To protect the premises from outside cold air during standby of the ventilation through ventilation ducts, air intake and air discharge devices are equipped with multi-leaf insulated valves with manual or mechanical drive. In the latter case, the valve is blocked along with the fan closing the apertures. At low temperature of the outside air, the valves are supplied with an electric heating system in order to protect their flaps from freezing. Electric heating is turned on for 10–15 minutes before starting the fan (Fig.2).

Fig.2. Electric air valve

The outer walls of exhaust ducts and shafts are insulated to avoid condensation and ice of water vapor from the extracted moist air. The air velocity in the supply channels and shafts is supported between 2 and 5 m/s, in the channels and shafts of exhaust devices: 4–8 m/s, but not less than 0.5 m/s, including for natural ventilation.

The main ventilation equipment of supply and exhaust installations, as a rule, is installed in special rooms called ventilation chambers. Supply chambers in public, administrative, residential buildings are usually designed on the ground floor or in the technical underground. Exhaust chambers should be located in the upper part of the building. In multi-storey buildings with a large number of ventilation systems, ventilation chambers are arranged in technical floors.

In buildings with a large number of ventilation systems (more than 5), a room for equipment repair is provided. The operation of ventilation systems is controlled from special remote controls using automation and remote control devices.

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).

The supply units (Fig.5) filter fresh air, if necessary, heat it (in the cold season) and supply it to the duct system for subsequent distribution around the premises.

Fig.5. The supply unit

Inlet ventilation units consist of a housing in which are mounted: filter, water or electric heater, fan, automation system, sound insulation material,

Conditionally, Inlet installations can be divided into several types: