| In this paper,the coupled system of the direct expansion solar heat pump(DX-SAHP)system and the enhanced vapor injection(EVI)system is studied in experimental method for the extreme cold weather.The system performance is analyzed and optimized.The results and conclusions of the research are as follows:The evaporator’s structure of DX-SAHP system,which is composed of hexagon and quadrangle elements,is designed and optimized.The hexagon and quadrangle channel units are simulated using CFD to analyze the heat transfer performance and pressure loss.Complete the structure design of the evaporator through the combination and arrangement of hexagon and quadrangle unit.Establish the mathematical model of the system and solve the problem.The experiment platform of DX-SAHP is built to verify and optimize the new-structured evaporator and improve the performance of DX-SAHP system through the matching research of components in the system.The maximum COP is about 4.5 when the ambient temperature is 14 ~oC and the solar irradiance is 732 W/m~2 in winter,while the maximum COP is about 6.6when the ambient temperature is 33 ~oC and the solar irradiance is 855 W/m~2in summer.Based on the experimental data,the simulation model is modified.The experiment platform of DX-SAHP coupled with EVI system is built to explore the system performance in low temperature.In winter,during the daytime when the ambient temperature is 8.5 ~oC and the solar irradiance is630 W/m~2,the average COP is 4.42 during the temperature-rise period,and the COP is 3.61 during the steady period.While the COP is 2.2 when the ambient temperature is-2.5 ~oC at night.The COP in the daytime is increased by 9%compared with ASHP,while the COP at night is decreased by 8%compared with ASHP.The COP can be increased to 4.04,4.16 and 4.22 by simulation when the number of evaporators increases to 12,14 and 16.And the COP can be increased by 27%,30%and 32%compared with ASHP.Under the ambient temperature of-10,-15 and-20 ~oC and without solar irradiance,the COP is 2.09,1.96 and 1.79,when the system runs steadily,respectively.By adjusting openings of the EXV both in the main loop and the injection loop,the compressor frequency and the number of evaporators,the matching of components in the system is analyzed.The simulation model verified by the experiment results is used to predict the system performance under ultra-low temperature conditions.When the ambient temperature is-10 ~oC and solar irradiance of 600 W/m~2,the COP is 3.01during the steady period.COP decreases with the decrease of ambient temperature and solar irradiance.Take LCoH as the evaluation index to carry on the economic analysis of heating systems.Under the typical climate in the heating season with an average ambient temperature of 6 ~oC and an average daily irradiance of9.94 MJ/m~2,LCoH of the DX-SAHP system is 0.492 yuan/k Wh,14%lower than that of ASHP,25%lower than that of gas boiler and 37%lower than that of electrical heating.Under the typical climate in the heating season with an average ambient temperature of 1.8 ~oC and an average daily irradiance of 10.80 MJ/m~2,LCoH of DX-SAHP coupled with EVI system is 0.481 yuan/k Wh,30%lower than that of ASHP and 35%lower than that of gas boiler.Compared with coal heating,DX-SAHP coupled with EVI system is economically inferior.However,due to its characteristic of high efficiency,energy saving and environmental protection,it has great potentiality and prospect in heating. |
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