Lecture: Classification of ventilation systems and their principle of operation

When designing a ventilation system, its type is primarily determined. Classification of types of ventilation systems is based on the following basic features:

natural or artificial ventilation system.

B) To destination:

supply or exhaust ventilation system.

B) By service area:

local or general ventilation system.

D) By design:

channel or channelless ventilation system.

Figure 1 shows the classification of ventilation systems.

Figure 1 - Classification of ventilation systems

A) By way of moving air:

natural and artificial ventilation system

Natural  ventilation is created without the use of electrical equipment

(fans, electric motors) and occurs due to natural factors:

Due to the temperature difference between the outside (atmospheric) air and the air in the room, the so-called aeration;

Figure 2 - Air flow diagram

Due to the pressure difference of the “air column” between the lower level (serviced room) and the upper level — an exhaust device (deflector) installed on the roof of the building;

1 - supply grilles; 2 - exhaust grilles; 3 - ventilation shaft

Figure 3 - General view of natural ventilation

As a result of exposure, the so-called wind pressure.

Figure 4 - Ventilation under the action of wind pressure

Natural ventilation

Natural ventilation is the movement of air in the following ways:

BUT) Aeration  - natural air movement due to the difference between the temperature in the room and the temperature of the atmospheric (outdoor) air. This method is applicable in workshops with enhanced heat generation, but under the condition that the concentration of dust and harmful substances in the supply air is within acceptable limits. Aeration is not applicable if the conditions of the production technology require pre-treatment of the incoming air, as well as in cases of formation of mist or condensate caused by the influx.

B) Convection  - occurs due to the difference in air pressure between the upper and lower levels (exhaust equipment installed on the roof of the building and the room). It is known that indoor air is warmer than outside, therefore lighter indoor air is displaced by a heavier outdoor air.

AT) Wind pressure  - the wind pressure is increased from the side of the building, turned to the wind and, accordingly, lowered from the leeward side. Atmospheric air enters the buildings of the building from the upwind side and comes out from the lee side.

The advantages of natural ventilation systems are that they are fairly simple, do not require energy consumption and the acquisition of sophisticated equipment.

However, the disadvantage is that the efficiency of natural ventilation systems directly depends on changeable factors (wind speed and direction, temperature) and relatively low pressure.

Mechanical ventilation

Mechanical ventilation is a system of various ventilation equipment and appliances, which supplies and removes air from the room, regardless of the variability of environmental conditions. In cases of necessity, it is possible to treat the air, such as, for example, cleaning, moistening, heating, which is practically impossible in natural ventilation systems. The work of mechanical ventilation systems can be spent enough.

large amount of electricity.

It should be noted that often both natural and mechanical ventilation, or so-called mixed, are used in practice at the same time. In each individual project, the most profitable type of ventilation is individually selected.

Natural (gravitational) ventilation systems

Natural ventilation can be:

a) exhaust without organized air supply (channel system);

b) supply and exhaust air with an organized air flow (aeration system, and in some cases, channel air).

Duct ventilation system.

Channel ventilation system is used mainly in residential and public buildings with a small air exchange of rooms (no more than once in 1h) and with unorganized air flow through the leakiness of the surrounding surfaces, window transom and open air vents.

1 - louvered grill; 2 - window; 3 - exhaust shaft

Figure 4, but  - Scheme of channel exhaust ventilation system

with natural circulation

The air moves through the channels under the action of the difference in pressure and outside the room.

Figure 4 shows a diagram of the duct exhaust ventilation system without organized air flow, and in figure 4, b  - diagram of the duct ventilation system with organized air inflow and calorific thermal stimulation. Ventilating air in these systems is moved either through vertical ducts laid down in the thickness of the walls, or along additional channels. Vertical channels in the attic are combined into precast channels through which the exhaust air through the exhaust shaft enters the atmosphere.

In the channel supply and exhaust ventilation system (Figure 4, b) outdoor air enters through the air intake chamber located in the basement floor and equipped with a heater (air heater). The air heated in the chamber up to the required temperature passes through the channels and through the pinholes with louver grilles installed in them into the rooms. The polluted air leaves the premises through the exhaust ducts, the exhaust openings of which are also equipped with louvered grilles, from there the air enters the collecting ducts and then through the exhaust shaft is removed to the atmosphere.

To increase the available pressure in the channel ventilation system, they often resort to installing a nozzle over the exhaust shaft.

