Implementing the amended EPBD needs a proper assessment of windows

The implementation of the recently amended EPBD 2018/844 offers a unique possibility for member states to focus on the renovation of their building stock in a cost-optimal way.


Windows’ assessment needs an urgent change when it comes to cost-optimal solutions for the building envelope. Why?

The energy performance of buildings today is still mainly focused on reducing the heating need as the most important factor in energy consumption and CO2 emission. However, the trend is shifting towards more cooling need due to climate change and temperature rises. Furthermore, many national reports stress that new buildings which are better insulated and airtight have a reduced heating need but tend to more overheat. By 2050 energy consumption for cooling is expected to increase sharply by 150% up to 600% globally (1).

(1) Technology Roadmap Energy Efficient Buildings, IEA 2013

Using the energy balance approach to assess the energy performance of windows

The assessment of the energy performance of glazed areas in the building envelope is often based on insulation properties, i.e. the thermal transmittance (U-value) of windows. The U-value alone does not include for the significant impact of solar gains. Moreover, cost-optimal calculations for performance requirements in many Member States that overlook the g-value have resulted in suboptimal outcomes. In reality, windows are also exposed to heat gains, with a risk of overheating in summer when there is no solar shading/protection strategy used to reduce the solar factor or g-value of windows.
Therefore, adopting a dynamic energy balance approach would give a more accurate picture of the performance of windows in their specific environments.

In a common position paper, the building glass, façade, window  and shading industries represented by European Aluminium, EuroWindoor, ES-SO, FAECF and Glass for Europe propose to pursue 3 key objectives to maximize the contribution of windows to ensure a decarbonized building stock by 2050:

* Increasing the replacement rate of windows as part of the long-term renovation strategy.
* Using the “energy balance” approach to assess the energy performance of windows.
* Recognizing the benefits of daylight, natural ventilation and solar management.

Download the joint position paper of the five stakeholders  

EPBD implementing guidelines for a proper assessment of windows with dynamic shading

Dynamic (moveable) shading has the advantage to be able to lower the g-value of the window below the g-value 0.10, which means that shading on glazed areas can keep more than 90% of the heat outside. 

Thanks to the use of the energy balance methodology, shading on windows in Europe can achieve 22% energy savings and reduce 137.52 Mt/yr of CO2 emissions in buildings. (2) Cost Efficient Solar Shading Solutions in High-Performance Buildings, Sonnergy Report 15/498 October 2015

The energy balance of a window

is the balance between the heat gains (g-value) and the heat losses (U-value) of a window, using

  • Shading as a minimum requirement to prevent overheating on southern-, eastern- and western-oriented window façades
  • Dynamic shading on glazing achieving a minimum total g-value of 0.15 to reject heat effectively from windows while still being able to make use of the free energy gains from the sun during the heating season
  • Dynamic shading with natural ventilation (night cooling by opening of windows)

Read the ES-SO Position Paper on Implementing EPBD 2018/844 

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