A study of the effects of thermal capacity on domestic heating energy requirements

Abstract

This paper presents the results of a simplified analytical method of assessing the effects of variation in building thermal capacity on heating energy requirements. The calculation method, which can be applied manually, introduces approximations but gives a broad insight into the effects of thermal capacity. This is in contrast to detailed computer models which provide more accurate results but usually relate to particular situations. The analytical method adopted is based on the admittance procedure developed at the Building Research Station and recommended by the CIBS. The method does not take account of diurnal variations in external temperature or of the response times of different heating systems. The effects of such approximations are not considered to be significant in this study. The aim of the paper is to evaluate the thermal behaviour of the present housing stock rather than to make recommendations about houses as passive solar collectors. In situations where heating is provided on an intermittent basis and there are no incidental heat gains, application of the admittance procedure indicates that structures of higher thermal capacity require a greater amount of energy for heating than those of lower thermal capacity. In addition to this must be considered the effects of utilisation of incidental gains, in particular solar gains, and the imposition of a minimum acceptable internal temperature. These two factors are discussed in detail with particular reference to different heating schedules. It is concluded that in certain intermittent heating situations where thermal insulation standards are high, increasing thermal capacity does not lead to a significant increase in energy consumption.