Axial Fans for Factory and Industrial Building Ventilation

General industrial ventilation is the most common job for an axial fan and the one most often specified by rule of thumb. That works until the building is hot, the site is at altitude, or the fans need to keep running when one fails. This page sets out how to size ventilation for heat removal and air changes, how to arrange fans and openings so the air goes where you want it, and how to split large duties across fans in our range.

What Ventilation Has to Achieve

Factory ventilation usually serves one or more of these purposes.

• Heat removal. Carrying away heat from machinery, processes, lighting, and solar gain.
• Dilution. Reducing general contamination from fumes, odours, and particles below acceptable levels.
• Make-up air. Replacing air removed by local exhaust systems.
• Comfort and safety. Keeping conditions acceptable for workers, and protecting equipment.

Each purpose has its own airflow calculation, and the largest result governs.

Sizing for Heat Removal

Airflow = heat load ÷ (air density × specific heat × allowed temperature rise)

Example. A hall gains 400 kW of sensible heat. You allow a 6 K rise, using 1.15 kg/m³ and 1.006 kJ/kg·K.

Airflow = 400 ÷ (1.15 × 1.006 × 6) = 57.6 m³/s, or about 207,000 m³/h.

In a 60,000 m³ hall this is about 3.5 air changes per hour. It exceeds one fan in our range, which reaches 185,000 m³/h, so it is naturally split across two fans of about 103,700 m³/h each. Two fans keep the hall ventilated if one fails, and allow staged operation when the load is lower.

Sizing for Air Changes

Many spaces are sized by air changes per hour. Convert with:

Airflow (m³/s) = room volume × air changes per hour ÷ 3,600

A 30,000 m³ hall at 6 air changes per hour needs 30,000 × 6 ÷ 3,600 = 50 m³/s, or 180,000 m³/h. Required air changes come from codes, client standards, and the process, so confirm them for your case. The figure of six here is for illustration only.

Correct for Hot and High Sites

Real air is not standard. Density falls with temperature and altitude, and both the pressure a fan develops and its heat-removal capability change. At sea level and 45 °C density is about 92% of standard, and at 1,800 m with 35 °C air it is about 77%. Calculate heat-removal airflow with the density at the design air temperature, and select fans from density-corrected curves. See how to size an axial fan and fan laws and air density.

Arranging Fans and Openings

Roof or wall extraction with low-level make-up air. The most common arrangement. Heat rises and leaves through the roof fans, and cooler air enters low. Openings must be large enough for low inlet velocity, or they add resistance and starve the fans.

Cross-flow ventilation. Wall fans on one side and openings on the other sweep air across the hall. Works for narrow buildings, and less well for wide ones where the far side sees stale air.

Local supply and spot cooling. Directing air at workstations or heat sources helps where whole-building ventilation is impractical.

Avoid short circuits. Place supply and exhaust so air does not simply travel from inlet to nearest fan.

Balance the building. Total air extracted should be matched by inlet area. Too little leaves the building under negative pressure, which draws air through doors and cracks unpredictably, and raises the resistance the fans work against.

Wind, Backdraught, and Idle Fans

Wind pressure can oppose roof fans and drive air backward through idle ones. Backdraught shutters or dampers on each fan prevent outside air, hot air, or rain from entering when the fan is off. Check performance in wind and consider the effect of neighbouring buildings.

Redundancy and Control

Split large duties across several fans so partial operation continues if one fails. Plan the control approach from the start: fixed duty, staged fans, speed control, or blade-pitch control. A load that varies with production or season saves a lot of energy with speed control, since power varies roughly with the cube of speed. See adjustable pitch versus VFD control.

Noise and Vibration

Fans mounted on light roof structures can transmit vibration into the building, and fans near neighbours need noise checks. Use isolation, attenuation where needed, and check the fan against stall. See axial fan noise and how to read an axial fan curve.

Commissioning and Verification

Once the ventilation is installed, measure what it delivers. Check that each fan runs in the correct direction, record speed, motor current, and airflow against the curve, and measure the temperature rise across the building at a representative heat load. Look for stagnant areas and short circuits with simple smoke tests. Record baseline vibration and current for each fan so later changes stand out. Verification often finds openings that are blocked, dampers that are closed, or a fan turning the wrong way, and each is far cheaper to fix at commissioning than after complaints begin.

Where Our Range Fits

NextAir Systems manufactures axial fans with impeller diameters up to 1,600 mm, static pressure up to 2,400 Pa, and air volume up to 185,000 m³/h. That covers general roof and wall ventilation, heat removal, make-up air supply, and spot cooling in factories and industrial buildings. Ventilation systems with heavy filters or long ducts can be served up to 2,400 Pa static pressure, and beyond that a centrifugal fan is the right choice.

What to Specify

1. Heat load and allowed temperature rise, or required air changes.
2. Design ambient temperature and altitude.
3. Building dimensions, roof and wall arrangement, and opening sizes.
4. Number of fans and redundancy requirement.
5. Control approach.
6. Noise limits.
7. Any dust, corrosion, or hazardous-area conditions.

Get a Fan Selection for Your Factory

Send your building dimensions, heat load, and site conditions, and we’ll size the fans and confirm the arrangement. Contact us for a free quote.

Frequently Asked Questions