Quantification of solar and daylight availability in the urban fabric by irradiation mapping

Pao Yue-kong Library Electronic Theses Database

Quantification of solar and daylight availability in the urban fabric by irradiation mapping


Author: To, Tak-tung
Title: Quantification of solar and daylight availability in the urban fabric by irradiation mapping
Degree: M.Phil.
Year: 2005
Subject: Hong Kong Polytechnic University -- Dissertations
Daylight -- Measurement
Solar buildings -- Energy conservation
Department: Dept. of Building Services Engineering
Pages: xxi, 168 leaves : ill. (some col.) ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1809964
URI: http://theses.lib.polyu.edu.hk/handle/200/3911
Abstract: With increasing public awareness of energy conservation and benefits of daylight, assessing solar access and daylight availability becomes more important in the design of buildings and the urban layout. Currently used methods such as those based on obstruction angles are too simple and ambiguous. These measures lack details which are required in assessing the amount of solar energy or daylight available over a period of time. A new approach to measure solar and daylight availability has recently been developed at De Montfort University in the UK. This approach is based on irradiation mapping using the rigorously validated and freely available lighting simulation software RADIANCE. This study aims to apply the irradiation mapping approach to quantify solar and daylight availability on facades and inside buildings within a dense urban setting using realistic climate data. The irradiation mapping technique was applied to compute the total annual and monthly irradiation on the building facades in Hong Kong's central business district where is densely-packed with high-rise buildings. The irradiation mapping is an image-based technique and hence the solar and daylight availability can be visualized as either irradiation or daylight exposure images in any selected view. With the recent recommendation by the Buildings Department of Hong Kong of using the vertical daylight factor (VDF) for performance-based assessment of daylighting on buildings, a comparison was made between the total annual irradiation and VDF. Their relationship allows us to infer realistic annual solar access from VDF by using a non-overcast sky. Calculation of solar and daylight availability inside buildings was demonstrated by using a typical residential unit of Hong Kong at different floor levels facing the four cardinal directions with common obstruction conditions. It was found that different ranges of total annual irradiation should be expected in different directions, and at different floor levels for a given value (say 1%) of daylight factor based on the CIE overcast sky. Total 120 case studies were undertaken to determine optimum building forms and layouts to maximize solar and daylight availability. These case studies enabled the formulation of a solar access index for indicating available solar irradiation on facade(s), and a daylighting index based on the total annual irradiation per unit floor area for assessment of daylight utilization. New building developments are recommended to be governed by these indices such that rights to light are protected. The significance of this study is to enhance our understanding of the power of RADIANCE in the detailed quantification of solar and daylight availability using an image-based irradiation mapping technique with realistic climate data. This understanding provides insight for us to formulate various applications of the technique in different areas such as in building environmental assessment schemes, in environmental planning and in the design of building integrated photovoltaics.

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