Design optimization of multi-functional building envelope for thermal insulation and exhaust air heat recovery in different climates

Exhaust air insulation wall (EAIW) utilizes the exfiltration process of low-grade exhaust air within porous material to improve the thermal insulation of wall. Previous studies tend to neglect the pressure loss of exfiltration process and its impact on optimal design of EAIW. This paper quantitatively estimates the pressure loss of exfiltration process and proposes a methodology to determine the optimal design for maximizing energy saving potential of EAIW. In this study, a network heat transfer model was validated and used to calculate the hourly cooling and heating load of EAIW. The pressure loss of exfiltration process and its related energy consumption was estimated by Darcy's law. The optimal design was identified for minimizing the overall annual energy consumption of EAIW in different climates. Influences of exfiltration velocity and porous material selection on the optimal design of EAIW were investigated. The results demonstrate the pressure loss of exfiltration process significantly affects the overall energy performance and optimal design of EAIW. The optimal thickness of porous material component are 40 mm, 50 mm, and 50 mm for three climate zones, which correspond to a minimum annual overall energy consumption of 0.51 kWh/m(2), 0.48 kWh/m(2), and 0.49 kWh/m(2), respectively. The porous materials with high permeability and thermal resistance are recommended as air-permeable component of EAIW. The optimal design can achieve a trade-off between cooling/heating energy consumption and fan power consumption for maximizing the energy saving potential of EAIW.