HVAC Standards Bodies Weigh In

Guidelines are ever changing, but both ASHRAE (the standard setting body in the US for heating, AC and refrigeration) and REHVA (the European equivalent) have been coming out with some warnings and recommendations.

ASHRAE’s Environmental Health Committee says we need to take the threat of virus spreading through the HVAC systems seriously:

ASHRAE Statement on airborne transmission of SARS-CoV-2:

  • “Transmission of SARS-CoV-2 through the air is sufficiently likely that airborne exposure to the virus should be controlled. Changes to building operations, including the operation of heating, ventilating, and air-conditioning systems, can reduce airborne exposures.”
  • Source document

REHVA describes 3 methods of transmission:

  1. Small droplets from people coughing, sneezing, talking, and breathing, can remain active in the air for 3 hours in indoor air.
  2. Large droplets also caused by people sneezing and coughing settle on surfaces where they can remain active for 2-3 days.  People contract the virus by touching these surfaces and then touching their eyes, nose or mouth.  If within about 6 feet of a person who sneezes, coughs, or even talks, the virus can be inhaled directly.
  3. Restroom transmission.  Flushing a toilet creates droplets which can get on surfaces or into the air and infect people.

Practical Actions to Take with HVAC Systems

Increase Fresh Air Into The building:

  • Activate mechanical ventilation systems at normal speed 2 hours before occupancy, and for 2 hours after.
  • Activate bathroom ventilation 24×7
  • If your building has demand controlled ventilation based on CO2 levels, increase the ventilation by lowering the CO2 setpoint to 400PPM.  Since this is generally below the level of CO2 in outside air it will cause the system to run all the time.  Lower the speed of ventilation systems when the building is unoccupied but do not shut them off.
  • Open operable windows, warehouse doors, use warehouse fans.

And a Non-HVAC related Measure:

  • Put toilet seats down before flushing, or flush before getting up from the toilet
Click Here: 4 Low-Cost Steps to Mitigate Coronavirus in Your Building

Summary from the REHVA:

We recommend you read the entire REHVA document, but here is the complete list of practical HVAC recommendations from that document:

  1. Secure ventilation of spaces with outdoor air
  2. Switch ventilation to nominal speed at least 2 hours before the building usage time and switch to lower speed 2 hours after the building usage time at nights and weekends, do not switch ventilation off, but keep systems running at lower speed
  3. Ensure regular airing with windows (even in mechanically ventilated buildings)
  4. Keep toilet ventilation 24/7 in operation
  5. Avoid open windows in toilets to assure the right direction of ventilation
  6. Instruct building occupants to flush toilets with closed lid
  7. Switch air handling units with recirculation to 100% outdoor air
  8. Inspect heat recovery equipment to be sure that leakages are under control
  9. Switch fan coils either off or operate so that fans are continuously on
  10. Do not change heating, cooling and possible humidification setpoints
  11. Do not plan duct cleaning for this period
  12. Replace central outdoor air and extract air filters as usual, according to maintenance schedule
  13. Regular filter replacement and maintenance works shall be performed with common protective measures including respiratory protection
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