Potentially counterintuitive given recommended ventilation system design during the pandemic, it is possible to achieve Standard 241 equivalent clean airflow (ECAi) objectives while also reducing outdoor air under the Indoor Air Quality Procedure. Achieving both at the same time relies on system design with air
cleaning and filtration as proven by ASHRAE standards 52.2 and the 241 Appendix A Testing Procedure.
The following example illustrates an approach. Under 241 a classroom has a target ECAi of 40cfm/person. In this example, the room is 950ft2 and ventilation is sized for 25 people. In the “Existing” space[1], designed to the V.R.P., the AHU is fed with 450cfm of O.A. and cleans recirculated air with a MERV8 filter. This configuration provides an ECAi of 18cfm/person. Boosting the AHU’s filter to a MERV11[2] delivers ECAi of 38cfm, below the target.
Alternatively, applying the IAQP via smartIAQ [3] to the same classroom with MERV11 filter in the AHU delivers an ECAi of 46.6cfm. A passing score. This works because smartIAQ’s filtration is rated to MERV13A (77% removal value under 241) with 500cfm of capacity delivering 385cfm of equivalent clean air. By lowering O.A. the additional recycled air to the AHU with MERV11 boosts the VECAi via filtration to 630cfm.
Another alternative is using smartIAQ [4] under the IAQP across two zones (far right column). In this case, the on board filtration is boosted to a HEPA filter, with a 99% removal value under Standard 241. This provides 250cfm of ECAi into each room achieving 41.2cfm of equivalent clean air, a passing score.
