Volumetric tracking maintains a fixed difference between which two flow rates?

• A. Supply and Exhaust.
• B. Return and Outside Air.
• C. Outside Air and Exhaust.
• D. Supply and Return.

Answer: (D)

Volumetric tracking is about keeping the net amount of air moving through the occupied space at a set value by holding the difference between what is supplied to the space and what returns from the space constant. The outdoor air that actually enters the space is determined by that net difference, so controlling the flow to maintain a fixed S minus R ensures a consistent ventilation rate. In other words, the two flow rates involved are the supply to the space and the return from the space, because their difference represents the air that must be brought in (outdoor air) to meet the ventilation target. The other pairings don’t directly define that net in-and-out through the space in the same way.