The volume of air in the room. Calculation of local exhaust. Types of air exchange used in industrial enterprises

Installation of ventilation is absolutely necessary in any premises, be it an apartment, a private house, a barn, a garage or a warehouse. The scheme of its creation is discussed at the design stage of the building. The house, which does not have ventilation, especially residential, will be uncomfortable, and soon unsuitable for living, since it will always be damp and stuffy, mold will appear in the corners, the wooden building elements rot, and it will eventually collapse much faster than laid. In this article we will talk about how to calculate the ventilation in the room.

What is the use of ventilation?

Some believe that you can completely do without ventilation - our ancestors lived somehow before the invention of any newfangled systems. And if in summer in such a house you can always open windows for ventilation, then in winter you will fully experience the "charm" of life in the old-fashioned way - condensation begins to appear on the windows, doors and walls, which in case of severe frosts turns into a beautiful ice crust, corners will start to grow gardens of black and green mold, and if you are lucky, in a year or two, harvest the mushrooms ... Is it worth saying that such a house will not last very long, and life in it will be a constant test for nerves and health.

With a constant inadequate influx of fresh air, the lungs of a person begin to work worse - there are diseases that can quickly become chronic. A child growing up in a house without ventilation can earn serious health problems for life.

Continues the "parade" of constant dust and zakopchennost - if the room does not arrive fresh air, then everything in it is cooked, fried, dusted, cleaned, settles on walls and furniture with a thick layer of plaque. On the kitchen ceiling in six months you will notice a large yellowish patch above the stove - these fatty vapors have settled and absorbed in the plaster, because there is nowhere else to go. In the bathroom on the ceiling and in the corners, there will also be eloquent evidences of the lack of ventilation in the form of mold spots due to constant humidity.

And, finally, it should be taken into account that at least once a year someone is sick in the house - germs from coughing and sneezing fly instantly around the room, settling on furniture, wallpaper, curtains, carpet. Hospital chambers are ventilated several times a day for a reason, and now imagine in what setting you will find yourself after a year of living in an apartment where there are no regular inflows of air. We hope that we have given weighty arguments in favor of the need for a ventilation system for living quarters and now it is possible to move from words to deeds.

Checking the ventilation

It happens that some of the above "symptoms" are manifested even in ventilated houses. This may mean that the system is weak or has stopped functioning for any reason. To check if the ventilation is working, light a match or lighter and bring the flame to the vent - if the fire is bent towards the grating that covers the hole, then there is traction and everything works. If there were no changes, vent channel  either blocked or jammed with leaves. In the case of apartments, this is very often the case if the neighbors made redevelopment and blocked the air duct.

It also happens that the thrust is present, but with interruptions, and at the same time it can bring smells from neighbors from above or below. In this case, you will need to equip the vent check valve, or install automatic blinds, closing with the return thrust.

Types of ventilation systems

All ventilation systems can be conditionally divided into categories depending on the functional load, the mode of transportation air masses  and that which sets them in motion.

Depending on the functional purpose, the following ventilation systems are available:

1. Fresh air - fresh air from the street constantly enters the premises.
2. Exhaust air is discharged from the house through ventilation ducts.
3. Recirculation - the system takes out the exhaust air and simultaneously "pumping" into the house fresh.

If you think about the principles of the above systems, the question arises: "And why does the air move to leave or enter the room?". For this purpose, the sorting of ventilation systems is used according to the nature of the awakening of air masses. These sources can be natural and mechanical (artificial).

In systems with natural ventilation, air moves due to pressure drops. You will immediately understand what you are talking about, if you recall the ventilation holes in the kitchen and in the bathroom that are in each multi-storey house - warm air and steam (shower, laundry, cooking) gets into this hole and is pulled outward due to pressure and gravitational forces .

In systems with mechanical sources of awakening, the air is driven by exhaust fans, which take it out of the room, acting on the principle of a conventional cooker hood.

