Installation, starting and adjustment of ventilation and air conditioning systems A Guide. Alexey Vasilyevich Antipov
used in air heating systems.
General exchange exhaust ventilation systems usually remove air from the upper, less often from the middle zone of buildings. Before removal, the air in general exchange exhaust systems usually does not undergo cleaning. General exchange exhaust systems can be channelless if the air is removed by roof fans that are installed on the floors, and ducted. In ducted exhaust ventilation systems, air is sucked into air intake apertures or grilles, it is fed through the ducts to the fan and, after passing the exhaust shaft, enters the atmosphere. To protect the exhaust shaft from atmospheric precipitation, an umbrella is installed above it, and the air ducts are blocked with a flap when the fan is not working.
Local exhaust ventilation systems are designed to take harmful emissions from the places of their formation with the help of shelters or local suction, transport polluted air, clean it in filters or dust collectors and release it into the atmosphere. Local suction and shelters have the most diverse design and shape: these are umbrellas, fume hoods, full shelters, side and ring suction at baths and shaft furnaces, suction panels, casings, etc.
Many harmful substances released during technological processes actively affect local suction pipes, air ducts, fans, filters, causing their severe corrosion, in addition, they can be explosive and fire-hazardous. In these cases, air ducts and other devices in contact with an aggressive environment are made of materials that are not subject to intense corrosion by the moving medium (corrosion-resistant alloy steels, aluminum, titanium. metal, vinyl, polyethylene, etc.), or apply special coatings of steel ducts with acid- and alkali-resistant dyes, enamels and varnishes. In such systems, fans and other equipment are installed in an intrinsically safe protected design.
Questions for chapter 2
1. Name the main parameters of the air environment.
2. What is the main purpose of the ventilation system?
3. In which cases the use of natural ventilation systems is justified.
4. What is the advantage of mechanical ventilation systems?
5. What is the name of the process of heat recovery of the removed air, what are its technical and economic advantages?
6. What material is used to produce ventilation ducts most often?
7. What, in your opinion, is affected by the thickness of the metal in the production of air ducts?
8. In which cases air showering is used?
9. Name the main processes of air treatment in the supply ventilation system.
10. In which cases a special design of air ducts and ventilation equipment is used?
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).
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.
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).
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