In order for the ventilation system in the house to work efficiently, it is necessary to make calculations during its design. This will not only allow you to use the equipment with optimal power, but also save on the system, fully preserving all the required parameters. It is carried out according to certain parameters, while completely different formulas are used for natural and forced systems. Particular 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 a room, it is necessary to determine what the cross section of the pipe will be, the volume of air passing through the ducts, and the flow rate. Such calculations are important, since the slightest errors 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 for ventilation.
To calculate the ventilation for a room, find out the area of the air duct, you must use the following formula:
Sc = L * 2.778 / V, where:
- Sc is the estimated area of the channel;
- L is the value of the air flow passing through the channel;
- V is the value of the speed of air passing through the air duct;
- 2.778 is a special factor that is needed to match the 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 must use the formula based on the type of duct. For a round pipe, the formula applies: 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.
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Correspondence of area and flow
The pipe diameter is 100mm, it corresponds to a rectangular duct of 80*90mm, 63*125mm, 63*140mm. The areas of rectangular channels will be 72, 79, 88 cm². respectively. The speed of the air flow can be different, the following values \u200b\u200bare commonly 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 it will correspond to rectangular air ducts of 100 * 200 mm, 90 * 250 mm with cross-sectional areas of 200 cm² and 225 cm², respectively. In order for the room to be well 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.
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Calculations for the heater
A heater is a piece of equipment designed to air-condition a room with heated air masses. This device is used to create a more comfortable environment in the cold season. Heaters are used in the forced air conditioning system. Even at the design stage, it is important to calculate the power of the equipment. This is done based on the performance of the system, the difference between the outside temperature and the air temperature in the room. The last two values are determined according to SNiPs. In this case, it must 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 taking into account climate zone. On average, during switching on, the air heater provides heating of the air up to 40 ° C, in order to compensate for the difference between the warm internal and external cold flow.
I = P / U, where:
- I is the number for the maximum current consumed by the equipment;
- P is the power of the device required for the room;
- U - voltage to power the heater.
If the load is less than required, then the device must be chosen not so powerful. The temperature at 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 difference observed at the inlet and outlet of the air conditioning system;
- P is the power of the device;
- L is the value of equipment productivity.
In a residential area (for apartments and private houses), a heater can have a power of 1-5 kW, but for office space, a larger value is taken - this is 5-50 kW. In some cases, electric heaters are not used, the equipment here is connected to water heating, which saves electricity.
The design of ventilation of a residential, public or industrial building takes place in several stages. Air exchange is determined on the basis of 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 serious work is required for a production facility. The method for calculating ventilation 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 order of design is very important, since the efficiency of the final product depends on its observance:
- Determining the type of ventilation system. The designer analyzes the source data. If you want 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 flow is small, there are no harmful impurities. If you need to calculate a large ventilation complex for a factory or a public building, then preference is given to mechanical ventilation with the function of heating / cooling the supply, and if necessary, with the calculation of hazards.
- Outlier analysis. This includes: thermal energy from lighting fixtures and machine tools; fumes 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 premises with an equilibrium or slightly different supply of fresh air. For this, the air exchange rate is determined, according to which the equipment is selected.
- Equipment selection. It is produced according to the obtained parameters: the required volume of air for supply / exhaust; indoor temperature and humidity; the presence of harmful emissions, ventilation units or ready-made multi-complexes are selected. The most important of the parameters is the volume of air required to maintain the design expansion rate. Filters, heaters, recuperators, air conditioners and hydraulic pumps come as additional network devices providing air quality.
Emission calculation
The volume of air exchange and the intensity of the system depends on these two parameters:
- The norms, requirements and recommendations prescribed in SNiP 41-01-2003 "Heating, ventilation and air conditioning", as well as another, more highly specialized normative documentation.
- actual emissions. Calculated by special formulas for each source, and are shown in the table:
|
Heat dissipation, J |
||
| Motor electric | N – engine power at nominal value, 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 that the body of one person releases. Depends on air temperature and intensity of work. |
|
| 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 | P is the mass transfer coefficient; F-surface area of evaporation, m 2 ; Рн1, Рн2 - partial pressures of saturated water vapor at certain temperature water and indoor air, 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 from the calculation of harmful emissions, the designer continues to calculate the parameters ventilation system.
Air exchange calculation
Experts use two main schemes:
- According to aggregated indicators. This method does not provide for harmful emissions such as heat and water. We will conditionally call it "Method No. 1".
- Method taking into account excess heat and moisture. Conditional name "Method No. 2".
Method number 1
Unit of measurement - m 3 / h ( Cubic Meters in hour). There are two simplified formulas:
L=K×V(m 3 /h); L \u003d Z × n (m 3 / h), where
K is the air exchange rate. The ratio of the volume of supply for one 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 measure.
