Volume 32: A Sustainable, Clean and Carbon-free Energy Future

Design Analysis of Building Radiative Cooling Windows in Infrared Band: Regularity Exploration and Universality Verification Yue Fei, Bin Xu, Xing-ni Chen, Xing Xie, Gang Pei

Abstract

Research on radiative cooling windows suitable for hot climate regions is a hot topic of building energy conservation. Most existing researches default that windows should be ideal radiators with high emissivity (~1) in wide infrared band (2.5-20μm). However, the universality of such an assumption is unproven. To explore the optimal design scheme of emissivity of radiative cooling windows in infrared band, Comsol Multiphysics software was used to simulate the building with radiative cooling windows, and the reliability of the model was verified by experiments. First, based on the spectral properties of ordinary glass, the window with different outer surface emissivity in the atmospheric window (AW,8-13μm) and remaining infrared bands (RIB,2.5-8μm＆13-20μm) were simulated by traversal. Second, the influence of emissivity of the above two bands on radiative cooling effect of the window and the building is studied. Finally, the radiative cooling potential of the window in these two bands was compared. The results show that the lower the RIB emissivity of the window outer surface in daytime, the more favorable the radiative cooling of the window. As the solar radiation decreases, it gradually changes to the larger the RIB emissivity is, the more favorable the radiative cooling of the window. At different time periods, the adjustment trend of the RIB emissivity of the window outer surface to radiative cooling may be reversed. Through data analysis, compared with the high emissivity in wide infrared band design, it is more beneficial to reduce the window and indoor air temperature by reducing the RIB emissivity of the window outer surface as much as possible. The smaller RIB emissivity reduces the heat flow into the room and extends the time that the window becomes a “cooler” during the day. In addition, the temperature regulating effect of the window emissivity in AW is almost 8-9 times that in RIB, and the energy regulating effect is almost 9-11 times that in RIB. This work clarifies the default assumption of non-universality of building radiative cooling windows in infrared band and quantifies the importance of the atmospheric window in radiative cooling of building windows, which can provide valuable guidelines for material developers.

Keywords Radiative cooling windows, Infrared emissivity, Building energy conservation, Numerical modeling