Authored by Kalyan Kottapalli, Ph.D., Marwa Zaatari, Ph.D., and Sam Molyneux of Poppy Health and Mark Jackson, Ph.D., of Daikin Comfort Technologies North America.
This fall, a column entitled “A Game Changer in Building Assessment and Commissioning: Aerosol Tracer Testing Comes of Age in ASHRAE Standards 241” was published in ASHRAE Journal. With the recent introduction of ASHRAE Standard 241, building owners, managers, and HVAC professionals are exploring how this standard and aerosol tracer testing can support health and efficiency in our buildings.
In this post, the authors answer key questions about the standard, the process, and what operators of buildings can expect from managing an ASHRAE 241-compliant building. You can explore the findings from the published data in our article “New findings: ASHRAE Standard 241 shows a new key to energy savings”.
Q: What is ASHRAE Standard 241? Why is ASHRAE Standard 241 important?
A: ASHRAE Standard 241-2023, Control of Infectious Aerosols, sets the first global standard for minimizing airborne disease transmission indoors. This standard guides building owners and managers on maintaining ventilation and air filtration levels that help reduce infection risks in diverse indoor settings.
Unlike previous standards, which often focus on new buildings and major retrofits, ASHRAE 241 applies to both new and existing buildings, ensuring that all spaces—whether newly constructed or decades old—are equipped to provide measurably healthier environments.
Q: How does the aerosol tracer test fit into ASHRAE 241?
A: The aerosol tracer test, detailed in Normative Appendix C of ASHRAE 241, is designed to assess “Equivalent Clean Airflow” (ECAi), which measures how effectively a space's ventilation and filtration systems remove infectious particles. This test differs from traditional air quality assessments by releasing food-grade tracer particles into the air to track particle removal over time.
The test provides real-time data on how well a space can dilute, filter, and remove potentially infectious particles in the breathing zone.
Q: How does aerosol tracer testing work?
A: To conduct an aerosol tracer test, the Poppy sensors are set up in a quadrant around the air diffuser in the room. The diffusers release a saltwater-based mist, and the sensors monitor the rate at which these particles decay over time. This decay rate gives us an ECAi measurement, (Equivalent Clean Airflow per person) for infection risk mitigation, which Poppy compares against ASHRAE 241’s clean airflow targets for various space types (like offices, classrooms, and gyms). The results reveal how well the HVAC system supports clean airflow for the given space and occupancy.
Q: What are the key findings from recent testing in schools and offices?
A: In office settings, over 80% of Class A office spaces met the new ECAi targets as set in ASHRAE Standard 241, often exceeding the ventilation levels needed to control infectious aerosols. This presents an opportunity to optimize these systems for energy savings.
Conversely, many school classrooms tested failed to meet ASHRAE 241 targets. Factors contributing to this include higher occupant densities, older HVAC systems, and limited budgets for regular system updates, maintenance, and access to purification.
Q: How does this testing process support energy efficiency goals?
A: The tracer test identifies spaces that are over-supplying clean airflow (over-ventilating), which is common in offices with high existing clean airflow rates. For example, in some cases, this allows for reducing outdoor airflow—an energy-intensive process—while relying more on filtration to meet the ECAi target. This approach reduces energy use without compromising health or ventilation standards. Testing showed potential annual energy savings of 2–4 kWh per square foot in offices across various climate zones. By matching ventilation rates to actual needs, the test enables buildings to balance health standards with energy efficiency, reducing operational costs and supporting decarbonization.
Q: How does ASHRAE 241 benefit building managers and HVAC professionals?
A: For building and HVAC professionals, ASHRAE Standard 241 and aerosol tracer testing provide valuable, actionable insights. This testing allows for real-world assessments of HVAC performance and can inform adjustments to support both compliance and occupant health. By maintaining the right balance of clean airflow, facilities can reduce energy waste and extend HVAC equipment lifespan, enhancing overall building performance. Since the testing is conducted within the breathing zone, stakeholders can validate the performance of clean air investments in natural and mechanical ventilation dilution, filtration and purification.
Q: How can buildings use aerosol tracer testing to meet ASHRAE 241?
A: Implementing aerosol tracer testing involves minimal disruption to regular building operations, making it suitable even for occupied spaces. Property managers, facility managers, and sustainability teams can engage with providers like Poppy to perform these tests and make the necessary HVAC adjustments. Many buildings already meet or exceed clean airflow needs, so fine-tuning these settings to ASHRAE Standard 241 levels could yield quick energy savings without additional investments in HVAC retro-commissioning.
By adopting ASHRAE 241, building operators can ensure their indoor spaces operate at the gold standard of indoor air quality while achieving energy efficiency, which is essential for running sustainable buildings. This balanced approach represents a significant advancement for indoor air quality, public health, and energy optimization in commercial and educational buildings.