Damon Binder recently wrote
up an argument for prioritizing air filtration over
far-UVC for pathogen control:
UVC and filtration are close substitutes—both deliver effective air
changes per hour, both reduce airborne pathogen concentrations by the
same amount per eACH—and on current pricing, filtration is cheaper.
There's a lot of good stuff in his analysis, but I see [1] three
considerations that really change the bottom line:
Cost is actually much lower.
Noise is a serious issue.
Performance is dramatically higher in larger rooms.
Cost is straightforward. Binder priced far-UVC based on the
high-quality Care222 lamp with the Krypton-11 at $2,500, but
there's a much cheaper option, the Aerolamp at $500.
It's also moderately higher output.
Binder analyzes a 30m2 room with a 2.5m ceiling. I'll assume this
means 6x5x2.5. If I configure Illuminate with an Aerolamp
in one corner pointed 0.5m above the far corner the installation is
within TLVs and I get a median effective number of hourly air changes
(eACH) of 11.6. The lamp degrades approximately
linearly over Binder's 11,000 hour evaluation period down to 70%
capacity, so we're averaging an eACH of 9.8. Over that time you're
paying $500 for the lamp and $16.50 for the electricity (0.01kW *
11,000hr * 0.15 $/kWh) for a 5-year $/eACH of $53. Adding this to the
best-performers from Binder's table, the Aerolamp is now the same cost
as the cheapest filter:
Technology
5-year $/eACH
AirFanta 3Pro
$53
Aerolamp
$53
Box fan + MERV-13
$79
Corsi-Rosenthal box
$95
Now let's consider noise. I have an AirFanta 3Pro, and it absolutely
works. On high, it clears cooking smoke from my kitchen very
quickly. But, like all commercial air purifiers that clean
significant amounts of air, when you put it on high it's very
noisy. As in, "hard to have a conversation in the same room"
noisy. Binder describes this as "audible fans", but that's a huge
understatement when you're talking about running them on high. When
filters are too noisy, people unplug them. Here's one I saw this
weekend, just before I took the initiative to plug it back in:
So lets say we we model running these filters at half speed, which
cuts filtration by about half and noise by a lot more:
Technology
5-year $/eACH
AirFanta 3Pro
$106
Aerolamp
$53
Box fan + MERV-13
$158
Corsi-Rosenthal box
$190
Now the filters are significantly more expensive per ACH than the
Aerolamp. And they're still moderately noisy while far-UVC is silent.
The advantage grows for larger rooms. Consider one that's 20m
by 12m, with the same 2.5m ceiling. This room has 8x the volume, and
how much air you need to clean to "change out" the whole room is
proportional to volume, so an eACH now represents 8x more cleaning.
Modeling filters is simple, since they clean air at a constant rate,
so their $/eACH values are now 8x higher. For UVC, however, the lamp
cleans more air because it's light: it can go further in a larger
room. Modeling with Illuminate and pointing the lamp from a ceiling
corner to a spot in the middle of the floor I get a median eACH of 2.2
(1.9 with degradation), compared to the 1.4 you'd expect if it was
linear with volume. Here's the same table for this 8x bigger room:
Technology
5-year $/eACH
AirFanta 3Pro
$848
Aerolamp
$230
Box fan + MERV-13
$1,264
Corsi-Rosenthal box
$1,520
Getting to somewhat uncommon room shapes, if the room is also taller,
say 6m (20ft), as large gathering places can be, we've added another
factor of 2.4 to the room's volume. The filter costs go up by 2.4x,
but modeling with Illuminate I get a median eACH of 1.6 (1.4 with
degradation). Costs are now:
Technology
5-year $/eACH
AirFanta 3Pro
$2,035
Aerolamp
$316
Box fan + MERV-13
$3,033
Corsi-Rosenthal box
$3,648
In this large room, for a given level of filtration the Aerolamp is
1/6th the cost of the next cheapest option. Far-UVC really shines
here. This is why I've advocated
for it in dance halls, and why the dance I helped organize
until very recently decided to deploy
far-UVC:
In the other direction, while Binder is right that fans are commodity
items, fans that move large volumes of air extremely quietly are not.
No one makes a commercial air purifier that approaches the limits of
what's possible if you design for maximum air
cleaning at minimum noise. So while the best far-UVC options
outperform the best filter options in medium to large rooms today,
future improvements in air purifier design might change that.
