Knowing how to calculate fan requirements is essential for designing reliable ventilation in industrial plants and mines. Instead of starting from a catalogue, you begin by defining what the fan must do: how much air it must move, against what resistance, at what conditions. The result is a required duty point, expressed as airflow (CFM or m³/s) and static pressure (inches wg or Pa), which you then use to select a suitable fan.
The first step is to calculate the required airflow. There are several common methods:
- Air changes per hour (ACH): For general room ventilation, multiply the room volume by the desired air changes per hour and divide by 60 to obtain CFM.
- Contaminant control: For fumes, dust or gases, use recommended capture velocities at hoods and dilution guidelines to calculate the necessary local and general exhaust flows.
- Heat removal: For hot industrial or mine environments, estimate total heat load and use heat-balance equations to determine the air quantity needed to keep temperatures within limits.
- Regulations: In underground mining, regulations often specify minimum airflows per person, per kilowatt of diesel power or per heading, which define baseline fan requirements.
The second step is to estimate the system static pressure the fan must overcome. This includes:
- Friction losses in ducts, airways and mine roadways.
- Losses through filters, dampers, louvers, bends and fittings.
- Entrance and exit losses at inlets, hoods and discharge points.
- Any additional pressure required for special equipment, such as scrubbers or cooling coils.
Engineers typically use duct calculation methods or mine ventilation network software to sum these losses along the intended airflow path and obtain a total static pressure at the design flow.
The third step is to apply air density corrections if the system operates at high altitude, high temperature or with special gas mixtures. Fan curves are normally given for standard air, so actual pressure and power requirements must be converted accordingly.
Once you have the required airflow and static pressure at site conditions, you can translate them to equivalent standard-air values and then use fan selection charts or software to choose a fan type, size and speed that can deliver that duty point. You also check the corresponding efficiency and power to ensure the motor, electrical system and controls are appropriately sized.
Finally, fan requirements should be validated by considering future changes and safety margins. Mines may extend, production may increase, or additional equipment may be installed. Allowing a reasonable margin for growth and resistance increases, while avoiding excessive oversizing, leads to a robust and energy-conscious fan selection.
