Performance analysis of a sorption heat storage-photocatalytic combined passive solar envelope for space heating and air purification

Efficient energy storage technology is a crucial step in achieving the broad deployment of solar energy. Salt hydrate-based sorption thermochemical energy storage (TCES), which relies on reversible gas-solid reactions, can provide an option for building energy conservation. In this article, a solar building envelope combining TCES and photocatalysis, which can fully utilize outdoor solar radiation and achieve dual-function of space heating and formaldehyde degradation is proposed. The thermal efficiency and the formaldehyde degradation effectiveness of the system under dynamic exterior conditions, as well as the influences of solar radiation, ambient temperature and wind speed, and channel width, are numerically studied. Results indicate the outlet air temperature and formaldehyde degradation rate surge first and then drop during charging, with the maximum outlet temperature of 47.9 °C at 14:30. The average ventilation volume rate of air, clean air delivery rate, and formaldehyde degradation rate are 38.8 m3/h, 29.4 m3/h, and 8.9425 μg/s, respectively. The discharging starts at 20:00 to upgrade the outlet temperature from 30 °C to around 40 °C, and the period can last for more than 10 h. The overall thermal efficiency of this sorbent wall is 66%. Increasing solar radiation and ambient temperature and lowering wind velocity can generally enhance the air purification effect and thermal efficiency; an interlayer width range of 6–8 cm is optimal to obtain better thermal and air purification performances. The results of this study demonstrate the significant potential of developing such a dual-function solar building envelope for air purification and space heating concurrently.