Consumption in the ventilation system. How to calculate the supply and exhaust ventilation system of industrial premises

Regular requirements are presented to working conditions in production and industry. Various standards must be respected. Proper execution Many requirements affect the quality of the air environment. It provides the right air exchange. On most industrial enterprises It cannot be provided at the expense of natural ventilation, so the installation of special hoods is required. To properly establish air exchange, you need to calculate ventilation.

Types of air exchange used in industrial enterprises

Industrial ventilation systems

Regardless of the type of production, the quality of air at any enterprise is presented fairly high demands. There are standards for the content of various particles. To fully fulfill the requirements of sanitary standards developed different kinds ventilation systems. The quality of air is dependent on the type of air exchange. Currently, the following types of ventilation are used in production:

• aeration, that is, the general ventilation with natural source. It regulates air exchange in the entire room. It is used only in large industrial premises, for example, in workshops without heating. This is the oldest type of ventilation, is currently used less often and less often, as it does not work well with air pollution and is not able to adjust the temperature mode;
• the local exhaust, it is used in the production where there are local sources of emissions of harmful, polluting and poisonous substances. It is installed in close proximity to emission locations;
• supply-exhaust ventilation with artificial motivation used to regulate air exchange on large squares, in the shops, in various premises.

Ventilation functions

Currently, the ventilation system performs the following functions:

• removal of production harmful substances allocated during operation. Their content in the air in the working area is regulated regulatory documents. For each type of production, their requirements are established;
• removal of excess moisture in the working area;
• filtering of polar out production premises contaminated air;
• release of remote pollutants to the height necessary for dispersion;
• regulation temperature mode: removal of air-heated in the process (heat is highlighted from working mechanisms, heated raw materials, substances entering chemical reactions);
• filling with air from the street, while filtering is carried out;
• heating or cooling of retractable air;
• moisturizing air inside the production premises and drawn from the street.

Types of air pollution

Before proceeding with the settlement work, it is necessary to find out which sources of pollution are available. Currently, the following types of harmful discharge are found at work:

• excess heat from working equipment, heated substances and so on;
• evaporation, pairs and gases containing harmful substances;
• excretion of explosive gases;
• excess moisture;
• allocations from people.

As a rule, there are various types of contamination in modern industries, such as working equipment and chemicals. And none of the productions can do without discharge from people, since in the process of activity a person breathes, the smallest particles of the skin are creepy, and so on.

The calculation must be performed on each of the types of pollution. At the same time, they are not summarized, but are taken for the final greatest result of calculations. For example, if you most need air to remove chemical air pollution, it is this calculation and will be accepted to calculate the required volume of secrementary ventilation and exhaust power.

Execution of calculations

As can be seen from the foregoing, ventilation performs many different functions. To ensure high-quality air purification can only be enough devices. So when installing it is necessary to calculate required capacity Installed exhaust. Do not forget that for different purposes use different types ventilation systems.

Calculation of local exhaust

If there are emissions of harmful substances in production, they need to be trapped directly at the most close distance from the source of pollution. This will make them removal more efficient. As a rule, various technological containers become sources of emissions, also to contaminate the atmosphere. To capture the distinguished harmors use local exhaust devices - suction. Usually they have the kind of umbrella and are installed above the source of vapors or gases. In some cases, such installations are included with the equipment, in other - power and sizes are calculated. It is easy to fulfill, if you know the correct calculation formula and have some source data.

To make the calculation, you need to spend some measurements and find out the following parameters:

• the size of the emission source, the length of the parties, the cross section, if it has a rectangular or square form (parameters a x b);
• if the source of pollution has a round shape, it is necessary to know its diameter (parameter D);
• air movement speed in the zone where the emission is released (parameter VV);
• suction rate in the area of \u200b\u200bthe exhaust system (umbrella) (parameter VZ);
• the planned or existing exhaust installation height over the source of the contamination (parameter z). It should be remembered that the closer the exhaust to the source of the emission is located, the more effective pollutants are collected. Therefore, the umbrella needs to be as low as possible above the tank or equipment.

The calculation formulas for rectangular hoods look like this:

A \u003d a + 0.8zwhere A is the side of the ventilation device, A is the side of the contamination source, Z is the distance from the emission source to the exhaust.

B \u003d B + 0.8Zwhere B is the side of the ventilation device, B is the side of the contamination source, Z is the distance from the emission source to the exhaust.

If a exhaust installation It will have a round shape, its diameter is calculated. Then the formula will look like this:

D \u003d d + 0.8zwhere D is the drawing diameter, the d-diameter of the contamination source, z- distance from the emission source to the exhaust.

The exhaust device is made in the form of a cone, and the angle should be no more than 60 degrees. Otherwise effective ventilation system It will decrease, since zones are formed along the edges, where the air is formed. If the indoor air velocity indicators are more than 0.4 m / s, the cone must be equipped with special folding aprons to prevent dispersion of the substances and protect them from external influence.

