Effects of Upward Reflective Film Applied to Window Glass on Indoor and Outdoor Thermal Environments in a Mid-Latitude City

Abstract

The effect of upward reflective film applied to a window on the thermal environment inside and outside the window was investigated, considering the reflection and transmission characteristics depending on the angle of incident solar radiation. In terms of controlling the amount of solar radiation on a building’s windows, it is sufficient if the reflected solar radiation returns upward and does not need to be retroreflected in the azimuthal direction. Therefore, in this study, only the incident angle was considered and treated in two dimensions. The amount of incident solar radiation on the vertical façade is greater around 9:00 and around 16:00. Therefore, it is important to take measures in the morning for east-facing windows and in the afternoon for west-facing windows. The indoor MRT in front of upward reflective film is lower than in front of a transparent window due to lower transmittance. The outdoor MRT in front of upward reflective film is suppressed to the same level as in front of a transparent window, because the downward reflectance does not increase as much as in transparent windows. Upward reflective films applied to windows can improve the indoor thermal environment without worsening the outdoor thermal environment compared to thermal barrier films.