Degree days are the most underused performance metrics in energy data analysis. Simultaneously, they are widely misunderstood and therefore misused.
Weather conditions are the most influential factor when it comes to the variability of energy use in buildings. Even in a moderate climate such as the UK’s, changes in the requirement for heating and cooling typically accounts for 50%-70% of the variation in usage over the course of a typical year. In other words, regardless of everything else that’s going on inside or outside our buildings, changes in weather account for nearly all fluctuations we see day to day, week to week or month to month.
If you’re not going to use degree days for your energy data analysis, then you may as well be blindfolded. It would be like going on a diet but not tracking how much you eat.