Volume flow rate specification of controlled residential ventilation for heating load calculation

Hello everyone,

I think I need your expertise again.
I originally did not want to install ventilation during the house renovation, but after seeing in the energy consultant's calculations how much heat loss he assumes for the ventilation, I decided to install 2 decentralized ventilation systems in the open kitchen-living area. I did not involve any expert for this.
Now the volume flow of the ventilation is requested for the exact heating load calculation of the heat pump, and before I provide any total nonsense here, I wanted your opinion on my calculation:

So, it is about an approx. 57m2 large open living-kitchen-dining area according to the floor plan. Ceiling height 2.68m. That makes a volume of 153m3. However, there will be quite a bit of furniture in this room, such as a fitted kitchen, fireplace, large fridge, couch, sideboards, etc., which I subtract from the room volume.
Let's say roughly minus 10m3. Remaining 143m3 of room air volume.

Now we come to the point where I am unsure. I have 2x Blauberg Vento Expert A-50, which will operate in counter phase. One blows air in and one out.
That should mean the double moved air. So everything times 2.
The fan has 3 levels with heat recovery
Level 1: 8 m3/h
Level 2: 15 m3/h
Level 3: 25 m3/h
Additionally, the data sheet states a max. exhaust air volume flow of 50 m3/h.

Now I am unsure which value I should take. For acoustic reasons, most probably run the system at level 2. Since I have 2 fans, that would be 2 x 15 m3/h = 30 m3/h. That is then my volume flow in this room, right?
Or do you take the highest possible value of 2x25 m3/h here, or a combination of 2/3 at level 2 and 1/3 at level 3?

I only need the room volume for the air exchange rate (That would be with 30 m3/h for me 143m3 / 30 m3/h = 0.21 1/h, which is below the recommended 0.5).

Does anyone here know better than I do??

Do not double. 15 go in, 15 go out. Then you have changed 15, not 30.

As you yourself have already noticed, the volume of your devices is far too low for the described room

Don't double it. 15 go in, 15 go out. Then you have exchanged 15, not 30.

As you already notice yourself, the volume of your devices is far too low for the described room

and on level three too loud for a higher air exchange rate, especially for the open living, kitchen, dining area :oops:

A decentralized controlled residential ventilation is modest, at least everything I have seen or heard so far. But please feel free to prove me wrong.

Do not double. 15 go in, 15 go out. Then you have exchanged 15, not 30.

As you already noticed yourself, the volume of your devices is far too low for the described room

Somehow sounds logical and yet confusing that 2 systems should have no effect on the volume flow compared to one.
The counteracting operation is then only a support of each other’s fan to reduce the resistance they have to work against.

and too loud at level three for a higher air exchange rate, especially for the open living, kitchen, dining area :oops:

A decentralized controlled residential ventilation is modest, at least everything I have seen or heard so far. But please feel free to prove me otherwise.

Yep, I fully agree with you. That’s why the original decision was against it. But then about 40% of the total heat loss was stated for the ventilation. Since energy costs are not getting lower, I wanted to achieve a reduction in the room where people will most likely stay the most. And only during the heating months. In summer the terrace door is almost always open.

But decentralized controlled residential ventilation really is not the holy grail.

It's not just about being there, and even if it is, it's usually the bedroom. The bathrooms are also important to avoid mold. In the large living area, there must be either more or bigger ones.

Sounds somehow logical and yet confusing that 2 systems should not affect the volume flow rate against each other. The counteracting operation is then only a support of each fan to reduce the resistance against which it has to work.

You have to look at the conditions. 15 m³/h with 150 m³ room volume is 10%. But it does not work permanently blowing in or out but in pendulum mode, i.e. it blows a good bathtub full of air into this large room, then switches and blows the amount out again. If you only have one fan, this will hardly change the pressure conditions in the room, the resistance is very low. With 2 fans, the other respectively absorbs this minimal pressure change. But since it always works in the opposite direction, this will hardly change the volume flow rate.