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 pipelines of ventilation systems at projects or newly built objects - it is enough to coordinate the location of the systems in relation 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:
- 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.
- 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.
- 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:
- 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.
- 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.
- 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:
- 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.
- We start the calculation from the most distant from the fan and the most loaded sections.
- 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.
- We calculate the pressure loss due to friction Ptr.
- According to the tabular data, we determine the sum of local resistances Q and calculate the pressure loss due to local resistances z.
- 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.
- 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.
- 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.
- 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.
- Multiply the equivalent system length by the head loss from step 2. The head loss at the diffusers is added to the value obtained.
- 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:
- If space permits, it is better to choose round or square ducts.
- 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, select optimal speed air, which does not increase the vibrational 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 |
| 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 for known speed it is possible to calculate the volume of air moving through the ducts per unit of time.
L \u003d 3600 × S (m 3) × V (m / s). The volume (flow) is obtained in square meters.
As already described earlier, the noise indicators of ventilation systems also depend on the air speed. To minimize the negative impact of this phenomenon, engineers made calculations of the maximum allowable air speeds for various rooms.
The same algorithm is used to determine the air velocity in the air duct when calculating the heat supply, set tolerance fields to minimize losses for the maintenance of buildings in the winter period, and select fans by power. Airflow data is also required to reduce pressure losses, which improves the efficiency of ventilation systems and reduces consumption. electrical energy.
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 adjusted taking into account the temperature of the coolant at the inlet and outlet, for uniform dissipation of the flow of warm air, the installation scheme and dimensions of the ventilation grilles are thought out. Modern air heating systems provide for the possibility of automatic adjustment of the speed and direction of flows. The air temperature cannot exceed +50°C at the outlet, the distance to the workplace is at least 1.5 m. The air mass supply rate is normalized by the current state standards and industry acts.
During calculations, at the request of customers, the possibility of installing additional branches can be taken into account; for this purpose, a margin of equipment productivity and channel bandwidth is provided. The flow rates are calculated in such a way that, after increasing the power of the ventilation systems, they do not create an additional sound load on the people present in the room.
The choice of diameters is carried out from the minimum acceptable, the smaller the dimensions - the more universal the ventilation system, the cheaper its manufacture and installation. Local suction systems are calculated separately, they can work both offline and connected to existing ventilation systems.
State regulations establish recommended travel speeds depending on the location and purpose of the air ducts. When calculating, you must adhere to these parameters.
| Type and location of the air duct and grille | Ventilation | |
| Natural | Mechanical | |
| Air inlet shutters | 0,5-1,0 | 2,0-4,0 |
| Supply mine channels | 1,0-2,0 | 2,0-6,0 |
| Horizontal collection channels | 0,5-1,0 | 2,0-5,0 |
| Vertical channels | 0,5-1,0 | 2,0-5,0 |
| Supply grilles near the floor | 0,2-0,5 | 0,2-0,5 |
| Ceiling grills | 0,5-1,0 | 1,0-3,0 |
| Exhaust grilles | 0,5-1,0 | 1,5-3,0 |
| exhaust shafts | 1,0-1,5 | 3,0-6,0 |
Indoor air cannot move at a speed of more than 0.3 m / s, a short-term excess of the parameter is allowed no more than 30%. If there are two systems in the room, then the air velocity in each of them must provide at least 50% of the calculated volume of air supply or removal.
Fire organizations put forward their requirements for the speed of movement of air masses in air ducts, depending on the category of the room and the characteristics of the technological process. The regulations aim to reduce the rate at which smoke or fire spreads through air ducts. If necessary, valves and shut-off valves should be installed on ventilation systems. Device activation occurs after a sensor signal or is performed manually by a responsible person. Only certain groups of rooms can be connected to one ventilation system.
During the cold period of time in heated buildings, the air temperature as a result of the functioning of the ventilation system cannot fall below the normalized ones. The normalized temperature is provided before the start of the work shift. In the warm period of time, these requirements are not relevant. The movement of air masses should not worsen the standards provided for by SanPin 2.1.2.2645. To achieve the desired results, during the design of systems, the diameter of the ducts, the power and number of fans and flow rates are changed.
