Features and procedure for calculating exhaust and supply ventilation. Calculation of exhaust ventilation all formulas and examples How to calculate ventilation correctly

- this is a system in which there is no forced driving force: a fan or other unit, and air flows under the influence of pressure drops. The main components of the system are vertical channels that start in a ventilated room and end 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 building.

The temperature difference at the lower and upper points of the channel contributes to the fact that the air (in the house it is warmer than outside) rises. 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 mine, turns, obstacles, narrowings in the passages, as well as the wind, and it can both contribute to traction and 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 works silently. But natural ventilation also has disadvantages:

• work efficiency directly depends on atmospheric phenomena, therefore 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 downwards;
• in the cold season is the cause of significant heat loss;
• does not work in the heat (there is no temperature difference) and air exchange is possible only through open windows;
• if the work is inefficient, dampness and drafts may occur in the room.

Performance standards and natural ventilation channels

The best option for the location of the channels is a niche in the wall of the building. When laying it should be remembered that the best traction will be with a flat and smooth surface of the air ducts. For system maintenance, that is, cleaning, you need to design a built-in hatch with a door. A deflector is installed above them so that debris and various sediments do not end up inside the mines.

According to building codes, the minimum performance of the system should be based on the following calculation: in those rooms where people are constantly there should be a complete renewal of the air every hour. As for other premises, the following should be removed:

• from the kitchen - at least 60 m³ / h when using an electric stove and at least 90 m³ / h when using a gas stove;
• baths, restroom - 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 provides for 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;
• pantry - provided that its door opens into the living room. If it leads to the hall or kitchen, then only the supply channel can be equipped;
• 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 are entrance doors from the stairs, channels are also laid from the corridor, and if not, from each room.

When calculating the number of channels, it is necessary to take into account how the floor on the ground floor is equipped. If it is wooden and mounted on logs, 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 the optimal section of the channels.

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Channel parameters and ventilation calculation

When laying air ducts, both rectangular blocks and pipes can be used. In the first case, the minimum side size is 10 cm. In the second case, the smallest cross-sectional area of ​​the duct is 0.016 m², which corresponds to a pipe diameter of 150 mm. Through a channel with such parameters, an air volume equal to 30 m³ / h can pass, provided that the height of the pipe is more than 3 m (with a lower indicator, natural ventilation is not provided).

Table 2. Performance of the ventilation channel.

In the event that it is required to strengthen the performance of the duct, then either the cross-sectional area of ​​\u200b\u200bthe 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 are required, 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 to rooms with exhaust shafts and is removed through them.

The calculation is carried out step by step:

1. The smallest amount of air that should be supplied from the outside is determined - Q p, m³ / h, the value is found according to the table from SP 54.13330.2011 "Residential multi-apartment buildings" (table 1);
2. 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 indicated in the section "Performance standards and channels of natural ventilation";
3. The results obtained are compared. For the minimum productivity - Q p, m³ / h - take the largest of them;
4. For each floor, the height of the channel is determined. This parameter is set based on the dimensions of the entire structure;
5. According to the table (table 2), the number of standard channels is found, while their total performance should not be less than the minimum calculated;
6. The resulting number of channels is distributed between the rooms where the air ducts must be without fail.

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. Separate attention should be paid to the fact that a forced system is 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 need to use a 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 air 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 ​​​​are usually used: 2, 3, 4, 5, 6 m / s. In this case, the air flow in a rectangular duct will be:

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

If the calculation of ventilation is carried out for a round duct with a diameter of 160 mm, then 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, the following flow rate must be observed at certain speeds of air mass movement:

• 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 for air conditioning of a premise 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. At the same time, 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 by taking into account the climatic 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 performance of a system serving up to 4 rooms.
• Dimensions of air ducts and air distribution grilles.
• Air line resistance.
• Heater power and estimated electricity costs (when using an electric heater).

If you need to choose a model with humidification, cooling or recuperation, use the calculator on the Breezart website.

An example of calculating ventilation using a calculator

In this example, we will show how to calculate the supply ventilation for a 3-room apartment in which a family of three lives (two adults and a child). During the day, relatives sometimes come to them, so up to 5 people can stay in the living room for a long time. The ceiling height of the apartment is 2.8 meters. Room options:

We will set the consumption rates for the bedroom and the nursery in accordance with the recommendations of SNiP - 60 m³ / h per person. For the living room, we will limit ourselves to 30 m³ / h, since a large number of people in this room are infrequent. According to SNiP, such air flow is acceptable for rooms with natural ventilation (you can open a window for ventilation). If we also set an air flow rate of 60 m³/h per person for the living room, then the required performance for this room would be 300 m³/h. The cost of electricity to heat this amount of air would be very high, so we made a compromise between comfort and economy. To calculate the air exchange by the multiplicity for all rooms, we will choose a comfortable double air exchange.

The main air duct will be rectangular rigid, the branches will be flexible and soundproof (this combination of duct types is not the most common, but we chose it for demonstration purposes). For additional purification of the supply air, a carbon-dust fine filter of the EU5 class will be installed (we will calculate the network resistance with dirty filters). The air velocities in the air ducts and the permissible noise level on the gratings will be left equal to the recommended values ​​that are set by default.

