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Designers and contractors often face a lot of uncertainties about correctly estimating disruptions in the thermal building envelope, especially when it comes to fasteners and installation structures, which are often either not considered or assigned disproportionately high or low parameters during planning. These mistakes inevitably lead to a heating demand energy balance for the building that is not in line with reality. Designers rarely have reliable thermal bridge parameters available, especial for punctual disruptions. Correctly simulating and calculating thermal bridge values often requires time-intensive and expensive (three-dimensional) calculations that are not given sufficient (if any) time or budget in planning. This makes it even more important to be able to realistically estimate these aspects. This paper uses a number of examples of thermal bridge issues to clarify uncertainties, increase understanding of the importance of correctly estimating disruptions in the thermal envelope and how they affect the overall energy balance, and, with the help of examples of thermal bridge-free construction, provide designers and contractors with solutions for ensuring high-quality Passive House building envelopes.
An existing, planned Passive House is used as originally planned in order to investigate a variety of punctual and linear thermal bridges and their impact on the energy balance. Both standard solutions and high-quality system variants suitable for Passive House will be analyzed. The study looks at the influence of foundation molding, installation systems for boxes for blinds, window mounting structures, angle supports for French balconies, balcony connections, and outside equipment boxes and installation structures.
The analyses demonstrate the influence of individual components on total energy balance and show which components absolutely must be included when planning a project and determining its energy balance as well as which components can be considered to have no thermal bridges. Additional heat demand resulting from thermal bridge-related disruptions is also discussed. Careful planning and the use of high-quality components can ensure a building envelope's high thermal quality, even in the case of the special construction systems often required for unique architecture.
This in-depth article is available exclusively to IPHA members
Planning a structure that is free of thermal bridges is very complex. With consideration of structural damage prevention and financial aspects, a reasonable relationship must be created between planning effort, the use of special solutions, and the total energy balance depending on the project, standard construction, and building geometry. Of particular importance is the ability to carefully estimate the impact a solution's thermal bridges will have on the overall energy balance and determine whether it is significant.
The examples investigated show that individual penetrations have a negligible influence on heating demand, even for solutions of low thermal quality. They can generally be compensated for with the substitution potential of negative geometric thermal bridges. Still, designers must take these parameters into account and strive for reliable values when the relevant lengths for thermal bridges are large and/or there are several disruptions in the building envelope. Heating demand is much more easily influenced in buildings with a small surface area.
Special solutions of high thermal quality make financial sense in the planned example here while also contributing to structural damage prevention and an exterior envelope that is also of high thermal quality.