Know dimensions Hoods are necessary, since the quality of the air exchange will depend on these parameters. Define quantity exhaust air It is possible according to the following formula: L \u003d 3600VZ X SZwhere the air flow rate (M 3 / h) is understood, the air velocity in the exhaust device (to determine this parameter, a special table is used), Sz is an area of \u200b\u200bopening of the ventilation unit.

If the umbrella has a rectangular or square shape, then its area is calculated by the formula S \u003d A * Bwhere A and B are the parties of the figure. If a exhaust device has a circle form, its size is calculated by the formula S \u003d 0,785dwhere D is the diameter of the umbrella.

The results should be taken into account when designing and calculating the general ventilation.

Calculation of secrerative supply-exhaust ventilation

When the required volume and parameters of the local exhaust, as well as the volumes and types of contamination, can be attached to the calculation of the required volume of air exchange in the production room.

The easiest option when there are no harmful discharge when working different types, And there are only those pollutants that distinguish people. Optimal number clean air Provide normal working conditions, compliance with sanitary standards, as well as the necessary purity of the technological process.

To calculate the required amount of air for working people, use the following formula: L \u003d N * Mwhere L is the required amount of air (m 3 / h), n is the number of working people in the production site or in a particular room, M is air flow for breathing 1 person per hour.

The specific air flow per hour per hour is a fixed value designated in special slips. The norms state is indicated that the volume of the mixture of 1 person is 30 m 3 / h, if the room is carried out if there is no possibility, then the norm becomes twice as much and reaches 60 m 3 / h.

It is more complicated by the fact if there are on the plot various sources Emission of harmful substances, especially if there are many of them and they are dispersed on a large area. In this case, local hoods will not be able to fully get rid of harmful substances. Therefore, production is often resorted to the next reception.

Emissions dissipate and then removed with the help of general influencing exhaust ventilation. All harmful substances are installed their MPC (maximum permissible concentrations), with their values \u200b\u200bcan be found in the special literature, as well as regulatory documents.

L \u003d MB / (YP - YP)where L is the required amount fresh air, MW is the mass of a harmful substance (mg / h), said a specific concentration of the substance (mg / m 3), the supplies of the jaette concentration in the air entering through the ventilation system.

If several types of pollutants are distinguished, then it is necessary to calculate the required amount of pure air mixture for each of them, and then summarize them. As a result, the total air volume, which should be included in the production room to ensure implementation sanitary requirements and normal working conditions.

Calculation of ventilation is a difficult matter requiring great accuracy and special knowledge. Therefore, it is possible to use online services for independent computing. If production has to work with dangerous and explosives, it is better to trust the calculation of ventilation by professionals.

In accordance with applicable in the territory Russian Federation sanitary standards and the rules of the organization of premises, both domestic and production destinationThe optimal parameters of the microclimate should be ensured. Ventilation norms regulate such indicators as air temperature, relative humidity, air movement speed in the room and the intensity of thermal radiation. One of the means to ensure the optimal characteristics of the microclimate is ventilation. Currently, organizing the air exchange system "on the eye" or "approximately" will be rooted incorrectly and even harmful to health. When adjusting the ventilation system, the calculation is the key to its proper functioning.

IN residential buildings And air bidding apartments is often ensured by natural ventilation. Such ventilation can be implemented in two ways - chamberless and channel. In the first case, the air exchange is carried out when carrying out the room and the natural infiltration of the air masses through the slots of doors and windows, and the pores of the walls. The calculation of the ventilation of the room in this case is impossible to produce, this method is called the unorganized, has low efficiency and is accompanied by significant heat loss.

The second way is to accommodate in the walls and overlap of the channels of air ducts through which the air exchange is carried out. In most apartment housesbuilt in 1930-1980, equipped with a exhaust channel ventilation system with natural motivation. The calculation of exhaust ventilation is reduced to the definition of the geometric parameters of air ducts that would provide access to the necessary amount of air in accordance with GOST 30494-96 "Buildings Residential and Public. Parameters of microclimate in rooms. "

In most areas of public use and production buildings, only the organization of ventilation with mechanical motion of air can provide sufficient air exchange.

Calculation of production ventilation can be entrusted with an exclusively qualified specialist. Engineer Ventilation Designer will make the necessary computing, will make a project and approves it in relevant organizations. They will also be issued and documentation for ventilation.

The design of ventilation and air conditioning is focused on the task set by the client. In order to select equipment for an air exchange system with optimal characteristics that meet the conditions set, with the help of specialized computer programs Perform the following calculations.

Determination of air performance

Air performance is calculated in two ways: by the multiplicity of air exchange and by the number of people. When calculating the performance of ventilation, the multiplicity of the air exchange shows how many times the air is changing in a room with a given area.

Performance by multiplicity of air exchange (L, m³ / h) are calculated by the formula:
L \u003d N * S * H
Where
N is the multiplicity of air exchange for a specific type of room. In accordance with the SNIP for residential apartments, n \u003d 1 is taken; for public rooms (offices, shops, cinemas) and manufacturing workshops n \u003d 2;
S - room area, m²;
H - the height of the premises, m.

