Online calculation of the diameter of the exhaust ventilation pipe. Features and procedure for calculating exhaust and supply ventilation

In order for the ventilation system in the house to work effectively, it is necessary to make calculations during its design. This will allow not only the use of equipment with optimal power, but also save on the system, completely retaining all the required parameters. Conducted according to certain parameters, while for the natural and compulsory systems, completely different formulas are used. Separate attention should be paid to the fact that forced system not always required... For example, for a city apartment, natural air exchange is quite enough, but subject to certain requirements and norms.

Calculation of the size of the ducts

To calculate the ventilation of the room, it is necessary to determine what the cross-section of the pipe will be, the volume of air passing through the air ducts, and the flow rate. Such calculations are important, since the slightest mistakes lead to poor air exchange, noise of the entire air conditioning system or large cost overruns during installation, electricity for the operation of equipment that provides ventilation.

To calculate ventilation for a room, find out the area of the air duct, you must use the following formula:

Sc = L * 2.778 / V, where:

Sс is the estimated area of the channel;
L is the value of the flow rate of air passing through the channel;
V is the value of the speed of the air passing through the air duct;
2.778 is a special coefficient that is necessary for the consistency of dimensions - these are hours and seconds, meters and centimeters used when including data in the formula.

To find out what the actual area of the duct pipe will be, you need to use a formula based on the type of duct. For a pipe of a round format, the formula is applied: S = π * D² / 400, where:

S is the number for the actual cross-sectional area;
D is the number for the channel diameter;
π is a constant equal to 3.14.

For rectangular pipes, you will need the formula S = A * B / 100, where:

S is the value for the actual cross-sectional area:
A, B is the length of the sides of the rectangle.

Back to the table of contents

Correspondence of area and consumption

The pipe diameter is 100 mm, it corresponds to a rectangular duct of 80 * 90 mm, 63 * 125 mm, 63 * 140 mm. The areas of rectangular channels will be 72, 79, 88 cm². respectively. The air flow velocity can be different, the following values are usually used: 2, 3, 4, 5, 6 m / s. In this case, the air flow in a rectangular duct will be:

when moving at 2 m / s - 52-63 m³ / h;
when moving at 3 m / s - 78-95 m³ / h;
when moving at 4 m / s - 104-127 m³ / h;
at a speed of 5 m / s - 130-159 m³ / h;
at a speed of 6 m / s - 156-190 m³ / h.

If the calculation of ventilation is carried out for a round duct with a diameter of 160 mm, then rectangular air ducts of 100 * 200 mm, 90 * 250 mm with cross-sectional areas of 200 cm² and 225 cm² will correspond to it. In order for the room to be perfectly ventilated, it is required to observe the following flow rate at certain speeds of movement of air masses:

at a speed of 2 m / s - 162-184 m³ / h;
at a speed of 3 m / s - 243-276 m³ / h;
when moving at 4 m / s - 324-369 m³ / h;
when moving at 5 m / s - 405-461 m³ / h;
when moving at 6 m / s - 486-553 m³ / h.

Using such data, the question of how is solved quite simply, you just need to decide whether there is a need to use a heater.

Back to the table of contents

Calculation for air heater

A heater is an equipment designed for air conditioning a room with heated air masses. This device is used to create a more comfortable environment in the cold season. Heaters are used in a forced air conditioning system. Even at the design stage, it is important to calculate the capacity of the equipment. This is done based on the performance of the system, the difference between the outside temperature and the room temperature. The last two values are determined according to SNiPs. At the same time, it should be taken into account that air must enter the room, the temperature of which is not less than +18 ° C.

The difference between outdoor and indoor conditions is determined by taking into account the climatic zone. On average, the air heater heats the air up to 40 ° C during switching on in order to compensate for the difference between the warm indoor and outdoor cold air flow.

I = P / U, where:

I is the number for the maximum current drawn by the equipment;
P is the power of the device required for the room;
U - voltage for supplying the heater.

If the load is less than required, then the device must be chosen not so powerful. The temperature to which the air heater can heat the air is calculated using the following formula:

ΔT = 2.98 * P / L, where:

ΔT is the number of air temperature differences observed at the inlet and outlet of the air conditioning system;
Р - device power;
L is the value of the equipment productivity.

In a residential area (for apartments and private houses), the air heater can have a capacity of 1-5 kW, but for office buildings, the value is taken more - this is 5-50 kW. In some cases, electric heaters are not used, the equipment is connected here to water heating, which saves energy.