The accepted design data on the parameters of movement in the air ducts should provide:
- 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.
- 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.
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
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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 manufacturing process fast and economical, as even the largest orders take less 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 conditions supplies 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.
Equipping housing with all the benefits of civilization is a necessity for any owner. It is impossible not to include ventilation and air conditioning in the list of engineering systems at home. The arrangement of these complexes must be approached with the utmost responsibility, which is impossible without calculating the area of air ducts and fittings. At the slightest mistake, the microclimate in the room will be disturbed, which will affect the comfort of all family members.
- Calculation of individual zones limited by tees or dampers. If there are branches, then they are added to this segment. The oxygen consumption along the entire length is considered to be stable.
- Determination of the main line with the maximum air consumption. This will be the longest element of the circuit.
- Cross-sections on the calculated sections are selected in accordance with the recommendations of the state standard - ≤ 8 m/s in mains, ≤ 8 m/s in branches, ≤ 3 m/s in blinds and gratings.
- All sections are marked from the least loaded in order of increasing pressure.
- Exhaust, installed on industrial, commercial, sports grounds and in residential buildings mounted both inside and outside the building.
- Supply air, supplying rooms of various types with prepared air.
- Combined with recovery unit.
- Provide the necessary heating of the mixture and the removal of excess heat at their economic expediency.
- The speed indicators of the movement of air flows should not violate the comfort of being in the premises.
- The limiting concentration of harmful substances, not exceeding the values defined by GOST 12.1.005–88.
- Metal (galvanized, stainless or black steel).
- Made of flexible film (plastic or aluminium).
- Hard plastic.
- Fabrics.
- Drawing up a plan indicating the required amount of air supplied or removed. This is the baseline on which all design work is based.
- Marks on the diagram of individual sections with data on the amount of oxygen moving through them. It is necessary to specify gratings, cross-section differences, bends and valves.
- After selection top speed the calculation of the caliber, diameter or size of the sides of the channel is performed.
- Branches are ordinary and S-shaped (ducks).
- Adapters in diameter and geometric shape.
- Tees.
- Umbrellas.
- Vent-Calc for calculating cross-sectional area, thrust and resistance in sections.
- GIDRV 3.093 provides control over the calculation of channel parameters.
- Ducter 2.5 selects system elements according to certain characteristics.
- CADvent based on AutoCAD with a maximum database of elements.
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Causes of ventilation problems
If the calculations are made correctly, then the supply of clean air of normal humidity, as well as the removal unpleasant odors will be the maximum allowed. Otherwise, the formation of mold, fungus in bathrooms and toilets, constant stuffiness in kitchens and rooms is guaranteed. The situation is aggravated by the fact that almost all premises are equipped with airtight plastic windows without slot ventilation. We have to make up for the lack fresh air forcibly.
Another cause of problems with the elimination of waste masses, unpleasant odors and excess water vapor are blockages and depressurization of ventilation pipes. The redevelopment of premises can have a negative impact on the microclimate if you do not resort to engineering assistance when calculating the area of air ducts when upgrading ventilation in accordance with the new parameters.
The easiest way to fix problems in this system is to check for the presence of traction. To do this, bring a sheet of paper or a burning match to the exhaust channel. The use of open fire in rooms with gas heating equipment is not recommended. If the deviation is clearly noticeable, then there is no need to talk about problems. If the result is the opposite, you should find out the reasons for the lack of fresh air supply and proceed to eliminate them, which may require re-calculating all parameters.
Air duct area
Grounds for determining areas
The ventilation communications system is a complex structure. When designing it, it is necessary to calculate the quadrature of rectangular and the cross section of round sections of the network, convert them to square meters. m, calculate the area of tie-ins, transitions. This can be done using special mathematical expressions. or special program- online calculator for calculating air ducts.