The selection of ventilation grilles is carried out according to a special table. The selection also takes into account the average speed 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 releases from all sources, W;
c is the thermal capacity of air, 1 kJ/(kg*K);
tyx is the temperature of the air directed to the exhaust, °С;
tnp - temperature of the air directed to the supply, ° С;
Extract air temperature:
where tp.3 is the normative temperature in working area, 0 С;
ψ - coefficient of temperature increase, depending on the measurement height, equal to 0.5-1.5 0 C / m;
H is the length of the arm from the floor to the middle of the hood, m.
When technological process involves the release of a large amount of moisture, then another formula is used:
where G is the volume of moisture, kg/h;
dyx and dnp - water content per kilogram of dry air supply and exhaust.
There are several cases, described in more detail in the regulatory documentation, when the required air exchange is determined by the multiplicity:
k is the frequency of air changes in the room, once per hour;
V is the volume of the room, m 3.
Section calculation
The cross-sectional area of the duct is measured in m2. It can be calculated using the formula:
where v is the speed of air masses inside the channel, m/s.
It differs for the main air ducts 6-12 m/s and side appendages no more than 8 m/s. The quadrature affects the bandwidth of the channel, the load on it, as well as the noise level and installation method.
Pressure loss calculation
The walls of the air duct are not smooth, and the inner cavity is not filled with vacuum, so part of the energy of the air masses during movement is lost to overcome these resistances. The amount of loss is calculated by the formula:
where ג is friction resistance, is defined as:
The formulas given above are correct for circular channels. If the duct is square or rectangular, then there is a formula for converting to the diameter equivalent:
where a,b are the dimensions of the sides of the channel, m.
Head and motor power
The air pressure from the blades H must fully compensate for the pressure loss P, while creating the calculated dynamic P d at the outlet.
Power electric motor fan:
Selection of a heater
Often heating is integrated into the ventilation system. For this, heaters are used, as well as the recycling method. Device selection is carried out according to two parameters:
- Q in - limiting consumption of thermal energy, W / h;
- F k - determination of the heating surface for the heater.
Calculation of gravitational pressure
It is used only for natural ventilation system. 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 periods of operation, air ducts are selected taking into account the aggressiveness of the environment and ventilation volumes, and heaters and recuperators are selected based on the thermal demands of the system.
Design errors
At the stage of creating a project, errors and shortcomings are often encountered. This may be reverse or insufficient draft, blowing out (upper floors of multi-storey residential buildings) and other problems. Some of them can be solved even after the installation is completed, with the help of additional installations.
A vivid example of a low-skilled calculation is insufficient draft at the exhaust from the production room without particularly harmful emissions. Let's say the ventilation duct ends with a round shaft, rising above the roof by 2,000 - 2,500 mm. Raising it higher is not always possible and advisable, and in such cases the principle of flare emission is used. A tip with a smaller diameter of the working hole is installed in the upper part of the round ventilation shaft. An artificial narrowing of the cross section is created, which affects the rate of gas release into the atmosphere - it increases many times over.
The method of calculating ventilation allows you to get high-quality internal environment, correctly estimating negative factors that worsen it. Mega.ru employs professional designers engineering systems any complexity. We provide services in Moscow and neighboring regions. The company is also successfully engaged in remote collaboration. All methods of communication are indicated on the page, please contact.
Proper ventilation in the house significantly improves the quality of human life. With the wrong calculation of inflow - exhaust ventilation there are a lot of problems - 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
According to the method of operation, at present, ventilation schemes are divided into:
- Exhaust. To remove used air.
- Supply. For clean air intake.
- Recovery. Supply and exhaust. Remove the used one and let in the clean one.
AT 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 quantities are taken into account:
- Air consumption in cubic meters / hour.
- Pressure in air channels in atmospheres.
- Heater power in kWh.
- Cross-sectional area of air channels in sq.cm.
Exhaust ventilation calculation example
Before the beginning exhaust ventilation calculation it is necessary to study the SN and P (System of Norms and Rules) devices of ventilation systems. According to CH and P, the amount of air needed for one person depends on his activity.
Little activity - 20 cubic meters / hour. Average - 40 kb.m./h. High - 60 kb.m./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 for an hour. For a 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.
Suppose two people live in a house, then:
V (volume) of the room is equal to: SxH, where H is the height of the room (standard 2.5 meters).
V \u003d S x H \u003d 20 x 2.5 \u003d 50 cubic meters.
In the same order, we calculate the performance of exhaust ventilation of the whole house.
Calculation of exhaust ventilation of industrial premises
At calculation of exhaust ventilation of the 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 \u003d 120 cubic meters / hour.
V - 60 cubic meters. x 3 (multiplicity) = 180 kb.m./h.
