Abstract
The evaluation of thermal bridges in buildings, following the UNI TS 11300-1:2014 standard, must be carried out with finite element analysis or through the use of atlases compliant with the UNI EN ISO 14683:2018. The paper illustrates the development of an analytical tool to determine the internal linear thermal transmission coefficient (ψi) for the thermal bridge between concrete wall and inter-floor slab, neglected in the main existing catalogs or atlases. This type of thermal bridge is relevant in multi-story buildings, and is typical of public housing districts built between the 1960s and 1970s throughout Europe by means of industrialized systems. Considering energy requalification, due to their low energy efficiency, these buildings require adaptation to the standards imposed by law, and this thermal bridge, which has a high percentage incidence on the total heat losses, cannot be overlooked. From the survey of a representative number of such buildings in Italy, three different technological solutions were examined, with dimensional variations in the individual technical elements and the related functional layers. The combination of these variables resulted in 216 different case studies. The analysis of the existing atlases and catalogues has demonstrated their inapplicability for the selected case studies. For each one of these, ψi was calculated, using off-the-shelf software. The correlation of the data made it possible to determine an analytical mathematical modeling process to assess heat losses due to the analyzed thermal bridge. The validity of this mathematical formula was verified by recalculating the typologies investigated, reaching an error evaluated by means of the mean square deviation equal to ±4%.
Highlights
The evaluation of heat losses through thermal bridges is a much-debated topic at an international level, as evidenced by the several energy saving standards issued in recent years, up to UNI/TS 11300-1:2014, which put an end to the use of approximate methods or percentage increases
Gao et al estimated 14% of the total heat loss depends on thermal bridges in a French building, by means of a simplified model in a graphically based software environment used to simulate the behavior of transient systems (TRNSYS) [13]
Sustainability 2020, 12, 9964 of the thermal bridge, in particular conditions, after retrofitting, increases from 21% to 31% [39]. Considering this high contribution to the calculation of heat losses in industrialized buildings, from the view point of requalification intervention, and the lack of an analytical determination method, this study aims at providing a mathematical method to correctly assess the main and relevant thermal bridges found in this type of construction
Summary
The evaluation of heat losses through thermal bridges is a much-debated topic at an international level, as evidenced by the several energy saving standards issued in recent years, up to UNI/TS 11300-1:2014, which put an end to the use of approximate methods or percentage increases. The evaluation of thermal bridges is no longer negligible and must be carried out with finite element analysis or with the use of thermal bridge atlases compliant with the recently updated UNI EN ISO 14683:2018 This issue becomes increasingly important given the need to adapt existing buildings to the standards imposed by regulations aimed at improving energy performance, especially following Directive (EU) 2010/31, proposing to consider thermal bridges in the calculation of the energy performance of buildings. This Directive was amended by Directive (EU) 2018/844, which aims to increase the energy performances of existing and new buildings, focusing on technological solutions in the building envelope, but even on passive techniques reducing the energy needs for heating and/or cooling. From the analysis of the existing literature [26,27,28], it emerges that, except for a few studies [29,30] and the recent catalog of thermal bridges by PHI (Passive House International) [31], thermal bridges of the wall/inter-floor slab are mostly neglected
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