Ventilation is one of the most common and demanded processes at many facilities - domestic, industrial, public. In addition to devices for replacing indoor air, the same group may include forced convection systems of various heat exchangers, cooling towers, dryers, etc. Also, a ventilation unit can be part of a climate control complex, each of the blocks of which (heater, cooler, dehumidifier, humidifier, ionizer, ozonator, dust collector, etc.) requires air circulation. Fan power ranges from tens of watts (in local hoods above a soldering station or gas stove in a small kitchen) to several kilowatts - in production shops and storage facilities, at large medical, educational, cultural, commercial, and sports facilities. In the direction there is exhaust, supply and combined supply and exhaust ventilation - both switchable and with two independent air ducts and at least two electric motors to carry out both processes simultaneously. Structurally, fans can be located not only in the common outlet for all channels to the outside atmosphere (they are mandatory there), but also directly behind the air grille of each room, as well as along long channels (such a “pumping halfway” is hydrodynamically and mechanically more profitable than creating too much pressure and/or vacuum at the ends of the channel).

Fan motors

Depending on the above location, the following requirements apply to the fan motors:

 •Those on the ceilings of each room or in the local exhaust above the workplace, as a rule, do not require high power, but they should have a minimum noise level. It is created mainly by the impeller, and it already determines the required torque and engine speed. In this case, electronic controllers can be used to reduce the rotation speed (and in general, in such a location, the fan is often equipped with a remote control). When using centrifugal impellers "squirrel wheel" very suitable for this application, the motor can have a double-sided shaft.

• In-duct fans are usually axial in order to avoid kinking of the air flow at a right angle, which increases the hydrodynamic resistance and complicates the design of the duct. For them, noise and efficiency are not so critical, but the longest possible service life without repair and maintenance is desirable (“eternal” bearings, non-evaporating grease, etc.), since at many facilities access to the channel is quite difficult and involves working at height, disassembly / assembly of metal structures, often with thermal insulation.

• Common for several channels (as a rule, external) fans are characterized, first of all, by high power and, accordingly, three-phase power supply. They account for the bulk of the total energy consumption of the entire system. Therefore, the main requirements for them are the greatest resistance to adverse climatic influences (up to icing directly on structural elements, including moving parts) and efficiency, efficiency. According to hydrodynamic calculations for a capacity of tens of thousands of cubic meters per hour, the optimal diameter of the axial impeller often turns out to be very large, and the required speed is relatively small, significantly (not by a slip factor) lower than synchronous with a mains frequency of 50 Hz.

On the other hand, the use of pulse-width controllers, frequency converters and stepper motors at such powers is not rational. In practice, as a rule, one of three solutions is used:

• multi-pole electrical machines (not 3, but 6, 12, etc. windings in the stator), which create a rotating magnetic field with a multiple of the lower frequency;
  
• mechanical gearboxes (mainly belt ones), which certainly reduce reliability, but in some cases are more cost-effective;
  
• centrifugal fans (radial impeller even with high performance has a smaller optimal size and high speed). In any location, there can be no talk of collector or phase rotor motors with a brush mechanism. Ventilation systems use exclusively asynchronous machines with a squirrel-cage rotor or (rarely) stepper motors with an appropriate electronic unit.