WHAT WOULD IT TAKE to get sufficient ventilation in our Social Hall, in order to allow it to be used again safely, despite pandemic waves? What kind of mechanical equipment would be needed, and how much would it cost?
How Much Ventilation Is Enough?
According to Mishkon member Dr. Kevin Metzger (who serves on our pandemic health committee), the Social Hall would need to have active ventilation — not only open doors — that would exchange or clean the equivalent of the room’s entire volume every 10 minutes. In the terms used by engineers, it would provide 6 air changes per hour.
According to the architectural drawings supplied in the 2003 Historic Structure Report, our Social Hall dimensions are as follows: 87 ft long, 46 ft wide, and 13 ft high (plus or minus a couple of inches).
1 air change = 87 x 46 x 13 = 54,300 cubic feet
UPDATE 9/29/22: The above methodology is considered to be accurate only for ceilings about 8 feet high. To adjust for a 13-foot ceiling, it appears that the filtration units should be wall-mounted at about 8 feet up. Then it is justifiable to discount the volume above that height.
1 air change = 87 x 46 x 8 = 32,016 cubic feet
What Is the Easiest Way to Provide Clean Air?
Several reliable sources recommend an effective, low-cost, do-it-yourself (DIY) air filtration system. It can be made by simply using a bungee cord (or duct tape) to attach a HEPA filter onto the upstream side of an ordinary box fan.
Here are the results from a quickie window-shopping trip on HomeDepot.com, to get a ballpark idea of what’s involved in constructing such a filtration unit:
1. Typical 20-inch box fan:
2. MERV-13 HEPA filter (rated as appropriate for droplets that carry viruses):
Honeywell 20" x 20" x 1" Elite Allergen Pleated MERV 13 (FPR 10) Air Filter
3. Bungee cord:
How Many Units Would Be Needed?
In theory, each DIY filtration unit is capable of producing 1 air change (54,300 cubic feet) every half hour.
1820 cu. ft./min. x 30 min. = 54,600 cu. ft.
I.e., each unit takes care of 2 air changes per hour. So in order to achieve the desired goal of 6 air changes per hour, we would need three filtration units to be dispersed around the room.
Of course, that rough calculation assumes that the fan is kept on its highest setting, which might be uncomfortably noisy. And the flow capacity of the fan is probably reduced somewhat by the presence of a filter. So to be on the safe side, we could double the number of DIY filtration units and run them at a lower speed. So let’s say we deploy six filtration units.
UPDATE 9/29/22: Published testing results have shown that the effective clean-air delivery rate for a DIY unit, when run at low speed for the sake of noise control, is more like 200 cfm. This suggests that we would need 16 fan units distributed around the periphery of the room, blowing in a circular pattern. So figure on spending about $800 for the units, not including wiring and mounting costs.
How Much Would This Cost?
Using the prices on the Home Depot website:
- Cost of a typical 20-inch box fan: $24
- Cost of a MERV-13 air filter (the rating appropriate for droplets that carry viruses): $21, or $16 each if buying 4 or more
- Cost of a bungee cord: $1
Total cost per filtration unit, including tax: $50
Total cost for all 6 units (with quantity pricing of filters): $271
Each filter is supposed to last for a couple of months’ worth of regular use before it becomes dirty enough to be replaced. So at 4 hours of use per Shabbat, they should last for about 3 years.
SOURCES:
https://www.youtube.com/watch?v=ujUFj2G9_-Y
https://deohs.washington.edu/sites/default/files/AirFilterInfographic_FINAL.pdf
https://www.latimes.com/opinion/story/2022-04-24/ba2-covid-prevention-ventilation-testing
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