So, when the air masses have acquired the ability to move, they should provide a safe and directional outlet (entrance). In connection with this, another classification was developed for the method of air flow movement - channel and non-channel. With the channel system, is it ever more or less clear - the air flows through special taps, and when it is channelless, it leaves the room or penetrates it through the slightly opened window openings, doors, slots, etc.

Calculation of the ventilation system

To ensure quality ventilation at home, it is not enough just to choose any system you like - it is necessary to find out how much air will be removed from the premises, and how much fresh air should be supplied from the street. In other words, it is necessary to find out the optimal air exchange at home, and based on these data to choose the ventilation system, buy fans of a certain capacity, channels, etc.

There are many ways to calculate the ventilation of the room, for example, to remove excess warm air  or fumes, dilution of contaminants and so on. However, they all require professional knowledge and experience. We need a method that every landlord or landlady can use. You should start by getting acquainted with special normative documents, which are developed for each state or region (GOST, SanPin, DBN, SNiP). In them you will find information on the requirements for ventilation systems for any premises, o necessary equipment, its capacities and location. By and large, there is everything you need to know for choosing a system.

But the architectural features of buildings dictate their conditions, and on the basis of these, engineers make up a ventilation project, focusing on the norms specified in state documents. Below we give an example of such a calculation of ventilation for a residential building, using the simplest methods: by multiplicity, sanitary standards and the total area.

Calculation by multiplicities

This calculation is rather complicated, but still feasible. The table below shows the ventilation rates of the premises required for the calculation.

Before this, it is worth explaining what is multiplicity. This is a value that shows how many times in 1 hour the air in the house has been replaced by fresh air. The multiplicity depends on the specifics of the building and its area. For example, consider a single air exchange - this means that an hour from the room was withdrawn and at the same time received an air quantity equal to the volume of the building itself. In the 2 lower columns of the table you will find the requirements for ventilation by the inflow and exhaust of air.

The calculation is made using the formula: L = n * V (cubic meter / hour), where n is the multiplicity (see in the table), and V is the room volume.

To calculate the ventilation for the whole house consisting of several rooms, consider from "without walls", that is, as one room with a common air volume. To do this, find out the volume of each room by multiplying the length, height and width of the walls, and then use the above formula.

It is worth noting that for most rooms you can do only inflow or extract, but for spaces with high humidity (kitchen, bathroom) you will need to organize a recirculation system. If there is a dash in the table, then the room does not need to be ventilated. As a result, you should agree the equation of the volume of the inflow and the volume of the hood. If this does not happen, the number of air exchange in these rooms can be increased to the required level.

If the table does not specify a room, calculate for it the ventilation rate of living quarters according to 3 cube of air per hour per 1 sq. Km. m, that is, according to the formula: L = S * 3, where S is the area of ​​the room.

All values ​​of L must be a multiple of 5, so, if necessary, round them up to five in the larger side. Calculate L for all rooms individually first for airflow, then for exhaust, add up the values ​​and compare the total L inflow and L extracts - they should be equal. If the inflow value is greater than the drawing, then in order to maintain the balance, increase the air exchange for those rooms where the air exchange was minimally permissible.

We calculate the ventilation by the multiplicities for a house with a square of 140 square meters. m with such rooms:

• kitchen area of ​​20 square meters. m (S1);
• bedroom for 24 square meters. m (S2);
• study - 16 square meters. m (S3);
• living room - 40 square meters. m (S4);
• entrance hall - 8 sq. m. m (S5);
• toilet - 2 square meters. m (S6);
• bathroom - 4 square meters. m (S7).

The height of the ceilings is 3.5 m. There is a young couple without children in the house.

It is necessary to calculate the volumes of rooms by multiplying the quadrature by the height of the ceilings. As a result, we get the kitchen = 70 cubic meters, the bedroom = 84, the office = 56, the living room = 140, the hallway = 28, the toilet = 7 and the bathroom = 14 cubic meters.

