[blairanderson]

I recently visited a national trade show for HVACR folks and found this company:

https://www.amazon.com/Blue-Tube-UV-Light/dp/B00D48XDO0/

Thought it might be applicable to computers, but realized that UV breaks-down PLASTICS as well, which is why you mostly find in ducting.

Very cool stuff if you're into clean/sterile living.

Note: Most of the dust in your home is comprised of human skin. Unless you've had an industrial vacuuming, other people's skin is moving around your house or gumming up the walls of your ducts. UV lights (and chemicals) are the only way to break that shit down.

[throw0101c]

> Very cool stuff if you're into clean/sterile living.

One concern I've heard about UV (and ionization) stuff is that you're adding 'active chemistry' into your ventilation system, which could possibly cause strange reactions you may not want.

Besides 'bugs' and dead skin, there are are VOCs and other chemicals that we use in our homes: how will those reaction? If these units are new and working properly, things may be fine, but how many homeowners will do (or have someone do) regular inspections/maintenance? Having this stuff in non-residential places may be fine because Facilities has a role in keeping HVAC working: regular people don't do that.

Having good filters (MERV ≥13) will get rid of most of stuff you don't want in a simpler fashion.

[schiffern]

HEPA gets all the hype, but if you can afford to recirculate the air for multiple passes (ie regular filtering, not a surgical theatre) then MERV-13 is the GOAT. It strikes a near perfect balance between particle interception efficiency and airflow volume.

Paradoxically, a 'more efficient' filter will generally achieves lower real-world performance (CADR) because the airflow drops so much.

The MERV rating are often hidden, instead you may need to look for numbers from a company-specific rating system like 3M's 'MPR 1900' or Home Depot's (yes, really) 'FPR 10.'[0]

(I almost don't want to include this last paragraph of info, because by sounding like an ad it will automatically 'taint' everything else, but fuck it....)

I find myself generally buying the 3M version (which is ~30% more expensive locally) which I observe has a much higher pleat count. That means more surface area (lifetime) and better pressure drop (airflow). By my math I come out ahead in cost per area of medium, which for me is a better metric than cost per filter.

[0] https://airfiltersdelivered.com/blogs/helpful-tips/merv-mpr-...

[tempestn]

Aprilaire 413 are our MERV 13 go-to. One other note not everyone may be aware of: if you have a central blower (aka furnace) that takes a standard 1" filter cartridge, it's usually not too expensive to add in a larger filter housing in the adjacent ducting. You just leave the default slot empty, or if you like, put a low-filtration backup filter in there. (Low filtration so as not to further restrict airflow.) So basically just because your existing unit only takes 1" filters doesn't mean you're stuck with that. Upgrade to 4" and you'll get better filtration and much longer filter lifespan.

[schiffern]

Great tip. I should compare the cost-per-area across 4" filters too. Often I'm just making a Corsi Box[0], so the filter thickness is unconstrained.

Anyone got recommendations for a reputable vendor online? Something other than BezosMart?

[0] https://cleanaircrew.org/box-fan-filters/

[tempestn]

It might be a bit more challenging to make one of those with 4" filters, but yeah, worth a look at least. The other reason I like it is that our furnace is in the crawlspace, so having to get down there less often to change the filters is a pretty significant benefit. I'd do it even if the total cost were equal or higher.

[JoshTriplett]

> put a low-filtration backup filter in there

It isn't just a backup; you want it there before the expensive fine-grained filter, to catch the big stuff and extend the life of the more expensive filter.

[tempestn]

That's not always feasible, as the built-in filter is usually integrated with the air handler. The add-on will generally have to be in the inlet ducting, so it will come first. I'm not sure that approach would even reduce cost though; much of the benefit of the large filter is that it has way more surface area, and so it lasts longer before restricting airflow too much. If you put a 1" filter in front of it, now you'll have two filters you need to replace regularly. You might preserve the life of the larger filter a bit, but not enough to make up for the cost of the whole extra filter. So I think I'd prefer to either just use a 4" alone (which is what we indeed do), or have the 1" as a backup, and basically use its condition to test whether anything significant is getting past the main filter. It would very rarely need to be replaced, as the primary filter should be catching everything.

