How to choose the section of the duct. Calculation of air ducts. How to make the correct calculation of the area of ​​​​air ducts Calculation of duct ventilation online

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 the air ducts are known (their length, cross section, air friction coefficient 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, according to 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
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
Stock	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.

According to the same algorithm, the air velocity in the duct is determined when calculating the heat supply, tolerance fields are set to minimize losses for the maintenance of buildings in the winter period, and fans are selected 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 own 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 task of organized air exchange in the rooms of a residential building or apartment is to remove excess moisture and exhaust gases, replacing them with fresh air. Accordingly, for the exhaust and inflow device, it is necessary to determine the amount of air masses to be removed - to calculate the ventilation separately for each room. Calculation methods and air flow rates are accepted exclusively according to SNiP.

Sanitary requirements of regulatory documents

The minimum amount of air supplied to and removed from the cottage rooms by the ventilation system is regulated by two main documents:

1. "Residential multi-apartment buildings" - SNiP 31-01-2003, paragraph 9.
2. "Heating, ventilation and air conditioning" - SP 60.13330.2012, mandatory Appendix "K".

The first document sets out the sanitary and hygienic requirements for air exchange in residential premises of apartment buildings. On these data, the calculation of ventilation should be based. 2 types of dimensions are used - air mass flow rate by volume per unit of time (m³ / h) and hourly multiplicity.

Reference. The air exchange rate is expressed as a figure indicating how many times within 1 hour the air environment of the room is completely updated.

Ventilation is a primitive way to renew oxygen in a home.

Depending on the purpose of the room, supply and exhaust ventilation should provide the following flow rate or the number of updates of the air mixture (multiplicity):

• living room, nursery, bedroom - 1 time per hour;
• kitchen with electric stove - 60 m³/h;
• bathroom, bathroom, toilet - 25 m³ / h;
• for and a kitchen with a gas stove, a multiplicity of 1 plus 100 m³ / h is required during the operation of the equipment;
• , burning natural gas - three times the renewal plus the volume of air required for combustion;
• pantry, dressing room and other utility rooms - multiplicity 0.2;
• drying or laundry room - 90 m³ / h;
• library, office - 0.5 times per hour.

Note. SNiP provides for a reduction in the load on general ventilation when the equipment is not working or there are no people. In residential premises, the multiplicity decreases to 0.2, technical - to 0.5. The requirement for rooms where gas-using installations are located remains unchanged - an hourly one-time renewal of the air environment.

The emission of harmful gases due to natural draft is the cheapest and easiest way to renew the air

Clause 9 of the document implies that the volume of the extract is equal to the amount of inflow. The requirements of SP 60.13330.2012 are somewhat simpler and depend on the number of people in the room for 2 hours or more:

1. If 1 resident has 20 m² or more of the area of ​​​​the apartment, a fresh influx of 30 m³ / h per 1 person is provided to the rooms.
2. The volume of supply air is calculated by area when there are less than 20 squares per 1 tenant. The ratio is as follows: 3 m³ of inflow is supplied per 1 m² of housing.
3. If the apartment does not provide for ventilation (there are no vents and opening windows), 60 m³ / h of a clean mixture must be applied to each resident, regardless of the quadrature.

The listed normative requirements of two different documents do not contradict each other at all. Initially, the performance of the ventilation general exchange system is calculated according to SNiP 31-01-2003 "Residential buildings".

The results are checked against the requirements of the Code of Rules "Ventilation and Air Conditioning" and, if necessary, corrected. Below we will analyze the calculation algorithm using the example of a one-story house shown in the drawing.

Determination of air consumption by multiplicity

This typical calculation of supply and exhaust ventilation is performed separately for each room of an apartment or a country cottage. To find out the flow of air masses in the building as a whole, the results obtained are summarized. A fairly simple formula is used:

Explanation of designations:

• L is the desired volume of supply and exhaust air, m³/h;
• S is the quadrature of the room where ventilation is calculated, m²;
• h - ceiling height, m;
• n is the number of room air updates within 1 hour (regulated by SNiP).