In the first table there is no multiplicity for the living room, therefore it is possible to calculate the norm for it, proceeding from the fact that for 1 sq. m room requires 3 cubic meters of air per hour. Multiply the area of ​​the living room by 3 and get 120 cubic meters per hour.

Now it remains to add air exchange of all rooms for inflow and separately for extraction and compare these figures. It turned out that the inflow was 265 cubic meters, and the exhaust is 165, so it needs to be increased. Add the values ​​of the hood for those rooms where stronger ventilation is required or where the values ​​were minimally acceptable - in the bathroom and the kitchen.

In the toilet and bathroom it is better to install only the hood, and in the bedroom, living room and office - only the inflow. This measure will prevent stale unpleasant odors.

Calculation of Sanitary Norms

To calculate the air exchange in an administrative-household or public building by sanitary standards, it will be necessary to know the approximate number of people who are constantly in the room. According to the norms of a person who is constantly in the room, at least 60 cubic meters of fresh air are needed per hour, 20 cubic meters will suffice for the temporary visitor.

Calculate the air exchange for the same house. If you recall the norms for 1 person, you get the formula (for the bedroom): L = 2 (human) * 60 cubic meters. To calculate the air exchange for the cabinet, one permanent and one temporary person should be considered: L = 1 * 60 + 1 * 20. In the living room, a young couple sometimes meets with two or three friends or parents, so for this room should also take into account temporary visitors.

If we calculate the air exchange for all rooms, taking the data from the first table, it becomes obvious that the volume of fresh air is much more than the amount of waste, and therefore the extracts should be increased by adding 195 cubic meters per hour to create a balance. It is recommended to increase evenly, distributing to all rooms, but it is also possible to serve in one room, the most requiring ventilation, for example, in the kitchen or bathroom. That is, to the volume indicator in the kitchen should be added 195, and will be 285 cubic meters per hour.

The exhaust air from the other large rooms will move into the kitchen and exit through the hole through natural draft or sucked in exhaust fans. It is very important to ensure the movement of air masses so that smells and moisture do not stagnate in the apartment.

Area calculation

Make the calculations, we have the following picture: L drawing 3 = 114 * 3 = 342 cubic meters / h

Summarizing

From all the above examples it can be seen that the value of air exchange in each of the options is different, but all of them are considered correct. Which of them should be guided by you, but the calculation by area and multiplicities will be cheaper than the sanitary norms. He also guarantees more comfortable conditions for life, so often the decisive factor in choosing ventilation system  is the financial position of the customer.

Duct selection

When the calculations are over, you can proceed with the selection of the ventilation scheme of the premises, that is, plan the plan, draw the drawings and select the equipment. Today, for ventilation systems, rectangular and circular air ducts are used. If you choose rectangular duct, make sure that the aspect ratio does not exceed 3: 1, otherwise the ventilation will constantly rustle, and the pressure in it will not be high enough (there will be no thrust).

Also, when choosing, it is necessary to take into account that the normal speed in the main line should reach about 5 m / s (in branches about 3 m / s). To determine the required cross-section dimensions, use the diagram below - it shows the dependence of the cross-sectional dimension on the air flow and its speed. Horizontals indicate air flow, verticals - speed, oblique lines - the corresponding dimensions of the duct.

Select the required cross-section of the branch lines that will go to each room and the ventilation line itself, so that air is supplied at a flow rate of 360 cubic meters per hour (as in the example with our house).

If you organize a natural hood, then the speed of air flow in the highway according to the norms should not be more than 1 m / h. Calculation of the exhaust ventilation of the room should take into account the normalized air speed of not more than 5 m / s for the main line and 3 m / s for the branches.

We hope this article will help you calculate air ventilation in the room and make your house comfortable. Well-executed calculations will allow you to save not only on the arrangement of the ventilation system, but also on major repairs in the distant future.

