Centrifugal Blowers for Cooling Air: Motors, Electrical Equipment, Ovens and Kilns

Cooling is one of the most common jobs for a centrifugal blower, and one of the most overlooked. Blowers force air through motors and electrical equipment, over parts leaving ovens and kilns, across heat exchangers and process lines, and through quench zones. The duty looks simple, but it turns on three details that decide whether the cooling works: how much heat has to be carried off, how much resistance the air path adds, and whether the cooling air itself is clean and cool enough.

Where Cooling Blowers Are Used

• Forced ventilation of motors, including large AC and DC motors and traction motors, where the motor’s own fan is not enough.
• Cooling electrical equipment, such as drives, transformers, panels, and rectifiers.
• Cooling parts leaving ovens and kilns, including quench and cooling zones on conveyor lines.
• Process cooling, such as blowers on glass-tempering ovens and on skids that cool exhaust gases ahead of catalytic or filter equipment, often in a duty and standby pair.
• Heat-exchanger and cooler air supply, where a blower forces air through a compact air path.

The high-pressure class matters here. A cooling path of dense finned surfaces or tightly packed parts can add several hundred pascals, which is beyond what a low-pressure fan comfortably handles.

Sizing Cooling Air from Heat Load

Air removes heat in proportion to its mass flow and temperature rise: airflow equals heat load divided by air density times specific heat times the temperature rise.

Example 1: Motor forced ventilation. A motor has 40 kW of losses to remove, and the cooling air may warm by 20 K.

Airflow = 40 ÷ (1.2 × 1.006 × 20) = 1.66 m³/s, or about 5,970 m³/h.

Example 2: Cooling parts from an oven. A conveyor line delivers 2,000 kg/h of steel parts at 300 °C and they must leave at 100 °C. Steel’s specific heat is about 0.5 kJ/kg·K.

Heat to remove = 2,000 × 0.5 × 200 = 200,000 kJ/h, about 55.6 kW.

If the cooling air can rise from 30 to 110 °C (80 K), the air mass flow is 55.6 ÷ (1.006 × 80) = 0.69 kg/s. At 1.2 kg/m³ that is about 0.58 m³/s, or 2,070 m³/h. A tighter air-temperature limit, or a shorter cooling zone, needs more air.

Always check the assumptions: real parts do not give up heat evenly, and radiation and conduction also carry heat, so treat calculated airflow as a starting point and confirm it against the process.

Cool Enough, Clean Enough

The cooling air is only as good as the air taken in. Hot inlet air reduces cooling capacity, and dust or oil mist coats motor windings and heat-exchange surfaces, which cuts cooling further and shortens equipment life. Take air from a clean, cool location, filter it where the environment demands it, and allow for filter resistance in the blower selection. Filters load, so size for the fouled condition. See dust collection system design for how filter loading moves the operating point.

High-Temperature Cooling Duty

Some cooling duties handle hot air. A blower pulling hot air off an oven discharge zone, or recirculating warm process air, sees temperature that a standard blower is not built for. Density falls with temperature, so the same blower moves the same volume but develops less pressure, and materials, bearings, and motor position all need attention. Our blowers for ovens (to 500 °C), kilns (to 650 °C), and furnaces (to 800 °C) are covered under furnaces, kilns and ovens and high-temperature centrifugal blowers.

Duty and Standby Arrangements

Where cooling is critical, such as process cooling on a skid, two identical blowers are commonly mounted as a pair, so that the process keeps running if one is out of service. Plan the changeover: isolation dampers or backdraught shutters so the idle blower does not short-circuit the flow, and a controller that starts the standby on failure. Exercise the standby regularly, because an untested standby is an assumption, not a safeguard.

Control

Cooling loads change with production and weather. A damper wastes energy, while speed control follows the load and saves a lot, since power varies with the cube of speed. On motor cooling in particular, temperature-controlled speed keeps the motor cool without running the blower flat out. See flow control for blowers.

Noise

Cooling blowers often run continuously near workers. Larger wheels at lower speed reduce noise and energy, and inlet and outlet silencers help where needed, at the cost of added resistance. See blower noise and silencers.

Where Our Range Fits

NextAir Systems manufactures centrifugal blowers up to 800 HP (about 597 kW) and up to 500 mm WC (about 4.9 kPa) static pressure, with backward-curved and forward-curved wheels, single-inlet and double-inlet designs, and high-temperature blowers for ovens up to 500 °C, kilns up to 650 °C, and furnaces up to 800 °C. That covers forced ventilation of motors and electrical equipment, cooling zones on ovens and kilns, and process cooling skids. Airflow and drive arrangement are confirmed for each selection.

What to Specify

1. Heat load to remove, and the allowed air temperature rise.
2. Cooling air source: temperature, cleanliness, and altitude.
3. Resistance of the air path, at clean and fouled conditions.
4. Whether the air handled is hot, and its temperature.
5. Duty and standby requirement.
6. Control approach and noise limits.
7. Drive arrangement and motor position.

Get a Blower Selection for Your Cooling Duty

Send your heat load, air conditions, and resistance, and we’ll size the blower and confirm the arrangement. Contact us for a free quote.

Frequently Asked Questions