An Assessment of Ceiling Depth Effects on Skylight Daylighting and Energy Performance

Abstract

The purpose of this study was to evaluate the impact of ceiling depth on both daylighting and energy performance of skylight. Through OpenStudio’s integrated Radiance and EnergyPlus simulation programs, skylight daylighting and energy performance were assessed under two different local climate conditions of Ulsan and Seoul cities in South Korea. The influence of ceiling depth on skylight energy efficiency was analyzed by including ceiling depths of 1.5 m to 3 m into a simulation model with a skylight-to-roof ratios ranging from 1% to 20%. Through simulation predictions, energy efficient skylight-to-roof ratios were defined for each ceiling depth and for each of the two cities under consideration. The results indicated that the energy performance of smaller apertures (small skylight-to-roof ratio) were more affected by the ceiling depth than were larger apertures and the range for energy efficient skylight-to-roof ratios became smaller as the ceiling depth increased. Under Ulsan climate conditions, the range for energy efficient skylight-to-roof ratios changed from 1–20%, when no ceiling depth was included into simulation model to 1–17%, 5–17%, 7–17%, and 9–17% for 1.5 m, 2 m, 2.5 m, and 3 m ceiling depth, respectively. The optimal skylight-to-roof ratio in terms of both daylighting and energy performance was 8%, 9%, 10%, and 11% for ceiling depths of 1.5 m, 2 m, 2.5 m, and 3 m, respectively. The results for Seoul climate conditions showed no energy efficient skylight-to-roof ratio for a ceiling depth greater than 2 m. The range for energy efficient skylight-to-roof ratios changed from 2-18%, when no ceiling depth was considered in the simulation, to 6-13% and 9-13% for a ceiling depth of 1.5 m and 2 m, respectively. The optimal skylight-to-roof ratio was 8% and 9% for 1.5 m and 2 m ceiling depth, respectively. This study induced that unlike side windows, ceiling depth plays a crucial role in daylighting and energy performance of a building with skylight. Actual solar heat gains and transmitted visible light can only be accurately reflected in simulation predictions when a ceiling depth is included into simulation model. Hence, ceiling should be carefully modeled for investigation involving top-lighting system.