Calculation example. The area of ​​the living room of a one-story building with a ceiling height of 3 m is 15.75 m². According to the requirements of SNiP 31-01-2003, the multiplicity n for residential premises is equal to one. Then the hourly flow rate of the air mixture will be L = 15.75 x 3 x 1 = 47.25 m³/h.

An important point. Determination of the volume of air mixture removed from the kitchen with a gas stove depends on the installed ventilation equipment. A common scheme looks like this: a single exchange according to the standards is provided by a natural ventilation system, and an additional 100 m³ / h is emitted by a household one.

Similar calculations are made for all other rooms, a scheme for organizing air exchange (natural or forced) is developed and the dimensions of the ventilation ducts are determined (see the example below). A calculation program will help automate and speed up the process.

Online calculator to help

The program calculates the required amount of air according to the multiplicity regulated by SNiP. Just select the type of room and enter its dimensions.

Ventilation plays an important role in creating an optimal microclimate in the home. A properly designed ventilation system ensures the removal of polluted air, harmful gases, vapors and dust outside the premises, which affect the health of people in a residential area. When designing ventilation systems, a huge number of calculations are made, which take into account many factors and variables.

Air ducts play an important role in the performance of the ventilation system, namely their length, cross section and shape. It is extremely important that the calculation of the cross-section of the air ducts be made correctly, since it will depend on this whether the air duct system can pass a sufficient amount of air, the air flow rate and the uninterrupted operation of the ventilation system as a whole. Thanks to a competent calculation of the area of ​​​​air channels, vibration and aerodynamic noise produced by air flows will be within the acceptable range.

• Turn to professionals. The calculation will be made qualitatively, but expensive.
• Make an independent calculation using the formulas for calculating specific air losses, gravity backwater, cross-section of air ducts, the formula for the speed of air masses in gas ducts, determining friction and resistance losses.
• Use the online calculator.

Calculation of the duct section

On this page, using a special calculator, you can make a calculation based on the parameters you set: type, dimensions, thickness of steel. Enter the height, width and length or diameter of the duct (in millimeters), metal thickness (in millimeters).

The calculator will calculate the approximate price of the product with the specified parameters.

Calculation of the cost of rectangular ducts

results

Calculation of the cost of round ducts

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Pricing

The company "VentSystems" pursues a flexible pricing policy aimed at maintaining the minimum selling price of products for customers. Several factors contribute to this. Firstly, the company sells goods of its own production - all goods are made in their own workshops. Therefore, there are no intermediaries and additional monetary markups. Secondly, all work is carried out on modern high-performance equipment that can produce large volumes in a short period. Such technologies make the production process fast and economical, since even the largest orders do not take so much time to complete.

An important factor for pricing is the supply of raw materials. The material for air ducts and fittings is high-quality sheet steel. It is purchased and delivered to the VentSystems plant regularly and in large volumes from the country's leading suppliers. Long-term contracts with sheet steel manufacturers, long-term cooperation and optimal delivery conditions can significantly reduce costs, which favorably affects the cost of production.

The company's management has built and optimized the process of production and sale of goods in such a way as to exclude causes and sources that could unnecessarily increase the cost of products. All functions and tasks are solved using our own resources without involving additional parties. This makes it possible to confidently maintain a balance between the quality of the proposed ventilation products and their affordable cost. Studies show that there are many offers on the market for similar products with prices significantly higher than those presented by us. The opposite problem is cheap air ducts of dubious quality. The VentSystems company is far from both extremes and offers reliable products that meet all standards at reasonable prices.

Special conditions

For all customers, it is possible to discuss individual terms of cooperation. Regular customers have special discounts and offers. In addition, special conditions for the form and terms of payment may apply to individual orders. Large orders can be paid in installments. All organizational issues can be discussed directly with the management of the enterprise. Enterprise "VentSystems" is always ready for any constructive proposals and is interested in fruitful cooperation with all contractors.

