The size of the windows in a passive house
Passive house windows are to maximize the use of solar energy and minimize the building's thermal losses.
And how is it in practice?
The standard definition of a passive house is the maximum solar yield. In passive house designs, this translates into huge glazing on the south side while minimizing the window area on the north side.
In practice, as I watch, most passive or nearly passive houses (highly energy-saving) built in Poland does not follow this recommendation. Yes, glazing on the sunny side is much larger than on the north side, but they are far from powerful glazing in model projects of typical passive houses.
Why big windows are avoided? Below are my assumptions:
1. Climatic conditions.
In Poland, the weather conditions are not optimal for the use of solar energy, additionally, it is regionally different - the number of sunny days during the heating season in Wrocław will be different, and another - in Białystok. In the regions, where there aren't many of them, solar gains are small enough, that many investors consciously give them up.
2. Cost of passive windows.
Dedicated windows for a passive house are expensive. Except that, that they should be warm (low Uw factor), this additionally should ensure high solar energy gains. Most of the warm glazing units, along with good thermal insulation, have a reduced transmittance of solar radiation energy, which results in lower solar gains. Maintaining both parameters at a high level (in other words: heat does not escape from the house through the windows, and at the same time we derive a lot from the sun) requires the use of expensive technologies, which affects the high price of windows.
I will write about the installation of windows in a passive house in another article, but here I will mention - installing large windows in accordance with the guidelines for a passive house (installation in the insulation layer) is problematic. The problem is both the cost and finding a team with the appropriate qualifications.
Great, active windows also work in the summer ... When the sun is full, we can cover them with roller shutters (the visual effect during the day is not overwhelming), otherwise we will fry in our own home (or we spend a lot of money on air conditioning).
It is often used in energy-saving or almost passive houses, a financially sound solution is therefore:
a) standard or slightly enlarged window area on the south side (the current projects have much larger glazing than before)
b) minimalization (or none) windows on the north side
In addition to the size of the windows, we also have to decide about it, what windows to buy and how to install them, but I will write about it in the next articles.