ᐅ Heating of the incoming air in the duct

Hello,

We built a passive house and moved in around Easter. Unfortunately, we experienced an almost unbearable summer. Despite shading, the indoor temperature stayed above 26°C (79°F) almost continuously, even at night.

We have a ventilation system from Paul (Novus 450) with an active ground-source pre-cooling feature. The ventilation is not yet properly adjusted; it currently operates at about 30% higher airflow than necessary. The problem is that no matter the supply air temperature, the vents deliver roughly 0.5°C (0.9°F) less than the room temperature. Even with the active bypass engaged and supply air reduced to 16°C (61°F), the room temperature remains at 22.9°C (73°F) (our current indoor temperature without additional heating is 23.5°C (74°F)). The technician measured the values and said it was not optimal but still acceptable. However, I find that hard to believe, since we are sweating every night and don’t even get cooler air into the house overnight. Has anyone experienced something similar? Thanks for any help...

Best regards,

Thorsten

Can’t you just open the windows now that it’s cooler? Or did you avoid that? Otherwise, without air conditioning, it’s normal for it to get warm inside after a while, no matter how well insulated the building is. Only with good insulation does the heat take longer to escape. We also have a KfW70 house / energy saving ordinance 2009 standard and, so far, without heating, the indoor temperature is still comfortable. A real passive house is designed to be heated by normal household heat sources, so it shouldn’t get cold inside quickly. The only suggestion I have is to check if you have high humidity, as that can make a living space feel uncomfortable. In our case, humidity was relatively high during the first year because of moisture from screed, plaster, and such. But after the first winter, it improved.

Good morning,

We have opened the windows as well, so that is not the issue. The point is that the air being supplied is always close to room temperature because the airflow warms up inside the duct. Even when I activate the bypass and cool it down to 16°C (61°F), no cool air comes out. In that case, I could have saved money on the more expensive system with the heat exchanger if a few pipes alone were enough.

We also checked the temperature at the manifold in the utility room behind the ventilation unit; it is slightly above the outside temperature, so the bypass is working.

What experiences do you have with such systems? Ideally, the warming should only be around 1–2 degrees.

The heating of the pipes in my case is not that high. The pipe lengths are at most around 15 meters (50 feet), but most of the distance runs through the fully insulated yet unheated attic (which is usually below room temperature). From there, the pipes go down into the rooms within the insulated building envelope.

However, the thermal mass of the screed, plaster, etc., is so large that the small amount of air, even with a bypass, does not cool the house down. This also makes sense if you consider the heat capacity of air per cubic meter. I can definitely imagine that the air in longer pipes warms up slightly if they lie within the warm building envelope.

Yes, the pipes probably heat up beforehand, but this is the case for other people as well and has been mentioned several times.
What kind of active cooling are you using? There is no information on the manufacturer's website. They only offer geothermal heat exchangers.
Without the comment "active cooling," I would casually say the bypass is faulty or the outside temperature is high.

Hmm, I don’t see any problem; everything works as it should. The mechanical ventilation system is not designed for cooling but for ventilating, no matter what the salesperson told you...