The company's management invites representatives of organizations and interested parties to visit the production complex, inspect the plant's workshops, get acquainted with product samples and negotiate with the management. The office and production complex are located in the village of Yam, Domodedovo district, Moscow region.

Comments:

• Why do you need to know about the area of ​​​​air ducts?
• How to calculate the area of ​​​​the material used?
• Calculating the area of ​​ducts

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 rooms, 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 complicated 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 amount 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 - 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 - 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.

In order for the air exchange in the house to be “correct”, an aerodynamic calculation of the air ducts is needed even at the stage of drawing up a ventilation project.

Air masses moving through the channels of the ventilation system are taken as an incompressible liquid during calculations. And this is quite acceptable, because too much pressure is not formed in the air ducts. In fact, pressure is formed as a result of air friction against the walls of the channels, and even when resistances of a local nature appear (these include it - pressure - jumps at places where the direction changes, when connecting / disconnecting air flows, in areas where control devices or where the diameter of the ventilation duct changes).

Note! The concept of aerodynamic calculation includes the determination of the cross section of each section of the ventilation network that provides the movement of air flows. Moreover, the injection resulting from these movements is also determined.

In accordance with many years of experience, we can safely say that sometimes some of these indicators are already known during the calculation. The following are situations that are often encountered in such cases.

1. The cross-sectional index of the cross channels in the ventilation system is already known, it is required to determine the pressure that may be required in order for the desired amount of gas to move. This often happens in those air conditioning lines where the sectional dimensions were based on characteristics of a technical or architectural nature.
2. We already know the pressure, but we need to determine the cross section of the network to provide the ventilated room with the required amount of oxygen. This situation is inherent in natural ventilation networks, in which the already existing pressure cannot be changed.
3. It is not known about any of the indicators, therefore, we need to determine both the pressure in the line and the cross section. This situation occurs in most cases in the construction of houses.

Features of aerodynamic calculations

Let us get acquainted with the general procedure for carrying out such calculations, provided that both the cross section and the pressure are unknown to us. Let's make a reservation right away that the aerodynamic calculation should be carried out only after the required volumes of air masses have been determined (they will pass through the air conditioning system) and the approximate location of each of the air ducts in the network has been designed.

And in order to carry out the calculation, it is necessary to draw an axonometric diagram, in which there will be a list of all network elements, as well as their exact dimensions. In accordance with the plan of the ventilation system, the total length of the air ducts is calculated. After that, the entire system should be divided into segments with homogeneous characteristics, according to which (only separately!) The air flow will be determined. What is typical, for each of the homogeneous sections of the system, a separate aerodynamic calculation of the air ducts should be carried out, because each of them has its own speed of movement of air flows, as well as a permanent flow rate. All the indicators obtained must be entered into the axonometric scheme already mentioned above, and then, as you probably already guessed, you need to select the main highway.

How to determine the speed in the ventilation ducts?

As can be judged from all that has been said above, it is necessary to choose as the main highway that chain of successive segments of the network that is the longest; in this case, the numbering should begin exclusively from the most remote section. As for the parameters of each of the sections (and these include air flow, section length, its serial number, etc.), they should also be entered in the calculation table. Then, when the introduction is finished, the cross-sectional shape is selected and its - sections - dimensions are determined.

LP/VT=FP.

What do these abbreviations stand for? Let's try to figure it out. So in our formula:

• LP is the specific air flow in the selected area;
• VT is the speed at which the air masses move through this area (measured in meters per second);
• FP - this is the cross-sectional area of ​​​​the channel we need.

Tellingly, when determining the speed of movement, it is necessary to be guided, first of all, by considerations of economy and noise of the entire ventilation network.

