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

Without correct distributed ventilation It is impossible to comfortable accommodation in the house.

Ventilation of any room - prerequisiteEven if this is a warehouse not visited by people. And in public and residential buildings, the ventilation system must be carefully calculated and arranged with regard to standards. For each closed room, including the attic, it is necessary to take into account the system of air exchange, which contributes to the comfortable finding of people. In any residential building you can see the ventilation holes that are responsible for admission fresh air. IN public rooms, where people are assumed, should be arranged supply-exhaust ventilation Circulation of air masses. Sanitary standards strictly regulate the device of ventilation systems, taking into account the volume of rooms and the intended number of people in it. Below will look at the types of ventilation systems and the methodology for calculating air exchange.

Validation of ventilation systems

Ventilation systems differ in the degree of complexity of their design. There are several types:

From the quality of work ventilation system Depends the comfort of finding people inside the building. Standards for the amount of incoming air are developed and published by Rospotrebnadzor, which monitors the operation of ventilation in public buildings.

General painting of ventilation of modern houses

What you need to know about airflows

The main stages of settlements

Natural ventilation In residential and public buildings it is arranged in their construction and does not require additional calculations. Therefore, the conversation will go about forced systems.

The priority for the accurate calculations of the ventilation systems is to record the microclimate of the premises. These are permissible and regulatory and recommended values \u200b\u200bof humidity, temperature and air circulation volumes. Depending on the types of the selected system, the tasks are determined - only air exchange or integrated air conditioning.

A large selection of specialized equipment is presented on the market that can not only file the "right" air, but also filter it.

The calculation of the airflow received from outside is the first and most important parameter adjustable by sanitary and hygienic standards. It is built on the minimum amount of consumption and air expenditures due to the minimum channels and the operation of technological equipment.

Definition of air exchange, which is measured by cubic meters of replaceable air per hour depends on the volume of room and its purpose. For apartments, the outdoor air supply is carried out in the room, where, as a rule, residents are for a long time. It is a living room and a bedroom, less often a cabinet and halls. In the corridors, kitchens and bathrooms of the tributary, usually do not, only exhaust holes are installed in them. Air masses come naturally from neighbor roomswhere the influx is made. Such a scheme causes airflow to move through residential rooms in the technical, "squeezing" spent air-gas mixture into exhaust channels. At the same time, unpleasant odors are removed, without turning around the apartment or house.

An important point is the presence in the fireplace room open typeconsuming a lot of oxygen when working.

Calculations include two air exchange values:

• By productivity - based on air mass standards per person.
• By multiplicity - how many times the air change in the room in one hour is occurring.

Important!

To select the performance of the planned ventilation system, the largest of the values \u200b\u200bobtained.

Air performance

For residential premises, the amount of air arrived must be calculated in accordance with the construction norms and rules (SNiP) No. 41-01-2003. Here is the number of consumption by one person - 60 cubic meters per hour. This volume should be compensated by the influx of external air. For bedrooms, fewer volume is allowed - 30 cubic meters per hour per person.

When calculating, only permanent people should be considered, i.e. You should not take the number of guests attending the room from time to time. For comfortable holding parties, there are systems regulating air inflows in different rooms. Such equipment will allow you to increase the air flow into the living room, by reducing it in the bedroom.

Typically, the ventilation control panel is carried out in a separate shield.

And technology " smart House"Allows you to do the same with mobile devices.

Calculations are carried out according to the formula: L \u003d n x ln, where:

N. - the alleged number of people;

LN. - regulatory flow air 1 person. - For bedrooms - 30 cubic meters per hour and for other rooms - 60 cubic meters per hour.

Performance by multiplicity

The calculation of the multiplicity of air exchange in the premises should be carried out based on the parameters of the room, this will require a plan of a house or apartment. The plan should contain the purpose of the room and its dimensions (height, area or length and width). For a comfortable sensation, a minimum is required to complete the entire volume of air.

