Air ducts are round how to count. How to make the correct calculation of the area of ​​​​air ducts. How to calculate pipe area: fittings

The main parameter characterizing the efficiency is air consumption. It is defined as the sum of the values ​​in individual sections of ducts with a stable flow rate, limited by branches or dampers. On each such section, the area of ​​air ducts and fittings is calculated. When determining the shape of ventilation ducts and their quadrature, the main parameter is the air flow rate. It is indicated in the standards and building regulations (SP). For main pipelines, it should not exceed 8 m / s, for branches - no more than 5 m / s. And at the place of entry into the premises, the speed is limited to 3 m / s.

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Why is it necessary to calculate the area of ​​air ducts and fittings?

Determining the squaring of air ducts is necessary to create an efficiently functioning and optimize its characteristics:

• volumes of moved air;
• speed of air masses;
• noise level;
• energy consumption.

In addition, the calculation should provide a whole list of additional performance characteristics. For example, the proper temperature in the room. That is, it must remove excess heat and humidity or minimize heat loss. At the same time, the maximum / minimum temperature and the speed of the air entering the room are brought to the relevant standards.

The quality parameters of the incoming air are also regulated, namely: its chemical composition, the amount of suspended particles, the presence and concentration of explosive elements, etc.

What data is needed to calculate the performance characteristics of air ducts?

First of all, the main parameters of the structure are taken into account, such as the purpose of the building itself, the volume of premises, the number of permanently staying staff and visitors, the features of the production process (for industrial buildings), etc.

Design is carried out in accordance with the following regulatory documents:

• SP 60.13330.2016 (current edition of SNiP 41-01-2003);
• SP 7.13130.2013;
• GOST 12.1.005-88 and some others.

How to calculate the area of ​​the duct of various types of sections?

The calculation of the quadrature of air ducts of different sections has its own characteristics, since their air flow will differ significantly even with the same parameters for the speed of movement of air masses and area. In addition, when calculating ventilation networks of great length and / or branching, air temperature is also taken into account (if it exceeds +20 ° C). As well as the aerodynamic resistance of air ducts and fittings, depending on the shape and material of manufacture (different coefficients of friction). Accounting for these parameters is expressed in the use of various correction factors in the calculation formulas.

Important information! Channel quadrature parameters and air flow velocity are inversely proportional. That is, with a large cross section of the duct, a lower speed is sufficient to provide the required volume of air to be moved.

The quadrature is calculated according to two parameters taken from the standards (in fact, these parameters describe the air exchange rate):

1. air consumption - R (m³ / hour);
2. air flow velocity - V (m / s).

The duct area formula operates with air flow parameters taken from the standards:

S = R/k × V, where

K - coefficient equal to 3600.

There are alternative formulas that operate with other coefficients, for example:

S = R × 2.778/V.

When using large-section air ducts, the noise level of air flows and the cost of electricity for their movement are significantly reduced. However, the material consumption of such structures is much higher, which increases their initial cost.

The shape of the section has a significant impact on the efficiency of moving air flows. In rectangular ducts, the air flow receives more resistance. However, a rectangular shape is more convenient for installation, especially when there is a lack of space, and can be placed close to the main building structures. Round ducts have the best aerodynamics, but do not always fit into the interior. And products with high aesthetic performance have a much higher cost. Given the above facts, as an alternative, it is recommended to pay attention to oval ducts, which combine ergonomics and efficiency.

How to calculate the area of ​​a circular duct?

To calculate the diameter of a round ventilation duct, the standard cross-sectional area is used:

The actual area is obtained from the formula:

How to calculate the area of ​​a rectangular duct?

For rectangular boxes, the same formulas are used as for round boxes. The length of the sides is calculated by the formula:

Dp is the diagonal of a rectangle inscribed in a circle (actually equivalent to the diameter of the circle);

a, b - sides.

The actual area is found from the formula:

Also, designers use tables to calculate the main parameters.

Calculation of the area of ​​an oval duct

The diameters of an oval duct are calculated from its area. The following formulas are used:

R is the perimeter of the ovaloid circle,

The area of ​​an oval duct is calculated by the formula:

a, b are the large and small diameters of the oval, respectively.

Calculation of the area of ​​shaped parts of air ducts

When creating branched systems, various shaped products are used:

• bends - tees with the same or different cross sections;
• duck - s-shaped branch;
• umbrella;
• adapters:

• between different sections of the same shape (as a rule, different diameters);
• between different types of sections (for example, from rectangular to round).

Each of the presented fittings is calculated according to separate formulas, as a result of which their overall calculation is rather complicated. Even experienced designers need engineering help with duct area calculations. To do this, they use special programs.

What programs exist for determining the parameters of shaped parts of air ducts?

Many programs have been developed for calculating the area of ​​duct fittings:

• Vent Calc v2.0- a universal tool for designing and calculating the main parameters. According to the developers, the key parameters for the calculation are the air flow and the length of the air ducts. Having received this data from the operator, the program independently generates a prototype of the ventilation network with an indication of the aerodynamic resistance for each branch limited by shaped products. The sum of these indicators is the basis for the selection of a power ventilation unit. Recently, this software package has become free;
• MagiCAD– software for designing all types of engineering communications. Project files can be imported into ADT and AutoCAD;
• GIDRV 3.093– calculator for calculating the area of ​​air ducts and fittings for natural type, taking into account the aspiration of the building;
• Fans 400– specialized software for calculating smoke ventilation;
• Ducter 2.5- a program for calculating the area of ​​shaped parts of air ducts.

There are several simpler programs and macros written in Microsoft Excel. Basically, they perform the calculation of the aerodynamics of air ducts of various sections.

Also on some sites you can find online calculators for the surface area of ​​air ducts, which are offered by companies involved in the provision of relevant services.

Before starting the installation of ventilation communications, it is necessary to calculate the area of ​​​​air ducts and fittings. The performance of the entire system as a whole will depend on the correctness of the calculations made. Natural and forced ventilation require a separate course of action in the design work, although they have a common purpose.

Before installing the ventilation system, it is necessary to calculate the correct size of the duct

The sequence of calculations of ventilation systems

When determining the resistance to air movement, the shape and properties of the material of the ventilation ducts, their total length, kinematic diagram, and the presence of branches are taken into account. Additional heat loss calculations are also performed to maintain favorable microclimatic conditions and reduce the cost of maintaining the premises in winter.

The cross-sectional area is calculated according to the data of the aerodynamic calculation of the air ducts. Given the obtained values, the following is performed:

• selection of the most appropriate size of the cross section of the ventilation duct, depending on the speed of the air flow;
• setting the maximum possible pressure drop in the ventilation system.

Calculation of the quadrature of air ducts is carried out using formulas, but it is easier to use the online calculator for the area of ​​air ducts and fittings. It already includes all the required formulas and the order of calculations. Another positive side of the program for calculating the area of ​​​​air ducts is the impossibility of making a mistake due to the fault of a person.

A clear plus of using an online calculator is the elimination of human error

In order to correctly calculate the area of ​​the duct using formulas, it is first necessary to determine the cross section of the fittings. Most often they are made round (rarely in the form of an ellipse), square or rectangular.

Calculation of the area of ​​air ducts using formulas

An inaccuracy in the calculations of this indicator of the ventilation complex can be fatal. Reducing the required value will inevitably cause an increase in pressure in the ventilation shafts, therefore, it will provoke the appearance of an extraneous hum. You can calculate the area of ​​a rectangular ventilation duct using the formula:

S = L * k / V, where:

• S - cross-sectional area (m 2);
• L - air consumption (m 3 / h);
• k is the required coefficient, equal to 2.778;
• V - air mass flow rate.

In addition, using mathematical calculations, you can find the real cross-sectional area of ​​​​the ventilation duct. For this, the formula is used:

S = A x B / 100 - for square or rectangular boxes;

S = π * D² / 400 - for round boxes, where:

• A - box height (mm);
• B - box width (mm);
• D - diameter of the round box (mm).

To get more accurate values, you can compare the data obtained using engineering calculations and an online calculator. The area of ​​the air ducts should not differ significantly.

The dimensions of the ventilation ducts are calculated individually for each site. It should be noted that air flow speed can be ≈ 8 m/s, since the dimensions of the connecting flange of the ventilation system are limited by the dimensions of its core. In order to reduce the air flow rate and the level of noise pollution, the dimensions of the ventilation units are made several sizes larger than the flange. In such conditions, the central air duct is connected to the ventilation unit through an adapter.

For domestic ventilation systems, round or rectangular air ducts with a diameter of 100–250 mm are most often used.

