Abstract
The interest of calculating the effects of thermal bridges in buildings energy consumption is growing, due to recent energy saving regulations applied in different countries. The widespread use of insulating materials to reduce energy requirements of buildings, often employed for intermediate insulation of the building envelope, makes thermal bridges a crucial point in the energy analysis of building envelopes. Furthermore, heat losses through thermal bridges often lead to building pathologies due to moisture condensation. Therefore, thermal bridges need to be correctly characterized in the building design stage in order to reduce heat losses and avoid materials degradation. The authors numerically simulate, by using finite elements, the steady-state and dynamic three-dimensional (3D) heat and vapor transport in inhomogeneous thermal bridges and building envelopes. The aim of the present work is to show the importance of taking into account the presence of inhomogeneities (i.e., metal stud) in building materials for the calculation of actual heat losses and water condensation in 3D thermal bridges. The obtained heat transfer results are verified against the reference data of the technical standard UNI EN ISO 10211. The proposed microscopic approach is essential to calculate the actual heat losses of three-dimensional thermal bridges and building envelopes and to overcome condensation problems.
Highlights
The concept of energy saving includes a variety of techniques aimed at reducing the energy consumption needed for the different human activities
In order to show the importance of taking into account the presence of internal inhomogeneities of the materials employed in constructions to correctly estimate heat losses and condensation, two different cases are considered: the pillar and the slab are made of concrete of natural aggregates with closed structure; a steel stud in the pillar and a brick-concrete slab are considered
The authors highlight the importance of using a microscopic approach to take into account the inhomogeneities present in structures commonly employed in building envelopes, such as steel-concrete pillars or brick-concrete slabs, in order to estimate heat losses and water condensation in
Summary
The concept of energy saving includes a variety of techniques aimed at reducing the energy consumption needed for the different human activities. The attention to the issue of energy efficiency in buildings is demonstrated by international and national directives [2,3,4,5], which describe the procedure for energy certification of buildings, and require member states to ensure that new and existing buildings meet minimum energy performance requirements, monitoring the actual energy demand or the estimated energy necessary to meet the various needs related to standard building uses, such as heating and cooling In this perspective, the methodology used to calculate the heat losses through the building envelope plays a crucial role, as well as the correct determination of the constitutive properties of the materials used. One-dimensional and two-dimensional models do not correctly
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