I found it interesting that I haven't really seen the UV sterilisation to be popular at healthcare points at large. Where I grew up, the local surgery had the UV on in the whole building after hours, and that was in early 90s EE. None of the places I've seen since then used it (as far as I'm aware), across many countries.
Naomi Wu did some videos/articles about this and was working on some sort of product you could setup. Things like a light that shone upwards in a room to clean the air above people's heads.
My main take-away was this was very easy to screw up and cause eye damage, especially in an home setting where less care would be taken.
I looked into implementing this once. Some surprising things I learned:
1. You need UV-C (typically 222 nm), not just any old UV bulb off Alibaba/Wish/Amazon.
2. You need an extremely high UV light intensity to kill viruses if the air is just flowing past the bulb (vs shining UV on a coil to prevent bacterial/fungal growth, which is the typical usage), and you need more intensity the faster the air is flowing. Usually this requires multiple bulbs.
3. You need to replace your UV-C bulbs every 1,000 hours or so, because they rapidly lose intensity with operating time.
Just putting a "black light poster" bulb in your ducts won't accomplish anything, other than perhaps giving you a false sense of security.
> You need to replace your UV-C bulbs every 1,000 hours or so
I don't think this should need to be the case. Low pressure mercury arc lamps (253.7nm) last 10,000 hours in water treatment applications - a much more palatable replacement timeline (1 year) vs every few weeks!
The short-lifetime bulbs are usually 222nm Far-UVC bulbs, which are safe for human exposure. These shouldn't be necessary to treat air as part of an enclosed HVAC system. I feel that the hype around 222nm / "safe" UVC has done a disservice to just using "dirty" 253nm UVC, which kills everything just as well as long as you keep people from being able to look at it.
Thanks for the correction. It's been a while since I looked into it!
Even replacing bulbs every 1 year seems like a lot more than people are bargaining for. Most people seem to expect UV will be a "Set It And Forget It" solution (hence why they prefer it over filters), so they risk neglecting the necessary replacement interval.
Hmm, I wonder how effective that would be. My small home's ventilation system is currently taking in about 100m³ of fresh air per hour. That's about 1600L/minute. Let's assume the intake duct is about 20cm in diameter, and assume we can place a bulb to illuminate a 50cm stretch of pipe. That's a volume of about 16 liters. So the air would be in visible range of the bulb for about half a second. Would that be enough for a UV bulb to do anything?
This was back of napkin maths, could be way off.
Edit: sanitizing incoming air is probably pretty useless, as the outdoor concentration of pathogens is likely very low to begin with.
I’ve seen some claims that it can destroy viruses on some medium. Imagine a filter in the light catching virus particles or particles that have viruses. The light destroys them while they’re stuck in place. I would need some independent testing to verify that claim.
If you have an appropriately sized filter holder, I would just install a MERV 13 or 16 filter. They’re very cost effective, widely available, and they will remove non-living crud, too.
The main problem is that many central air systems use crappy thin filter holders. A good low-resistance filter needs a lot of area, and a 4” or 5” thick format works well, 2” is marginal, and 1” sucks. A good filter holder costs under $200, takes very little effort to install in a new system, and is an incredible pain to retrofit into an existing system. And good filters are essentially unsupported in ductless systems.
You can, but it does not leave any residual ability for the water to neutralize pathogens once you're done treating the water.
If you dip a Nalgene bottle to fill it, then purify the contents, you would typically then bleed the threads by holding the bottle upside down and loosening the cap.
With chemical treatment, the iodine in the water works to neutralize any pathogens that aren't flushed out of the threads. If you've used UV, you're kind of hoping that the flushing action has physically washed out anything lingering in the threads.
Anecdotally, people using UV get more cases of waterborne illness, but I don't know if anyone has rigorously studied this. Hikers are naturally resistant to controlled experiments.
If you don't like the flavor of iodine tablets, I recommend AquaMira instead.
Source: AT ME-MA 2003, GA-ME 2010. UV was pretty popular by 2010 and for a couple years after. Not planning a thru hike at the moment, but I believe the Sawyer squeeze filter is super popular now.
> UVGI for water treatment // Using UV light for disinfection of drinking water dates back to 1910 in Marseille, France. The prototype plant was shut down after a short time due to poor reliability. In 1955, UV water treatment systems were applied in Austria and Switzerland; by 1985 about 1,500 plants were employed in Europe. In 1998 it was discovered that protozoa such as cryptosporidium and giardia were more vulnerable to UV light than previously thought; this opened the way to wide-scale use of UV water treatment in North America. By 2001, over 6,000 UV water treatment plants were operating in Europe
And yes, there are also commercial products for home use.
One of the biggest takeaways seemed to be that UV light destroys viruses in seconds.
Seems like there a lot of things we could do