General requirements

In ventilation systems designed to remove flammable volatile substances, air ducts must be made of refractory materials. The main transit segments of ventilation must be made of metal.

Air ducts are made of refractory materials or metal

When calculating the final parameters of the air ducts, it is necessary to provide:

1. Possibility of installation of fire dampers both in horizontal, and in vertical position.
2. Installation of air shutters on the platforms between floors. The functionality of these devices must comply with the regulatory requirements for emergency blocking of selective system segments.
3. A maximum of five air ducts can be connected to each floor manifold.
4. Installation of an automatic fire warning system.

In all calculations, the recommendations of building codes were used.

In all calculations, the recommendations of building codes and regulations were used. These standard values ​​allow you to find out the minimum possible ventilation efficiency that can provide a comfortable indoor climate. In other words, the SNiP rules are focused primarily on minimizing the cost of installing and operating a ventilation system, which is important when developing ventilation systems for public and administrative buildings.

For private houses and apartments, the situation is somewhat different, since this is a personal project in which you can not strictly adhere to the instructions of SNiP. Because of this, ventilation performance may deviate from the standard values, since everyone has their own idea of ​​​​comfort.

Aerodynamic calculation of mechanical ventilation and air conditioning systems is carried out to determine the diameters or dimensions of rectangular sections of air ducts or ducts, as well as to determine the pressure loss during air movement in the duct and select the appropriate fan.

One of the important factors in the design of ventilation systems is the speed of air movement in the duct. At high air speed, noise is created from friction against the walls of the duct and turbulence at bends and outlets, and the resistance of the duct system will also increase, which leads to the need to install a fan of greater productivity, and subsequently to an increase in capital and operating costs.

• 1.5 ... 2.0 m / s - in the distribution channel with supply or exhaust ventilation grilles and deflectors;
• 4 ... 5 m / s - for side branches of air ducts for supply and exhaust ventilation;
• 6 m / s - for the main channels of supply and exhaust ventilation;
• 8 ... 12 m / s - for the main channels of industrial enterprises.

For the calculation, an axonometric diagram of the supply and exhaust ventilation systems is built. The main direction of the air ducts in the diagram is divided into sections - segments of the same length and with a constant air flow. Then the sections are numbered and all values ​​​​are applied to the diagram. The total air flow is added up by successive summation of the air flow through the branches that join the main direction.

Calculation of the cross-sectional area of ​​the duct

The calculation of the cross-sectional area of ​​the duct for each section is made according to the following formula:

where L - air flow (m³ / h);

V is the speed of the air flow (m/s);

Then calculate the preliminary diameter of the duct in the area

D=1000∙√(4∙S/"π") mm, and round to the nearest standard size. The dimensions of the air ducts must be taken strictly in accordance with the values ​​\u200b\u200bgiven in the reference manual.

If it is necessary to use rectangular air ducts, the dimensions of the sides are also selected according to the approximate section, i.e. so that a×b ≈ S according to the size table, taking into account that the aspect ratio, as a rule, should not exceed 1:3. The minimum rectangular section is 100×150 mm, the maximum is 2000×2000.

The choice of round or rectangular air ducts and the material from which they will be made is made according to the technical conditions of the facility.

Rectangular ducts are smaller and can be used in rooms with limited space for ventilation ducts. Circular air ducts reduce air resistance and, consequently, the noise of the structure, eliminate air loss and are more convenient for installation.

For your convenience, we have made such a calculation for the most commonly used sizes and cross-sections of air ducts. Address for applications for the selection of equipment for finished projects and the development of Terms of Reference for the design of air conditioning and ventilation systems:

Comments:

• Factors influencing the size of air ducts
• Calculation of air duct dimensions
• Selection of dimensions for real conditions

To transfer supply or exhaust air from ventilation units in civil or industrial buildings, air ducts of various configurations, shapes and sizes are used. Often they have to be laid through existing premises in the most unexpected and equipment-cluttered places. For such cases, the correctly calculated cross-section of the duct and its diameter play a crucial role.

Factors influencing the size of air ducts

It is not a big problem to successfully lay the pipelines of ventilation systems at the facilities under design or under construction - it is enough to coordinate the location of the systems relative to workplaces, equipment and other engineering networks. In existing industrial buildings, this is much more difficult to do due to limited space.