Without a detailed plan of the house, it is extremely difficult to organize correct ventilation.

It should be noted that the supply channels, as a rule, give the volume of air for two-time metabolism, while the exhaust is designed for one-time air exchange. There is no contradictions in this, since the air flow occurs also naturally - through slots, windows and doors.

After calculating air exchange for each room we add values \u200b\u200bto calculate the performance of the ventsy system. After which it will be possible to choose the power of the air intake and exhaust fans. Regulatory performance indicators for different rooms Next:

• ventilation systems of residential premises - 150-500 cubic meters per hour;
• in private houses and cottages - 550-2000 cubic meters per hour;
• in office premises - 1100-10000 cubic meters per hour.

We carry out the calculation according to the formula:L \u003d NXSXH, where:

L. - the estimated volume of the incoming air cubic meters per hour;

N. - standard of multiplicity of air exchange: houses and apartments - 1-2, office rooms – 2-3;

S - area, sq.m;

N - height, m;

Example of calculating the aerodynamic calculation of ventilation

In the calculations, you can also help this calculator

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

• Efficiency and performance by air;
• Califer power;
• Fan operating pressure;
• Airflow speed and duct diameter;
• Maximum noise indicator;

Calculation and compilation of the ventilation system project must be started with the calculation of the necessary air performance (cubic meter / hour). In order to correctly calculate power needed detailed plan Buildings or premises for each floor with explication indicating the type of room and its purpose, as well as the area. Start counting from measuring the desired multiplicity of air exchange, showing the number of times the air change in the room for an hour. So for the room with a total area of \u200b\u200b100 m2, the height of the ceilings in which 3 m (volume of 300 m3) is one-time exchange of air - 300 cubic meters per hour. The required multiplicity of air exchange is caused by the type of room use (residential, administrative, industrial), the number of people who stay there, the power of heating equipment and other devices that allocate heat and is indicated in SNiP. Usually, for residential premises there is enough single air exchange, for office buildings, two - three-time air exchange is optimal.

1. We consider the multiplicity of air exchange:

L \u003d n * s * h, values

n is the rate of multiplicity of air exchange: for household premises N \u003d 1, for administrative N \u003d 2.5;
S - total area, square meters;
H - ceiling height, meters;

2. Calculation of air exchange by the number of people:
L \u003d n * l norms, values
L - required system performance supply ventilation, cubic meters per hour;
N - the number of man indoors;
L norms - the magnitude of air consumption by one person:
a) minimal physical activity - 20 m3 / h;
b) average - 40 m3 / h;
c) intense - 60 m3 / h.

Calculating the required air exchange, start the selection ventilation equipment Suitable performance. It must be remembered that due to the resistance of the air duct network decreases the efficiency of work. The interrelation of performance from the full pressure indicator is easy to learn from the ventilation characteristics indicating in technical description. For example: a network of air ducts with a length of 30 m with a single ventilation grid produces a decrease in pressure indicator of about 200 pa.

Standard Power Indicators 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 calorifer, if necessary, heels the outer cold air in the supply ventilation system. The power of the carrier is considered according to this data as: ventilation performance required by air temperature and a minimum temperature street air. The second and third indicators are installed SNiP. The room temperature in the room should not be lowered below the mark of +18 ° C. Most low temperature The air for the Moscow region is considered -26 ° C. Therefore, the calorifer at maximum power should fit the airflow by 44 ° C. Frosts in the Moscow region are usually rarely and quickly pass, in supply ventilation systems, it is possible to install calorifications with a power less calculated. The system must have a fan speed regulator.

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

2. Maximum power consumption. Electricity consumed by the calorifer can be calculated by the formula:
I \u003d p / u in which
I is the maximum power consumption, and;

U is the voltage of the power grid (220 V is one phase, 660 V - three phases);

The temperature on which the calorior of this performance can heat the trim airflow, it is possible to calculate according to the formula:
Δt \u003d 2.98 * p / l, in which
Δt - delta temperatures of the incoming and outgoing air in the supply ventilation system, ° C;
P is the capacity of the carrier, W;
L is the power of the ventilation system, m3 / h.

