Study On The Characteristics Of Phase-change Energy Storage Of Active Internal Wall In Dual Working Conditions

In the hot summer and cold winter region,there is a strong demand for heating and cooling for residential buildings.According to the climatic characteristics of the region,the air source heat pump can provide heating and cooling and meet the personalized requirements of users.It is suitable for being the local cold and heat source.In order to improve energy efficiency and reduce operating costs,phase change energy storage technology is applied to the wall of the building envelope,and the night off-peak electricity is used to drive the heat pump to store energy.The phase-change energy storage wall with capillary is built on the inner wall forms a radiant heating and cooling panel.In this paper,the theoretical simulation method is mainly used to study the energy storage and energy release characteristics of the hybrid capillary and phase change wall in winter and summer,and the reliability of the simulation method is verified through experiments.An energy storage structure namely phase change material(PCM)and capillary composite wall was designed in active form,a mathematical model of transient heat transfer for the composite wall was established in this paper.The Fluent software was used to simulate the heat transfer and temperature distribution in the process of energy storage and energy release.The specific contents include:(1)the effect of the phase change temperature on the heat transfer process,(2)the effect of the cooling and heating medium temperature on the heat transfer process,(3)the effect of the thermal conductivity of the phase change material on the heat transfer,(4)the effect of mass latent heat on the heat transfer process,(5)the effect of the position of the two phase change materials on the heat transfer process under dual operating conditions,(6)the heat transfer process of the composite wall under the condition of indoor variable heat load,(7)the heat transfer characteristics of composite wall with embedded PCM intube.The simulation results show that increasing the thermal conductivity of PCM can increase the phase change rate,thereby reducing the temperature of the water supply in heating conditions,increase the temperature of the water supply in cooling conditions.Thus increasing the thermal conductivity of PCM,COP of heat pump in heating and cooling modes can be improved.If the energy storage time is 6h,under heating conditions,the optimized phase change temperature is 26℃,the thermal conductivity is 0.5W/(m?K)and the water temperature of the heating medium is 30℃,under cooling conditions,the optimized phase change temperature is 18℃,the thermal conductivity is 0.5W/(m?K)and the refrigerant temperature is 13℃.For the double-PCM-layer structure of dual operation conditions,the thicker summer PCM layer is arranged on the inner side,the thinner winter PCM layer is arranged on the outer side(indoor side),and the capillary is arranged in the thicker PCM layer of summer,this arrangement has the best heat transfer characteristics.The PCM is placed in the middle of dual layer tube,which solves the problem of shaping and combination of PCM with wall.Compared with the method of covering the entire wall surface with double-layer phase change material,the heat flow is greater,the energy storage time is shortened,and the temperature of the heating medium is low,the temperature of the cooling medium is high.During the phase transition,the volume changes,resulting in additional thermal resistance.An experimental test stand for a phase-change composite wall was established in the constant temperature and humidity environment room,the capillary is embedded in the wall,and the heat pump is used as a heat source.Conducted an experiment under heating conditions.Comparing the experimental results with the corresponding simulated conditions,the results show that the data obtained by two groups of experiment are slightly lower than the values obtained by the simulation,and the errors of the temperature of the surface of concrete are 14.94% and 11.04%,respectively,the errors of the temperature of the surface of PCM layer are 5.87% and 2.72%,respectively,indicating that the mathematical model is suitable.