Last month we reviewed the benefits of enhanced indoor air quality (IAQ), and the synergy between IAQ engineering controls and smart building systems to establish and maintain healthy indoor environments. To recap, the need for systems to clean air will not end with the COVID-19 pandemic. Many other pathogens spread through the air, and it is a matter of when, not if, we will face another outbreak. More importantly, recent scientific evidence confirms that our brains function better, and we stay healthier when we have fresh air to breath. Many existing buildings have substandard ventilation and the minimum standards used for new construction do not lead to optimal air quality.
During the pandemic, we have been inundated with clean air solutions, ranging from simple advice to crack windows and deploy HEPA air cleaners, to promotion of exotic air sanitizing devices. There is no one-size-fits-all solution, as the ideal approach will differ based on building type, interior space use, HVAC system type, ambient climate and other factors. To avoid unnecessary capital investment and achieve the best results, the unique circumstances in each building must be considered.
My colleagues and I recently completed in-situ comparative efficacy testing of several air cleaning technologies in a high-rise office building, built in the 1980s in the Pacific Northwest. While the limitations of this investigation prevent reaching definitive and broadly applicable conclusions, it does provide instructive insights. The subject property is well maintained and managed to provide tenants with good indoor environmental quality. The floor-by-floor HVAC system had already been adjusted to provide increased outside air and filters had been upgraded to MERV 14, but the building manager wanted to make sure they were providing tenants with a safer, healthier indoor environment during and after the pandemic.
Bioaerosol and particulate matter sampling
The building engineer was contemplating three options: installing ultraviolet germicidal irradiation (UVGI) or needlepoint bipolar ionization (NPBI) or upgrading to MERV 15 filters. For the comparative testing, they installed UVGI on one floor, NPBI on two floors (one upstream and one downstream of the cooling coils) and prepared for a filter upgrade on another floor. The investigation measured changes in ambient bioaerosols (bacteria, fungi and microbes) and particulate matter before and after activating air cleaning technologies, as proxies for airborne pathogens, as it was neither practical nor safe to inoculate the air with a bacteriophage or virus outside a controlled laboratory environment. The investigation also measured aldehydes and ozone on the floors with NPBI to confirm that potential unintended IAQ impacts did not occur. Baseline measurements of these air quality parameters were taken before air cleaning technologies were activated, and then again one week afterward.
The floors on which the investigation was conducted were occupied at approximately 15 to 20% of normal. Air sampling was conducted during occupied hours in two locations on each floor, in a common area of the office spaces and in the mechanical room return air plenum. Bioaerosols were sampled using an Andersen N6 Microbial Sampler that pulled in a set volume of air at each sampling location, depositing the contents on agar petri dish collection plates. The plates were sent to a lab, incubated for seven days, and analyzed for total viable microbial organisms, measured in colony forming units (CFU).
Particulate matter was measured using a high sensitivity light-scattering laser photometer, quantifying PM10, PM2.5, PM1.0 and total particulate matter. The investigation revealed that the baseline air quality in the building was already superior to typical buildings and industry standards, likely due to the high-efficiency filters, increased ventilation, and reduced occupancy. There is no standard for bioaerosol concentrations, but the measured colony forming units per cubic meter of air (CFU/m3) in the baseline condition averaged 4% to 14% of the levels found in published studies of comparable air conditioned office buildings. Likewise, all baseline measurements of fine particulate matter (PM2.5) were below the 0.015 mg/m3 threshold established by the WELL Building standard.
In-situ testing can help bridge a gap and reveal the relative benefits of air quality interventions in real-world conditions.
Air samples taken after activating air cleaning technologies showed that each one reduced bioaerosols, on average, 8% to 46% compared to baseline measurements. The largest reduction was seen on the floor with NPBI installed downstream of the coils, but the measured differences were not statistically significant and may be more due to observed variations in occupant activity in the sampling area than the relative efficacy of the devices evaluated.
Particle counts indicated post-activation reductions of particulate matter in the common areas (PM2.5 reduced 44% to 100%) on all sampled floors, but conversely revealed increases in mechanical room samples (slightly above WELL Building thresholds). The largest common area reductions were measured on the floors with NPBI, supporting manufacturer’s claims that increasing ion concentrations results in agglomeration and reduction of airborne particles. There was no measurable increase in ozone or aldehydes after activating NPBI devices.
While there are limitations to this type of investigation compared to testing in a laboratory under controlled conditions, in-situ testing can help bridge a gap and reveal the relative benefits of air quality interventions in real-world conditions. A key takeaway for the subject property is that the basic measures (increased ventilation and high efficiency filters) can significantly improve IAQ, including reducing bioaerosols, and that more exotic technologies provide diminishing returns. In another building, where HVAC system limitations or climate extremes might limit the potential for ventilation and filtration enhancements, air cleaning technologies like UVGI or NPBI may provide greater air quality improvement potential. Additionally, while the data in this investigation was incomplete, it hints that localized air cleaning technology in areas with concentrated occupancy might be more efficacious than property-wide applications. Bottom line, there is no one IAQ solutions that is best in all scenarios, and options should be considered carefully to make smart investments and deliver desired results.
Alan Scott, FAIA, LEED Fellow, LEED AP BD+C, O+M, WELL AP, CEM, is an architect with over 33 years of experience in sustainable building design. He is a senior consultant with Intertek Building Science Solutions in Portland, Ore. To learn more, follow Scott on Twitter @alanscott_faia.