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# Fan Pressure Rise Here is metioned that the total static pressure has to be used for the Fan Pressure Rise parameter in EnergyPlus.

Can someone explain why the total pressure (= total static pressure + dynamic pressure) should not be used? Thank you in advance!

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Short answer, total static pressure in the HVAC community includes dynamic losses from fittings and is equal to total pressure. Losses from fittings (elbows, branches, tees) is sometimes converted to an equivalent length of "straight duct" and then applied a friction loss. This might be why there is the misnomer of total "static" pressure. Or the loss coefficient ("C") for a fitting is looked up in a table and multiplied by velocity pressure ("Vp") to determine the loss.

The total pressure includes external static pressure and internal static pressure. External static pressure includes losses from volume control dampers, fire dampers, air outlets, duct length pressure drop (i.e. friction losses), duct fittings (i.e. dynamic/velocity losses), louvers, etc.

Internal static pressure includes things like filters, cooling coils, heating cools, and heat exchangers.

So, you should use the "total" pressure in your numbers below, as it includes the dynamic/velocity pressure loss from fittings.

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I would like to simulate a HVAC system with the following fan specifications: system effect: 76 Pa, external static pressure: 350 Pa, total static pressure: 831 Pa, dynamic pressure: 74 Pa, total pressure: 905 Pa.

So in this case I should also not use the total pressure?

I revised my above answer to be a bit more clear. You should use the "total" pressure in your numbers above, as it includes the dynamic/velocity pressure loss from fittings.