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Hong Kong is one of the most densely populated cities in the world. Its buildings are largely high-rise blocks constructed close to each other and, hence outdoor obstructions play significant roles in daylighting designs. The light reflected from the ground and surrounding buildings can be important sources of interior lighting and detailed computations are required. We currently propose a calculation procedure in terms of a number of regression equations to determine the daylight illuminance on vertical surfaces. This paper presents the work to assess this approach via full-scale measurements under real sky conditions. The mean surface reflectance for external obstructions was estimated using lighting simulation techniques. It was shown that daylight illuminance obtained by the proposed method were in reasonably good agreement with measured readings. The simple nature of the proposed approach offers building professionals and students a reliable and convenient alternative to predict daylight illuminance particularly when different daylighting schemes and concepts are being considered.

Daylighting has long been recognized as an important issue in architecture. In Hong Kong many buildings are constructed close to each other and hence the external environment plays a significant role in building designs. Recently, vertical daylight factor (VDF) has been used as a criterion to justify the provision of natural lighting in buildings. This paper studies the calculation approach of VDF in a heavily obstructed environment. The techniques for determining the sky component and the reflected daylight from surrounding buildings and ground surfaces are described. Calculation tools in the form of simple equations and diagrams through computer-simulation analysis were established. The performance of the proposed method was evaluated against the daylight illuminance obtained by other independent computer simulations. It was found that predictions from the proposed approach were in good agreements with those produced by simulated results. The findings provide architects and building designers with a simple method for estimating the daylight illuminance at early design and planning stage.

The quality and quantity of natural light entering a building depends on both internal and external factors. In Hong Kong, many buildings are high-rise blocks constructed close to each other and hence the external factor plays a significant role in daylighting designs. This paper studies the daylighting performance and energy use for residential flats facing large sky obstructions via computer simulations. Key building parameters affecting daylighting designs are presented. The daylighting performance for typical interior rooms was investigated in terms of illuminance level and daylight factor. The daylight levels of residential flats can be severely reduced by neighboring buildings and hence the externally reflected component would be the main source of natural light. The indoor daylight levels for kitchen and living/dining faced large neighboring building were found always less than the standard maintenance illuminance during daytime period. These imply that many residential flats in Hong Kong would have to rely on supplementary electric lighting.

An accurate estimation of the amount of daylight entering a building is the key step in evaluating daylighting designs. The concept of the daylight coefficient (DC), which considers changes in the luminance of the sky elements, offers an effective way of computing indoor daylight illuminances under various sky conditions and solar positions. We currently propose a numerical procedure in the form of nomograph to compute the interior daylight illuminance using the DC concept. This paper presents the work to validate this method via scale model measurements under different actual sky patterns. It was shown that daylight illuminances calculated by the proposed method were in reasonably good agreement with measured results. The findings will hopefully provide building professionals and students with a reliable and simple alternative to current practices that incorporate sky luminance variations to predict the indoor daylight illuminance and assess visual performance under various real sky conditions.

The first step in evaluating the visual performance and energy efficiency provided by daylight requires an accurate estimation of the amount of daylight entering a building. The actual daylight illuminance of a room is mainly influenced by the luminance levels and patterns of the sky in the direction of view of the window at that time. The daylight coefficient concept, which considers the changes in the luminance of the sky elements, offers a more effective way of computing indoor daylight illuminances. Recently, Kittler et al. have proposed a new range of 15 standard sky luminance distributions including the CIE (International Commission on Illumination) standard clear sky. Lately, these 15 sky luminance models have been adopted as the CIE Standard General Skies. This paper presents a graphical method to calculate interior illuminance for the CIE standard clear sky using the daylight coefficient approach. The simplified techniques in the form of a nomograph and Waldram diagram were established and described. The performance of the proposed approach was evaluated against the results obtained by an independent calculation approach and a computer simulation program. It was shown that the daylight illuminances estimated by our graphical tool were in reasonably good agreement with those produced from the other two methods. The findings provide building professionals and students a reliable and simple alternative that incorporates the daylight coefficient concept to estimate the interior daylight illuminance and assess daylighting performance.