Calculation of the length of the ducts online calculator. Calculation of the ventilation system and its individual elements: area, pipe diameters, parameters of heaters and diffusers. Aerodynamic calculation of air ducts - an algorithm of actions
Ventilation system capacity calculation:
Duct cross-section: Round Rectangular
Diameter: mm
Length: mm
Width: mm
Duct material: Brick Steel Ventilation block Slag gypsum
Room: Kitchen with gas. stove Kitchen with electric stove Bathroom Toilet Combined bathroom
Height H: m
Clean air, normal humidity, optimal temperature - all this is supported by the ventilation system. Therefore, it is very important to monitor its correct operation.
Air is sucked into the ventilation mine due to the difference in air pressure inside and outside the building. And on the path of air movement, there are some kind of obstacles (turns, constrictions, gratings, friction on the ventilation duct), which prevent the passage of air through the ventilation duct itself. And if the difference in air pressure in the room and outside is less than the pressure loss from these barriers, then normal ventilation will not be observed.
It is considered optimally when the pressure difference across 10-15% more than the pressure loss.
Operating procedure:
1. Select the cross-section of the duct / duct (rectangular or round)
2. Set the geometric characteristics of the duct / duct
3. Select the duct / duct material (brick, steel, ventilation block and slag gypsum)
4. Select the room in which you are checking ventilation
5. Set the height H shown in the figure (distance from the ventilation grill to the top of the duct / duct)
6. Click the "Read" button
The result will be summarized below and will show whether your ventilation system is working properly.
For reference:
- the aerodynamic calculation of the ventilation system can be completely carried out in
The calculation of the area of \u200b\u200bair ducts and fittings is carried out before the installation of ventilation communications. The efficiency of the entire ventilation system depends on the correctness of their implementation. In practice, experienced craftsmen use two main methods of measurement: using a formula and using an online calculator. Calculation of the area of \u200b\u200bair ducts and fittings is a laborious and responsible business. The editors of the online magazine Homius.ru prepared a review on this topic specially for their readers, using all modern capabilities and knowledge experienced craftsmen... In this article you will find helpful advice for calculating data, as well as a convenient online calculator.
There may be an error in calculating areas using formulas
1 Why do you need to calculate the area of \u200b\u200bthe duct and fittings
2 What data are needed to calculate the parameters of the duct
4 Calculation of the area of \u200b\u200bthe fittings of the duct
4.1 What programs exist for finding the parameters of the fittings of the duct
5 Calculation square meters (cross-sectional area) of the duct
5.1 Calculator for calculating the required diameter of the duct
6 Calculation of the air velocity in the duct
7 Calculation of the resistance of the duct network
8 Pressure loss in straight sections
9 Pressure loss at local resistances
10 Calculation of materials for duct and fittings
11 Calculation of the power of the heater in the network
12 Conclusion
Why do you need to calculate the area of \u200b\u200bthe duct and fittings
The ventilation complex consists of different elements. To select all the parts correctly, you need to calculate their area, which is affected by the following parameters:
volume and speed of air masses;
tightness of connections;
noise during operation of the ventilation system;
electricity consumption.
It is important! Thanks to correctly performed calculations, you can determine the optimal number of fittings for organizing a ventilation system for a particular room. This will prevent unnecessary spending on the purchase of items that will not fit later.
Various designs and materials of the duct
What data is needed to calculate the parameters of the duct
To calculate the duct, two indicators should first be determined:
the norms established for the supply of fresh flows per 1 m² of the room per hour or the frequency of air exchange are taken from regulatory sources. Based on these data, knowing the volume of the room, you can easily determine the value of the ventilation system performance. Accordingly, the volume of air is calculated by multiplying the multiplicity by the volume of the room;
according to sanitary standards. In this case, 60 m³ should be taken for each person who is permanently in the room, and 20 m³ for a temporary person.
Air purification efficiency in production depends on correct calculations
The main task of the ventilation system is to improve the microclimate in the room and purify the air masses by removing the exhaust air outside. For high-quality performance, first of all, it is necessary to perform design work and calculate the squaring of the air ducts. During planning, the shape of the pipes, the number of elements required to connect the sections, the size of the section will also be determined.
Calculations can be done in two ways:
independently using formulas;
using an online calculator.
