Daylighting Design Tools in Atria for Minimum Cooling Loads in Atrium Buildings

Abstract

The daylighting and sunlighting value of an atrium are considered the main reasons for including the atrium use in the built environment. However, most atria today are either overlit, which causes tremendous cooling loads, or underlit, requiring continuous artificial lighting. Furthermore, rules-of-thumb for sizing atrium physical parameters do not exist. The objective of this study was to determine the optimum transmittance of the top-fenestration that would meet the lighting criteria at the atrium floor, so that the cooling loads could be minimized. Illumination measurements were collected in physical scale models of two and four-story atria in a sky simulator. The two key variables of the study were: a) horizontal and vertical south-facing top-glazing area, and b) the percentage and the reflectance of the solid area of the atrium walls. The calculated Daylight Factors (DF) were then compared to the daylight availability of selected cities with warm climates. The increase of the effective reflectance (i.e., solid area and the reflectance) reduced the optimum top-fenestration transmittance, which would reduce the heat gain in the atrium space. Rules-of-thumb were developed to size the optimum top-fenestration for efficient daylighting and low heat gain.