A former colleague has submitted 62MZCalc spreadsheets to show compliance with the IEQc2 additional ventilation credit. We have had to following comment back from the an assessor and I am unsure how to update the spreadsheets to represent a fan powered terminal unit rather than a single duct system with standard VAV terminals.

"It is unclear how the primary and secondary airflows have been accounted for in the VRP calculations. It appears that the calculations have been performed based on a single duct system with standard variable air terminal units with a 100% primary to supply air ratio. Based on the mechanical plans and schedules provided in PIf4: Schedule and Overview Documents, it appears that the project is served by fan-powered terminal units where the terminal units serve as recirculation units. Refer to the Directions tab of the VRP Calculator for additional guidance on documenting compliance for fan-powered terminal units. Revise the calculations to account for the effects of mixing from the fan-powered terminal unit boxes and ensure the primary airflow supplied is sufficient to document compliance."

OA is mixed with return air at the central AHU's to create the primary air. This primary air is distributed around the floor in a complete floor ring duct. Branches off the ring duct then go to the Fan assisted terminal VAV boxes which provide an additional 10% recirculation air

The following comment was in our original submission describing the system:

“All relevant zones on each floor have been inputted in to the 62MZCalc calculator. Each floor has been reported together, as each floor is served by multiple central AHUs. However these cannot be separated per system as each floor's air distribution ductwork comprises of a central ring around the core, which is supplied directly by the different AHUs. As such each "System Name and Number" for the calculation is per floor.”

Could I please get some guidance on the values/factors that I need to update? The EZ value used is CSCRH. As this is about OA rates I don't understand why the additional 10% recirculation flow will change the credit as the OA rates are compliant and would not change.

Thanks for your help, please ask questions if this is unclear.