Energy efficiency, visual comfort, and thermal comfort of suspended particle device smart windows in a residential building: A full-scale experimental study

Abstract

Smart window controls the visible light transmittance and solar heat gain coefficient through the transition to a clear or tint state. When applied in buildings, it can be an effective solution in terms of visual and thermal environment by controlling solar radiation. Various previous studies have provided smart windows’ effective performance results related to the visual or thermal environment, however, these studies were mostly based on numerical simulations or small-scale test cells. Few studies have comprehensively analyzed smart windows’ performance when applied to real buildings. Accordingly, this study aimed to analyze and evaluate the performance of smart windows applied in residential buildings related to the visual and thermal environments from various perspectives. For this purpose, we installed suspended particle device smart windows in an apartment building, i.e., a typical residential building type in South Korea, set up related sensors and equipment and collected data from July to September 2022. Based on this campaign, we evaluated visual and thermal comfort and lighting and cooling energy performance according to the sky condition (cloudy, partly cloudy, and clear days) and smart window tinting control method (always tinting, automatic control to maintain the indoor daylight illuminance at 200 lx, and automatic control to maintain the illuminance at 400 lx). In terms of glare, on partly cloudy and clear days, smart windows effectively controlled glare regardless of the tinting control method. In terms of the indoor daylight illuminance, automated control was more effective than always tinting in terms of providing useful daylight under all sky conditions. In terms of thermal comfort, tinting at all times was the most effective on partly cloudy and clear days. The lighting energy consumption increased by 3.9–17.9% when smart windows were used, while the cooling energy consumption was reduced by 0.0–20.5%. Overall, this study revealed that the appropriate smart window operation method varied depending on the sky condition. On cloudy day, maintenance of the indoor daylight illuminance at 200 lx using automated control was efficient. On partly cloudy and clear day, the automated control (200 lx or 400 lx) was efficient in terms of visual comfort, however, in terms of thermal comfort and energy consumption, tinting at all times was effective. This suggested that completely tinting smart window in conjunction with automatic artificial lighting control to ensure proper indoor illuminance could be the most effective on a partly cloudy day and a clear day. Based on this study, it is necessary to derive more detailed optimal smart window operation strategies in terms of glare, indoor daylight illuminance, thermal comfort, and energy consumption for all seasons.