IEQp1 Design Supply Air Question

You would use the 250 cfm for heating mode (and the Ez of 0.8 to match overhead air distribution in heating mode). The calculator embedded in the form asks you which condition you are analyzing, and your worst case is probably heating mode so it sounds like you're on the right track.

Michael, You have two options: Vdzd =250 cfm Ds=100% or Vdzd=1000 cfm Ds=25% In the end you get the same value. We tend to do that latter. We put in the full capacity of the terminal unit and then what the turn down is for the design condition analyzed.

If it's a Cooling-only system (no heating in the building), should Ds be 100% or the minimum operating setting for that particular VAV? Any input or advice is much appreciated.

Simon, Unless your cooling only system is constant volume, then your worst case is when the zone needs minimum cooling. Typically you'll have a Ds around 50%-30%.

I submitted a project that has parallel terminal boxes. I used the cooling primary max for the Vdzd value (no recirc). For Ds I calculated a value that would correspond the Total supply air to zone at condition being analyzed (box primary min + locally recirculated airflow or Vdz) = Vdzd * Ds In certain cases the scheduled locally recirculated air, used during heating only, was larger than the maximum primary design airflow resulting in zone Ds values > 100%. I received review comments that "Vdzd values should represent the design airflow supplied in the worst case ventilation condition (peak heating mode in this case) including local recirculation." I believe this comment to be conflicting with an additional review comment: "For VAV systems in the cooling condition, Zone Ds is typically 100% In the heating condition Ds will be much lower than 100% reflecting the reduction in airflow rate at each zone." 1. If the submission is modified per the initial comment, should the zone Ds be 100% as there would be no reduction for the heating condition? 2. If using the cooling condition for Vdzd, is it reasonable to have a Ds > 100% for conditions where parallel terminal units have a recirculated airflow > than the primary?