The heating degree days model is accepted for the calculations. This means that we accept that the heat lost through the window panes must be offset through additional heating energy. In doing so, the dynamics of the building when heating up and cooling down are not taken into consideration. Energy generated through heat influx is ignored.
The calculation is performed in a simplified form for glazing in Central Switzerland with 3,100 heating degree days. Heating degree days (HDD) - HEV Schweiz (hev-schweiz.ch)
The results may differ for other locations and real-life, future conditions.
Dynamic calculations that take into account solar heat influx in more detail (energy simulator) produce a typical payback period for the energy input of between 0.8 and 3 years, depending on the location, use and characteristics of the building such as the orientation of the glazing.
Basis:
Single-family house built in 1975 with 30 m² of old double glazed insulating glass and oil heating. Double glazed insulating glass: Ug value 2.9 W/(m2K)
New triple glazing:
Single-family house built in 1975 with 30 m² of new triple glazed insulating glass and oil heating. Triple glazed insulating glass: Ug-value 0.6 W/(m2K)
MIG design: 4 EN2plus/14Ar/4/14Ar/4 EN2plus
Number of heating degree days: 3,100 (corresponds to Central Switzerland)
Energy input through heat lost through windows:
Conversion into CO2
One litre of heating oil provides around 10 kWh of thermal energy (based on the calorific value).
The utilisation factor of the heating is assumed to be 0.9. 1 kWh of thermal energy from the heating oil generates 0.9 kWh of useful energy.
As a result, 5,134 kWh/10 kWh/0.9 = 570 l of heating oil is required to generate 5,134 kWh of useful energy. When it is burnt, 1 l of heating oil generates 2.65 kg of CO2 (explanations from erneuerbarheizen.ch).
More efficient glazing can save 2.65 kg of CO2/l x 570 l ≈ 1,500 kg of CO2.
The assumption that 267 kWh of energy is required per m2 to produce the glazing is based on the Coordination Conference for Public Sector Construction and Property Services’ 2022 life cycle assessment data for the construction sector.