Calculation of the length of air 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 - algorithm of actions
Calculation of the power of the ventilation system:
Air duct cross section: Round Rectangular
Diameter: mm
Length: mm
Width: mm
Air 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 shaft due to the difference in air pressure inside and outside the room. And on the way of air movement there are some kind of barriers (turns, narrowings, gratings, friction on the ventilation duct), which prevent the passage of air through the ventilation duct itself. And if the difference in air pressure between the room and the street is less than the pressure loss from these barriers, then normal ventilation will not work.
It is optimally considered when the pressure difference on 10-15% more than pressure loss.
Operating procedure:
1. Select the section of the duct/duct (rectangular or round)
2. Define the duct/duct geometry
3. Select the material of the channel / duct (brick, steel, ventilation block and slag gypsum)
4. Choose the room you're testing the ventilation in
5. Set the height H indicated in the figure (distance from the ventilation grille to the top point of the duct/duct)
6. Click the "Calculate" button
The result will be summarized below and will show if your ventilation system is working properly.
For reference:
- you can fully carry out the aerodynamic calculation of the ventilation system in
The calculation of the area of air ducts and fittings is made before the installation of ventilation communications. The efficiency of the entire ventilation system depends on the correct implementation of them. In practice, experienced craftsmen use two main measurement methods: using a formula and using an online calculator. Calculation of the area of air ducts and fittings is a time-consuming and responsible business. The editors of the online magazine Homius.ru have prepared a review on this topic especially for their readers, using all modern possibilities and knowledge. experienced craftsmen. In this article you will find useful advice for calculating data, as well as a convenient online calculator.
There may be an error in area calculations using formulas.
1 Why do we need to calculate the area of the duct and fittings
2 What data is needed to calculate the parameters of the duct
4 Calculation of the area of duct fittings
4.1 What programs exist for finding the parameters of duct fittings
5 Calculation square meters(cross-sectional area) of the duct
5.1 Calculator for calculating the required duct diameter
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 losses due to local resistances
10 Calculation of materials for duct and fittings
11 Calculation of heater power in the network
12 Conclusion
Why do we need to calculate the area of the duct and fittings
The ventilation complex consists of different elements. In order to correctly select all the details, it is necessary 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, it is possible to determine the optimal number of fittings for organizing a ventilation system for a particular room. This will prevent unnecessary spending on the purchase of elements that will not fit later.
Variety of duct designs and materials
What data is needed to calculate the parameters of the duct
To calculate the duct, you must first determine two indicators:
the norms established for the supply of fresh flows per 1 m² of the room per hour or the frequency of air exchange, information is 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 permanently in the room, 20 m³ for a temporarily staying person.
The effectiveness of industrial air purification 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 to the outside. For high-quality performance, first of all, it is necessary to perform design work and calculate the quadrature of the ducts. During planning, the shape of the pipes, the number of elements required to connect the sections, and 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 that are used in the calculations. For an online calculator, it is enough to enter the initial data, the software package will independently perform all the calculations. One of the main parameters for designing an air duct and fittings is its design. You can choose pipes of rectangular or round cross-section. The throughput of round products is much higher than that of rectangular ones.
Maximum accuracy in calculations
the least amount of air masses moved;
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;
consequently, 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 the duct:
S \u003d A × B / 100, where A and B are, respectively, the height and width of the section.
The rectangular air duct is almost invisible above the furniture
The duct with a cross section in the form of a circle does not cause difficulties during installation and has an excellent air flow capacity, since internal resistance is minimized. Choosing the form of communication should be based on the personal preferences of consumers and external design premises.
The actual area is calculated as follows:
S = π × D²/400, where:
π is a constant equal to 3.14;
D - element length.
Special methods have been developed, for example, SNiPs, in which the calculated actual areas are compared with the required indicators. They make it easy to choose optimal size communications.
When making calculations, the following factors must be taken into account:
the cross-sectional area for straight sections of the duct should be calculated separately;
be sure to take into account the resistance that will be exerted on the 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.
Circular area product
Calculation of the area of duct fittings
It will be difficult for a person who is not connected with mathematical formulas to perform 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 the duct, you can use an online calculator and special programs that perform all the algorithms, for this you only need to enter the primary indicators.