The first case is the most difficult option, it is important to understand all the values \u200b\u200bthat are used in the calculations. For an online calculator, it is enough to enter the initial data, the software complex will independently perform all the calculations. One of the main parameters for designing an air duct and fittings is its design. You can choose rectangular or round pipes. The throughput of round products is much higher than that of rectangular ones.
Maximum precision in counting
the smallest amount of moving air masses;
air transport speed.
And also a few more parameters directly depend on the size of the section:
the larger the cross section, the less noise the flows move;
accordingly, the cost of electricity is reduced.
On the other hand, such a system will require more material, respectively, and the cost will be much higher. Thanks to the calculation formula, you can determine the actual cross-sectional area of \u200b\u200bthe duct:
S \u003d A × B / 100, where A and B are, respectively, the height and width of the section.
The rectangular duct is almost invisible above the furniture
An air duct with a circular cross-section is easy to install and has an excellent air flow capacity, since internal resistance is minimized. The choice of the form of communication follows from the personal preferences of consumers and the external design of the premises.
The actual area is calculated as follows:
S \u003d π × D² / 400, where:
π is a constant equal to 3.14;
D is the length of the element.
Special techniques have been developed, for example, SNiPs, in which the calculated actual areas are compared with the required indicators. With their help, you can easily pick up optimal size communications.
During the calculations, the following factors must be taken into account:
the cross-sectional area for straight sections of the duct should be calculated separately;
it is imperative to take into account the resistance that will be exerted on air masses during their transportation;
design should start from the central highway.
If the air flow rate exceeds the required values, and this directly affects the noise during operation, it is necessary to additionally purchase special silencers or increase the cross-section of the flange element of the central channel.
Product with a circular cross-section
Calculation of the area of \u200b\u200bthe fittings of the duct
It will be difficult for a person who is not connected with mathematical formulas to make the calculations correctly, an error in one indicator will affect the performance of the ventilation system, respectively, and the quality of air purification.
To simplify the process of calculating the surface area of \u200b\u200bthe duct, you can use an online calculator and special programs that perform all the algorithms, for this you only need to enter primary indicators.
Counting and selection program
What programs exist for finding the parameters of the fittings of the duct
To help engineering workers to eliminate errors associated with the human factor, as well as to speed up the process, special programs were created with which you can not only perform competent calculations, but also 3D modeling of the future structure.
Program
Short description
The program calculates the cross-sectional area, thrust, resistance on different segments.
GIDRV 3.093 The program will perform a new and checkout duct data.
Ducter 2.5 In the program, you can select the elements of the ventilation system, calculate the cross-sectional areas of the structure.
This complex was created on the basis of AutoCAD, has the most detailed library of elements and capabilities.
Software calculation and design of ventilation
Calculation of square meters (cross-sectional area) of the duct
By size ventilation pipe many factors affect: flow rate, pressure on the walls, air volume. If calculations are performed with an error, for example, to reduce the cross-section of the trunk network, the speed of air masses will increase, noise will appear, pressure and electricity consumption will increase.
Calculation of the cross-sectional area of \u200b\u200bthe duct is calculated using the following formula:
S \u003d L × κ / ω, where:
L - air consumption, m³ / h;
ω — speed of air flow, m / s;
κ - calculated coefficient equal to 2.778.
Calculator for calculating the required diameter of the duct
Payment options Spam protection Enter the code from the picture Send the result to me by mail
Calculation of the air velocity in the duct
When calculating the ventilation system, one of the main indicators is the frequency of air exchange. In other words, how much air mass is needed for comfortable ventilation of 1 m³ of a room in 1 hour. In this case, you can also refer to the development tables, but you should be aware that all indicators in them are rounded, therefore more accurate data are obtained by independent calculations. You can calculate the air exchange rate using the formula:
N \u003d V / W, where V is the amount of fresh air masses that enter the room in 60 minutes (m³ / hour);
W - room volume, m³.
To carry out aerodynamic calculations and calculate the speed of air movement, you can use the following formula:
ω \u003d L / 3600 × S, where L is the volume of air used for 1 hour;
S is the cross-sectional area of \u200b\u200bthe duct.
Air exchange rates for an apartment
Calculation of the resistance of the duct network
Air flows during transportation through pipes experience resistance, especially for pipes with a rectangular cross-section. To ensure normal system performance, you need to select a fan of the appropriate capacity. It is difficult to manually determine these parameters on your own; project team all calculations are performed using the program.