1 - intake channel; 2 - exhaust channel; 3 - channel assembly;

4 - exhaust shaft; 5 - inlet channel; 6 - camera for

air heating

Figure 4, b  - Scheme of the channel supply and exhaust ventilation system

Natural hood through the attic

Not a single ventilation, even from the basement, even from the room, even from the sewer riser can not be taken to the attic.

Ventilation basement - by itself. Ventilation sewer riser - by itself. Ventilation from the cooker - by itself. Never, under any circumstances, and in any combination can not combine them.

Ventilation from other rooms (bathroom, bathroom, kitchen, pantry, etc.) can be combined if it is forced and the fan is above the duct connection point. If the ventilation is natural, then it is impossible to combine the kitchen with the bathroom and it is necessary to exclude the horizontal sections of the air ducts and various knees - there should not be any, otherwise there will be no traction.

but

b

Figure 5, but  and b  - Types of natural exhaust through the attic

Aeration

Organized natural ventilation of industrial premises, in which the ventilation is carried out continuously and carried out without the installation of air ducts, ducts or ducts, and the amount of air is regulated by the degree of opening of special transoms, is called aeration.

External air through the air intake device enters the supply chamber located in the basement. In the inlet chamber, the air is heated by the heater to the temperature from which it must enter the room. The air heated in the chamber enters the supply channels from which it enters the ventilated rooms through louvered grilles.

Figure 6 - Building aeration under the influence of gravitational pressure

Polluted air from the premises enters through the louvered grilles into the exhaust ducts, through which it rises into the collecting duct in the attic. From the collecting channel polluted air is thrown out through the exhaust shaft. To enhance the traction, an additional air heater is sometimes installed in the exhaust shaft or a deflector is installed in the exhaust shaft.

In the cold season, aeration is carried out in factories and plants, where the main hazard is excess heat, such as, for example, in blacksmithing, casting, thermal, rolling and other workshops.

In the warm season, aeration can be very widely used for ventilation of most industrial enterprises. Aeration is not applied at enterprises where, during the warm season, the process requires the treatment of outside air (humidification, cooling or dust removal). These include food industry enterprises, enterprises for the production of medical drugs, electric lamps, weaving, spinning, etc.

Aeration is used in workshops with significant heat generation, if the concentration of dust and harmful gases in the incoming air does not exceed 30% of the maximum allowable in the working area. Aeration is not used if the conditions of the production technology require pre-treatment of the incoming air or if the influx of outside air causes the formation of mist or condensate.

In rooms with large excess heat, air is always warmer than outside.

go Heavier outside air, entering the building, displaces less

dense warm air.

In this case, air circulation circulates in a closed space of the room, caused by a heat source similar to that caused by the fan-tor.

In systems of natural ventilation, in which the movement of air is created by the pressure difference of the air column, the minimum difference in height between the level of air intake from the room and its release through the deflector should be at least 3 meters. In this case, the recommended length of horizontal duct sections should not be more than 3 m, and the air velocity in the ducts should not exceed 1 m / s. The impact of wind pressure is expressed in the fact that increased on the leeward (facing the wind) sides of the building, and reduced pressure (vacuum) on the leeward sides, and sometimes on the roof.

If there are openings in the building fences, then atmospheric air enters the premises from the windward side, and leaves the premises from the leeward side, and the air velocity in the openings depends on the wind speed blowing the building and, accordingly, on the values ​​of the resulting pressure differences.

Advantages and disadvantages of a natural ventilation system

The natural ventilation system is simple and does not require sophisticated equipment and electrical energy consumption. However, the dependence of the efficiency of these systems on the displaced factors (air temperature, wind direction and speed), as well as a small disposable pressure, do not allow solving all complex and diverse tasks in the field of ventilation with their help, since natural ventilation can not always provide the necessary air exchange.

Merits  The natural ventilation systems are low cost, ease of installation and reliability, caused by the lack of electrical equipment and moving parts. Because of this, such systems are widely used in the construction of typical housing and represent a ventilation duct, located in the kitchen and bathrooms.

Reverse  The side of cheapness of natural ventilation systems is a strong dependence of their efficiency on external factors - air temperature, wind direction and speed, etc. In addition, such systems are unregulated in principle and they can not solve many problems in the field of ventilation.

