Daylighting and energy performance of the window with transparent insulation slats in the humid subtropical climate zone

Abstract

The window with transparent insulation slats (WTIS) is a promising glazing system to balance building energy efficiency with adequate indoor illumination. It was investigated in several studies before, but the strengths and weaknesses of WTIS have yet to be unveiled compared with other commonly used windows regarding natural lighting and energy-saving potential. Without this information, it is hard for an architect or engineer to design and choose the optimal window type for an improved visually comfortable indoor environment and energy-efficient buildings. To address this research gap and exploit WTIS’s potentialities more comprehensively, this study used a cellular office room in Changsha as a case study to evaluate the annual daylighting and energy performance of WTIS and three commonly representative windows (double-glazing, double-glazing with interior aluminum blinds, and the Low-E window) in the humid subtropical climate zone. The analysis considered the impact of window-to-wall ratios (WWRs) and window orientations. A comprehensive approach was presented in this study, and the experiment data verified the thermal and optical models of WTIS in the simulation. The results indicate that the WTIS (Frosted slats) has better daylighting performance than other windows when WWR is larger than 40% in south orientation, which can increase the proportion of the indoor daylight illumination (100–3000 lx) to more than 86%. Considering both daylighting and energy performance, the WTIS (Smooth slats) is suitable for small WWRs, especially for north-facing windows.