Energy Certification Label vs. Passive Discomfort Index for existing dwellings

Abstract

Several studies highlight the significant differences between theoretical energy consumptions, - considered in the Energy Certification Schemes (ECS), following the Energy Performance of Buildings Directive (EPBD) -, and the actual energy household consumptions, obtained from extended surveys and monitoring campaigns, especially in Southern European countries. These differences are referred in the literature as “heating gaps”. Actual consumptions are significantly unpredictable (depending on outdoor climate, income, energy prices, cultural habits, etc.), but, in most cases, lower than permanent heating/cooling assumptions, present on regulations. This inaccuracy may lead to the suggestion of inappropriate measures on ECS, for low energy-consumption dwellings. Inappropriate because the impact of the same measure on energy consumptions and thermal comfort is different for cases with a permanent heating behavior and cases without it, and because it may lead to hygrothermal pathologies and, finally, an economic mistake, as the real payback time of that measure will be higher than the one suggested, misleading economically more vulnerable households. A complementary approach for the evaluation of thermal performance in existing dwellings, considering intermittent heating scenarios is proposed, by the definition of the “Passive Discomfort Index” (PDI), complementary to the energy label. This index is quantified by the calculation of the temperatures outside the comfort range within the building, in realistic use conditions. A 19^th century building, located in Porto, was used to perform a monitoring campaign of temperature and HR to calibrate a numerical model, developed using an advanced simulation tool. It was then performed a sensivity analysis, comparing the energy label with the PDI value, for different retrofitting scenarios, mainly with different insulation thicknesses. The results show that there is no obvious relation between the energy label and the comfort conditions, for intermittent heating scenarios, among others, reinforcing the need of a complementary approach. This is especially important for existent buildings and for Southern European countries, where the “heating gap” is higher.