Fan Pressure Rise

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A very old question, but I couldn't pass it up. I think @Anna Osborne Brannon 's explanation is not correct. It seems she is confusing "Dynamic pressure" (Velocity pressure) with "Dynamic loss". Dynamic loss which results from flow disturbances in the fitting correlates Dynamic pressure which is the kinetic energy per unit volume of a fluid, but they are differenct concepts.

Short answer: strictly speaking, total pressure (total static pressure + dynamic pressure) shoud be used, but energy modellers use total static pressure case by case. More details below.

In general, the following formula holds:

Fan power consumption [W] = Air flow rate [m3/s] * Fan total pressure [Pa] / Fan total efficiency

EnergyPlus uses the wording Pressure Rise instead of Fan total pressure, but they refer to the same thing.

Fan airflow and rated fan power are always in the fan equipment schedule, but other information available depends on projects.

For constant speed fans, the fan total pressure can be calculated backward by using the rated fan power in the fan equipment schedule as the excess pressure is adjusted with a volume damper i.e. Fan total pressure (=Pressure Rise)[Pa] = Fan Power [W] / Air flow rate [m3/s] * Fan total efficiecny

For variable speed fans,

1. If the total static pressure (= internal static pressure and external static pressure) is in the equipment schedule or in Fan/AHU/PAU's data sheet, I guess many energy modellers use the value for Pressure Rise in the idf file. It is becasue the external static pressure calculated by MEP engineers is overestimated i.e. a safety factor of around 10% is taken into account or/and it is rounded up in 50Pa or 100Pa increments (e.g. Calculated external pressure + internal pressure = 930Pa → Entered total pressure in the equipment schedule = 1000Pa). On the other hand, dynamic pressure (= 1/2 * ρ * v^2) is normally less than 50Pa. Dynamic pressure is consequently included in the margin of the external static pressure. I think that's why many energy modellers ignore fan dynamic pressure and input only the total static pressure (= internal static pressure and external static pressure) into Pressure Rise field.
2. If the total static pressure (= internal static pressure and external static pressure) and the dynamic pressure is known, as in @KC 's case, the total pressure (the total static pressure + the dynamic pressure) should be used for Pressure Rise in the idf file, but this case is very rare. MEP engineers do not normally calculate fan dynamic pressure because their concern is whether fans can supply air to the farthest room, and because static pressure is the force that pushes air out by overcoming the resistance of ducts.
3. If the external static pressure is in the schedule but the internal static pressure for AHU/PAU/Ventilation unit, etc., I don't think this estimation is justified. I will ask the equipment manufacturers to provide the data sheet including internal static pressure first. If I cannot get the internal static pressure, I have no choice ...