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# Fans - Efficiency and Power Consumption

### Fan Power Consumption

The ideal power consumption for a fan (without losses) can be expressed as

Pi = dp q                                          (1)

where

Pi = ideal power consumption (W)

dp = total pressure increase in the fan (Pa, N/m2)

q = air volume flow delivered by the fan (m3/s)

Power consumption at different air volumes and pressure increases are indicated below:

Note! For detailed engineering - use manufacturers specifications for actual fans.

### Fan Efficiency

The fan efficiency is the ratio between power transferred to airflow and the power used by the fan. The fan efficiency is in general independent of the air density and can be expressed as:

μf = dp q / P                                     (2)

where

μf = fan efficiency (values between 0 - 1)

dp = total pressure (Pa)

q = air volume delivered by the fan (m3/s)

P = power used by the fan (W, Nm/s)

The power used by the fan can be expressed as:

P = dp q / μf                                     (3)

The power used by the fan can also be expressed as:

P = dp q / (μf  μb μm)                                 (4)

where

μb = belt efficiency

μm = motor efficiency

Typical motor and belt efficiencies:

• Motor 1kW - 0.4
• Motor 10 kW - 0.87
• Motor 100 kW - 0.92
• Belt 1 kW - 0.78
• Belt 10 kW - 0.88
• Belt 100 kW - 0.93
.

### Power Consumption - Imperial Units

Fan energy use can also be expressed as

Pcfm = 0.1175 qcfm dpin / f  μb μm)                                (4b)

where

Pcfm = power consumption (W)

qcfm =  volume flow (cfm)

dpin = pressure increase (in. WG)

### Fan and Installation Loss (System Loss)

The installation of a fan will influence on the overall system efficiency

dpsy = xsy pd                              (5)

where

dpsy = installation loss (Pa)

xsy = installation loss coefficient

pd = dynamic pressure in the nominal intake and outlet of the fan (Pa)

### Fan and Temperature Increase

Near all of the energy lost in a fan will heat up the air flow and the temperature increase can be expressed like

dt = dp / 1000                              (6)

where

dt = temperature increase (K)

dp = increased pressure head (Pa)

### Standards for Fan Efficiency

• ISO 12759 "Fans – Efficiency classification for fans"
• AMCA 205 "Energy Efficiency Classification for fans"

## Related Topics

### • Ventilation Systems

Design of systems for ventilation and air handling - air change rates, ducts and pressure drops, charts and diagrams and more.

## Related Documents

### Efficiency

Efficiency is the ratio useful energy output to energy input.

### Fan AMCA Classification

Fan classification established by AMCA.

### Fan Capacity Diagrams

Pressure, head, air flow volume and fan capacity diagrams.

### Fan Motors - Starting Torques

The motor must be capable of accelerating the fan wheel to it's operating speed.

### Fans - Calculate Air and Brake Horsepower

AHP - Air Horse Power and BHP - Brake Horse Power.

### Fans - Capacity Control

How to modulate fans and their capacities.

### Fans - Noise Power Generation

The sound generated by a fan depends on the motor power, the volume capacity, the static pressure increase and the discharged volume.

### Fans - Volume Flow, Pressure Head and Power Consumption vs. Air Temperature and Density

The temperature and density of the air influences on the volume flow, pressure head and power consumption in a fan.

### Power

Power is the rate at which work is done or energy converted.

### Pumps, Fans and Turbines - Horsepower

British Horse Power as used for pumps, fans and turbines - and how to convert to other units.

### Types of Fans

Axial and propeller fans, centrifugal (radial) fans, mixed flow fans and cross flow fans.

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