Development, testing, and evaluation of the daylighting, thermal, and energy-saving performance of semitransparent radiative cooling glass in cooling-dominated regions

Abstract

Glass-made building envelopes play an essential role in buildings’ thermal/daylighting environment and energy behavior. To enhance its overall energy efficiency in cooling-dominated regions, a double-layer film that combines the concepts of selective solar utilization (SSU) and radiative cooling (RC) is proposed to form the semitransparent energy-saving glass (SESG). The SSU film (∼0.1 mm) is a multilayer optical film that contains polyethylene terephthalate (PET) and thin reflective metal layer. The RC film (∼0.1 mm) consists of a PET layer and an adhesion layer. To evaluate the daylighting, thermal, and energy-saving performance of the SESG on buildings, comparative field tests using reduced-size model boxes and whole-building energy simulation analysis on a larger-scale office building are conducted. Compared with the normal clear glass, the developed SESG decreases the indoor air temperature of the modeled box by maximum values of 19.1℃ and 17.8℃ while reducing the daylighting level by 68 % to support a more comfortable thermal/daylighting environment. In addition, a single-story office building modeling using EnergyPlus was developed to evaluate the energy-saving and daylighting performance of the SESG in two different cooling-dominated cities, Male (Maldives) and Hong Kong (China) considering different glazing ratios. Compared with normal clear glass which will add amounts of extra cooling load and cause serious glare problems due to its high transmittance to visible light and near-infrared solar radiation, the annual cooling energy savings of the SESG reach 15 %—60 % in two selected cities under different glazing ratios. By considering both energy-saving potential and daylighting quality, the simulation results show that in Male, within the glazing ratios of 0.4 to 0.6, the UDI (Useful Daylighting Illuminance) values and energy-saving potential both reach the highest value of 0.5–0.6 and ∼ 55 %. In Hong Kong, the UDI values and energy-saving potential both reach the highest value of 0.4–0.5 and ∼ 57 % when the glazing ratio ranges between 0.5 and 0.9. The experimental and simulation results validate that combining selective solar utilization and radiative cooling for the glass envelopes is able to seek a more efficient balance between the energy behaviors and daylighting environment for buildings in cooling-dominated regions.