Note! According to the indicator obtained in this way (we are talking about the cross section), it is necessary to select an air duct with standard values, and its actual cross section (indicated by the abbreviation FF) should be as close as possible to the previously calculated one.

LP/ FФ = VФ.

Having received the indicator of the required speed, it is necessary to calculate how much the pressure in the system will decrease due to friction against the walls of the channels (for this, you need to use a special table). As for the local resistance for each of the sections, they should be calculated separately, and then summarized into a general indicator. Then, by summing up the local resistance and the losses due to friction, you can get the total loss in the air conditioning system. In the future, this value will be used to calculate the required amount of gas masses in the ventilation ducts.

Air heating unit

Earlier we talked about what an air-heating unit is, talked about its advantages and areas of application, in addition to this article, we advise you to familiarize yourself with this information

How to calculate the pressure in the ventilation network

In order to determine the expected pressure for each individual section, you must use the formula below:

H x g (PH - PB) \u003d DPE.

Now let's try to figure out what each of these abbreviations means. So:

• H in this case denotes the difference in the marks of the mine mouth and the intake grate;
• РВ and РН is an indicator of gas density, both outside and inside the ventilation network, respectively (measured in kilograms per cubic meter);
• Finally, DPE is a measure of what the natural available pressure should be.

We continue to disassemble the aerodynamic calculation of air ducts. To determine the internal and external density, it is necessary to use a reference table, and the temperature indicator inside / outside must also be taken into account. As a rule, the standard temperature outside is taken as plus 5 degrees, and regardless of in which particular region of the country construction work is planned. And if the temperature outside is lower, then as a result the injection into the ventilation system will increase, due to which, in turn, the volumes of incoming air masses will be exceeded. And if the temperature outside, on the contrary, is higher, then the pressure in the line will decrease because of this, although this trouble, by the way, can be completely compensated by opening the vents / windows.

As for the main task of any described calculation, it consists in choosing such air ducts, where the losses on the segments (we are talking about the value? (R * l *? + Z)) will be lower than the current DPE indicator, or, alternatively, at least equal to him. For greater clarity, we present the moment described above in the form of a small formula:

DPE? ?(R*l*?+Z).

Now let's take a closer look at what the abbreviations used in this formula mean. Let's start from the end:

• Z in this case is an indicator indicating a decrease in the speed of air movement due to local resistance;
• ? - this is the value, more precisely, the coefficient of what is the roughness of the walls in the line;
• l is another simple value that indicates the length of the selected section (measured in meters);
• finally, R is an indicator of friction losses (measured in pascals per meter).

Well, we figured it out, now let's find out a little more about the roughness index (that is?). This indicator depends only on what materials were used in the manufacture of channels. It is worth noting that the speed of air movement can also be different, so this indicator should also be taken into account.

Speed ​​- 0.4 meters per second

In this case, the roughness index will be as follows:

• for plaster with the use of reinforcing mesh - 1.48;
• for slag gypsum - about 1.08;
• for an ordinary brick - 1.25;
• and for cinder concrete, respectively, 1.11.

Speed ​​- 0.8 meters per second

Here, the described indicators will look like this:

• for plaster with the use of reinforcing mesh - 1.69;
• for slag gypsum - 1.13;
• for ordinary brick - 1.40;
• finally, for slag concrete - 1.19.

Let's slightly increase the speed of the air masses.

Speed ​​- 1.20 meters per second

For this value, the roughness indicators will be as follows:

• for plaster with the use of reinforcing mesh - 1.84;
• for slag gypsum - 1.18;
• for an ordinary brick - 1.50;
• and, consequently, for slag concrete - somewhere around 1.31.

And the last indicator of speed.

Speed ​​- 1.60 meters per second

Here the situation will look like this:

• for plaster using a reinforcing mesh, the roughness will be 1.95;
• for slag gypsum - 1.22;
• for ordinary brick - 1.58;
• and, finally, for slag concrete - 1.31.