Formula calculation
There are several definitions for making calculations. The main ones are:
MagiCAD duct area
Sequence of operations
In order not to be mistaken in the projected indicators, it is necessary to break the entire work cycle into stages. Approximately the following sequence will turn out:
Given the preconditions, it is possible to calculate the performance of ventilation systems. The formulas to be used are:
It is assumed that special reference books will be used during the calculations. They indicate the practical losses due to friction, air consumption at various flow rates:
A diaphragm is used to dampen excess pressure. The coefficient of its resistance is determined as follows:
The data from these tables is used for several types of ventilation installations. Among them:
Calculation of pressure drop in ducts
Calculation of the diameter of the channels
Having determined the speed of the air masses inside the route, we can proceed to the calculation of the next parameter. It is determined by the formula S=R\3600v, where S is the cross-sectional area of the line, R is the cost of oxygen in m3/h, v is the speed of the air flow, 3600 is the time correction factor. Having learned it, the diameter is calculated:
When determining the size of the main pipelines, certain conditions must be met. The project must meet the following criteria:
Basic concepts of aerodynamic calculation LESSON 1 (total 10 lessons)
Channel types
Before you start calculating air ducts and fittings, you need to know what material they are made of. The recalculation of the cross-sectional area and the manner of movement of air masses inside depend on this. Channels for ventilation are:
Their shape is mainly rectangular or round, less often - oval. They are made on industrial enterprises, since it is quite difficult to organize production directly at the facility.
Diameter definition
This task becomes the main one when creating design documentation for the ventilation system. The process can be carried out both by specialist installers and independently, using the calculator of air ducts and fittings. This can be done in two ways.
The variant with the use of allowable speeds is based on the normalized speed of movement inside the pipe. The indicators are selected for a particular type of premises and a section of the highway according to the recommended values.
Each building is characterized by the maximum permitted rate of air distribution, which is unacceptable to exceed. For regular use, you should take this scheme:
Simple calculation of ventilation with a heat exchanger.
And also you can select these parameters according to the method of determining pressure losses, summing them up on indirect sections and bends, gratings and tees. This will require geometric formulas and special tables.
Material selection
This procedure is performed at the facility that manufactures the duct and accessories. In this case, the quantity of raw materials for the production of the required quantity of products is determined. For such purposes, a profile development is created and formulas from geometry are used. For round sections, this will be the diameter of the pipe multiplied by the circumference.
Shaped products are more difficult to calculate, since there are no ready-made formulas for them. You have to produce for each element separately. It is not possible to carry out the operation on site, therefore all additional parts are supplied by the manufacturer together with the main structural elements.
The most common components for ventilation and air conditioning systems are:
Each of these components has a special role in the ventilation system complex, so each of them is designed separately. It is not difficult to calculate both shaped products and the area of air ducts with an online calculator.
Assistance Programs
To eliminate human factors in the calculations, as well as reduce the design time, several products have been developed that allow you to correctly determine the parameters of the future ventilation system. In addition, some of them allow the construction of a 3D model of the complex being created. Among them are the following developments:
Everyone solves the problem of selecting the dimensions of future ventilation independently. For an inexperienced installer, it will be preferable to design and install all components with the help of specialists who have experience in creating such highways and the appropriate equipment and fixtures.
Industrial ventilation is designed taking into account several facts, the cross-section of air ducts has a significant effect on everything.
- Air exchange rate. During the calculations, the features of the technology are taken into account, chemical composition emitted harmful compounds, and the dimensions of the room.
- Noise. Ventilation systems should not worsen working conditions in terms of noise. The cross section and thickness are selected in such a way as to minimize the noise of air flows.
- Efficiency of the overall ventilation system. Several rooms can be connected to one main air duct. Each of them must maintain its own ventilation parameters, and this largely depends on the correct choice of diameters. They are selected in such a way that the dimensions and capabilities of one common fan can provide regulated system modes.
