Abstract
Renovation of old apartment buildings is a topic of current research interest throughout the Eastern Europe region where similar typology is derived from the period of 1960–1990. Thermal bridges, essential components of the transmission heat loss of a building, have to be properly evaluated in the energy audit during current state-of-the-art situation as well as in the comparison of renovation solutions. Resulting from field measurements and calculations, we propose linear thermal transmittances Ψ of thermal bridges for four types of apartment buildings: prefabricated concrete large panel element, brick, wood (log), and autoclaved aerated concrete. Our results show that thermal bridges contribute 23% of the total transmission heat loss of a building envelope before renovation. After renovation thermal bridges account for only 10% if windows are repositioned into additional external thermal insulation and balconies are rebuilt as best practice. Inversely, impact of the thermal bridges might be up to 34%, depending on the wall insulation thickness. We have also found that the relative percentage of thermal bridges after renovation increases and the negative impact of the thermal bridges of certain junctions cannot be compensated with thicker wall insulation. Results obtained in this paper are useful for energy audits.
Highlights
The thermal bridge is a part of the building envelope where the otherwise uniform thermal transmittance is locally significantly larger
Since leaky 2-frame windows were typically used in wooden buildings, low surface temperatures caused by air leakage rather than by the thermal bridge were determined around the windows
Linear thermal bridges in the transmission heat loss were evaluated in four apartment building types – prefabricated reinforced concrete large-panel elements, bricks, wood, and autoclaved aerated concrete large-blocks
Summary
The thermal bridge is a part of the building envelope where the otherwise uniform thermal transmittance is locally significantly larger. The European Directive on the Energy Performance of Buildings (EPBD 2010) states that the methodology for calculating the energy performance of buildings should take into account thermal bridges. From seven essential requirements set in the Construction Products Regulation (EU) No 305/2011 (2011), thermal bridges influence the requirements for “hygiene, health and the environment” and “energy economy and heat retention”. The share of thermal bridges in the transmission heat loss depends on the climate and construction. In cold Sweden, the impact of thermal bridges may be accounted for by the increasing heat transfer between 20% and 38% for precast concrete sandwich walls and between 12% and 26% for wooden frame walls (Berggren, Wall 2013) in terms of internal dimensions of the building envelope
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