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Is it standard practice for commercial HVAC to have some kind of UV light/ozone/X pathogen killing mechanism somewhere in the ducts? Or would that only be insta

Is it standard practice for commercial HVAC to have some kind of UV light/ozone/X pathogen killing mechanism somewhere in the ducts? Or would that only be installed on a HEPA style system going for a certified clean environment? I would naively think that exposing the forced airflow to the treatment would be both simpler and safer than installing a system into every room with people.

bradknowles 5y ago
We have UV filters on our HVAC units here at our house, in addition to the whole-house HEPA filters. They’re expensive, but if you have a lot of allergies, IMO they are well worth the extra cost.
DannyBee 5y ago
It's not standard because you can just use filters. Keep in mind the filters have to be able to filter the dead pathogens anyway (usually same size) or else you are breathing them, which isn't great either. Better than live ones for sure, but not great. As for UV, you can add it to either residential or commercial easily (some preschools and schools I've visited added them in the past year). It doesn't make sense to install in every room, as you say. On ozone, see https://www.epa.gov/coronavirus/air-cleaners-hvac-filters-and-coronavirus-covid-19 https://www.epa.gov/coronavirus/air-cleaners-hvac-filters-an... and the section on ozone.
- cipheredStones 5y ago
  What's the risk from dead pathogens - immune overreaction? It's a screwball idea, but I wonder if there might actually be health benefits to reliably killing pathogens without filtering them out of the air - sort of like low-dose inactivated-agent vaccines for everything you would have actually been exposed to otherwise.
- bradknowles 5y ago
  UV can kill stuff that gets through the filters. Even HEPA filters go down to objects of a certain size, and some viruses are smaller than that. But UV can kill even those smaller viruses.
  - ddxxdd 5y ago
    HEPA filters block particles smaller than it's rated size, and they block those particles more easily than larger particles because of Brownian motion and the physics of electrostatically capturing particles.
    - bradknowles 5y ago
      They can block smaller particles, yes. But it’s non-deterministic. More importantly, they don’t block all or even most of the smaller particles. If they did, then they would be rated for the smaller particles that they are blocking.
      - ddxxdd 5y ago
        N95 filters are rated based on how many 0.3-micron particles they can block. They are rated for that particle size because that particle size is the hardest particle size to block and therefore serves as a proper test of the filter's efficiency. If you look at a graph of the blocking efficiency of an N95 filter vs particle size, that graph is a curvy "V" shape, with the bottom of that "V" being at 0.3 microns.
  - DannyBee 5y ago
    This is like theoretically true but mostly useless. There is filtration beyond even HEPA. For example, MERV-20 is 99.9999% efficient at 0.1->0.2um particle sizes. It is 99.99% efficient at particle sizes like 0.01um. The bigger issue is not whether you can get filters to do it, it's whether your system was built for the pressure drop you'd need to do it. IE UV's advantage is that it doesn't really drop pressure (but does require some dwell time), not that you can't filter air well enough.
    - bradknowles 5y ago
      I was referring to standalone systems that are designed to filter all the air in a room, and use so-called “HyperHEPA” filters to get particles way below the size that HEPA is designed for. Of course you can also get higher filtration rating filters to attach to your whole-house air handling units, and — as you point out — those would have to be sized and designed for that. But the whole house units weren’t what I was talking about.
JulianMorrison 5y ago
That would treat the ducted air but it wouldn't treat the air already in the room. And if the air is being recycled, it would still linger for some bounded time before being pumped back through treatment. Having the UV in the room with the people means it treats every breath immediately.
- DannyBee 5y ago
  It's not quite that simple - the lingering also depends on particle size (ie is it in a droplet, or bare, or ...) Most places with lots of people also have very high acph - often 20-30 air changes per hour.
giarc 5y ago
I work in this field (infection control) and see a lot of products being pushed, especially lately. One we actually installed in our hospital is a replacement for the regular fluorescent lights you see in every building. It's a direct swap out so pretty easy for any maintenance crew to complete. Instead of directing the UV light into the room, it simply has a duct inside with a fan that directs air to pass by powerful UV lights. The UV light is contained to a small box within the unit and the people around never are exposed. The only drawback is the fan noise, but in hospitals, the background sound is already pretty high. I believe you can schedule the fan to stop overnight. Otherwise it basically continuously circulates the air in the room, always passing over a UV source to kill pathogens that might be in the air. EDIT - just to clarify, you swap out the whole box, not just the bulb. Like this (http://2.bp.blogspot.com/-etoHnNVcOnw/Tu0xY9sDwCI/AAAAAAAAA3s/eBAdYcoFnAE/s1600/IMG_0592.JPG http://2.bp.blogspot.com/-etoHnNVcOnw/Tu0xY9sDwCI/AAAAAAAAA3...) but usually in a drop ceiling.
- alliao 5y ago
  I thought the UV is for the insides of the duct/filter rather than for the air passed through it?
  - giarc 5y ago
    This is a different purpose. These units aren't connected to the facility HVAC system at all. If I could remember the name I would link the companies website.

bradknowles 5y ago

We have UV filters on our HVAC units here at our house, in addition to the whole-house HEPA filters. They’re expensive, but if you have a lot of allergies, IMO they are well worth the extra cost.