- Profitability. The smaller the energy losses in the air ducts, the lower the consumption of electrical energy. At the same time, it is necessary to take into account the cost of equipment, to choose economically justified dimensions of the elements.
Efficient and economical system ventilation requires complex preliminary calculations; only specialists with higher education can do this. Currently, plastic air ducts are most often used for industrial ventilation, they meet all modern requirements, make it possible to reduce not only the dimensions and cost of the ventilation system, but also the cost of its maintenance.
Calculation of the diameter of the air duct
To calculate the dimensions, you need to have the initial data: the maximum allowable speed of the air flow and the volume of air passed per unit of time. This data is taken from specifications ventilation system. The speed of air movement affects the noise of the system, and it is strictly controlled by sanitary state organizations. The volume of air to be passed must correspond to the parameters of the fans and the required exchange rate. The calculated air duct area is determined by the formula Sc = L × 2.778 / V, where:
Sc - cross-sectional area of the duct in square centimeters; L - maximum supply (flow) of air in m 3 / hour;
V is the estimated operating airflow speed in meters per second without peaks;
2.778 is a coefficient for converting various metric numbers to diameter values in square centimeters.
Designers of ventilation systems take into account the following important dependencies:
- If it is necessary to supply the same volume of air, reducing the diameter of the air ducts leads to an increase in the air flow rate. This phenomenon has three negative consequences. First, an increase in air speed increases noise, and this parameter is controlled by sanitary standards and cannot exceed permissible values. Secondly, the higher the air speed, the higher the energy loss, the more powerful the fans are needed to ensure the specified modes of operation of the system, the larger their size. Thirdly, the small dimensions of the air ducts are not able to properly distribute flows between different rooms.
- An unjustified increase in the diameter of the air ducts increases the price of the ventilation system, creates difficulties during installation work. Large dimensions have a negative impact on the cost of system maintenance and the cost of manufactured products.
The smaller the diameter of the air duct, the faster the speed of air movement. And this not only increases noise and vibration, but also increases the resistance of the air flow. Accordingly, to ensure the required calculated exchange rate, it is required to install powerful fans, which increases their size and is economically unprofitable at current prices for electrical energy.
With an increase in diameters, the above problems disappear, but new ones appear - the complexity of installation and the high cost of overall equipment, including various shut-off and control valves. In addition, large-diameter air ducts require a lot of free space for installation; holes have to be made for them in the main walls and partitions. Another problem is that if they are used for space heating, then the large size of the air duct requires increased costs for thermal protection measures, which further increases the estimated cost of the system.
In simplified versions of calculations, it is taken into account that the optimal speed of air flows should be in the range of 12–15 m/s, due to this, it is possible to somewhat reduce their diameter and thickness. Due to the fact that the main air ducts in most cases are laid in special technical channels, the noise level can be neglected. In the branches that enter directly into the premises, the air speed decreases to 5–6 m/s, thereby reducing noise. The air volume is taken from the SaNiPin tables for each room, depending on its purpose of dimensions.
Problems arise with main ducts of considerable length in large enterprises or in systems with many branches. For example, with a normalized air flow rate of 35,000 m 3 / h and an air flow rate of 8 m / s, the diameter of the air duct must be at least 1.5 m with a thickness of more than two millimeters, with an increase in air flow speed to 13 m / s, the dimensions of the air ducts are reduced to 1 m.
Pressure loss table
The diameter of the branches of the air ducts is calculated taking into account the requirements for each room. It is allowed to use the same dimensions for them, and to change the air parameters, install different adjustable throttle valves. Such options for ventilation systems allow you to automatically change performance indicators, taking into account the actual situation. There should be no drafts in the rooms caused by ventilation. Creating a favorable microclimate is achieved through right choice places of installation of ventilation grilles and their linear dimensions.
The systems themselves are calculated using the constant velocity method and the pressure loss method. Based on these data, the dimensions, type and power of fans are selected, their number is calculated, installation sites are planned, and the dimensions of the air duct are determined.