Note! We figured out the roughness, but it is worth noting one more important point: in this case, it is desirable to take into account a small margin, fluctuating within ten to fifteen percent.

We deal with the general ventilation calculation

When making an aerodynamic calculation of air ducts, you must take into account all the characteristics of the ventilation shaft (these characteristics are listed below).

1. Dynamic pressure (to determine it, the formula is used - DPE? / 2 \u003d P).
2. The flow of air masses (it is denoted by the letter L and is measured in cubic meters per hour).
3. Pressure loss due to friction of air against the internal walls (denoted by the letter R, measured in pascals per meter).
4. Air duct diameter (to calculate this indicator, the following formula is used: 2 * a * b / (a ​​+ b); in this formula, the values ​​\u200b\u200bof a, b are the dimensions of the cross section of the channels and are measured in millimeters).
5. Finally, speed is V, measured in meters per second, as we mentioned earlier.

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As for the actual sequence of actions in the calculation, it should look something like this.

Step one. First, the required channel area should be determined, for which the following formula is used:

I/(3600xVpek) = F.

Understanding the meanings:

• F in this case is, of course, the area, which is measured in square meters;
• Vpek is the desired speed of air movement, which is measured in meters per second (for channels, a speed of 0.5-1.0 meters per second is taken, for mines - about 1.5 meters).

Step three. The next step is to determine the appropriate duct diameter (indicated by the letter d).

Step four. Then the remaining indicators are determined: pressure (denoted as P), speed of movement (abbreviated as V) and, therefore, decrease (abbreviated as R). For this, it is necessary to use nomograms according to d and L, as well as the corresponding tables of coefficients.

Step five. Using already other tables of coefficients (we are talking about indicators of local resistance), it is required to determine how much the effect of air will decrease due to local resistance Z.

Step six. At the last stage of calculations, it is necessary to determine the total losses in each individual section of the ventilation line.

Pay attention to one important point! So, if the total losses are below the already existing pressure, then such a ventilation system can be considered effective. But if the losses exceed the pressure indicator, then it may be necessary to install a special throttle diaphragm in the ventilation system. Thanks to this diaphragm, excess pressure will be extinguished.

We also note that if the ventilation system is designed to serve several rooms at once, for which the air pressure must be different, then during the calculation it is necessary to take into account the underpressure or back pressure indicator, which must be added to the total loss indicator.

Video - How to make calculations using the program "VIKS-STUDIO"

Aerodynamic calculation of air ducts is considered a mandatory procedure, an important component of planning ventilation systems. Thanks to this calculation, you can find out how efficiently the premises are ventilated with a particular section of the channels. And the effective functioning of ventilation, in turn, ensures the maximum comfort of your stay in the house.

Calculation example. The conditions in this case are as follows: an administrative building, has three floors.

Although there are many programs for it, many parameters are still defined the old fashioned way, using formulas. The calculation of the ventilation load, area, power and parameters of individual elements is carried out after drawing up the diagram and distributing the equipment.

This is a difficult task that only professionals can do. But if you need to calculate the area of ​​some ventilation elements or the cross section of air ducts for a small cottage, you can really do it yourself.

Air exchange calculation

If there are no toxic emissions in the room or their volume is within acceptable limits, air exchange or ventilation load is calculated by the formula:

R= n * R1,

here R1- air requirement of one employee, in cubic meters per hour, n- the number of permanent employees in the premises.

If the volume of the room per employee is more than 40 cubic meters and natural ventilation is working, it is not necessary to calculate the air exchange.

For domestic, sanitary and auxiliary premises, the calculation of ventilation by hazards is carried out on the basis of the approved norms of the air exchange rate:

• for administrative buildings (hood) - 1.5;
• halls (serving) - 2;
• conference rooms for up to 100 people with a capacity (for supply and exhaust) - 3;
• rest rooms: supply 5, extract 4.

For industrial premises in which hazardous substances are constantly or periodically released into the air, ventilation is calculated according to hazards.