Despite the critical tone, I'm very happy Binder shared
this, and there's a lot of good thinking in the piece. The
point that filters are useful for a lot more scenarios, including
pollen and smoke (I couldn't replace my kitchen AirFanta with an
Aerolamp!) is an important one, especially as we push for everyday clean
air. But I do hope he'll reconsider the potential for far-UVC to
produce much more clean air for a given budget in dollars and noise.
[1] After drafting this I asked Opus 4.7 "What are the errors Jeff
Kaufman would point out on
https://defensesindepth.bio/on-far-uvc-and-air-filtration-2/ ?" It
found (1) and (2) but not (3).
Damon Binder recently wrote up an argument for prioritizing air filtration over far-UVC for pathogen control:
There's a lot of good stuff in his analysis, but I see [1] three considerations that really change the bottom line:
Cost is straightforward. Binder priced far-UVC based on the high-quality Care222 lamp with the Krypton-11 at $2,500, but there's a much cheaper option, the Aerolamp at $500. It's also moderately higher output.
Binder analyzes a 30m2 room with a 2.5m ceiling. I'll assume this means 6x5x2.5. If I configure Illuminate with an Aerolamp in one corner pointed 0.5m above the far corner the installation is within TLVs and I get a median effective number of hourly air changes (eACH) of 11.6. The lamp degrades approximately linearly over Binder's 11,000 hour evaluation period down to 70% capacity, so we're averaging an eACH of 9.8. Over that time you're paying $500 for the lamp and $16.50 for the electricity (0.01kW * 11,000hr * 0.15 $/kWh) for a 5-year $/eACH of $53. Adding this to the best-performers from Binder's table, the Aerolamp is now the same cost as the cheapest filter:
Now let's consider noise. I have an AirFanta 3Pro, and it absolutely works. On high, it clears cooking smoke from my kitchen very quickly. But, like all commercial air purifiers that clean significant amounts of air, when you put it on high it's very noisy. As in, "hard to have a conversation in the same room" noisy. Binder describes this as "audible fans", but that's a huge understatement when you're talking about running them on high. When filters are too noisy, people unplug them. Here's one I saw this weekend, just before I took the initiative to plug it back in:
So lets say we we model running these filters at half speed, which cuts filtration by about half and noise by a lot more:
Now the filters are significantly more expensive per ACH than the Aerolamp. And they're still moderately noisy while far-UVC is silent.
The advantage grows for larger rooms. Consider one that's 20m by 12m, with the same 2.5m ceiling. This room has 8x the volume, and how much air you need to clean to "change out" the whole room is proportional to volume, so an eACH now represents 8x more cleaning. Modeling filters is simple, since they clean air at a constant rate, so their $/eACH values are now 8x higher. For UVC, however, the lamp cleans more air because it's light: it can go further in a larger room. Modeling with Illuminate and pointing the lamp from a ceiling corner to a spot in the middle of the floor I get a median eACH of 2.2 (1.9 with degradation), compared to the 1.4 you'd expect if it was linear with volume. Here's the same table for this 8x bigger room:
Getting to somewhat uncommon room shapes, if the room is also taller, say 6m (20ft), as large gathering places can be, we've added another factor of 2.4 to the room's volume. The filter costs go up by 2.4x, but modeling with Illuminate I get a median eACH of 1.6 (1.4 with degradation). Costs are now:
In this large room, for a given level of filtration the Aerolamp is 1/6th the cost of the next cheapest option. Far-UVC really shines here. This is why I've advocated for it in dance halls, and why the dance I helped organize until very recently decided to deploy far-UVC:
youtube; see the stand with four lights on stage
In the other direction, while Binder is right that fans are commodity items, fans that move large volumes of air extremely quietly are not. No one makes a commercial air purifier that approaches the limits of what's possible if you design for maximum air cleaning at minimum noise. So while the best far-UVC options outperform the best filter options in medium to large rooms today, future improvements in air purifier design might change that.
Despite the critical tone, I'm very happy Binder shared this, and there's a lot of good thinking in the piece. The point that filters are useful for a lot more scenarios, including pollen and smoke (I couldn't replace my kitchen AirFanta with an Aerolamp!) is an important one, especially as we push for everyday clean air. But I do hope he'll reconsider the potential for far-UVC to produce much more clean air for a given budget in dollars and noise.
[1] After drafting this I asked Opus 4.7 "What are the errors Jeff Kaufman would point out on https://defensesindepth.bio/on-far-uvc-and-air-filtration-2/ ?" It found (1) and (2) but not (3).
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