One of the conditions for creating a comfortable microclimate in residential and industrial premises is the presence engineering system which allows air to circulate. To ensure its effective operation, it is necessary to correctly calculate the length and diameter of the ventilation pipe. To do this, several methods are used, depending on the characteristics of the engineering system.
Ventilation diagram for a private house
Consequences of poor ventilation
If the inflow system is not organized correctly fresh air there will be a lack of oxygen in the rooms and high humidity. Errors in the design of the hood are fraught with the appearance of soot on the walls of the kitchen, fogging of the windows and the appearance of fungus on the surface of the walls.
Fogging of windows due to insufficient exhaust
It should be taken into account that round or square pipes can be used to install the ventilation system. When removing air without the use of special devices, it is advisable to install round air ducts, since they are stronger, more airtight and have good aerodynamic characteristics. Square pipes It is better to use for forced ventilation.
Calculation of the ventilation system
Standard volume of supply air
Typically, residential buildings use systems natural ventilation. In this case, outside air enters the premises through transoms, vents and special valves, and is removed using ventilation ducts. They can be attached or located in interior walls. The construction of ventilation ducts in external enclosing structures is not allowed due to the possible formation of condensation on the surface and subsequent damage to the structures. In addition, cooling can reduce the air exchange rate.
Ensuring natural air flow through ventilation
Defining parameters ventilation pipes for residential buildings is carried out on the basis of the requirements regulated by SNiP and others regulatory documents. In addition, the exchange multiplicity indicator is also important, which reflects the operating efficiency ventilation system. According to it, the volume of air flow into the room depends on its purpose and is:
- For residential buildings -3 m 3 /hour per 1 m 2 area, regardless of the number of people staying on the territory. According to sanitary standards, 20 m 3 / hour is enough for temporary residents, and 60 m 3 / hour for permanent residents.
- For ancillary buildings (garage, etc.) - at least 180 m 3 /hour.
To calculate the diameter, a system with natural air flow is taken as a basis, without installing special devices. The simplest option is to use the ratio of the area of the room and the cross-section of the ventilation hole.
In residential buildings, 5.4 m2 of air duct cross-section is required per 1 m2, and in utility buildings - about 17.6 m2. However, its diameter cannot be less than 15 m2, otherwise air circulation will not be ensured. More accurate data is obtained using complex calculations.
Algorithm for determining the diameter of a ventilation pipe
Based on the table given in SNiP, the parameters of the ventilation pipe are determined based on the air exchange rate. It is a value that shows how many times per hour the air in the room is replaced, and depends on its volume. Before determining the diameter of the pipe for ventilation, do the following:
Diagram for determining the diameter of the ventilation pipe
Features of determining the length of ventilation pipes
One more important parameter when designing ventilation systems is the length outer pipe. It unites all the channels in the house through which air circulates and serves to remove it outside.
Calculation according to the table
The height of the ventilation pipe depends on its diameter and is determined from the table. Its cells indicate the cross-section of the air ducts, and the column on the left shows the width of the pipes. Their height is indicated in the top line and is indicated in mm.
Selecting the height of the ventilation pipe according to the table
In this case, you need to take into account:
- If the ventilation pipe is located next to, then their heights must match to avoid smoke entering the premises during the heating season.
- When the air duct is located from the ridge or parapet at a distance that does not exceed 1.5 m, its height must be more than 0.5 m. If the pipe is located within 1.5 to 3 m from the roof ridge, then it cannot be lower his.
- Height of ventilation pipe above the roof flat shape cannot be less than 0.5 m.
Location of ventilation pipes relative to the roof ridge
When choosing a pipe for ventilation construction and determining its location, it is necessary to provide sufficient wind resistance. It must withstand a storm of 10 points, which is 40-60 kg per 1 m 2 of surface.
Using the Software
An example of calculating natural ventilation using special programs
Calculating natural ventilation is less labor-intensive if you use a special program for this. To do this, first determine the optimal volume of air flow, depending on the purpose of the room. Then, based on the data obtained and the features of the designed system, a calculation of the ventilation pipe is made. In this case, the program allows you to take into account:
- average temperature inside and outside;
- geometric shape of air ducts;
- roughness of the internal surface, which depends on the material of the pipes;
- resistance to air movement.
Ventilation system with round pipes
As a result, the required dimensions of ventilation pipes are obtained for the construction of an engineering system that must ensure air circulation under certain conditions.
When calculating the parameters of a ventilation pipe, you should also pay attention to the local resistance during air circulation. It can occur due to the presence of meshes, gratings, outlets and other design features.
.Correct calculation of ventilation pipe parameters will allow you to design and build effective system, which will make it possible to control the level of humidity in the premises and provide comfortable conditions for accommodation.
It is not always possible to invite a specialist to design the system utility networks. What to do if during the renovation or construction of your facility you need to calculate the ventilation air ducts? Is it possible to produce it on your own?
The calculation will allow you to create an effective system that will ensure uninterrupted operation of units, fans and air handling units. If everything is calculated correctly, this will reduce costs for the purchase of materials and equipment, and subsequently for further maintenance of the system.
