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Energy tune-up

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In spite of early doubts about its complexity, the Building Regulations' sap (Standard Assessment Procedure) for energy rating of dwellings has successfully ensured a new standard of thermal performance of new housing, writes Peter Burberry. A new edition came into effect on 1 July*.

It clarifies some anomalies, provides a very much more extensive coverage of heaters and their performance, includes community heating schemes and contains revised fuel costs. In addition, it sets out the conditions under which manufacturers' own data for some types of boiler may be used. Details of CO2 emissions are included, although at present there is no limit for CO2 emissions under the Regulations.

Overall, the new edition follows the original pattern. Tables provide data to be used in assessing the performance of plant, windows and doors. Worksheets present the calculations in a simplified form. However, this simplicity is based on a sophisticated understanding of the thermal behaviour developed by bre which has created a domestic energy model and tested its predictions against dwellings in use.

A single manual calculation using the worksheets is relatively simple. But exploring design alternatives can require repeating the process - time-consuming and increasing the risk of error. Recognising this, detr accepts the use of the sap procedure embodied in computer programs. It does not produce the software. Rather, it has a scheme by which bre can approve programs, the output from which can be used as part of a Building Regulations application. At least five programs have been approved so far and it is anticipated that more will follow. In addition, five companies have been approved to provide a sap service, both carrying out calculations and issuing official sap ratings.

Peter Burberry is emeritus professor of building engineering at university of ManchesterInstitute of Science and Technology.

*sap 1998: The Government's Standard Assessment Procedure for Energy Rating of Dwellings - 1998 Edition. Published 1999. Free from brecsu at bre, tel 01923 664258.

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