Installation, starting and adjustment of ventilation and air conditioning systems A Guide. Alexey Vasilyevich Antipov
100, 200 and 400 mm for plate silencers. To prevent the entrainment of the fiber with the air flow, the sound-absorbing layer is protected with fiberglass and metal mesh or perforated sheets with a perforation of at least 20%.
The plate silencer is a box made of a thin metal sheet. A tubular silencer is made in the form of two round or rectangular pipes inserted into one another. Tubular silencers are used on air ducts with a diameter of up to 500 mm.
Currently, active silencers have been developed that carry out broadband active noise suppression (especially effective at low frequencies). Noise neutralization is carried out by introducing antiphase noise.
3.10. Check valves
Check valves are used to allow air to pass in one direction and prevent it from moving in the opposite direction. They are available in two of the simplest modifications: the "butterfly" type and the "inertial lattice" type (Fig. 15).
Fig. 15. Check valves
The butterfly valve is made of galvanized steel, has two spring-loaded lobes, and can be installed in any position.
A petal check valve of the "inertial grid" type with light plastic blinds inserted into a galvanized steel box can only be installed on horizontal air ducts, under the action of the air flow in the permitted direction, the petals rise, in all other cases they are lowered.
One of the main characteristics of check valves is the maximum possible air velocity.
Check valves are used to prevent air flow: when several supply units are operating on the same network; when installing a backup supply or exhaust fan; when connecting several exhaust systems to one exhaust shaft.
They are also installed to prevent backflow of air when exhaust air is released onto the facade or in front of roof fans.
3.11. Air curtains
Air curtains (without air heating) they are arranged between rooms with the same or similar thermal conditions. They are used to prevent access of air from some rooms in which harmful vapors or gases are released to others.
The principle of operation of air-heat curtains is as follows: air is taken from the upper area of the lobby, heated in heaters up to 50 °C, fed by a fan into the air distribution chamber and then released through the uniform distribution duct at the door. The air is discharged through cracks or holes in the duct. The resulting jet creates a vertical air curtain. The air can be released from the bottom at the door or from the side to the desired height. Air is supplied to the air curtain from the supply ventilation without additional heating.
According to the principle and effect of the curtain, there can be gate and mixing types. In the first case, the curtain maximally or completely prevents (blocks) air access to the enclosed space; the air velocity from the installation to create such curtains should be high (up to 25 m/s). Such curtains are arranged at low outdoor temperature and frequent opening of doors. In mixing type installations, the rushing cold air is mixed with the heated air of the heat curtain. As a result, warm air enters the room through the door and the curtain, which does not create a feeling of cold blowing.
Questions to Chapter 3
1. What is the reason for the location of outdoor air intake devices in ventilation systems?
2. Name the main types of fans by type and design.
3. What is the reason for the mandatory installation of the filter in front of the heat exchange equipment (heaters and coolers)?
4. Give an example in which cases it is advantageous to use electric air heaters.
5. What are the advantages of using water heaters?
6. Why the range of air velocity in heat exchange equipment is strictly limited?
7. What is the fundamental difference between water (water-glycol) and freon air coolers?
8. What measures are envisaged to reduce noise in ventilation systems?
9. Which device is used to prevent air flow when the fan is turned off?
10. In which places of the building are provided air heat curtains with heated air?
Chapter IV. Ducts and Fittings
4.1 Air ducts of ventilation systems
According to the type of section, the ducts are divided into round, square or rectangular. Circular air ducts are much stronger than rectangular ones, and their manufacture is less laborious.
However, circular air ducts often do not fit into the interior of public and civil buildings. In addition, in a confined space (under false ceilings, etc.), as a rule, only rectangular air ducts can be used.
According to the manufacturing method, the air ducts can be folded or welded. (Fig. 16.).
The first ones are connected with seam seams. The thickness of the metal for such ducts should not exceed 2.0 mm (if aluminum is used) and 1.0 mm (if corrosion-resistant steel is used).
The welded air ducts are connected by an overlap weld. The thickness of the metal with this type of connection is allowed in the range of 1.2 -3.0 mm.
Fig.16. Types of seam and welded joints of metal ducts:
1 – on a simple recumbent seam; 2 – on a double–cut seam; 3 – on an angular seam; 4 – on a transverse seam; 5 – on a seam with a latch; 6 – with a connecting bar; 7 – on zigs; 8 – butt; 9 – butt–to–butt with flanging; 10 – lap; 11 – corner
This type of duct is classified as dense.
All the various ventilation systems are assembled from only four standard parts.
The first is pipes with a length of 2000 mm or 2500 mm, depending on the metal used.
The second is from water, usually consisting of two or three segments and two glasses with an average radius of curvature equal to the diameter (Fig.17). They are used for general exchange ventilation systems.
Fig. 17. Outlet for air ducts
The third is rectangular bends, which are characterized by only two neck radii: 150 mm (for bends with a side less than 1000 mm) and 300 mm (with a larger size).
The fourth is the tees (branch nodes) of circular cross section. They exist in 3 versions:
– normalized, they are characterized by low coefficients of local resistance, but are laborious to manufacture;
– direct embedding;
– rectangular tees, they are usually equipped with one-sided unified transitions, which allows you to establish a constant ratio of the duct route from the wall along which it is laid.
According to the material used for the manufacture of air ducts, they are divided into several groups:
1. Folded air ducts made of thin-sheet galvanized steel, up to 1 mm thick (without painting).
2. Folding air ducts made of thin-sheet black steel, up to 1 mm thick (with subsequent painting inside and outside).
3. Welded air ducts made of sheet steel, 1.2- 3.0 mm thick (with subsequent painting with primer).
4. Seam and welded air ducts made of corrosion–resistant steel, thickness from 0.5 mm to 3 mm (usually grades X18N9T) – without painting.
5. Folding air ducts made of titanium (ρ = 4,500 kg/m3), which have the highest corrosion resistance when moving an aggressive medium.
6. Folding ducts made of metal plastic, clad on one or both sides with PVC or PVC film. With a one-sided coating, the film must be inside the duct, in contact with an aggressive environment.
The connection of individual parts of round air ducts to each other is performed by flanging bandages (with a diameter of up to 800 mm) or on flanges made of