Darkside wrote:
There are quite a few different products out there like the Halo but they all make very similar claims and the systems work very much the same. Most of my direct experience comes from Air Scrubber by Aerus and one of Remes earlier RGF solutions. What is below should apply to any modern air cleaner.
Quick answer: snake oil.
Long answer:
The thing about air cleaners like this is like any good bullshit product, on the surface the facts make sense. Strong UVC light can quickly kill pathogens and or render them inactive. That second part I'll get back to in a minute. What they're not getting into is pass time. Pass time is how long a pathogen is actually exposed to the uv light. So basically to kill an average virus with uv light, it would require exposure of anywhere between 6 and 33 seconds. When your furnace is running (we're talking heat, ac, or fan on when im saying furnace running for this post), and air is moving chances are the particle or virus flying thru your duct work is going to be going past that light is less than a second. It did not have sufficient exposure to actually damage the DNA of the pathogen.
Now uv lights are very effective in aquariums for controlling algae and pathogens. Why? Just like uv gets attached to ductwork typically uv is installed in line with a canister type filter. And although the pass time is short, maybe oy a half second and kls require 6-33 seconds, the thing is that repeated passes can add up over time to a proper kill time. Why doesn't that really work in a home then? Well an aquarium is essentially a closed loop. No water is changed out for fresh water regularly so the volume is fair static and easier to filter. A house, even a modern one, still experiences 2 to 3 air changes per hour or ACH.
If your house is not exactly the tightest one in the world, average doors average windows average siding average insulation... you're probably experiencing 3 ACH, meaning at least every 20 minutes, the entire volume of air in your home is replaced with air from outdoors.
We measure the amount of air delivered by a furnace in cubic feet per minute. So lots look at cfm for a second. Let's say you have a 2100 Sq foot home. I guess we can say that your cubic feet of air would be around say around 25,000 cubic feet. With let's 3 ACH you need to treat 75000 cubic feet. Your furnace (ac) size is probably around 3.5 tons, at 400 cfm per ton you're moving 1400 cubic feet per minute, which brings us to 84000 cubic feet in an hour which would be JUST enough to treat the air if A) one pass killed the pathogen with it won't and B) each air change didn't bring in fresh contamination.
On part I'm ambivalent on is is the claim that these products can convert water vapor and pathogens into h2o2 which floats in the air and settles on every surface in the home and essentially steralizes everything. That's the claim. Ok. I'm not sure that is really what is happening. It's possible. But it seems unlikely to me that the h2o2 vapor can last long in the uv environment which it's created in the first place and last long in the environment in general because we all know hydrogen peroxide is in brown bottles because light destroys it.
Another problem is that the uv light ain't doing without the fan running all day every day. If you leave your thermostat fan setting on auto and your heat only runs 15 minutes an hour and even colder days, you ain't doing shit with that UV for 45 minutes of each hour. You need to leave your fan on 24/7 to get any benefit.
DS whipping out science and math! And on a Saturday! Thanks for the detailed response and that’s kinda what I thought about it initially. I’ll reach out to folks in my group at work (microbiologists) to see if H2O2 could be made in that process.
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