Standard calorfer power parameters - 1 - 5 kW for residential premises, from 5 to 50 kW for administrative. If it is impossible to operate an electric carrier, an optimal installation of a water canopy is optimal using water from a central or individual heating system as a coolant.

Comments:

• Harmful discharges affecting the microclimate of the premises
  • Calculation of enlarged indicators
• Description of calculation methods

The microclimate of the premises of the building of any destination must comply with sanitary and hygienic standards to ensure the optimal or permissible mode of operation or human activity. The microclimate parameters preferably provide the supply ventilation systems, and its calculation is reduced to determining the number inlet air.

Harmful discharges affecting the microclimate of the premises

The composition and the number of hazards allocated to the premises depends on functional purpose Buildings and taking place in it technological processes. In residential and public buildings only there are allocations from the vital activity of people, while in the production premises the composition of the harm can be whatever, it all depends on the technological process. All hazards are divided into several types:

1. Harmfulness of human vital activity (moisture isolation, carbon dioxide, heat).
2. Allocation of harmful vapors or aerosols various substances during the technological process. High concentration of these substances has indebid effect On the health of people working in the room.
3. IN production buildings We are often technological processes with increased highlighting water vapor, which causes high humidity and condensate falling on cold surfaces. Such conditions for work do not correspond to sanitary standards.
4. Heat outlook from preheated technological equipment or products. Surplus heat acting on human health during working shiftAlso have a negative impact on it.

For civilian buildings, the calculation is implemented, as a rule, the harmfulness specified in paragraph 1. In industrial buildings, it is required to calculate the amount of supply air required to reduce the concentration of each of the types of harmful discharges, and make a value from the greatest results.

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Calculation of enlarged indicators

The enlarged indicators for the calculation reflect the flow of supply air per unit of room volume, one person or one source of harmful discharges. The parameters of the microclimate in the premises of civil buildings are regulated sanitary standards and requirements. For each type of building, there are regulations, there are values \u200b\u200bof the multiplicity of air exchange for rooms. various destination. In this case, the calculation is made by the formula:

• V - the size of the room, m3;
• k is the multiplicity of air exchange at 1 hour.

The multiplicity is the number that shows how many times in one hour the air in the room will be completely updated. With a value of 1, the amount of air will be equal to the volume of the room. In other cases that do not take into account these standards, there are indicators of the optimal amount of supply air per person. These standards are prescribed in SNIP 41-01-2003 and are 30 m3 / h for ventilated rooms per person, and for non-refined - 60 m3 / h. Then the formula is used to calculate:

• L is the required amount of outdoor air for the tributary, m3 / h;
• N - the number of people constantly located in indoors;
• m is the number of inflow per person per hour.

The calculation for this formula is also acceptable if other types of harmful discharge into the room space production destination Very insignificant. When there is one or more identical sources, from which harmful pairs or aerosols proceed, the calculation method according to enlarged indicators is applicable, provided that the number of outdoor air is known for each of them. Then the value M will show the value of the inflow by 1 source, and the N parameter in the formula means their number.

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Description of calculation methods

In the presence of B. industrial building Multiple sources, which, during the technological process, emit pairs of harmful substances, must be carried out on each of these substances. For this, it is found out exactly which substances are allocated in what quantity, after which it is possible to calculate the concentration of 1 m3 within the same room and compare it with the value of the maximum permissible concentration (MPC) for each type of substances. These values \u200b\u200bare set regulatory documentation. In case of exceeding the PDC, calculate the number of inflows that ventilation systems should provide. To do this, use the formula:

L \u003d MB / yd - y0, where:

• L is the required value of the inflow, M3 / h;
• MB is the intensity of excretion of the harmful substance per unit of time, mg / h;
• ydop - the concentration of this substance in the air of the room, mg / m3;
• y0 is its concentration in the supply air, mg / m3.

