State of Knowledge of Thermal Bridges—A Follow up in Sweden and a Review of Recent Research

Abstract

It is important to minimize transmission heat transfer losses through the building envelope when designing and building energy efficient buildings in heating dominated climates. In such a climate, a large part of the space heating demand is caused by transmission heat transfer losses through the building envelope. Calculations of these losses must be carried out in a correct way to ensure a properly sized heating system and a good indoor climate. Furthermore, underestimating the transmission heat transfer may lead to energy costs that exceed expectations. A Swedish study was published five years ago which concluded that the state of knowledge was low and simplified methods used were not accurate. Five years has passed since the previous study. The purpose of this follow-up is to investigate whether the state of knowledge among Swedish consultants has increased and to review the progress within the international field. The study shows that little has changed in Sweden. The state of knowledge regarding different measuring methods and the effect on thermal bridges is still not satisfying. Furthermore, the review of recent research shows that the relative effect of thermal bridges vary greatly. More guidelines and education/training are needed. Further research should be carried out with a holistic approach where thermal bridges are investigated with varying construction types, energy efficiency of building envelopes and different measuring methods. climate is achieved by constructing an air tight and well insulted building envelope combined with balanced mechanical ventilation with high heat recovery efficiency. Designing a building according to these principles will result in that the majority of the heating demand is due to transmission heat transfer through the building envelope. Hence, it is important to calculate the transmission heat transfer in a correct way and not underestimate or exclude potential thermal bridges.A heating dominated climate may be defined as a climate where 70% or more of the space conditioning needs is related to heating [4]. It should be noted that also in a heating dominated climate up to 30% of the space conditioning needs may be related to cooling. Hence, buildings still need to be designed to avoid excess temperatures during the warmer part of the year.As mentioned, EPBD2 states that methodology for calculations should take into account European standards and be expressed in a transparent way. Standards are important as they provide reliability, predictability and security. Furthermore, they facilitate communication between different actors, minimizing the risk of misunderstanding. This leads to profits, both from a business perspective and from a macroeconomic perspective [5].A commonly used standard to calculate transmission heat transfer through a building envelope is EN ISO 13789 [6] which in turn refers to two standards regarding thermal bridges; EN ISO 14683 [7] provides a simplified method including default values of linear thermal transmittance and EN ISO 10211 [8] provides...

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