Calculation of air ducts of the ventilation system for premises can be carried out 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. Nowadays, products made of steel, plastic, fabric, aluminum foil, etc. are used. Air ducts are often made of galvanized or of stainless steel, this can be organized even in a small workshop. Such products are easy to install and calculating such ventilation does not cause problems.
In addition, air ducts may vary in appearance. They can be square, rectangular and oval. Each type has its own advantages.
- Rectangular ones allow you to make ventilation systems small height or width, while maintaining required area sections.
- Round systems have less material,
- Oval ones combine the pros and cons of other types.
For the calculation example, let’s choose round pipes made of tin. These are products that are used for ventilation of housing, office and retail spaces. We will carry out the calculation using one of the methods that allows us to accurately select the air duct network and find its characteristics.
Method for calculating air ducts using the constant velocity method
You need to start with a floor plan.
Using all standards, determine required quantity air into each zone and draw a wiring diagram. It shows all grilles, diffusers, cross-section changes and bends. The calculation is made for the most remote point of the ventilation system, divided into areas limited by branches or grilles.
Calculation of an air duct for installation consists of selecting the required cross-section along the entire length, as well as finding the pressure loss for selecting a fan or air handling 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 air duct. To do this you will need a pressure loss graph.
The schedule is different for each type of duct. Typically, manufacturers provide such information for their products, or you can find it in reference books. Let's calculate round tin air ducts, the graph for which is shown in our figure.
Nomogram for choosing sizes
Using the chosen method, we set the air speed of each section. It must be within the limits of the standards for buildings and premises of the selected purpose. For main air supply and exhaust ventilation The following values are recommended:
- residential premises – 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;
- residential premises – 3.0–5.0 m/s;
- production – 4.0–9.0 m/s.
When the speed exceeds the permissible limit, the noise level increases to a level that is uncomfortable for humans.
After determining the speed (in the example 4.0 m/s) we find required section air ducts according to schedule. There are also pressure losses per 1 m of network, which will be needed for the calculation. The total pressure loss in Pascals is found by the product specific value for the length of the section:
Manual=Manual·Manual.
Network elements and local resistances
Losses on network elements (grids, diffusers, tees, turns, changes in cross-section, etc.) also matter. For grids and some elements, these values are indicated in the documentation. They can also be calculated by multiplying the coefficient of local resistance (k.m.s.) and the dynamic pressure in it:
Rm. s.=ζ·Rd.
Where Рд=V2·ρ/2 (ρ – air density).
K. m.s. determined from reference books and factory characteristics of products. We summarize all types of pressure losses for each section and for the entire network. For convenience, we will do this using the 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 install dampers or diaphragms on the bends. To do this, we calculate the required k.m.s. according to the formula:
ζ= 2Rizb/V2,
where Rizb is the difference between the available pressure and losses on the branch. Use the table to select the aperture diameter.
The required diaphragm diameter for 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 the total air flow in the network, this will be easy to do.
Proper ventilation in the home significantly improves a person’s quality of life. If incorrect calculation of supply and exhaust ventilation A lot of problems arise - for a person with health, for a building with destruction.
Before starting construction, it is mandatory and necessary to make calculations and, accordingly, apply them in the project.
PHYSICAL COMPONENTS OF CALCULATIONS
According to the way of working, currently, ventilation circuits are divided into:
- Exhaust. To remove used air.
- Inlet. To let in clean air.
- Recuperative. Supply and exhaust. Remove the used one and bring in a clean one.
IN modern world ventilation schemes include various additional equipment:
- Devices for heating or cooling supplied air.
- Filters for purifying odors and impurities.
- Devices for humidification and air distribution throughout rooms.
When calculating ventilation, the following values are taken into account:
- Air consumption in cubic meters/hour.
- Pressure in air channels in atmospheres.
- Heater power in kW.
- Cross-sectional area of air channels in sq. cm.
Calculation of exhaust ventilation example
Before the beginning exhaust ventilation calculations it is necessary to study the SN and P (System of Norms and Rules) design 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 kb.m./hour. 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 frequency - 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 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 = S x H = 20 x 2.5 = 50 cubic meters.
In the same order, we calculate the exhaust ventilation performance of the entire house.
Calculation of exhaust ventilation for industrial premises
At calculation of exhaust ventilation for production premises 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 kb.m./h.
We choose a larger one - 180 cubic meters / hour.
As a rule, unified ventilation systems are divided into:
- 100 – 500 cubic meters/hour. - apartments.
- 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
In climate middle zone, the air entering the room must be heated. To do this, set supply ventilation with heating of incoming air.
Heating of the coolant is carried out in various ways - with an electric heater, inlet 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 power of the air heater is calculated depending on the lowest (in a given region) street temperature. Formula for calculating the maximum heating temperature of a room with an air heater:
N/V x 2.98 where 2.98 is a constant.
Example: air flow – 180 cubic meters/hour. (garage). N = 2 kW.
Thus, the garage can be heated to 18 degrees. At outside temperature minus 15 degrees.
