Assessing the Impact of Degree Day Base Temperatures on The Development of an Energy Index to Measure Energy Reduction

Refurbishment projects must be monitored before and after technology or behavior changes implementations to be able to assess their effectiveness and to drive conclusions on their applicability. An Energy Index approach has been previously developed and at its foundation, is the implication of base temperature selection on Degree Day for assessing energy reduction. The base temperature used to calculate Degree Days in the UK is 15.5 degrees. The aim of this study was to assess the impact of Degree Day base temperatures on the development of an Energy Index by means of correlation between energy consumption and Degree Days. The methodology was based on a low budget energy management strategy, in which the following information was collected: meter readings, internal temperature and outdoor conditions by means of degree-days. The methodology was employed in thirteen flats, with a control group of six flats having electric storage heaters and a further seven flats retrofitted with heat pumps. The flats were retrofitted with heat pumps; meter readings were collected around monthly intervals, while internal temperature was collected at 20 minutes intervals. Energy consumption was correlated to Degree Days based on 15.5 degrees and then compared to the correlation when the base temperature for Degree Days matches the internal flat temperature. The results show that by matching the base temperature to internal flat temperature, the average correlation improves from 0.55 to 0.76 and the average standard deviation improves from 0.36 to 0.19, meaning that the spread of results is reduced and a better evaluation of refurbishment technology or behavior changes can be achieved. The control group, with electric heater storages, experiences the greater correlation and standard deviation improvements. Matching the Degree Day base temperature to the internal temperature allows a more realistic accountability for the energy consumption to assess refurbishments by the Energy Index