This and several other factors affect the calculation of the diameter of the duct:

1. One of the main factors is the consumption of supply or exhaust air per unit of time (m 3 / h), which must pass this channel.
2. The capacity also depends on the air speed (m/s). It cannot be too small, then, according to the calculation, the size of the air duct will be very large, which is not economically feasible. Too high a speed can cause vibrations, increased noise level and increased power of the ventilation unit. For different sections of the supply system, it is recommended to take a different speed, its value lies in the range from 1.5 to 8 m/s.
3. The material of the duct matters. Usually this is galvanized steel, but other materials are also used: various types of plastics, stainless or black steel. The latter has the highest surface roughness, the resistance to flow will be higher, and the channel size will have to be taken larger. The diameter value should be selected according to the normative documentation.

Table 1 shows the normal dimensions of air ducts and the thickness of the metal for their manufacture.

Table 1

Note: Table 1 does not fully reflect the normal, but only the most common channel sizes.

Air ducts are produced not only round, but also rectangular and oval. Their sizes are taken through the value of the equivalent diameter. Also, new methods of manufacturing channels allow the use of thinner metal, while increasing the speed in them without the risk of causing vibration and noise. This applies to spirally wound air ducts, they have a high density and rigidity.

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Calculation of air duct dimensions

First you need to determine the amount of supply or exhaust air that you want to deliver through the channel to the room. When this value is known, the cross-sectional area (m 2) is calculated by the formula:

In this formula:

• ϑ – air velocity in the channel, m/s;
• L - air consumption, m 3 / h;
• S is the cross-sectional area of ​​the channel, m2;

In order to link the units of time (seconds and hours), the number 3600 is present in the calculation.

The diameter of a circular duct in meters can be calculated based on its cross-sectional area using the formula:

S \u003d π D 2 / 4, D 2 \u003d 4S / π, where D is the value of the channel diameter, m.

The procedure for calculating the size of the air duct is as follows:

1. Knowing the air flow in this area, determine the speed of its movement, depending on the purpose of the channel. As an example, we can take L = 10,000 m 3 / h and a speed of 8 m / s, since the branch of the system is the main one.
2. The cross-sectional area is calculated: 10,000 / 3600 x 8 = 0.347 m 2, the diameter will be - 0.665 m.
3. Normally take the closest of the two sizes, usually take the one that is larger. Next to 665 mm there are diameters of 630 mm and 710 mm, you should take 710 mm.
4. In the reverse order, the actual speed of the air mixture in the air duct is calculated to further determine the fan power. In this case, the cross section will be: (3.14 x 0.71 2 / 4) = 0.4 m 2, and the real speed is 10,000 / 3600 x 0.4 = 6.95 m / s.
5. In the event that it is necessary to lay a rectangular channel, its dimensions are selected according to the calculated cross-sectional area, equivalent to a round one. That is, the width and height of the pipeline are calculated so that the area is 0.347 m 2 in this case. It can be 700mm x 500mm or 650mm x 550mm. Such air ducts are mounted in cramped conditions, when the space for laying is limited by technological equipment or other engineering networks.

When the parameters of air ducts are known (their length, cross-section, coefficient of friction of air on the surface), it is possible to calculate the pressure loss in the system at the projected air flow.

The total pressure loss (in kg/sq.m.) is calculated using the formula:

P \u003d R * l + z,

where R- pressure loss due to friction per 1 running meter of the air duct, l z- pressure loss due to local resistances (with variable cross section).

1. Friction loss:

Friction pressure loss in a circular duct Ptr are considered like this:

Ptr \u003d (x * l / d) * (v * v * y) / 2g,

where x- coefficient of friction resistance, l- duct length in meters, d- duct diameter in meters, v y g- free fall acceleration (9.8 m/s2).

Comment: If the air duct has not a round, but a rectangular cross section, the equivalent diameter must be substituted into the formula, which for an air duct with sides A and B is equal to: dequiv \u003d 2AB / (A + B)

2. Losses due to local resistance:

Pressure losses due to local resistances are calculated according to the formula:

z = Q* (v*v*y)/2g,

where Q- the sum of the local resistance coefficients in the section of the duct for which the calculation is made, v- air flow velocity in m/s, y- air density in kg/cu.m., g- free fall acceleration (9.8 m/s2). Values Q are contained in a table.

Permissible speed method

When calculating the air duct network using the method of permissible speeds, the optimal air speed is taken as the initial data (see table). Then, the required cross-section of the duct and the pressure loss in it are considered.

