Why and how should ventilation be carried out?
When we are outside, we usually have enough fresh air (except perhaps in cities with a lot of traffic and/or industry). If we are indoors, e.g. during work, at school or even at home in the flat, fresh air is just as irreplaceable. Here, however, access to fresh air is not automatic; we have to actively do something about it. A little air always gets into the flat from the outside - through cracks, crevices or the moment you open the outside door. But this is clearly too little to be able to speak of "fresh" or healthy air in the building.
Humans have "built-in sensors". This means that when air is used up in a room, we "know" when we should open a window. We can "notice" when it becomes uncomfortable. Mostly, however, we then ventilate too much, i.e. the window (or door) simply stays open for far too long. If it is cooler outside, heating energy is wasted. So these sensors are not really "accurate". Or we simply forget to close or open the window again. And that's one of the reasons why there is technical support. There are sensors that remind us when we should ventilate. But there are also devices that actively support us in ventilating and take over some of the necessary work. We will find out later how these systems work and what they achieve. Basically, everyone should feel comfortable, no matter how and with what aids they ventilate. It should not be too loud in the flat (e.g. street noise), there should be no "draughts" and of course "fresh air" should get into the house. However, the primary aim is to reduce moisture that is generated in the building. Of course, there are also gases such as CO2 or softeners from furniture and much more that can and should be removed from the home with ventilation. However, moisture can cause by far the greatest damage in and to the building and has a significant impact on the health of the people who live there. So we ventilate to reduce moisture rather than for other reasons, because only with too much moisture can there be mould in the building or damage to building components, for example.