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Air Ventilation Systems and Virus Transmission

Restaurant operators are now reopening their doors to dine-in guests amid controversy and concern. As much as full-service restaurant owners hope to resume and guests hope to enjoy dine-in service, everyone is moving forward on faith in best practices promoted by government and health authorities.

So, you may well ask if social distancing, screening employees with temperature checks, and staff donning personal protection equipment (PPE) are sufficient to protect guests, employees and the public from COVID-19 infection. These are important preventative measures.

You should also be aware, according to virologists and ventilation experts, COVID-19 can remain airborne for a few minutes to a few hours, and it can be pulled into the HVAC system and distributed throughout the dining area. I spoke to several of these experts to learn what they believe restaurateurs should understand about COVID-19 and ventilation systems as they invite guests back into their dining room.

Your restaurant's heating ventilation and air conditioning (HVAC) system can spread airborne diseases within your four walls.

Donald Milton, M.D., professor of environmental health at the University of Maryland School of Public Health, and Qingyan Chen, Ph.D., a professor of mechanical engineering at Purdue University, both study communicable disease transmission in public places, and the role of ventilation systems in that process.

Joe Davis and Ed Neese are president and vice-president, respectively, for Eldridge Ventilation and Noise Control, founded in 1946. Eldridge is a national consulting company that is applying its expertise to help restaurant operators insure their ventilation systems are set up to reduce circulation of pathogens in their business.

The Routes of Transmission

Operators need to consider the routes of spreading the disease individually, says Chen. These include direct and indirect contact. You are likely familiar with them, but let's review.

Indirect contact transmission is addressed by single-use menus and taking care to sanitize surfaces and small wares. If there is any good news regarding the COVID-19 virus, according to Chen, it doesn't survive at higher temperatures over 60 degrees C (140 degrees F).

Standard diligent restaurant dishwashing methods are effective, as long as utensils and small wares are handled carefully. Other forms of indirect contact include touching contaminated surfaces. Frequent disinfection of surfaces addresses these routes of transmission. Measures to help guests and employees avoid touching door handles are also useful.

Complying with government health recommendations, restaurants are requiring staff to submit to having their temperatures taken upon arrival. If they indicate a fever they are sent home. Milton notes, however, persons might be contagious even if showing no symptoms.

Milton and fellow researchers are trying to determine if people who were infected and recovered from COVID-19 "continue to shed the virus a month after they got sick." Even healthy appearing guests and staff might be shedding the virus to others simply by talking. Diners are certainly not wearing PPE as they enjoy their meals. "Aerosolization", or airborne disease transmission, is a form of indirect-contact transmission that social distancing and PPE are designed to minimize. Your restaurant's ventilation system can also play a role in either contributing or mitigating the spread of airborne pathogens -- including COVID-19.

The tactics to mitigate the spread are well-established. One way is to bring in more outdoor air, says Milton. A study in China suggests most COVID-19 transmission occurs in enclosed spaces and rarely outdoors. Chen recommends retrofitting HVAC systems with HEPA filters and ultraviolet germicidal irradiation (UVGI) light, which kills viruses.

Now that we've reviewed the science, the questions remain: How do you evaluate if your restaurant's HVAC system is sufficient to mitigate the spread of disease within your four walls, and what are the practical solutions?

Where the Rubber Meets the Road

The COVID-19 crisis was largely responsible for Eldridge Ventilation and Noise Control to apply its expertise in restaurants, says Neese. Operators reached out to the company for advice as they anticipated reopening. "Our customers have driven it," says Neese. Indeed, the pandemic has spurred restaurateurs to think about the role of their HVAC systems in protecting guests.

Neese believes operators should consider addressing the role of HVAC systems in spreading disease is not only valuable in addressing COVID-19, but any airborne pathogen, including influenza.

In short, it might be a sound health and safety investment going forward, regardless how this pandemic plays out. Nevertheless, as every restaurateur knows, the first rule of economics is "there's no such thing as a free lunch". Practical measures to upgrade and retrofit HVAC systems can be expensive. On the other hand, notes Neese, operators can promote their efforts to increase guest confidence, which is critical to winning back their patronage in the wake of the pandemic.

