Rotary heat exchanger and hygiene

Hello everyone,

I would need your opinions and assessments on the following topic. We are planning a central controlled residential ventilation system with moisture recovery. I do not want to discuss the purpose and usefulness of this here, as it could probably escalate into a war of beliefs.

We are considering a rotary heat exchanger because we are attracted by the controllable moisture recovery and especially the fact that no condensate drain is necessary. An Austrian website on comfort ventilation presents the different types of rotors and mentions rotors without coating and with coating for moisture recovery (enthalpy or sorption). An inquiry with our preferred manufacturer revealed that "our" rotor consists only of aluminum and does not have a coating.

Now, on the same page in a brochure on this topic, there is a passage that reads:

The type of surface texture of rotors determines their ability to transfer moisture. There are basically condensation rotors, enthalpy and sorption rotors, whereby condensation rotors, as the name suggests, can only transfer moisture when condensate occurs, which is considered hygienically questionable. Condensation rotors generally do not allow effective influence on indoor air humidity.

I therefore assume that our rotor is a condensation rotor. Does anyone have any idea / clue what "which is considered hygienically questionable" is supposed to mean here or what is meant by this?

Interestingly, I cannot find any other connection between hygienic concerns and rotor type elsewhere. Would you therefore ignore the note or take it seriously when selecting the heat exchanger?

Background:
The manufacturer offers the planning that makes the most sense for our floor plan in terms of the duct system – also with ceiling outlets in the basement, ground floor and upper floor, which we definitely prefer over floor or wall outlets. Almost every other provider (of plate heat exchangers) would at least in the upper floor (bedroom, children’s rooms, bathroom, etc.) work with floor outlets... hence the question: what would you do or recommend? Ignore the note "considered not entirely hygienically flawless" or bite the bullet and choose floor outlets?

Thank you very much and best regards!

In the rotary heat exchanger, moisture is transferred directly, there is a slip between the exhaust and supply air. The enthalpy heat exchanger is permanently more hygienically reliable than the plate heat exchanger. Nevertheless, rotary heat exchangers are also an established technology.

How important is moisture recovery to you? In the proposed design, it only takes place during condensation.

In my opinion, floor outlets are not a disadvantage. The duct network can be shorter (pressure loss) and no one will experience unpleasant drafts in the neck/head area.

How important is humidity recovery to you? In the proposed version, it only occurs during condensation.

In my opinion, floor outlets are not a disadvantage. The duct network can be shorter (pressure loss) and no one will feel unpleasant drafts at the neck/head area.

HRV is very important to us since my wife and I both wear contact lenses and immediately notice too dry air. However, our "provider" / manufacturer informed us that in their own tests and many installed houses, the HRV was always at least 50% even in winter, which would be completely sufficient.

Now I don’t want to be more naive than I already am, but due to lack of information, one inevitably has to trust the "professional," as there is nothing contrary at hand.

So the hygienic concerns would be justified by internal leakage? The manufacturer referred in this context to the leakage proven and passed by the PHI-Institute (I think it was) < 3%. Besides the PHI certificate, the device also has the EUROVENT certification, whatever significance that may have...

Regarding the floor outlet: drafts should not occur with correct design of volume flow and duct cross-section for ceiling vents either, right? On the other hand, floor outlets are said to pose a possible risk of "cold air pockets." Is that true?
At least the point is plausible that things could fall into the floor outlets (liquids, "toys"), and at least certain restrictions in furniture positioning are likely, right?

The outlet is placed, for example, in front of/under the window, where naturally there is no furniture anyway. Liquids are collected by a "siphon," so they do not simply run into the pipe. Cold air pool ... well, with heat recovery >80% there should be nothing noticeable, especially since the air is in motion. The only disadvantage I see is the additional cost of floor outlets (nice stainless steel grilles plus extra effort when laying the flooring). On the other hand, the piping is shorter/simpler.

The outlet comes, for example, in front of/under the window, as there naturally aren’t any furniture there anyway.

Maybe desks?

Cold air pool ... well, with heat recovery >80% nothing should be noticeable there, especially since the air is moving.

Hm.... is that thermodynamically different with ceiling outlets then? There is a recommendation not to plan those things near the head area because of possible drafts.

No idea if there is any truth to that or if people generally worry too much about it...

Cleaning floor outlets/inlets can be quite unpleasant if you have pets.. Something will definitely end up in there (especially with cats). I also think that people tend to be more restricted with floor things, because you are much less likely to place something ceiling-high in the rooms than something on the floor.. These don't have to be cabinets either, runners, small furniture, decorative items as well as changes to the flooring are then less easy. Besides, exhaust air should also rather be at the top, so overall you probably won't save that much. Depending on where the [Kontrollierte-Wohnraumlüftung] is located, even less (if it is on the attic, the route to the ceiling is shorter, for example)....