Window glass in a passive house - what do you have to pay attention to here?

Houses with high energy efficiency (low-energy houses) and passive house-standard houses place special demands on the window glass. What you have to pay special attention to, and what values ​​you must be particularly attentive when buying a window, read in this post.

U-values ​​for passive houses

For passive houses, a U-value of at most 0.8 W / (m²K) is a mandatory requirement. Even low-energy houses (KfW50 and lower) have the same conditions at the windows.

Values ​​of 0.6 W / (m²K) are usually optimal in both cases, as with the extreme values ​​of 0.4 or 0.5 W / (m²K), the respective cost-benefit calculation is important. Depending on the size and location of the window surfaces, an excessively high insulation of the windows is often not necessary or expedient. This then only causes high window costs, which are no longer fully amortized.

Include total energy transmission

Especially in the field of low-energy houses and passive houses there is another important value: the total energy permeability (g). It is often only announced on demand in many windows, but is important for the overall concept.

The total energy transmission rate indicates how much of the solar heat can get into the room through the glass. In the winter months, this is a very high quality heat source, if the windows are located correctly (south side with optimal sunshine angle).

example calculation

The effect of well-planned high g-value windows can be illustrated by a passive house example:

On two consecutive, clear winter days with -15° C outside temperature solar radiation leads to a rise in the room temperature from 20° C to 24° C. On the next three cloudy days without direct sunlight, the room temperatures will always remain above 21.5° C without additional heating.

The prerequisite for this is, of course, that the walls in the passive house also have a correspondingly high-performance insulation. (Passive house standard are U-values ​​at the wall of less than 0.15 W / (m²K)).

Planning according to U-value and g-value

The planning for the windows should therefore always take place according to U-value and g-value. The higher solar radiation can lead to high indoor temperatures in the summer, here must be provided via the ventilation or a cooling device remedy.

Avoid ventilation heat losses

For passive houses, a central ventilation system with heat exchanger is practically standard. This is not mandatory for low-energy houses.

To exclude ventilation heat loss in this case, you can install window ventilation with heat recovery. This minimizes ventilation heat losses. Ideally, these window vents can transmit up to 85% of the room heat for forced ventilation to the supply air.

Pay attention to "warm edge"

Particularly problematic in many high-quality energy saving windows are the glass edges. High heat losses can occur in this area, unless losses are limited with special spacers. Also on this point you should pay special attention to the window purchase for passive and low energy house.

Video Board: EXCLUSIVE HOUSE PLAN, Energy saving design