Question 1 of 18
How do you establish the duct-system static-pressure budget when a fan serves filters, coils and accessories?
Strong Interview Answer
Start with the fan's available external static pressure at the design airflow and the applicable rating point. Subtract the pressure drops of components that must be carried within that external-static budget, then use the remainder for the supply and return duct path. For example, 0.50 in. w.c. available minus 0.18, 0.12 and 0.10 leaves 0.10 in. w.c. for the ducts. I would then verify that the proposed duct layout and fan operating point can actually deliver design airflow.
What to Listen For
- available external static pressure
- component pressure drops
- duct pressure budget
- fan operating point
- design airflow
Caution
Listen for subtraction of component losses from available external static pressure—not adding the fan rating as another loss.