[cjlars]

I recently retrofit a new HVAC system and as a result have also gone on a bit of a deep dive on indoor air quality. The big thing I learned is that most homes -- even old "leaky" builds -- have rather poor ventilation, meaning all sorts of compounds build up in the air... CO2, formaldehyde, VOCs, PFAS, etc. Air purifiers work for particulate, but don't really make a dent for chemicals. IIRC, You would need like a 50 gallon drum of activated carbon to do anything on the chemical front.

A quick solution is to crack the windows, or if you live in a non-temperate climate, install an energy recovery ventilating system.

[verisimilitude]

Energy Recovery Ventilators or Heat Recovery Ventilators are absolutely essential (and, I think, part of code in many places!) in this era of tight and sometimes extraordinarily tight (e.g. Passivhaus) home building.

When we bought our home, the HRV wasn't working and once I replaced a bunch of parts in it, the difference in the quality of the air was noticeable just in the fact that it smelled fresh like the outdoors.

In your deep dive, you probably ran into the evergreen debate about running ERV/HRVs in the summer... I just gave up, turn it off when we run the A/C and open the windows occasionally... BUT I think you could probably run a humidistat/hygrostat hooked to the HRV (a common option in the new units, I believe).

[darkteflon]

I’m based in Tokyo and have spent the past few months going down the rabbit hole of indoor air quality. It started out of concern for the health of our four-year old - lots of time indoors on account of the pandemic, etc.

We have HEPA filters in every room now and portable CO2, PM2.5, VOC monitors, etc for keeping an eye on things. As others have stated, however, this does nothing to address the VOC issue and so I am very keen to take the additional step of installing an Energy Recovery Ventilator or Heat Recovery Ventilator, as you suggest.

If anyone here has Japan or Tokyo-specific information on manufacturers, suitable systems and/or contractors capable of doing the work, I for one would certainly be grateful to hear it!

[cjlars]

I'm in SF. The tricky thing here is that outdoor humidity is often so high that a humidistat would only result in an 'always on' system. I think CO2 is an objectively better measure anyway. You can remove humidity and particulate with energy efficient machines. You can't (realistically) do that with CO2 / VOCs.

[bumby]

Did you find any industry ventilation standards related to all the compounds you listed? IIRC, ASHRAE 60.1 is the industry standard but years ago at least, it was based mainly on using "bio-effluence" as a proxy for air quality. I.e., reducing stink.

>install an energy recovery ventilating system.

These are a good idea, but the exact type is important or else you risk cross-contamination between the exhaust and intake. That's why many designs (e.g., heat recovery wheels) are generally banned in some applications like healthcare.

With the crowd that HN attracts, I'd be interested if anybody has implemented some sort of demand-control ventilation in their home.

[cjlars]

I think an ideal heat recovery system would probably sit mid-stream in a central air system with a built in CO2 trigger. Basically, the return air gets exhausted while heating the incoming/supply air when CO2 concentration > X. Obviously you run into the capex vs ongoing energy cost tradeoff in designing the system.

Strangely, I couldn't find a ventilator on market with a CO2 sensor, but there are plenty with humidity sensors. I think CO2 sensors are on the horizon though, here's a study featuring such a system: https://core.ac.uk/download/pdf/43245317.pdf

My current system is actually ductless however, so I will probably have to rely on natural diffusion... I do have an air quality monitor which indicates that diffusion is likely sufficient (for a one floor open plan condo), but you'll optimally need to sleep with the bedroom doors open.

Edit: I haven't looked too deeply at the standards. My little sensor indicates that if you keep CO2 in range, VOCs will also also be in range, which conforms with my intuition.

[EricE]

CO2 sensors are common in commercial HVAC systems - especially for large auditoriums or rooms where you expect high occupancy. Economizers will automatically open to increase the exchange of outside air. My church has an auditorium that can seat up to 1500 - all four AC units have CO2 detection built into them and the concentration is displayed on the controls too.

[bumby]

>Basically, the return air gets exhausted while heating the incoming/supply air when CO2 concentration > X.

That’s the basic idea of demand control ventilation but how are the two air streams interfacing? If our concern is air quality, how is cross contamination between the two mitigated?

[cjlars]

I was confused at first by a lot of diagrams I found online, but the wiki is pretty good. Basically think of a two way radiator. Hot air flows through air channel blades on the way out, cold air flows around the blades on the way in, with filtering optional at this point. Some systems indicate that they literally mix the air, which is obviously not going to be optimal, the air needs to be fully separated with the energy exchanging through a metal layer.

https://en.wikipedia.org/wiki/Energy_recovery_ventilation