The procedure for the aerodynamic calculation of air ducts according to the method of permissible speeds:

1. Draw a diagram of the air distribution system. For each section of the duct, indicate the length and amount of air passing in 1 hour.
2. We start the calculation from the most distant from the fan and the most loaded sections.
3. Knowing the optimal air velocity for a given room and the volume of air passing through the duct in 1 hour, we determine the appropriate diameter (or cross section) of the duct.
4. We calculate the pressure loss due to friction Ptr.
5. According to the tabular data, we determine the sum of local resistances Q and calculate the pressure loss due to local resistances z.
6. The available pressure for the next branches of the air distribution network is determined as the sum of the pressure losses in the sections located before this branch.

In the process of calculation, it is necessary to sequentially link all the branches of the network, equating the resistance of each branch to the resistance of the most loaded branch. This is done with diaphragms. They are installed on lightly loaded sections of air ducts, increasing resistance.

Table of maximum air speed depending on duct requirements

Purpose	Basic requirement
	Noiselessness	Min. head loss
	Main channels	main channels		Branches
		tributary	Hood	tributary	Hood
Living spaces	3	5	4	3	3
Hotels	5	7.5	6.5	6	5
Institutions	6	8	6.5	6	5
Restaurants	7	9	7	7	6
The shops	8	9	7	7	6

Note: The airflow speed in the table is given in meters per second.

Constant Head Loss Method

This method assumes a constant pressure loss per 1 linear meter of the duct. Based on this, the dimensions of the duct network are determined. The method of constant pressure loss is quite simple and is used at the stage of the feasibility study of ventilation systems.

1. Depending on the purpose of the room, according to the table of permissible air velocities, the speed on the main section of the duct is selected.
2. Based on the speed determined in paragraph 1 and on the basis of the design air flow, the initial pressure loss is found (per 1 m of the duct length). This is the diagram below.
3. The most loaded branch is determined, and its length is taken as the equivalent length of the air distribution system. Most often this is the distance to the farthest diffuser.
4. Multiply the equivalent system length by the head loss from step 2. The head loss at the diffusers is added to the value obtained.
5. Now, using the diagram below, determine the diameter of the initial duct coming from the fan, and then the diameters of the remaining sections of the network according to the corresponding air flow rates. In this case, the initial pressure loss is assumed to be constant.

Diagram for determining head loss and duct diameter

Using Rectangular Ducts

The head loss diagram shows the diameters of round ducts. If rectangular ducts are used instead, find their equivalent diameters using the table below.

Notes:

1. If space permits, it is better to choose round or square ducts.
2. If there is not enough space (for example, during reconstruction), choose rectangular ducts. As a rule, the width of the duct is 2 times the height). The table shows the height of the duct in mm horizontally, the vertical width, and the cells of the table contain equivalent duct diameters in mm.

Table of equivalent duct diameters

Dimensions	150	200	250	300	350	400	450	500
250	210	245	275
300	230	265	300	330
350	245	285	325	355	380
400	260	305	345	370	410	440
450	275	320	365	400	435	465	490
500	290	340	380	425	455	490	520	545
550	300	350	400	440	475	515	545	575
600	310	365	415	460	495	535	565	600
650	320	380	430	475	515	555	590	625
700		390	445	490	535	575	610	645
750		400	455	505	550	590	630	665
800		415	470	520	565	610	650	685
850			480	535	580	625	670	710
900			495	550	600	645	685	725
950			505	560	615	660	705	745
1000			520	575	625	675	720	760
1200				620	680	730	780	830
1400					725	780	835	880
1600						830	885	940
1800						870	935	990

The parameters of microclimate indicators are determined by the provisions of GOST 12.1.2.1002-00, 30494-96, SanPin 2.2.4.548, 2.1.2.1002-00. Based on existing state regulations, the Code of Rules SP 60.13330.2012 was developed. The air speed in must ensure the implementation of existing standards.

What is taken into account when determining the speed of air movement

To perform calculations correctly, designers must fulfill several regulated conditions, each of which is equally important. What parameters depend on the speed of the air flow?

Noise level in the room

Depending on the specific use of the premises, sanitary standards establish the following indicators for the maximum sound pressure.

Table 1. Maximum noise levels.

Exceeding the parameters is allowed only in short-term mode during the start/stop of the ventilation system or additional equipment.
Vibration level in the room Vibration is generated during operation of the fans. Vibration indicators depend on the material of manufacture of air ducts, the methods and quality of vibration damping pads and the speed of the air flow through the air ducts. General vibration indicators cannot exceed the limit values ​​established by government organizations.

