The Calculation of Energy Performance of Buildings with Summer Degrees

The energy performance of buildings (EPB) is usually calculated by reference to winter conditions. All standards, technical, normative and national laws consider building calculation of costs and energy performance during winter months. The energy performance of a building is related to outside temperature and comfortable inside temperature, therefore EPB depends on external weather trends. The “measure unit” of weather trends, used in some calculation models, is the Day Degree which represents the hours when the outside temperature is below the inside temperature standard. However, world climate changes and the diffusion of HVAC (Heating, Ventilation and Air Conditioning) systems, especially single-unit systems (split system), introduced the concept of comfort in the summer months and weather derivates - Hot Day Degree (HDD) and Cool Day Degree (CDD) used to establish weather risks for insurance purposes. HDD and CDD can be used to plan, check and evaluate energy performance before and after an energy project. To evaluate energy performance in a building in summer conditions we can use the studies on comfort perceptions to translate a Day Degree concept in “measured units” to evaluate with respect to a normalised cooling regime. In this article the outside temperature Summer Day Degree trend is proposed, within fixed temperature values (comfort range), humidity, wind velocity, and radiation incidence. Moreover, an example of how the Summer Day Degree can be applied is presented.