Small airborne particles contribute to the spread of infectious diseases of all sorts, and current concerns about the novel coronavirus COVID-19 are highlighting the role of HVAC systems to minimize airborne disease transmission and to ensure better indoor air quality in general.

Because small particles can remain airborne for some period of time, HVAC systems can play a positive role in minimizing disease transmission, specifically by:

  • Supplying clean air to susceptible occupants.
  • Containing contaminated air and/or exhausting it to the outdoors.
  • Diluting the air in a space with cleaner air from outdoors and/or by filtering the air.
  • Cleaning air within the room.

Developing resources

ASHRAE has developed resources to help maximize how HVAC systems can have a positive impact as the coronavirus spreads. The society recommends strategies such dilution ventilation, laminar and other in-room flow regimes, differential room pressurization, personalized ventilation, source capture ventilation, filtration (central or unitary), and ultraviolet germicidal irradiation (UVGI) (upper room, in-room and in the airstream). 

ASHRAE suggests that owners, operators and engineers should collaborate with infection prevention specialists knowledgeable about transmission of infection in the community and the workplace and about strategies for prevention and risk mitigation.

“The recent escalation in the spread of coronavirus disease 2019 is alarming on a global scale,” said ASHRAE President Darryl K. Boyce. “While [we support] expanded research to fully understand how coronavirus is transmitted, we know that healthy buildings are a part of the solution." ASHRAE offers guidance to building owners, operators, and engineers on how to best protect occupants from exposure to the virus and specifically how airborne particles might be circulated by HVAC systems.

Practical standards and guidelines

For example, ASHRAE’s recently approved position document on Airborne Infectious Diseases summarizes practical standards and guidelines that all types of facilities should follow.

ASHRAE Standards that can have a positive impact on the spread of COVID-19 include those covering ventilation for acceptable indoor air quality, testing methods for general ventilation air-cleaning devices, thermal environmental conditions for human occupancy, and air quality within commercial aircraft. Another ASHRAE standard covers a method for testing UV lamps for use in HVAC units or air ducts to inactivate microorganisms on irradiated surfaces.

ASHRAE also advises that new and existing healthcare intake and waiting areas, crowded shelters and similar facilities should go beyond minimum requirements.

The virus

Since the first notification on Dec 31, 2019, of more than 40 cases of an unusual viral pneumonia of unknown origin in Wuhan, China, the infection has spread to all of mainland China and later throughout the world, according to Healix International. The coronavirus, later designated COVID-19, infects the lungs, causing a viral pneumonia, and causes initial symptoms of fever with cough and sore throat. It can progress to shortness of breath and breathing difficulties leading to pneumonia. There is currently no vaccine or specific treatment.

Among the available ASHRAE resources are a full position document, standards, publication, technical committees, research projects and material to prepare for COVID-19. ASHRAE is a global society advancing human well-being through sustainable technology for the built environment.

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