Condensation risk of exhaust air heat recovery window system : assessment, key parameters, and prevention measure

Abstract

The exhaust air window (EAW) can be regarded as a combination of exhaust air heat recovery unit and window system. The window can locally and directly utilize the exhaust air from each air-conditioned room to reduce the heat loss/gain through window. However, condensation may occur at the internal glazing surface of EAW in winter. To avoid the condensation risk of EAW, some prevention measures were proposed and estimated. In this study, a two-dimensional zonal model of EAW was established to calculate its temperature distribution, and to further identify whether condensation will occur under different boundary conditions. The calculated results were compared with the measured data for verifying the accuracy and reliability of model. A sensitivity analysis was conducted to identify the effects of indoor air temperature and relative humidity, exhaust airflow velocity, and adding a low-e coating on prevention of condensation in winter. The results indicated that adding a low-e coating or decreasing the indoor relative humidity can effectively reduce the critical outdoor temperature of condensation and prevent the occurrence of condensation within the EAW. It was estimated that even under the outdoor air temperature of -20 °C, condensation risk can be avoided by employing a low-e glazing.