| Solar energy and air energy are both clean energy sources.Improving the utilization of these two energy sources is of great significance to improve the utilization rate of clean energy in China.However,due to the intermittent and instability of solar energy,it is necessary to equip it with stable auxiliary heat sources to ensure the reliability of energy supply.Air source heat pump(ASHP)is a widely used energy supply equipment in recent two years,but it has the problems of heat attenuation and high discharge temperature when it operates in low temperature environment.In order to solve the problem of using two kinds of energy separately,this paper combines solar energy heat utilization technology with two-stage compressed air source heat pump technology,proposes a solar-air energy graded coupled heat pump cycle,and applies it to the production of domestic hot water,and carries out relevant research on the operation characteristics of solar-air energy graded coupled heat pump water heater.Firstly,the solar collector is introduced into the intermediate injection branch of the two-stage compression heat pump,and a solar-air energy graded coupled heat pump cycle(hereinafter referred to as the hierarchical coupled heat pump cycle)is proposed.At the same time,the performance differences between the graded coupled heat pump cycle and the traditional two-stage compression intermediate vapor injection cycle are compared and analyzed based on the enthalpy diagram.The results show that when the evaporation temperature and condensation temperature are the same,the heating capacity and heating coefficient of the graded coupled heat pump cycle are better than that of the traditional two-stage compression cycle with intermediate vapor injection,which proves that the graded coupled heat pump cycle proposed in this paper has superiority over the traditional pure air source two-stage compression cycle with intermediate vapor injection.Secondly,the simulation model of solar and air energy graded coupled heat pump water heater is established,and the model is solved by using MATLAB software.The variation of system operating parameters and the influence of solar radiation intensity and outdoor environment temperature on its characteristic parameters are studied when 150 L water is heated from 20-50℃by heat pump water heater.The simulation results show that with the increase of solar radiation intensity,the intermediate injection pressure and relative injection quantity increase,the discharge temperature of the compressor decreases,the heating power increases,the heating time to reach the target water temperature decreases,and the heating coefficient of the system increases as a whole.When the solar radiation intensity I=200 W/m~2 and I=400 W/m2,the heating time is 213 minutes and 187 minutes,which are 11.62%and 22.41%shorter than the241 minutes of the traditional two-stage compression air source heat pump.With the increase of outdoor ambient temperature,the intermediate injection pressure of the graded coupled heat pump water heater and the mass flow rate of the low-stage compressor increase,the relative injection volume decreases,the discharge temperature of the compressor increases,the heating power increases,the heating time to reach the target water temperature becomes shorter,and the heating coefficient of the system increases as a whole.When the outdoor ambient temperature is increased,the heating time is 164 minutes when the outdoor temperature is-10℃,which is 9.4%shorter than the 181 minutes when the outdoor temperature is-15℃.The average heating time is3.6 minutes shorter when the outdoor ambient temperature is increased by 1 C.Finally,by observing the variation of the heating coefficient of heat pump water heater with the volume ratio of compressor at different water temperatures,it is found that with the increase of the volume ratio of compressor,the heating coefficient of heat pump water heater increases first and then decreases,and there exists an optimal volume ratio to maximize the heating coefficient of graded coupled heat pump water heater under each working condition.When the temperature of water rises from 20 to 50,the optimal volume ratio decreases from 0.6 to 0.4.Based on this,this paper proposes to use frequency conversion technology to drive high-stage compressor to realize dynamic adjustment of volume ratio of compressor,so that the heating coefficient of heat pump water heater is close to the optimal value at all times during heating process. |
