the heat storage tanks of different structures on the thermal performance of the solar energy and CO₂ air source heat pump hot water system was compared and analyzed.Within the scope of this paper,the following conclusions are drawn:?1?The experimental results of solar hot water system show that:When the solar radiation on that day increased from 5.13 MJ/m² to 21.15 MJ/m²,the daily useful heat was increased from 12.14 MJ to 44.18MJ,which is increased by 263.92%,the heat collecting efficiency decreases from 0.48 to 0.43,and reduced by 10.42%.When the initial temperature of the water tank of the heat collecting system increases from 10.34?to29.88?,the daily useful heat is reduced from 43.69MJ to 35.16MJ,which is reduced by19.52%,the heat collecting efficiency decreases from 0.45 to 0.37,and reduced by 17.77%.It can be seen that the daily solar irradiation is closely related to the daily heat gain of the heat collecting system,but has little influence on the heat collecting efficiency of the heat collecting system.The lower the initial temperature of the water tank in the heat collecting system is,the higher the daily heat gain and heat collecting efficiency of the heat collecting system will be.?2?Experimental study on CO₂ air source heat pump system shows that:When the set outlet temperature of the heat pump increases from 45?to 85?,system heating increases from 3.81KW to 4.09KW,which is increased by 7.35%,system COP decreases from 4.43to 2.88,and reduced by 34.99%.When the inlet temperature of gas cooler increases from13.9?to 41.5?,the heat production decreases from 4.62KW to 3.43KW,which is reduced by 25.76%,the COP of the system decreases from 4.49 to 2.95,and reduced by34.30%.The influence between the system COP and the variable parameters is greater than that between the system heat production and the variable parameters.?3?By ansys fluent to simulate temperature stratified water tank of different structure,the results show that when the ratio of height to diameter of water tank is 1,2 and 3respectively,at the same time,with the increase of the ratio of height to diameter,the temperature stratification inside the water tank will be more obvious,and the temperature difference between the upper and lower parts of the water tank will be larger,so the average temperature of the water in the tank is going to be lower,and the average temperature rise of the water in the tank will be slower;When the water tank with hot coil is compared with the water tank with the height to diameter ratio of 3,the temperature stratification inside the water tank is relatively obvious at the same time due to the change of heating mode of the water tank.However,the average temperature of the water inside the water tank will be lower,so the average temperature rise rate of the water inside the water tank will be slower.When the height to diameter ratio of the water tank increases from 1 to 3,average temperature at the upper end of the central axis of the water tank is basically the same.But the temperature rise rate of the average temperature at the water tank outlet decreases accordingly.At the same time,the larger the height to diameter ratio is,the lower the average temperature of the outlet of the tank will be;When the water tank with hot coil is compared with the water tank with the height to diameter ratio of 3,due to the change of the heating mode of water tank,the tank top average temperature of the temperature rise rate and the center of a water tank temperature rise rate are both less than the average temperature at the outlet of the water tank which height to diameter ratio is 3,at the same time,the outlet average temperature of water tank with hot coil is lower than the water tank which height to diameter ratio is 3.?4?Experimental study on the combined application of different structure heat storage tank,solar energy and CO₂ air source heat pump shows that:when the water tank combined with solar energy and CO₂ air source heat pump which height to diameter ratio is 3 and has the hot coil inside,the supply temperature of the water tank is about 3 degrees lower than the water tank combined with solar energy and CO₂ air source heat pump which height to diameter ratio is 1and do not has hot coil inside,however,it reduces the inlet temperature of the solar collector by about 7 degrees,increases the heat gain of the system by about 900W,increases the heat collection efficiency of the system by about 48.6%,and reduces the inlet temperature of gas cooler by about 4 degrees,increases the heat production of the system by about 700W,and increases the COP of the system by about 15.1%.Therefore,when use the water tank with hot coil inside which height to diameter ratio is 3 and combined with solar energy and CO₂ air source heat pump,the improvement of the heat collecting efficiency of the solar energy collection system is greater than that of COP of the CO₂ air source heat pump system.At the same time,when running under the same conditions,the water tank with hot coil inside which height to diameter ratio is 3 and combined with solar energy and CO₂ air source heat pump make the temperature of the tank supply water slightly decreased,however,it can obviously improve the thermal performance of the two systems,and thus improve the thermal performance of the solar-CO₂ air source heat pump hot water system.