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throw0101b

> Ultraviolet germicidal irradiation (UVGI)

Please do not do/use this.

Generally anything that is 'active', like UV lamps or ozone emitters, is not a good idea:

* https://www.youtube.com/watch?v=hSFQQpgvgeo&t=6m1s

* Interviewee: https://civmin.utoronto.ca/home/about-us/directory/professor...

All that's needed for good indoor air quality (IAQ) is an ERV/HRV which exhausts stale indoor air and brings in fresh outdoor air (through a filter).

For comfort you want a furnace+AC/heatpupmp and a dehumidifier.

And try to make the enclosure as air-tight as possible so the air comes in and out on your terms and not 'randomly' through cracks (where it can carry dust and pollen, and bugs can perhaps get through as well).

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I share their sentiment, especially because they are trying to explain the topic for the novice buyer - but I think it oversimplifies the issue and the discussion/benefit of UVGI.

UVGI does not create Ozone, some companies even sell certified lamps that will definitively not go into the UV spectrum that can cause Ozone.

This is true for UV-C and in the postings mention of new far-UVC LEDs.

https://www.uvresources.com/the-ultraviolet-germicidal-irrad...

For personal homes UVGI is most likely not needed, unless immunocompromised I'd guess. For hospitals, pharmacies, schools, airplanes and other high risk institutions I would guess that this could prevent plenty of deaths.

Edit: Their criticism is about the high-voltage needed for Mercury-vapor UV-C lamps. This can leak ozone, also if the glass is not filtering the 185nm wavelength properly that will contribute even further. The article talks about LEDs which will definitively not leak into this range. Also as far as I know the specific wavelength of pressure-lamps is not input-frequency defined as implied by the interviewed guy - not exactly sure what he's referring to. My takeout would be only buy mercury-pressure lamps from trusted sources with proper certifications in place.

> I share their sentiment, especially because they are trying to explain the topic for the novice buyer - but I think it oversimplifies the issue and the discussion/benefit of UVGI.

Most people probably don't change their air filters often enough at home: I have zero confidence of them maintaining an UVGI (themselves, or wanting to shell out the cash for someone to come in).

The best thing to do is circulate air per ASHRAE-recommendations and get high-MERV filters (and hope they are swapped regularly).

I work in medical physics. The issue of ozone generation from ionizing radiation has come up from time to time. In radio/fluoro rooms, it's basically undetectable. In radiotherapy, it might reach the odor threshold after long treatments, but this is rare.

These are systems that produce radiation way beyond the energies that can create ozone via UVC. The ozone level is barely measurable and not considered a serious risk. In the video you linked, the narrator opens by saying that ozone barely even makes it through the ventilation system, which is consistent with my understanding of ozone: a reactive, unstable gas. And Dr. Siegel emphasizes this as well: O3 doesn't stick around easily. He doesn't seem to share the presenter's obsession with ozone.

Frankly, I found the video tedious and gave up after a minute. Also, the Siegel's background is mechanical engineering, and he's obviously hedging his statements. Here's an actual scientific review of O3 generation by lamps:

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

Critical quote: "Again, soft glass UV-C lamps cannot generate ozone".

>I have zero confidence of them maintaining an UVGI

An unmaintained mercury-vapor lamp will not suddenly violate the laws of physics by emitting radiation below the 254 nm spectral line of mercury. The only mechanism that would alter the ozone generation rate is electrical arcing outside the device, which is really a concern with any electrical equipment and not specific to Hg lamps.

Frankly, most of your posts on this sound like you watch too many videos and don't read enough. "Performing chemistry experiments on yourself" — really? This stuff has been studied for centuries.

A more realistic concern with UVGI is that they don't kill everything and can't replace other ventilation components. Some microbes are very, very radioresistant and you're just not going to deliver 10 kilogray in a continuous flow duct using reasonable levels of power.

you don't have to have arcing in the device. Coronal discharge is the normal way to create ozone.

I used to have the air-filter changing forgetfulness problem; I got an online subscription to the filter my furnace takes and now I change it like clockwork.

> All that's needed for good indoor air quality (IAQ) is an ERV/HRV which exhausts stale indoor air and brings in fresh outdoor air (through a filter)

The recommendations you mention are together features of the Passive House[1] building standard that seeks low energy use as well. If you build a building to a high standard, it will have a tighter envelope to retain heat/cool and protect against water intrusion. If the envelope is tight, you must actively manage airflow through an ERV/HRV. The consequence is that these buildings are supplied with continuous fresh air, and their ERV can be set up to dynamically react to air quality and other issue to ramp up the transfer.[2]

There's a subculture of builders pursuing these qualities in their building, represented for example by groups like "Building Science and Beer" in Austin[3], and Matt Risinger's Build Show[4].

[1] https://www.treehugger.com/what-is-a-passive-house-principle...

