Humidity linked to COVID-19 transmission

Coronavirus SARS-CoV-2 spreads more indoors at low humidity.

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By Kara MacSwain, Marketing Communications Specialist, TSI Incorporated

The best way to prevent illness from the novel coronavirus (COVID-19) is to avoid being exposed to it. In addition to wearing masks, washing hands and keeping a safe distance from others, studies now show that there are more actions we can take to minimize the spread of infection indoors—and HVAC system adjustments are high on that list. 

When the pandemic began, it was thought the main method of transmission was through large droplets from infected people sneezing or coughing. However, there was soon mounting evidence that the virus that causes COVID-19, known as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), was transmissible via aerosols. The World Health Organization (WHO) defines droplets as particles of more than 5 μm in size, and defines aerosols as those less than 5 μm. Furthermore, when infected individuals expel the virus—which could be by simply breathing—it travels further and remains airborne longer in dry environments. 

What should you do?

With accumulating evidence that individuals have improved immunity against respiratory infections in that range and microorganisms have a less chance of survival, ASHRAE recommends maintaining indoor relative humidity between 40-60% RH.  

Seems simple—Is there a catch?

Not all HVAC systems are flexible enough to implement the recommendation since they were designed mainly for energy efficiency and occupant comfort. Now they are being tasked to handle the additional recommendations specifically for reducing the risk of exposure to the building occupants.

Before you proceed with the recommendations, consider these questions:

• Can the existing humidification/dehumidification components consistently maintain the recommended humidity set points?  
• Changes may require increased cleaning and maintenance of the heating and cooling coils and humidification systems
• Additional humidification in cold climates can lead to increased condensation on cold surfaces.  
  • The changing seasonal temperatures and humidity can also impact the HVAC system and settings on a daily basis.
  • Without proper building insulation, there is an increased potential for mold growth, especially in areas not readily accessible or visible (behind an interior wall adjacent to the buildings structural wall)

When major adjustments are made to the HVAC system, especially those that were not part of the original design intent, it requires professionals to inspect the system and to make recommendations to the building owners. This may involve Test and Balance (TAB), Commissioning, Building Automation System firms and others to thoroughly review the HVAC components, building plans, mechanical schedule, sequence of operations, and automation controls to effectively implement the desired change requests.