To create a truly efficient ventilation system, a lot of tasks must be solved, one of which is a competent air distribution. Without focusing on this aspect in the design of ventilation and air conditioning systems, you can eventually get increased noise, drafts, the presence of stagnant zones, even in ventilation systems with high performance characteristics. The most important device affecting the correct distribution of air flow through the room is the air distributor. Depending on the installation and design features, these devices are called grids or diffusers.
Classification of air distributors
All air distributors are classified:
- By appointment. They can be supply, exhaust and overflow.
- By the degree of exposure to air masses. These devices can be agitating and displacing.
- On installation. The air distributors can be used for indoor or outdoor installation.
Internal diffusers are divided into ceiling, floor or wall.
Supply, in turn, are classified according to the shape of the outgoing air jet, which can be:
- Vertical compact air jets.
- Conical jets.
- Full and incomplete fan streams of air.
In this publication we will consider the most common diffusers: ceiling, slit, nozzle and low-speed.
Requirements for modern air distributors
For many, the word ventilation is synonymous with constant background noise. The consequences of this chronic fatigue, irritability and headache. Proceeding from this, the air distributor should be quiet.
In addition, it is not very pleasant to be in the room, if you constantly feel the cooled air flows. This is not only unpleasant, but can lead to illness, so the second requirement: the diffuser should not create drafts.
Various circumstances often require a change in the situation. You can change furniture or rearrange the office equipment. It's also easy to order a new original room design, but it's difficult to change the air distributors, which were calculated at the design stage. From this "the third requirement" follows: the air distributor should be barely noticeable, or as the designers say "is dissolved in the interior of the room".
Slotted air flow distributors
Slot diffusers are ventilation equipment designed to supply fresh and exhaust air from premises with high requirements to the design and quality of the air mixture. For optimum air distribution, ceiling height when using such equipment is limited to 4 meters.
The construction of the device consists of an aluminum body with horizontal slotted holes, the number of which, depending on the model, can vary from 1 to 6. A diffuser is mounted inside the cylindrical roller to monitor the direction of the air flow. As a rule, such diffusers are equipped with a static pressure chamber to control air flow.
The height of the gap can also be different: from 8 to 25 mm. The length of the device is not regulated and can be from 2 cm to 3 m, so they can be mounted in continuous lines of almost any shape. Linear slot diffusers are characterized by good aerodynamic properties, attractive design and a high degree of induction, thanks to which there is a rapid heating of the supply air flow. Such devices are installed in suspended ceilings and wall structures. The installation height must not be less than 2.6 m.
Ceiling diffusers
Ceiling diffusers can be supply or exhaust. These devices are different: the design, shape, size, performance, the formation of an air jet. In addition, the diffusers differ in their aerodynamic characteristics, in the distribution of the air flow, and in the material from which they are made.
- The design of these devices consists of a decorative grill behind which the impeller is attached (if the diffuser is an inlet) and a statistical pressure chamber. In the adjustable "plafonds" there are elements that direct the air flow.
- The form. Most ceiling diffusers have a round or square shape. But do not forget that the slotted air distributors are also considered ceiling, and they have a rectangular shape.
- Dimensions of round air distributors range from 10 cm to 60 cm. For square ones, from 15x15 cm to 90x90 cm.
- Method of installation. Installed in a false ceiling, cut into a panel of plasterboard or mounted in a stretch ceiling with additional rings.
- Ceiling diffusers form fan, turbulent, vortex, conical and nozzle air flows.
- Air distribution in these devices can vary on different sides (in square supply) or be circular.
Most often these devices are used in residential and office buildings, shops, as well as restaurants and places of public catering.
Nozzle diffusers
Air nozzle nozzles are used to supply clean air streams for long distances. To increase the range of air flow, nozzle valves are combined into blocks that can have different shapes and be made of different materials.
According to the design, nozzle diffusers can have movable and stationary nozzles, which have an optimal profile, which provides low aerodynamic resistance and low noise level. This type of air flow distributor is mounted on the surface using glue, screws or rivets, and some models can be installed directly into the circular air duct.
These devices are made of anodized aluminum, which allows them to be used for distribution of heated air and air masses of high humidity. Such adaptations are applied in the ventilation systems of industrial enterprises, commercial buildings, parking lots, etc.
Low-speed diffusers
Low-speed air distributors operate on the principle of displacing polluted air from the serviced premises. They are designed to supply clean air directly to the service area, with a low airflow rate and a small temperature difference between the inflow and the air mixture of the room. These devices differ in the manner of installation, shape, size and design.
There are several types of low-speed air distributors:
- The wall.
- The floor.
- Built-in.
Floor and wall low-speed diffusers are designed for small, medium and large air flow rates. Most often they are installed under seats in cinemas, large concert and educational facilities, shops, museums, sports facilities. Built-in, floor-standing devices can be mounted in stairways and stairs.
Low-speed devices are made of powder coated metal or anodized aluminum. The device consists of an external and internal shell and a body with a supply branch pipe. Some distributor models can be equipped with rotary nozzles to regulate the direction of the air flow.
Calculation of diffusers
Calculation of air distributors is quite complicated, but necessary process, which consists in choosing a device that meets the following requirements:
- The outlet air flow rate should be optimal.
- The temperature difference of the air flow at the entrance to the working area should be minimal.
Algorithm of calculation
- Initially, a calculation is made of the supply of air mixture for placing certain dimensions and architectural forms, with a given output L p (m3 / h) and a drop in supply air temperatures Δt 0 (° C); the mounting height of the device h (m) and other air distribution characteristics.