Natural ventilation of the room - is a spontaneous movement of air masses as a result of the difference in its temperature regimes in not at home and inside. This kind ventilation is divided into channelless and channel ventilation, it is relatively capable of work being continuous and periodic.

The systematic movement of transoms, vents, doors and windows implies by itself airing procedure. Channelless ventilation, formed on a stable base in industrial-type rooms with noticeable thermal emissions, organizing the required frequency of exchange of air masses in the middle of them, this process is called aeration.

In private and multi-storey buildings the natural ventilation system of the duct type is used more, the channels in which are located in upright position in specialized blocks, mines, or located in the walls themselves.

Calculation of aeration

Aeration of industrial rooms in summer ensures the flow of air through the gaps below gate and entrance doors... In cooler months, the right sizes is performed under the means of the upper gaps, from 4 m or more above the floor level. Ventilation throughout the year was carried out using shafts, deflectors and vents.

In winter, transoms are only opened in areas above the generators. increased heat emission. During the generation of excess obvious heat in the rooms of the building, then temperature regime there is always more air in it than the temperature regime outside the building, and, accordingly, the density is less.

This phenomenon leads to the presence of a difference in atmospheric pressure outside and inside rooms... In a plane at a specific height of the room, which is referred to as a plane of equal pressures, this difference is absent, that is, it is equated to zero.

Above this plane, there is some excess stress, which leads to removing the hot atmosphere to the outside, and below this plane, is the rarefaction that causes the inflow fresh air... The pressure forcing air masses to move during natural ventilation can be set based on their calculations:

Natural ventilation formula

Pe = (ext - n) hg

where n is the density of air outside, kg / m3;
vn is the density of air masses in the room, kg / m3;
h is the distance between the supply opening and the exhaust center, m;
g - acceleration due to gravity, 9.81 m / s2.

The method of ventilation (aeration) of buildings with the help of drop-down transoms is considered to be quite correct and effective.

When calculating the natural ventilation of the premises, the establishment of the area of the lower and upper gaps is taken into account. First, the value of the area of the lower lumen is obtained. The model of aeration of the building is set.

Calculation of natural exhaust ventilation

Then, in connection with the opening section of the upper and lower, respectively, supply and exhaust transoms in the room approximately in the center of the height of the structure, the degree of equal pressures is obtained, in this place the influence is also zero. In accordance, the influence in the degree of concentration of the lower lumens will become equal to:

where cp– is equal to average temperature density of air masses in the room, kg / m3;
h1 - height from the plane of equal pressures to the lower gaps, m.

At the level of the centers of the upper gaps, above the plane of equal pressures, an excess stress is formed, Pa, equal to:

It is this pressure that affects the air extraction. The total voltage available for the exchange of air flows in the room:

Natural ventilation rate

Air velocity in the center of the lower gaps, m / s:

where L is the required exchange of air masses, m3 / hour;
1 - flow coefficient, depending on the design of the flaps of the lower gaps and the angle of their opening (at 90 opening, = 0.6; 30 - = 0.32);
F1 - area of the lower gaps, m2

Then the losses, Pa, in the lower gaps are calculated:

Assuming that Pe = P1 + P2 = h (n - avg), and the temperature of the removed air tsp = trz + (10 - 15oC), we determine the densities n and av, which correspond to the temperatures tn and tav.

Excess pressure in the plane of the upper lumens:

Their required area (m2):

F2 = L / (2V22) = L / (2 (2P2g / sr) 1⁄2)

Calculation and calculation of ventilation ducts

Calculation of the natural ventilation system of the duct type approaches the establishment of an active section of air ducts, which, in order to access the required amount of air, express a reaction corresponding to the calculated voltage.

For the longest network path, the voltage cost in the duct channels is set as the sum of the voltage cost in absolutely all its places. In each of them, the pressure costs are formed from the friction losses (RI) and the costs in the counteraction points (Z):

where R is the specific stress loss along the length of the section from friction, Pa / m;
l - section length, m.

Air duct area, m2:

where L is the air flow rate, m3 / h;
v - speed of air movement in the duct, m / s (equal to 0.5 ... 1.0 m / s).

Setting the speed of air movement through the ventilation, and read the area of its active section and scale. With the help of specialized nomograms or tabular calculations for the rounded shape of the air ducts, the cost of friction stress is established.

