Thread by @joeyfox85

Time to combat some serious misinformation in this article.

thehill.com/opinion/techno…

1/16

Let's start with the author, Bruce L Davidson @bldmdmph

Apparently, good tooth brushing and mouthwash are underused resources to fight COVID. Is there any real evidence for this?

2/16

https://twitter.com/bldmdmph/status/1328766851409604609?s=20&t=wDtLwrL6SYf5fryzjy8xSg

How did he get membership to ASHRAE? Between being a doctor, MPH with specialty in pulmonary medicine and associate prof, he got an engineering degree with 12 years HVAC experience? It's not listed anywhere. (I'm an associate member because I only have 11 years experience).

3/16

Now onto the misinformation:

1. HVAC upgrades are noisy and windy

In future posts, I will deal with switching to a dedicated outdoor air system, but putting 1000 CFM into classrooms is common and not noisy or windy.

4/16

Removing the recirculation gives you about 7 air changes per hour - up from 2-3 air changes.

5/16

2. "Filtering air after it leaves the room does zero to prevent transmission to people sitting in a room with someone repeatedly exhaling viruses. "

Filtering air takes air with viruses and removes them. It's basic physics.

nature.com/articles/d4158…

6/16

3. "High-efficiency particulate air filters — HEPA filters can remove 99.7 percent of particles larger than 0.3 microns...coronavirus and the flu virus are both 0.2 microns or smaller. "

The naked virus myth. It's not true.

See this post:

https://twitter.com/joeyfox85/status/1484357860494508033?s=20&t=-PvO379-3bqSR-TRtQkkeg

7/16

And this one:

https://twitter.com/joeyfox85/status/1484357862537134088?s=20&t=-PvO379-3bqSR-TRtQkkeg

8/16

4. "Ventilation and filtration advocates are now promoting even less efficient filters, (MERV-13) that are only 66 percent effective "

You don't care about filter efficiency. You care about the clean air delivery rate = efficiency x flow.

9/16

5. "A 9,000 cubic feet classroom requires 10 cubic feet per minute (CFM) of fresh outside air per occupant. That’s 300 CFM..."

He must not have read 62.1. Here's how you actually do a ventilation requirement calculation:

ashrae.org/technical-reso…

10/16

You calculate it based on occupancy & area
9000 cubic ft room with 9' ceilings = 1000 sq ft area (bigger than most classrooms)

Outdoor air = 10 CFM/person * 30 ppl + 0.12 CFM/sq ft * 1000 sq ft = 420 CFM

If heating is required, you multiply by 1.25 = 525 CFM

11/16

He's only off by 75% when discussing how to mitigate virus transmission. No big deal.

6. "...recommended 6 to 12 air changes per hour for minimal disinfection, multiply that 900 CFM by three to reach the minimum of 6 ACH and arrive at 2,700 CFM."

12/16

He's right it's difficult to achieve 6 ACH alone with a recirc system. You can get 2.5 to 3 ACH easily. Add MERV 13 and that adds an extra 2.5. CR box gives you another 2. Or, you can use a dedicated outdoor air system and get 7 ACH easily.

13/16

He then goes on to praise upper room UVGI which is correct. It's better for mitigating virus transmission alone.

But the discussion about ventilation and filtration is bogus nonsense and should be removed.

14/16

Also see this:

https://twitter.com/marwa_zaatari/status/1501961863055216640?s=20&t=EgKkMj_S9a4i0zYh2b57fw

15/16

And this:

https://twitter.com/WBahnfleth/status/1501918758415253507?s=20&t=EgKkMj_S9a4i0zYh2b57fw

16/16