[2] https://www.broan-nutone.com/en-us/ai-series

[3] https://www.instagram.com/bs_and_beer_atx/

[4] https://www.youtube.com/@buildshow/videos

> The recommendations you mention are together features of the Passive House[1]

ERV/HRV are actually part of regular building codes in many areas. The province of Ontario:

* https://www.greenbuildingadvisor.com/article/ontario-imposes...

* https://airfixture.com/blog/ontario-building-code-ventilatio...

* http://www.mah.gov.on.ca/AssetFactory.aspx?did=15947

* https://web.archive.org/web/20180626073728/http://www.mah.go...

Reme Halo is what you want. That's what I put in when I installed my ERV.

Reme uses UV against titanium dioxide which releases airborne peroxides which takes out bacteria/viruses/yeast/mold

This is the same tech used in self-cleaning concrete -- just add titanium dioxide and let the sun do the work

> Reme Halo is what you want. That's what I put in when I installed my ERV.

Please view the video. The interviewee:

> Jeffrey Siegel, Ph.D., is Professor of Civil Engineering at the University of Toronto and a member of the university’s Building Engineering Research Group. He holds joint appointments at the Dalla Lana School of Public Health and the Department of Physical & Environmental Sciences. He holds an M.S. and Ph.D. in Mechanical Engineering from the University of California, Berkeley as well as a B.Sc. from Swarthmore College. He is fellow of ASHRAE and a member of the Academy of Fellows of ISIAQ. His research interests including healthy and sustainable buildings, ventilation and indoor air quality in residential and commercial buildings, control of indoor particulate matter, the indoor microbiome, and moisture interactions with indoor chemistry and biology. Dr. Siegel is an active member of ISIAQ and ASHRAE and was an associate editor for the journal Building and Environment from 2014-2018. He teaches courses in indoor air quality, sustainable buildings, and sustainable energy systems. Prior to his position at the University of Toronto, Dr. Siegel was an Associate Professor at the University of Texas.

* https://civmin.utoronto.ca/home/about-us/directory/professor...

Peroxide has at best generally been found to useless, and at worst you're introducing active chemistry to your ventilation system (including ozone). If you want to get rid of garbage in your air then (a) exchange it at ASHRAE-recommended volumes, and (b) use high-MERV/HEPA filters.

In wildfire zones and in wildfire season you can perhaps add charcoal filters—if your system is designed to handle the pressure/head loss—to get rid of the smoke-y smells.

There is no need to conduct chemistry experiments on yourself.

You might actually want to do some research on these first. These have been installed with great success at Chipotle stores, meatpacking plants, hospitals, veterinary hospitals, hotels, schools (Chicago Public Schools 138), universities, Office Depot's corporate HQ, the IRS facility in Austin TX to name a few...

How is that 'great success' measured and verified?

That is an interesting explanation. I won’t summarize other than to say that as someone who might have added UV next hardware cycle, there were several A-Ha moments. Well worth watching.

UV is more than UV, there is UVA UVB UVC, etc.

Some UVC generates Ozone, some do not. Wavelength and spectral Q factor matter.

It’s possible to have a UV system that does what you want without the downside, but it does cost.

> It’s possible to have a UV system that does what you want without the downside, but it does cost.

The main downside is that you are introducing a chemistry experiment into your ventilation system.

If you want clean air, then (a) cycle in/outside air at ASHRAE-recommended volumes, and (b) use high-MERV/HEPA filters.

In wildfire zones and in wildfire season you can perhaps add charcoal filters—if your system is designed to handle the pressure/head loss—to get rid of the smoke-y smells.

What I really want is a system that has

• Positive pressure maintenance, so that any air leak paths are not introducing outside air pollutants

• HEPA filtration, using two filters in series so I can "cycle through" filters, moving the post-filter to the pre-filter location and using a brand-new post-filter (this is similar to the ISS water filter change procedure, and maximizes expendable filter utilization); by the series-parallel circuit math, this should requires four times the total area of HEPA filter

• pressure drop sensors, so I only need to replace the HEPA filter when necessary

• activated carbon post-filter that lets me to replace only the granules themselves, using bulk activated carbon

• washable screen prefilter, to avoid premature saturation of the HEPA medium with >10 micron particles

• washable electrostatic prefilter, to avoid premature saturation of the HEPA medium with <1.0 micron particles

• HRV/ERV, to avoid unwanted heat and humidity transfer to the outside air

• HRS/ERV Bypass, so I can use "free cooling" / "free heating" to exploit natural temperature differences over the day

• (optional) MERV-13 post-prefilter, to intercept ~95% of PM2.5 and greatly extend the life of the HEPA filter train

Does anyone know of a system that has all these features?

One of the critical points to the video is that in order to prevent bad side effects of UV, a deployment is not only costly on the front end but also costly in ongoing maintenance. In addition to UV, there is also a hazard of high voltage induced ozone.

My overall impression is that it isn’t a technology at a consumer grade maturity.

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