Performance by the number of people (L, m³ / h):
L \u003d N * LNORM
Where
N is an estimated number of people indoors;
LNORM - normalized air flow per person, m³ / h. This value is governed by SNiP. For a person who is at rest (meaning residential apartments and at home);
LNAM is 20 m³ / h. For people who are at work in the office LNOR \u003d 40 m³ / h, and for performing physical Load, LNORM \u003d 60 m³ / h.

More than two values \u200b\u200breceived for performance supply-exhaust installation or fan. When choosing this type of equipment, make a correction to the performance loss, which occur in the network of air ducts due to aerodynamic resistance.

Calf power determination

Ventilation standards suggest that during the cold season, air entering the room should warm up at least to +18 degrees Celsius. For air heating, the exhaust ventilation uses the calorifer. The criterion for choosing the heater is its power, which depends on the performance of the ventilation, the temperature at the outlet of the duct (usually received +18 degrees) and the lowest air temperature in the cold season (for middle strip Russia -26 degrees).

Various models of the canopy can be connected to a network with 3 or 2 phase power. In residential premises, a 2-phase network is usually used, and for production buildings It is recommended to use 3 phase, since in this case there is less the value of the current current. The 3-phase network is used in cases where the calorie power exceeds 5 kW. For residential premises, calorific properties are used with a capacity of 1 to 5 kW, and for public and industrial, respectively, high power is required. When the heating ventilation is calculated, the carrier power must be sufficient to ensure air heating at least to +44 degrees.

Calculation of the network air ducts

For premises where it will be installed channel ventilation, the calculation of air ducts is to determine the necessary fan working pressure, taking into account losses, air flow rates and permissible level noise.

Airflow pressure is created by a fan and it is determined by it. technical characteristics. This value depends on the geometric parameters of the air duct (round or rectangular cross section), its lengths, the number of rotation of the network, transitions, distributors. The more productivity that the supply ventilation provides, and, accordingly, the working pressure, the greater the air speed in the air duct. However, with an increase in the air flow rate, noise level increases. Reduce the speed and noise level by applying air ducts larger diameterthat is not always possible in residential premises. For comfortable human well-being, the air velocity speed should be between 2.5 to 4 m / s and noise level of 25 dB.

Create an example of calculating ventilation can be only having room parameters and a technical task. Assist in performing preliminary calculations, to give a qualified advice, as well as to issue relevant documents can specialized firms that often monitors the design and installation of ventilation.

Installing ventilation is absolutely necessary in any rooms, be it apartment, a private house, Shed, garage or warehouse. The scheme of its creation is negotiated at the building design. The house in which there is no ventilation, especially residential, will be uncomfortable, but soon and unsuitable for living, because there will always be raw and stuffy, the mold will begin to appear in the corners wooden elements Buildings rot, and it ultimately collapses much faster than the laid. In this article we will talk about how to calculate ventilation indoors.

Why do you need ventilation

Some believe that you can completely quietly do without ventilation - our ancestors lived somehow before the invention of all kinds of newcomers. And if in the summer in such a house you can constantly open windows for airing, then in winter you will fully experience the whole "charm" of life in the old way - condensate will begin to appear on the windows, doors and walls, which in case of severe frosts will turn into a beautiful ice crust, The corners will begin to grow the gardens of black and green mold, and if you are very lucky, in a year or another we will collect the crop of mushrooms ... Is it worth saying that such a house will not have a very long time, and life in it will be a constant test for nerves and health.

With a constant insufficient inflow of fresh air, light people are starting to work worse - diseases appear that can quickly become chronic. A child growing in a house without ventilation can earn major health problems for life.

The "parade" continues constant dustiness and crying - if fresh air does not come to the room, then everything that is brewed in it is fried, dust, it is cleaned, settles on the walls and furniture with a thick layer of plaque. On a kitchen ceiling, after six months it will be possible to notice an extensive yellowish stain over the stove - these fat evaporation dated and absorbed into the plaster, for they have nowhere to go. In the bathroom on the ceiling and in the corners, eloquent evidence of the lack of ventilation in the form of mold spots due to constant humidity will also appear.

And finally, it should be taken into account that at least once a year in the house someone sick - cough and sneezing microbes are instantly scattered around the room, settled on furniture, wallpaper, curtains, carpet. Hospital chambers are raised several times a day not just like that, and now imagine what atmosphere you will find yourself after the year of life in an apartment where there is no regular air tributaries. We hope we led weighty arguments in favor of the need for a system of ventilation of residential premises and now you can go from words to business.

Checking the work of ventilation

It happens that some of the above "symptoms" are manifested even in ventilated houses. This may mean that the system works weakly or ceased to function for any reason. To check whether the ventilation works, burn the match or lighter and bring the flame to the ventilation hole - if the fire leaned towards the grid, covered the hole, then there is a traction, and everything works. If the changes did not follow - ventilation channel Either blocked, or clogged with leaves. In the case of apartments, this very often happens if the neighbors made redevelopment and blocked the air duct.

