Alexey Antipov – Installation, starting and adjustment of ventilation and air conditioning systems A Guide (страница 3)
Questions for chapter 2
Chapter III. Equipment of air ventilation systems
As indicated above, the required state of the air environment in the premises is maintained by general exchange ventilation methods by pumping clean ventilation air into the premises with the necessary temperature-humidity parameters and removal of air that does not meet regulatory requirements. In accordance with this, general exchange ventilation systems should include equipment and devices for intake of outdoor air, its processing, transportation and distribution around the premises, as well as for the removal of exhaust air.
3.1. Air intake and air discharge devices
These include air intake and air discharge devices in mechanical ventilation systems, which are made in the form of holes in the fences of buildings, attached or freestanding shafts. When air is taken from above, the air intake devices are placed in the attic or upper floor of the building, and the channels are removed above the roof in the form of shafts.
For aeration, air intake and ejection devices are made in the form of rotating transoms, opening lanterns, windows or other overlapping apertures in the fences of buildings.
The location and design of the air intake devices are selected taking into account the cleanliness of the intake air and the satisfaction of architectural requirements. Thus, air intake devices should not be located near sources of air pollution (emissions of polluted air or gases, chimneys, kitchens, unpaved roads, etc.).
Air intake apertures should be located at a height of at least 2 m from the ground surface and closed with louvered grilles (in the green zone – at a height of at least 1 m).
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).
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.
3.2. Ventilation chambers
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.
3.3. Fans
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).
Currently, modifications of radial fans are used – direct-flow, disk, vortex, tornado (Fig.4).
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).
3.4. Supply installations
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.
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:
by type of heater (with an electric heater or with a water heater), by air consumption (up to 200–3000 m3/h – mini-supply installations, more than 3000 m3/h – central supply installations), by design (for vertical installation, for horizontal mounting, universal)
The automatic control system of the supply unit allows you to gradually or smoothly adjust the thermal power of the electric heater. If a water heater is used in the supply unit, then the automation has a more complex design, since in this case it is necessary to provide additional protection against freezing of the heater in winter.
In ventilation systems with supply installations, the following additional elements can be used: air intake grilles, a valve for supply air (with an electric drive or manual drive), mufflers, devices for adjusting air flow in rooms, air distribution devices (diffusers, grilles, plafonds).
Structurally, the chambers are a monoblock structure and can be equipped with automatic control of various levels of complexity from simple functions such as START, STOP, OPEN-CLOSE VALVE, to programmable control of parameters (room temperature, performance, temperature inside the chamber, etc.) along a continuous circuit.
The supply chamber includes the following elements:
A double-sided suction fan, which is attached to the frame traverses through rubber vibration isolators. The frame is made of aluminum profiles and connecting corners.
Insulated panels made of galvanized steel on the outside and inside. Foam insulation is laid in the panel as a heater and sound insulator. For tightness, a self-adhesive sealer is laid between the panels and the frame. On one side of the camera, for ease of maintenance, the panels are made quick-detachable, for which they are equipped with rotary clamps.
Heater (water heater or electric heating elements).
Soft insert made of rubberized fabric with flanges on both sides. The flanges are made of a galvanized tire connected by corners.