The resistance is not affected by the number of rooms that the ventilation system serves, the value of the coefficient depends on the structure and length of the communication.
Flow rate in direct relation to resistance
Pressure loss in straight sections
To calculate the performance of ventilation equipment, you can simply add up the required amount of air masses and select a model that suits these parameters. However, the product passport does not include the air duct network. Therefore, when it is connected to the system, the performance will drop significantly depending on the resistance parameter in the pipeline. To determine the pressure drop in the system, it is necessary to clarify its decrease on flat areas, pivoting and connecting elements. The pressure drop on flat areas is determined by the formula:
Р \u003d R × L + Еi × V2 × Y / 2, where R is the specific pressure loss caused by the frictional force during air movement, Pa / m;
L is the length of the straight section of the duct, m;
ω — speed of air movement, m / s; Y — density of air masses, kg / m³;
Еi - the sum of head losses on local resistances (bends, transitions, grids, etc.), the data can be taken from the reference book.
Straight ventilation section
Pressure loss on local resistances
To calculate the losses on the rotary elements, it is necessary first of all to determine all the areas that will interfere with the direct movement of flows. You can use the formula, but all data depending on the duct element and material of manufacture are already defined and are reference information. So, gradually section by section should be walked along its entire length, then add up all the indicators. We must not forget about the section that is located behind the fan, because there should also be enough pressure to divert the flows.
During the calculation, you need to take into account all curved connections.
Calculation of materials for duct and fittings
To select sizes and structural elements, for example, tees, elbows, transitions, there is no need to do it manually, especially since the nomenclature is quite large. Everything can be done in a special program, including the area of \u200b\u200bair duct fittings, for this you just need to enter the primary data. The result will be ready in a few seconds. And also, if necessary, you can use the tabular form of equivalent cross-sections of round-diameter air ducts, in which the decrease in pressure due to friction is equal to the decrease in pressure in rectangular sections.
The calculation of materials was performed using the program
Calculation of the power of the heater in the network
To calculate the supply ventilation system, it is first of all necessary to take into account the power of the heater that heats the incoming masses in the cool season. According to the approved standards, the temperature of the flow that enters the room must be at least 18 ° C, the outdoor air indicators depend on the location of the region. IN modern equipment it is possible to regulate the speed of circulation of air masses, thus, you can save in winter time electricity. Before choosing a model, the temperature of heating the air that comes from outside is calculated by the formula:
ΔТ \u003d 2.98 × Р / L, where Р - equipment power, W;
L is the flow rate of air masses.
Correctly made calculations are the key to many years of equipment operation
Conclusion
If necessary, you can understand all the calculations, however, with the help of the program, the possibility of an error is excluded, which will be quite expensive during operation. It is enough just to enter the primary parameters into the program and analyze the obtained indicators in fractions of seconds. And you can also ask for engineering assistance in calculating the area of \u200b\u200bair ducts in professional design workshops.
We tried to describe in as much detail as possible the entire process of self-calculation, and also talked about software products. In the comments, you can clarify incomprehensible points, the team of our magazine will be happy to answer them.
The principle of ventilation can be found in the video
- Performance of the system serving up to 4 rooms.
- Dimensions of air ducts and air distribution grilles.
- Air line resistance.
- Air heater power and approximate energy costs (when using an electric air heater).
If you need to choose a model with humidification, cooling or recuperation, use the calculator on the Breezart website.
An example of calculating ventilation using a calculator
With this example, we will show how to calculate supply ventilation for a 3-room apartment in which a family of three (two adults and a child) lives. In the afternoon, relatives sometimes come to them, so up to 5 people can stay in the living room for a long time. The ceiling height of the apartment is 2.8 meters. Room parameters:
We will set the consumption rates for the bedroom and the nursery in accordance with the SNiP recommendations - 60 m³ / h per person. For the living room, we will limit ourselves to 30 m³ / h, since a large number of people in this room are rare. According to SNiP, this air flow rate is permissible for rooms with natural ventilation (for ventilation, you can open a window). If we also set the air flow rate for the living room to 60 m³ / h per person, then the required capacity for this room would be 300 m³ / h. The cost of electricity to heat this amount of air would be very high, so we made a compromise between comfort and economy. To calculate the air exchange rate for all rooms, we will choose a comfortable double air exchange.
