Читать книгу Installation, starting and adjustment of ventilation and air conditioning systems A Guide - - Страница 9

The fan is a mechanical device designed to move air through the ducts of ventilation systems, as well as to carry out direct air supply to the room or suction from the room, and creating the pressure drop necessary for this (at the inlet and outlet fan). According to the design and principle of operation, fans are divided into:), radial (centrifugal), diametral (tangential) (Fig.3).

Fig.3.Fan designs

Currently, modifications of radial fans are used – direct-flow, disk, vortex, tornado (Fig.4).

Fig.4. Modifications of radial fans

Fans are evaluated by specific speed, which relates the rotational speed and pressure.

We divide fans into three groups, depending on the magnitude of the total air pressure they create: low pressure (up to 1 kPa), the maximum circumferential speed of such wheels does not exceed 50 m/s; medium pressure (up to 3 kPa), the maximum circumferential speed reaches 80 m/s; high pressure (up to 12 kPa), the circumferential speed of the impellers is more than 80 m/s.

The separation of fans by pressure is conditional, since any high-pressure fan with a decrease in the speed of rotation can be used as a medium-pressure fan.

In the direction of rotation of the impeller (when viewed from the suction side), the fans can be of right rotation (the wheel rotates clockwise) and left rotation (the wheel rotates counterclockwise).

Depending on the composition of the transported medium and operating conditions, fans are divided into: conventional – for air (gases) with a temperature of up to 80 °C, corrosion-resistant – for corrosive environments, heat-resistant – for air with a temperature above 80 °C, explosion-proof – for explosive environments, dust-proof – for dusty air (solid impurities in the amount of more than 100 mg/m³). According to the method of connecting the fan impeller and the electric motor, the fans can be: with a direct connection, with a connection on an elastic coupling, with a V-belt transmission, with an adjustable stepless transmission.

At the place of installation, fans are divided into: conventional, mounted on a special support (frame, foundation, etc.), ducted, installed directly in the duct, roof, placed on the roof.

The main characteristics of the fans are the following parameters: air consumption (m³/h), total pressure (Pa), rotation speed – rotations per minute (rpm), power consumption spent on the fan drive (kW), EFFICIENCY – the efficiency of the fan, taking into account mechanical power losses due to various types of friction in the fan working bodies, volume losses as a result of leaks through seals and aerodynamic losses in the flow part of the fan, the sound pressure level (dB).