It also happens that the thrust is present, but with breaks, and at the same time it can bring relaxes from the neighbors from above or below. In this case, you will need to equip the vent check valveor install automatic blindsclosed when reverse.

Types of ventilation systems

All ventilation systems can be divided into categories depending on the functional load, the method of moving air masses and what leads them in motion.

Depending on the functional purpose The following ventilation systems are:

1. Supply - Fresh air from the street constantly enters the room.
2. Exhaust - air is output from the house along the ventilation channels.
3. Recycling - systems displays spent air and at the same time "pumps" in the house of fresh.

If you think about the principles of the work of the above systems, the question is subject to: "And at the expense of which the air moves to leave or penetrate the room?". To do this, use the sorting of ventilation systems by the nature of the awakening of the air masses. These sources can be natural and mechanical (artificial).

In S. systems natural ventilation Air moves due to pressure drops. You will immediately understand what it is about, if you remember the ventilation holes in the kitchen and in the bathroom, which is in each multi-storey house - Warm air and steam (shower, washing, cooking) falls into this hole and stretches outward due to pressure and gravitational forces.

In systems with mechanical sources of awakening, air is driven by means of exhaust fans that take it out of the room, acting on the principle of conventional kitchen exhaust.

So, when the air masses have gained the ability to move, they should provide a safe and directional output (input). In this regard, another classification was developed by the method of movement of air flows - channel and non-vacant. With a channel system, it is more and less clear - the air flows through special removals, and when it does not leave the room, it leaves the room or penetrates it through the axle window openings, doors, cracks, etc.

Calculation of the ventilation system

To ensure high-quality ventilation of the house, it is only enough to choose any system you like - it is necessary to find out how much air will be output from the premises, and how much fresh air should be supplied from the street. Speaking otherwise, you should find out the optimal air exchange at home, and on the basis of this data to select the ventilation system, buy fans of certain power, channels, etc.

There are many ways to calculate the ventilation of the room, for example, to remove excess warm air or evaporation, dilution of pollution and so on. However, they all require professional knowledge and experience. We also need such a method that every owner or hostess could take advantage. To begin with acquaintance with special regulatory documents, which are designed for each state or region (GOST, SanPiN, DBN, SNiP). In them, you will find information on the requirements for ventilation systems for any premises, required equipment, its facilities and location. By big accountThere is everything you need to know to select the system.

But the architectural features of buildings dictate their conditions, and on the basis of them, engineers constitute a ventilation project, focusing on the norms specified in state documents. Below we will give an example of such a calculation of ventilation for a residential building using the most simple ways: in multiples, sanitary standards and total area.

Calculation of multiplications

This calculation is quite complex, but still feasible. The table below shows the ventilation regulations necessary for the work of calculations.

Before it is worth explaining what kind of multiplicity is. This is a magnitude showing how many times for 1 hour the air in the house was replaced by fresh. Multiplicity depends on the specifics of the building and its area. For example, consider a single air exchange - this means that in an hour from the room was derived and at the same time came the amount of air equal to the volume of this building itself. In the 2nd Table Speakers, you will find the requirements for ventiling on the influx and exhaust air.

The calculation is made according to the formula: L \u003d n * V (cubic meters / hour), where n is a multiplicity (view in the table), and V is the volume of the room.

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 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 only do the influx or exhaust, but for spaces with high humidity (Kitchen, Bathroom) It will be necessary to organize a recycling system. If the table is stuck, then the room does not need ventilating. As a result, you should have the equation of the volume of inflow and exhaust volume. If this did not happen, the number of air exchange in these rooms can be increased to the required indicator.

If a table is not specified in the table, calculate the rate of ventilation rate of residential premises according to 3 cube air per hour per hour. m, that is, according to the formula: L \u003d S * 3, where S is an area of \u200b\u200bthe room.

All values \u200b\u200bl must be multiple of the number 5, so if necessary, round them up to five to the biggest side. Calculate L for all rooms individually first for air inflows, then - for drawing, fold the indicators and compare the total l of influx and l hoods - they must be equal. If the value of the tributaries turned out more exhaust, then to keep the balance to increase the air exchange for those rooms where the air exchange was minimally permissible.

Calculate ventilation by multiple houses with a quadrature of 140 kV. m with such rooms:

• the kitchen is 20 square meters. m (S1);
• bedroom for 24 square meters. m (S2);
• the working office is 16 square meters. m (S3);
• the living room is 40 square meters. m (S4);
• hall - 8 square meters. m (S5);
• toilet - 2 square meters. m (S6);
• bathroom - 4 square meters. M (S7).

The height of the ceilings at the same time is 3.5 m. A young couple lives in the house without children.

It is necessary to calculate the volume of rooms, multiplying the square to the height of the ceilings. As a result, we get the kitchen \u003d 70 cubic meters, bedroom \u003d 84, Cabinet \u003d 56, living room \u003d 140, hallway \u003d 28, toilet \u003d 7 and bathroom \u003d 14 cubic meters.

