5 HVAC Strategies for Covid-19
This is our second in a series of articles discussing the impact of Covid-19 on Senior Living design. In this article we will share the five (5) strategies we are exploring for designing HVAC systems for Covid-19.
As we are all now painfully aware, Covid-19 and similar viruses can be aerosolized by coughs, sneezes, and perhaps even normal breathing, contaminating indoor air. We’re all gaining more IQ about IEQ (Indoor Environmental Quality)! Mechanical HVAC (Heating, Ventilation, Air Conditioning) systems control indoor air quality to greater or lesser degrees based on their design, installation, and operation. Even the best HVAC systems cannot completely prevent the spread of infectious aerosols. However, they can be designed to dramatically reduce the amount of disease circulating in the air. Here we will discuss five HVAC design strategies that should be considered for new and existing facilities.
Isolation. We rank this first because the most effective thing we can do to limit the spread of disease is to prevent contact. Like bulkheads in a ship, HVAC systems can be designed to limit air from circulating between areas of the building, thereby stemming the migration of pathogens. Isolated areas can be an individual room, group of rooms, or entire wing of a building. Engineers should consider atmospheric pressure differentials and the direction of flow between spaces. For instance, a room with a negatively pressurized atmosphere may draw air from an adjacent space, potentially bringing airborne pathogens into the room. This can be mitigated through careful design. Another factor that is easy to overlook is the access and maintenance of equipment. Designers should think through these scenarios and make equipment access decisions that prioritize keeping workers out of resident areas as much as possible.
Diagram showing how HVAC air handlers introduce fresh air into the system.
Ventilation. Introducing sufficient amounts of fresh outdoor air is another critical strategy for reducing airborne contaminants. This works by a combination of dilution and removal of particles from the indoor environment. Mechanical codes have been steadily increasing fresh air ventilation requirements. This trend will almost certainly continue given the new realities of Covid-19. It should be noted that this has a negative impact on energy usage because all of that outdoor air has to be tempered.
Ultra Violet Germicidal Irradiation (UVGI). UVGI is long-established technology which is proven to be effective at killing bacteria, viruses, mold and fungus. Special lamps are designed to emit light waves in the Ultraviolet C spectrum. With enough exposure (irradiance x time), this spectrum of light waves irradiation damages DNA, rendering viruses inactivated (effectively ‘killing’ the virus). This is very promising but very technical and warrants a more thorough discussion in a future article in this series.
Irradiation Wavelengths and their effectiveness against germs.
Humidity Control. There is evidence that indicates Covid-19 and similar viruses degrade faster with higher levels of humidity. This is believed to partly explain why viruses seem to spread more in the Winter season when indoor air can be extremely dry. The evidence is compelling enough that CDC, AIA, and ASHRAE recommend maintaining indoor humidity levels between 40 and 60% for the purpose of disease mitigation. However, with more humidity comes more potential for mold growth. For this reason, our recommendation is to target 40 to 50% relative humidity.
Sorry, I ran out of professional looking diagram ideas.
HEPA filters catch increasing percentages of particles depending on the grade of filter.
HEPA (High Efficiency Particulate Air) filters. Mixed messages are being sent about the effectiveness of HEPA filters in mitigating Covid-19. But don’t be fooled by the latest ‘news’ article. Hospitals have HEPA systems for a reason! While HEPA filters only catch particles that are larger than .3 microns (Covid-19 is .1 microns), most virus microbes float in droplets and clumps that would be large enough to be caught. Incidentally, N95 mask filters only catch particles larger than .3 microns but are generally recognized to be relatively effective against transmission. It is also important to note that there are different grades of HEPA filters that catch increasing percentages of particles. Using a HEPA filter in combination with UVC treatments discussed above can increase the effectiveness of both systems. However, keep in mind that HVAC systems must be designed with the proper sizes of ductwork and fans. You shouldn’t just throw a HEPA filter in an existing system without consulting with a professional engineer to ensure that you don’t ruin your system.
Summary Recommendations. Properly designed HVAC systems can and should be used to help mitigate the spread of disease. The strategies discussed here are not particularly expensive if they are properly planned and executed. Which is where we come in! Vessel is experienced at guiding project teams through these decisions and understands how to properly coordinate HVAC systems with the other systems in our buildings. Please don’t hesitate to reach out to us about your particular questions or situation. We’ll be glad to help however we can!
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