Table 2. Maximum values ​​of permissible vibration.

When calculating, the optimal air speed is selected, which does not increase the vibration processes and the associated sound vibrations. The ventilation system must maintain a certain microclimate in the premises.

Values ​​for flow rate, humidity and temperature are given in the table.

Table 3. Microclimate parameters.

Another indicator taken into account during the calculation of the flow rate is the frequency of air exchange in ventilation systems. Taking into account their use, sanitary standards establish the following requirements for air exchange.

Table 4. Air exchange rate in different rooms.

household
Domestic premises	Air exchange rate
Living room (in an apartment or in a hostel)	3m 3 / h per 1m 2 living quarters
Apartment or dorm kitchen	6-8
Bathroom	7-9
shower room	7-9
Toilet	8-10
Laundry (household)	7
Walk-in closet	1,5
Pantry	1
Garage	4-8
Cellar	4-6
Industrial
Industrial and large spaces	Air exchange rate
Theatre, cinema hall, conference hall	20-40 m3 per person
office space	5-7
Bank	2-4
A restaurant	8-10
Bar, Cafe, beer hall, billiard room	9-11
Kitchen area in a cafe, restaurant	10-15
Supermarket	1,5-3
Pharmacy (shopping room)	3
Garage and car repair shop	6-8
Toilet (public)	10-12 (or 100 m 3 per toilet bowl)
Dance hall, disco	8-10
Smoking room	10
Server	5-10
Gym	not less than 80 m 3 per 1 student and not less than 20 m 3 per 1 spectator
Hairdressing salon (up to 5 workplaces)	2
Hairdresser (more than 5 jobs)	3
Warehouse	1-2
Laundry	10-13
Swimming pool	10-20
Industrial dyeing plant	25-40
mechanical workshop	3-5
Classroom	3-8

Calculation algorithm The air velocity in the duct is determined taking into account all the above conditions, the technical data are specified by the customer in the assignment for the design and installation of ventilation systems. The main criterion in calculating the flow rate is the exchange rate. All further approvals are made by changing the shape and cross-section of the air ducts. The flow rate depending on the speed and diameter of the duct can be taken from the table.

Table 5. Air consumption depending on the flow rate and duct diameter.

Self-calculation

For example, in a room with a volume of 20 m 3, according to the requirements for effective ventilation, it is necessary to provide a three-time air change. This means that in one hour at least L = 20 m 3 × 3 = 60 m 3 must pass through the duct. The formula for calculating the flow rate is V= L / 3600× S, where:

V is the air flow velocity in m/s;

L - air consumption in m 3 / h;

S - cross-sectional area of ​​​​air ducts in m 2.

Take a round duct Ø 400 mm, the cross-sectional area is:

In our example, S \u003d (3.14 × 0.4 2 m) / 4 \u003d 0.1256 m 2. Accordingly, to ensure the required air exchange rate (60 m 3 / h) in a round duct Ø 400 mm (S \u003d 0.1256 m 3), the air flow rate is: V \u003d 60 / (3600 × 0.1256) ≈ 0.13 m/s.

Using the same formula, at a predetermined speed, you can calculate the volume of air moving through the ducts per unit time.

L \u003d 3600 × S (m 3) × V (m / s). Volume (flow) is obtained in square meters.

As already described earlier, the noise indicators of ventilation systems also depend on the air speed. To minimize the negative impact of this phenomenon, engineers made calculations of the maximum allowable air speeds for various rooms.

The same algorithm is used to determine the air velocity in the air duct when calculating the heat supply, set tolerance fields to minimize losses for the maintenance of buildings in the winter period, and select fans by power. Air flow data is also required to reduce pressure losses, which improves the efficiency of ventilation systems and reduces electrical energy consumption.

The calculation is performed for each individual section, taking into account the data obtained, the parameters of the main highways are selected in terms of diameter and geometry. They must have time to pass the pumped air from all individual rooms. The diameter of the air ducts is chosen in such a way as to minimize noise and resistance losses. For calculations of the kinematic scheme, all three indicators of the ventilation system are important: the maximum volume of injected / removed air, the speed of movement of air masses and the diameter of the air ducts. Works on the calculation of ventilation systems are classified as complex from an engineering point of view, they can only be performed by professional specialists with special education.

