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How COVID-19 Affected HVAC and What's Ahead for Our Industry

July 7, 2021
CLARK'S REMARKS: Our resident sustainability expert steps back to assess our industry's spotty pandemic performance so far and what measures may remain long term.

The following is excerpted from a recent webinar that I hosted for Lorman Education Services. You can access the full webinar on demand here, but there is a cost to purchase it...

Many building operators made changes to their HVAC systems and equipment in response to the Covid-19 pandemic. One of the questions frequently being asked by HVAC professionals is: which of those will continue post-pandemic?

At the beginning of the pandemic, there was a basic lack of understanding as to how the virus was being spread. Was it predominantly surface transmission? Or nearby exposure? Or, was it airborne transmission over a longer distance? And what part did HVAC play in airborne transmission?

Navigating early confusion

Many of those in the HVAC industry looked to organizations like ASHRAE for guidance, but they also had conflicting recommendations and somehow our industry even ended up at odds with the CDC over an outbreak at a restaurant in Guangzhou, China

In March 2020, I shared a 2013 study from the CDC, where scientists found that at relative humidity levels of 23 percent, 70 to 77 percent of flu viruses were still able to cause an infection an hour after they were released into the air. At a relative humidity of 43 percent, that dropped to 14 percent of the viruses still capable of causing infection. Apparently, most of the flu viruses were inactivated after only 15 minutes in the more humid air.

Most now agree that viruses die off faster in higher relative humidity.

The research suggests that virus particles suspended in the air die more rapidly when the relative humidity is higher and, in those environments where viral particles decay faster, less viral material remains suspended in the air, leading to a reduced risk of infection. So, if warm and wet environments are less favorable for the coronavirus, as appears to be the case, it becomes a tradeoff between safety and comfort. Because high relative humidity can be extremely uncomfortable to building occupants, and in this instance comfort appears to have won over safety. Few if any buildings appear to have introduced high humidification as a means of controlling the spread of the novel coronavirus.

UV light systems for coils and ductwork have been around for a while, and broad-spectrum UV light, with wavelengths of 200 to 400 nanometers has long been recognized as effective against viruses.

So it’s no surprise that interest in UV surged during the pandemic. Unfortunately, broad-spectrum UV light can be harmful to humans, causing skin cancers and cataracts. However, a narrower spectrum of UV light in the range of 207 to 222 nm, known as far-UVC, has been shown to effectively kill viruses without penetrating (and damaging) human skin or eyes.

Another technology, known as needlepoint bipolar ionization (BPI), was also being promoted for use in HVAC systems to help control the spread of the virus. It claimed that it could both neutralize viruses and possibly lower outside air requirements by reducing particulates and VOCs. However, after Boeing tested BPI, they concluded that it was not effective enough to install on its commercial planes, and now their study is being cited in a federal lawsuit against a leading BPI manufacturer, seeking class-action status, that alleges the claims about the technology are “deceptive, misleading, and false”.

Increasing outdoor air and related energy tradeoffs

Increased outdoor air has, of course, been one of the most prevalent changes made to commercial HVAC systems during the pandemic. Dilution has long been recognized as a means to address contaminated air, whether it’s with pathogen-containing droplets, particulate, or VOCs. Some of the specific measures that were recommended in order to achieve increased ventilation rates in buildings included:

  • Opening outside air dampers;
  • Opening any operable windows;
  • Performing a comfort balance to ensure that all occupied spaces are receiving adequate fresh air;
  • Disabling CO2-based demand-controlled ventilation systems and occupancy sensors;
  • Flushing spaces with outside air between or before periods of occupancy; adjusting VAVs so that outside air is not reduced when temperature is satisfied; and...
  • Running air handler fans continuously.

Of course, the obvious downside to increased ventilation rates is the increase in energy consumption required to provide and condition that air.

Higher efficiency filtration was another primary HVAC solution. The commercial guidance from ASHRAE’s Epidemic Task Force issued on April 20, 2020, recommended a minimum of MERV 13 or the highest compatible with the filter rack. Unfortunately, some building operators installed even higher efficiency filters, in some cases HEPA, and burned out fans in a lot of older air handlers.

A number of experts have now concluded that improving filtration is a far more effective response to airborne virus transmission control than is increasing ventilation rates.

As with higher outside air rates, higher filter efficiencies also come with an energy penalty. The future of buildings continuing to provide higher than ASHRAE 62.1-minimum ventilation rates and maintaining MERV 13 filters will probably depend on the likelihood of future endemics or pandemics and the number of workers who return to the office.


A regular contributor to HPAC Engineering and a member of its editorial advisory board, the author is a principal at Sustainable Performance Solutions LLC, a south Florida-based engineering firm focusing on energy and sustainability. Contact him at [email protected]