HVAC trends in the fight against COVID-19Penny Hoelscher | May 23, 2022
Can COVID-19 be transmitted through ventilation systems? The jury, including the U.S. Centers for Disease Control and Prevention (CDC), is out on that one. However, concerned office workers have a right to voice their concerns about workplace safety. This may be a good time for organizations to jack up their ventilation systems as part of a preventative maintenance solution for heating, ventilation and air conditioning (HVAC) equipment and appease their staff.
Evidence of airborne transmission of COVID-19
Like measles, tuberculosis and influenza, the severe acute respiratory syndrome (SARS) virus is an airborne disease. Research done after an outbreak in 2003 of SARS-CoV-1 in the Amoy Garden complex in Hong Kong indicated the virus was spread through a faulty drainage system into the ventilation system, and then passed into adjacent buildings in windy conditions.
There are multiple differences between SARS-CoV-1 and SARS-CoV-2, which is the virus that causes COVID-19. The main difference is that COVID-19 is more easily transmitted; potentially bad news for ventilation systems.
Standards for acceptable air quality
In 2020, the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) published a comprehensive COVID-19 Preparedness Resources web page to assist building industry professionals on how best to protect building occupants from COVID-19 exposure. ANSI/ASHRAE 62.1-2019 and 62.2-2019 are the de facto standards in the building industry for ventilation system design and acceptable indoor air quality (IAQ).
Trends in ventilation to mitigate the spread of COVID-19
- More fresh air: Increasing the number of naturally ventilated areas, for example by opening windows instead of relying only on HVAC systems.
- Social distancing: Reducing occupant densities in rooms, for instance by allowing some employees to work from home, or relocating some people to underutilized areas of a building.
- Displacement ventilation: This strategy works by systematically removing contaminated indoor air and replacing it with fresh outside air. Options include fans to extract stale air in combination with IAQ-responsive building fabric openings like windows and louvers to let in fresh air, and solar chimneys.
- Higher temperatures: There is some evidence that higher room temperatures are associated with decreasing survival times for COVID-19 particles but the advantage must be offset against energy costs and the potential impact on other parts of HVAC system.
- Humidification: Although an unproven technique, there is some evidence that humidification may reduce the number of viral particles in the air.
Air-cleaning options include installing or upgrading HVAC systems and using in-room devices that utilize different combinations of air cleaning technologies, like mechanical or electronic filters, and ultraviolet and ionization techniques.
- Modifications to existing equipment: Improvements to existing fan coil units (FCUs) in re-circulatory systems, for example by increasing the number of filters. The downside to this strategy is that, unless properly configured, modifying HVAC systems has the potential to increase energy consumption.
- UVGI/UV-C light treatment: Ultraviolet germicidal irradiation (UVGI) was originally used to reduce the spread of tuberculosis (TB) pathogens. The technique uses ultraviolet C (UV-C) irradiation to inactivate viral, bacterial and fungal organisms. Upper-room UVGI refers to a method of using UVGI that concentrates UV energy in a particular zone above room occupants to prevent direct UV exposures to people in the room. The CDC recommends upper-room UVGI for indoor areas where there are inadequate HVAC system controls or where natural ventilation is not possible.
- Air cleaners: Air purifiers are used to remove small airborne particles. Their efficacy is measured against the Clean Air Delivery Rate (CADR) standard, which specifies the size of airborne particles that should be filtered under certain conditions, for example by room size or use. Portable units may be used to supplement HVAC system filters where other controls, like opening windows, are not feasible.
- HEPA filter: According to a CDC FAQ, high-efficiency particulate air (HEPA) filters are a viable solution for filtering COVID-19 particles, which are between 0.12 µm and 0.16 µm in size. By definition, HEPA filters are up to 99.97% efficient for filtering particles between 0.12 µm and 0.25 µm in size.
- Bipolar ionization (BPI): BPI is a controversial technology used to deactivate harmful substances, like viruses and bacteria. It works by generating positive and negative ions into the air that induce particles to clump together, resulting in more effective filtration. Numerous proprietary solutions have been touted as effective air cleaners for facilities like schools and medical facilities. However, a Boeing study on the use of BPI for disinfecting airplanes concluded that “air ionization has not shown significant disinfection effectiveness”. Other experts who do not recommend its use put forward the argument that it has not yet been fully tested. The efficacy of BPI and other filtration methods is still under review by ASHRAE.
- Optical biosensors: Currently successfully detecting COVID-19 particles on surfaces, an optical biosensor developed by researchers from Empa, ETH Zurich and Zurich University Hospital in the future could be used to measure the concentration of COVID-19 particles in the air.
COVID-19 is changing the way building industry professionals design HVAC systems. However, it is not always economically feasible for building owners to overhaul their existing HVAC systems entirely. Organizations need to take a holistic look at all areas of their building and how people use the spaces. There is no “best” solution across the board for improving ventilation. For example, increasing social distancing sounds cost-effective but only works if there is underutilized space available. Using air purifiers can be expensive and provide fewer benefits than simply opening more windows, if there are any.
The way forward is to start with CDC’s feasibility plan. The CDC recommends a layered system, including ventilation interventions like opening windows, using fans, adding HEPA filtration, and using upper-room UVGI.
Organizations should be cautious and research proprietary solutions and new technologies thoroughly before adopting them. According to the aforementioned Boeing study, “Due to a lack of both iterative and standardized protocols for testing the technology, there have been variances in test reports, from both Boeing and also external evaluations of similar nature.”
The good news is that continued maintenance of ventilation systems in public areas like airports and hospitals and in the workplace will help to assuage people’s fears and at the same time ensure compliance with government ventilation regulations.