There is no multiplicity for the living room in the first table, so it can be calculated for it, based on the fact that 1 square meter. The room of the room requires 3 cubic meters of air per hour. We multiply the area of \u200b\u200bthe living room at 3 and we get 120 cubic meters per hour.

Now it remains to fold the air exchanges of all rooms for the influx and separately for the exhaust and compare these indicators. It turned out that the influx was 265 cubic meters, and the extract was 165, so it must be increased. Add drawing values \u200b\u200bfor those rooms where stronger ventilation is required or where the values \u200b\u200bwere minimally allowed - in the bathroom and kitchen.

In the toilet and the bathroom it is better to install only an exhaust, and in the bedroom, living room and desktop - only the influx. This measure will prevent the stacking of unpleasant odors.

Sanitary standards

To calculate air exchange in administrative and domestic or public building According to sanitary standards, it will be necessary to know an approximate number of people constantly located. According to the norms of a person who is constantly located in the room, at least 60 cubic meters of fresh air must be needed, 20 cubic meters will be enough to a temporary visitor.

Calculate the air exchange for the same house. If you recall the norms per person, it will turn out to be a formula (for a bedroom): L \u003d 2 (Human) * 60 cubic meters. To calculate the air exchange for the office, one constant and one temporary person should be taken into account: l \u003d 1 * 60 + 1 * 20. In the living room, the young couple is sometimes found with two-three friends or parents, so there should also be considered temporary visitors for this room.

If you calculate the air exchange for all rooms, taking the data from the first table, it will become obvious that the volume of fresh air is much larger than the exhaust volume, and therefore the drawing data should be increased by adding 195 cubic meters / hour to create a balance. It is recommended to increase evenly, distributing in all rooms, but you can apply in one room that needs ventilating, such as in the kitchen or bathroom. That is, the volume of volume in the kitchen should be added 195, and it will be 285 cubic meters per hour.

Spent air from the rest large rooms will move to the kitchen and go out through the hole through natural traction or suck exhaust fans. It is very important to ensure such a movement of the air masses so that smells and moisture in the apartment are stood.

Calculation by Square

Production calculations, we have the following picture: L exhaust 3 \u003d 114 * 3 \u003d 342 cubic meters / h

Summarizing

Of all the above examples, it can be seen that the meaning of the air exchange in each of the options is different, but they are all considered correct. What of them are guided by - to solve you, but the calculation on the area and multiples will cost more cheaper than by sanitary standards. It also guarantees more comfortable conditions for life, so often the decisive factor in choosing the ventilation system is the financial position of the customer.

Selection of an air duct

When the calculations are completed, you can proceed to the choice of the ventilation scheme of the premises, that is, think over the plan, make drawings and choose equipment. Today, rectangular and round air ducts are used for ventilation systems. If you choose rectangular air duct, Watch that the aspect ratio does not exceed 3: 1, otherwise the ventilation will be constantly noise, and the pressure in it will not be high enough (there will be no traction).

Also, when choosing, it is necessary to take into account that the normal speed in the highway should reach about 5 m / s (in branches of approximately 3 m / s). To determine necessary sizes Sections, use the diagram below - it shows the dependence of the size of the section from the flow of air and the speed of its movement. The horizontals marked air flow, verticals - speed, oblique lines - the corresponding duct dimensions.

Select the desired cross section of the highway, which will go to each room and the most highway highway so that the air is supplied to the cost of 360 cubic meters per hour (as in the example with our home).

If you organize a natural exhaust, the air flow rate in the highway according to the norms should be no more than 1 m / h. The calculation of exhaust ventilation of the room should occur taking into account the normalized air velocity no more than 5 m / s for a highway and 3 m / s - for branches.

We hope this article will help you correctly calculate air ventilation indoors and make your home comfortable. Competently produced calculations allow you to save not only on the arrangement of the ventilation system, but also on overhaul in the distant future.

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Air exchange in buildings can be performed as at the expense naturalAnd at the expense of artificialmove air with special mechanical devices. In the first case, ventilation is called natural ventilation (aeration)in the second case - mechanical ventilation.

By appointmentventilation distinguish:

exhaust;

inlet;

supply-exhaust.

Exhaustventilation with help technical means provides an extract from the room that does not correspond to the composition or state of air sanitary standards in environment, And the influx of pure outer air occurs through natural supply processes (doors, windows, etc.). Inflowventilation on the contrary provides with the help of technical means only the inflow into the room of pure outer air, and the removal of air of the production room is carried out through the natural exhaust pasumes (windows, doors, lights, pipes, shafts, etc.).

By character of workventilation shares:

community, providing air exchange throughout the size of the room;

local air shift on the local area of \u200b\u200bthe room.

Natural ventilationit is widely used due to its obvious advantages: no additional operating costs for maintenance of technical devices are required, fee for the consumption of electrical energy when the engine operation of mechanical fans, etc.

Naturalthe air exchange indoor occurs under the action of the difference in temperature of the air inside and outside the building, as well as due to the presence of pressure difference from the wind action on the building.