Air exchange by hazards (vapors and gases) is determined by the formula:

Q= K\(k2- k1),

here To- the amount of steam or gas appearing in the building, in mg / h, k2- the content of steam or gas in the outflow, usually the value is equal to the MPC, k1- the content of gas or steam in the inflow.

The concentration of hazards in the inflow is allowed up to 1/3 of the MPC.

For rooms with the release of excess heat, air exchange is calculated by the formula:

Q= Ghut\c(tyx - tn),

here Gib- excess heat drawn to the outside, measured in W, with- specific heat by mass, c=1 kJ, tyx- the temperature of the air removed from the room, tn- supply temperature.

Heat Load Calculation

The calculation of the heat load on ventilation is carried out according to the formula:

Qin =Vn*k * p * CR(text -tnro),

in the formula for calculating the heat load on ventilation Vn- external volume of the building in cubic meters, k- air exchange rate, tvn- the temperature in the building is average, in degrees Celsius, tnro- outside air temperature used in heating calculations, in degrees Celsius, R- air density, in kg / cubic meter, Wed- heat capacity of air, in kJ \ cubic meter Celsius.

If the air temperature is lower tnro the air exchange rate decreases, and the heat consumption indicator is considered equal to Qv, a constant value.

If, when calculating the heat load on ventilation, it is impossible to reduce the air exchange rate, the heat consumption is calculated from the heating temperature.

Heat consumption for ventilation

The specific annual heat consumption for ventilation is calculated as follows:

Q=*b*(1-E),

in the formula for calculating the heat consumption for ventilation Qo- total heat loss of the building during the heating season, Qb- household heat inputs, Qs- heat input from outside (sun), n- coefficient of thermal inertia of walls and ceilings, E- reduction factor. For individual heating systems 0,15 , for central 0,1 , b- heat loss coefficient:

• 1,11 - for tower buildings;
• 1,13 - for multi-section and multi-access buildings;
• 1,07 - for buildings with warm attics and cellars.

Calculation of duct diameter

Diameters and sections are calculated after the general scheme of the system is drawn up. When calculating the diameters of ventilation ducts, the following indicators are taken into account:

• Air volume (supply or exhaust), which must pass through the pipe for a given period of time, cubic meters per hour;
• The speed of air movement. If, when calculating the ventilation pipes, the flow rate is underestimated, air ducts of too large a section will be installed, which entails additional costs. Excessive speed leads to the appearance of vibrations, increased aerodynamic hum and increased equipment power. The speed of movement on the inflow is 1.5 - 8 m / s, it varies depending on the site;
• Ventilation pipe material. When calculating the diameter, this indicator affects the resistance of the walls. For example, black steel with rough walls has the highest resistance. Therefore, the calculated diameter of the ventilation duct will have to be slightly increased compared to the norms for plastic or stainless steel.

Table 1. Optimum air flow rate in ventilation pipes.

When the throughput of future air ducts is known, it is possible to calculate the cross section of the ventilation duct:

S= R\3600 v,

here v- the speed of the air flow, in m / s, R- air consumption, cubic meters \ h.

The number 3600 is a time factor.

here: D- diameter of the ventilation pipe, m.

Calculation of the area of ​​ventilation elements

The calculation of the ventilation area is necessary when the elements are made of sheet metal and it is necessary to determine the quantity and cost of the material.

The ventilation area is calculated by electronic calculators or special programs, which can be found in many on the Internet.

We will give several tabular values ​​​​of the most popular ventilation elements.

Diameter, mm	Length, m
	1	1,5	2	2,5
100	0,3	0,5	0,6	0,8
125	0,4	0,6	0,8	1
160	0,5	0,8	1	1,3
200	0,6	0,9	1,3	1,6
250	0,8	1,2	1,6	2
280	0,9	1,3	1,8	2,2
315	1	1,5	2	2,5

table 2. The area of ​​straight circular ducts.

