Case study: Using IAQP in design

Indoor air quality procedure was used to calculate the design of a community center’s HVAC system.

By Cory Duggin, PE, LEED AP BD+C, BEMP; TLC Engineering for Architecture, Brentwood, Tenn. August 21, 2018

The Southwest Florida Community Foundation Collaboratory in Fort Myers, Fla., chose to employ an innovative HVAC design using the indoor air quality procedure (IAQP). Because carbon dioxide (CO2) is a major contaminant of concern in high occupancy spaces, a gas-phase-adsorption air scrubber was integrated into the HVAC system. The adsorption media adsorbs CO2, volatile organic contaminants, formaldehyde, and other contaminants from a fraction of the return airstream and injects cleaned air back into the return. The device chosen even has sensors on the inlet and outlet to measure the change in contaminants to ensure the design air quality is being achieved. 

The design team knew it wanted to employ the IAQP to reduce the energy consumption of the building, but they were challenged by the need for return air to run through the air-cleaning device. The community center was designed with a variable refrigerant flow (VRF) system, which doesn’t return air to a central air handling unit that the air-cleaning device could be connected to. The only air being returned was exhaust/relief air to the dedicated outdoor-air systems (DOAS).  

The team came up with an innovative solution of using some of the exhaust/relief air as the air to be cleaned. After being cleaned by the air scrubber, it is then mixed with the incoming outdoor air. The air scrubber includes total volatile organic compound (TVOC) and CO2 sensors at the inlet and outlet to ensure the air is being cleaned. When the unit sees the difference in contaminants drop below a certain level, it triggers a regeneration cycle. During regeneration, the dampers to the building air system close and the air in the unit is heated and recirculated through the sorbent media to allow it to release the contaminants. The regeneration air is then exhausted.  

Unlike other air-cleaning technologies, the air scrubber used does not create any byproducts in the cleaning process. Essentially, a small amount of return air was added to the DOAS for cleaning, but it resulted in the DOAS needing approximately 50% less outdoor air than would have been required by using the ventilation-rate procedure. 

The Southwest Florida Community Foundation Collaboratory is on target to achieve U.S. Green Building Council (USGBC) LEED Gold Certification. Previously, IAQP was not allowed on LEED projects; however, a pilot credit titled Performance-based indoor air quality design and assessment can now be used. The USGBC does not allow all air-cleaning technologies to be used to meet the requirements of the IAQP on LEED projects, though.  

The pilot credit language states, “Electronic air-cleaning devices must also be third-party tested to produce no harmful byproducts including ozone, formaldehyde, ultrafine particles, and other volatile organic compounds. An active monitoring device must be installed at all times to continuously monitor contaminant levels, and appropriate mitigation measures must be performed for above-average levels.”  

The system employed at the Collaboratory includes sensors and creates no byproducts, as required in ASHRAE 62.1-2016: Ventilation for Acceptable Indoor Air Quality and the LEED pilot credit. In fact, it also makes it easier to achieve the low-emitting materials credits. This project was able to achieve LEED credits as a result of the gas-phase-adsorption air-cleaning technology in conjunction with IAQP, and it achieved a 43.97% energy-cost savings over the ASHRAE 90.1-2010 Appendix G baseline while reducing the peak cooling load of the HVAC system by 11 tons or 21%.

Author Bio: Cory Duggin is the energy modeling wizard at TLC Engineering for Architecture, providing building-performance simulation efforts and high-performance design solutions. He is a member of the Consulting-Specifying Engineer editorial advisory board.