七月 30, 2020

While there are many questions about COVID-19, the World Health Organization and the Centers for Disease Control and Prevention agree on how it’s spread. Current evidence suggests that the coronavirus is primarily transmitted through the air when an infected  person coughs, sneezes, speaks or sings, with secondary transmission through contact with surfaces.  This information, however, leads to more questions—namely related to how we can limit airborne transmission and what level of surface decontamination is effective.

From healthcare settings and commercial spaces to industrial  sites and service provider workplaces, facilities managers are looking to adjust their buildings’ HVAC systems to limit the spread of the virus. Many professional organizations, such as the American Society for Health Care Engineering, the American Society of Heating, Refrigerating and Air-Conditioning Engineers and the National Institute of Building Sciences’ Whole Building Design Guide, have already released design and operations guidance for making these changes, and it’s likely that the next series of code updates will take these considerations into account as well.

We hear a lot of references to  anti-microbial technology, and there are a lot of misconceptions about “killing the  COVID,” but COVID-19 is a virus—not a living organism—so technically you can’t kill it. Further, an antimicrobial coating is not a certain way to kill COVID-19. Anti-microbial surfaces may be effective in helping control transmission of COVID, but these surfaces rely on contact time to be effective or deactivate the pathogen. Relying upon anti-microbial surfaces alone does not eliminate virus transmission—active disinfection is necessary to limit the spread.

One of the more popular active disinfection suggestions we’ve seen circulating is ultraviolet germicidal irradiation, a disinfection method that uses short-wavelength ultraviolet light to kill or inactivate pathogens. For microorganisms (bacteria), it works by destroying nucleic acids and disrupting their DNA. However, its effectiveness in deactivating viral pathogens is a little more complex and less certain.

While guidance for mechanical system modifications are developing daily, building owners and managers must remember that there’s no single, sure-fire fix. Mitigating pathogen transmission requires a comprehensive plan that includes housekeeping and building systems while also balancing risk and cost.

In this “new normal,” the safety and well-being of building occupants is at the forefront of facilities managers’ minds. We’re outlining ways to modify mechanical systems as part of your comprehensive strategy whether you’re looking to adjust existing systems, invest in larger capital improvement projects or implement an entirely new design.

 

 

Incremental Adjustments to Existing Systems

 

Follow CDC Guidelines

It’s important we remember that some of the most effective practices for limiting COVID-19 (or any pathogen)  transmission have nothing to do with mechanical systems at all. Following CDC guidelines, which include wearing a face covering, distancing yourself from others, washing your hands regularly, improving and increasing cleaning protocols and reducing occupant touchpoints, play a large part in reducing the spread of the virus.

 

Conduct an HVAC Check-Up

Before making adjustments, give your HVAC unit a check up to verity that space conditions are being met and fans and dampers are operating correctly. You should also make sure the fans are operating continuously while the building is occupied, as this will improve air turnover to reduce concentrations of infectious aerosols. It is common for a facility operator to  consider a building evaluation or commissioning inspection for an in-depth look at your devices.

 

Increase Ventilation Intake

Increasing the amount of outdoor air intake can improve air quality and air turnover. If the HVAC equipment can handle the additional stress, an incremental increase likely won’t move the dial much when it comes to operating costs.

 

Fix Your Filter

Whether you simply replace your filter or upgrade to a higher level of filtration, this fix will help remove harmful contaminants from the air. Before making a change, make sure your existing filter rack can accommodate increased size and thickness and make sure the filters fit, with the gasket sealing to the frame with no gaps. Increasing the filter efficiency will be pointless if air leaks around them and goes back to the space untreated! You should also examine your fan’s performance to see if it will meet airflow and static pressure requirements without system modification.

 

 

Capital Improvements to Existing Systems

 

Add Outdoor Air

Adding additional outdoor air will increase air turnover, creating what’s known as a dilution ventilation strategy. Creating a schedule to flush a facility with outdoor air after occupancy can play an important part in an overall disinfection/decontamination plan. An engineer should do appropriate calculations to validate the performance of your existing system before you make any adjustments. The changes may require larger equipment, coils or valves, or may require additional equipment such as fans, controls, dedicated outdoor air systems or energy recovery ventilators.

 

Examine the Distribution System

Evaluate your air distribution system to verify that your diffuser placement is minimizing the spread of infectious aerosols. After a computational fluid dynamics analysis to pinpoint optimal layouts, your ducts and diffusers may need to be reconfigured.

 

Increase Filtration Media

Adding more filtration media can improve your equipment’s overall filtration and reduce the dissemination of virus particles. This adjustment may require a larger fan, variable frequency drive or motor to accommodate the increased static pressure from the additional filtration media.

 

Implement Ultraviolet Germicidal Irradiation

As mentioned earlier, ultraviolet germicidal irradiation, or UVGI (UV-C), uses ultraviolet light to kill or inactivate pathogens. Adding UVGI to your facility, in conjunction with increased filtration, can reduce the risk of disseminating or recirculation infectious aerosols. Properly locating the UV and calibrating the intensity correctly are essential to this method’s effectiveness, as the UV must be tailored to the pathogens being targeted. In addition to the UV lights themselves, the system will also require controls, safety measures and electrical connections.

 

Improve the Pressure

Improving the relationships between the pressure in adjacent rooms can limit airborne transmission. To implement this solution, you’ll need to provide ducted supply returns, add additional fans and controls and add room pressure monitors.

 

 

Considerations for New Designs

 

Go Beyond Codes

If you choose to design a new system, improve the ventilation beyond code requirements. It may require additional equipment and will lead to increased heating, cooling and utility loads, but it will be worth the investment.

 

Increase Zoning

While additional independent HVAC zones within your facility will increase costs for mechanical and electrical design, independent zones will better contain infectious airborne particles.

 

Increase Unit Filtration

If you choose to increase your units’ filtration, add larger fans, variable frequency drives and motors to accommodate the additional static pressure from filtration media. While this solution will better circulate air and limit virus transmission, it will also lead to higher operating costs and require more frequent filter changes.

 

Clean with UVGI

By cleaning your systems’ coils with UVGI, you can reduce the potential for harboring infectious colonies and the chance that infectious aerosols will be distributed through the air. A side benefit may be a reduction in cooling coil pressure loss, which will allow you to increase filter efficiency. This solution will require UV-C lights, controls, safety measures and electrical connections.

 

We know there are many ways to limit the transmission of infectious aerosols, and we recognize that a comprehensive approach will require establishing priorities for any facility improvements.  Whether you’re looking to adjust your existing HVAC system or you’re undertaking a mechanical system makeover, there are a variety of ways to safeguard the health and wellbeing of building occupants. From conducting equipment check-ups and replacing filters to implementing UVGI and upsizing equipment, a thoughtful combination of modifications will help all of us as we navigate the “new normal.”