PRESSURE AND SECTION
The pressure and, accordingly, the speed of movement of air masses is 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 diameter of the channels, the following values are empirically taken:
- For residential premises – 5.5 sq.cm. per 1 sq.m. area.
- For garage and others production premises– 17.5 sq.cm. per 1 sq.m.
In this case, a flow speed of 2.4 – 4.2 m/sec is achieved.
ABOUT ELECTRICITY CONSUMPTION
Electricity consumption directly depends on the duration of operation of the electric heater, and 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. The formula used for calculation is:
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 – amount of electricity.
Т1 – maximum daytime temperature.
T2 – minimum night temperature.
L – productivity 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 – price of electricity during the day.
n – price of electricity at night.
N – number of days in a month.
Thus, if you stick 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.
is a system in which there is no forced driving force: a fan or other unit, and the flow of air occurs under the influence of pressure changes. The main components of the system are vertical channels starting in the ventilated room and ending at least 1 m above the roof level. The calculation of their number, as well as the determination of their location, is carried out at the design stage of the structure.
The temperature difference at the lower and upper points of the duct causes the air (it is warmer in the house than outside) to rise upward. The main indicators that affect the traction force are: the height and cross-section of the channel. In addition to them, the efficiency of the natural ventilation system is affected by the thermal insulation of the shaft, turns, obstacles, narrowing in the passages, as well as wind, and it can either contribute to the draft or reduce it.
Such a system has a fairly simple arrangement and does not require significant costs both during installation and during operation. It does not include mechanisms with electric drives, it operates silently. But natural ventilation also has disadvantages:
- operational efficiency directly depends on atmospheric phenomena, so it is not used optimally for most of the year;
- performance cannot be adjusted, the only thing that needs to be adjusted is air exchange, and then only downward;
- in the cold season it causes significant heat loss;
- does not work in hot weather (there is no temperature difference) and air exchange is possible only through open vents;
- If work is ineffective, dampness and drafts may occur in the room.
Performance standards and natural ventilation channels
The optimal location for the channels is a niche in the wall of the building. When laying it should be remembered that the best traction will be when it is level and smooth surface air ducts To service the system, that is, cleaning, you need to design a built-in hatch with a door. To prevent debris and various sediments from ending up inside the mines, a deflector is installed above them.
According to building regulations minimum system performance should be based on next calculation: in those rooms where people are constantly present, the air should be completely renewed every hour. As for other premises, the following should be removed:
- from the kitchen - at least 60 m³/hour when using an electric stove and at least 90 m³/hour when using a gas stove;
- baths, toilets - at least 25 m³/hour, if the bathroom is combined, then at least 50 m³/hour.
When designing a ventilation system for cottages, the most optimal model is one that involves laying a common exhaust pipe through all rooms. But if this is not possible, then the ventilation ducts are laid from:
Table 1. Ventilation air exchange rate.
- bathroom;
- kitchens;
- storage room - provided that its door opens in living room. If it leads to the hall or kitchen, then only a supply duct can be installed;
- boiler room;
- from rooms that are separated from rooms with ventilation by more than two doors;
- if the house has several floors, then starting from the second, if there is entrance doors From the stairs, channels are also laid from the corridor, and if there are none, from each room.
When calculating the number of channels, it is necessary to take into account how the floor on the first floor is equipped. If it is wooden and mounted on joists, then a separate passage is provided for air ventilation in the voids under such a floor.
In addition to determining the number of air ducts, the calculation of the ventilation system includes determining optimal cross section channels.
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Channel parameters and ventilation calculations
When laying air ducts, both rectangular blocks and pipes can be used. In the first case minimum size side is 10 cm. In the second smallest area air duct cross-section is 0.016 m², which corresponds to a pipe diameter of 150 mm. A channel with such parameters can pass a volume of air equal to 30 m³/hour, provided that the pipe height is more than 3 m (with a lower value, natural ventilation is not provided).
Table 2. Ventilation channel performance.
If it is necessary to increase the performance of the air duct, then either the cross-sectional area of the pipe expands or the length of the channel increases. The length, as a rule, is determined by local conditions - the number and height of floors, the presence of an attic. In order for the traction force in each of the air ducts to be equal, the length of the channels on the floor must be the same.
To determine what size ventilation ducts need to be laid, it is necessary to calculate the amount of air that needs to be removed. It is assumed that outside air enters the premises, then it is distributed into rooms with exhaust shafts and is exhausted through them.
The calculation is made floor by floor:
- The smallest amount of air that should come from outside is determined - Q p, m³/hour, the value is found according to the table from SP 54.13330.2011 “Residential multi-apartment buildings” (Table 1);
- According to the standards, the smallest amount of air that needs to be removed from the house is determined - Q in, m³/hour. The parameters are specified in the section “Performance standards and natural ventilation channels”;
- The obtained indicators are compared. The minimum productivity - Q р, m³/hour - is taken to be the largest of them;
- For each floor, the height of the channel is determined. This parameter is set based on the dimensions of the entire building;
- According to the table (Table 2), the number of standard channels is found, and their total performance should not be less than the minimum calculated;
- The resulting number of channels is distributed between rooms where air ducts must be present.