The main duct will be rectangular rigid, the branches will be flexible and sound-insulated (this combination of duct types is not the most common, but we chose it for demonstration purposes). For additional purification of the supply air, a fine coal-dust filter of the EU5 class will be installed (we will calculate the network resistance when the filters are dirty). Let us leave the air velocities in the ducts and the permissible noise level on the grilles equal to the recommended values, which are set by default.
Let's start the calculation by drawing up a diagram of the air distribution network. This diagram will allow us to determine the length of the ducts and the number of turns, which can be both horizontal and vertical plane (we need to count all the right angle turns). So, our scheme:
The resistance of the air distribution network is equal to the resistance of the longest section. This section can be divided into two parts: the main duct and the longest branch. If you have two branches of approximately the same length, then you need to determine which of them has the greatest resistance. For this, we can assume that the resistance of one turn is equal to the resistance of 2.5 meters of the duct, then the branch will have the greatest resistance, for which the value (2.5 * number of turns + duct length) is maximum. It is necessary to select two parts from the trace in order to be able to set different type air ducts and different air speeds for the main section and branches.
In our system, balancing throttle valves are installed on all branches, allowing you to adjust the air flow rate in each room in accordance with the project. Their resistance (in the open state) has already been taken into account, since this is a standard element of the ventilation system.
The length of the main duct (from the air intake grille to the branch to the room No. 1) is 15 meters, there are 4 turns at right angles in this section. The length of the supply unit and the air filter can be ignored (their resistance will be taken into account separately), and the resistance of the silencer can be taken equal to the resistance of the air duct of the same length, that is, simply count it as part of the main air duct. The longest branch is 7 meters long and has 3 right angle bends (one at the branch, one in the duct and one in the adapter). Thus, we have set all the necessary initial data and now we can proceed to the calculations (screenshot). The calculation results are summarized in tables:
Calculation results for roomsResults of calculating general parameters
| Ventilation system type | Regular | VAV |
| Performance | 365 m³ / h | 243 m³ / h |
| Cross-sectional area of \u200b\u200bthe main air duct | 253 cm² | 169 cm² |
| Recommended dimensions of the main duct | 160x160 mm 90x315 mm 125x250 mm |
125x140 mm 90x200 mm 140x140 mm |
| Air line resistance | 219 Pa | 228 Pa |
| Heater power | 5.40 kW | 3.59 kW |
| Recommended supply unit | Breezart 550 Lux (in 550 m³ / h configuration) |
Breezart 550 Lux (VAV) |
| Maximum productivity recommended PU |
438 m³ / h | 433 m³ / h |
| Electric power heater PU | 4.8kw | 4.8kw |
| Average monthly energy costs | 2698 rubles | 1619 rubles |
Calculation of the air supply network
- For each room (subsection 1.2), the capacity is calculated, the cross-section of the duct is determined and a suitable duct of standard diameter is selected. According to the Arktos catalog, the dimensions of distribution grids with a given noise level are determined (data for the AMN, ADN, AMR, ADR series are used). You can use other grilles with the same dimensions - in this case, a slight change in the noise level and resistance of the network is possible. In our case, the grilles for all rooms turned out to be the same, since at a noise level of 25 dB (A), the permissible air flow through them is 180 m³ / h (there are no smaller grilles in these series).
- The sum of the air flow rates for all three rooms gives us the overall performance of the system (subsection 1.3). When using a VAV system, the performance of the system will be one third lower due to the separate regulation of the air flow rate in each room. Next, the cross-section of the main duct is calculated (in the right column - for the VAV system) and rectangular ducts of suitable size are selected (usually several options are given with different aspect ratios). At the end of the section, the resistance of the air supply network is calculated, which turned out to be very large - this is due to the use of a fine filter in the ventilation system, which has a high resistance.
- We have received all the necessary data to complete the air distribution network, with the exception of the size of the main duct between branches 1 and 3 (this parameter is not calculated in the calculator, since the network configuration is not known in advance). However, the cross-sectional area of \u200b\u200bthis section can be easily calculated manually: the cross-sectional area of \u200b\u200bbranch No. 3 must be subtracted from the cross-sectional area of \u200b\u200bthe main duct. Having received the cross-sectional area of \u200b\u200bthe duct, its size can be determined by.