The program for counting and selecting elements
What programs exist for finding the parameters of duct fittings
To help engineers, to eliminate errors associated with the human factor, as well as to speed up the process, special programs were created that can not only perform accurate 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 check calculation of the 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 features.
Software calculation and design of ventilation
Calculation of square meters (sectional area) of the duct
For size ventilation pipe many factors influence: flow rate, pressure on the walls, air volume. If you perform calculations with an error, for example, reduce the cross section of the main network, the speed of air masses will increase, noise will appear, pressure and electricity consumption will increase.
The calculation of the cross-sectional area of the duct is calculated using the following formula:
S = L × κ / ω, where:
L - air consumption, m³/h;
ω - speed of air flow, m/s;
κ - design coefficient equal to 2.778.
Calculator for calculating the required duct diameter
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Calculation of air velocity in a 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 necessary 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 the indicators in them are rounded, so more accurate data is obtained with independent calculations. The air exchange rate can be calculated 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 is the volume of the room, m³.
You can carry out aerodynamic calculations and calculate the speed of air movement using the following formula:
ω = L / 3600 × S, where L is the volume of air used in 1 hour;
S - cross-sectional area of the 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 cross section in the form of a rectangle. To ensure the normal performance of the system, it is necessary to select a fan of the appropriate capacity. It is difficult to manually determine these parameters on your own; in the project team, all calculations are performed using the program.
The resistance is not affected by the number of rooms served by the ventilation system, 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 choose a model that fits these parameters. However, the product data sheet does not take into account 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 in flat areas, rotary and connecting elements. The pressure drop in flat areas is determined by the formula:
Р = R × L + Еi × V2 × Y / 2, where R is the specific head loss caused by the friction force during air movement, Pa/m;
L is the length of the straight section of the duct, m;
ω – air velocity, m/s Y – air mass density, kg/m³;
Ei - the sum of the pressure losses due to local resistances (bends, transitions, gratings, etc.), the data can be taken from the reference book.
Rectilinear section of ventilation
Pressure loss at local resistances
To calculate the losses on the rotary elements, it is necessary first of all to determine all the sections that will interfere with the direct movement of flows. You can use a formula, but all data depending on the duct element and the material of manufacture are already defined and are reference information. So, gradually section by section should be passed along its entire length, then add up all the indicators. We must not forget about the segment that is located behind the fan, because there should also be enough pressure to drain the flows.
During the calculation, all curvilinear connections must be taken into account
Calculation of materials for the duct and fittings
To select the dimensions and structural elements, for example, tees, bends, reducers, there is no need to do it manually, especially since the range is quite large. Everything can be done in special program, including the area of shaped parts of air ducts, 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 circular diameter air ducts, in which the reduction in friction pressure is equal to the pressure reduction in rectangular sections.
The calculation of materials was carried out using the program
Calculation of heater power in the network
To calculate the supply ventilation system, it is necessary first of all 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 heating temperature of the air that enters from the outside is calculated by the formula:
ΔT \u003d 2.98 × P / L, where P is the power of the equipment, W;
L - air mass consumption.
Proper 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 during operation will be quite expensive. It is enough to enter the primary parameters into the program and analyze the obtained indicators in a fraction of a second. You can also seek engineering assistance in calculating the area of air 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 operation of ventilation can be found on the video
- The performance of a system serving up to 4 rooms.
- Dimensions of air ducts and air distribution grilles.
- Air line resistance.
- Heater power and estimated electricity costs (when using an electric 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
In this example, we will show how to calculate supply ventilation for a 3-room apartment in which a family of three lives (two adults and a child). During the day, 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 options:
We will set the consumption rates for the bedroom and the nursery in accordance with the recommendations of SNiP - 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 infrequent. According to SNiP, such air flow is acceptable for rooms with natural ventilation (you can open a window for ventilation). If we also set an air flow rate of 60 m³/h per person for the living room, then the required performance 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 by the multiplicity for all rooms, we will choose a comfortable double air exchange.
