“Particles Matter”: Achieving Healthy, Energy-Efficient Indoor Spaces

Particulate Matter is the term for particles in the air we breathe most of which are invisible due to their size and thanks to recent research fueled by the pandemic, wildfires, and climate change, we know that these particles are a major health threat.  For Covid, influenza and other viruses, airborne transmission is how people get infected. When an infected person coughs, sneezes, yells or even talks, they expel respiratory droplets (aka “aerosols”) of different sizes up to 80 thousand per breath. The heavier particles (5-10 microns in size) drop to surfaces before travelling 2 meters (ie. 6 feet). The smaller, lightweight particles (<1.0 micron) are invisible and simply float away on their own or attach themselves to other particles remaining airborne for up to 18 hours in plume-like clouds which move around the interior airspace, following the path of air currents in a room or building.

The scientific, infectious disease communities’ interest in potentially toxic “floating and lingering” particles is not limited to COVID. In the report State of the Air 2022 from the American Lung Association, about 137 million Americans continue to live with unhealthy levels of air pollution in homes and workplaces in part because of climate-change-driven wildfires. In Sept. 2021, the World Health Organization cut in half (to 5 micrograms per cubic meter of air) its annual recommended limit for PM2.5 (particles <2.5 microns). The EPA and others are expected to follow with a target of 9-10 micrograms. Clinical studies show indoor air quality is a bigger health threat due to outdoor infiltration and additional sources created by human activities such as cooking, smoking, vaping, cleaning, etc. As a result, healthy indoor air has been added to energy efficiency as ‘must haves’ for building owners and operators as people return to offices, schools, and indoor public spaces.


At Piera we often get asked, “What is the benefit of measuring individual particles vs the EPA metric of particle mass (weight) PM 2.5?”  PM 2.5 was adopted by the EPA 50 years ago to monitor outdoor pollution from vehicles and industrial sources. The EPA’s AQI scale based on PM2.5 is useful in telling us air is good, poor, bad, dangerous but not explain why. Accurate data on the size and distribution of particles delivers insight into the sources, their impact and removal strategies for the pollutants. “It is more energy efficient to eliminate sources of pollution than to increase outdoor air supply rates”. In short, Particles Matter.

How Particles affect air quality in a building

ASHRAE, the leading organization developing standards and making recommendations for the “Built Environment” published a May 2022 article in the ASHRAE journal, “Airborne Disease Transmission Risk and Energy Impact of HVAC Mitigation Strategies”. It provides guidance on how to optimize a ‘typical’ building to reduce airborne transmission of viruses in an energy-efficient manner (Figure 1) by achieving a ‘balance point’ between particle generation and removal since particles are the carrier for the virus with sub-micron (<1.0 micron) particles the deadliest. In summary, the lower the particle count, the less likely transmission will occur, and the additional health benefits are substantial. Since every building is different, the guidelines are simply a starting point. Key findings include:

  • A new metric, Equivalent Outdoor Air (EOA) delivery as a basis for infection-risk and energy-consumption analysis instead of Air Changes per Hour (ACH) which is a widely used metric.
  • Increasing ventilation is effective for reducing infection risk, but it can be costly or infeasible depending on climate and equipment configuration.
  • Improved filtration is often the most cost-effective source of EOA (install MERV-13 filters in existing systems)
  • High risk zones may need supplementary in-zone filtration (air purifiers or other stand-alone disinfection devices (UV-cleaning and other ‘active’ methods).
  • For buildings and spaces with different HVAC configurations the observations may or may not hold but quantitative analysis can be performed to inform the course of action.

The last point is key: the air in every building is different and it changes continuously based on occupancy, use, pollutants, HVAC systems and devices that ‘clean’ the air.  What’s needed is a way to make the invisible visible and make spaces safer before there is a problem. Actively scans and mapping of how airborne particles travel, pool, and clear is vital and this requires real-time air monitoring.

A new Indoor Air Quality Standard and its impact on Energy Efficiency

Building on this work and partnering with the White House, EPA and CDC, ASHRAE released a new IAQ and pathogen mitigation standard in May 2023. “Nowhere in the world do we have a standard that universally addresses the concept of mitigating pathogen spread and IAQ and ASHRAE is proud to lead in the development of the guidance,” ASHRAE noted in this release. This new standard requires that buildings meet indoor air quality standards based on Effective Air Changes per Hour (eACH)  Studies show that eACH values between 6 and 8 ensure dramatically reduced virus transmission.  The CDC recommends an eACH of 5 or more to reduce infection. The average home is 1-2.