Natural ventilation calculation of air ducts

For rectangular ducts of this ventilation concept, the diameter dE is planned in equilibrium with the rounded duct:

dЭ = 2 а b / (а + b)

where, a and b are the length of the sides of the rectangular duct, m.

In the case of using air ducts not made of metal, their unit friction pressure costs R, taken from the nomogram for steel air ducts, are changed by multiplying by the corresponding coefficient k:

for slag gypsum - 1.1;
for slag concrete - 1.15;
for brick - 1.3.

Excess pressure, Pa, to overcome certain resistances for different sections is calculated by the equation:

where is the sum of the reaction coefficients at the site;
v2 / 2 - dynamic stress, Pa, taken from the standards.

To create the concept of relaxed ventilation, it is preferable to avoid twisting turns, plural gate valves and valves, since losses due to local countermeasures, as a rule, in air duct channels reach up to 91% of all costs.

Natural ventilation contains a small radius of influence and an average efficiency for rooms with excess heat in which we are quite small, which can be attributed to disadvantages, and the advantage is the lightness of the system, low price and ease of maintenance.

Natural ventilation calculation example

Total area - 60 m2;
bathroom, kitchen with gas stove, toilet;
storage room - 4.5 m2;
ceiling height - 3 m.

Concrete blocks will be used for the equipment of the air ducts.

Air inflow from the street according to the standards: 60 * 3 * 1 = 180 m3 / hour.

Air extraction from the room:
kitchens - 90 m3 / hour;
bathroom - 25 m3 / hour;
toilet - 25 m3 / hour;
90 + 25 + 25 = 140 m3 / hour

The frequency of renewal of air masses in the pantry is 0.2 per 1 / hour.
4.5 * 3 * 0.2 = 2.7 m3 / hour

Required air outlet: 140 + 2.7 = 142.7 m3 / h.

Ventilation design for residential, public or industrial building takes place in several stages. Air exchange is determined based on the regulatory data, the equipment used and the individual wishes of the customer. The scope of the project depends on the type of building: a one-story residential building or apartment is calculated quickly, with a minimum number of formulas, and a production facility requires serious work. The ventilation calculation method is strictly regulated, and the initial data are prescribed in SNiP, GOST and SP.

The selection of the optimal air exchange system in terms of power and cost takes place step by step. The design order is very important, since the efficiency of the final product depends on its observance:

Determination of the type of ventilation system. The designer analyzes the source data. If you need to ventilate a small living space, then the choice falls on supply and exhaust system with a natural urge. This will be enough when the air consumption is low, there are no harmful impurities. If it is required to calculate a large ventilation complex for a plant or a public building, then mechanical ventilation with the function of heating / cooling the supply air is preferred, and if necessary, then with the calculation of hazards.
Outlier analysis. This includes: thermal energy from lighting fixtures and machine tools; evaporation from machine tools; emissions (gases, chemicals, heavy metals).
Calculation of air exchange. The task of ventilation systems is to remove excess heat, moisture, impurities from the room with an equilibrium or slightly different supply of fresh air. For this, the frequency of air exchange is determined, according to which the equipment is selected.
Equipment selection. It is produced according to the obtained parameters: required air volume for supply / exhaust; indoor temperature and humidity; Availability harmful emissions, ventilation units or ready-made multicomplexes are selected. The most important of the parameters is the air volume required to maintain the design expansion. Filters, heaters, recuperators, air conditioners and hydraulic pumps are used as additional network devices to ensure air quality.

Calculation of emissions

The volume of air exchange and the intensity of the system depend on these two parameters:

Norms, requirements and recommendations prescribed in SNiP 41-01-2003 "Heating, ventilation and air conditioning", as well as other, more highly specialized regulatory documents.
Actual emissions. Calculated using special formulas for each source, and are shown in the table:

Heat dissipation, J
Electric motor		N is the rated power of the engine, W; K1 - loading factor 0.7-0.9 k2η - coefficient of work at one time 0.5-1.
Lighting devices
Human		n is the estimated number of people for this room; q is the amount of heat emitted by the body of one person. Depends on air temperature and work intensity.
Pool surface		V is the speed of air movement over the water surface, m / s; Т - water temperature, 0 С F - water surface area, m2
Moisture release, kg / h
Water surface, such as a pool		Р - coefficient of mass transfer; F-surface area of evaporation, m 2; Рн1, Рн2 - partial pressures of saturated water vapor at a certain temperature of water and air in the room, Pa; RB - barometric pressure. Pa.
Wet floor		F is the area of the wet floor surface, m 2; t s, t m - temperatures of air masses measured by dry / wet thermometer, 0 С.

