An industrial ventilation system is designed by first surveying the contaminant and heat load, then calculating airflow in cubic metres per hour, laying out ducts at 6 to 10 m/s, selecting a fan on the system curve, and commissioning by balancing every branch to within 10% of design. The core components are intake, filter, fan, ducts, air-handling unit, and exhaust stack.
Good design is governed by ventilation standards that turn comfort into a number. ASHRAE 62.1 and the European EN 16798 set minimum outdoor-air rates per person, typically 10 L/s in offices and up to 30 L/s in dusty or occupied-heavy spaces, and tie them to a CO2 concentration target of about 1,000 ppm above outdoor. When indoor CO2 passes 1,000 ppm the space is implicitly under-ventilated and occupants report drowsiness and error rates climb, so designers size the fresh-air fraction from occupancy, not habit. Heat and contaminant load set the total flow, and the standard then splits it between outdoor air and recirculation through filtration. Ignoring the standard produces two failures: too little air leaves a stuffy, unsafe plant, while too much air heats or cools massive volumes and wastes 20 to 40% of the HVAC energy. The economic weight is large because fans and coils run every hour; a system 15% oversized on flow can add 15 to 25% to the annual bill with no comfort benefit. Commissioning to the calculated rate, then verifying with a pitot traverse in the main duct, closes the gap between the drawing and the real building.
Component Map of a Complete System
Every industrial system shares the same chain. Outside air enters through a louvred intake fitted with a G4 bird-and-dust screen, passes pre-filtration, then the fan. The fan pushes air through the duct network into an air-handling unit holding cooling or heating coils, humidification, and final filtration. Variable-air-volume boxes or motorised dampers trim flow to zones, and ceiling diffusers or local hoods deliver it. Exhaust is collected at source and expelled through a stack above roof height, often 3 to 5 m, to disperse residuals. Sizing each part to the same design flow, typically 5,000 to 200,000 m³/h, prevents one section from starving another.
Design Process Step by Step
The comparison below shows how a correct sequence differs from the common shortcut that produces a failing system.
| Step | Correct method | Common shortcut | Result |
|---|---|---|---|
| 1 Load survey | Measure contaminant and heat | Guess from floor area | Wrong flow by 30 to 50% |
| 2 Airflow | Calculate m³/h from load | Use rule of thumb | Stuffy or wasteful |
| 3 Duct | 6 to 10 m/s velocity | Oversize blindly | Doubled pressure drop |
| 4 Fan | Select on system curve | Pick nearest catalogue | Off-best-efficiency point |
| 5 Commission | Balance to plus/minus 10% | Skip | 15 to 30% energy waste |
Choosing the Right Approach
- Choose dilution ventilation when the hazard is low-rate and spread across a large space, sizing flow from total heat load.
- Choose local exhaust hoods when the contaminant is concentrated at a machine, capturing at the source at 0.5 to 1 m/s face velocity.
- Choose a central AHU with VAV when many zones need different temperature but shared filtration.
- Choose direct evaporative cooling in hot dry climates to cut coil energy by 20 to 40%.
- Choose heat-recovery wheels (ERV) when exhaust air is 22°C and fresh air is 35°C, recovering 60 to 80% of energy.
Duct Sizing and Fan Selection
Duct velocity sets the friction loss, and friction rises with the square of velocity, so a main run at 8 m/s needs far less fan pressure than one at 14 m/s. A 1,000 mm round duct at 8 m/s moves about 22,600 m³/h; a 500 mm duct at the same flow runs 32 m/s and can double pressure drop. Pick a fan on the plotted system curve, not the catalogue peak, so it runs near best efficiency at 1,000 to 3,000 Pa. Add 10 to 15% margin for filter loading but never 50%, or you oversize the motor and waste kW daily.
Worked Example: A 20,000 m³/h Paint Shop
A paint shop needs 20,000 m³/h of tempered air and extract at the same rate. The load survey shows 30 kW of process heat and 15 mg/m³ of overspray, so the design flow is set, not guessed. Main ducts are sized for 8 m/s: a 1,000 mm duct carries about 22,600 m³/h, so one main with a branch meets the flow. The supply AHU holds a 50 kW heating coil and an F9 pocket filter at 200 Pa, while the extract uses a cartridge bank at 400 Pa. Plotting the system curve gives a duty point of 1,200 Pa at 20,000 m³/h, and the selected centrifugal fan runs at 78% efficiency, drawing 8.5 kW. Had the duct been sized at 14 m/s, pressure would nearly double to 2,200 Pa and the motor to 15.5 kW, an 82% energy penalty for the same air. Balancing the branches to within 10% after install kept the booth at setpoint and saved the projected 15 to 30% that unbalanced systems waste.
The 10% balance tolerance is not arbitrary; it is the point where branch error starts to cost real money and comfort. A branch 20% over design steals air from a sister branch that then falls 20% short, so two spaces miss setpoint from one mis-set damper. Closing that gap with a balancing hood takes an hour per branch but recovers the 15 to 30% energy and the occupant complaints in the same afternoon. Document the final damper position on the as-built drawing so the next technician does not unknowingly reopen it during a filter swap.
Common Mistakes to Avoid
- Skipping the load survey and using floor-area rules, which miss 30 to 50% of the true flow need.
- Oversizing ducts then the fan, because a 50% margin adds capital and a motor that loafs off its best point.
- Mixing supply and exhaust without balancing, so one starves and the other short-cycles.
- Forgetting filtration pressure in the fan curve, so the unit cannot hold flow once filters load.
- Commissioning by eye, which leaves branches 20% off and the energy budget blown for the whole life.
Keruite manufactures this equipment at an 80,000 m² facility in Dezhou, China, with an in-house AMCA-210-style test laboratory; every unit is balanced to G2.5 and performance-tested before shipment.
FAQ
What are the main components of an industrial ventilation system?
A complete system has an air intake, pre-filter, fan, duct network, air-handling unit with cooling or heating coil, VAV or dampers, diffusers, and an exhaust stack. Each part is sized to the same design flow, typically 5,000 to 200,000 m³/h, so no section starves another of air.
What is the step-by-step design process?
Begin with a contaminant and heat load survey, then calculate required airflow in m³/h, lay out the duct with 6 to 10 m/s velocity, select a fan at the system curve, add filtration and controls, and commission by balancing every branch to plus or minus 10% of design. Skipping the load survey is the usual cause of failure.
How do I size ducts without wasting fan power?
Size ducts for 6 to 10 m/s in main runs and 2 to 5 m/s near outlets, because friction loss rises with the square of velocity. A 1,000 mm duct at 8 m/s carries about 22,600 m³/h; halving diameter at same flow quadruples velocity and can double the pressure drop the fan must beat.
Why does the system need commissioning and balancing?
Even a correct design drifts once built, because fittings and dampers differ from the model. Balancing measures each branch and sets dampers so flow lands within 10% of target, preventing short-cycling, noise above 65 dB, and rooms that never reach setpoint. Unbalanced systems waste 15 to 30% of fan energy.