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This paper describes a three year UK initiative—Applicability Study 1-to enhance the usability and credibility of detailed thermal simulation programs with particular reference. to the design of passive solar dwellings. Researchers at Leicester Polytechnic and the Building Research Establishment are working with ESP, HTB2 and SERIRES. The aims are to identify the problems for which these programs can be used reliably and those for which they cannot, to provide guidance on the best modelling techniques, indicate the uncertainty inherent in predictions, identify the attributes of programs which are necessary to obtain reliable results, and indicate areas in which additional theoretical or experimental research is needed. The results to date show that good agreement in some design trends can be obtained provided a high level of quality control is exercised and program users have a good understanding of the theoretical basis of the programs. There were, however, some situations in which the programs still predicted significant differences in the trends in energy consumption as the building design changed. These may be explained by the different algorithms employed by the detailed thermal simulation programs and errors in them.

The Government's Standard Assessment Procedure (SAP) for the energy rating of dwellings, in the Building Regulations, is compared with detailed simulations using SERI-RES. The emphasis here is on the passive solar contribution to heating load. In this context the aspects of SAP being questioned are: the fact that solar gain and heating load refer to a single location (Sheffield); the fact that solar fluxes refer to October to April for a heating season of October to May; the limited window transmission coefficients; fixed percentage of frame; and neglect of solar gain on the walls and roof. Other aspects of SAP are: nonlinearity of heating load with heat loss, and neglect of uninsulated roof space. SAP is meant to be a rating system but the above points should be noted when values of solar gain or heating load are required.

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