Using the data obtained as a result of the calculation of harmful emissions, the designer continues to calculate the parameters of the ventilation system.

Calculation of air exchange

Experts use two main schemes:

On aggregated indicators. This method does not provide for harmful emissions such as heat and water. Let's call it “Method # 1”.
Method taking into account excess heat and moisture. The conditional name is "Method No. 2".

Method number 1

The unit of measurement is m 3 / h (cubic meters per hour). Two simplified formulas are used:

L = K × V (m 3 / h); L = Z × n (m 3 / h), where

K is the rate of air exchange. The ratio of the supply volume per hour, to the total air in the room, times per hour;
V is the volume of the room, m 3;
Z is the value of the specific air exchange per unit of rotation,
n is the number of units of measurement.

The selection of ventilation grilles is carried out according to a special table. The selection also takes into account average speed the passage of the air flow through the channel.

Method number 2

The calculation takes into account the assimilation of heat and moisture. If in production or public building excess heat, then the formula is used:

where ΣQ is the sum of heat release from all sources, W;
s - thermal capacity of air, 1 kJ / (kg * K);
tyx is the temperature of the air directed to the hood, ° С;
tnp is the temperature of the air directed to the supply air, ° С;
Exhaust air temperature:

where tp.3 is the standard temperature in working area, 0 C;
ψ - coefficient of temperature increase, depending on the height of measurement, equal to 0.5-1.5 0 С / m;
H is the length of the shoulder from the floor to the middle of the hood, m.

When technological process assumes the release of a large amount of moisture, then a different formula is used:

where G is the volume of moisture, kg / h;
dyx and dnp - water content per kilogram of dry air supply and extract air.

There are several cases, described in more detail in the regulatory documentation, when the required air exchange is determined by the frequency:

k is the frequency of changing the air in the room, once an hour;
V is the volume of the room, m 3.

Section calculation

Square cross section duct is measured in m 2. It can be calculated using the formula:

where v is the speed of air masses inside the channel, m / s.

Differs for main ducts 6-12 m / s and lateral appendages no more than 8 m / s. Quadrature affects throughput channel, the load on it, as well as the noise level and installation method.

Calculation of pressure losses

The walls of the duct are not smooth, and the inner cavity is not filled with vacuum, therefore, part of the energy of the air masses during movement is lost to overcome these resistances. The amount of loss is calculated using the formula:

where ג - frictional resistance, is defined as:

The above formulas are correct for circular ducts. If the duct is square or rectangular, then there is a formula for converting to the equivalent diameter:

where a, b are the dimensions of the channel sides, m.

Head and motor power

The air pressure from the blades H must fully compensate for the pressure loss P, while creating a calculated dynamic P d at the outlet.

Fan electric motor power:

Air heater selection

Heating is often integrated into the ventilation system. For this, heaters are used, as well as the recirculation method. The choice of a device is carried out according to two parameters:

Q in - the maximum consumption of thermal energy, W / h;
F k - determination of the heating surface for the air heater.

Calculation of gravitational pressure

Applicable only for natural ventilation systems. With its help, its performance is determined without mechanical stimulation.

Equipment selection

Based on the data obtained on air exchange, the shape and size of the cross-section of air ducts and grilles, the amount of energy for heating, the main equipment is selected, as well as fittings, a deflector, adapters and other related parts. Fans are selected with a power reserve for peak operation periods, air ducts are selected taking into account the aggressiveness of the environment and ventilation volumes, and air heaters and recuperators - based on the thermal requirements of the system.

Design errors

Errors and shortcomings are often encountered at the stage of project creation. This can be reverse or insufficient draft, blowing out (upper floors of multi-storey residential buildings) and other problems. Some of them can be solved after the completion of installation, with the help of additional installations.

A striking example of a low-skilled calculation is insufficient draft at the exhaust from the production facility without particularly harmful emissions. Suppose the ventilation duct ends in a round shaft, towering 2,000 - 2,500 mm above the roof. It is not always possible and advisable to raise it higher, and in such cases the principle of flare emission is used. A tip with a smaller working hole diameter is installed in the upper part of the circular ventilation shaft. An artificial narrowing of the section is created, which affects the rate of gas emission into the atmosphere - it increases many times over.

