Do not assume the physically longest duct run is the index path. A shorter run with multiple acoustic linings, tight elbows, and VAV boxes often creates higher static pressure than a long, straight run.
Where:
ESP (Total) = Supply Side Total + Return Side Total esp calculation hvac excel sheet
At installation, after filter change type, after duct modifications, and annually for maintenance.
Total length multiplied by the friction rate (usually from a Duct Fitting Database). Do not assume the physically longest duct run
VP = (Velocity_FPM / 4005)^2 Fitting_Loss_in_wc = C * VP
His problem wasn't the chiller capacity or the duct sizing. It was the —External Static Pressure. Total length multiplied by the friction rate (usually
The outward push of air against duct walls, independent of velocity.
Using the airflow (CFM) and duct size, you calculate the friction rate. In a manual calculation, you’d use a Friction Chart; in Excel, you can use the or Colebrook-White formulas to automate this. 5. Pressure Drop Calculation The formula for each segment is:
Note: Always use manufacturer data where available.