ASHRAE Standard 62 and the Future of HVAC

Rethinking Ventilation for Energy Efficiency and Indoor Air Quality

Standards and Society

Technical standards do not emerge in isolation. They reflect the priorities, constraints, and realities of the industries and time periods that produce them. As those conditions evolve, through technological advancement, shifting energy demands, and environmental change, so too must the standards that guide engineering practice.

Today, the built environment is facing a new kind of pressure. Electricity demand in Ontario alone is projected to increase by nearly 75% by 2050 [1], driven by the rapid growth of data centers, electric vehicles, and the electrification of existing building stock. At the same time, expectations for indoor air quality have risen significantly, driven by greater awareness of its impact on health, safety, and the overall occupant experience.

This creates a fundamental challenge for engineers: how do we maintain high-quality indoor environments while reducing the energy required to operate them?

With HVAC systems accounting for an estimated 40% of total building energy [2], ventilation strategies sit directly at the center of this challenge.

ASHRAE’s Standard 62, which defines ventilation and air quality requirements for buildings, offers a clear example of how engineering standards evolve alongside these competing demands, and how the industry is beginning to rethink traditional approaches to balance performance with efficiency.

ASHRAE Standard 62

First introduced in 1973, the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) specifies minimum airflow requirements for a variety of building types. It provides a simple, effective set of rules for designing ventilation equipment that maintains acceptable indoor air quality for building occupants. There are separate standards for commercial and residential buildings, standards 62.1 and 62.2, respectively.

The minimum ventilation rates are expressed as airflow per square foot and per person, with the floor-area component accounting for building-related pollutants and the per-person component accounting for exhalation and bioaerosols. These two coefficients are combined to calculate the minimum ventilation rate required for a given space in the original design method, the Ventilation Rate Procedure (VRP) [3].

It’s quick to implement in a design and can accommodate a wide range of buildings, since the design engineer only needs to select the correct airflow coefficients and enter their building’s size and occupancy details. Further, it is easy to update. ASHRAE continually publishes updated requirements for space ventilation as more data becomes available to track both the expected pollutant concentrations and their known effects on human health.

Since its release, Standard 62 has been widely adopted across most North American building codes to standardize ventilation requirements. Again, ease of implementation is a main strength here. Building inspectors can simply check the floor plan, reference the standard, and confirm that the related air equipment meets the requirements.

The main issue with a prescriptive standard such as ASHRAE 62 is exactly that: it’s prescriptive. Comparatively little is done to ensure the final project, as-built, is able to deliver the performance promised by the design. Through updates, addenda, and appendices, many of these issues have since been addressed, but adoption of these new practices varies.

Simply delivering the required volume of outdoor air does not ensure that pollutant concentrations remain within acceptable limits. In real ductwork, pressure loss and temperature stratification mean that not 100% of the air in a building is ventilated. A 2007 addendum to the standard adds a ventilation efficiency coefficient that increases airflow to account for these duct losses [4], but it still can’t completely eradicate them in a prescriptive sense. If there is a building region with poor air circulation, no amount of over-ventilating will correct it, since the problem lies in the very design of the ductwork itself.

The standard also assumes that outdoor air is clean. During wildfire events, periods of heavy smog, or in polluted regions, this isn’t the case. No amount of ventilation will deliver a healthy indoor space if the fresh air being used to ventilate it isn’t clean to begin with. Once again, an addendum was created to address the issue. In 2004, air quality reports became standard practice in the design phase, and in the 2020s, air-cleaning equipment, such as filtration or adsorption devices, was officially adopted as standard to clean outdoor air [4].

Finally, the VRP does not account for natural ventilation. Opening a window to bring in fresh air is the simplest form of ventilation we have access to, though it can be difficult in practice to quantify the effect of open windows from a design standpoint. An alternate compliance path, the Natural Ventilation Procedure, was introduced in 2019 to allow for such designs. While effective at diluting gas-phase pollutants like VOCs and CO₂, natural ventilation can cause an increase in fine particulate pollution due to a lack of filtration [5].

As the built environment evolves and we learn more about the health effects of poor air quality and a changing environmental landscape, the standard has been amended and revised to address the challenges of the day. In response to the COVID-19 pandemic, ASHRAE released Standard 241, Control of Infectious Aerosols [6], to describe best practices and lessons learned from combatting airborne disease transmission.

Recently, industry focus has shifted from infection control to energy efficiency, as pandemic concerns ease and energy demands continue to rise. The VRP is an inherently conservative estimation tool and can often lead to over-ventilated spaces, where more air (and therefore more energy) is used than necessary. An underutilized alternative compliance pathway from ASHRAE, the Indoor Air Quality Procedure, is now gaining renewed attention as designers and operators seek more efficient ways to maintain performance.