Mechanical ventilation

In mechanical ventilation systems, equipment and appliances (fans, electric motors, air heaters, dust collectors, automatic devices, etc.) are used to move air over considerable distances. The cost of electricity for their work can be quite large. Such systems can supply and remove air from the local areas of the room in the required amount, regardless of the changing conditions of the surrounding air environment. If necessary, the air is subjected to various types of treatment (cleaning, heating, moistening, etc.), which is almost impossible in systems with natural stimulation.

It should be noted that in practice they often provide for so-called mixed ventilation, i.e. both natural and mechanical ventilation.

In each particular project, it is determined which type of ventilation is the best in terms of hygiene, as well as economically and technically more rational.

Local  - Local ventilation is called the one in which air is delivered to certain places (local ventilation) and polluted air is removed only from the places where harmful emissions are formed (local exhaust ventilation).

Local ventilation

It has several varieties:

- Air showers

An air shower is a concentrated inflow of clean air at high speed to workplaces, reducing the temperature of surrounding air in their zone. They must supply clean air to permanent workplaces, reduce the ambient air temperature in their zone and blow workers exposed to intense thermal radiation.

Figure 7 - Air showers

The air flow is directed at working to ensure a comfortable state of health or improve working conditions. Air showers are used to get rid of radiant overheating of workers exposed to heat exposure (blacksmiths, mining). To this end, the air is directed to the irradiated areas of the body, the horizon, or inclined (from top to bottom) jets. In cramped conditions, air is sometimes supplied to strictly fixed jobs and vertical jets from top to bottom. Air showers are also used to improve working conditions in fixed workplaces in areas with a hot climate and to reduce gas pollution in workplaces, if it is impossible to construct shelters for technological equipment or localized ventilation. The choice of a combination of temperature and air mobility in the workplace is determined by the requirement of ensuring a person’s comfortable well-being. An undesirable effect on the body of increased intensity of thermal radiation or air mobility can be eliminated by appropriate selection of air parameters “temperature - speed”. With intensive thermal radiation, it is advisable to blow a stream with a lower temperature than that of the surrounding air. In order to reduce the gas content of the workplace, an increased temperature of the air flow is required compared to the room. The basic air temperatures of the working area for the operation of light I and medium II gravity categories are assumed to be plus +28, for heavy - plus + 26 ° С. Higher airspeeds at the workplace allow the use of higher temperatures, which makes it possible to use a comparatively inexpensive adiabatic air cooling method during the warm period of the year.

Air showers are preferable to carry out the outside air treated in stationary airborne subsidy systems. The air is supplied by nozzles of special design, creating air flow with a uniform speed and temperature. The nozzle allows you to change the direction of flow in the horizontal and vertical planes, creating optimal cooling conditions for the irradiated parts of the human body. The existing designs of the shower nozzles are a variation of the very successful construction of this device, proposed by prof. V.V. Baturin. Baturin pipe consists of a bevelled diffuser with a transition from round to square. The plane of the outlet is 45 ° with the axis of the diffuser. Parallel to the outlet is an adjustable grille of guide vanes, allowing you to change the angle of inclination of the air flow relative to the horizon. In mobile installations, the dusharny unit is usually performed in the form of an axial fan mounted on the frame. The distance-speed of the jet is increased by confusion, which presses the flow, and the cooling effect is increased by spraying water into the air flow. When evaporating, water droplets create additional adiabatic cooling.

- Air oases

Air oases are areas of premises that are separated from the rest of the premises by portable partitions with a height of up to 3 m (usually 2 ... 2.5 meters). Air is supplied to these separated areas at a lower temperature.

Figure 8 - Air Oasis

- Air curtains

Air curtains are designed to change the direction of air flow or to create air barriers.

1 - air supply channels; 2 - lattice;

3 - fan; 4 - air intake

Figure 9 - Example of an air curtain

Air curtains are designed to separate zones with different temperatures on each side of the openings of working windows, entrance doors and mouths. Due to the blowing of high-speed air flow, a “invisible door” is formed, which does not allow the warm air to go outside and does not let cold air into the room. In this way, internal temperature comfort is improved, drafts disappear, heat losses are significantly reduced, and consequently heating costs.

Figure 10 - The process taking place in the veil

To improve the internal climate and additional heating of rooms, there is a choice of models, both with electric elements and heat exchangers with hot water supply for heating the air coming out of the curtains. When closed, the air curtain can work as a fan heater. In summer, in areas with a warm climate, the air curtain is equally energy-efficient equipment, which provides a significant reduction in the cost of air conditioning of the premises and maintaining a low temperature in cold rooms.

