Page - 70 - in Intelligent Environments 2019 - Workshop Proceedings of the 15th International Conference on Intelligent Environments

Tt is the weighted average temperature for day t and Tref is a reference temperature that must be adequately selected to separate the hot and cold branches of the demand-temperature relationship. In combination, these functions reflect the number of days on which the temperature falls below or rises above the heating and cooling thresholds and by how many degrees. Since there is no strict quantification of the values of the “threshold” temperatures, there can be many different versions of the HDD and CDD functions. In the context of this study, the selected reference temperature is equal to 17°C for high temperatures and 12°C for low temperatures. Figure 1Daily electricity consumption in the Balearic Islands Additionally, because of the particularly high degree of humidity that characterizes the Balearic Islands, a Heat Index (HI) was incorporated as an alternative to the use of the simple mean temperature variable. Measurements have been taken in other studies, based on subjective descriptions of how hot subjects feel for a given temperature and humidity, allowing for the development of an index where a combination of a certain temperature and humidity corresponds to a higher temperature in dry, non-humid conditions. Whatever the case, the most commonly used formulation of an HI was proposed by Steadman and it is also adopted in this study [24].2 For the measurement of the Balearic index, a population-weighted temperature index was constructed from the mean daily temperatures measured separately on the different islands. The population was selected as a weighting factor because climate influences electricity consumption through people’s response to the weather; the larger population, the greater the influence of weather conditions on the electricity demand. Finally, for the case of the population pressure, airport and port data were taken as reference in order to undertake two different measures. First, an estimation of the daily population stock of people on the islands, namely Human Pressure Daily Indicator (HPDI), was used as the most suitable variable from a theoretical point of view, to account the idea of population pressure. The HPDI was developed by Riera and Mateu 2 Thus HI = -42.379 + 2.04901523T + 10.14333127R - 0.22475541TR - 6.83783·10-3T2-5.48171710- 2R2 + 1.22874·10-3T 2R + 8.5282·10-4TR2 - 1.99·10-6T2R2, with T = ambient dry bulb temperature degrees in Fahrenheit and R = relative humidity. M.BakhatandJ.RosselloNadal / ImprovingDailyElectricityLoadsForecasting70