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Comments:

• Harmful discharge, affecting the microclimate of the premises
  • Computation by aggregated indicators
• Description of calculation methods

The microclimate of the premises of a building of any designation must comply with sanitary and hygienic norms to ensure the optimal or acceptable mode of operation or life activity of people. Microclimate parameters are mainly provided by systems air supply ventilation, and its calculation is reduced to determining the amount of fresh air.

Harmful discharge, affecting the microclimate of the premises

The composition and amount of harmful substances allocated to the premises depends on the functional purpose of the building and what is taking place in it technological processes. In residential and public buildings there are only allocations from the life of people, while in production facilities the composition of hazards can be anything, everything depends on the technological process. All hazards are divided into several types:

1. Harmfulness from the life of a person (release of moisture, carbon dioxide, heat).
2. The release of harmful vapors or aerosols of various substances during the process. The high concentration of these substances has a detrimental effect on the health of people working in the room.
3. In industrial buildings, technological processes with increased release of water vapor are frequent, which causes high humidity and condensation on cold surfaces. Such conditions for work do not correspond to sanitary norms.
4. Heat release from hot process equipment or products. Excess heat, affecting human health during the work shift, also have a negative impact on it.

For civil buildings, the calculation is carried out, as a rule, for the hazards specified in item 1. In industrial buildings, it is necessary to calculate the amount of supply air necessary to reduce the concentration of each type of harmful emissions, and to take the value from the largest of the results.

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Computation by aggregated indicators

The enlarged figures for calculation reflect the consumption of fresh air per unit of room volume, one person or one source of harmful emissions. The microclimate parameters in the premises of civil buildings are regulated by sanitary norms and requirements. For each type of building there are own standards, they indicate the values ​​of the multiplicity of air exchange for rooms of different purposes. In this case, the calculation is made by the formula:

• V - volume of the room, m3;
• k - the frequency of air exchange in 1 hour.

Multiplicity is a number that shows how many times in one hour the air in the room will be completely updated. At a value of 1, the amount of air will be equal to the volume of the room. In other cases, which do not take into account these standards, there are indicators of the optimal amount of fresh air per person. These standards are prescribed in SNiP 41-01-2003 and make up 30 m3 / h for one person for ventilated rooms, 60 m3 / h for unventilated rooms. Then the formula is used for the calculation:

• L - required amount of outside air for inflow, m3 / h;
• N - number of people permanently staying in the room, people;
• m - amount of inflow per person per hour.

Calculation by this formula is also acceptable in the event that other types of harmful emissions into the space of the industrial room are very small. When there is one or more of the same sources from which harmful fumes or aerosols emanate, the scoring method for aggregated indicators is applicable provided that the amount of outdoor air required for each is known. Then the value of m will show the amount of inflow to 1 source, and the parameter N in the formula means their number.

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Description of calculation methods

If there are many sources in the industrial building that emit harmful vapors during the process, it is required to carry out each of these substances. To do this, find out which substances are allocated and in what quantities, after which it is possible to calculate their concentration per 1 m3 in one room and compare it with the maximum permissible concentration (MPC) for each type of substances. These values ​​are established by normative documentation. In case of exceeding the MPC, calculate the amount of inflow that ventilation systems must provide. To do this, use the formula:

L = MB / yop - y0, where:

• L - necessary inflow, m3 / h;
• MB - the intensity of the release of harmful substance per unit time, mg / h;
• ydop - concentration of this substance in room air, mg / m3;
• y0 is its concentration in the incoming air, mg / m3.

The amount of inflow is calculated for each harmful release, after which the greatest of the results is taken for ventilation.