If ventilation in a house or apartment does not cope with its tasks, then this is fraught with very serious consequences. Yes, problems in the operation of this system do not appear as quickly and sensitively as, say, problems with heating, and not all owners pay adequate attention to them. But the results can be very sad. This is stale waterlogged indoor air, that is, an ideal environment for the development of pathogens. These are misted windows and damp walls, on which mold foci may soon appear. Finally, this is simply a decrease in comfort due to smells spreading from the bathroom, bathroom, kitchen into the living area.
In order to avoid stagnation, air must be exchanged with a certain frequency in the premises for a period of time. The inflow is carried out through the living area of the apartment or house, the hood - through the kitchen, bathroom, bathroom. It is for this that windows (vents) of exhaust ventilation ducts are located there. Often, homeowners who are starting repairs ask if these vents can be repaired or reduced in size in order, for example, to install certain pieces of furniture on the walls. So - it is definitely impossible to completely block them, but transfer or change in size is possible, but not only on the condition that the necessary performance will be ensured, that is, the ability to pass the required volume of air. And how to define it? We hope that the proposed calculators for calculating the cross-sectional area of the ventilation vent will help the reader.
Calculators will be accompanied by the necessary explanations for the calculations.
Calculation of normal air exchange for effective ventilation of an apartment or house
So, during normal operation of ventilation for an hour, the air in the premises must constantly change. The current guidelines (SNiP and SanPiN) set the norms for the influx of fresh air into each of the premises of the residential area of the apartment, as well as the minimum volume of its exhaust through the channels located in the kitchen, in the bathroom in the bathroom, and sometimes in some other special rooms.
| Room type | Minimum air exchange rates (multiplicity per hour or cubic meters per hour) | |
|---|---|---|
| INFLOW | HOOD | |
| Requirements under the Code of Rules SP 55.13330.2011 to SNiP 31-02-2001 "Single-apartment residential buildings" | ||
| Residential premises with permanent residence of people | At least one volume exchange per hour | - |
| Kitchen | - | 60 m³/hour |
| Bathroom, toilet | - | 25 m³/hour |
| Other premises | Not less than 0.2 volume per hour | |
| Requirements according to the Code of Rules SP 60.13330.2012 to SNiP 41-01-2003 "Heating, ventilation and air conditioning" | ||
| Minimum outdoor air consumption per person: living quarters with permanent residence of people, in conditions of natural ventilation: | ||
| With a total living area of more than 20 m² per person | 30 m³/h, but at the same time not less than 0.35 of the total air exchange volume of the apartment per hour | |
| With a total living area of less than 20 m² per person | 3 m³/hour for every 1 m² of room area | |
| Requirements according to the Code of Rules SP 54.13330.2011 to SNiP 31-01-2003 "Residential multi-apartment buildings"
|
||
| Bedroom, nursery, living room | One volume exchange per hour | |
| Cabinet, library | 0.5 volume per hour | |
| Linen, pantry, dressing room | 0.2 volume per hour | |
| Home gym, billiard room | 80 m³/hour | |
| Kitchen with electric stove | 60 m³/hour | |
| Premises with gas equipment | Single exchange + 100 m³/h for a gas stove | |
| A room with a solid fuel boiler or stove | Single exchange + 100 m³/h per boiler or furnace | |
| Home laundry, dryer, ironing | 90 m³/hour | |
| Shower, bath, toilet or shared bathroom | 25 m³/hour | |
| home sauna | 10 m³/h per person | |
An inquisitive reader will surely notice that the standards for different documents are somewhat different. Moreover, in one case, the norms are set exclusively by the size (volume) of the room, and in the other - by the number of people permanently staying in this room. (Under the concept of permanent residence is meant being in the room for 2 hours or more).
Therefore, when carrying out calculations, it is desirable to calculate the minimum volume of air exchange according to all available standards. And then - choose the result with the maximum indicator - then there will definitely be no error.
The first proposed calculator will help you quickly and accurately calculate the air flow for all rooms of an apartment or house.