Let's start the calculation by drawing up a diagram of the air distribution network. This scheme will allow us to determine the length of the ducts and the number of turns that can be both in the horizontal and vertical plane (we need to count all the turns at a right angle). So our schema is:

The resistance of the air distribution network is equal to the resistance of the longest section. This section can be divided into two parts: the main duct and the longest branch. If you have two branches of approximately the same length, then you need to determine which one has more resistance. To do this, we can assume that the resistance of one turn is equal to the resistance of 2.5 meters of the duct, then the branch with the maximum value (2.5 * number of turns + duct length) will have the greatest resistance. It is necessary to select two parts from the route in order to be able to set different types of air ducts and different air speeds for the main section and branches.

In our system, balancing throttle valves are installed on all branches, allowing you to adjust the air flow in each room in accordance with the project. Their resistance (in the open state) has already been taken into account, since this is a standard element of the ventilation system.

The length of the main air duct (from the air intake grille to the branch to room No. 1) is 15 meters, there are 4 right-angle turns in this section. The length of the supply unit and the air filter can be ignored (their resistance will be taken into account separately), and the silencer resistance can be taken equal to the resistance of an air duct of the same length, that is, simply consider it a part of the main air duct. The longest branch is 7 meters long and has 3 right angle bends (one at the branch, one at the duct and one at the adapter). Thus, we have set all the necessary initial data and now we can proceed to the calculations (screenshot). The calculation results are summarized in tables:

Calculation of the air duct network

• For each room (subsection 1.2), the performance is calculated, the cross-section of the duct is determined, and a suitable duct of standard diameter is selected. According to the Arktos catalog, the dimensions of distribution grids with a given noise level are determined (data for the AMN, ADN, AMR, ADR series are used). You can use other gratings with the same dimensions - in this case, there may be a slight change in the noise level and network resistance. In our case, the grilles for all rooms turned out to be the same, since at a noise level of 25 dB(A) the allowable air flow through them is 180 m³/h (there are no smaller grilles in these series).
• The sum of the air flow rates for all three rooms gives us the total system performance (subsection 1.3). When using a VAV system, the system performance will be one third lower due to the separate adjustment of the air flow in each room. Next, the section of the main air duct is calculated (in the right column - for the VAV system) and suitable rectangular air ducts are selected (usually several options are given with different aspect ratios). At the end of the section, the resistance of the air duct network is calculated, which turned out to be very large - this is due to the use of a fine filter in the ventilation system, which has a high resistance.
• We have received all the necessary data to complete the air distribution network, with the exception of the size of the main air duct between branches 1 and 3 (this parameter is not calculated in the calculator, since the network configuration is not known in advance). However, the cross-sectional area of ​​this section can be easily calculated manually: from the cross-sectional area of ​​the main duct, you need to subtract the cross-sectional area of ​​\u200b\u200bbranch No. 3. Having obtained the cross-sectional area of ​​\u200b\u200bthe duct, its size can be determined by.

Calculation of heater power and selection of air handling unit

The recommended Breezart 550 Lux model has programmable parameters (capacity and power of the heater), therefore, the performance that should be selected when setting up the remote control is indicated in brackets. It can be seen that the maximum possible power of the heater of this launcher is 11% lower than the calculated value. The lack of power will be noticeable only at outdoor temperatures below -22 ° C, and this does not happen often. In such cases, the air handling unit will automatically switch to a lower speed to maintain the set outlet temperature (Comfort function).

In the calculation results, in addition to the required performance of the ventilation system, the maximum performance of the PU at a given network resistance is indicated. If this performance turns out to be noticeably higher than the required value, you can take advantage of the possibility of programmatically limiting the maximum performance, which is available for all Breezart ventilation units. For a VAV system, the maximum performance is indicated for reference, since its performance is adjusted automatically during the operation of the system.

Calculation of the cost of operation

This section calculates the cost of electricity used to heat the air during the cold season. The costs for a VAV system depend on its configuration and mode of operation, so they are assumed to be equal to the average value: 60% of the costs of a conventional ventilation system. In our case, you can save money by reducing the air consumption at night in the living room, and during the day in the bedroom.

Do you dream that the house has a healthy microclimate and that no room smells musty and damp? In order for the house to be truly comfortable, even at the design stage, it is necessary to carry out a competent calculation of ventilation.

If this important point is missed during the construction of the house, in the future you will have to solve a number of problems: from removing mold in the bathroom to new repairs and installing an air duct system. Agree, it’s not very pleasant to see black mold nurseries in the kitchen on the windowsill or in the corners of the children’s room, and even plunge into repair work again.

The article presented by us contains useful materials on the calculation of ventilation systems, reference tables. Formulas, illustrative illustrations and a real example for premises for various purposes and a certain area, shown in the video, are given.

With correct calculations and proper installation, the ventilation of the house is carried out in a suitable mode. This means that the air in the premises will be fresh, with normal humidity and without unpleasant odors.

If the opposite picture is observed, for example, constant stuffiness in the bathroom or other negative phenomena, then you need to check the condition of the ventilation system.

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Conclusions and useful video on the topic

Roller #1. Useful information on the principles of operation of the ventilation system:

Roller #2. Together with the exhaust air, heat also leaves the home. Here, the calculations of heat losses associated with the operation of the ventilation system are clearly demonstrated:

The correct calculation of ventilation is the basis for its successful functioning and the guarantee of a favorable microclimate in a house or apartment. Knowing the basic parameters on which such calculations are based will allow not only to correctly design the ventilation system during construction, but also to correct its condition if circumstances change.