[dylan604]

It is amazing how tight we can make buildings today. I had to learn a lot about HVAC on a remodeling job a few years ago. I had no idea that the drywall can be sealed so tight that when the HVAC system is running it can be next to impossible to open a door without a pressure release duct. Also saw how the HVAC system had vents to bring in air from outside with baffles controlled by the system. Can't remember exact purpose something about helping help control humidity as well as regulation to bring in "fresh" air to mix with the "stale" air in the building.

So some parts of construction techniques and building materials have improved significantly. However, when comparing the framing lumber used today to what was used in the 60s, I'm shocked that new construction doesn't fall over the first time the wolf huffs and puffs.

[sparker72678]

The outdoor fresh air intakes are typically via ERVs (Energy recovery ventilation systems). These systems bring in fresh air, filter it, and typically run it through a heat exchanger to minimize energy losses as the fresh air comes and and the stale air goes out.

The purpose is to prevent buildup of harmful gasses and VOCs (everything from CO2 to CO to regular out-gassing of furnitures, etc) that can become dangerous if not cycled regularly.

[londons_explore]

2020: ”Poisonous stuff in our houses... Bad! Let's vent it to the environment!”

2120: The environment is all full of poisonous gasses from the people of 2020. Each house needs its own air purifier to make the outdoor air safe to breathe.

[MaxBarraclough]

This is already a reality.

> the first Cordis hotel on mainland China boasts something that is genuinely rare in big Chinese cities: clean indoor air.

https://www.theguardian.com/cities/2018/mar/27/china-clean-a...

[adrianN]

Luckily most organic compounds you find in indoor air aren't very stable.

[cyberdrunk]

> 2120: The environment is all full of poisonous gasses from the people of 2020. Each house needs its own air purifier to make the outdoor air safe to breathe.

That's the case in much of the world already... I live in area where there's tons of smog in the colder months and consider installing a system for bringing in filtered air from the outside, so that I won't have to open windows for the 6+ months smog period.

[userbinator]

It's been my experience that the newer high efficiency buildings seem to be optimising for that rather aggressively to the detriment of breathable air, because the air in them certainly feels a lot stuffier than in the older ones I've been in. I can certainly see building owners setting the recirculation as high as they can get away with, for the lowest cost.

[londons_explore]

"Stuffy" air is your body detecting CO2. You should totally do something about it.

[scottlamb]

> Also saw how the HVAC system had vents to bring in air from outside with baffles controlled by the system. Can't remember exact purpose something about helping help control humidity as well as regulation to bring in "fresh" air to mix with the "stale" air in the building.

One reason is efficiency. In the Bay Area, it's common when the daytime high temperature is 80–90˚F for the nighttime low to be 50–60˚F. You can set your thermostat to 76˚F until sunset, then bring in outside air to cool down to 68˚F or below by sunrise. You get cool air when you're trying to sleep and avoid running the AC in the night or morning.

I'm getting my furnace & AC replaced today and was sad to learn I couldn't get one of these. The fresh air intake has to be at least 10' from the furnace flue vent, and that isn't practical with my home's design.

[Scoundreller]

Can’t you run a pipe outside to extend the distance of your cold air intake?

[scottlamb]

The HVAC folks didn't seem to think that would be possible/practical. I don't know exactly why. It'd have to run along the top of the roof because I don't have an attic.

[lathiat]

Full Fresh Air is typically called an "economizer" at least in California. The idea of those is to save energy.

But there is also typically fresh air requirements to bring in some percentage of fresh air.

And lastly the HRV/ERV mentioned in the other comment is typically more a residential thing from what I've seen but that's totally a thing I want in my next house.

[akeck]

For regular posts on this topic, see the @buildingsciencefightclub Instagram account. Christine writes delightfully clear posts about modern building science.

[sd_mikey]

I also suggest Matt Risinger’s YouTube channel. Lately he’s been talking about Passive House construction, which supposedly uses only 10% of the energy of a standard built house.

[yourapostasy]

Adding to PassiveHaus and Passive House (separate standard from the original PassivHaus) standards, look into NetZero, and Perfect Wall (especially Lstiburek's institutional Perfect Wall).