At the gates and openings of warehouses, it is recommended to arrange curtains of the sliding type; it is them that we will consider below. The main nodes of such an air curtain are air duct, fan, heater, air duct of uniform distribution, crevice nozzle. The main element of the design is a duct of uniform distribution, equipped with a slit nozzle with guide plates through which the air jet is directed at a certain angle to the plane of the door (Figure 11).

but) b)

at) g)

but  - down up; b  - top down;

at  - curtain side one-sided;

g  - side curtain

Figure 11 - Diagrams of curtain-type air curtains with different jet directions

Local ventilation is used most often at furnaces, gates, between workshops, etc.

Local ventilation is less expensive than general ventilation. In industrial premises, in the allocation of hazards (gases, moisture, heat, etc.), a mixed ventilation system is usually used — common to eliminate hazards in the entire volume of the room and local (local suction and influx) for servicing workplaces. . Local exhaust ventilation is used when places of hazardous emissions in the room are localized and it is possible to prevent their distribution throughout the room. Local exhaust ventilation in industrial premises provides for the capture and removal of harmful emissions: gases, smoke, dust, and partially the heat generated from the equipment. To remove the hazards used local suction (shelters in the form of cabinets, umbrellas, side suction, curtains, shelters in the form of casings at the machines, etc.).

Basic requirements that they must meet:

Where possible, the formation of harmful emissions should be completely covered.

The design of the local suction should be such that the suction does not interfere with normal operation and does not reduce productivity.

Harmful excreta must be removed from the place of their formation in the direction of their natural movement (hot gases and vapors must be removed upwards, cold heavy gases and dust should be removed downwards).

Half-open suction (hoods, umbrellas). Air volumes are determined by calculation.

Open type (side suction). Removal of harmful emissions is achieved only with large volumes of suction air.

System with local suction.

Local exhaust ventilation

Local exhaust ventilation is used in cases where areas of the premises with the release of harmful substances are localized and it is possible to prevent the spread of pollution throughout the room. For removal of harmful substances, local suction is used, which must meet the requirements: the place of contamination should be completely covered, the design of the local suction should not interfere with work, contamination must be removed in the direction of their natural movement (heavy gas and dust - down, light gas and steam - up).

Constructions of local suction are conditionally divided into three groups:

Semi-suction pumps (hoods)

1 - table; 2 - window; 3 - damper; 4 - mine

exhaust; 5 - regulator

Figure 12 - Exhaust Cabinet

a b

but  - at the slit hole with the release of combustion products through it;

b  - at the opening provided with a door when burning products are released

through gas windows

Figure 13 - Sun visors at heating furnaces

Umbrella hoods at the heating furnaces: a) - at the slot opening with the release of combustion products from it; b) - at the opening provided with a door with the release of combustion products through gas windows. The air volume is determined using calculations.

Pumps open type (side)

Figure 14 - Onboard Pumps

Onboard pumps Removal of harmful emissions is achieved only with large amounts of suction air.

Airborne pumps are used to prevent the ingress of harmful discharges from the surface of solutions in baths, where the processes of etching, degreasing and metal plating occur.

The main reason for the removal of harmful substances from the baths is the convective flow of air, which is formed above the evaporation mirror. The principle of operation of the onboard exhaust: the air that is removed through the onboard suction forms a suction spectrum that is superimposed on the convective jet and creates the resulting velocity field directed to the air inlet of the onboard suction.

Figure 15 - Types of side suction

Single-sided suction can be distinguished when the suction gap is located along one of the long sides of the bath, double-sided when the slots are located at two opposite sides, and angular - when the slots are located at two adjacent sides.

One-sided side suction is applied with a bath width of 600 mm, while for the overturned side suction the estimated bath width is measured from the side suction to the opposite side of the bath. In the case of simple side suction, the width is measured from side to side of the bath. Double sided suction is used with a bath width of 1200mm. In the case of simple side bends, the calculated width of the bath is measured from side to side, for overturned - between the edges of the side suction inside the bath. Removal of harmful emissions is achieved only with large amounts of suction air.

An on-board suction is called simple when the air intake slots are located in a vertical plane, and tilted when the slot is horizontal, parallel to the bath mirror. The overturned onboard suction units provide the same efficiency as the hazardous material trapping with less air flow.