The value of the area in square meters. at the intersection of the horizontal and vertical lines.

Diameter, mm		Angle, degrees
	15	30	45	60	90
100	0,04	0,05	0,06	0,06	0,08
125	0,05	0,06	0,08	0,09	0,12
160	0,07	0,09	0,11	0,13	0,18
200	0,1	0,13	0,16	0,19	0,26
250	0,13	0,18	0,23	0,28	0,39
280	0,15	0,22	0,28	0,35	0,47
315	0,18	0,26	0,34	0,42	0,59

Table 3. Calculation of the area of ​​bends and semi-branches of circular cross section.

Calculation of diffusers and grilles

Diffusers are used to supply or remove air from a room. The purity and temperature of the air in every corner of the room depends on the correct calculation of the number and location of ventilation diffusers. If you install more diffusers, the pressure in the system will increase, and the speed will decrease.

The number of ventilation diffusers is calculated as follows:

N= R\(2820 * v *D*D),

here R- throughput, in cubic meters / hour, v- air speed, m/s, D- diameter of one diffuser in meters.

The number of ventilation grilles can be calculated using the formula:

N= R\(3600 * v * S),

here R- air consumption in cubic meters per hour, v- air velocity in the system, m/s, S- cross-sectional area of ​​one lattice, sq.m.

Calculation of the duct heater

The calculation of the electrical type ventilation heater is as follows:

P= v * 0,36 * ∆ T

here v- the volume of air passed through the heater in cubic meters / hour, ∆T- the difference between the air temperature outside and inside, which must be provided to the heater.

This indicator varies between 10 - 20, the exact figure is set by the client.

The calculation of the heater for ventilation begins with the calculation of the frontal cross-sectional area:

Af=R * p\3600 * vp,

here R- inflow flow rate, cubic meters per hour, p- density of atmospheric air, kg\cubic meters, vp- mass air velocity in the area.

The section size is necessary to determine the dimensions of the ventilation heater. If, according to the calculation, the cross-sectional area turns out to be too large, it is necessary to consider the option of a cascade of heat exchangers with a total calculated area.

The mass velocity index is determined through the frontal area of ​​the heat exchangers:

vp= R * p\3600 * Af. fact

For further calculation of the ventilation heater, we determine the amount of heat required to warm the air flow:

Q=0,278 * W * c (TP-Ty),

here W- consumption of warm air, kg / hour, Tp- supply air temperature, degrees Celsius, That- outdoor air temperature, degrees Celsius, c- specific heat capacity of air, constant value 1.005.

To create a favorable microclimate in industrial and residential premises, it is necessary to install a high-quality ventilation system. Particular attention must be paid to the length and diameter of the pipe for natural ventilation, since the efficiency, performance and reliability of air ducts depend on the correct calculations.

What are the requirements for ventilation pipes?

The main purpose of the duct for natural ventilation is to remove exhaust air from the room.

When laying systems in homes, offices and other facilities, the following points must be considered:

• the diameter of the pipe for natural ventilation must be at least 15 cm;
• when installing in residential premises and at food industry facilities, anti-corrosion characteristics are important, otherwise metal surfaces will rust under the influence of high humidity;
• the lighter the weight of the structure, the easier the installation and maintenance;
• performance also depends on the thickness of the duct, the thinner, the greater the throughput;
• fire safety level - no harmful substances should be released during combustion.

If you do not follow the standards (norms) when designing, installing and choosing the material of manufacture and the diameter of PVC ventilation pipes or galvanized steel, then the air in the rooms will be “heavy” due to high humidity and lack of oxygen. In apartments and houses with poor ventilation, windows often fog up, walls in the kitchen smoke, and fungus forms.

What material to choose an air duct?