We choose more - 180 cubic meters / 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
Under climate conditions middle lane, the air entering the room must be heated. For this, set supply ventilation with heating incoming air.
Heating of the coolant is carried out in various ways - with an electric heater, the intake of air masses near the battery or furnace heating. According to SN and P, the temperature of the incoming air must be at least 18 degrees. celsius.
Accordingly, the power of the air heater is calculated depending on the lowest (in the given region) outdoor temperature. The formula for calculating the maximum temperature for heating a room with 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 outdoor temperature minus 15 deg.
PRESSURE AND SECTION
The pressure and, accordingly, the speed of movement of air masses are affected 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 channel diameter, the following values are empirically taken:
- For residential premises - 5.5 sq.cm. per 1 sq.m. area.
- For a garage and other industrial premises - 17.5 sq.cm. per 1 sq.m.
At the same time, flow rates of 2.4 - 4.2 m / s are achieved.
ABOUT ELECTRICITY CONSUMPTION
Electricity consumption directly depends on the duration of the electric heater operation, and the time is a function of the ambient temperature. Usually, the air needs to be heated 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 daily temperature.
T2 is the minimum night temperature.
L - performance cubic meters / hour.
c - volumetric heat capacity of air - 0.336 W x hour / kb.m. / deg.c. 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.
Thus, if you adhere to sanitary standards, the cost of ventilation increases significantly, but the comfort of residents improves. Therefore, when installing a ventilation system, it is advisable to find a compromise between price and quality.
in residential and office buildings where people are constantly located, comfortable conditions for their work and life should be created. These conditions are regulated by state sanitary standards and other documents. Options and required amount air for residential and administrative buildings are prescribed in the relevant building normative documents. To calculate the ventilation in the room, you should be guided by these documents.
Initial data for calculating air exchange
The purpose of the calculation is to determine how much clean air is required to be supplied to each room and how much exhaust air to remove from it. After that, they choose a method for organizing air exchange and calculate for the cold season thermal power, which must be spent to heat the inflow from the street. First you need to determine the frequency of exchange for each room of a residential building.
Multiplicity of exchange - a number showing how many times in everyone volume The air in the premises will be completely renewed within 1 hour.
The multiplicity values for offices and rooms for various purposes are prescribed in SNiP 31-01-2003, for convenience they are given in Table 1.
The SNiP indicates the calculated values \u200b\u200bof the flow rate and multiplicity, but for furnaces, the amount of air for combustion must be specified according to technical specifications hot water boiler.
Calculation methods
Building codes allow the calculation of the supply ventilation of the room in several ways:
- According to the frequency of exchange, the value of which for each room is fixed by the norms.
- According to the normalized specific consumption of air masses per 1 m 2 of the room.
- According to the specific volume of fresh air mixture per 1 person staying in the house for more than 2 hours daily.
In accordance with SNiP 41-01-2003 "Ventilation and air conditioning" for residential buildings, the following formula for calculating ventilation according to the normalized multiplicity is used:
- L - the required amount of supply air, m 3 / h;
- V is the volume of an office or room, m 3;
- n is the calculated air exchange rate (Table 1).
The volume of each room is determined by measuring its dimensions or, in the case of a house under construction, according to the drawings included in the project. The inflow flow rate for some rooms has a certain normalized value, for example, in bathrooms or laundry rooms. Then the dimensions are not required to be determined, a fixed value is taken, indicated in Table 1. After calculating each room, the results are summed up and the total amount of supply air required for the whole house is obtained.
The determination of the inflow by the specific consumption of fresh air mixture for each person is carried out by the following method:
In this formula:
- L - the same as in the previous formula, m 3 / h;
- N - the number of people in the building for more than 2 hours during the day, people;
- m - specific amount of supply air per 1 person, m 3 / h (Table 2).
This method can be used not only for residential, but also for administrative buildings, in the offices of which many people work. In this case, the specific consumption value is normalized by Appendix M of SNiP 41-01-2003, which is reflected in Table 2.
The volume of extract from the office to maintain balance is equal to the inflow, - 1200 m 3 / h.
If in terms of 1 tenant there is less than 20 m 2 of the total area of \u200b\u200ba residential building, then the calculation is made according to the area of \u200b\u200bthe premises:
- L is the required amount of inflow, m 3 / h;
- A - the area of \u200b\u200bthe office or room, m 2;
- k- specific consumption clean air supplied to 1 m 2 of the area of the room.
SNiP 41-01-2003 sets the value of k in the amount of 3 m 3 per 1 m 2 of living space. That is, in a bedroom with an area of 10 m 2, you will need to supply at least 10 x 3 \u003d 30 m 3 / h of fresh air mixture.
