The role of air tightness in assessment of building energy performance: case study of Lithuania

Abstract

The aim of this work was to evaluate the reliability of building energy performance methodology and to determine the significance of the building air tightness. This paper presents a study on the significance of the building air tightness for 27 single-family detached houses, which were built in Central Lithuania during 2007–2011. Results of the field study and calculations indicated that air tightness of A class buildings corresponded to regulation requirements, ACH50 ≤ 0.6 (air changes per hour at a 50 Pascal pressure difference between interior and exterior). There was a large variation in respect of B and C class buildings. The 90% confidence interval of ACH50 value was between 4.17 and 8.05. The results showed that Lithuanian buildings of B and C energy performance class were not sufficiently tight. The average the air change rate, when air pressure of 50 Pa was present, was 2 times higher than the regulatory value (ACH50 = 3 air change per hour). This work presents the ACH50 values' distribution according to the qualifying indicator Cq for A, B, C class buildings. Part of the presented ACH50 values of B class buildings are close to the value applicable to C class buildings. When air tightness of the buildings is evaluated, B energy performance class buildings can turn out to be C class. Results of an existing building's energy performance calculations are reliable only after verifying that the building is air tight. Otherwise, the actual heating energy consumption in buildings can significantly differ from the value calculated as per regulations if air tightness is ignored.