To know whether a mine ventilation fan is doing its job, you must calculate and measure airflow in the underground airways and ducts. Fan catalogues provide performance curves, but real mine conditions, leakage and system resistance can change the delivered quantity. Reliable airflow measurement is therefore essential for verifying compliance with ventilation regulations and for optimizing fan operation and energy use.
The basic calculation is based on the simple relationship Q = V × A, where Q is airflow (m³/s), V is average air velocity (m/s) and A is cross-sectional area (m²). In a tunnel, raise or drift, first measure the effective area: width multiplied by height, minus any significant obstructions. In ducts, area is usually circular (πD² / 4) or rectangular (width × height). Once area is known, you measure velocity and multiply to obtain the airflow.
Velocity can be measured using several types of anemometers. Handheld vane anemometers are common for mine ventilation surveys; they are swept across a cross-section to capture an average velocity. Hot-wire or ultrasonic anemometers may be used for more precise measurements, especially in low-velocity or turbulent flows. In ducts or large airways, an engineer may perform a velocity traverse, taking readings at a grid of points and averaging them to obtain a representative velocity for the whole cross-section.
For large main fans, it is often more practical to measure airflow in nearby main airways rather than at the fan outlet itself. Survey teams select straight sections of intake or return airways and perform systematic traverses at multiple stations. From these measurements, they calculate airflow for each branch and check that circuit balances are reasonable. Software tools can be used to reconcile flows and identify unusual resistance or leakage.
In some installations, fixed monitoring instruments are used to measure airflow continuously. These may include ultrasonic flow meters, differential pressure devices across calibrated orifices, or pitot tubes connected to transmitters. Data from these instruments is fed to a control system that can alarm on low airflow and adjust fan speeds or regulators as part of a ventilation-on-demand strategy.
Calculating airflow also involves understanding system resistance and fan curves. Once you know measured Q at a given fan speed, you can compare it with the manufacturer’s fan curve to estimate actual system pressure. Repeating measurements at two or more speeds helps build a clearer picture of how the mine ventilation fan interacts with the network. This is useful when selecting new fans, adjusting regulators or deciding whether to install a booster fan.
In summary, airflow for mine ventilation fans is calculated from cross-sectional area and average velocity, and measured using anemometers, duct traverses, fixed sensors and fan performance checks. Consistent, well-documented measurements ensure that mine air quantities meet design targets and regulatory requirements while allowing operators to run ventilation fans efficiently.
