Daylight and Energy Performance Assessment of Passive Design Strategies in a Subtropical Commercial Building Using Honeybee–Radiance in Bhutan

Abstract

The increasing reliance on artificial lighting and mechanical cooling in warm-humid climates highlights the need for climate-responsive passive design in commercial buildings. This study evaluates a prototype commercial building in Gelephu, Bhutan using Honeybee–Radiance and a parametric assessment of building orientation, window-to-wall ratio (WWR), glazing type, and interior surface reflectance. The base case, representing a conventional commercial building configuration, recorded sDA 0.49, ASE 0.24, UDI 0.61 and DGP 0.25, indicating insufficient daylight distribution, excessive solar exposure and perceptible glare. The optimized configuration (45° orientation, 40% WWR, Low-E glazing and wall/floor/ceiling reflectance of 0.70/0.40/0.90) improved performance to sDA 0.78, ASE 0.09, UDI 0.84, DGP 0.11 and average illuminance of 560 lux. These results represent a 59% increase in sDA, a 63% reduction in ASE and a 56% reduction in glare probability. The findings demonstrate that integrated passive design strategies can substantially improve daylight quality and visual comfort while supporting more energy efficient commercial building design in Bhutan's subtropical climate.