The flow of air, meeting on its path the obstacle (for example, the wall of the building) loses its speed. Due to this in front of the obstacle on the windward side of the building, an increased pressure is created, the air partially rises up and partially flows around the building on both sides. On the reverse taped side of the building, the flowing jet of the building at the expense of speed loss creates a vacuum. This difference of pressures from different sides of the building when streamling its wind is called windwardsand is one of the components of the natural air exchange in the premises.

In contrast, the pressure difference arising due to the difference in the magnitude of the masses of warm (more lung) and cold (more heavy) air is called thermal pressure.

Inside the room, the air heats up when heated with heating elements of heating, and in the industrial premises, due to contact with the technological equipment and heat release from heating furnaces, operating machines and machines. According to the law of Gay-Loursak (French scientist, J.L. Gay-Loursak, 1778-1850) the relative change in the volume of the mass of the ideal gas at constant pressure is directly proportional to the temperature change:

where V.- gas volume at temperature t.;

V. 0 - the volume of the same mass of the gas at 0 0 s;

 V. - The coefficient of the volume expansion of the gas, equal to 1/273.15 0 S.

When the gas is heated by 1 0 with the volume of it according to this law, part 1 / 273.15 part of the original value, therefore the density and mass of the limited volume decreases accordingly. When cooling, a reverse phenomenon occurs. The same pattern is true for a mixture of gases (dry air).

The heated air rises into the upper part of the room and displaces through existing exhaust pasumes (framugues windows, exhaust mines, pipes, etc.) with a heavier cold air, incoming through the inlets (open doors, windows, etc.) in the bottom Parts of the building. Due to this process, the pressure vector appears, called thermal pressure.

Initial data when calculating Natural ventilationare the temperature and humidity standards in the rooms, the multiplicity of air exchanges, the MPC of poisonous gases, vapors, dust kPN.

The first stage of the ventilation calculation is to determine the necessary air exchange (ventilation performance) indoors L.measured in m 3 / h.

The necessary air exchange is determined depending on the purpose of the ventilation:

for air purification from harmful substances allocated as a result of the production process:

(1.8)

where TO IN - the number of distinguished harmful substances in the room, mg / h;

TO D. - MPC of harmful substances or dust dust in the air of the working area under sanitary standards, mg / m 3;

TO N. - Maximum permissible emissions of harmful substances in the environment, mg / m 3.

for premises with excess heat dissipation manufacturing processFor cooling:

(1.9)

where Q. Spin - overhaul of heat, J / h;

t. W. , t. ETC - respectively, the temperature is removed and inlet air, K (0 s);

 ETC - the density of the supply air, kg / m 3;

from- Specific heat, J / kg.

for premises with excess moisture secretions:

(1.10)

where G.- weight of water vapor released into the room, g / h;

d. W. , d. ETC - respectively permissible moisture content working area At normalized temperature, relative humidity and moisture content of the supply air, g / kg.

for household and administrative premises, sometimes sanitary standards are provided for the rationing of the multiplicity of air exchange in 1 hour TO ABOUT , in this case:

(1.11)

where V.- Volume of ventilated room, m 3.

The second stage of the valuation of ventilation is the definition of the area of \u200b\u200bsupply and exhaust openings.

Based on the equation of hydrogazodynamics on continuity when the steady flow of incompressible fluid in the pipe, the productivity of natural ventilation can be determined from the relationship:

where L. ETC , L. B. - Accordingly, the performance of the supply and exhaust ventilation, m 3 / h;

 - the coefficient determining the degree of opening of the supply or exhaust openings;

F. ETC , F. IN - respectively, the total area of \u200b\u200bsupply and exhaust openings, m 2;

V. ETC , V. IN - respectively, the speed of air in the supply and exhaust pens, m / s.

Initially determine the speed of air in the openings.

Speedair in the door V.determined on the basis of the ratio for the high-speed pressure obtained from the Bernoulli equation (Swiss scientist D. Bernoulli, 1700 - 1782):

(1.13)

where N.- high-speed pressure, determined by the sum thermaland windowheads, kg / m 2;

g.- acceleration of gravity, m / s 2;

 Cf. – average density air, kg / m 3.

When moving from high-speed pressure N.(kg / m 2) to the pressure difference  R(PA) It is necessary to keep in mind the ratio:

Fig. 1.6. Scheme of natural ventilation

Thermalpod N. T. determined from the expression:

(1.14)

where h.- The vertical height between the axes of the supply and exhaust openings, m;

 ETC , IN - The density of the appropriate and exhaust air, kg / m 3.

A part of the thermal head in the building determines the speed in the supply of the pits, and the other part is in the exhaust. In the moulderness with the equality of the area of \u200b\u200bthe supply and exhaust openings and the correct (equal in height) of the building configuration (Fig. 1.6), when the plane of equal pressure inside the building (neutral zone) is located in the middle part of the room height, in formula (1.13), you can substitute the value

For miscellaneous Square Support and exhaust outlooks, when the imbalance is made to increase, for example, the removed air volume from the room compared to the supply volume of the air, the plane of equal pressures (neutral zone) will change its location with respect to the middle part of the room in height. In this case, the location of the neutral zone can be found from the ratios:

(1.15)

where h.- the height of the room between the axes of the supply and exhaust openings, m;

h. BB , h. VN - respectively, the distance up and down from the zone of equal pressures, m.