Calculation of the power of the heater and the choice of the supply unit
The recommended model Breezart 550 Lux has software adjustable parameters (capacity and power of the heater), therefore the capacity that should be selected when setting up the control panel is indicated in brackets. It can be noted that the maximum possible power of the heater of this PU is 11% lower than the calculated value. Lack of power will be noticeable only when the outside air temperature is below -22 ° C, and this does not happen often. In such cases, the air handling unit will automatically switch to a lower speed to maintain set temperature at the outlet (function "Comfort").
In the calculation results, in addition to the required performance of the ventilation system, the maximum performance of the PU at a given network resistance is indicated. If this performance turns out to be noticeably higher than the required value, you can take advantage of the programmable limitation of maximum performance, which is available for all Breezart ventilation units. For a VAV system, the maximum performance is indicated for reference, since its performance is adjusted automatically during the operation of the system.
Operating cost calculation
This section calculates the cost of electricity spent on heating the air during the cold season. The costs for a VAV system depend on its configuration and operating mode, therefore, they are taken equal to the average value: 60% of the costs of a conventional ventilation system. In our case, you can save money by reducing the air consumption in the living room at night and in the bedroom during the day.
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When installing a ventilation system, it is important to correctly select and determine the parameters of all elements of the system. It is necessary to find the required amount of air, select equipment, calculate air ducts, fittings and other components of the ventilation network. How is ventilation duct calculated? What affects their size and cross-section? Let's take a closer look at this issue.
Air ducts must be calculated from two points of view. First, the required section and shape are selected. In this case, it is necessary to take into account the amount of air and other parameters of the network. Also, already during production, the amount of material is calculated, for example, tin, for the manufacture of pipes and fittings. This calculation of the area of \u200b\u200bthe ducts allows you to determine in advance the amount and cost of the material.
Duct types
To begin with, let's say a few words about the materials and types of air ducts. This is important due to the fact that, depending on the shape of the ducts, there are features of its calculation and the choice of the cross-sectional area. It is also important to focus on the material, since the features of air movement and the interaction of the flow with the walls depend on it.
In short, air ducts are:
- Metal from galvanized or black steel, stainless steel.
- Flexible from aluminum or plastic film.
- Hard plastic.
- Tissue.
The shape of the air ducts is made of round, rectangular and oval sections. The most commonly used are round and rectangular pipes.
Most of the described air ducts are manufactured in the factory, for example, flexible plastic or fabric, and it is difficult to manufacture them on site or in a small workshop. Most of the products that require calculation are made of galvanized steel or stainless steel.
Both rectangular and round air ducts are made of galvanized steel, and the production does not require particularly expensive equipment. In most cases, a bending machine and a device for making round pipes... Apart from small hand tools.
Calculation of the cross-section of the duct
The main task that arises when calculating air ducts is the choice of the cross section and shape of the product. This process takes place during system design both in specialized companies and self-production... It is necessary to calculate the diameter of the duct or the sides of the rectangle, choose optimal value cross-sectional area.
The cross-section is calculated in two ways:
- permissible speeds;
- constant pressure loss.
The method of admissible speeds is simpler for non-specialists, so we will consider it in general terms.
Calculation of the cross-section of air ducts by the method of permissible speeds
Calculation of the ventilation duct cross-section by the method of permissible speeds is based on the normalized maximum speed. The speed is selected for each type of room and duct section, depending on the recommended values. For each type of building, there are maximum permissible speeds in the main ducts and branches, above which the use of the system is difficult due to noise and strong pressure losses.
Figure: 1 (Network diagram for calculation)
In any case, a system plan must be drawn up before starting the calculation. First, you need to calculate the required amount of air that needs to be supplied and removed from the room. Further work will be based on this calculation.
The very process of calculating the cross-section by the method of permissible velocities simplistically consists of the following stages:
- A duct diagram is created, on which the sections and the estimated amount of air that will be transported through them are marked. It is better to indicate on it all the grilles, diffusers, section changes, turns and valves.
- Based on the selected maximum speed and amount of air, the cross-section of the duct, its diameter or the size of the sides of the rectangle are calculated.
- After all the parameters of the system are known, it is possible to select a fan of the required performance and pressure. Fan selection is based on calculating the pressure drop in the network. This is much more difficult than simply choosing the cross-section of the duct at each section. We will consider this issue in general terms. Since sometimes they simply select a fan with a small margin.
For the calculation, you need to know the parameters of the maximum air speed. They are taken from reference books and normative literature. The table shows values \u200b\u200bfor some buildings and sections of the system.