The main air duct will be rectangular rigid, the branches will be flexible and soundproof (this combination of duct types is not the most common, but we chose it for demonstration purposes). For additional cleaning of the supply air, a carbon-dust fine filter of the EU5 class will be installed (we will calculate the network resistance with dirty filters). The air velocities in the air ducts and the permissible noise level on the gratings will be left equal to the recommended values that are set by default.
Let's start the calculation by drawing up a diagram of the air distribution network. This scheme will allow us to determine the length of the ducts and the number of turns that can be both horizontal and vertical plane(we need to count all right angle turns). So our schema is:
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 one has more resistance. To do 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 with the maximum value (2.5 * number of turns + duct length) will have the greatest resistance. It is necessary to select two parts from the route in order to be able to set different type 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 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 air duct (from the air intake grille to the branch to room No. 1) is 15 meters, there are 4 right-angle turns 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 silencer resistance can be taken equal to the resistance of an air duct of the same length, that is, simply consider it a part of the main air duct. The longest branch is 7 meters long and has 3 right angle bends (one at the branch, one at the duct and one at 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 the calculation of general parameters
| Type of ventilation system | Plain | VAV |
| Performance | 365 m³/h | 243 m³/h |
| Cross-sectional area of the main air duct | 253 cm² | 169 cm² |
| Recommended main duct dimensions | 160x160mm 90x315mm 125x250mm |
125x140mm 90x200mm 140x140mm |
| Air network resistance | 219 Pa | 228 Pa |
| Heater power | 5.40 kW | 3.59 kW |
| Recommended air handling unit | Breezart 550 Lux (in 550 m³/h configuration) |
Breezart 550 Lux (VAV) |
| Maximum performance recommended PU |
438 m³/h | 433 m³/h |
| Electric power heater PU | 4.8 kW | 4.8 kW |
| Average monthly electricity costs | 2698 rubles | 1619 rubles |
Calculation of the air duct network
- For each room (subsection 1.2), the performance 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 gratings with the same dimensions - in this case, there may be a slight change in the noise level and network resistance. In our case, the grilles for all rooms turned out to be the same, since at a noise level of 25 dB(A) the allowable 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 total system performance (subsection 1.3). When using a VAV system, the system performance will be one third lower due to the separate adjustment of the air flow in each room. Next, the section of the main air duct is calculated (in the right column - for the VAV system) and suitable rectangular air ducts are selected (usually several options are given with different aspect ratios). At the end of the section, the resistance of the air duct 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 air 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 this section can be easily calculated manually: from the cross-sectional area of the main air duct, you need to subtract the cross-sectional area of branch No. 3. Having obtained the cross-sectional area of \u200b\u200bthe duct, its size can be determined by.
Calculation of heater power and selection of air handling unit
The recommended Breezart 550 Lux model has programmable parameters (capacity and power of the heater), therefore, the performance that must be selected when setting up the remote control is indicated in brackets. It can be seen that the maximum possible power of the heater of this launcher is 11% lower than the calculated value. The lack of power will be noticeable only at outdoor temperatures 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 outlet (comfort function).
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 possibility of programmatically limiting the 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.
Calculation of the cost of operation
This section calculates the cost of electricity used to heat the air during the cold season. The costs for a VAV system depend on its configuration and mode of operation, so they are assumed to be 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 at night in the living room, and during the day in the bedroom.
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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 are ventilation ducts calculated? What affects their size and cross section? Let's analyze this issue in more detail.
Air ducts must be calculated from two points of view. First, the required section and shape is selected. In this case, it is necessary to take into account the amount of air and other parameters of the network. The amount of material, such as sheet metal, for the manufacture of pipes and fittings is also calculated already during production. This calculation of the air duct area allows you to pre-determine the amount and cost of the material.
Duct types
First, 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 duct, there are features of its calculation and the choice of 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.
- Fabric.
Air ducts are made in shape of round section, rectangular and oval. The most commonly used are round and rectangular pipes.
Most of the air ducts described are factory fabricated, such as flexible plastic or fabric, and are difficult to fabricate on site or in a small workshop. Most of the products that require calculation are made from 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 when designing a system both in specialized companies and in self-manufacturing. It is necessary to calculate the diameter of the duct or the sides of the rectangle, select optimal value cross-sectional area.
