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>> Whether it works is of secondary importance to making people feel like something is being done, even though in practice there's very little anyone can do. T

>> Whether it works is of secondary importance to making people feel like something is being done, even though in practice there's very little anyone can do. There might be stuff we can do indoors, but state government agencies aren't funding fast research into it - efficacy of filters and alterations to HVAC systems like installing UV-C lamps in them. Instead it's just "wear masks and take temperatures and get mad at people when they don't wear masks," which is perfect shirking of responsibility that large organizations love to do.

amluto 6y ago
I would be surprised if a UVC lamp in an HVAC system is an effective way to spend money. You would need to retrofit in a sizable contact chamber to get a large fraction of the air exposed to enough UVC, and you would need to deal with the facts that UVC lamps are power-hungry, not that long lived, and don’t like to be switched on and off frequently. And you would need to confirm that the UVC dose in use is effective against actual infectious particles. In contrast, a plain old filter is likely to be extremely effective. A HEPA filter will catch almost all particles big enough to contain a virus, and a MERV 13 or better filter is quite good. All you need is a filter with enough surface area that a good filter has low pressure drip. Almost all HVAC systems already have filters, so upgrading them is usually straightforward. (I used to have a fancy electrostatic precipitator in my HVAC system. What a waste of power and effort in keeping it clean.)
- icelancer 6y ago
  >> In contrast, a plain old filter is likely to be extremely effective. A HEPA filter will catch almost all particles big enough to contain a virus, and a MERV 13+ or better filter is quite good. All you need is a filter with enough surface area that a good filter has low pressure drip. The problem with installing a MERV 13 filter in a normal HVAC system is that the pressure (usually) isn't rated for it and can cause serious damage to the motor(s) as you noted, which is more common than people think (definitely the case in my home system). UV-C installation is fairly simple; though I agree they are power hungry and you need to keep them on most of the time with maximum one power cycle per 24 hour period. They're cheap upfront and do work on normal coronaviruses, though. Still the real problem is very little state-funded research on the topic, or development of some mitigation techniques for businesses that must run indoors. It's once again fairly useless bureaucracy.
  - amluto 6y ago
    Are they cheap upfront? I would imagine that just sticking a UV lamp in your furnace manifold by poking a hole in the side risks rapid UV damage to your furnace. And, if you’re going to slice up the manifold to make it appropriate for UV, you might as well put in a proper filter box instead. A decent MERV 13 or 15 filter from Aprilaire or another major vendor is not very expensive.
    - icelancer 6y ago
      Yeah not too bad - a few hundred for reputable ones. Need to keep it far enough away from the filter, obviously, or risk damage over time (or just change out the filter more frequently). I liken using UV-C (potentially) and a good filter as a defense-in-depth technique, just like masks, social distancing, sanitizer, temp checks (all which do very little on their own, but in the aggregate help).
    - rainbowzootsuit 6y ago
      UVC lamps are relatively inexpensive to install. Usually they're put before and/or after the cooling coil where, if you have a clean coil, the light will bounce through the fins and increase the path length of exposure. If it's not clean, the UVC helps to break down anything organic over time and cleans them up. With a few exceptions of more complex units all of the recirculated air spends time passing through the coil. UVC doesn't damage metal parts, but does effect some materials that would be common in residential installations https://customer.honeywell.com/resources/techlit/TechLitDocuments/50-0000s/50-8788.pdf https://customer.honeywell.com/resources/techlit/TechLitDocu...

amluto 6y ago

I would be surprised if a UVC lamp in an HVAC system is an effective way to spend money. You would need to retrofit in a sizable contact chamber to get a large fraction of the air exposed to enough UVC, and you would need to deal with the facts that UVC lamps are power-hungry, not that long lived, and don’t like to be switched on and off frequently. And you would need to confirm that the UVC dose in use is effective against actual infectious particles. In contrast, a plain old filter is likely to be extremely effective. A HEPA filter will catch almost all particles big enough to contain a virus, and a MERV 13 or better filter is quite good. All you need is a filter with enough surface area that a good filter has low pressure drip. Almost all HVAC systems already have filters, so upgrading them is usually straightforward. (I used to have a fancy electrostatic precipitator in my HVAC system. What a waste of power and effort in keeping it clean.)

icelancer 6y ago
>> In contrast, a plain old filter is likely to be extremely effective. A HEPA filter will catch almost all particles big enough to contain a virus, and a MERV 13+ or better filter is quite good. All you need is a filter with enough surface area that a good filter has low pressure drip. The problem with installing a MERV 13 filter in a normal HVAC system is that the pressure (usually) isn't rated for it and can cause serious damage to the motor(s) as you noted, which is more common than people think (definitely the case in my home system). UV-C installation is fairly simple; though I agree they are power hungry and you need to keep them on most of the time with maximum one power cycle per 24 hour period. They're cheap upfront and do work on normal coronaviruses, though. Still the real problem is very little state-funded research on the topic, or development of some mitigation techniques for businesses that must run indoors. It's once again fairly useless bureaucracy.
- amluto 6y ago
  Are they cheap upfront? I would imagine that just sticking a UV lamp in your furnace manifold by poking a hole in the side risks rapid UV damage to your furnace. And, if you’re going to slice up the manifold to make it appropriate for UV, you might as well put in a proper filter box instead. A decent MERV 13 or 15 filter from Aprilaire or another major vendor is not very expensive.
  - icelancer 6y ago
    Yeah not too bad - a few hundred for reputable ones. Need to keep it far enough away from the filter, obviously, or risk damage over time (or just change out the filter more frequently). I liken using UV-C (potentially) and a good filter as a defense-in-depth technique, just like masks, social distancing, sanitizer, temp checks (all which do very little on their own, but in the aggregate help).
  - rainbowzootsuit 6y ago
    UVC lamps are relatively inexpensive to install. Usually they're put before and/or after the cooling coil where, if you have a clean coil, the light will bounce through the fins and increase the path length of exposure. If it's not clean, the UVC helps to break down anything organic over time and cleans them up. With a few exceptions of more complex units all of the recirculated air spends time passing through the coil. UVC doesn't damage metal parts, but does effect some materials that would be common in residential installations https://customer.honeywell.com/resources/techlit/TechLitDocuments/50-0000s/50-8788.pdf https://customer.honeywell.com/resources/techlit/TechLitDocu...