The standard includes normative appendix C which defines “an in-place method of testing the equivalent clean air flow rate for Infection Risk Mitigation for indoor spaces as induced by all physical removal mechanisms (i.e., those that remove particles from the air) including passive and mechanical ventilation, filtration, and deposition.  The method does not measure contributions of pathogen inactivation techniques that do not remove particles, such as UVC.” The technique is based on measurement of the decay rate of tracer particles using ‘diffusers’ that distribute safe NACL particles into a room and measuring how quickly the sub-micron particles are cleared out.  The data is used to approximate how long it will take to ‘clean’ the air. ASHRAE requires particle counts must be collected by ‘aerosol detectors’ that report particle count and size in sizes from 0.3-10 microns and are within +/- 10% of reference instruments. Piera’s Canāree Air Quality Monitors are the only cost-effective commercial solution that meets this new standard.

Many commercial spaces have eACH values greater than 5 and during COVID were often ‘over ventilated’ or ‘purging’ using much more energy than required. eACH does not include energy consumption whereas EOA determines the volumetric flow of outdoor air that would provide an equivalent removal rate of infectious particles.  EOA can be calculated from eACH.

Once you know the EOA of various mitigation approaches and their power consumption you can begin to improve energy efficiency across multiple ‘climate zones’. ASHRAE’s Building Readiness Guide (May 17, 2022) provides details on EOA including the size of the particles likely to carry Covid.  This table suggests you should plan for particles of size 1.0 um or less.  Measuring particles in size E1 yields the best results.

Why not just use CO2 as a proxy for Ventilation Rates?

CO2 levels are easily misinterpreted and may generate confusion. It can be difficult to collect accurate data in poorly mixed spaces, especially when occupancy is low, or the interior air volume is large. Low CO2 levels measured in such spaces may not reflect conditions throughout the space. Another potential way a CO2 reading could be misinterpreted is if there are HEPA filters (in the HVAC or in purifiers) in a room being monitored. HEPAs, which work to remove harmful particles from the air including ones containing COVID and other viruses, do not impact CO2 levels. So, a high CO2 reading may not be as noteworthy in a room with an air filtration system.

The best approach is to create a ‘living’ model of the airflow in the building while it’s in use to actively scan and map how airborne particles travel, pool, and clear. Once the model is known, EOA can be used to manage the building’s health and energy efficiency.

Piera partners with our customers to ensure compliance and reduce energy costs.

Working closely with our customers, Piera leveraged the industry’s most advanced air tracer technology to monitor air health and certify indoor spaces providing fast, accurate, comprehensive, air wellness data.

Piera’s state of the art particle sensor is a breakthrough in measuring the smallest particles below 1.0-micron cost-effectively.  Piera’s custom particle processor was developed originally for x-ray devices to ‘count and size’ particles while they are in motion. Diffusers release breath-like particles (1.0 micron in size) called tracers and our sensors collect tracers as they move through the physical site in aerosol particles. Particle data is then used for real-time air monitoring reporting key indoor air quality Metrics. Deployed throughout a building, diffusers and sensors under software control generate particles and measure them to calculate eACH for each room, identify transmission pathways, pathogen and pollution hotspots, and clearance rates delivering a compelling ROI for a healthy, energy-efficient building. Piera’s technology also delivers Air Quality Index metrics (AQI), alerts to pollution hot-spots, and classifies likely sources of pollution. The system analyzes the movement over time to produce data about how indoor air transports particles and bioaerosols.

Once the initial model of the building is determined it can be used to manage the building. As the building air changes due to occupancy, use, temperature, humidity, outdoor and indoor pollution, real-time continuous monitoring of particle data ensures clean air by knowing the exact density of the problematic sub-micron (and larger) sized particles that must be diluted and/or filtered.  Simply put, the higher the number of particles, the more air filtering and fresh air intake is required to dilute and cleanse /filter the particles. In addition, the ability to classify pollutant sources (vape, smoke, cooking, aerosols) can be used to eliminate sources.

HVAC systems were designed for energy efficient comfort control, primarily relating to temperature and humidity levels. These systems were not designed for air purification and are insufficient. Upgrading to MERV 13 filters (If the system can handle the pressure drop) only captures a small portion of the sub-micron sized (dangerous) respiratory droplets that are floating in the air and may contain viruses. Even other floating particles potentially become “transport vehicles” for these lightweight infections’ droplets to “hitch a ride”. So, increasing air flow (purging) WITHOUT addressing the enhanced filtering of the air content may simply be facilitating the movement of these floating aerosols between all spaces in the building which share a common air supply.  Virus-spreading risks may not be getting mitigated despite well-meaning “HVAC system upgrade” intentions.

In summary, the 3 ‘pillars’ of achieving healthy and energy efficient spaces are Monitor, Inform, and Mitigate in a continuous real-time loop. Piera Systems’ sensor technology enables the delivery of the 3 key indoor air quality metrics; eACH, EOA, and the EPA AQI along with particle data and alerts that can integrate with your existing Building Management Systems and a wide range of air cleaning products.


To learn more, go to pierasystems.com.