Practical Methods: the IAQP

To address the limitations of a purely prescriptive approach, ASHRAE developed the Indoor Air Quality Procedure (IAQP). Rather than specifying a fixed airflow requirement, the IAQP uses a practical, performance-based approach to maintaining acceptable indoor pollutant concentrations.

The IAQP relies on a mass-balance approach, wherein pollutant concentrations are determined based on the rate at which they are generated in the space and the rate at which they are removed through ventilation, filtration, or air cleaning technologies. Key pollutants like CO2, VOCs, and particulate matter are maintained below standard thresholds.

Another benefit of the IAQP is flexibility: designers can select the pollutants most relevant to the building type, so a climbing gym will have different contaminants than a nail salon, for example.

With this method, air cleaning devices can be used to reduce the required proportion of outdoor air, allowing more recirculation and re-use of already treated air. Treating and recirculating return air requires much less energy than treating fresh air, generating massive energy savings.

Once the calculations are complete, rigorous testing must be undertaken to ensure that the design matches reality- air quality data is tracked and monitored extensively. If pollutant concentrations exceed thresholds, the proportion of fresh air is increased until they are properly diluted.

Despite being released in 1981, there has been limited industry adoption of the IAQP, with professionals finding the language of the requirements ambiguous and the calculations confusing. Without clear guidance, designers fell back on the tried-and-tested VRP method, despite the energy performance benefits demonstrated by the IAQP. ASHRAE has since updated the procedure to clarify how pollutants must be tracked and how the calculations must be applied. ASHRAE has also released a calculation tool to assist design engineers in applying the IAQP method.

A large benefit of the IAQP is that it can be implemented in existing buildings. In many cases, ventilation systems already include the necessary recirculation and filtration systems to support IAQP operation, and the systems can be reprogrammed to take advantage of this. Proliferation of air quality sensing devices makes it easier to prove that the air is safe after IAQP implementation, and better control systems allow for finer tuning of the indoor environment. Since no new air handling equipment is required, implementing the IAQP is a cost-effective way to reduce a building’s energy consumption without compromising occupant safety.

Conclusion

The evolution of ASHRAE Standard 62 illustrates an important truth about the engineering profession: technical standards are never truly finished. They represent an ongoing conversation between technical experts, researchers, clients, and society at large.

The first solution is rarely perfect, and one must instead focus on an iterative approach to arrive at a system that is derived through testing, feedback, and real-world experience. It is also important not to blindly rely on these design guidelines, as applying rules without context or careful consideration can lead to over-designed, poorly optimized results. Design work requires critical thinking, professional judgement, and an understanding of the broader goals that the standards are intended to serve.

Each revision reflects lessons learned from past designs, new scientific understanding of the built environment and our own biology, and changing societal priorities. It is the combined effort of a dedicated team all working toward a brighter, healthier future. By rising to meet today's challenges, engineers help ensure that the buildings they create are not only safe and comfortable but also sustainable and resilient throughout their useful lifetimes.

[1] Dow, A. (2024, October 16). News and updates. Electricity Demand in Ontario to Grow by 75 per cent by 2050. https://www.ieso.ca/Corporate-IESO/Media/News-Releases/2024/10/Electricity-Demand-in-Ontario-to-Grow-by-75-per-cent-by-2050

[2] M. González-Torres, L. Pérez-Lombard, Juan F. Coronel, Ismael R. Maestre, Da Yan, A review on buildings energy information: Trends, end-uses, fuels and drivers, Energy Reports, Volume 8, 2022, Pages 626-637, ISSN 2352-4847, https://doi.org/10.1016/j.egyr.2021.11.280

[3] ASHRAE. (2022). ANSI/ASHRAE Standard 62.1-2022, Ventilation and Acceptable Indoor Air Quality. Atlanta: ASHRAE.

[4] ASHRAE. (2007). ANSI/ASHRAE Standard 62.1-2007, Addenda g, r, and t. Atlanta: ASHRAE. https://www.ashrae.org/file%20library/technical%20resources/standards%20and%20guidelines/standards%20addenda/62_1_2007_addendum_g_r_t_final.pdf

[5] Troye Sas-Wright, Jordan D. Clark, Numerical assessment of indoor air quality in spaces in the United States designed with the ASHRAE 62.1–2019 Natural Ventilation Procedure, Building and Environment, Volume 243, 2023, 110671, ISSN 0360-1323, https://doi.org/10.1016/j.buildenv.2023.110671.

[6] ASHRAE. (2023). ANSI/ASHRAE Standard 241, Control of Infectious Aerosols. July 7, 2023.