| The active phase change material(PCM)energy storage wall has attracted much attention for its advantages to cut peak and fill valley in electricity consumption,save energy in buildings and improve indoor comfort.In order to solve the problems of PCM leakage,high encapsulation cost and difficult to realize the integration of heating and cooling in the existing PCM wall,this paper proposes a casing type PCM wall for heating and cooling integration.The effects of the physical properties of PCM,the arrangement of PCM layer and the structural parameters of the casing on its thermal performance were simulated.An experimental model of the casing type PCM wall for heating and cooling integration was made and the experimental research was carried out in the climate chamber.The main works and achievements are as follows:(1)The air source heat pump and solar collector were selected as heat and cold source device.The active PCM wall radiation terminal was designed.The physical and mathematical models were built to simulate the energy storage and release characteristics of PCM wall under cooling/heating conditions.The effects of physical parameters of PCMs on wall temperature,heat flux and energy storage and release rates were investigated.The results show that the phase change temperature has an important effect on the wall heat flux during the process of energy storage and energy release.The optimal phase transition peak temperature of PCM in summer and winter is 15℃and30℃,respectively.Increasing latent heat of PCM is beneficial to reduce the temperature fluctuation,improve the thermal comfort and reduce the thickness of PCM layer.Increasing the thermal conductivity of PCM can significantly increase the energy storage rate amd wall heat flux,and the heat transfer of PCM wall is also better.(2)A casing type PCM wall for heating and cooling integration is designed,and the effects of PCM layer arrangement,PCM dosage and casing structural parameters on the energy storage and release characteristics of PCM wall are simulated.The results show that the interval arrangement of cold and heat storage layers shows the best comprehensive performances.The thickness of PCM layer(PCM dosage)determines the latent heat of the wall and affects the heat transfer performances of PCM wall.After optimization study,it is concluded that the filling amount of PCM of 1.04 m~3 in each casing can meet the design requirements.The inner pipe diameter,outer pipe diameter and casing spacing all have significant effects on the heat transfer performance of PCM wall.The optimal inner pipe diameter,outer pipe diameter and casing spacing are 20mm,46 mm and 5 mm respectively.Adding a small amount of fins to the casing can improve the heat transfer performance of PCM wall slightly,while adding a large number of fins will reduce the filling amount of PCM significantly.(3)The optimal operation scheme of the phase change energy storage system under different room temperature was simulated.It is found that the optimal operation scheme is that the average water supply temperature is 15℃in summer and 35℃in winter under the indoor design temperature of 26℃in summer and 20℃in winter,energy storage for 8 h and energy release for 16 h.Under the optimal operation scheme,the average wall temperatures are 20.5℃in summer and 26.8℃in winter;the average heat fluxes are 45.9 W/m~2 in summer and 57.2 W/m~2 in winter,and there is no risk of condensation and meets the practical application requirements perfectly.(4)Expansive graphite-paraffin composite PCM was prepared.Based on the simulated and optimized casing structure,a casing PCM wall test model was constructed,and the energy storage and release characteristics of the casing under summer working conditions were investigated in the climate chamber.The results show that the wall heat flux is significantly affected by the fluctuation of room temperature,while the wall temperature is slightly affected by the fluctuation of room temperature and has no effect on the temperature of PCM layer.The heat flux distribution of the whole PCM wall is relatively uniform with an average value of 40.8 W/m~2 and there is no condensation risk on PCM wall.By comparing the simulated and experimental values of phase change layer temperature and wall temperature,they are well correlated with average errors of 9.5%and 6.2%respectively. |
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