Simple suction should be used when the level of the solution in the bath is high, when the distance from the solution mirror to the edge of the suction gap is less than 80 ... 150 mm; overturned with a lower standing level of the solution (D = 150 ... 300mm and more).

Figure 16 - Types of side suction

Local suction

The ventilation system with local suction is shown in Figure 17. The main elements of such a system are local suction - shelter (MO), suction duct network (VS), fan (V) of centrifugal or axial type, VS - exhaust shaft.

Figure 17 - Diagram of local exhaust ventilation

In most cases, local exhaust ventilation systems are very effective, as they help to remove pollutants directly from the place where they formed, minimizing the possibility of distribution in the room.

Supply and exhaust ventilation system

The intake ventilation system serves to supply fresh air to the room. If necessary, the supplied air is heated and cleaned from dust. Exhaust ventilation, on the other hand, removes polluted or heated air from the room. Usually both ventilation and exhaust ventilation is installed in the room. At the same time, their performance must be balanced, otherwise the room will generate insufficient or excessive pressure, which will lead to the unpleasant effect of “slamming doors”.

Figure 18 - Supply and exhaust ventilation with mechanical impulse

General ventilation system

Local ventilation is designed to supply fresh air to certain places (local ventilation) or to remove polluted air from the places of formation of harmful emissions (local exhaust ventilation). Local exhaust ventilation is used when the places of hazardous emissions are localized and it is possible to prevent their distribution throughout the room. In these cases, local ventilation is quite effective and relatively inexpensive. Local ventilation is mainly used in production. In domestic conditions, general ventilation is used.

The exceptions are kitchen hoods, which are local exhaust ventilation.

Figure 19 - Exhaust Ventilation

General exchange  ventilation, in contrast to local, is intended for the implementation of ventilation throughout the room. General ventilation can also be supply and exhaust. The inlet general ventilation, as a rule, must be performed with heating and filtration of the intake air. Therefore, such ventilation must be mechanical (artificial). General exhaust ventilation may be easier to supply and run in the form of a fan installed in a window or a hole in the wall, since the exhaust air does not need to be processed. With small volumes of ventilated air, natural exhaust ventilation is installed, which is noticeably cheaper than mechanical.

Figure 20 - General ventilation

The inlet mechanical ventilation system serves to supply fresh, suitably treated air into the room.

Outside air must be taken from unpolluted and ventilated places. For air intake arrange special air intake devices. Holes in the air intake devices, through which outside air is taken, are covered with special gratings that protect them from snow, rain and debris.

The outside air is pretreated before being supplied to the room: as a rule, it should be warmed up in the cold season, and sometimes cooled in the summer. In many cases, the outside air has to be humidified, and before being brought into the room it is often necessary to clean the dust.

The supply air is processed in the supply chambers (Fig. 8). The figure shows a diagram of the simplest inlet chamber for heating the air.

Fig. 8. The simplest inlet chamber

Air enters the chamber into the air intake shaft 1 through an opening closed by a louvre grille 2. The amount of intake external air is regulated by valve 3. Next, the air enters the air heaters 4, where it is heated. The temperature of the supply air is regulated by mixing the heated air with a part of the external unheated air entering through the bypass valve 5 into room 6, bypassing the heaters. Through the same bypass valve air enters in the summer, when the heaters are turned off.

The treated air from the inlet chamber is sucked in by the fan 7 and is injected into the duct network 8 by it, from which air is discharged into the room at the appropriate places and in the required amount through special devices.

In addition to the above general exchange ventilation system, local ventilation systems are also organized in the form of air showers, air curtains and air oases.

Air dushirovanie  It is a concentrated air flow directed at a person working under conditions of elevated temperature or with great physical exertion, when irradiated from heat sources such as hot surfaces of industrial furnaces, red-hot metal, etc., and increased dustiness and pollution of the room air gases.

The cooling effect of the air shower is based on the temperature difference between the air of the soul and the body, as well as the increased air flow around the body.

With the help of air showering, it is possible to change the air velocity, its temperature, humidity and concentrations of gases, vapors and dust in it in a space bounded by the airflow.

Installations for the air shower have different designs.

The main ones are: installations in which air is supplied by a fan through a network of air ducts and is discharged at a specific place from several pipes (Fig. 9); units in which the concentrated air flow is supplied to the workplace; mobile air-drier units that can be located at the desired distance from the workplace; fan plants serving workplaces and driving the internal air of the workshop.

