Ameliorating the Simple Calculation Procedures for Interior Daylight Illuminance and Formulating Design Metrics for Architectural and Daylighting Designs under the 15 CIE Standard Skies

Project: Research

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Daylighting is an effective and sustainable development strategy for enhancing health benefits,visual comfort, energy-efficiency and green building development. Interior daylight illuminanceis often computed using the daylight factor (DF) approach with estimations of the traditionalovercast sky, which provides the worst daylighting condition. Consequently, under other skytypes the diversity of daylight improves. The DF approach can be analytically calculated usingsimple design aids; annual daylight data are not required. Constancy and association with theconcept of adaption are the advantages. Daylight criteria are usually expressed in the DFapproach, which is used in many countries. In Hong Kong, the vertical DF is used to specify thedaylighting performance of buildings. However, such DF methods do not consider the dynamicvariations in daylight illuminance when the sun’s location varies and the sky becomes non-overcast.The DF is invariant to building orientation and cannot take realistic or time-varyingclimatic conditions into account, thus daylight glare indices cannot be accurately determined. In2003, the International Commission on Illumination (CIE) adopted a range of 15 skies asinternational standard models of actual sky conditions. Each sky represents a unique and well-definedluminance pattern. The associated mathematical expressions can be rather complex,especially for non-overcast skies, which strongly depend on the sun’s position. The daylightcoefficient (DC) concept, which considers changes in the luminance of sky elements, offers amore effective means of computing indoor daylight illuminance under different sky conditionsand solar positions. Daylight illuminance determination based on the DC approach is quitecomplicated. With advancements in computer technology, daylight in buildings can be estimatedvia computer simulation techniques. However, full-scale computer simulations can be verycomplicated, costly and time consuming, particularly during the initial design stage whendifferent building options and design schemes are analysed and evaluated. Practitioners welcomesimple design tools produced through comprehensive analysis. The calculated results may beused to verify simulated findings. Some simple methods of estimating daylight illuminance forrooms facing various obstructed environments under different overcast and non-overcast skieshave been developed. The proposed project will aim to ameliorate the simple calculation toolsfor interior daylight illuminance and formulate design metrics for daylighting under the variousCIE standard skies. The findings should be globally adopted and useful to practitioners engagedin visual comfort, fenestration and daylighting design and evaluation.?


Project number9042504
Grant typeGRF
Effective start/end date1/11/178/04/22