Coil face velocity
Work the steps in order. The page figures the airflow from the Velocity Grid readings, corrects it for the static pressure change, and gives a target discharge static. Nothing is saved on this page.
Use a Velocity Grid only. An RVA or hot wire on a coil face gives very inaccurate results. This method is less accurate than a traverse, so compare the answer with another CFM (fan curve, grille or box totals) and expect to be within 5%.
1 Design and coil area
Gross area = length × width ÷ 144. Area used = gross area × 0.84, the Velocity Grid correction applied to the coil face area. You can type the coil face area from the submittals instead.
2 Baseline discharge static, filters in
With the filters installed and all unit doors closed, read the discharge static pressure.
3 Remove the filters
Safety: lock out any part you reach into, keep hands, clothing and tools away from a running fan, and open access doors only as far as needed (on a unit with a fan running, doors can slam or pull shut).
4 Show only one side of the coil
Block or cover the other side of the coil so the Velocity Grid reads only the face you are testing. Keep the unit doors closed as much as you can.
Safety: block with solid material that can't be pulled into the fan, and don't stand where you could be drawn against the coil.
5 Velocity Grid readings
Traverse the coil face with the Velocity Grid. Keep your body out of the air path. Enter every FPM reading (separate with commas, spaces, or new lines); the page averages them.
Most coil velocities are around 500 FPM. If your average is near that, the readings are probably good.
6 Discharge static during the test, filters out
Read it at the same spot as step 2, while the Velocity Grid readings are being taken.
7 Results and target static
Put the filters back, close the doors, and remove any blocking before you leave the unit running.