Return to Operations: Part 3 — Clearing the Air on HVAC Systems in a Pandemic
As the gates swing open and fans walk through the turnstiles for the first time in several months, arena, stadium, and ballpark owners and operators must find ways to create a safe environment for their guests. Public confidence must be restored in order to get fans back in the seats. The COVID-19 pandemic has taught many important lessons about the way we live our lives and interact in social settings, and these lessons are only magnified when we consider a large public assembly space with thousands of seats.
More than ever, we know and understand that viruses and pathogens similar to SARS-CoV-2, the coronavirus responsible for COVID-19, are spread through both the air and surfaces. Airborne transmission occurs when respiratory droplets containing virus are passed from one person to the next, and, in most cases, surface transmission begins with respiratory droplets landing on surfaces or passed from direct contact between persons. So, in a majority of cases, virus transmission occurs in the air that we breathe. Of course, we know the importance of social distancing to limit transmission, but keeping six feet of distance can be difficult in assembly spaces especially with entry and exiting protocols. Masks and facial coverings are simple, proactive, and effective means of limiting airborne transmission by limiting the number of airborne particles that we both breathe in or out. While many stadiums and arenas will most likely require masks and facial coverings as guests return, owners and operators should also be asking the question: What more can we do to protect our guests? One answer is HVAC system operations to properly treat and clean the air inside their buildings.
As far as standards to reference, both ASHRAE and the CDC have guidelines and recommendations on the operation of HVAC systems and air treatments to help mitigate transmission. ASHRAE Standard 180-2018, Standard Practice for the Inspection and Maintenance of Commercial HVAC Systems presents simple and direct measures to re-start building HVAC systems. Another source for the evaluation HVAC systems is the ASHRAE Position Document on Filtration and Air Cleaning published in 2015 and reaffirmed in 2018. Finally, the ASHRAE Position Document on Infectious Aerosols provides additional resources. These documents highlight the need to increase building ventilation rates to flush internal building air with fresh outdoor air and to maximize filtration media effectiveness to capture airborne particles. The ASHRAE Position documents specifically addresses impacts to human health related to filtration and air cleaning. Here is a key statement from ASHRAE:
“…at present, there is only significant evidence of health benefits for porous media particle filtration systems. For a few other technologies, there is evidence to suggest health benefits, but this evidence is not sufficient to formulate firm conclusions. A key position is that filtration and air-cleaning technologies are not recommended for use if they produce significant amounts of contaminants that are known or expected to be harmful for health. Finally, it is stated that there are limited data documenting the effectiveness of gas-phase air cleaning as an alternative to ventilation.” — ASHRAE – Position Document 2018
Ventilation and Building Flushing
From the ASHRAE information, it is clear that there’s no substitute for proper building ventilation or, during a pandemic, increased or over ventilation. Flushing the building with outside air is a key to the control of airborne contaminates and pathogens that are harmful to humans. Closing outside air dampers, a practice common among arena and stadium operators to save energy, should be a thing of the past. First and foremost, this practice does not save energy because exhaust air in each building must have outside air for make-up, and in turn, creates an unsafe environment especially during a pandemic. We recommend the following operational procedures:
- Utilize the highest supply rate of outdoor air the current mechanical system can provide
- Modify system controls to increase supply of outdoor air (e.g., ventilating for longer hours, changing the setpoint for demand-controlled ventilation systems)
- Evaluate the extent to which the current mechanical system can operate without recirculating air
- Post-event, operate all HVAC systems at 100% outside air for a period of two to four hours to flush the building
- Consider flushing the building at night with 100% outside air
- Open all exterior doors, operable windows, and operable roofs for two hours prior to the event pending local weather conditions
- The following potential effects should not be overlooked:
- Energy consumption
- The ability to manage thermal comfort conditions (e.g., higher ventilation leading to draft, recirculation elimination straining cooling, and/or heating capacity)
- Maintenance processes
Based on data and empirical evidence presented by ASHRAE, mechanical filtration has been proven to reduce airborne particles and have a positive impact on human health. Bottom line, filtration works if properly maintained. The days of deferring change-out of filter media or replacing with less effective media, for example replacing an 8” or 12” cartridge filter with a 2” thick pleated filter, should be in the past.
- Use the highest efficiency of media or other particle filters (particularly for recirculated air, if any) that can be installed with the current mechanical system — operator should consider increasing the level of filtration in all air handling units for two replacement cycles upon re-opening the building
- Consider adding HEPA filtration, where applicable
Not all filters are created equal. Be sure to focus on the overall effectiveness of the filter media. Effectiveness is rated on the Minimum Efficiency Reporting Value (MERV) scale of 1 to 20 depending on the capture rate of minimum particle sizes. High MERV values capture very small particles at a higher rate.
High Performance Particulate Air (HEPA) is a type of pleated media filtration that can remove at least 99.97% of duct, pollen, mold, bacteria, and any airborne particles with a size of 0.3 microns. The 0.3 micron particle size corresponds to the worst case or the most penetrating particle size (MPPS). Most viruses are smaller than 0.1 microns, and HEPA filters are effective at removal of these from the air stream. HEPA filters add from 1” water gauge to 2” water gauge of additional static pressure to a duct system; if the filters are added to an existing system, the fan capacity and motor for the additional static pressure must be verified.
HEPA filters can be installed several ways: in the air handling system, at a return grille, or in a portable fan/filter unit installed directly at the space served. Adding HEPA filters to an air handling unit will add length to the unit; since HEPA filters are usually rated at 500 fpm and most duct systems are sized for higher velocities, adding duct-mounted HEPA filters requires significant modification to enlarge a section of duct to accommodate the filter. HEPA filters can be installed at return grilles, which may help reduce the static pressure on the fan system because return grilles and associated filters can easily be oversized to reduce velocity and static pressure. HEPA filters can also be used in portable units that recirculate room air.
In summary, HVAC systems have a large impact on overall indoor air quality and airborne pathogens with stadiums, arenas, and ballparks. Owners and operators should evaluate their systems and take the proper measures to provide a safe environment and increase the overall fan experience. SSR is here to provide the support that you need. We are all in this together when it comes to restoring public confidence and getting the fans back in the seats. Learn more about air cleaning and treatment technologies in Return to Operations: Part 4 — Air Cleaning and Treatment.