General ventilation device in the house
After the demand for supply and exhaust for all rooms of the house is calculated by one of the methods described above, you should select the type general ventilation: with natural or mechanical urge. The first type fit for apartments, small private houses and offices. Here the main role will be played natural extract, since it is she who creates a rarefaction inside the house and induces the air masses to move in their direction, drawing in fresh ones from the street. In this case, the calculation natural ventilation room is reduced to calculating the height of the vertical exhaust shaft.
An example of ventilation in a residential building
Calculations are made by the selection method, since vertical exhaust channels are made standard sizes and heights. Having taken a certain value of the shaft height, it is substituted into the formula:
p \u003d h (ρ H - ρ B)
- h is the height of the channel, m;
- ρ H is the density of outdoor air, on average it is taken equal to 1.27 kg / m 3 at a temperature of + 5ºС;
- ρ B - the density of the air mixture removed from the apartment, is taken according to its temperature.
When air masses move in the mine, frictional resistance against its walls arises, the traction force must overcome it. Calculation and design vertical channel consist in the fact that the traction force in it is somewhat greater than the friction resistance and the following condition is observed:
H ≤ 0.9 p
- р – gravitational pressure in the channel, kgf/m 2 ;
- H is the resistance of the exhaust shaft, kgf / m 2.
The value of H is calculated using the following formula:
In this formula:
- R - pressure loss per 1 m.p. mine, is a reference value, kgf / m 2;
- h is the height of the channel, m;
Substituting the values of the height of the exhaust shaft into the above formulas, calculations are made until the condition for the functioning of the thrust is met.
forced ventilation
When using local and centralized ventilation units in the organization of air exchange, the most important indicator is the flow of external air masses to ensure the necessary flow into the building. If local supply units with cleaning and heating are installed in the rooms, then their total performance should be equal to the volume of inflow into the building, calculated earlier.
Air exchange in rooms
When selecting the performance of the supply unit, it must be taken into account that not all rooms are located near the outer walls. The installation will serve not only its office, but also the adjacent one, located in the depths of the house.
Centralized air handling units it is better to select with the help of specialists, since it will be necessary to perform a rather complex calculation of ventilation systems. The unit can use the heat of the exhaust air, heating the outdoor air with it, it is important to choose the right heat exchanger here.
The processed air mixture will be distributed to the premises through a network of air ducts, it will be necessary to determine their parameters (diameter, length, pressure loss). This is needed for right choice ventilation unit, which for stable operation of the system must develop required pressure to overcome all resistance.
Conclusion
Calculate the required volume of supply air in a residential or administrative building- not so much difficult task. This is the first step towards creating comfortable conditions for the life or work of people. Knowing the necessary costs of supply and exhaust, you can make an estimate of the total cost of work and equipment for the installation of general ventilation. It is preferable to entrust further development and implementation to specialists.
How to make forced ventilation with your own hands
How to make ventilation in a private house
All about ventilation apartment building
Air ducts are used to transfer supply or exhaust air from ventilation units in civil or industrial buildings. different configuration, shape and size. 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 being designed or newly built - it is enough to coordinate the location of the systems relative to workplaces, equipment and other engineering networks. In the current 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:
- One of the main factors is the flow rate of supply or exhaust air per unit of time (m 3 / h), which must pass this channel.
- 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 speed can cause vibrations, elevated level noise and power ventilation unit. For different areas supply system recommended to take different speed, its value lies in the range from 1.5 to 8 m/s.
- The material of the duct matters. Usually it is galvanized steel, but other materials are also used: different kinds 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 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 is the air velocity in the channel, m/s;
- L - air consumption, m 3 / h;
- S is the cross-sectional area of the channel, m 2 ;
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:
- 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.
- The cross-sectional area is calculated: 10,000/3600 x 8 = 0.347 m 2, the diameter will be - 0.665 m.
- 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.
- AT reverse order calculate the actual speed of the air mixture in the air duct to further determine the power of the fan. AT this case the cross section will be: (3.14 x 0.71 2 / 4) \u003d 0.4 m 2, and the real speed is 10,000 / 3600 x 0.4 \u003d 6.95 m / s.
- In the event that it is necessary to lay a channel rectangular shape, 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. technological equipment or other engineering networks.
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Selection of dimensions for real conditions
In practice, duct sizing does not end there. The fact is that the entire system of channels for delivering air masses to the premises has a certain resistance, having calculated which, they take the power of the ventilation unit. This value must be economically justified so that there is no excessive consumption of electricity for the operation of the ventilation system. At the same time, the large dimensions of the channels can become a serious problem during their installation, they should not take away usable area premises and be within the limits of the route provided for them in terms of their dimensions. Therefore, often the flow rate in all parts of the system is increased so that the dimensions of the channels become smaller. Then you will need to recalculate, perhaps more than once.
The minimum design pressure developed by the fan is determined by the formula.
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