I have a couple HEPA filters in my house that hopefully keep particulate exposure down. Does this mean that I have to run them longer? That I need more of them continuously running to keep exposure to VOCs low?
For VOCs you need activated charcoal/carbon filters usually and replace them from time to time.
Where I live all new houses are pressure tested and have a ventilation system, replacing all air once every 1-2 hours or something (I think).
> The lifetime of these compounds indoors can be extended via partitioning to the surface reservoir as modulated by ACR. Higher ACR, which may be achieved by opening windows or through mechanical ventilation, leads to shorter t_half_surf because once indoor compounds partition from the surface reservoir to the gas phase as controlled by gas diffusion across the boundary layer, they would be removed from indoor air more quickly before repartitioning to the surface reservoir.
So they do state active ventilation can help, as you reduce the vapor pressure of VOCs allowing them to partition back into the gaseous env, where they can be promptly ejected. How much exactly is hard to ascertain from their graph since I don't have the exact data they used in the plots. But from squinting at it, it seems 1 OOM change in ACR gives you close to 1 OOM change in the VOC half life, which seems substantial to me.
So adding an active ventilation system might be a good idea for this particular concern. Of course it will add to your energy bill.
Still worth it for better air quality.
And that's for the entire house, zero is such a small number.
Then when you run it 24/7 it's 24 times as effective compared to a single hour. That's an impressive multiple itself, on top of bumping the baseline above zero to begin with.
This can really add up to a lot more ventilation than commonly assumed from some of the crummiest fans.
If you can't tell the difference when you walk in, between zero and running one of these all day before you get there, you're gonna need a bigger fan.
But you may be surprised and you never know until you try.
Most of us don't eat wooden furniture -- granted my toddler didn't get the memo :)
Thus, continuous ventilation (while not perfect) is hopefully still a decent alternative. Probably better than active charcoal filter.
Granted I should probably out a charcoal filter on the ventilation intake to reduce pollutants coming in from nearby traffic. (All depending on your level of paranoia)
EDIT: And yes, charcoal filters aren't as effective if they're not part of your critical airflow/ventilation path. :D
What you're looking for are not HEPA filters but organic vapor filtering. If you were shopping for a respirator it would be easy but organic vapor extractors I think are a lot more expensive than HEPA filters. I looked in to it when I was doing a couple of oil based coatings for a home renovation project.
They won't do anything against VOCs, you need activated charcoal filters
The only difference are some materials like charcoal, which does permanently bind many substances (but as a result can also saturate).
No idea which kind lime and clay are (i.e. "absorb and permanently bind with limited capacity" or "act as a buffer both ways").
> Combined with a HEPA filter in the air circulation system
HEPA filters are not effective against VOCs.
Because carbon is such an effective adsorbent for contaminants, the partitioning coefficient for contaminants to remain in the solvent being filtered is lowered quite dramatically compared to so many other kinds of affordable alternative filtration media.
Most times people do need to afford to discard the carbon eventually, but it doesn't even really absorb contaminants like it's supposed to unless it is activated carbon to a good degree.
Activation only means that is it porous enough to begin with so it has enough surface area to be effective, then it is heated with adequate air exchange to about 250 Celsius for as many hours as it takes for virtually all of the VOC's or moisture it may have accumulated to be baked out. Then sealed up tightly, otherwise it can sit around for ages and gradually become saturated passively with any contaminants or humidity admitted through leaks to the ambient environment.
Sometimes, you can reactivate almost indefinitely to keep reusing the same carbon, and it works with VOCs because by their volatile nature they are basically baked back out easily and virtually completely each time. Different amounts of time if using different temperatures though, if equipped.
The stronger the activation, the more tightly with higher capacity the carbon wants to absorb things it encounters that are dissimilar to the fluid being filtered.
With clay the indoor problem is more about radioactivity, but it's best in terms of humidity control. Chalk creates an alkaline environment on the surface which makes it inhabitable for mold (however the wooden furniture you put in front of it can still get mold if the indoor air humidity is too high).
For clay I know you can add color pigments to the clay itself, most likely you can do the same with stucco for some limited amount of colors. But painting over it with modern products mostly destroys the diffusion properties.
Many people put plastics or other sealing products on top of a clay or lime-based wall and it's a shame.