The ventilation calculation method allows you to obtain a high-quality internal environment, correctly assessing the negative factors that worsen it. The company "Mega.ru" employs professional designers engineering systems of any complexity. We provide services in Moscow and neighboring regions. The company is also successfully engaged in remote collaboration. All communication methods are indicated on the page, please contact.

The correct ventilation device in the house significantly improves the quality of human life. With the wrong calculation of supply - exhaust ventilation a lot of problems arise - for a person with health, for a building with destruction.

Before starting construction, it is imperative and necessary to make calculations and, accordingly, apply them in the project.

PHYSICAL COMPONENTS OF CALCULATIONS

By the way of work, at present, ventilation circuits are divided into:

Exhaust. To remove used air.
Supply air. For the intake of clean air.
Recuperative. Supply and exhaust. Remove used and let in clean.

V modern world ventilation schemes include various additional equipment:

Devices for heating or cooling the supplied air.
Filters for cleaning odors and impurities.
Devices for humidification and air distribution in rooms.

When calculating ventilation, the following values are taken into account:

Air consumption in cubic meters / hour.
Pressure in air ducts in atmospheres.
Heater power in kW-ah.
Cross-sectional area of air ducts in sq. Cm.

Exhaust ventilation calculation example

Before the start exhaust ventilation calculation it is necessary to study the SN and P (System of Norms and Rules) of the device of ventilation systems. According to SN and P, the amount of air required for one person depends on his activity.

Low activity - 20 cubic meters / hour. Average - 40 m3 / h. High - 60 m3 / h. Next, we take into account the number of people and the volume of the room.

In addition, you need to know the multiplicity - a complete exchange of air within an hour. For the bedroom, it is equal to one, for household rooms - 2, for kitchens, bathrooms and utility rooms - 3.

For example - calculation of exhaust ventilation rooms 20 sq.m.

Let's say two people live in the house, then:

V (volume) of the room is equal to: SxH, where H is the height of the room (standard 2.5 meters).

V = S x H = 20 x 2.5 = 50 cubic meters.

In the same manner, we calculate the performance of the exhaust ventilation of the whole house.

Calculation of exhaust ventilation of industrial premises

At calculation of exhaust ventilation of a production room the multiplicity is 3.

Example: garage 6 x 4 x 2.5 = 60 cubic meters. 2 people work.

High activity - 60 cubic meters / hour x 2 = 120 cubic meters / hour.

V - 60 cubic meters x 3 (multiplicity) = 180 cbm / h.

We choose more - 180 cubic meters per hour.

As a rule, unified ventilation systems, for ease of installation, are divided into:

100 - 500 cubic meters / hour. - apartment.
1000 - 2000 cubic meters / hour. - for houses and estates.
1000 - 10000 cubic meters / hour. - for factory and industrial facilities.

Calculation of supply and exhaust ventilation

AIR HEATER

Climate middle lane, the air entering the room must be heated. For this, supply ventilation is installed with heating of the incoming air.

Heating of the coolant is carried out in various ways - by an electric heater, the inlet of air masses near the battery or stove heating... According to SN and P, the temperature of the incoming air must be at least 18 degrees. celsius.

Accordingly, the capacity of the air heater is calculated depending on the lowest (in the given region) outdoor temperature. Formula for calculating the maximum temperature for heating a room by an air heater:

N / V x 2.98 where 2.98 is a constant.

Example: air consumption - 180 cubic meters / hour. (garage). N = 2 kW.

Thus, the garage can be heated up to 18 degrees. At outside temperature minus 15 degrees

PRESSURE AND CROSS-SECTION

The pressure and, accordingly, the speed of movement of air masses is influenced by the cross-sectional area of the channels, as well as their configuration, the power of the electric fan and the number of transitions.

When calculating the diameter of the channels, the following values are empirically taken:

For residential premises - 5.5 sq. Cm. for 1 sq.m. area.
For a garage and other industrial premises - 17.5 sq. Cm. for 1 sq.m.

At the same time, a flow rate of 2.4 - 4.2 m / s is achieved.

ON ELECTRICITY CONSUMPTION

Electricity consumption directly depends on the duration of the operating time of the electric heater, and the time is a function of the ambient temperature. Usually, the air needs to be warmed up in the cold season, sometimes in the summer on cool nights. For the calculation, the formula is used:

S = (T1 x L x d x c x 16 + T2 x L x c x n x 8) x N / 1000

In this formula:

S is the amount of electricity.

T1 is the maximum daytime temperature.

T2 is the minimum night temperature.