- The speed and the amount of air supplied from one diffuser are determined by the permissible parameters of the airspeed velocity Ud (m / s) and the temperature difference between the supply air and the air at the entrance to the working zone.
- After, the necessary location and number of devices necessary for optimal air distribution in a particular room is calculated.
Tip:
If you do not have special engineering knowledge, then for the correct calculation of air distributors, contact organizations specializing in this type of activity. If you decide to do the calculations on your own, then use specialized software.
, page 4 
(19)
According to the manufacturer's catalog, we accept for installation three external grilles AVR with protective mesh 750х1000, white color - RAL9016: ARN + C 750 x 1000, with a living area of 0.358 m 2. The total live cross section of three grids is 1.074 m 2.
Air velocity in the total live cross section of three gratings
(20)
Aerodynamic resistance at passage of air through lattices
(21)
where is the coefficient of local resistance of the grating, is taken according to the manufacturer's data, = 2.36
The dimensions of the live section of the air intake shaft are taken on the basis of the requirements (Appendix 19) to the maximum permissible speed of air movement in it.
Let's find the area of the live section of the shaft, based on the permissible velocity of air movement in it and the geometric dimensions of the grids. The value is taken in the same way as (19).
We take the size of the mine (by internal measurement) 1,0х1,2 m. Area of the live section of the mine
Air velocity in the live section of the shaft
Dynamic pressure when moving air through the shaft
CCM lattices
The type of the air intake shaft is presented in the graphic part of the project.
3.2. Selection of air valve HLC
The calculation procedure for HLC is similar to the calculation of the air intake grate.
The approximate area of the live section is taken in the same way as (18) 
According to the technical specifications from the manufacturer's site we accept the valve KVU 1600h1000, with a living area of 1.48 m 2.
Adopted in the same way as the resistance of the throttle valve with the angle of rotation of the blades 15⁰.
3.3. Aerodynamic calculation of unbranched air ducts
The task of aerodynamic calculation of an unbranched air duct is to detect the angle of installation of the adjustable device in each inlet opening, which ensures the flow of a given air flow into the room. This determines: the pressure loss in the air distributor and the maximum aerodynamic resistance of the air duct and the ventilation network as a whole.
When installing a multi-leaf flow regulator on the branch (grate ADN-K), outside the main duct, the influence of the position of the flow regulator blades on the pressure losses in the transit flow is practically eliminated. For the calculation of air ducts, there are aerodynamic characteristics that take into account the position (angle of installation) of the regulator blades: flow, direction, and shape of the jet.
The air duct is divided into separate sections with a constant air flow along the length. The numbering of sections begins at the end of the duct. Since the flow regulator is not installed in the end grate (a grating is installed ADN-K 400x800), the pressure before the second (or each subsequent) lattice is known. With this in mind, the estimated pressure losses are determined to be found by the aerodynamic characteristic of the angle of rotation (position) of the flow controller.
3.3.1. Method of calculation of unbranched air duct P1
Initial data
- 22980 m 3 / h;
- 3830 m 3 / h;
- 3.58 m / s;
The distance between the grids is 2.93 m;
The angle of incline of the incomplete fan jet is 27⁰;
We determine the dimensions of the initial section of the air duct of the end section 1-2 (see graphical part), trying to keep its constant height.
Page 4
The authors studied the conditions for the formation of a gas cushion under a sectioning grid and the effect of the live cross section of redistribution gratings on the uniformity of fluidization.
To reduce the loss with a failure with a large amount of fines in the peat, a reduction in the live cross section of the grating and a corresponding increase in the blast pressure are required.
Consideration of the data of Table. 5 shows that the depth of destruction is practically independent of the live cross-section of the lattice, but the degree of hydrogen saturation increases in this case, which allows increasing the yield of diesel fuel with a given iodine number.
The sum of the areas of the holes in the grate for air passage to the fuel layer is called the live cross-section of the grid. In the grate, designed for burning large-lump fuel, the living cross section is 25 - 30% of the lattice area.
The ratio of the total area of the air gaps or holes in the lattice to its other area is called the live cross section of the lattice. Distinguish lattices with small (5 - 15%) and large (15 - 40%) living section. The required value of the live cross section is determined by the properties of the burned fuel.
With the decrease in the number of holes in the lattice from 223 to 61 for the same area of the live section of the lattice, the height of the cushion remains practically constant. It also does not change with an increase in the height of the fixed bed on the redistribution grating from 270 to 350 mm.
Losses with a failure Q p are related to the grate gratings and depend mainly on the design and the live cross section of the grating.
The gas velocity in the section of the apparatus is usually taken within the range of 1 to 3 m / s, and the living cross-section of the grid is chosen so that the gas velocity in the holes is 6-13 m / s. A decrease in speed leads to a violation of the integrity of the foam layer, an increase in speed above these limits sharply increases the losses due to splashes.
The diameter of the hole of the upper grate is 3 mm, the distance between the holes and their number are determined from the calculation of the provision of a live section of the grating within 5-7% of its total area. Thus, the air velocity in the apertures of the array is about.
The product is installed at such an altitude above the grid so that the rate of leakage of air is no more than the speed of its movement in the live section of the lattice. Supply air is supplied from above evenly over the entire area of the ceiling of the chamber. It is necessary to use a false ceiling equipped with filter cassettes.
The ratio of the area of all gaps R in the grate, through which air enters the layer, is called the entire cross-section of the lattice, and is usually expressed as a percentage. The necessary size of the live section of the grate depends on the type of fuel burned and the size of the pieces. So, when burning lumpy peat and firewood, beams are used.