To ensure constant values ​​of air velocity in channels with different sections, the following formulas are used:

After calculation, the nearest values ​​of standard pipelines are taken as the final data. Due to this, the installation time of the equipment is reduced and the process of its periodic maintenance and repair is simplified. Another plus is the reduction in the estimated cost of the ventilation system.

For air heating of residential and industrial premises, the speeds are regulated taking into account the temperature of the coolant at the inlet and outlet, for a uniform dissipation of the flow of warm air, the installation scheme and dimensions of the ventilation grilles are thought out. Modern air heating systems provide for the possibility of automatic adjustment of the speed and direction of flows. The air temperature cannot exceed +50°C at the outlet, the distance to the workplace is at least 1.5 m. The air mass supply rate is normalized by the current state standards and industry acts.

During calculations, at the request of customers, the possibility of installing additional branches can be taken into account; for this purpose, a margin of equipment productivity and channel bandwidth is provided. The flow rates are calculated in such a way that, after increasing the power of the ventilation systems, they do not create an additional sound load on the people present in the room.

The choice of diameters is carried out from the minimum acceptable, the smaller the dimensions - the more universal the ventilation system, the cheaper its manufacture and installation. Local suction systems are calculated separately, they can work both offline and connected to existing ventilation systems.

State regulations establish recommended travel speeds depending on the location and purpose of the air ducts. When calculating, you must adhere to these parameters.

Type and location of the air duct and grille	Ventilation
	Natural	Mechanical
Air inlet shutters	0,5-1,0	2,0-4,0
Supply mine channels	1,0-2,0	2,0-6,0
Horizontal collection channels	0,5-1,0	2,0-5,0
Vertical channels	0,5-1,0	2,0-5,0
Supply grilles near the floor	0,2-0,5	0,2-0,5
Ceiling grills	0,5-1,0	1,0-3,0
Exhaust grilles	0,5-1,0	1,5-3,0
exhaust shafts	1,0-1,5	3,0-6,0

Indoor air cannot move at a speed of more than 0.3 m / s, a short-term excess of the parameter is allowed no more than 30%. If there are two systems in the room, then the air velocity in each of them must provide at least 50% of the calculated volume of air supply or removal.

Fire organizations put forward their requirements for the speed of movement of air masses in air ducts, depending on the category of the room and the characteristics of the technological process. The regulations aim to reduce the rate at which smoke or fire spreads through air ducts. If necessary, valves and shut-off valves should be installed on ventilation systems. Device activation occurs after a sensor signal or is performed manually by a responsible person. Only certain groups of rooms can be connected to one ventilation system.

During the cold period of time in heated buildings, the air temperature as a result of the functioning of the ventilation system cannot fall below the normalized ones. The normalized temperature is provided before the start of the work shift. In the warm period of time, these requirements are not relevant. The movement of air masses should not worsen the standards provided for by SanPin 2.1.2.2645. To achieve the desired results, during the design of systems, the diameter of the ducts, the power and number of fans and flow rates are changed.

The accepted design data on the parameters of movement in the air ducts should provide:

1. Fulfillment of microclimate parameters in the premises, maintenance of air quality within the regulated limits. At the same time, measures are taken to reduce unproductive heat losses. The data is taken both from existing regulatory documents and from the technical specifications of customers.
2. The speed of movement of air masses in the working areas should not cause drafts, ensure acceptable comfort in the room. Mechanical ventilation is provided only in cases where it is impossible to achieve the desired results due to natural ventilation. In addition, mechanical ventilation must be installed in workshops with harmful working conditions.

During the calculation of air movement indicators in systems with natural ventilation, the average annual value of the difference in the density of indoor and outdoor air is taken. The minimum actual performance data should provide acceptable standard values ​​for the air exchange rate.

The possible concentration of indoor air contaminated with dust, water vapor and gases, products of thermal processing of food, forces the installation of ventilation systems. For these systems to be effective, serious calculations have to be made, including the calculation of the area of ​​\u200b\u200bair ducts.

Having found out a number of characteristics of the facility under construction, including the area and volume of individual premises, the features of their operation and the number of people who will be there, specialists, using a special formula, can establish the design ventilation performance. After that, it becomes possible to calculate the cross-sectional area of ​​\u200b\u200bthe duct, which will provide the optimal level of ventilation of the interior.

