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Climate-Based Daylight Analysis for Residential Buildings

Impact of various window configurations, external obstructions, orientations and location on useful daylight illuminance

The IESD were commissioned by VELUX to carry out a parametric climate-based daylight analysis for two residential building types with various window configurations and external obstructions. Each of the ten building configurations was evaluated for all combinations of eight orientations and six climate zones. Thus there were 480 sets of unique climate-based daylight simulations. The evaluation was founded on the useful daylight illuminance (UDI) scheme which determines the occurrence of absolute levels of illumination within four ranges: less than 100 lux; 100 to 500 lux, 500 to 2,500 lux; and, over 2,500 lux. The limits of these ranges are founded on human factors data from occupant surveys. The key indicator for 'good' daylighting is the degree of occurrence of illuminances in the range 500 to 2,500 lux (labelled the UDI-a metric) since this range: provides adequate illumination for the majority of tasks; is associated with a very low probability for the switching-on of electric lights; and, the higher values in this range are now believed to have beneficial effects for both productivity and long-term health. This study has shown that the addition of skylights invariably improves the overall daylighting performance of the space. For some designs, the addition of skylights led to a typical increase in the occurrence of the key UDI-a metric from 12% to 45% of the occupied period of the year (i.e. 08h00 to 20h00).

Main report on the VELUX Daylight site

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