Davis and Neese echo Chen's and Milton's advice, both on the importance of introducing fresh air into enclosed spaces, and the role of filtration and UVGI light to minimize and kill airborne pathogens. And they offer practical advice on accomplishing these tactics.

More Air

In terms of introducing fresh air into enclosed spaces, "air change rate" is critical, says Davis. "Air has to move to pick up aerosolized viruses and draw it into the ventilation system to filter or kill them."

Among the first ventilation system features to consider are placement of vents. Are there a sufficient number? Where are they located? According to Davis, you want air drawn into the space at low points in the room and pulled in at the ceiling as common knowledge tells us warm air rises.

The next thing to consider is increasing additional fresh or "make-up" air into the HVAC system. Make-up air is designed to "make up" the air in your interior space that has been removed by exhaust fans.

In short, it requires bringing fresh air from outside your building to replace existing air that cannot be recirculated. For example, if your system is only pulling in 10 percent make-up air, you might want your mechanical service to increase it to 50 percent or more.

The expense of drawing in additional make-up air includes the added energy to refrigerate or heat the increased make-up air. According to Davis "indirect evaporation cooling works wonderfully" to reduce the added energy costs of cooling the increased make-up air. Indirect evaporation cooling often uses heat exchangers to passively cool outside air; although as Davis notes, there is an expense of adding the unit to the existing system.

Filtration

"The second piece" of reducing the concentration of pathogens in the air is filtration, says Davis, echoing Chen's advice. There are a couple of approaches.

One is HEPA filtration, which is fine in theory, but can introduce mechanical challenges, says Davis. HEPA is an acronym for "high-efficiency particulate air" and describes filters that are able to trap nearly all particles that are 0.3 microns, says Davis. For perspective, says Davis, consider a grain of sand is 40 microns. HEPA filters can remove aerosolized viruses.

Commercial HEPA filters are larger and thicker than standard HVAC system filters, and thus are not necessarily an easy swap without significant modification to the system. In addition, says Davis, because they are denser they reduce the velocity of the air passing over the filter.

This additional drag can compromise the system by straining existing fans and the motors. Davis says you can speed up airflow and avoid overtaking the system by increasing the size of the fans and motors, he says. This, of course, can be a significant mechanical expense, not to mention additional maintenance.

HEPA filters stop almost everything, and thus have to be changed more frequently than standard filters that allow small particles to pass. According to Davis, one way to increase the life of HEPA filters is to install less expensive "pre-filters" upstream.

An alternative (or even possible compliment) to HEPA filters is UVGI light in the system. UVGI light kills pathogens, including COVID-19. As you might imagine, there can be significant cost to installing these lights, including the cost of the equipment and wiring. UVGI lights are not maintenance free, with about 9,000 hours of life before having to be replaced. For a typical restaurant that is about two years. And, of course, as with all lights, they draw energy.

Working with Your HVAC Contractor

As Davis and Neese point out, the main value of this article is to arm you with information in conversations with your HVAC contractor. Depending on the skills and profit motive of the company you work with, it might or might not offer these solutions. Hopefully, you will now be better prepared to ask questions and demand effective solutions.

Again, we cannot disregard the expense of the mentioned modifications and retrofits in light of the other financial challenges presented by the pandemic. Particularly if they can be funded with federally back SBA loans under the CAREs Act, however, they could be promoted as a competitive advantage.

POTTY TALK

A form of COVID-19 transmission in restaurants that has received little discussion is aerosolization in restrooms. Qingyan Chen, Ph.D., a professor of mechanical engineering at Purdue University says flushing toilets can release virus from stools and even urine in droplets in the air.

These include requiring only one guest to use the restroom at a time, closing a toilet lid when flushing (many public restrooms don't have lids for security reasons), encouraging guests to don PPE when using the restrooms, and increasing air exchange and filtration as discussed in the main article. There are also affordable compact ultraviolet germicidal irradiation (UVGI) light filtration systems on the market that can be installed in restrooms.