Definitions
Static pressure (SP) the pressure resulting from the gas density and its degree of compression and independant of the gas velocity the pressure resulting from the velocity of a gas and its air density VP = ½ ρV² the sum of the static pressure and the velocity pressure TP = SP + VP the difference between the average total pressure at the fan outlet (2) and the average total pressure at the fan inlet (1) FTP = TP2 - TP1 = SP2 + VP2 - SP1 - VP1 1 Fan static pressure (FSP) the difference between the fan total pressure and the velocity pressure at the outlet (2) FSP = FTP - VP2 = SP2 - SP1 - VP1 the difference between the static pressure at the fan outlet (2) and the static pressure at the inlet (1) SPR = SP2 - SP1 the minimum power required to move a specified rate of gas against a specified resistance then it is product of the flow (inlet and outlet conditions) and the fan total pressure Qin = flow (T1, SP1) Qout = flow (T2, SP2) Q = (Qin + Qout) / 2 Po = Q x FTP the power delivered to the fan shaft also known as fan shaft power the power delivered at the fan motor output (the shaft) also the fan input power divided by the fan drive efficiency Pmo = Ps / ηD the power delivered at the fan motor input (electrical power) also the fan output power divider by the motor efficiency Pe = Pmo / ηM then Ps = µM x µD x Pe Fan total efficiency (ηt) the ratio of the fan output power to fan input power also known as fan mechanical efficiency ηt = Po / Ps the product of mechanical efficiency and the ratio of fan static air in air out Po Ps Pmo ηD ηM Power source Pe
Velocity pressure (VP)
Total pressure (TP)
Fan total pressure (FTP)
2
Static pressure rise (SPR)
Fan output power (Po) or aeraulic power or air power
ηt
Fan input power (Ps)
Fan motor output power (Pmo)
Fan
Drive
Motor
Fan motor input power (Pe)
Fan static efficiency (ηs)
pressure to fan total pressure ηs = ηt x FSP / FTP Fan performance curve or fan pressure curve A curve showing the relationship between the gas flow rate delivered by a fan and the pressure generated at the different flow rates A curve showing the power of a fan at different flow rates
fan peak pressure operating point fan power curve
18 16
120 100 80
Fan power curve System resistance curve
14
Fan pressure
A curve showing how the resistance to flow through a system (pressure drop) changes with the flow rate. Typically, for turbulent flow, the curve follows the following relationship (parabola): ∆P = k ρ Q² The intersection of the fan pressure curve and the system resistance curve. The fan will operate at that point. The maximum pressure the fan can deliver. The fan should always operate on the right side of the peak pressure point