Fig. 9. Air shower at the casting site of the iron foundry

The choice of one or another air shower depends on the production conditions.

Examples of fan installations are air-cooling units of the Sverdlovsk Institute of Labor Protection of the All-Union Central Council of Trade Unions (SIOT-3, SIOT-5 and SIOT-6).

The SIOT-3 unit (fig. 10) is a portable fan unit designed to stifle working places at heating "furnaces, to cool working places at turbines, in drying sections, etc. It consists of an axial fan with a wheel diameter of 700 mm and electric motor connected on the same axis. The unit is mounted on a mobile carriage.

Fig. 10. Portable fan unit for air showers:
   1 - axial fan; 2 - electric motor; 3 - scapulae; 4 - fairing; 5 - stand; 6 - rollers; 7 - shell; 8 - grid; 9 - filter; 10 - crane; 11 - tube; 12 - nozzles

Spray / water is added to the air flow, which serves to cool it. Details of the device unit are shown in the figure.

The SIOT-5 unit is portable and consists of an axial fan with a wheel diameter of 500 mm. It is intended for the drowning of the workplaces of crane operators, machinery control stations and electrical equipment in hot workshops, etc.

The SIOT-6 unit is rotary, consists of an axial fan with a wheel diameter of 1,000 mm. It is applicable to the air damping of working sites of open-hearth, mine, smelting, furnace furnaces, etc.

Air curtains. In the cold season, through the opening gates to the workshops, to the vestibules and sluices of the entrance doors of public buildings with a large flow of people, a large amount of cold air penetrates the entrance doors of the theaters, which spreads along the floor, cooling the lower area of ​​the room.

To combat this phenomenon, ventilating installations are called air curtains.

When an air curtain is set up, warm air is taken from the upper zone of the room, or the outside air is specially heated and directed at an angle to meet the air that tends to rush into the room when the gate or door is opened.

Air is supplied in the form of a flat jet in the entire width or height of the gate from the channels located below or on the side of the gate.

With sufficient volume and the required velocity of the exhaust air, it is possible to stop or significantly reduce the amount of cold air entering the workshop through the gate.

In fig. 11 shows the operation of the air curtain in the gate of the shop

Air oases. The air oasis is a ventilated part of the production area limited by partitions.

In this part of the room through the air ducts comes clean air with a lower temperature than in the rest of the room. As a result, there is a more favorable air environment in the air oasis than in the whole room.

Ventilation is a set of measures and devices used in the organization of air exchange to ensure a given state of the air in rooms and workplaces in accordance with SNiP (Building Regulations).

Ventilation systems ensure the maintenance of acceptable meteorological parameters in various premises.

With all the variety of ventilation systems, due to the appointment of the premises, the nature of the process, the type of harmful emissions, etc., they can be classified according to the following characteristics:

1. By way of creating pressure to move air:  with natural and artificial (mechanical) motivation.
2. To destination:  supply and exhaust.
3. By service area:  local and general exchange.
4. According to the design:  channel and channelless.

Natural ventilation.

The movement of air in natural ventilation systems occurs:

• due to the temperature difference between the outside (atmospheric) air and indoor air, the so-called aeration;
• due to the pressure difference of the "air column" between the lower level (serviced room) and the upper level - exhaust device (deflector) installed on the roof of the building;
• as a result of the impact of the so-called wind pressure.

Aeration is used in workshops with significant heat generation, if the concentration of dust and harmful gases in the incoming air does not exceed 30% of the maximum allowable in the working area. Aeration is not used if the conditions of the production technology require pre-treatment of incoming air or if the influx of outside air causes the formation of mist or condensate.

In rooms with large excess heat, the air is always warmer than the outside. Heavier outside air, entering the building, displaces less dense warm air from it.

At the same time in the closed space of the room there is air circulation caused by a heat source, similar to that caused by the fan.

In natural ventilation systems, in which air movement is created due to the pressure difference of the air column, the minimum difference in height between the level of air intake from the room and its release through the deflector should be at least 3 m. At the same time, the recommended length of horizontal duct sections should not be more 3 m, and the air velocity in the air ducts should not exceed 1 m / s.

The impact of wind pressure is expressed in that increased on the windward (facing the wind) sides of the building, and reduced pressure (vacuum) on the leeward sides, and sometimes on the roof.

