The American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) has issued HVAC system guidance in response to the COVID-19 outbreak. Their resources are designed to improve and control indoor air quality (IAQ), support emergency preparedness, and integrate infection prevention as well as aid in response or recovery if required.

ASHRAE’s full statement on the airborne transmission of the SARS-CoV-2 virus (COVID-19), reads as follows:

“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 HVAC systems can reduce airborne exposures.”

The organization further stated that HVAC filtration and ventilation could reduce the airborne concentration of the virus, and help reduce transmission risk. Facility officials can create a COVID-19 response plan to reduce HVAC and critical systems operations by implementing the following guidance:

Building Closures

HVAC systems should not be shut down during building closures, and restarting systems can cause stress and failure. Instead, HVAC systems should be kept running to support preparedness for building reopening, and closure periods utilized for cleaning, maintenance, and filter changes. 

HEPA filters may be added if they fit securely and do not cause disproportionate drops in pressure. Old filters may be treated with a 10% bleach solution when being removed, to cut down on airborne transmission caused by filter disturbance during removal.

Building Upgrades

Upgrades to existing HVAC systems can improve air disinfection efficiency and reduce exposure to infectious aerosols. Suggested upgrades include:

  • Enhance filtration with higher minimum efficiency reporting value [MERV] filters. 
  • Exceed code minimums in occupant-dense and/or higher-risk spaces to improve central air and other HVAC filtration to MERV-13 (or the highest level achievable without undue pressure drops.)
  • Provide personalized ventilation systems for high-risk tasks and use local exhaust ventilation for source control. 
  • Add portable, free-standing high-efficiency particulate air (HEPA) filters where possible, and tighten parameters for temperature and humidity control. 
  • Increase outdoor air ventilation by disabling demand-controlled ventilation and opening any outdoor air dampers to 100% (assuming conditions permit.) 
  • Consider bypassing energy recovery ventilation systems to avoid leaking potentially contaminated exhaust air into the outdoor air supply.
  • Increase hours of operation for HVAC systems (run them around the clock, if possible.)

Ultraviolet Germicidal Irradiation (UVGI)

Ultraviolet energy (UVC) with wavelengths of 100 – 280 nm has been deemed capable of inactivating viral, bacterial, and fungal organisms, rendering them incapable of replication and potentially cause disease.

Ultraviolet germicidal irradiation (UVGI) devices can be added to HVAC systems to provide a greater level of disinfection. Most UVGI lamps create UVC energy by transmitting an electrical discharge through a low-pressure gas enclosed in a quartz tube. 

The majority of this energy (around 95%) radiates at 253.7 nm, a near-optimal wavelength. UV-C energy of 265 nm is considered to be the optimum wavelength, which can provide the most significant germicidal effect.

Devices with UVGI capability can be positioned for in-duct air disinfection, upper-air disinfection, in-duct surface disinfection, or used for portable room decontamination in shielded devices that protect the eyes of room occupants. 

For best results, integrate UVGI devices in high-density spaces (such as waiting rooms.) These should be connected to in-room fans when possible to supplement the room’s supply airflow. 

Building Reopening

ASHRAE recommends all building owners and service professionals consider PPE use when maintaining ventilation materials such as filters and condensate. In addition, any custodial staff, tenants, or others who may come into contact with HVAC systems should be advised of the risk of handling filters and other materials without PPE.

Before reoccupation, all outside air intake dampers should be opened to their maximum capacity for a minimum of four hours. During this “flush out” mode, the system must be monitored continuously to ensure proper humidity and temperature levels are not adversely affected. Post-flush, all damper positions should be restored to the recommended positions.  

The status of any heat recovery wheels must be checked for system leakage or cross-contamination. If a service technician is not available, deactivation should be considered as a temporary precautionary measure. 

Fans and dampers for airside systems must also be checked to ensure fans are working and both outside and return dampers are functioning correctly. Damper Rebalancing may be required to reestablish design airflows. Overall, building pressure should be positive. 

Following this guidance can help reduce the risk of airborne transmission of SARS-CoV-2 and make reopening buildings safer for occupants and visitors. 

If you’re wondering how to implement ASHRAE’s COVID-19 guidance in an upcoming build, or curious about improving the internal air quality in an existing or future build, reach out to the IAQ experts at Therma today.