Thermal property optimization and energy-saving potential of building integrated heat pipes and phase change materials

The novel solar building integrated heat pipes and phase change materials (BIHPPCM) can greatly improve the indoor thermal environment in winter and reduce heating energy consumption by using the variable thermal conductivity of flat gravity heat pipes and the variable specific heat of phase change materials. The heating energy consumption of BIHPPCM is closely related to the thermal properties of the interior envelope. In this paper, the thermal properties of the interior envelope of BIHPPCM are optimized and the optimal heating effect is obtained at 61 locations in severe cold and cold regions of China. The relationship between the ratio of solar radiation to temperature difference during the local heating season RRTDHS and the energy-saving potential of BIHPPCM is analyzed. The results show that: (1) The optimal phase change materials of the interior wall are of high thermal conductivity and maximum phase change enthalpy, and the phase change temperature is higher than the lower limit of the thermal comfort zone by 1-2°C; (2) The energy-saving ratios of BIHPPCM at the studied locations are between 20%-100% and can reach more than 30% at most locations; (3) A linear correlation between the RRTDHS and the energy-saving ratio is obtained, and the energy-saving ratio increases by 14.8% for every 1 W/(m2·K) increase of the RRTDHS. This study is of great significance for the application of BIHPPCM in severe cold and cold regions of China to reach zero-carbon heating.