Energy Consumption Variation due to Different Thermal Comfort Categorization Introduced by European Standard EN 15251 for New Building Design and Major Rehabilitations

European CEN Standard EN 15251 (2007) requires indoor thermal comfort conditions to be assessed and to fall within a category system for different levels of expectation and building purpose.  The COMMONCENSE project has prepared and provided information about the energy implications of the Standard and in particular whether the Standard is encouraging high-energy buildings in the case of new buildings and major rehabilitations. Qualitative and quantitative information about the energy implications of the Standard are given, using a range of different cooling and heating techniques and building forms.  More specifically, the required energy consumption of twenty eight buildings of different types (offices, hospitals, schools, residences) in Europe was calculated, assuming that the buildings belong to each of the three thermal comfort categories I, II, III as described in the Standard. From these calculations, it was determined if the thermal comfort categories of the Standard express real satisfaction with the environment and, at the same time, if low energy buildings could easily comply with the Standard. The calculated energy consumption for each type of building was compared against the existing national benchmarks. In general, by changing the thermal comfort category from I to II or to III as defined in EN 15251, a passage of the building from a higher to a lower energy category is noticed, according to each the existing national benchmarks and legislation. Finally, new forms for future standards which are more in keeping with the aspirations of the European Energy Performance of Buildings Directive (EPBD) are suggested. The new standard should be framed in order to encourage low energy buildings since buildings must be comfortable and energy efficient at the same time.