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Authors: Dr. Jürgen Schnieders
Passive House Institute, Rheinstr. 44/46, 64283 Darmstadt, Germany
By using a tool for district energy balances that was developed in Sinfonia, different renovation strategies for a residential district were investigated. The resulting recommendation is to always renovate to high efficiency levels, but not necessarily renovate as quickly as possible.
Within Sinfonia, a tool was developed to assess the energy balances of city districts and their time evolution. The tool was applied in an example residential district in order to compare different renovation scenarios.
Four renovation scenarios were considered:
A) Renovation of walls, roof, floor, and windows following the current legal requirements in Germany (roof 0.24, basement ceiling 0.30, exterior wall 0.24, windows 1.3 W/(m²K)) whenever a renovation of the respective building element is necessary anyway. Ventilation remains unchanged and takes place via the windows.
B) Like A), but with twice the renovation rate between 2018 and 2028. This approach is modelled by reducing the average lifetime of the building components, i.e. the probability of renovation is higher for older building components.
C) Renovation of wall, roof, floor, and windows to the economic optimum. In most cases this means that Passive House components are applied when, at the end of the component's lifetime, a major renovation is necessary. An MVHR is installed together with improved airtightness if the windows are exchanged. This strategy is equivalent to step-by-step EnerPHit retrofit.
D) During the first 10 years like B), afterwards like C).
It was found that C), the renovation with Passive House components, provided the best overall results after 50 years, regarding both the total CO2 emissions and the emissions in the final year (cf. image below). Moderate renovations, even with increased renovation rates, lead to significantly higher overall emissions. In addition it must be noted that supporting or enforcing quick renovations with moderate qualities inhibit further improvements in the following decades and are therefore counterproductive.
The best strategy to improve the energy demand of the building stock is to carry out deep refurbishments whenever the respective components require renovation. Although the reduction in energy demand may start rather slowly during the first years in this case, this approach is economically feasible and provides substantial improvements in the long run.
This article was written in the framework of the EU-funded project Sinfonia and is part of its Set of Solutions giving insight in the experiences and lessons learned from a smart city project.
This project has received funding from the European Union’s Seventh Programme for research, technological development and demonstration under grant agreement No 609019.