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ASHRAE Makes Adopting the IAQ Procedure Easier with Addendum aa

March 1, 2022

Authored by Christian Weeks, CEO, enVerid Systems Inc.  and originally published on the enVerid blog: 

On February 14 ASHRAE published Addendum aa to Standard 62.1-2019, Ventilation for Acceptable Indoor Air Quality. The publication of Addendum aa is significant because it directly addresses the largest barrier to using ASHRAE’s IAQ Procedure (IAQP) to improve building energy efficiency and indoor air quality: the complexity of applying the IAQP. There is broad recognition of the importance of both indoor air quality (IAQ) and the need to lower buildings’ carbon emissions, and the signing of the Bipartisan Infrastructure Deal in November addresses this with funding for improving building energy efficiency and IAQ.

ASHRAE Standard 62.1 is one of ASHRAE’s most prominent standards because it specifies “minimum ventilation rates and other measures intended to provide indoor air quality (IAQ) that is acceptable to human occupants and that minimizes adverse health effects.” Standard 62.1 applies to the design and operation of commercial and industrial buildings, excluding inpatient health care facilities which are covered by ASHRAE Standard 170. ASHRAE Standard 62.2 applies to residential buildings.

Standard 62.1 sets out two procedures to calculate mechanical ventilation rates for commercial buildings: the Ventilation Rate Procedure (VRP) and the IAQ Procedure (IAQP). Despite the IAQP’s inclusion in the standard since 1981, most HVAC systems in non-residential buildings have been designed using the less efficient VRP because it is simpler to apply. Effective immediately, Addendum aa changes this by making the more energy efficient IAQP as easy to use as the VRP for HVAC system designers and operators.


According to the latest Standard 62.1 User’s Manual, “The VRP is a prescriptive procedure in which outdoor air intake rates are predetermined for various space types (occupancy categories) based on contaminant sources and source emission rates that are typical for the space type.” (Pg. 63) When the VRP is used, IAQ is achieved by diluting contaminated indoor air with “fresh” outside air without any consideration for the actual quality of outside air, actual building emission rates, or other environmental factors that impact IAQ.

In contrast, the IAQP is a “performance-based procedure” that allows “any method to be used to achieve the contaminant concentration limits, including source control, air cleaning, or dilution of indoor contaminants with outside air.” Because it is performance-based, “The IAQP allows ventilation air to be reduced below rates that would have been required by the VRP if it can be reliably demonstrated that the resulting air quality meets the required criteria” set out in the standard. (Pg. 100)

According to Standard 62.1-2019, “Although the intake airflow determined using each of these approaches [the VRP or IAQP] may differ significantly…any of these approaches is a valid basis for design.” (ASHRAE Standard 62.1, Section 6.1)

ASHRAE Makes Using the IAQP Easier

Even though the IAQP with air cleaning is a more direct way to ensure good IAQ and is often more cost effective and energy efficient compared to the VRP, many engineers have been reluctant to use the IAQP because it requires them to identify specific contaminants that need to be controlled and the appropriate concentration limits and exposure periods for each contaminant within each zone.

ASHRAE recognized these barriers to adoption of the IAQP and has now addressed them in Addendum aa by specifying fourteen Design Compounds (formerly contaminants of concern) plus PM2.5 that must be controlled when using the IAQP. Addendum aa also provides Design Limits for each compound and PM2.5 based on guidance from recognized cognizant authorities and adds an objective IAQ verification requirement post installation.

This update by ASHRAE removes any ambiguity for engineers or building owners using the IAQP. Using tools developed by Daikin Applied, enVerid and others, applying the IAQP is now as straightforward as applying the VRP and delivers better IAQ more energy efficiently.

Here is the list of fourteen Design Compounds plus PM2.5 that must be accounted for when applying the IAQP. The list also shows Design Limits for each Compound and PM2.5.

ASHRAE Addendum Table Blog2

How ASHRAE Created the Design Compound List

This list of Design Compounds was determined by members of the Research & Education Subcommittee of the ASHRAE Standard 62.1 Committee based on a thorough literature review. If published data were sufficient to indicate a compound was likely to be found in any building type covered by Standard 62.1 at concentrations that were a substantial fraction of the proposed design threshold, then the contaminant was added to the list. ASHRAE’s goal was not to include every possible compound that may appear in indoor air, but rather to include a sufficient number of compounds and diversity thereof such that the control of the compounds is anticipated to result in air quality that meets Standard 62.1’s definition of “acceptable.”

The Design Limits were obtained from cognizant authorities such as US EPA, California EPA, and the Committee for Health-Related Evaluation of Building Products. At present, no single organization develops acceptable concentration limits for all indoor compounds, nor are limits available for all compounds of potential concern. Therefore, the Subcommittee determined Design Targets for each compound based on the value specified by a cognizant authority and as close as possible to the limit obtained by the Ventilation Rate Procedure. For example, formaldehyde thresholds established by different cognizant authorities vary by two orders of magnitude. The committee determined that a limit of 33 μg/m3 is appropriate because this is the level that people are subjected to in typical buildings under the Ventilation Rate Procedure.

One of the advantages of using the IAQP is its flexibility compared to the VRP. Additional compounds may be added to the list for a specific project. Lower Design Limits may also be used for any of the compounds. For example, if CO2 is of concern, then it may be added to the list of compounds with whatever Design Limit the designer deems appropriate. CO2 was not included in the list of Design Compounds in Addendum aa due to a lack of consensus as to whether CO2 is itself a contaminant or simply an indicator of good IAQ, and due to the lack of a recognized cognizant authority for CO2.


As we enter our “new normal” with a heightened focus on both IAQ and decarbonizing buildings, the IAQP offers the most direct way to ensure good IAQ most energy efficiently. With the main barrier to IAQP adoption now addressed by Addendum aa, all engineers and building owners should embrace the IAQP as best practice for achieving sustainable IAQ.

Click here to learn how Rebel Applied's Sorbent Ventilation Technology uses ASHRAE 62.1’s IAQ Procedure to enhance IAQ, while trimming annual operating expenses by up to 30%.