Major Updates by ASHRAE Make the IAQP Simple to Use

There are many benefits to achieving indoor air quality (IAQ) goals with less outside air ventilation. They include improved IAQ when outside air is polluted and cost savings from extending the life of particle filters. Another big benefit is reducing the cost and climate impact of HVAC systems by reducing the conditioning load on buildings. Reducing conditioning load associated with outside air ventilation allows buildings to install smaller HVAC systems that cost less and use less energy. 

The way to achieve IAQ goals with less outside air ventilation is to use an air cleaning system to filter harmful gaseous contaminants from indoor air so that cleaned indoor air can be safely recirculated. Numerous studies such as this one show that cleaning indoor air is much more energy efficient than achieving IAQ targets by “refreshing” indoor air with outside air, which is often not fresh. 

But there is a catch. No engineer designing HVAC systems will reduce outside air ventilation if doing so is not clearly supported by building standards. For many engineers, design procedures that support this appraoch must also be simple to apply without creating potential liability for the designer. 

Recent updates by ASHRAE make designing ventilation systems with gas-phase air cleaning simple while also eliminating potential liability for designers. This is leading to increased adoption of gas-phase air cleaning to deliver lower cost, more energy efficient HVAC designs. 

ASHRAE Standard 62.1 is the most referenced standard globally for “ventilation and acceptable indoor air quality”. Within Standard 62.1, there are two procedures to calculate mechanical outside air rates: 

• Ventilation Rate Procedure (VRP) – A prescriptive procedure in which outdoor air rates are determined based on rule of thumb rates per space area and design occupancy, which vary by space type, without any consideration for the benefits of gas-phase air cleaning.  

• Indoor Air Quality Procedure (IAQP) – A performance-based procedure in which outdoor air rates are determined using a combination of outdoor air and gas-phase air cleaning. This combination can be optimized for cost, energy efficiency, and IAQ.  

Whereas the VRP is fully reliant on outdoor air “dilution ventilation” to maintain IAQ, the IAQP is a more flexible approach that allows for the benefits of air cleaning to be considered in the design. This flexibility is key as we seek to design buildings that are more energy efficient without being more expensive. Cleaning indoor air also makes buildings more resilient to polluted outside air.  

The IAQP has been part of Standard 62.1 since the 1980s, but until recently few engineers used the procedure because it was complex to apply. The main critiques were that the IAQP did not define the contaminants to be controlled, and to what levels, to achieve acceptable IAQ. Additionally, there were no standard test methods to determine the efficiency of air cleaning systems to control specific contaminants. Finally, performing the “mass balance” calculations required by the IAQP was tedious. 

Since 2022, ASHRAE has published three major addendums to Standard 62.1 that address all these critiques and make the IAQP as simple and risk free as the VRP for designers. 

Update #1 – Defining IAQ: Design Compounds & Limits 

For the first time, Addendum aa to 62.1-2019 provided a specific definition of IAQ for all space types covered by Standard 62.1. This definition can be found in tables 6-5 and 6-6, which lists 14 design compounds (formally called “contaminants of concern”), mixtures of design compounds, and PM2.5 that must remain below specified limits to achieve what ASHRAE defines as “acceptable IAQ”.  

Table 6-5 is shown below. This blog post discusses how ASHRAE came up with this list. 

Now that ASHRAE has provided a specific definition of “acceptable IAQ”, engineers can confidently use the IAQP to combine outside air and air cleaning to cost effectively, energy efficiently achieve IAQ.  

Update #2 – Test Methods for Gas-Phase Air Cleaners  

Next, we needed standardized test methods to know the effectiveness of gas-phase air cleaners for all the ASHRAE defined contaminants. Addendum n to 62.1-2022 addressed this by requiring gas-phase air cleaners to report cleaning efficiencies for all compounds included in the design (see Table 6-5) in accordance with ASHRAE Standard 145.2 or ISO 10121-2. Gas-phase air cleaners that do not test to one of these two test methods must be tested, for all contaminants in Table 6-5, to another “national consensus standard” or “custom efficiency test” that is approved by the local code official. This IAQP Air Cleaner Compliance Checklist may be used to determine air cleaner compliance with Addendum n.  

To manage risk, engineers can now simply specify that air cleaners must achieve minimum cleaning efficiencies based on ASHRAE Standard 145.2 or ISO 10121-2 testing for all contaminants in the design.  

Update #3 – ASHRAE Calculator for Outside Air 

The final major update to simply the IAQP was Addendum c to 62.1-2022. This addendum provided “a calculator for mass balance equations used with the revised Indoor Air Quality Procedure.” Anyone can purchase the calculator, which may be used to calculate outside air rates for single-zone and multiple-zone systems, from the ASHRAE Bookstore. The ASHRAE IAQP Calculator includes data for all the contaminants and PM2.5 and facilitates the calculation of System Ventilation Efficiency (Ev). The calculator also features a compliance sheet to streamline the code approval process.  

This final update to the IAQP made applying the IAQP as simple and risk free as applying the VRP. All engineers now need to do is enter the project specific parameters and air cleaner efficiencies into the ASHRAE Excel calculator, and the calculator will determine new, lower outside air rates to comply with Standard 62.1 incorporating the benefits of air cleaning.  

Brandon Harwick, President of Engenium Group, a MEP firm that has used the IAQP on multiple projects, summed up ASHRAE’s updates to the IAQP when he said,

“The challenge with the IAQP had been the lack of guidance on acceptable levels for indoor contaminants, test standards for gas-phase air cleaners, and simple tools to make applying the IAQP easy. ASHRAE’s recent updates address these concerns, which will drive adoption especially with the growing focus on cost, efficiency, and IAQ. I expect that in the next 10 years use of the IAQP will surpass use of the VRP.”

For more of Brandon’s thoughts on the IAQP, click here.  

For free access to enVerid’s IAQP Calculator, click here. The enVerid IAQP Calculator is based on the ASHRAE IAQP Calculator and is pre-populated with Standard 145.2 cleaning efficiencies for enVerid’s products. The enVerid IAQP Calculator also includes emission rates for additional space types.