There are several types of pipes on the market, differing from each other in the material of manufacture:

Advantages of plastic pipes:

• low cost when compared with air ducts made of other materials;
• anti-corrosion surfaces do not need additional protection or treatment;
• ease of maintenance, when cleaning, you can use any detergent;
• a large selection of PVC pipe diameters for ventilation pipes;
• simple installation, also, if necessary, the structure can be easily dismantled;
• dirt does not accumulate on the surface due to smoothness;
• when heated, there is no release of harmful and toxic substances for human health.

Metal air ducts are made of galvanized or stainless steel, when considering the characteristics, the following advantages can be distinguished:

• galvanized and stainless pipes are allowed to be used at facilities with high humidity and frequent temperature changes;
• moisture resistance - structures are not subject to the formation of corrosion and rust;
• high heat resistance;
• relatively small weight;
• easy installation - basic knowledge required.

Aluminum foil is used as a material for the manufacture of corrugated air ducts. Main advantages:

• during installation, a minimum number of connections is formed;
• ease of dismantling;
• if necessary, the pipeline is placed at any angle.

Advantages of fabric structures:

• mobility - easy to install and dismantle;
• there are no problems during transportation;
• lack of condensate under any operating conditions;
• low weight facilitates the fastening process;
• no additional insulation required.

What are the types of air ducts?

Depending on the scope and direction of use, not only the diameters of PVC pipes are selected, but also the shape:

1. Spiral forms are distinguished by increased rigidity and attractive appearance. During installation, the connections are made using a cardboard or rubber seal and flanges. Systems do not need isolation.

Advice! If there is no experience in this area, then in order to save your own money and time, it is better to immediately contact the specialists, since it will be very problematic to calculate the diameter of the pipe for ventilation, taking into account the air flow, and to carry out the installation yourself.

1. For residential buildings (country and country houses), flat forms are ideal due to the following advantages:

• if necessary, round and flat pipes can be easily combined;
• if the dimensions do not match, then the parameters are easily adjusted using a construction knife;
• structures differ in relatively small mass;
• tees and flanges are used as connecting elements.

1. Installation of flexible structures takes place without additional elements for connection (flanges, etc.), which greatly simplifies the installation process. The material used is laminated polyester film, woven fabric or aluminum foil.
2. Round air ducts are more in demand, the demand is explained by the following advantages:

• minimum number of connecting elements;
• simple operation;
• air is well distributed;
• high rates of rigidity;
• simple installation work.

The material of manufacture and the shape of the pipes are determined at the stage of development of project documentation, a large list of items is taken into account here.

How is the diameter of the ventilation pipe determined?

On the territory of Russia, there are a number of SNiP regulatory documents that say how to calculate the diameter of a pipe for natural ventilation. The choice is based on the frequency of air exchange - a determining indicator of how much and how many times per hour the air in the room is replaced.

First you need to do the following:

• the volume of each room in the building is calculated - you need to multiply the length, height and width;
• air volume is calculated by the formula: L=n (normalized air exchange rate)*V (room volume);
• the obtained indicators L are rounded up to a multiple of 5;
• the balance is drawn up so that the exhaust and supply air flows coincide in the total volume;
• the maximum speed in the central duct is also taken into account, the indicators should not be more than 5 m / s, and in the branch sections of the network not more than 3 m / s.

The diameter of PVC ventilation pipes and other materials is selected according to the data obtained from the table below:

How to determine the length of the ventilation pipe?

When writing a project, in addition to calculating the diameter of the pipe for natural ventilation, an important point is to determine the length of the outer part of the duct. The total value includes the length of all channels in the building through which air circulates and is discharged outside.

Calculations are made according to the table:

The following indicators are taken into account in the calculation:

• if a flat duct is used on a roof installation, the minimum length must be 0.5 m;
• when installing a ventilation pipe next to the flue, the height is made the same in order to prevent smoke from entering the room during the heating season.

The performance, efficiency and uninterrupted operation of the ventilation system largely depends on the correct calculations and compliance with installation requirements. It is better to choose trusted companies with a positive reputation!