In relation (1.14), as a height vertically, when determining the exhaust heat pressure and the supply heat pressure, respectively, substituted h. BB and h. VN .

Calculation of ventilation, taking into account the wind pressure, is significantly complicated, as it depends not only on the "wind roses", i.e. The directions of the vectors of medium perennials per year (season) wind speeds for the locality, in relation to the location of the building, but also from the aerodynamic properties of the building itself.

Windpod N. IN (kg / m 2) in approximated calculations can be determined from the relation:

(1.16)

where R IN - Wind pressure, PA;

V. B. - wind speed, m / s;

 - average air density, kg / m 3;

to BUT - Aerodynamic building coefficient:

from a windward side to BUT = 0,7…0,85;

from the topped side to BUT = 0,3…0,45.

After determining the air velocity in the openings, it is transferred to the third stage of the calculation of natural ventilation - the calculation of the total area of \u200b\u200bsupply and exhaust discovers by relations (1.11), (1.12).

In cases where in the production premises it is necessary to create large air exchange, a special organization of air exchange and management of them is required.

Natural, organized and managed, ventilation is called aeriation.

The main elements of natural, organized and managed, ventilation (aerations) are:

clear binders(sash), which are used with the upper, middle and lower axis of rotation, if the direction of the air does not matter, then apply sashes with the upper or middle axis of rotation (Fig. 1.7); When the air flow must be used up, sash with lower axis of rotation;

lanterns- the special designs of the roof of the building, significantly increasing the height of exhaust opening, which significantly enhances the effect of thermal and wind flow (Fig. 1.8);

exhaust mines and pipesused in order to increase the height of exhaust openings in the absence of lanterns (Fig. 1.8);

deflectorsinstall on the roof on exhaust pipes and mines, they enhance thermal and wind pressure (Fig. 1.9).

When calculating mechanical ventilationthe first stage to determine the necessary air exchange rooms in the room coincides with the calculation of natural ventilation (aeration) in accordance with relations (1.8) ... (1.11).

R iP. 1.7. Scheme of the location of the finished bindings

Fig. 1.8. Schemes cross-sections Buildings

1 - typical, 2 - having a roof with a lantern, 3 - having a pipe (shaft) with a deflector

Fig.1.9. The main dimensions of the deflector of the TsAGI

The second stage of calculation mechanical ventilation(Fig.1.10, 1.11) It consists in a laying according to the plan of the building of exhaust and supply air ducts of a round or rectangular cross section. This is due to the fact that fans and engines are located in a small exception (ceiling fans, etc.) in separate rooms. In this case, it requires an air duct device to supply air from the surrounding space to the fan and from the fan to the industrial premises (supply ventilation). Also for exhaust ventilation. The second stage consists of calculating the pressure loss in the air ducts and the required full pressure necessary to create mechanical fans.

The pressure loss in the air duct is determined by hydrostatic and aerodynamic losses that can be determined from the ratio:

(1.17)

where R. i. - hydrostatic pressure loss in i.- Tom of the duct of round or rectangular cross section l. i. (determined by reference books), P / m;

- aerodynamic (high-speed) pressure loss, PA;

 i. - aerodynamic coefficient of local resistance i.- of that region of the duct;

V. i. - air speed in i.- volume of the duct, m / s.

R iP. 1.10. Schematic scheme Exhaust mechanical ventilation

1 - local suction; 2 - taps; 3 - general suction duct; 4 - air purifier; 5 - sump; 6 - fan; 7 - Electric fan motor; 8 - discharge air duct; 9 - ventilation pipe.

R iP. 1.11. Concept of supply mechanical ventilation

1 - air actor; 2 - air filter; 3 - heater (calorifer); 4 - humidifier; 5 - bypass channel; 6 - fan; 7 - electric motor; 8 - air duct; 9 - inlet nozzles.

The coefficients of local resistance with various structural elements of air ducts (local suction, taps, intake nozzles, turns of the duct, filters, thermal magazine processing devices, narrowing, extensions, branching, supply devices) are determined from aerodynamic tests and are given in reference books.

Required pressure at the outlet of the duct (supply or exhaust) R N. determined from relations (1.11), (1.12) and (1.13). Based on the required calculated air exchange, the area of \u200b\u200bsupply or exhaust nozzles of the air duct, the air speed is determined to the inflow or extractor, and the air velocity V.- necessary pressure or pressure N. N. .

Full pressure R, representing the amount of the required pressure at the outlet of the duct and the pressure loss in the air duct, can be determined from the ratio:

(1.18)

The third stage of the calculation of mechanical ventilation consists of selecting the fan number and calculating the power and select the engine to it. Fans are divided by numbers depending on the possible performance. L. ETC in m 3 / h. When choosing a fan (fans) of its (them) performance should be greater than the accommodated air exchange room L.:

(1.19)

Engine power (engines) to fan (fans) N., kW is determined from the ratio:

(1.20)

where L. - Required air exchange or required fan production (fans), m 3 / h;

P.- full pressure, PA;

 IN - Fan efficiency;

 P - Motor efficiency.