[schiffern]

For a prefilter I sometimes wedge in a fiberglass "stick filter" to catch larger dust and pet hair. At service time I vacuum it off (or just bang it off in the trash) and reuse.

I wouldn't use a prefilter with any real pressure drop thought. Why not? Well...

In theory a two-stage filter is ideal, because you can cycle the filters through: swap the (mostly clean) post-filter over to the pre-filter during filter changes, optimizing both filtration level and using the full capacity of each consumable filter element. This is the procedure when changing the ISS water filters, incidentally.

There's a downside, of course...

Essentially it's the same as series and parallel resistors, so for two filter stages in series (to achieve the same rated pressure drop) you need double the rated size for each of the stages, therefore 4x the total filter area and size. In practice, nobody really wants to install that in their basement.

Some of the Chinese positive pressure systems have seemingly the ultimate low-consumables design: a washable stainless prefilter, washable electrostatic filter, two stages (supports cycling) of HEPA filter, and last a refillable granular activated carbon stage. Spent activated carbon could be used as a soil amendment, or returned to a local facility for regeneration into new activated carbon.

Very low consumables, but very costly up-front.

[wnevets]

Wouldn't UV-light in ducting generate ozone? Even relatively small amounts of ozone can be harmful.

> When inhaled, ozone can damage the lungs. Relatively low amounts can cause chest pain, coughing, shortness of breath and throat irritation. [0]

[0] https://www.epa.gov/indoor-air-quality-iaq/ozone-generators-...

[Eisenstein]

Ozone is produced at 185nm. Standard germicidal UV-C lights are ~250nm. The issue is that some germicidal bulbs do not filter out the lower wavelengths and thus produce ozone (sometimes on purpose since ozone is also germicidal). See [0].

[0] https://en.wikipedia.org/wiki/Ultraviolet_germicidal_irradia...

[jefftk]

> Standard germicidal UV-C lights are ~250nm.

The article is about KrCl 222-nm lights, which people want because they're safe [1] to shine on people, unlike Hg 254-nm lights.

[1] Probably -- I'd like to seem some specific additional experiments before widespread deployment.

[lazide]

222nm is not safe to shine on anyone! It will definitely cause skin cancer.

254nm is also not safe.

254nm destroys ozone, interestingly.

240nm and smaller (160nm being the highest producing freq.) produce ozone.

[https://onlinelibrary.wiley.com/doi/full/10.1111/php.13391]

[bsder]

> 222nm is not safe to shine on anyone! It will definitely cause skin cancer.

The whole point of using 222nm is that it doesn't cause effects on either the eyes or the skin. Consequently, you can use it at higher concentrations without worrying about the leakage.

The issue, as I understand it, is simply that we don't have a decent LED monochomatic source. All of the currently available sources have broad spectrums that have to be filtered out.

[hedora]

The claim that 222nm is an effective disinfectant seems to directly contradict the claim that it cannot penetrate skin. In particular, if it bounces off dead skin cells, and the environment contains dust, how can it possibly kill things on the dark side of the dust particles?

On top of that, reasonable disinfectant timeframes are a few minutes to a few hours, tops. Safety timeframes for human exposures need to be measured in decades if this technology catches on. Claims that lethal dosages of 222nm will penetrate typical glops of pathogens in the environment in seconds, but that cancer causing dosages will not penetrate human skin over years are extraordinary.

Extraordinary claims require extraordinary evidence. Are there long term safety trials for this technology? The article claims “reduced damage” in the abstract, implying routine 222 nm exposure is unsafe.

[lightedman]

Sadly, not even LEDs are truly monochromatic and typically have a ~20nm spread on either side of the peak. They also exhibit drift in wavelength peak. This is seen at my job, where I run the UV testing and production.

[jefftk]

I don't see anything in your link about 222nm causing skin cancer? It's short enough that it shouldn't be getting through the outermost layer of skin, which is dead.

[lazide]

Welders have plenty of experience to contradict it. UV-C is usually blocked by the atmosphere, and most people don't get exposed to it directly - so it rarely comes up. But if you're sitting next to a UV-C generator, don't.

