How many cubic meters per hour do I need for good indoor air quality?

You have managed to perfect my confusion ;-)

But it's true, I won't be able to calculate everything myself, and will certainly be happy to hand it over to professional hands.

Still, I had hoped that one of you could at least roughly explain to me how these two different and significantly differing calculation models come together in practice.

Let's stick to this one example:

Guest room (for 2 persons, 11 m² with 2.55 m room height = 28.05 m³):

1. Calculation method with air exchange rate of 0.3:
8.42 m³/h

2. Calculation method with 25 m³/h per person:
50 m³/h

The results regarding the air exchange are extremely different; both cannot be correct. But why are there both calculation methods?

Or have I completely misunderstood something here?

1. Calculation method with air exchange rate of 0.3:
8.42 m³/h

2. Calculation method with 25 m³/h per person:
50 m³/h

The results regarding the air exchange are extremely different, both cannot be correct. But why are there both calculation methods?

Do two people live permanently around the clock in the guest room at your place?
If yes, okay, if not, I find 50 m³/h exaggerated in the example. Just imagine if the room you stay in were completely ventilated twice per hour.

Are there permanently two people living around the clock in the guest room at your place?

I think you are drawing several conclusions at once again: in my opinion, the OP is more concerned with the calculation principle itself; adding all maximum values would of course be a bit excessive for the design of a central system.

Your second "calculation method" is not a second one but refers to the total volume flow from outside. So you include all rooms there, and in total that should then be met.

I think you are drawing several conclusions at once again: in my opinion, the OP is more concerned with the calculation principle itself; adding all maximum values would, of course, be somewhat exaggerated for the design of a central system.

But you have read his calculations, right? These are simply applied incorrectly, see post by . It makes no sense to fictitiously place people permanently in every room, to use this as the design basis, and thus to mercilessly oversize all the rooms. Hence the question whether he houses people in the guest room around the clock.

The first calculation method leads him, with 500m³ building interior volume, to a device sizing in the entry-level to mid-range class. The second method, as applied by the OP, is probably not encountered in single-family homes.

It makes no sense to fictitiously place people permanently in every room and thus relentlessly oversize all the rooms.

Of course not. Mis-sizing - whether over- or under- - is always a top-class efficiency killer.