The ASHRAE Epidemic Task Force recently released a position paper warning that, “Transmission of SARS-CoV-2 through the air is sufficiently likely that airborne exposure to the virus should be controlled.” The Task Force states that improving the operation of HVAC systems can reduce airborne exposure to the virus.

The overall concept ASHRAE recommends is to “increase outside air (OA) to the spaces and treat return air” along with “mechanical filtration of the supply air and maintaining indoor comfort as defined by the design temperature and relative humidity.”

• Size dedicated outdoor air systems (DOAS) for a capacity at least 150% of code minimum flow.
• During the Pandemic, disable any demand-control ventilation and introduce the maximum possible OA flow 24/7 until further notice (including DOAS).
• Winter classroom design guidelines 72°F/40-50% RH.
• Summer classroom design guidelines 75°F/50%-60% RH.
• Use the highest MERV filter applicable for the HVAC units (local, central and DOAS). HEPA or MERV 14 is recommended.
• Guideline minimum of 2 air changes/hour.

Nurse’s Offices are to be treated as isolation rooms-

• Isolation Room and Nurse’s Office will be Negative Pressure (-0.015” to –0.5” W.C).
• Protective Room will be Positive Pressure ((+ 0.015” to + 0.5” W.C).
• The HVAC operation will be “Isolation mode” OR “Normal Mode”.
• For “Isolation mode” design Dedicated HVAC system.
  • 100% OA system. No air re-circulation.
  • Design for a maximum of 10 Air Changes per Hour (ACH), can operate at 6 ACH.
• For “Normal Mode” the HVAC system can be (supplementary) standard HVAC system (VRF +DOAS, Fan coils, WSHP/GSHP, DOAS, etc.) with current design practices.

If existing HVAC filtration cannot be sufficiently upgraded, there are options-

• Provide a recirculation fan filtration device and duct into the return of existing HVAC units.
• Provide a HEPA filtration unit which re-circulates air within the space.