L - productivity of cubic meters per hour.

s - volumetric heat capacity of air - 0.336 W x hour / m3 / deg.ts. The parameter depends on pressure, humidity and air temperature.

d is the price of electricity during the day.

n is the price of electricity at night.

N is the number of days in a month.

So if you stick to sanitary standards, the cost of ventilation rises significantly, but the comfort of residents improves. Therefore, when installing a ventilation system, it is advisable to find a compromise between price and quality.

It is not always possible to invite a specialist to design the system engineering networks... What to do if, during the repair or construction of your facility, the calculation of ventilation ducts was required? Is it possible to produce it on your own?

The calculation will allow you to make effective system, which will ensure the uninterrupted operation of units, fans and air supply units. If everything is calculated correctly, then this will reduce the cost of purchasing materials and equipment, and subsequently on further maintenance of the system.

The calculation of air ducts of the ventilation system for rooms can be carried out using different methods. For example, like this:

constant pressure loss;
permissible speeds.

Types and types of air ducts

Before calculating the networks, you need to determine what they will be made of. Now products are used from steel, plastic, fabric, aluminum foil, etc. Often, air ducts are made of galvanized or stainless steel, this can be organized even in a small workshop. It is convenient to install such products and the calculation of such ventilation does not cause problems.

In addition, air ducts may differ in outward appearance... They can be square, rectangular and oval. Each type has its own merits.

Rectangular allows you to make ventilation systems of small height or width, while maintaining the desired cross-sectional area.
Round systems have less material
Oval ones combine the pros and cons of other types.

For an example of calculation, we will choose round pipes made of tin. These are products that are used for ventilation of housing, office and retail space. The calculation will be carried out by one of the methods that allows you to accurately select the duct network and find its characteristics.

Method for calculating air ducts using constant velocity method

You need to start with a floor plan.

Using all the norms define the right amount air in each zone and draw a wiring diagram. It shows all grilles, diffusers, section changes and bends. The calculation is carried out for the most distant point of the ventilation system, divided into sections bounded by branches or grilles.

The calculation of the air duct for installation consists in choosing the desired section along the entire length, as well as finding the pressure loss for selecting a fan or supply unit... The initial data are the values of the amount of air passing through the ventilation network. Using the diagram, we will calculate the diameter of the duct. This requires a pressure loss graph.
The schedule is different for each type of duct. Usually, manufacturers provide such information for their products, or you can find it in reference books. Let's calculate the round tin air ducts, the graph for which is shown in our figure.

Sizing chart

According to the chosen method, we set the air speed of each section. It should be within the standards for buildings and premises of the selected purpose. For main air ducts supply and exhaust ventilation, the following values are recommended:

living quarters - 3.5–5.0 m / s;
production - 6.0–11.0 m / s;
offices - 3.5–6.0 m / s.

For branches:

offices - 3.0–6.5 m / s;
living quarters - 3.0–5.0 m / s;
production - 4.0-9.0 m / s.

When the speed exceeds the permissible level, the noise level rises to an uncomfortable level for a person.

After determining the speed (in the example 4.0 m / s), we find the required cross-section of the air ducts according to the graph. There is also a pressure loss per 1 m of the network, which will be needed for the calculation. The total pressure loss in Pascals is found by the product of the specific value and the length of the section:

Ruch = Ruch · Ruch.

Network elements and local resistances

Losses on network elements (grilles, diffusers, tees, bends, section changes, etc.) are also important. For grilles and some elements, these values are indicated in the documentation. They can also be calculated by the product of the coefficient local resistance(c. m. s.) on dynamic pressure in him:

Rm. s. = ζ · Рд.

Where Рд = V2 · ρ / 2 (ρ - air density).

K. m. With. determined from reference books and factory characteristics of products. All types of pressure losses are summed up for each section and for the entire network. For convenience, we will do this using a tabular method.

The sum of all pressures will be acceptable for this duct network and branch losses should be within 10% of the total available pressure. If the difference is greater, it is necessary to mount dampers or diaphragms on the branches. To do this, we make the calculation of the required c. M. S. according to the formula:

ζ = 2Pisb / V2,

where Rizb is the difference between the available pressure and losses at the branch. We select the diameter of the diaphragm from the table.

The correct diaphragm diameter for the air ducts.

Correct calculation of ventilation ducts will allow you to choose the right fan by choosing from manufacturers according to your criteria. Using the found available pressure and total air flow in the network, it will not be difficult to do this.