Can HVAC Systems Help Prevent Spread of COVID-19?

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As the novel coronavirus and accompanying COVID-19 infection continue to dominate headlines – and rightfully so – many around the world still seek any additional information scientists can learn about the virus and how it is transmitted. After all, beneficial preventative measures can only be developed based on data. Why are some seemingly immune while others die, and what are the best ways to prevent the spread of COVID-19?

As the great mask debate of 2020 rages forward, some other options for controlling the pandemic might be overlooked. Can some types of disinfectant kill the virus better than others? Is there any way to deploy technology to battle COVID-19? How far can ventilation systems transmit the virus? Is there any way to control the indoor air flow to help prevent people from getting sick?

An Airborne Virus

According to the Centers for Disease Control (CDC), the virus that causes COVID-19 primarily spreads from person to person through respiratory droplets – liquid particles exhaled. When those particles land on another person or land on an object that is then touched by another person, the virus can infect them. Therefore, an entire building theoretically could become infected just by people breathing the same air as one another.

Could the likelihood of community spread be increased if the virus passes through an HVAC system? Will the ventilated air just distribute the virus from one area of a building to the next? Surprisingly, some industry experts say it’s unlikely.

“There have been thousands of papers and articles published since the pandemic started, and in all of the reports of how COVID-19 is transmitted, there are no reports of space-to-space transmission through an HVAC system,” Pennsylvania State University’s professor of architectural engineering William Bahnfleth told ACHR News. “However, HVAC systems do move air around in spaces, because that’s the only way to condition air. That has the potential to spread contaminants, but most HVAC systems… provide ventilation and filtration, which are both risk-reducing factors.”

At the same time, the World Health Organization (WHO) has ultimately expressed concern about possible in-room transmission, particularly buildings with strong airflows that force the air to travel greater distances. Likewise, the CDC cites at least one example of an asymptomatic patient transmitting the virus to families at two nearby tables in China. Therefore, many would agree it’s better to be safe than sorry. In response, the American Society of Heating, Refrigerating and Air-Conditioning Engineers has prepared a collection of proactive guidelines address concerns that COVID-19 might spread through the operation and maintenance of HVAC systems. The Environmental Protection Agency also offers its own HVAC guidance.

HVAC and Coronavirus

Taking such guidelines into account, is it then a shock to learn that HVAC systems might help prevent transmission of the coronavirus? According to the team from McKinsey & Company’s Advanced Industries Practice, modifying heating, ventilation and air-conditioning systems might actually reduce further spread of COVID-19 by “purifying air, improving ventilation, and managing airflows.”

In its report, the team acknowledged the different ways the coronavirus is spread before explaining how these methods support the primary recommended prevention measures: social distancing at least six feet apart and wearing masks.

In fact, WHO only recently acknowledged – after receiving a letter from  239 scientists – that the virus can be airborne and transmitted, especially among those who spend extended time in crowded and poorly-ventilated rooms.  Medical experts aren’t the only ones concerned with COVID-19 spreading via HVAC systems. Building managers, landlords, owners, safety experts and especially workers and residents have a dog in the fight against coronavirus.

“HVAC systems can potentially spread a virus across rooms when high-speed air flows past an infected person to others,” the McKinsey & Company team wrote. “If airborne transmission is also possible with the coronavirus, a few control-setting changes and upgrades may help decrease the risk of spread through this route. If building managers take such actions, they might help their residents feel more comfortable amid all the uncertainty about the coronavirus.”

HVAC as COVID-19 Prevention

So, how can an HVAC system be harnessed to help prevent the spread of COVID-19? It starts by optimizing indoor ventilation and airflow to limit the virus’ spread, much as might be done to improve overall air quality. Some of these adjustments might be as basic as tweaking a few control settings – like running the HVAC overnight or on weekends even when no one is there – or installing some simple upgrades to the HVAC system.

Specifically, some technicians will configure a ducted HVAC system to boost the rate of exchange with fresh air from outside the building, reducing how much air is recirculated throughout the inside. Other airflow management techniques that could help reduce transmission of the coronavirus include ensuring a slow and steady air speed and directing any potentially contaminated air out of rooms and away from people.

Other recommendations for upgrading an HVAC system so it helps prevent the spread of COVID-19 include:

  • Replace fixed-speed fan motors with the variable-speed variety to improve the control of airflow
  • Deploy more sophisticated airflow-control systems that are pressure sensitive and allow a smoother adjustment of airflow
  • Install a high-performance system for air purification

Filtering the air to slow the spread of COVID-19 seems like a no-brainer, right? Still, there actually are a variety of ways to accomplish purer air. Most property owners and operators will choose filtration as the best way to purify indoor air. Through this method, air is forced through a fiber-based material or a membrane of some sort. The filter manually collects particles that would otherwise blow back out through the vents and ductwork.

High-efficiency Particulate Air (HEPA) filters are particularly recommended as the most effective for removing particles. In fact, to achieve the highest filter ratings, they must remove 99.97 percent of particles of 0.3 microns or larger.

“The mechanical filters in HVAC systems have tangled fibers that trap particles too large to fit through the openings,” the McKinsey & Company team said while explaining filtration as an air purifier. “Mechanical filters have different ratings, based on the percentage of particles they remove, with the highest rated typically used in surgical or clean-room applications.”

Better yet, the engineers at McKinsey & Company describe how altering airflow patterns and establishing laminar vertical  airflow, which occurs when air moves the same speed and in a straight path, could be the most effective weapon in the arsenal when it comes to preventing airborne transmission of coronavirus-laden particles. Much like hospitals minimize contamination by directing air in operating rooms from the ceiling to the floor.

Unfortunately, creating laminar airflows isn’t a simple task. New buildings must include a certain number of air outlets, and existing construction probably needs air outlets upgraded.

“Technicians may need to upgrade the outlets in HVAC systems – for instance by adding some outlets in the space provided by suspended ceilings,” the McKinsey & Company team wrote. “In some cases, technicians may replace outlet covers, which are normally designed to mix and distribute air, with covers that produce laminar flows. For both new and existing buildings, the placement of air outlets is critical and must be based on planned occupancy, room architecture, furniture placement, and other factors that influence airflows.”

So, upgrading HVAC systems to help prevent the spread of COVID-19 might be complicated, and it might cost money. But are the lives of customers, vendors, workers and residents worth it? Even the experts agree it can make a difference.

“If we’re looking at ways to reduce the spread, it really comes down to trapping, diluting, and/or inactivating the virus. Ventilation will help with dilution, and on the commercial side, ASHRAE has addressed this topic pretty well on its website,” Johnson Controls director of marketing told ACHR News. “The key is to flush the building with outside air at rates that would not be sustainable for comfort control. This is particularly the case if buildings have been vacant for a while. There are even discussions about the need for periodic flushing when occupants leave the space, which would be a new ventilation strategy.”

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