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Return to Operations: Part 4 — Air Cleaning and Treatment

While ventilation and filtration are the best and most proven means for HVAC systems to positively impact human health in building, air cleaning and treatment can be considered for possible enhancement of indoor air quality. There are several air cleaning and treatment technologies in the market today, and with the onset of the COVID-19 pandemic, these technologies have attracted a lot of attention and include:

  • Ultraviolet germicidal energy (UVc)
  • Photocatalytic oxidation (PCO)
  • Bi-polar ionization (BPI)

Ultraviolet germicidal energy (UVc)

UVc technology has proven to kill viruses, bacteria, and fungi. Per ASHRAE, a few studies have shown that UVc air cleaning and disinfection, also called ultraviolet germicidal irradiation (UVGI), produce beneficial effects to human health. UVc has been used in air handling systems for many years to inhibit organic growth on wet cooling coils. The recent pandemic has increased interest in UVc as a method to combat the virus.  However, the application of UVc to HVAC systems can determine the overall success or effectiveness of the technology. The following items should be considered:

  • UVc intensity needed to kill pathogens in a moving airstream at 500 FPM is most likely more than what would be installed to keep a cooling coil clean
  • UVc application needs to provide the required exposure time by increasing air path length, reducing velocity, or a combination of both, which affects air handling system design and size
  • Direct exposure to UVc lamps can result in damage to skin and eyes so any equipment using UV must be shielded from occupants
  • UVc radiation, depending on the wavelength, may generate ozone

In addition to HVAC systems, UVc can also be applied directly in occupied spaces with permanently mounted units incorporated into lighting fixtures or ceiling fans and with portable units that can be moved from space to space.

Photocatalytic oxidation (PCO)

PCO produces oxidation products (hydroxyls and anions) when UV light reacts with a catalytic material; these oxidation products react with viruses to break up the compounds into more stable substances such as water vapor and carbon dioxide. The oxidation products work in an airstream, but may also disperse into a room to interact with microorganisms that may be present. PCO technology may also help to reduce odors and particulates. Some PCO systems use titanium dioxide as the catalyst, which is highly regarded as a possible carcinogen. Studies on PCO technologies have been inconclusive with some indicating the harmful contaminants are removed, while other indicated ineffectiveness.  Per ASHRAE, “there is no data on how their use affects human health.” Per SSR experiences, it is very difficult to get PCO manufacturers to provide testing data to validate their effectiveness.

Bi-polar ionization (BPI)

This technology generates positively and negatively charged ions in the airstream, which react with organisms (viruses, bacteria, mold, VOCs, etc.) in the air. In addition, particles of opposite polarity are attracted to each other, creating larger, benign particles which are more efficiently filtered out of the airstream. Two types of polar ionization systems are: tubular and needlepoint with the name indicating the shape of the equipment used.  BPI systems can be mounted in air handling units or directly in ductwork, but have maximum airstream velocity requirements of 500 FPM. An additional benefit of bi-polar ionization is that helps with particulate and odor control. Per ASHRAE, air cleaning technologies that generate electric fields and/or ions have been documented to range from highly effective to ineffective with no proven benefit to human health. In addition, some BPI technologies do produce ozone, even if at a low rate.

Bottom line, none of these are technologies have a proven track record. Owners and operators, along with designers and contractors, should be use caution with their claims of “effectiveness.” Some manufacturers of air cleaning and treatment systems make numerical or qualitative claims about their “effectiveness,” some even claiming a “99.99% kill rate.” Take a hard look and understand their testing and reported results. Ask important questions like:

  • How was the test conducted that resulted in the numerical claim?
  • Which testing agency performed the test?
  • What intensity was used in the test?
  • Did the test involve a high number of units being installed in a room?
  • Was the AHU or duct system modified to obtain the best conditions possible?
  • Would those conditions be needed obtain similar results at a different specific project?

Some manufacturers may claim a “99% kill rate,” only to find out the system was tested in a closed and isolated test chamber that’s only one cubic foot in volume for 60 minutes. In many cases, the testing and reported results are not equivalent to the air cleaning technology being applied in an air handling system with air velocities at 500 FPM up to 2500 FPM.

Some air treatment systems may generate ozone. Many manufacturers will acknowledge this fact upon request and provide documentation. Two good benchmark standards are UL 867, which addresses the safety and ozone generation of electrostatic air cleaning equipment both permanent and portable, and UL 2998, which is a validation claim procedure for “zero ozone emissions.”  Per ASHRAE, many negative health effects arise from exposure to ozone and its reaction products. Subsequently, any air cleaning technology that produces ozone, either intentionally or unintentionally, should not be utilized in HVAC systems serving occupied spaces.

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. Read more about ventilation and filtration in Return to Operations: Part 3 — Clearing the Air on HVAC Systems in a Pandemic.

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