To neutralize surplus heat, the following formula is used to determine the amount of inflow:

L = Lmo +

In this formula, the parameters are:

• Lmo - the volume of the hood from the working or serviced zone (the working area occupies a space at a height of 2 m from the zero mark of clean floors) by local suction or for technological needs, m3 / h;
• Q - the amount of heat from process equipment or hot products, W;
• tmo is the temperature of the air mixture, which is removed from the local suction systems from the working area, ⁰С;
• tpom is the temperature of the air mixture removed from the rest of the room above the working area exhaust ventilation, ⁰С;
• tп - temperature of the treated fresh air, ⁰С;
• C is the heat capacity of the air mixture, 1.2 kJ (m3 ° C) is assumed.

Excess heat from technological processes is removed with the help of exhaust system  and, as a rule, they are used repeatedly (recycling).

Strict requirements are imposed on working conditions in industry and in industry. Different standards must be observed. Correct performance of many requirements affects the quality of the air environment. It ensures correct air exchange. At most industrial enterprises it can not be provided at the expense of natural ventilation, therefore special hoods are required. In order to properly adjust the air exchange, it is necessary to calculate the ventilation.

Types of air exchange used in industrial enterprises

Industrial ventilation systems

Regardless of the type of production, rather high requirements are imposed on the quality of air in any enterprise. There are standards for the content of different particles. To fully meet the requirements health standards  various types of ventilation systems are developed. Air quality depends on the type of air exchange used. Currently, the following types of ventilation are used in production:

• aeration, that is, general ventilation with a natural source. It regulates the air exchange throughout the room. It is used only in large industrial premises, for example, in shops without heating. This is the oldest type of ventilation, it is now used less and less often, as it does not cope with air pollution and is not able to regulate the temperature regime;
• local extract, it is used in industries where there are local sources for the release of harmful, polluting and poisonous substances. It is installed in the immediate vicinity of the emission sites;
• supply and exhaust ventilation with artificial motivation, used to regulate air exchange in large areas, in workshops, in various rooms.

Ventilation functions

Currently, the ventilation system performs the following functions:

• removal of industrial harmful substances released in the course of work. Their content in the air in the work area is regulated by regulatory documents. For each type of production set their own requirements;
• removal of excess moisture in the work area;
• filtration of polluted air withdrawn from the industrial premises;
• emission of removed pollutants into the height necessary for dispersion;
• regulation temperature conditions: removal of air heated during production (heat is released from working mechanisms, heated raw materials, substances entering into chemical reactions);
• filling the room with air from the street, while its filtration is carried out;
• heating or cooling of the intake air;
• humidification of air inside the production room and drawn from the street.

Types of air pollution

Before proceeding to the settlement work, it is necessary to find out what sources of pollution are present. At present, the following types of harmful emissions are encountered in production:

• excess heat from operating equipment, heated substances and so on;
• vapors, vapors and gases containing harmful substances;
• allocation of explosive gases;
• excess moisture;
• separation from people.

As a rule, in modern industries there are various types of pollution, for example, working equipment and chemicals. And none of the productions can not do without excretions from people, because in the process of activity a person breathes, small particles of skin are scattered from him and so on.

Calculation must be carried out for each type of pollution. In this case, they are not summed up, but are taken as the final largest result of the calculations. For example, if air is most needed to remove chemical air pollution, then this calculation will be adopted to calculate the required volume of general ventilation and exhaust capacities.

Perform calculations

As can be seen from all of the above, ventilation performs many different functions. Provide quality air purification can only a sufficient number of devices. Therefore, during installation, it is necessary to calculate necessary capacities  installed hood. Do not forget that different types of ventilation systems are used for different purposes.

Calculation of local exhaust

If harmful substances are emitted at the plant, they should be collected directly at the closest possible distance from the source of pollution. This will make their removal more effective. As a rule, different technological capacities become sources of emission, and working equipment can also pollute the atmosphere. To catch the released harmful substances use local exhaust devices - suction pumps. Usually they look like an umbrella and are installed above the source of vapors or gases. In some cases, such installations are supplied with the equipment, in others - the capacities and sizes are calculated. It is not difficult to execute them if you know the correct calculation formula and have some initial data.

