ᐅ Solar or Ventilation? Energy Saving Regulations

Hello everyone,

…I have a small problem and would appreciate your expert advice 🙂

Next month, we will start building our single-family home. It will be a 1.5-story solid timber house made of vapor-permeable cross-laminated timber panels with about 170 sqm (1,830 sq ft) of living space.

The wall construction is as follows: cross-laminated timber (spruce, 100mm (4 inches)), Pavaflex wood fiber insulation (140mm (6 inches)), vapor-permeable breathable membrane (Rewa-Flex, 16mm (0.6 inches)), ventilation gap (30mm (1 inch)), OSB (18mm (0.7 inches)), and facade (dark stained planed spruce). The U-value of the exterior wall is 0.217 W/m²K (1.21 Btu/h·ft²·°F), and the moisture storage capacity (TA-value) is 29.7. The gable roof is covered with standing seam metal cladding.

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

There is still one open issue that leads to somewhat conflicting statements—depending on who you talk to :/ So I would like to ask for your experience: it concerns the implications of the energy-saving regulations. Our plumbing and heating installer informed us, as expected, that according to the energy-saving regulation we are required either to obtain part of our energy from renewable sources or to install additional technology to reduce energy demand. That’s all fine. He offered us two options: either two solar collectors with a corresponding 300-liter (79 gallons) storage tank, or a centralized ventilation system with heat recovery. The prices offered for both options are reasonable; my main concern is what makes more sense. The installer recommended the ventilation system because, he said, the solar option is not very effective. The roof does not have a south-facing orientation (but rather southeast), so you wouldn’t really notice the solar system. I can see some advantages of the ventilation system but I am not entirely convinced, for several reasons:

• The ventilation ducts need to be concealed and routed sensibly through the rooms (okay, this is a minor issue…)
• The filters must be cleaned or replaced regularly (does anyone have experience with what the costs for this are?)
• I have heard of cases where filters were contaminated with microbes despite regular maintenance, spreading mold spores through the ventilation system—despite the system’s purpose to prevent this
• It’s also reported that in some cases the relative indoor humidity drops so much in winter that it irritates the respiratory tract and eyes due to dryness—anyone with experience?
• The house is specifically designed to allow the walls to breathe—doesn’t a ventilation system contradict this concept?
• The ventilation transfers external noise inside and also has a noticeable operating noise

Indoor air quality is extremely important to us, which is partly why we decided on such an ecological building method (among other reasons, because of mold-related respiratory and skin conditions we struggle with). What would you do? Solar or ventilation? While the installer recommends the ventilation system (understandably, it also costs more), our architect has no strong preference... which makes our decision harder. I am not able to judge how effective the solar system would be. However, I do not want to commission something just because the energy-saving regulation requires it, only to find out later that this measure brings no real benefit.

Thank you for your help!
Best regards,

Willem

Use the ventilation system – even if, based on what you’ve heard, it seems like a widely installed torture device 😀
Your wall does not breathe – at least I hope so; otherwise, you can forget about the insulation and just move into a tent.
With central ventilation units, outside noise is usually limited; however, I wouldn’t place it in the utility room right next to the bedroom. But then again, I wouldn’t put the heating there either.

Hello!

When it comes to choosing between options, I would clearly recommend a ventilation system at this point. Central controlled residential ventilation with heat recovery. This provides more energy efficiency (at least on paper here) than a solar thermal system for domestic hot water heating. If you want a solar thermal system with heating support, you should definitely choose vacuum flat-plate collectors of the appropriate size, which are very expensive. Pure hot water support doesn't provide much benefit and also consumes electricity (circulation pump) and requires maintenance. I argue that the investment never really pays off (or only after more than 50 years). A nice gadget for an eco-conscious conscience.

I will address your questions below.

In general, I consider controlled residential ventilation to be very beneficial and positive, and I would always want to include one again in a new build.

Best regards
Thorsten

Willem81 schrieb:

• The ventilation ducts need to be concealed and routed sensibly through the rooms (okay, that’s a minor point...)
• Thorsten: Your plumbing designer will take care of that, no problem if they have experience.

• The filters need to be cleaned (or replaced?) regularly (does anyone have experience with the costs involved?)
• Thorsten: About 50 euros per year if I buy it at a premium price.

• I have heard of cases where filters, despite regular maintenance, were contaminated with germs, spreading mold spores through the ventilation system into the house — even though the system is supposed to prevent that
• Thorsten: Everything is possible, but I find that unlikely. Modern systems can and should be cleaned every 7-10 years with a specialized machine. Costs roughly 150 euros.

• It is also mentioned that some users experience a significant drop in relative humidity during winter, causing irritation of the respiratory tract and eyes due to dryness — does anyone have experience with this?
• Thorsten: That’s correct and physically inevitable. Here, the relative humidity stabilizes at around 29-34% at 21°C (70°F). I own a humidifier, which I use occasionally. Some ventilation systems can be equipped with integrated humidifiers or retrofitted with them.

• The house is specifically designed so the walls can breathe — doesn’t a ventilation system contradict that?
• Thorsten: Definitely not. The walls don’t breathe; the house is airtight. Here, you only have a diffusion-open construction method planned.

• The ventilation transmits noise from outside to inside and also has its own noticeable operating noise
• Thorsten: Audible noise only at the highest setting and then you really have to listen carefully. Otherwise, the system is not noticeable.

I definitely agree with using a controlled residential ventilation system!

Willem81 schrieb:
The ventilation ducts need to be properly enclosed and routed sensibly through the rooms (okay, that’s just a minor point...)

Easy work!

Willem81 schrieb:
The filters need to be cleaned regularly (or replaced?). Does anyone have experience with the related costs?

Yes, it takes about 2 minutes of work per month or roughly 20€ per year (unless you choose a system that doesn’t allow the use of custom-cut filter mats).

Willem81 schrieb:
I’ve heard of cases where despite regular maintenance, the filters were contaminated with germs, spreading mold spores through the ventilation system in the house – even though the system is supposed to prevent exactly that.

HEARD! Fungi and mold need moisture. The system dries the air (also inside the ducts), so with proper planning and installation, there should be no moisture inside the system.

Willem81 schrieb:
It’s also been said that during winter, the relative humidity drops so much that breathing passages and eyes get irritated by dryness – does anyone have experience with this?

Yes, it drops to around 30% in winter. We don’t find that problematic. However, there are units available with humidity recovery.

Willem81 schrieb:
The house is specifically designed so the walls can breathe – doesn’t a ventilation system contradict that?

Your house doesn’t breathe. If it does, I would sue the builder, because it wasn’t constructed properly. Modern houses are tightly sealed (and have to be) so that no air exchange happens naturally. That’s why a controlled residential ventilation system is necessary.

Willem81 schrieb:
The ventilation transmits noise from outside to inside and also has a noticeable operating noise.

Nonsense. With proper design, you only hear a faint rustling from the vents. But that only happens if the house is completely quiet and you are standing right in front of the vents. There is no noise transmission from outside or room to room.

These are very helpful answers – thank you! Yes, based on what you’ve said, the ventilation system definitely sounds like the better option to me, and you’ve addressed my concerns well 🙂

And your comments about solar ceilings match what our heating engineer told us. So it looks like we will go with a ventilation system with heat recovery!

How about the effectiveness? Have you noticed a significant saving in your heating energy?

No, but having fresh air constantly in the house is worth it.