As a further development of the degree-days concept, a simple parameter which takes into account site's metereological conditions as well as building envelope performance is proposed in this paper. Such a parameter shows good correlation with building energy requirements, both in winter and in summer conditions.

A new method is proposed to appraise the relative energy efficiency of designs for new or refurbished buildings. Based on the development of an energy efficiency index, it is simple to use and understand, and requires no particular expertise. The method offers a straightforward determination of likely energy performance. It addresses the total power rating of plant installed to achieve specified indoor environmental conditions, and the monitoring and control equipment which manages that capacity.