Solar or ventilation? Energy Saving Ordinance

Hello everyone,

...I have a small problem and need your expert help :)

We are starting the construction of our single-family house next month. It is a 1.5-story solid wood house made of diffusion-open cross-laminated timber panels with about 170sqm of living space.

The wall structure looks like this: cross-laminated timber (spruce, 100mm), Pavaflex wood fiber insulation (140mm), diffusion-open underlay membrane (Rewa-Flex, 16mm), ventilation gap (30mm), OSB (18mm) and facade (dark stained rough-sawn spruce wood). The U-value of the exterior wall is 0.217 W/m2, the TA value is 29.7. The gable roof is covered with standing seam metal roofing.

We have a gas condensing boiler and are installing underfloor heating with separate heating circuits for the different rooms or usage zones. So far so good, everything coordinated between our architect and the plumbing guy and approved by us.

Now there is one open point that leads to somewhat contradictory statements – depending on whom you talk to :/ Therefore, I would like to ask you for your experiences: it concerns the consequences of the Energy Saving Ordinance. Our plumbing and heating installer has informed us – as is appropriate – that according to the Energy Saving Ordinance we are obliged to generate part of our energy from renewable energy sources or alternatively to install more technology to reduce energy demand. So far so good. He offered us two options: either two solar collectors with a corresponding 300l storage tank, or a central ventilation unit with heat recovery. The prices offered are completely fine for both items; for me it’s primarily about what makes more sense. The plumbing guy said we should choose the ventilation system because the solar thing didn’t make much sense. The roof does not have a south orientation (but a southeast orientation instead) and one wouldn’t really notice the system’s effect. Basically, I can see some positive aspects of the ventilation system, but I also don’t like it unconditionally. And that for several reasons:

[*]the ventilation ducts must be covered and sensibly routed through the rooms (ok, that’s just a minor point...)
[*]the filters must be cleaned (or replaced?) regularly (does anyone have experience regarding the costs?)
[*]I have heard of cases where the filters were contaminated with germs despite regular maintenance and so mold spores were distributed throughout the house via the ventilation – even though the ventilation system is supposed to do exactly the opposite
[*]it is also reported that for some users the relative humidity in winter drops so much that airways and eyes become irritated from dryness – does anyone have experience with this?
[*]the house is deliberately designed so that the walls can breathe – doesn’t a ventilation system contradict this?
[*]the ventilation transmits sound from outside to inside and also has a perceptible operating noise

The quality of the air is extremely important to us right now, which is also the reason why we decided on such an ecological building method in the first place (among other things because of mold-related respiratory and skin diseases we struggle with). What would you do? Solar or ventilation? While the plumbing guy recommends the ventilation system (clear, it also costs more), our architect doesn’t have a clear preference... which makes it somewhat harder for us. I can’t judge how effective the solar system would be. But I also don’t want to commission something just because the Energy Saving Ordinance requires it, and later find out that this measure brings no benefit.

Thank you for your help!
Best regards,

Willem

Take the ventilation system - even if, according to what you've heard, it seems to be a torture device installed millions of times :D Your wall doesn't breathe - at least I hope not; otherwise, you might as well skip the insulation and move into a tent. With central systems, the noise from outside is limited; however, I wouldn't put it in the utility room right next to the bedroom; then again, I wouldn’t put the heating there either.

Hello!

When it comes to choosing one or the other, I would clearly recommend the ventilation system at this point. Central controlled residential ventilation with heat recovery. This provides more energy benefits (at least on paper in our case) than the thermal solar system for domestic hot water heating. If you want a TSA with heating support, you should definitely choose vacuum flat tube collectors of the appropriate size; these are very expensive. Pure hot water support doesn't bring much, also costs electricity (circulation pump) and maintenance. I claim that the investment never pays off (or only after > 50 years). A nice gimmick for the environmental conscience.

I will address your questions below.

In general, I see controlled residential ventilation as very enriching and positive and would always want to use one in new buildings again.

Best regards
Thorsten

[*]the ventilation ducts must be clad and sensibly routed through the rooms (ok, that's just a small point...)
[*]Thorsten: Your sanitary planner does that, no problem if he has experience.

[*]the filters must be cleaned regularly (or replaced?) (does anyone have experience with what the costs look like?)
[*]Thorsten: 50 euros per year if I buy it expensive.

[*]I have heard of cases where filters were contaminated with germs despite regular maintenance and spores of mold fungi spread through the ventilation in the house – and this although the ventilation system is supposed to do exactly the opposite
[*]Thorsten: Everything is possible, but I consider that unlikely. Modern systems can and should also be cleaned with a special machine every 7-10 years. Costs about 150 euros.

[*]it is also read that in some users in winter the relative humidity decreases so much that airways and eyes are irritated by dryness – does anyone have experience with this?
[*]Thorsten: That is correct and physically caused. In our case, the relative humidity stabilizes at around 29-34% at 21 degrees room temperature. I have a humidifier that is used occasionally. Some ventilation systems can be retrofitted with integrated humidifiers or have them from the start.

[*]the house is deliberately designed so that the walls can breathe – doesn’t a ventilation system make this absurd?
[*]Thorsten: Definitely not. The walls do not breathe; the house is airtight. In your case, only a diffusion-open building method is planned.

[*]the ventilation transmits sound from outside to inside and also has a noticeable self-noise
[*]Thorsten: Audible noise – only at the highest level and then you have to listen carefully. Otherwise, the system is not perceived.

Definitely join the controlled residential ventilation!

the ventilation ducts must be covered and routed sensibly through the rooms (ok, that’s just a small point...)

Simple work!

the filters must be cleaned regularly (or replaced?) (does anyone have experience with what the costs look like?)

Yes, it takes 2 minutes of work per month or about €20 per year (as long as you don’t use a system where you can’t insert self-cut filter mats)

I have heard of cases where the filters, despite regular maintenance, were contaminated with germs and thus spores of mold fungi spread through the ventilation in the house – even though the ventilation system is supposed to do the exact opposite

HEARD! Fungi, mold need moisture. The system dries out the air (also in the ducts), so with proper planning/installation there can be no moisture in the system.

it is also said that for some users the relative humidity drops so much in winter that respiratory tracts and eyes are irritated by dryness – does anyone have experience with this?

Yes, it sinks to about 30% in winter. We don’t find that bad though. However, there are also devices with humidity recovery.

the house is deliberately designed so that the walls can breathe – doesn’t a ventilation system contradict that?

Your house doesn’t breathe. If it does, I would sue the construction company because then it wasn’t built properly.
Nowadays houses are sealed so tightly (they have to be) that no air exchange takes place anymore. That’s exactly why controlled residential ventilation is needed.

the ventilation transmits sound from outside to inside and also has a noticeable own noise level

Nonsense. With proper planning, you only hear a fine rustling from the valves. But for that, the house must be completely silent and you standing directly in front of the valves. There is no sound transmission from outside or from room to room.

These are very helpful answers - thank you! Yes, from what you say, the ventilation system definitely sounds like the better option to me, you were able to dispel my concerns well :) And your statements regarding solar panels align with what our heating engineer said. So it will probably come down to the ventilation system with heat recovery! How about the effectiveness? Do you notice a significant saving in your heating energy?

No, but having fresh air in the house all the time is worth it