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