Want to know more about our COVID-19 building air quality HVAC report?
According to the World Health Organization (WHO) and other health authorities, the 2019 coronavirus (SARS-CoV-2) is transmitted mostly within short distances. When infected persons sneeze or cough, they release large droplets that contain the virus, which normally fall within six feet. These viral particles can also be released when speaking loudly or yelling, Other persons can get infected with direct exposure to these droplets, or when they touch an infected surface and then touch their eyes, nose or mouth.
However, coronavirus also appears to be transmitted by smaller droplets called aerosols, which stay suspended in the air for longer. Aerosols can travel longer distances than large droplets, especially when carried by air currents or HVAC ducts. Considering these risks, ASHRAE has provided detailed guidance on how to prevent airborne transmission of coronavirus. Each building and its systems are unique, but there are general principles that can be applied to prevent airborne transmission of COVID-19:
- Increasing ventilation with outdoor air, while reducing indoor air recirculation.
- Replacing air filters with more efficient units, such as MERV 13 or higher.
- Using Ultraviolet Germicidal Irradiation (UVGI) to complement air filtering.
- Keeping relative humidity between 40% and 60%, since this range minimizes the transmission of viruses and bacteria.
- Inspecting HVAC systems and ensuring they work optimally before reopening a building.
ASHRAE also warns about the Legionella bacteria, which proliferates in warm and stagnant water. Building owners should detect and eliminate any Legionella risks before a building resumes operation. Hot water piping and cooling towers are likely spots for Legionella growth. This bacteria can cause severe pneumonia, similar to coronavirus infection.
Before reopening a building after the coronavirus outbreak, a deep inspection by professional HVAC engineers is strongly recommended. Even if your building has not stopped completely, an indoor air quality assessment can help you prevent coronavirus infections.
HVAC design measures can help prevent the spread of coronavirus, but they cannot prevent infections by themselves. Building owners should make sure that occupants use personal protective equipment (PPE) whenever necessary while practicing social distancing and following all the guidelines provided by health authorities. NY Engineers can analyze your HVAC system and other key equipment, identifying measures to make your building more resilient against COVID-19.
COVID-19 Prevention with Increased Outdoor Air Supply
Many ventilation systems are designed to optimize the outdoor air supply: the outdoor ventilation rate is increased during high occupancy and reduced during low occupancy. This concept is called demand-controlled ventilation (DCV), and it saves fan power while reducing the workload on space heating and cooling systems. However, in response to the coronavirus emergency, ASHRAE recommends keeping the highest possible airflow in buildings, for as long as possible (even 24/7).
In other words, building owners should disable their DCV systems temporarily, and set the outdoor air supply as high as possible. ASHRAE is aware that keeping 100% outdoor air 24/7 is not possible in some climates, or when outdoor pollution is high. However, they recommend increasing outdoor air as much as possible under the operating conditions of each building.
The building should also reduce or eliminate air recirculation by HVAC systems, and also unwanted air movement between building areas. Indoor air should be exhausted without recirculation whenever possible, and replaced with 100% outdoor air.
- Positive pressurization can be used to keep air outside of a specific area. This is achieved by setting the air supply higher than the air exhaust.
- On the other hand, negative pressurization is used to prevent air leakage from a specific area. This is achieved by setting the air exhaust higher than the air supply.
For example, a place where important supplies are stored can be kept at positive pressure to keep air pollutants out. On the other hand, a room where coronavirus could be released should be at negative pressure, keeping the virus away from other building areas.
An increased outdoor air supply helps remove viruses and other air pollutants, by diluting them and removing them from indoor spaces before they spread. This can be complemented with filtering and disinfection, which have the goal of removing pollutants from the air. Filtering is a mechanical method that applies for organic and inorganic particles, while disinfection kills harmful organisms like viruses, bacteria, and fungi.
- Among its COVID-19 guidelines, ASHRAE recommends upgrading all filters to MERV 13 or better.
- The acronym MERV stands for Minimum Efficiency Reporting Value, and the scale goes from 1 to 16.
- A higher MERV means that the filter handles smaller particles, and filters in the range of MERV 13 to 16 are typically used for particles that measure 0.3 to 1.0 microns.
Consider that more efficient filters also create a larger pressure drop in air distribution systems. Before upgrading filters to MERV 13 or higher, you must ensure the HVAC system can handle the extra pressure drop. Simply upgrading to the highest MERV available is not recommended, since this can have a negative effect on ventilation. By having your system inspected by HVAC experts, you can use the optimal filter ratings.
High-Efficiency Particulate Air or HEPA filters are even more efficient than MERV 16, capturing 99.97% of particles with a diameter of 0.3 microns. However, HEPA filters create an even larger pressure drop than MERV 16. For this reason, HEPA filters are not suitable for many HVAC systems, but you can also find them as portable air cleaners.
Want to know more about our COVID-19 building air quality HVAC report?