To make a calculation it is necessary to make some measurements and find out the following parameters:

• size of the source of emission, length of sides, section if it has a rectangular or square shape (parameters a x b);
• if the source of contamination has a circular shape, it is necessary to know its diameter (parameter d);
• the velocity of air movement in the zone where the ejection occurs (parameter vb);
• suction speed in the area of ​​the exhaust system (umbrella) (parameter v3);
• the planned or available height of the hood installation above the source of contamination (parameter z). It should be remembered that the closer the exhaust is to the source of the release, the more efficiently the pollutants are trapped. Therefore, the umbrella should be placed as low as possible above the container or equipment.

Calculation formulas for rectangular hoods  look like this:

A = a + 0.8z, where A is the side of the ventilation device, a is the side of the pollution source, and z is the distance from the emission source to the exhaust.

B = b + 0.8z, where B is the side of the ventilation device, b is the side of the source of contamination, and z is the distance from the emission source to the exhaust.

If the hood is round, its diameter is calculated. Then the formula will look like this:

D = d + 0.8z, where D is the drawing diameter, d is the diameter of the contamination source, and z is the distance from the emission source to the drawing.

The exhaust device is made in the form of a cone, and the angle should be no more than 60 degrees. Otherwise, the efficiency of the ventilation system will decrease, as zones are formed along the edges where the air stagnates. If the indoor air velocity is more than 0.4 m / s, then the cone must be equipped with special flaps to prevent dispersion of the released substances and protect them from external influences.

Know the overall dimensions of the hood is necessary, because of these parameters will depend on the quality of air exchange. Determine the amount exhaust air  you can use the following formula: L = 3600v3 x S3, where L is the air flow rate (m 3 / h), vз is the air velocity in the exhaust device (a special table is used to determine this parameter), S3 is the area of ​​the ventilation system opening.

If the umbrella is rectangular or square, its area is calculated by the formula S = A * B, where A and B are the sides of the figure. If the hood is in the form of a circle, then its size is calculated by the formula S = 0.785D, where D is the diameter of the umbrella.

The results obtained should be taken into account in the design and calculation of general ventilation.

Calculation of general exchange of supply and exhaust ventilation

When the necessary volumes and parameters of the local extraction are calculated, as well as the volumes and types of pollution, it is possible to start calculating the required volume of air exchange in the production room.

The simplest option is when there are no harmful emissions during operation different types, but there are only those pollutants that people give out. The optimal amount of clean air will ensure normal working conditions, compliance with sanitary standards, as well as the necessary cleanliness of the process.

To calculate the required air volume for working people, use the following formula: L = N * m, where L is the required amount of air (m 3 / h), N is the number of working people at the production site or in a particular room, m is the air consumption for breathing 1 person per hour.

Specific air flow per person per hour is a fixed value, indicated in special SNiPs. The norms indicate that the volume of the mixture per person is 30 m 3 / h, if the premises are ventilated, if this is not available, the rate becomes twice as high and reaches 60 m 3 / h.

The situation is more complicated if there are various sources of harmful substances emission on the site, especially if there are a lot of them and they are dispersed over a large area. In this case local exhaust hoods  will not be able to completely get rid of harmful substances. Therefore, in production often resort to the following method.

Emissions are dispersed, and then removed using a general exchange combined extract and input ventilation. All harmful substances have their own maximum permissible concentrations (maximum allowable concentrations), their values ​​can be found in the specialized literature, as well as regulatory documents.

L = Mv / (ynom - yn), where L is the required amount of fresh air, Mv is the mass of the released harmful substance (mg / h), the specific concentration of the substance (mg / m3), yn is the concentration of this substance in the air through the ventilation system.

If several types of pollutants are released, then it is necessary to calculate the necessary amount of a clean air mixture for each of them, and then summarize them. As a result, the total volume of air that will flow into the production roomto ensure compliance with sanitary requirements and normal working conditions.

