When energy efficiency goes out the window: How highly insulated buildings contribute to energy-intensive ventilation practices in Germany

Abstract

Many national and international climate goals focus on lowering resource consumption in the building sector. In Germany, this is attempted in large part through increasing the thermal insulation of buildings, in order to achieve average room temperatures of 19 °C with as little heating energy as possible. However, research on the Energy Performance Gap shows that predicted heating-energy savings are seldom reached. Based on a case study conducted in six energy-efficient multi-apartment buildings in Southern Germany, we offer an explanation rooted in practice theory: There appears to be a mismatch between households’ practices and the building’s properties. While households have diverse and changing temperature needs, and a desire for quick adaptation, the energy-efficient building provides homogenous temperatures and slow temperature change. This leads households to open windows often and for long periods of time in order to reach their thermal comfort needs – even in the height of winter. The direct and indirect losses of heating energy from the observed ventilation practices can contribute to the Energy Performance Gap of energy-efficient buildings. If energy-efficient building regulations incorporated more realistic assumptions about household practices, the building designs could become more adequate and the estimated energy savings more realistic, potentially reducing the magnitude of Energy Performance Gaps.