It cleaves DNA the same as UV-B, and there is no reason to think it isn't cancer causing. There are a number of areas that can get exposed that have very thin epidermis, or none at all (eyes), though eyes would get retinal keratosis not cancer.

That said, hopefully no one is spending enough time close to a high enough power UV-C source for this to REALLY be a problem.

Welding Cite - [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5640727/]

Notably, while having a higher skin cancer risk despite being inside a lot (shop welders, not shipyard welders), the vast majority of welders in that sampled population will have been wearing heavy protective clothing continuously. There was a noticeable increase in risk of skin cancer on the neck, which is one of the few areas that is not always adequately covered.

Anecdotally, I knew folks who didn't wear proper full coverage PPE when welding and welded a lot (auto body repair in one case, farm equipment repair in another), and both died in their early 40's from multiple malignant melanomas. One of them, it was 10+ all at once, and he died in less than a year. No one was surprised, unfortunately. They were ALWAYS sunburned from it, and they didn't spend a huge amount of time outside otherwise. That is a pretty broad spectrum source though.

UV-C As Potentially Mutagenic/Causing Damage not caught by normal replication suppression mechanisms - [https://pubmed.ncbi.nlm.nih.gov/9951833/]

UV-C will also have no problem converting all sorts of organic chemicals into interesting, and often more toxic versions (albeit killing any organisms relying on their original structure in the process), same as UV-B or UV-A.

[wnevets]

>Ozone is produced at 185nm

Where did you find that 185nm number? Everything I see on google says ~250nm, not to mention the original post is about 222nm UV.

[lazide]

~ 250nm actually destroys ozone.

Smaller than 240nm creates it, to various degrees, with the ideal frequency being 160nm. 185nm is 'produces a noticeable amount'.

[https://onlinelibrary.wiley.com/doi/full/10.1111/php.13391]

[wnevets]

So the 254nm referenced by the linked product could actually reduce the amount ozone in the air? Assuming of course it wasn't also emitting lower frequencies.

[lazide]

Yes, but.... if you look at the paper, most of these lamps have some degree of lower wavelength light production. Some of them mitigate it through the glass they use, some of them make it worse. There is no good or easy way to tell. :(

[etiam]

I'm certainly not a physical chemist, but at that sort of energy levels wouldn't it rather be liable to drive the gas mix towards some sort of equilibrium?

I'd imagine it breaks down molecular oxygen (some of which goes on to form ozone), and it breaks down ozone (some of which goes on to re-form ozone).

At any rate, that seems like altogether too radical to be desirable near living creatures whose well-being one cares for.

[jefftk]

The linked product peaks at 222nm and is filtered to exclude longer wavelengths. It's being compared to Mercury vapor lamps that peak at 254nm.

[RetpolineDrama]

Carrier at least claims their UV upgrade does not produce ozone. Not sure how accurate that is though.

[KennyBlanken]

You'll note the installation location - in the evaporator unit. It's to reduce mold growth in the evaporator unit, not sterilize air.

UV units intended for installation in return or supply ducts are snake oil. A waste of electricity and money (the bulbs have a pretty finite lifespan.) The velocity of air in most ducts is such that anything flying by wouldn't be sterilized, and you can just install a large air filter (like the Aprilair 413 others have mentioned) and it'll bring a lot more benefits to the table, namely much better reduction of dust.

The greatest problem with indoor air quality is offgassing of VOCs and other pollutants from construction materials, furniture, electronics, etc.

If you want the best indoor air quality: install a large filter like the Aprilair or some equivalent, an air exchange device, and if you have a gas stove/oven, switch that to electric.

[lightedman]

"UV units intended for installation in return or supply ducts are snake oil. A waste of electricity and money (the bulbs have a pretty finite lifespan.) The velocity of air in most ducts is such that anything flying by wouldn't be sterilized,"

If you just do the simple thing and point the lights in a self-facing ring in the duct, no, they will not work. The trick is to beam the light down the incoming pathway to drastically-increase the exposure time. Clean reflective surfaces in the ducting to even out the photon flux density will greatly help with this.

[eutectic]

It's a myth that household dust is mostly skin cells. It only makes up a small percentage.

[thedougd]

I believe these are for keeping your evaporator coils clean and funk free rather than cleaning your air. The air movies past it much too quickly.