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Comment by mitxela | Hacker News Reader

What if it's only 1% of air escaping

Then it's 100x oversized for the purpose of pressurizing the structure. ;)

ERVs are great for increasing air exchange (two-way flow), but unnecessary when pressurizing because that's one-way flow by definition.

If you already bought an ERV it makes sense to combine the functions, simply because you already bought the expensive ERV hardware. But if you weren't planning to install an ERV anyway, it doesn't make sense to install one just for this project, because it won't do anything to reduce the heating/cooling loss from this type of system.

The one-way component of flow is still 100% non-recuperated. If you install a cheap 100 CFM positive pressure system and it burns an extra $100, then setting your ERV to be unbalanced by 100 CFM will cost that same $100. Same leak rate, same heat loss, same cost!

This is one of those deceptive math problems where it seems like it should work, but really it works out "six of one and half-dozen of the other."

I didn't understand the purpose as pressurising the structure. I understood the purpose as ventilating the interior, providing a central place to attach a filter, and preventing air from coming in from other places.

Yes, exactly! If you're ventilating the interior then using an ERV makes sense. If you're preventing air from coming in from other places, then the ERV doesn't save anything, because (intentionally) 100% of the incoming airflow is leaking out somewhere, so there's nothing for the ERV to do.

I edited my post above to hopefully make it a bit more clear, but it seems you get it right away! Cheers

Right but they didn't want to stop air coming in. They just wanted all incoming air to be filtered.

  >they didn't want to stop air coming in

They did, though! The entire point of positively pressurizing a structure is that any small leaks will instead result in clean air leaking out, which prevents dirty air from leaking in. This is how (most) cleanrooms work.

That's so the one central point of air ingress is the one with the filter. Air still gets in - through the filter.

Bingo.

The neat thing is, if you're already accepting this heat loss penalty anyway (in the service of positive pressure), it greatly reduces or even eliminates the ERV you need to maintain good indoor CO2. So in addition to better indoor AQI, positive pressure can greatly reduce total equipment cost.

Seems like a win/win to me!

Buckminster Fuller proposed a similar scheme in his Dymaxion House (even removing dust via baseboard vents), but it used passive heating and cooling so there was little penalty.

Are you an AI? You just spent several comments arguing against something you now claim to agree with.

Huh? No, my position has always been that an ERV doesn't make sense to combine with this project unless you wanted or have an ERV in your home anyway (and actually this can replace an ERV in some cases). This remains unchanged.

No AI of course.

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