Canadian Consulting Engineer

ASHRAE clarifies HVAC guidance for reopening buildings during COVID-19

August 19, 2020

Updates offer additional information to help prevent running HVAC systems 24-7.

ASHRAE COVID-19 building readiness guide

As buildings reopen during the global COVID-19 pandemic or are prepared to do so, ASHRAE’s epidemic task force has updated its ‘building readiness’ guide for HVAC systems to help mitigate the transmission of the novel coronavirus.

“By rolling out this updated guidance, we are providing a more robust structure for building owners to complete their plan and anticipate the needs of occupants,” says Wade H. Conlan, P.E., BCxP, the task force’s building readiness team lead.

The guide addresses commissioning, systems analysis, increased filtration, air cleaning, domestic and plumbing water systems and overall system improvements to mitigate virus transmission. The updates offer additional information and clarifications to help building owners avoid having to operate their systems 24-7, including the following recommendations:


Pre- and post-occupancy with outdoor air

The intent of this strategy is to ensure infectious aerosols in the building at the end of occupancy are removed prior to the next occupied period. The building is flushed for a duration sufficient to reduce concentration of airborne infectious particles by 95%. For a well-mixed space, this would require three air changes (i.e. three times the building volume) of outdoor air or three equivalent air changes, including the effect of filtration and air cleaners, as detailed in the calculation methodology. There are also methods to increase the quantity of outdoor air introduced by HVAC systems.


Energy recovery ventilation (ERV) systems operation

Guidance is provided to assist in determining if an energy recovery system using an energy wheel is well-designed and maintained and should remain in operation. Based on the assessment of ERV conditions, it may be possible to fix problems and return to service.


Building readiness modes of operation

These modes include:

  • epidemic operating conditions in place (ECiP).
  • occupied at pre-epidemic capacity.
  • occupied at reduced capacity.
  • temporarily unoccupied.
  • operating during closure for indefinite period.
  • post-epidemic conditions in place (P-ECiP).
  • prior to occupying.
  • operational considerations once occupied.


To view the complete guide and ASHRAE’s other COVID-19 resources, visit


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