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this post was submitted on 07 Aug 2023
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Today I Learned
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To people who says "they aren't airtight" are not correct. Living in a country where building houses like this is the norm I can say that they are build to be as airtight as possible to keep in humidity and thereby heat inside. What makes them livable and not a humid moldy plastic bag is a well tuned mechanical ventilation system with a heat regeneration system (air cross flow system, really simple actually) that recovers most of the heat. The ventilation system runs 24/7 and keep the air fresh, more fresh than most conventional houses in fact if it's tuned correctly that is. But yes the house is as airtight as posible and they pressure test them to ensure they meet the standards. The biggest issue with it is actually cooling them. We have issues here in summer because no method of removing heat is properly implemented yet. But in winter it's awesome. My heating bill is practically 0.
I moved into one of these buildings about 1.5 years ago and it's indeed awesome. We also have no gas and tons of solar panels on the roof so last year with the insane energy prices in the whole of Europe I spend €2,83 for all my energy including heating for 8 months, and I'm easily cold so I always have the heating on. The only problem is as you say to get rid of heat in summer, but they opted for smaller windows than is standard so less heat is getting in in the first place. And because of the great insulation you also have pretty much no traffic noise from outside. The only complaint I have is that the mechanical ventilation can get quite loud when it's windy outside, but the benefits are so overwhelming I can't be that bothered by it.
So from the article it seems that when the passive air vents are closed the total flow of air is supposed to be less than 10m³/hm². The air flow that occurs during the test is from cracks and leaks in the fixtures and doors. Calling it airtight might be confusing since people assume that would mean zero net flow.
I can see that might being confusing if you are not used to it, but houses are build to be "as airtight as practically posible" of course you could never bild a normal hous as airtight as a spaceship, but if you look at windows doors etc of a passive house you'd see rubber gaskets and seals everywhere. New tech keeps coming up. All houses since early 2000 here are required to have an inner airtight membrane and there are strict requirements about how to apply it. All seams, corners and nail holes etc. must be taped with special membrane tape. In theory the only holes in the house should be the ventilation system. I'm my current apartment even the kitchen hood is connected to the ventilation system so when it runs and an even amount of air is being exhausted and injected back into the house to avoid any pressure differential, minimizing leaks from the inevitable tiny leaks here and there. Airtight is the goal and we are damn close. Many houses are also better than the standards to account for small leaks over time.
Genuine question: if they're airtight, how do oxygen and CO2 levels remain livable? Spacecraft and submersibles require oxygen supply and CO2 scrubbers to keep occupants alive.
The ventilation system was explained.
I suppose what trips me up is that my brain sees the concepts of "airtight" and "ventilated" to be in conflict and I am seeking further clarification than what has already been provided.
The idea is that air exchange mostly happens through a heat exchanger, so the air leaving the house warms up the air that is entering the house, for this to actually work all other parts of the place need to be airtight, because otherwise your heat escapes.
I guess this is just a looser interpretation of "airtight" than what I've previously experienced in life. In my experience, "airtight" means "zero exchange of air in or out", but this setup is a controlled process where the only place air exchange occurs is through the heat exchanger. However, from these descriptions, it's not the same sort of "airtight" as what I'm accustomed to. Not trying to say that anyone is incorrect, just that it's different from what's familiar to me and that's why I was confused.
At least In NL, what you can do for cooling is to have cold water run through your in-floor heating. Brings things down to about 2-3C under ambient, so not perfect by any means, but a lot more pleasant than without it.
Unfortunately it's considered an optional upgrade that you can only really get when buying a newly built home and most people skip it in favour of things like a fancier kitchen.