Why do you need to know about the area of ​​​​air ducts?

Ventilation of premises is a rather complex system. One of the most important parts of the air distribution network is a complex of air ducts. Not only the correct location in the room or cost savings depends on the qualitative calculation of its configuration and working area (both the pipe and the total material necessary for the manufacture of the air duct), but most importantly, the optimal ventilation parameters that guarantee a person comfortable living conditions.

Figure 1. Formula for determining the diameter of the working line.

In particular, it is necessary to calculate the area in such a way that the result is a structure that can pass the required volume of air while meeting other requirements for modern ventilation systems. It should be understood that the correct calculation of the area leads to the elimination of air pressure losses, compliance with sanitary standards for the speed and noise level of the air flowing through the duct channels.

At the same time, an accurate idea of ​​the area occupied by the pipes makes it possible, when designing, to allocate the most suitable place in the room for the ventilation system.

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How to calculate the area of ​​​​the material used?

The calculation of the optimal duct area is directly dependent on factors such as the volume of air supplied to one or more rooms, its speed and air pressure loss.

At the same time, the calculation of the amount of material required for its manufacture depends both on the cross-sectional area (dimensions of the ventilation duct), and on the number of rooms into which fresh air must be injected, and on the design features of the ventilation system.

When calculating the size of the cross section, it should be borne in mind that the larger it is, the lower will be the speed of air passing through the duct pipes.

At the same time, there will be less aerodynamic noise in such a highway, and the operation of forced ventilation systems will require less electricity. To calculate the area of ​​​​air ducts, you must apply a special formula.

To calculate the total area of ​​the material that must be taken for the assembly of air ducts, you need to know the configuration and basic dimensions of the system being designed. In particular, for the calculation of round air distribution pipes, such quantities as the diameter and the total length of the entire line will be required. At the same time, the amount of material used for rectangular structures is calculated based on the width, height and total length of the duct.

In the general calculations of the material requirement for the entire line, bends and half-bends of various configurations must also be taken into account. So, the correct calculations of a round element are impossible without knowing its diameter and angle of rotation. Components such as the width, height and angle of rotation of the elbow are involved in calculating the material area for a rectangular bend.

It is worth noting that for each such calculation, its own formula is used. Most often, pipes and fittings are made of galvanized steel in accordance with the technical requirements of SNiP 41-01-2003 (Appendix H).

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Calculating the area of ​​ducts

The size of the ventilation pipe is affected by such characteristics as the array of air injected into the premises, the speed of the flow and the level of its pressure on the walls and other elements of the line.

It is enough, without calculating all the consequences, to reduce the diameter of the line, as the speed of the air flow will immediately increase, which will lead to an increase in pressure along the entire length of the system and in places of resistance. In addition to the appearance of excessive noise and unpleasant vibration of the pipe, electric ones will also record an increase in electricity consumption.

However, it is not always possible and necessary to increase the cross section of the ventilation line in the pursuit of eliminating these shortcomings. First of all, this can be prevented by the limited dimensions of the premises. Therefore, you should especially carefully approach the process of calculating the area of ​​\u200b\u200bthe pipe.

To determine this parameter, you must apply the following special formula:

Sc \u003d L x 2.778 / V, where

Sc is the calculated channel area (cm 2);

L is the flow rate of air moving through the pipe (m 3 / hour);

V is the speed of air movement along the ventilation line (m/s);

2.778 is the coefficient of matching of different dimensions (for example, meters and centimeters).

The result of the calculations - the estimated area of ​​the pipe - is expressed in square centimeters, since in these units of measurement it is considered by experts as the most convenient for analysis.

In addition to the estimated cross-sectional area of ​​the pipeline, it is important to establish the actual cross-sectional area of ​​the pipe. In this case, it should be borne in mind that for each of the main cross-sectional profiles - round and rectangular - its own separate calculation scheme is adopted. So, to fix the actual area of ​​a circular pipeline, the following special formula is used:

S \u003d π x D 2 / 400, where

S - actual duct cross section (cm 2);

D is the diameter of the air pipe (mm).

To calculate the actual cross-sectional area of ​​a rectangular configuration, the following formula is used:

S = A x B / 100, where

S - actual rectangular area (cm 2);

A - width of the air line (mm);

B is the height of the air line (mm).

It should be borne in mind that the calculations of the actual cross-sectional area are made separately - for a common main channel and for each branch in the direction of different rooms.