They consider the value of the inflow for each harmful selection, after which they are taken for ventilation the largest of the results.

For neutralization of excess heat, the following formula is used to determine the validity of the inflow:

L \u003d LMO +

In this formula, the parameters:

• LMO - the exhaust volume from the working or serviced zone (the work area takes the space to a height of 2 m from the zero mark of clean floors) by local suction or technological needs, M3 / h;
• Q - the amount of heat from the technological equipment or preheated products, W;
• tMO - the temperature of the air mixture, which is removed by local suction systems from working area, ⁰c;
• tpom - the temperature of the air mixture, removed from the remaining part of the room above the working zone by exhaust ventilation, ⁰С;
• tP is the temperature of the treated supply air, ⁰c;
• C is the heat capacity of the air mixture, 1.2 kJ (M3⁰C) is accepted.

Excessive heat from technological processes are removed using exhaust system And, as a rule, use repeated (recycling).

Urban ventilation system and country houses Almost similar. The only difference is that the requirements for noise insulation in country houses somewhat higher, because the noise created by the ventilation system is distinctly heard against the background of rural silence and pacification.

The calculation of any ventilation system must be started with the calculation of its performance. Before calculating the air exchange, you need to find out the area of \u200b\u200bthe building and its purpose, as well as the number of people in it for a long time.

For residential premises, the normal multiplicity of the air exchange is equal to one, and for the workers this value must be at least twice as high. This value shows the amount of complete change of air masses in the room for an hour.

How to calculate air exchange - we give the basic formulas

Requirements for ventilation premises say that in residential roomsWhere is absent natural ventilationThe air flow per person should be at least 60 m³ / h. When calculating, only those people who are indoors for a long time should be considered.

To calculate the required consumption, it is necessary to calculate the performance of air exchange performance by multiplicity and by the number of person. Calculate air exchange in the number of person is needed by the formula L \u003d N x L Normwhere

• N is the number of people;
• Lnorm - air flow per person (60 m³ / h).

The multiplicity of air exchange is calculated by the formula L \u003d S x H x nwhere

• L is the necessary performance of the ventilation system;
• S is the area of \u200b\u200bthe ventilated room;
• H - height of the ventilated room;
• n - the multiplicity of air exchange according to the standards (1-2 for residential, 2-3 for working rooms)

Manufacturing required calculations And choosing more of these values, you can get the amount of the required air exchange room. Folding the values \u200b\u200bof the required air exchange of all rooms, you can get the overall performance of the ventilation system of a particular building.

Requirements for ventilation of the premises and the features of "clean" rooms

The air exchange table normalizes the values \u200b\u200bfor certain types of buildings:

• for residential premises: 100-500 m³ / h
• for country houses: 500-2000 m³ / h
• for work premises: 1000-100 m³ / h

After the overall performance of the building ventilation system is defined, the design of the air distribution system, which is the ducts, throttle valves, distributors are determined. The diagram of the air ducts is designed in such a way that the pure stream is supplied only to those rooms, where people are located for a long time.

After that, he gets into the corridor, and from there to the kitchen and in the bathroom, where it is removed through the system exhaust ventilation. Such a system does not allow contaminated air masses and unpleasant smell around the room.

Ventilation clean rooms Distributes air on a special system. Clean and cooled air masses are fed through the dispenser system, which are located above the working area, and are removed using floor exhaust holes.

Thus, the polluted air is pressed against the surface of the floor weighing heavier arriving airflows and is removed through the exhaust system. Premises in which it is necessary to maintain in the atmosphere certain number Particles (dust, aerosol particles, microorganisms) are called clean.

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 of the removed and supply 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, the permissible moisture content of air of the working area at a 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, to supply air from the surrounding space to the fan and from the fan to production premises (Supply ventilation) requires a device of air ducts. 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.