The prediction of long term monthly mean daily solar gains through vertical single and double clear glazing at sites distributed throughout the UK

Abstract

A simple approximate method has been developed for estimating long term monthly mean daily solar heat gains per unit area for vertical windows for sites within the UK. The method enables the monthly mean solar gains through vertical single and double glazing of any orientation to be estimated for each of the Department of Energy degree day regions, using a simple desk calculator in conjunction with the tables provided. The window solar heat gain prediction method is also suitable for computer modelling and has been incorporated in the University of Sheffield, Department of Building Science interactive computer program ENGY which estimates the total monthly heating energy requirements of buildings and the associated energy costs, for different Department of Energy degree day regions taking account of mean monthly heat gains through windows. In the development of the prediction method, extensive use was made of existing solar energy computer programs developed with support from the Science and Engineering Research Council. These models had been extensively validated against European data, and, in a modified form, are being adopted as a standard EEC recommended calculation procedure. These more complex programs for estimating hourly heat gains take full account of glazing angle of incidence effects. They were used as the tool with which to develop the simplified solar gain methodology presented in this paper. The predictions of mean solar heat gains are based on long term observed means of sunshine in the UK between 1941–1970. Therefore, the method must not be used for the study of short term variations from place to place in any particular year. The method provides such a simple technique for accurately estimating average solar heat gains for clear single and double glazing across the UK that it becomes unnecessary for UK designers to rely any longer solely on the Kew solar design data, which is not representative of the whole country. The gains estimated are the gains based on 100 per cent utilisation of the transmitted energy. Preliminary procedures for estimating actual utilisation are provided. The utilisation will depend on the weight of the building.

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