The fact that this column is named “Granite Geek’ might give you a clue about my certain bias when solving complicated problems, such as how best to keep indoor spaces safe during the pandemic.

I want the solution to be geeky! Social distancing and wearing masks and cleaning surfaces regularly are all very fine, but what I really want is a gizmo or technology that will reduce infection as well as dazzle my gee-whiz gene. I want germicidal pulse cannons or backpack ionization wands or RNA-disrupting nanowavelets – something cool! Is that too much to ask?

Apparently, yes.

Unfortunately for my inner adolescent, a little querying of people who know more than me indicates that careful use of grandma’s advice about lots of fresh air combined with an old technology (filters) is our best bet. Plus maybe a little ultraviolet light on the side.

“We want appropriate ventilation of the space, an environment that is not stable for the virus to transmit in droplets easily,” said Alison Brisson, director of Concord Hospital Facility Operations.

Concord Hospital, of course, has lots of experience dealing with germs. The virulence of the SARS-CoV2 coronavirus and the fact that we’re contagious before symptoms show have raised the stakes, plus the novelty of the virus means we are still determining the best approach, as shown by the scientific debate about how “airborne” the virus is.

But in general, long experience tells them that keeping air moving so that moisture droplets containing the virus get diluted or passed through filters that pull them out of the air is key. Not that it’s simple.

“It’s not just ventilation – pressure, humidity control, temperature, they all play a role,” said Brisson. Humidity and temperature affect not just comfort but also important aspects of the environment, like mold growth.

Steve Caulfield, president of Turner Building Science in Concord, agreed that grandma’s mantra about “more fresh air is better” doesn’t always work.

“We’re seeing a lot of people trying to increase the amount of air replacement, the air change rate. The problem we run up against is the engineering problem that on a hot day your system is only designed to cool so much outside air. Beyond that you either raise the temperature or humidity in the space, or both,” Caulfield said. “You can’t just go to every building and open every outside air damper.”

This same complication comes up with air filters. As I have learned, these are calibrated on the MERV (Minimum Efficiency Reporting Value) scale, with bigger numbers removing smaller-sized particles.

Caulfield said MERV 8 is common, but “it’s not until you get to about a MERV 13 that you start removing 90% or more of virus-sized particles.”

But you can’t just stick a MERV 13 filter into a system that was sized MERV 8 because it’s much harder to move air through a tighter filter. The added work could burn out motors and will certainly reduce air flow, allowing viruses to build up – the exact opposite of what you want.

One possibility is to support filtration with ultraviolet light, which can kill viruses quickly. You can’t shine UVC light, the most effective wavelengths, around people because it can hurt our eyes, but UV systems are becoming more common within ventilation units. Concord Hospital has some, said Brisson.

Caulfield agrees but says caution is in order. “Air moves about 1,000 feet per minute in a duct. UVC needs quarter-second contact time (to kill viruses) so you need 250 feet of lights in a duct to be effective on one pass,” he pointed out.

Ionization – releasing charged ions into the air so viruses can be collected electrostatically – is an established technology and you’ll see it offered as a solution. Caulfield said the concern again is health effects when used around people so he doesn’t usually take that route.

Even with proper ventilation you face fluid dynamics, which I’ve heard described as the most complicated physics this side of the quantum world. Just because you move 1,000 cubic feet of air every hour doesn’t mean that all the air in your 1,000-cubic-foot room is being replaced. Eddies and turbulence could create stagnant air where viruses linger and it’s very hard to find without detailed smoke tests or other intrusive analysis.

“As the days go on I’m leaning more and more toward local filtration rather than filtration on a system scale,” Caulfield said. In other words, filters in the whole-building units are fine, but air filters in portable units may be needed, too.

There’s an extreme example at Concord Hospital. It sets up portable units with high MERV filters in patient rooms to create negative pressure space, meaning that pressure in the room is lower than out in the hall, so air only flows in. Virus breathed out by an asymptomatic COVID-19 patient won’t float out the door and spread to others.

Creating a negative pressure room is a little extreme but portable units might be part of the solution for a particularly difficult situation: homeless shelters.

Maintaining social distancing within group housing is hard, and expecting masks to be worn 24/7 is ridiculous.

“I think people will refuse to come in rather than wearing a mask all night long, or even in the resource center all day,” said Ellen Groh, executive director of Concord Coalition to End Homelessness. She, like many people in the industry, is preparing for cold weather, when the homeless services currently provided outdoors will have to move inside.

Concord’s homeless shelter is quite new and has “wonderful air exchange, in one big room,” said Groh, but its Resource Center is “the total opposite: an old building cut up into smaller rooms.”

Upgrading or replacing a building’s HVAC (heating-ventilation-air conditioning) system can be very expensive. Installing portable filtration units to clean up air in rooms might be an answer. It could even help in a large dormitory space overnight although other factors then come into play, such as the danger of people in crowded spaces tripping over extension cords.

For Groh and everybody else trying to make good choices, the question of how to proceed can seem overwhelming. She said the shelter is flooded with pitches from companies selling products or services that all sound good.

“It feels like with COVID in particular, it’s so new it’s hard to know what’s a fact and what’s not. When a company is selling something, they want to tell you the best thing about their product,” she said.

The federal CARES Act includes money for adaptation of homeless shelters, but Groh said everybody is trying to figure out how to spend it wisely.

“That’s the big question. It has all been sort of word of mouth. I’m asking everybody I know. We need expertise,” she said. “I’m sure lots of people are in the same boat.”

Finally, there’s one more complication. As we’ve seen with testing, industrial supply chains can be brittle.

“There’s a chance that if you find a technology that’s effective you’re not going to be able to get it because it’s going to be back-ordered,” said Caulfield. “I talked to a facility manager and he informed me that getting higher-efficiency filters that fit his air-handling units was probably going to take eight weeks. People have already started ordering them.”

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