Dynamic thermal performance and parametric analysis of a heat recovery building envelope based on air-permeable porous materials

Abstract

The exhaust air insulation wall (EAIW), which is made from air-permeable porous materials, can be treated as a heat recovery building envelope. It can prevent the heat transferring through the wall by an exfiltration process of low-grade exhaust air. To analyze the transient heat transfer of the EAIW, a numerical model was established based on finite-difference approach, and the model was verified by comparing the measured data and simulated results. Moreover, numerical simulations were performed to identify the ability of the EAIW to buffer and eliminate the heat gain on a typical summer day. In addition, parametric studies were conducted to estimate the influences of each key parameter on the dynamic thermal behavior of the EAIW, such as the hourly temperature field, heat gain, decrement factor, and time lag. The results indicate that the exfiltration airflow can adjust the inside surface temperature of the wall extremely close to the indoor temperature during the entire day. The daily total heat gain of the EAIW can be approximately eliminated for an exfiltration rate of 0.005 m/s. The thickness and exfiltration rate of the porous materials play a dominant role in the prevention of heat conduction through the EAIW into the indoor space.