Building HVAC Recommendations for COVID-19

The science on the transmission of the COVID-19, or SARS-CoV-2, continues to evolve. At VHV, we are continuing to monitor the latest recommendations and guidelines to best serve our employees as well as our customers. 

Previously, ASHRAE (the American Society of Heating, Refrigeration, Air Conditioning Engineers), through its Environmental Health Committee, created the Epidemic Task Force, and issued the following statements:

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.

Statement on operation of heating, ventilating, and air-conditioning systems to reduce SARS-CoV-2 transmission:

Ventilation and filtration provided by heating, ventilating, and air-conditioning systems can reduce the airborne concentration of SARS-CoV-2 and thus the risk of transmission through the air. Unconditioned spaces can cause thermal stress to people that may be directly life threatening and that may also lower resistance to infection. In general, disabling of heating, ventilating, and air-conditioning systems is not a recommended measure to reduce the transmission of the virus.

Facility and building managers continue to look for recommendations on how to prepare a facility for reopening and new standards of building operations amidst COVID-19. Based on the latest scientific findings, increasing filtration and disinfection are the two recommended methods by the CDC to provide a safe working environment for business operations for non-medical facilities.

Particulate Science Overview

Much of what is known of the virus is still open-ended, but the World Health Organization and the scientific community agree that the SARS CoV-2 virus is primarily spread through droplets of saliva or discharge from the nose and mouth of infected individuals. These droplets can be aerosolized, where they can linger in the air for hours, some reports suggest even days. The lifespan of the aerosolized virus is still under study. 

Some open studies suggest that a physical or social distance of 6 feet is not enough when an infected individual is projecting with force, which translates to actions like laughing, singing, yelling or sneezing, which can carry particulates further than breathing or talking. Accordingly, the CDC recommends installing physical barriers if possible in between work spaces if possible. 

According to an article in ASHRAE's September issue, "increasing evidence suggests that smaller aerosols remain suspended in the air, where they expose occupants (airborne transmission)." It is not yet known how long the virus can remain in the air, but the important understanding of exposure and infection can help determine the necessary proactive steps for HVAC system updates to reduce these risks. An individual's health risk is related to the duration of exposure, as well as the concentration virus particulates within the air. 

In addition to the current CDC recommended preventative measures of wearing masks, distancing, and diligently washing hands, there is now increasing demand for building operations to consider the risk of transmission through a building’s HVAC system to further protect those working or living inside. Recommended changes include:

• Improved mechanical hygiene
• Increased ventilation
• Advanced filtration
• Humidification

These recommendations are the result of specific environmental epidemiology case studies, where engineers and health scientists collaborated to understand the role HVAC has in the spread of the COVID-19 virus and infection risks. Each of these cases can be read more closely in ASHRAE's article on the subject. 

Case Study: Poorly Ventilated Restaurant

The role of different transmission routes was evaluated by comparing factors influencing
exposure of two groups, the infected and unaffected customers and staff.

• HVAC consisted of five fan coil units (FCU) with no outside air and exhaust fans (off at the time).
• Measured ventilation rates (infiltration only) were an order of magnitude below ASHRAE Standard 62.1- 2019.
• Modeling of airflow patterns established that a “bubble” was formed by each FCU, dividing the room into five separate zones containing contaminants released in that zone.
• Modeling results also suggested that discharge from the FCUs directed air in the breathing zone between customers. The tables with those who became infected were within the same zone.
• Waiters did have brief contact with infected customers, but exposure was insufficient to cause infection. 

Case Study: Poorly Ventilated Conference Center

In China, 30 people attended a 3-day event with one infected individual in a building with poor ventilation.

• HVAC cycled on only 15 minutes per four hours
• 15 attendees were subsequently infected.

Investigators concluded that some infections were due to airborne exposure after comparing the infection rate to similar outbreaks and that ineffective dilution because of poor ventilation appeared to be a major contributor.

Case Study Findings 

In these two case studies as well as multiple other epidemiological studies from around the world, experts conclude that while HVAC systems can play a role in spreading the virus beyond the immediate vicinity of an infected individual, optimal HVAC performance can effectively dilute the virus through increased ventilation to reduce disease spread.  

Furthermore, proper positioning of air distribution is key. In the restaurant case study, wall-mounted fan coil units blew air directly onto customers, effectively directing contaminants onto their table and into their direct air supply. Some experts suggest air directly blowing on surfaces could resuspend aerosolized virus particulates. Air distribution should be reviewed for increased circulation and filtration to increase the dilution of contaminated aerosols and decrease the risk of concentrating the virus for individuals near blower vents. 

High Occupancy Facility Measures to Reduce Airborne Transmission 

Concerns about cold climate transmission of the virus is starting to concern educators and administrators. Winter conditions mean that internal spaces stabilize with lower relative humidity (RH) which can directly affect indoor environmental quality (IEQ).  

In a recent study, researchers found that innovative variable air volume (VAV) design can reduce transmission of airborne pathogens through humidification of outdoor air ventilation while meeting the requirements for air ventilation currently recommended for high occupancy buildings.   

Indoor RH can stabilize at 20% or lower when cold ambient air is brought in to a building and heated before distribution, creating a dry environment that can lead to increased infection rates for any communicable disease. For decades, air-to-air heat exchangers have become the primary method used to recover building generated heat, as was necessary to comply with winter ventilation standards. This study introduced adiabatic cooling/humidification to deliver air at 40% RH in a central station air-handling unit. These findings provide a novel solution for high occupancy buildings like schools and offices to improve the IEQ as the winter months approach. 

Recommendations

ASHREA & VHV Company recommend taking the following steps to mitigate the spread of COVID-19 indoors:

• Air-handling systems that permit building air recirculation should increase outdoor air ventilation above code minimums.
• Installing MERV 13 (minimum) filters if they are not in place.
• Control indoor relative humidity between 40% and 60% RH.
• Flush the building prior to occupancy with all outdoor air to remove any residual infectious aerosols indoors. 

UV Light as a Disinfectant

In addition to increasing ventilation and installing higher efficient filters, UV light can be installed to decrease particulate and viral transmission. Ultraviolet energy emitted from lamps inactivates living microorganisms, including viral, bacterial and fungal organisms. While the entire wavelength of UV light can “disinfect”, the most effective germicidal wavelength is 265 nm. 

UV-C LEDs are currently reaching the market for a cost effective installation for small to medium size facility HVAC units. Types of systems using UV-Cs include:

• In-duct air disinfection
• Upper-air disinfection
• In-duct surface disinfection
• Portable room decontamination 

Have experts help with building HVAC system preparedness

When determining how to improve the HVAC system of any building, facility, or workspace, consult with the experts. The information online is only the tip of the iceberg, and the industry has been evolving as knowledge about the SARS-Co-V-2 virus does. Trust the expertise of specialized HVAC engineers and technicians with experience in finding HVAC solutions to help your business and organization combat the novel coronavirus.