DannyBee 5y ago

It's not standard because you can just use filters. Keep in mind the filters have to be able to filter the dead pathogens anyway (usually same size) or else you are breathing them, which isn't great either. Better than live ones for sure, but not great. As for UV, you can add it to either residential or commercial easily (some preschools and schools I've visited added them in the past year). It doesn't make sense to install in every room, as you say. On ozone, see https://www.epa.gov/coronavirus/air-cleaners-hvac-filters-and-coronavirus-covid-19 https://www.epa.gov/coronavirus/air-cleaners-hvac-filters-an... and the section on ozone.

cipheredStones 5y ago
What's the risk from dead pathogens - immune overreaction? It's a screwball idea, but I wonder if there might actually be health benefits to reliably killing pathogens without filtering them out of the air - sort of like low-dose inactivated-agent vaccines for everything you would have actually been exposed to otherwise.
bradknowles 5y ago
UV can kill stuff that gets through the filters. Even HEPA filters go down to objects of a certain size, and some viruses are smaller than that. But UV can kill even those smaller viruses.
- ddxxdd 5y ago
  HEPA filters block particles smaller than it's rated size, and they block those particles more easily than larger particles because of Brownian motion and the physics of electrostatically capturing particles.
  - bradknowles 5y ago
    They can block smaller particles, yes. But it’s non-deterministic. More importantly, they don’t block all or even most of the smaller particles. If they did, then they would be rated for the smaller particles that they are blocking.
    - ddxxdd 5y ago
      N95 filters are rated based on how many 0.3-micron particles they can block. They are rated for that particle size because that particle size is the hardest particle size to block and therefore serves as a proper test of the filter's efficiency. If you look at a graph of the blocking efficiency of an N95 filter vs particle size, that graph is a curvy "V" shape, with the bottom of that "V" being at 0.3 microns.
- DannyBee 5y ago
  This is like theoretically true but mostly useless. There is filtration beyond even HEPA. For example, MERV-20 is 99.9999% efficient at 0.1->0.2um particle sizes. It is 99.99% efficient at particle sizes like 0.01um. The bigger issue is not whether you can get filters to do it, it's whether your system was built for the pressure drop you'd need to do it. IE UV's advantage is that it doesn't really drop pressure (but does require some dwell time), not that you can't filter air well enough.
  - bradknowles 5y ago
    I was referring to standalone systems that are designed to filter all the air in a room, and use so-called “HyperHEPA” filters to get particles way below the size that HEPA is designed for. Of course you can also get higher filtration rating filters to attach to your whole-house air handling units, and — as you point out — those would have to be sized and designed for that. But the whole house units weren’t what I was talking about.

JulianMorrison 5y ago

That would treat the ducted air but it wouldn't treat the air already in the room. And if the air is being recycled, it would still linger for some bounded time before being pumped back through treatment. Having the UV in the room with the people means it treats every breath immediately.

DannyBee 5y ago
It's not quite that simple - the lingering also depends on particle size (ie is it in a droplet, or bare, or ...) Most places with lots of people also have very high acph - often 20-30 air changes per hour.

giarc 5y ago

I work in this field (infection control) and see a lot of products being pushed, especially lately. One we actually installed in our hospital is a replacement for the regular fluorescent lights you see in every building. It's a direct swap out so pretty easy for any maintenance crew to complete. Instead of directing the UV light into the room, it simply has a duct inside with a fan that directs air to pass by powerful UV lights. The UV light is contained to a small box within the unit and the people around never are exposed. The only drawback is the fan noise, but in hospitals, the background sound is already pretty high. I believe you can schedule the fan to stop overnight. Otherwise it basically continuously circulates the air in the room, always passing over a UV source to kill pathogens that might be in the air. EDIT - just to clarify, you swap out the whole box, not just the bulb. Like this (http://2.bp.blogspot.com/-etoHnNVcOnw/Tu0xY9sDwCI/AAAAAAAAA3s/eBAdYcoFnAE/s1600/IMG_0592.JPG http://2.bp.blogspot.com/-etoHnNVcOnw/Tu0xY9sDwCI/AAAAAAAAA3...) but usually in a drop ceiling.

alliao 5y ago
I thought the UV is for the insides of the duct/filter rather than for the air passed through it?
- giarc 5y ago
  This is a different purpose. These units aren't connected to the facility HVAC system at all. If I could remember the name I would link the companies website.