Research On Thermal Characteristics Of Solar-PCM Roofing System Which Takes Summer Ventilation In Account

The situation of energy shortage and environmental pollution have become more and more urgent.For the HVAC industry,the improvement of building envelopes and the energy saving and consumption reduction of building heating are of great significance.This paper proposes a solar-PCM roofing system that takes into account summer ventilation for heat insulation and winter heat storage for heating.It combines double-layer phase change materials,summer night ventilation and winter solar heating to improve the thermal performance of the building roof structure in winter and summer.This paper focuses on the heat storage performance and energy saving effect of the solar-PCM roofing system in winter.First,taking Shijiazhuang City,which is rich in solar energy resources,as the main research site,a solar air collector system simulation platform is built using TRNSYS software.The solar collector system is designed,and the outlet temperature of the collector under different heating wind speeds is simulated.When the cavity ventilation speed is 0.4m/s,the maximum supply air temperature is 92.2℃;when the cavity ventilation speed is2.4m/s,the maximum supply air temperature is 30.9℃.The three-dimensional heat transfer model of the roof structure is established using CFD numerical simulation software,and the optimal structure of the solar phase change roof in Shijiazhuang City is optimized.The effects of different factors such as the position of the phase change material,the phase transition temperature,the thickness of the phase change material,and the heating wind speed on the thermal performance and energy saving of the roof are analyzed and compared.The simulation results show that the best position of the phase change material is the bottom layer of the roof structure,the best phase transition temperature is 18～20℃,the best thickness of the PCM is 30mm,and the best solar cavity heating wind speed is 0.8m/s.Compared with the ordinary roof,the solar phase change roof can significantly increase the night temperature and average temperature of the inner surface of the roof,and reduce the temperature amplitude.Considering the solar radiation resources,different building climate zones are chosen as the research objects.The optimal structure of solar phase change roofs in Harbin and Wuhan has been optimized.The optimal phase transition temperature in Harbin is 17～19℃,the optimal thickness of the PCM is 30mm,and the best solar cavity heating wind speed is 1m/s;the optimal phase transition temperature in Wuhan is 18～20℃,the optimal thickness of the PCM is 30mm,and the best solar cavity heating wind speed is 0.8m/s.The energy-saving effects of solar phase change roofing systems applied in Shijiazhuang,Harbin and Wuhan are compared.The energy savings per unit area of Shijiazhuang,Harbin,and Wuhan in typical winter days are 7733.66k J/m~2,5569.09k J/m~2,and 2865.23k J/m~2,respectively.The system has the best energy-saving effect in Shijiazhuang City.The system is more suitable for areas with high solar radiation intensity and low outdoor temperature in winter.The solar PCM roofing system proposed in this study has a certain reference significance for improving the thermal performance of the building roofing envelope and reducing heating energy consumption in winter.