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Enabling health, energy efficiency, and compliance: The Role of tracer particles in ASHRAE Standard 241

Published on 13 October 2023

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Our industry is engaged in an important dialogue to improve sustainability through ESG transparency and industry collaboration. This article is a contribution to this larger conversation and does not necessarily reflect GRESB’s position.

Introduction

In the fast moving realm of sustainable real estate and infrastructure, keeping abreast of the latest standards and technologies is essential. The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) has been a driving force in shaping the industry’s approach to health and energy efficiency. ASHRAE Standard 241 for Control of Infectious Aerosols is a remarkable milestone in this journey (1). In this article, we delve into ASHRAE Standard 241, shedding light on the innovative use of tracer particles and its importance in measuring building readiness for optimal clean airflow, infection risk management, and energy-efficient operations.

Understanding ASHRAE Standard 241

ASHRAE Standard 241 is an extraordinary achievement that goes beyond traditional HVAC guidelines to establish health-based targets for acceptable clean airflow rates, for the purpose of airborne infection control.

The development of ASHRAE Standard 241 was a collaborative effort by a multidisciplinary team of experts. Comprising HVAC engineers, environmental scientists, indoor air quality specialists, architects, and medical professionals, this team brought diverse knowledge and experience to the table. Their collective expertise was instrumental in crafting a comprehensive guideline that addresses the challenges of meeting these goals in new and existing buildings.

ASHRAE Standard 241 is designed to address clean airflow requirements for a wide variety of spaces, as set out in Table 5.1 of the standard (compared in Figure 1). Specifically these standards are meant to be used in times of high prevalence of respiratory pathogens such as during the COVID-19 pandemic or during flu/RSV season. During these particular high risk times, buildings can go into infection risk management mode (IRMM) by activating their building readiness plans (BRP) where they will need to adhere to the minimum clean airflow requirements for infection control established in Standard 241, as applied to their specific space types and occupancies.

Measuring ASHRAE Standard 241 compliance: The role of tracer particles

Risk of respiratory infection increases with the number of people present in a space. Therefore, the ASHRAE 241 Standard uses the metric of Equivalent Clean Air delivered to the space per person (ECAi), measured in cubic feet/minute/person or liters/second/person. The chosen occupancy of a space will determine the amount of clean air that needs to be delivered to the space to provide 95% reduction of viral transmission. Clean air is defined as any source of air that is free of potentially infectious aerosols, including outdoor air, air filtered in the HVAC system, or air cleaners.

The measurement of clean airflow in actual spaces has historically been very challenging. Traditional methods have had to rely on design documentation and engineering calculations, combined with extensive component-level system verification, with no direct breathing-zone level tests occurring within rooms. While valuable, these approaches only offer estimates of total building performance for providing clean airflow, are forced to assume that rooms are well mixed, and it can be challenging to use these to accurately account for natural ventilation.

ASHRAE 241 provides us with a new tracer particle-based test that accounts for all particle removal, filtration and dilution mechanisms that are active in a given building or room. Importantly, this single measurement can be used as an alternative to benchtop calculations, system verification and TAB testing.

With this new standards-backed test, tracer particles have emerged as a transformative solution for assessing clean airflow, accounting for both ventilation and filtration, to comply with ASHRAE Standard 241 (2,3).

Figure 1. ASHRAE Standard 241-2023 minimum ECAi rates for different occupancy categories.

Tracer particles: A direct and rapid approach to ASHRAE Standard 241 compliance assessment

In this new approach, tracer particles, small and inert particles similar to respiratory aerosols, are introduced into a building’s air while it is occupied, and then measured using multiple specialized sensors. This highly accurate approach has gained prominence due to its potential to redefine how we measure compliance with ASHRAE Standard 241 and prepare for IRMM. These particles mimic the behavior of airborne contaminants, facilitating real-time assessments of ventilation system performance and occupant health.

Here’s why tracer particle testing is pivotal:

Real-Time Data: Tracer particles offer the advantage of real-time data collection. By tracking the movement and dispersion of these particles, building operators can gain immediate insights into system effectiveness for specific zones and make adjustments to align with their infection risk management plans.

Comprehensive Assessment: Tracer particles provide a holistic assessment of ventilation effectiveness, including factors such as air exchange rates and air distribution. This comprehensive view enables building operators to identify and rectify issues promptly.

Directly measurable metrics: ASHRAE Standard 241 includes specific metrics and target values, such as the Equivalent Clean Air (ECAi) for a given space type. These rates are measured directly by tracer particles testing in each space.

Balancing occupant health and energy efficiency: Over-ventilation can lead to increased energy costs, potentially compromising environmental, social, and governance (ESG) goals. Tracer particle testing helps strike the balance by fine-tuning HVAC systems based on real-time data to fully quantify and discover over- or under-ventilated zones, with a goal of optimizing energy use without sacrificing occupant health.

IRMM protocol: In times of heightened respiratory pathogen prevalence, IRMM protocol readiness is vital. Tracer particle testing enables IRMM airflow rates to be directly verified, to best ensure the safety and well-being of occupants.

Using tracer testing to uncover overventilation and energy savings

While optimal ventilation is critical for IAQ and infection risk management, it’s essential to be mindful of overventilation. While Standard 241 is strictly focused on reducing risk of occupant illness from infectious airborne particles, other standards such as ASHRAE 90.1 are focused on energy efficiency. Excessive ventilation and airflow can result in increased energy consumption and costs, which runs counter to ESG goals.

Tracer particles play a pivotal role in addressing this challenge by enabling the discovery of building zones that have excessive airflow beyond what is needed for IRMM. With a test that accounts for all particle removal mechanisms, including natural ventilation, and health-based targets from 241, we have a system to know when a building has too little, or too much clean airflow. By providing immediate, accurate data on ventilation effectiveness, building operators can make informed decisions and optimize their systems to strike the right balance for their space usage and target occupancy. This ensures that energy savings are achieved without compromising occupant health and safety, aligning with sustainability objectives.

Conclusion

ASHRAE Standard 241 stands as a remarkable achievement in the pursuit of healthy buildings. Crafted by a diverse team of experts, this standard offers comprehensive guidance for HVAC system design and operation, for airborne infection risk management.

Tracer particles represent an innovative approach to clean airflow measurement and compliance assessment, helping building owners and operators ensure their HVAC systems not only meet regulatory requirements but also create superior indoor environments. These particles facilitate more quickly and cost-effectively establishing building readiness plans outlined in the standard, underpinning the IRMM protocol that will be run during times of heightened respiratory pathogen prevalence.

In a world where indoor air quality is paramount to occupant wellbeing, and where energy efficiency is a key driver of sustainability, ASHRAE Standard 241 and tracer particles guide us toward a future of healthier buildings that better balance this priority with energy usage, when implemented thoughtfully. As we move forward, it is imperative to stay informed about the latest developments and best practices in implementing ASHRAE Standard 241 to unlock the full potential of healthy, sustainable real estate and infrastructure.

 

This article was written by Aaron Botham, Scientific Program Manager, and Sam Molyneux, Co-CEO and Co-founder, at Poppy Health.

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