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Title: Determining the critical insulation thickness of breathing wall : analytical model, key parameters, and design
Authors: Zhang, C 
Wang, J
Issue Date: Oct-2021
Source: Case studies in thermal engineering, Oct. 2021, v. 27, 101326
Abstract: Breathing wall (BW) based on air-permeable porous medium offers an alternative solution for utilizing the conductive heat loss of building envelope to preheat the infiltration ventilation airflow within porous medium. However, current studies neglect the influence of pressure drop within porous medium on the energy performance of BW, which may lead to an overestimation or non-optimal design. In this study, we proposed a framework to determine the critical insulation thickness of BW for minimizing its convective heat loss and pressure drop related energy loss. An analytical model was developed and validated to calculate the heat loss of BW under third-type boundary condition. Darcy's law was applied to estimate the pressure drop of infiltration airflow and its associated energy loss. Case studies were conducted to identify the critical insulation thickness of BW. The critical thickness of BW under different scenarios was investigated. The results demonstrate the existence of critical thickness, which yields the lowest overall heat loss of BW. A larger infiltration airflow rate or lower air permeability of porous medium will result in a downward trend of this critical thickness. The outcomes of this study can provide a design guideline of BW for maximizing its energy saving potential.
Keywords: Air preheating
Breathing wall
Building ventilation
Critical thickness
Darcy's law
Thermal insulation
Publisher: Elsevier BV
Journal: Case studies in thermal engineering 
EISSN: 2214-157X
DOI: 10.1016/j.csite.2021.101326
Rights: © 2021 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license(
The following publication Zhang, C., & Wang, J. (2021). Determining the critical insulation thickness of breathing wall: Analytical model, key parameters, and design. Case Studies in Thermal Engineering, 27, 101326 is available at
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