The calculation of the cross section is carried out in two ways:
- allowable speeds;
- constant pressure loss.
The allowable speed method is easier for non-specialists, so let's look at it in general terms.
Calculation of the section of air ducts by the method of permissible speeds
The calculation of the cross section of the ventilation duct by the method of permissible speeds is based on the normalized top 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 allowable velocities in the main ducts and branches, above which the use of the system is difficult due to noise and strong pressure losses.
Rice. 1 (Network diagram for calculation)
In any case, before starting the calculation, it is necessary to draw up a system plan. 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 process of calculating the cross section by the method of permissible velocities simply consists of the following steps:
- A duct scheme is created, on which sections and the estimated amount of air that will be transported through them are marked. It is better to indicate on it all grilles, diffusers, section changes, turns and valves.
- According to the selected maximum speed and the amount of air, the cross-section of the duct, its diameter or the size of the sides of the rectangle is 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 the calculation of the pressure drop in the network. This is much more difficult than just choosing the cross section of the duct in each section. We will consider this question in general terms. Since sometimes they just pick up a fan with a small margin.
To calculate, you need to know the parameters of the maximum air velocity. They are taken from reference books and normative literature. The table shows the values for some buildings and sections of the system.
Standard speed
The values are approximate, but allow you to create a system with a minimum level of noise.
Fig, 2 (Nomogram of a round tin air duct)
How to use these values? They must be substituted into the formula or use nomograms (schemes) for different forms and types of ducts.
Nomograms are usually given in the regulatory literature or in the instructions and descriptions of the air ducts of a particular manufacturer. For example, all flexible air ducts are equipped with such schemes. For tin pipes, 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 choose the area according to the diameter or width and length of a rectangular section.
Example
Consider an example. The figure shows a nomogram for a round tin duct. The nomogram is also useful in that it can be used to clarify the pressure loss in the duct section at a given speed. These data will be required in the future for the selection of a fan.
So, which air duct should be selected on the network section (branch) from the grid to the main, through which 100 m³ / h will be pumped? On the nomogram, we find the intersections 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 nearest (larger) diameter. This is a pipe with a diameter of 100 mm.
In the same way, we find the cross section for each section. Everything is selected. 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 allowable speed method is the calculation of pressure losses in the duct network to select a fan of the required capacity and pressure.
Pressure loss in straight sections
In principle, the required fan capacity can be found by adding up the required amount of air for all areas of 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 only be supplied without a network of air ducts. And when a pipe is connected, its performance will drop depending on the pressure loss in the network.
To do this, in the documentation, each fan is given a performance diagram depending on the pressure drop in the network. But how to calculate this fall? To do this, you need to define:
- pressure drop on flat sections of air ducts;
- losses on gratings, bends, tees and other shaped elements and obstacles in the network (local resistances).
The pressure losses in the duct sections are calculated using the same given 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 the length.
For our example with a 100 mm duct and a velocity of about 4 m/s, the pressure loss will be about 2 Pa/m.
Pressure loss at local resistances
Calculation of pressure losses on bends, bends, tees, changes in section and transitions is much more complicated than on straight sections. For this, in the same diagram above, all elements that may impede movement are indicated.
Figure 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 on each such element is found by the formula:
Pm. s.=ζ×Pd
where Pd=V2×ρ/2 - dynamic pressure (V - speed, ρ - air density).
For example, if on the section we are already considering with a diameter of 100 mm with an air speed of 4 m / s there will be a round outlet (rotation of 90 degrees) c.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 (Table example)
According to the parameters found, a fan is selected.
Calculation of material for air ducts and fittings
The calculation of the area of air ducts and fittings is necessary in 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, by multiplying which by the length of the section we get the area of the outer surface of the pipe.
For the manufacture of 1 meter of a 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 from 10-15 mm margin per connection. A rectangular duct is also calculated.
The calculation of shaped parts of air ducts is complicated by the fact that there are no specific formulas for it, as for a round or rectangular section. For each element, it is necessary to cut and calculate required amount materials. This is done in production or in tin shops.
