Controlled residential ventilation system - maximum duct lengths - consequences?

I just came from my construction site and have the feeling that the execution of my controlled residential ventilation is going completely in the wrong direction.

Initial situation:
Actually, I wanted to subcontract the ventilation system trade entirely without dealing with it much. At the sanitation guy, a Wolf CWL 400 with 50x140cm flat duct was ordered. The company then installed the valves for the basement rooms in the filigree ceiling during the basement construction and left a few meters of pipe standing up. These were then supposed to be continued into the installation level of the timber frame house up to the attic.
Recently, I was offered to install the remaining pipes myself on a time and material basis, which we accepted.

The device is hanging in the attic on the gable wall above the bathroom. The two air distributors are directly in front of it. From there, all supply and exhaust air valves in the house are controlled. All flat ducts are connected so far, the supply and outdoor air are not connected yet.

The installer came by a few times, briefly checked if everything fit, and was done. I increasingly had the feeling that everything was done roughly and I was still surprised that there were apparently no guidelines or anything similar. Recently, I received the ventilation concept, which I have now studied more closely.

It mentions a minimum and maximum duct length of 5-15m. I complied with the 5m, but the maximum length is mercilessly exceeded for the basement rooms:

Basement room exhaust air 12.50m
Basement room supply air 20.00m
Basement utility room exhaust air 17.00m
Basement corridor supply air 15.80m
Basement supply exhaust air 13.30m
Basement WC exhaust air 8.50m

What exactly does a pipe that is too long cause? Can the ventilator no longer handle it then? I might pull the long 20m duct out again and save a few meters by routing it along the floor, but I will not reach the 15m limit. There are already 4 bends here alone.
Does it make sense to swap the much shorter exhaust air with the supply air?

Other things I noticed:

-We were not provided with fixed bends and bent everything ourselves. Especially the 90-degree transition from floor to wall looks like in the pictures. Due to the kink, the pipe is somewhat compressed; what consequences can this cause?



Attached is also my ventilation concept

pretty messed up... The pressure losses for each individual pipe must be calculated precisely, especially including those great bends like in your photo. With 20 m of such bends (which is not done like that), nothing reaches the end anymore, all the air then comes from a valve upstairs, which is only 5 m away. That must of course be regulated, but probably turned down so far that nothing comes out anywhere anymore. You can't clean anything there anymore either, in case that ever becomes necessary. Have a proper plan made, and then start again, otherwise you might as well save your money.

New again is no longer, the material has now already been installed and also paid for. I was there again today, I could actually shorten the 20m length to about 15-16m by a different routing. The bends can also be replaced by the angles, which I will probably do as well. I should pass on the bends to the planner again so that the throttling discs can be calculated.

What was also noticeable is the high air volume according to the ventilation concept. This was based on the living area and not on the number of people. I have also posted the document in other forums in parallel. There are different opinions here:

-too high volume flows and air volume, resulting in more noise propagation in the ducts

-due to the high air volumes, the system can be operated at a low level, which in turn means less noise and lower energy costs.

What do you think about it?

You have several "problems":

1) (too) long ducts
2) ducts are flat-channel
3) kinks in the duct
4) as it sounds, there is only one duct per valve
5) the ducts have very different lengths

That means, on the one hand, you have very high pressure losses in the system and, depending on the room, you will have to push (too) much air through these ducts. This results, on the one hand, in a very high load on your central unit and the associated noise, and on the other hand, you will very likely have clearly noticeable flow noise at some valves.

By the way, I consider the unit undersized for the air volumes. Even at nominal ventilation, the unit runs at 84% capacity. For the volumes during intensive ventilation, it is definitely not sufficient anymore.

Regarding your comments from other forums: I would agree with the first one; the second, as it stands there, is nonsense. Did you misunderstand/misrepresent it?
A system can then be operated at a lower level if it has potential performance reserves. That is why it usually makes sense to size a controlled residential ventilation system larger than actually needed on paper.

1. The long ducts have been taken care of except for minimal exceedances.

2. Flat ducting was necessary because of the timber frame house with an installation level.

3. These are also unavoidable with valves in the ceiling.

4. This is how the manufacturer specified it. I would have found it impossible to fit two ducts per valve inside the walls.

5. Yes, that's true. However, I wonder what the alternative would have been for a 3-story house? The air distributor should be placed as close as possible to the unit, and the unit itself can only be in the technical room in the basement or in the attic.

The unit itself is already the largest that Wolf offers for private households; there is nothing bigger. I agree with you that the system has quite a lot of work to do. The question here would be whether the calculated air volumes are actually needed? Per person (later 4, currently 2 1/2) that is over 80 m³/h.
This is also the starting point of the second statement from another forum, that the system can actually be operated at a lower stage with less volume; in the basement there are subordinate rooms anyway ([Partyraum], [Gäste-WC], [Technikd] and [Hauswirtschaftsraum]).

By the way, Wolf has planning software available for download on the website. If you're interested yourself, you can recalculate everything.