The calculation of ventilation is a complicated matter, requiring great accuracy and special knowledge. Therefore, for self-calculation you can use online services. If the production has to work with dangerous and explosive substances, it is better to entrust the calculation of ventilation to professionals.

Before purchasing equipment, it is necessary to calculate and design ventilation systems. When selecting equipment for a ventilation system, it is worth considering the following characteristics:

• Efficiency and productivity by air;
• Power of air heater;
• Working pressure of the fan;
• Air velocity and diameter of air ducts;
• Maximum noise figure;

Calculation and drafting of the ventilation system must begin with the calculation of the required air capacity (cubic meter / hour). In order to correctly calculate the power, you need a detailed plan of the building or premises for each floor with an explication indicating the type of premises and its purpose, as well as the area. They start counting from the measurement of the required multiplicity of air exchange, showing the number of times the room air changes in an hour. So for a room with a total area of ​​100 m2 ceiling height in which 3 m (volume 300 m3) a single air exchange - 300 cubic meters per hour. The necessary multiplicity of air exchange is determined by the type of use of the premises (residential, administrative, industrial), the number of people staying there, the capacity of heating equipment and other devices that produce heat, and is indicated in SNiP. Usually there is a single exchange of air for living quarters, two to three times air exchange is optimal for office buildings.

1. We consider the multiplicity of air exchange:

L = n * S * H, the values

n is the rate of air exchange multiplicity: for residential premises n = 1, for administrative n = 2.5;
S - total area, square meters;
H - ceiling height, meters;

2. Calculation of the exchange of air by the number of people:
L = N * L norms, the values
L - the required capacity of the supply ventilation system, cubic meters per hour;
N is the number of people in the room;
L norms - the value of air consumption by one person:
  a) Minimum physical activity - 20 m3 / h;
  b) Average - 40 m3 / h;
  Intensive 60 m3 / h.

After calculating the required air exchange, we begin to select the ventilation equipment of suitable performance. It must be remembered that due to the resistance of the duct network, the efficiency of the work decreases. The relationship between performance and full pressure is easily recognized by the ventilation characteristics indicated in the technical description. For example: a 30 m duct with a single ventilation grid produces a pressure drop of about 200 Pa.

Standard performance of the ventilation system:

• For residential premises - from 100 to 500 m3 / h;
• For private houses and cottages - from 1000 to 2000 m3 / h;
• For administrative premises - from 1000 to 10,000 m3 / h.

The heater, if necessary, heats the outside cold air in the supply air system. The power of the air heater is calculated from such data as ventilation capacity, required room air temperature and minimum ambient air temperature. The second and third indicators are set by SNiP. The temperature of the air in the room should not fall below the mark at +18 ° C. The lowest temperature in the Moscow region is -26 ° С. Therefore, the air heater at maximum power should heat the airflow by 44 ° C. Frosts in the Moscow region tend to be rare and quickly pass, in the ventilation systems, it is possible to install air heaters that have less than calculated capacity. The system must have a fan speed control.

When calculating the performance of the air heater, it is important to consider:
1. Single-phase or three-phase voltage of electricity (220 V) or (380 V). If the power rating of the heater is more than 5 kW, three-phase power is required.

2. Maximum power consumption. The electricity consumed by the air heater can be calculated by the formula:
  I = P / U, in which
I - maximum electricity consumption, A;

U - mains voltage (220 V - one phase, 660 V - three phases);

The temperature at which the air heater of this capacity can heat the supply air flow can be calculated by the formula:
ΔT = 2.98 * P / L, in which
ΔT - delta of incoming and outgoing air temperatures in the supply ventilation system, ° С;
P - heater output, W;
L - capacity of the ventilation system, m3 / h.

The standard performance of the heater is 1 - 5 kW for residential premises, from 5 to 50 kW for administrative purposes. If it is not possible to operate the electric air heater, the installation of a water heater, which uses water from a central or individual heating system as a coolant, is optimal.