For a screw-type air compressor, the following parameters are typically specified on the motor nameplate (taking a conventional single-stage 132kW compressor as an example: flow rate = 24 m³/min, working pressure = 7 Bar):
Motor rated power (rated output power or rated shaft power): P = 132 kW Motor efficiency (using Huada Motor as an example): η = 94.7% Power factor: COSφ = 0.892 Service factor S.F = 1.15 (some manufacturers use a service factor of S.F = 1.2) Based on the above parameters, we can determine:
Ø The nominal rated input power of the motor of this machine (without considering the service factor and at full load):
P1 = (Motor rated output power P ÷ Motor efficiency η) = 132 kW ÷ 94.7% = 139.39 kW
Ø The nominal rated input power of this machine (considering the service factor and at full load):
P2 = (Main motor rated output power P ÷ Main motor efficiency η) x (Service factor S.F - 0.05) = (132 kW ÷ 94.7%) x (1.15 – 0.05) = 153.33 kW
(Note: Theoretically, a 5% margin should be considered when calculating the service factor; it cannot be calculated at full capacity.)
Ø The nominal specific power of this screw-type air compressor (at 7 bar, considering the service factor and at full load): PB1 = P2 ÷ 24 m³/min = 6.39 kW/(m³/min)
If it is an air-cooled machine, the input power of the fan also needs to be considered. If the screw air compressor is an air-cooled type, and the fan motor has a rated power of 4.5 kW and an efficiency of 85%, then the input power consumption of the fan motor is:
PF = 4.5 kW ÷ 85% = 5.29 kW
Ø The nominal total input power of the screw air compressor (considering fan power consumption, service factor, and full load) is: PZ = P2 + PF = 153.33 + 5.29 = 158.62 kW
Ø The nominal specific power of this air-cooled screw air compressor (at 7 bar, considering service factor and full load) is: PB2 = PZ ÷ 24 m³/min = 158.62 ÷ 24 = 6.61 kW/(m³/min).