What is External Static Pressure in HVAC Ducts?
External Static Pressure is basically and simply the pressure required by a fan (which is located inside any HVAC equipment) to deliver the required / design airflow rate and to allow air to reach from the HVAC equipment to the Index point so air can be discharged with the required airflow rate even from the furthest air outlet (Diffuser or air grille...etc).
To do that, the fan pressure has to overcome all loses in the direction of air flow (on the Suction and Discharge side of the equipment) including, but not limited to, Volume control dampers, Fire Dampers, pressure drop in air outlets, duct pressure drop, duct fittings losses, External air louvers (in case if the Outside Air Intake duct has the index run compared to the return air duct)... etc.
EASY STEPS TO CALCULATE THE ESP:
1.Find the longest route & Critical route of Duct.
2.Calculate the static loss in fittings(Elbows, reducer, y-piece, shoe neck branch connection & other air terminal devices) presence in the longest route.
3.Add other items Pressure drop like sound attenuator ,fire damper & volume control damper.
4.Finally add 10 -15% safety factor for safer side of design.
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