Standard speed
The values \u200b\u200bare approximate, but will allow you to create a system with the lowest noise level.
Fig, 2 (Nomogram of a round tin duct)
How do I use these values? They must be substituted into the formula or use nomograms (diagrams) for different forms and types of air ducts.
Nomograms are usually given in the normative literature or in the instructions and descriptions of the ducts of a particular manufacturer. For example, all flexible air ducts are equipped with such schemes. For pipes made of tin, the data can be found in the documents and on the manufacturer's website.
In principle, you can not use a nomogram, but find the required cross-sectional area based on the air speed. And select the area according to the diameter or width and length of a rectangular section.
Example
Let's look at an example. The figure shows a nomogram for a round tin duct. The nomogram is also useful in that it allows you to specify the pressure loss in the duct section at a given speed. These data will be required in the future to select a fan.
So, which duct to select on the network section (branch) from the grate to the main line, through which 100 m³ / h will be pumped? On the nomogram, we find the intersection of a given amount of air with the line of maximum speed for a branch of 4 m / s. Also, not far from this point, we find the closest (larger) diameter. This is a pipe with a diameter of 100 mm.
In the same way, we find the section for each section. Everything is matched. Now it remains to select the fan and calculate the air ducts and fittings (if necessary for production).
Fan selection
An integral part of the method of permissible speeds is the calculation of pressure losses in the air duct network to select the fan with the required performance and pressure.
Pressure loss in straight sections
In principle, the required fan capacity can be found by adding the required amount of air for all rooms in the building and selecting suitable model in the manufacturer's catalog. But the problem is that the maximum amount of air specified in the documentation for the fan can be supplied only without a duct network. And when the pipe is connected, its performance will decrease depending on the pressure loss in the network.
For this purpose, the documentation gives each fan a performance diagram versus the pressure drop in the network. How to calculate this fall? To do this, you need to determine:
- pressure drop on flat sections of air ducts;
- losses on gratings, bends, tees and other fittings and obstacles in the network (local resistances).
The pressure losses in the duct sections are calculated using the same nomogram. From the point of intersection of the line of air velocity in the selected duct and its diameter, we find the pressure loss in pascals per meter. Next, we calculate the total pressure loss in a section of a certain diameter by multiplying the specific loss by length.
For our example with a 100 mm air duct and a speed of about 4 m / s, the pressure loss will be about 2 Pa / m.
Pressure loss on local resistances
Calculation of pressure losses on bends, bends, tees, section changes and transitions is much more difficult than on straight sections. For this, in the same diagram above, all elements that may impede movement are indicated.
Fig. 3 (Some c. M. S.)
Further, it is necessary for each such local resistance in the regulatory literature to find the coefficient of local resistance (c.m.s), which is denoted by the letter ζ (zetta). The pressure loss at each such element is found by the formula:
Pm. s. \u003d ζ × Pd
where Pd \u003d V2 × ρ / 2 - dynamic pressure (V - speed, ρ - air density).
For example, if on the already considered section with a diameter of 100 mm with an air speed of 4 m / s there will be a round bend (turn 90 degrees) to. M. S. which is 0.21 (according to the table), the pressure loss on it will be
- Pm. s. \u003d 0.21 42 (1.2 / 2) \u003d 2.0 Pa.
The average air density at a temperature of 20 degrees is 1.2 kg / m3.
Fig 4 (Example table)
The fan is selected according to the parameters found.
Calculation of material for air ducts and fittings
Calculation of the area of \u200b\u200bair ducts and fittings is necessary during their production. It is done in order to determine the amount of material (tin) for the manufacture of a pipe section or any shaped element.
For the calculation it is necessary to use only formulas from geometry. For example, for a round duct, we find the diameter of the circle, multiplying it by the length of the section, we get the area of \u200b\u200bthe outer surface of the pipe.
For the manufacture of 1 meter of pipeline with a diameter of 100 mm, you will need: π · D · 1 \u003d 3.14 · 0.1 · 1 \u003d 0.314 m² of tin. It is also necessary to take into account a 10-15 mm margin for the connection. A rectangular duct is also calculated.
Calculation of fittings for air ducts is complicated by the fact that there are no definite formulas for it, as for a circular or rectangular section. For each element, it is necessary to cut and calculate required amount materials. This is done in production or in tin workshops.
