Ventilation system in single-family house without effect = planning error?

Whoever vandalized the facility should really be ashamed of themselves. I would definitely change a few things as already suggested here. For example, reposition valves, etc.

Whoever messed up the system should really be ashamed. I would definitely change a few things as already suggested here. For example, relocating valves etc.

Do you see any other sources of errors that may not have been mentioned here yet? The position of the valves will probably have to be changed, I understand that. Not nice, but well, what can you do....

Despite the need for optimization, the air on the ground floor should not be "used up" in the morning, right?

I would also measure CO2. Could the guest perhaps be something else, like floor coverings?

And can you show a photo of the "chimneys are the required >2.5m"? Just in case there can be short circuits between supply and exhaust air.

The position of the valves will probably have to be changed

Not only that. The system would then have to be recalculated (Wolf offers a free tool on their website) since the pipe lengths will change. Therefore, the system must also be remeasured afterwards, and if necessary, the sizes of the valves adjusted. Possibly also consider switching to a somewhat smarter control system and installing VOC sensors in the bedroom and/or living room.

Despite the need for optimization, the air on the ground floor shouldn’t be "used up" in the morning, right?

Yes, I would actually assume that too – hence the question whether there are other spots that might be relevant. Also, that dust is already coming out of the inlets after just two years seems a bit "suspicious" to me. I change the filters in the device almost monthly.

I would also measure CO2. Maybe the guest room has something else, like floor coverings?

I ordered a CO2 meter (Netatmo due to connection to iobroker/KNX). I obviously cannot rule out emissions from floors. The ground floor is completely tiled. The upper floor is fully laminated except for the bathroom, which is also tiled.

And can you show a photo of the "chimneys are the required >2.5m"? Just to make sure there can’t be any short circuits there.

I’m attaching it. However, I’m considering relocating them to the north side of the building, partly to create space for photovoltaic modules and partly to get them "out of the sun." I also expect somewhat cooler air in summer from this.

Currently, the intake is next to the chimney – no stove/fireplace is installed. Therefore, no interference should occur.
The outlet is next to the chimney of the gas condensing boiler.

Not only that. The system would then have to be recalculated (Wolf has a free tool on the website) as pipe lengths will change. Therefore, the system must also be re-measured afterwards and, if necessary, the sizes of the valves adjusted. Possibly also consider a somewhat more intelligent control system and install VOC sensors in the bedroom and/or living area.

I am actually doing that by currently setting up VOC/CO2 measuring systems and want to use them to control the ventilation system/later also the air conditioning via KNX.

I will take a look at the tool. Hopefully, a Wolf field service technician will come next week to take a look.