Variability of energy use for domestic space heating

The level of reported variability of domestic space heating energy use is extremely high, the coefficient of variation being 20% even for groups of similar houses. In consequence, there is a need for heating systems to work effectively and economically over a wide range of energy use levels and there is also a need for large sample sizes in evaluating field results if the effects of individual factors contributing to the overall variability are to be assessed. For dissimilar houses, samples of 25 or more are necessary for the detection of individual factors and hundreds may be required for their accurate estimation. The effect on energy use of night temperature set-back is shown theoretically to be equivalent to a 2% energy saving per degree Kelvin temperature depression. The effects of more intermittent heating system operation are provisionally estimated, a 50% energy saving being estimated for a 6-h period of daily use at the required temperature. Effects of choice of internal temperature and ventilation rate on energy use are assessed. The energy savings made by such personal control strategies can be nullified by equipment deficiencies. The magnitudes of the effects of three such deficiencies (pipe or duct losses, unresponsive emitter control and upstairs overheating in mild weather) are estimated as each adding around 20% to the heating energy use of a typical house. The combined effects of energy saving strategies and equipment deficiencies make possible annual energy use figures from half to one-and-a-half times the designed level. The implications of this variability for heating system design are discussed.