TO localmechanical supply and exhaust ventilation units include all types of devices for organizing the flow or air hoods on workplaces or other local sites (air souls, air curtains, ventilation welding posts, etc.). Using mechanical ventilation, you can exercise secretarysupply, exhaust and supply and exhaust ventilation.

The supply and exhaust mechanical ventilation and the influx, and the exhaust air from the industrial premises. In the case of the location of the workshops with harmful discharges and without them in the same building, the balance of the air exchange on the inflow and the hood is specifically violated in such a way that air flows prevailed in the workshops without harmful discharge, and in the workshops with harmful discharges. In this case, harmful discharge will not fall into the sets (premises) without harmful discharge.

Mechanical ventilation, in contrast to aeration, allows the impressive air to be pre-treated: cleaning, heating or cooling, hydration. When the air is removed from the room, the mechanical ventilation device allows you to catch harmful substances and clean air from them before emissions into the atmosphere. In recent years, ventilation systems with air recovery, i.e. are used to save energy resources (heat) The remote air is subjected to cleaning and air conditioning (from the word condition - quality, the term was previously applied only when the quality characteristic of the tissues) and returns back to the industrial premises.

Automatic supply and exhaust ventilation units that serve to create and automatically regulate predefined artificial climate parameters (air temperature, cleanliness, mobility and humidity) obtained the name of the installations air conditioning.

Ventilation performs an important role, providing not only the influx of fresh air, but also timely removal of waste carbon dioxide. Practice indicates that natural system The air vents, designed in the apartments of the old housing stock, do not cope with the responsibilities assigned to it, so there is often a high-quality upgrade of the entire system.

Why is the right calculation?

The installation of the air-circuit system should be approached very carefully, since the slightest inaccuracy can lead to a significant decrease in the efficiency of the entire system. The correct calculation of the supply and exhaust ventilation allows you to take into account all the important technical components, as well as the parameters of the room, guarantees a three-time air exchange indoor. It should not be thought that for the correct calculation it is necessary to have outstanding knowledge, it is enough to know the main formulas and those elements that affect the functioning of ventilation.

The most popular ventilation system is residential, which is equipped in private houses, apartments, summer cuisines. The supply and exhaust air circulation system indoors includes:

• Air valve
• Hearing grille
• Cleaning filters
• Heater
• Fans
• Airways, nozzles.

The whole design is mounted taking into account project data, as well as in places that are for this most suitable, that is, at the top of the room.

Example of calculating the ventilation system of residential premises

Many are interested in the question of how to calculate the supply ventilation competently in order for the effectiveness of its functioning to be maximal. For this, it is important to know several formulas that will help determine the parameters of the required ventilation. It should be known that the ventilation of the residential premises should ensure not only three-time air exchange on the outer air, but also its temperature.

There is a value of extremely permissible concentrations in the outer air. various substances, including carbon dioxide:

• for the city - 800-1000 mg / M. Kub.
• for countryside - 650 mg / M.Kub.

This indicator is needed to determine the main computational consumption of air in the apartment, as well as heat:

Q.vENT \u003d. fromr * ρ h * L.vENT * ( t.n - t.in)

• Q.vENT - air flow depending on the concentration of harmful substances
• ρ n - external air density
• fromp - heat capacity (calculated by the formula fromp \u003d 1.005 kJ / kg ∙ s;)
• t.n I. t.b is the calculated values \u200b\u200bfor air temperature (outside and inside) an apartment under the calculated conditions.

Important!
If, then the conditional temperature of the incoming flow in the calculation is taken for the value of + 15 ° C, and the formula remains the same.

Knowing this formulaEveryone can produce independent calculation of the supply and exhaust ventilation for household conditions without resorting to the help of a specialist. After that, it remains only to purchase everything. necessary materials And proceed to direct installation.

We reduce energy consumption with the recovery

For a long time, the main problem forced circulation air was rapid cooling of the room in winter Due to cold air from it. Today, this problem is successfully solved with the help of calorifers, heating air-incoming air masses. In addition, there are canorrifers working at the expense of circulation hot water (Water), however, they are most often used in the premises of a large area.

Modern calculation supply ventilation Recovers often include efficient devices that use heat removed air to heat the incoming flow. Recovers are divided into several types:

• Platery
• rotor
• Water
• Roof

Each of them has its own special advantages, but in general, anyone is able to reduce energy consumption for the heating of the ventilated room to 65%.

Thinking the ventilation of the room, regardless of its type and purpose, it is important to calculate everything carefully.

Important!
If despite all its efforts, you doubt the calculated data obtained, you should still call a specialist who can confidently calculate the power of the fans, the diameters of the incoming and outgoing air ducts, the type of the carrier or the recuperator.

It should be remembered that the ventilation system must be designed and designed in such a way as to create the most comfortable conditions for living and work.