If there are openings in the building fences, then atmospheric air enters the room from the windward side, and leaves it from the leeward side, and the speed of air movement in the openings depends on the wind speed blowing the building and, accordingly, on the values ​​of the resulting pressure differences.

Natural ventilation systems are simple and do not require complex expensive equipment and energy consumption. However, the dependence of the efficiency of these systems on variable factors (air temperature, wind direction and speed), as well as a small disposable pressure, do not allow solving all complex and diverse problems in the field of ventilation with their help.

Mechanical ventilation.

Mechanical ventilation systems use equipment and appliances (fans, electric motors, air heaters, dust collectors, automation, etc.), which allow to move air over long distances. The cost of electricity for their work can be quite large. Such systems can supply and remove air from the local areas of the room in the required amount, regardless of the changing conditions of the surrounding air environment. If necessary, the air is subjected to various types of treatment (cleaning, heating, humidification, etc.), which is almost impossible in systems with natural motivation.

It should be noted that in practice they often provide for so-called mixed ventilation, i.e., natural and mechanical ventilation at the same time.

In each particular project, it is determined which type of ventilation is the best in terms of hygiene, as well as economically and technically more rational.

Forced ventilation.

The inlet systems serve to supply clean air to the ventilated premises instead of the remote one. In necessary cases, the supply air is subjected to special treatment (cleaning, heating, humidification, etc.).

Exhaust ventilation.

Exhaust ventilation removes polluted or heated exhaust air from a room (workshop, building).

In the general case, both inlet and exhaust systems are provided for in the room. Their performance must be balanced, taking into account the possibility of air entering adjacent rooms or from adjacent rooms. Indoors can also be provided only exhaust or only the intake system. In this case, the air enters this room from the outside or from adjacent rooms through special openings or is removed from this room to the outside, or flows into adjacent rooms.

Both intake and exhaust ventilation can be arranged in the workplace (local) or for the whole room (general exchange).

Local ventilation.

Local ventilation is such that air is supplied to certain places (local forced ventilation) and polluted air is removed only from places where harmful emissions are formed (local exhaust ventilation).

Local ventilation.

Air showers (concentrated air inflow with increased speed) belong to local ventilation. They must supply clean air to permanent workplaces, reduce the ambient air temperature in their area and blow off workers exposed to intense thermal radiation.

The local supply ventilation includes air oases - areas of the premises, fenced from the rest of the premises by movable partitions of 2–2.5 m in height, into which air with a lower temperature is forced.

Local ventilation is also used in the form of air curtains (at the gate, furnaces, etc.), which create air-like partitions or change the direction of air flow. Local ventilation is less expensive than general ventilation. In industrial premises, in the allocation of hazards (gases, moisture, heat, etc.), a mixed ventilation system is usually used — common to eliminate hazards in the entire volume of the room and local (local suction and inflow) to service workplaces.

Local exhaust ventilation.

Local exhaust ventilation is used when places of hazardous emissions in the room are localized and it is possible to prevent their distribution throughout the room.

Local exhaust ventilation in industrial premises provides for trapping and removal of harmful emissions: gases, smoke, dust, and partially the heat generated from the equipment. To remove the hazards used local suction (shelters in the form of cabinets, umbrellas, airborne pumps, curtains, shelters in the form of casings at the machines, etc.). Basic requirements that they must meet:

• The place of formation of harmful secretions should be completely covered if possible.
• The design of the local suction should be such that the suction does not interfere with normal operation and does not reduce productivity.
• Harmful secretions must be removed from the place of their formation in the direction of their natural movement (hot gases and vapors must be removed up, cold heavy gases and dust - down).
• Constructions of local suction are conditionally divided into three groups:
• Semi-suction pumps (fume hoods, umbrellas, see fig. 1). Air volumes are determined by calculation.
• Open type (side suction). Removal of harmful emissions is achieved only with large volumes of suction air (Fig. 2).

The system with local suction is shown in Fig. 3

The main elements of such a system are local suction - shelters (MO), suction duct network (VS), fan (B) of centrifugal or axial type, VS - exhaust shaft.

When arranging local exhaust ventilation in order to trap dust emissions, the air removed from the workshop must be clean of dust before being released into the atmosphere. The most complex exhaust systems are those in which they provide for a very high degree of air purification from dust with the installation of two or even three dust collectors in series (filters).

Local exhaust systems, as a rule, are very effective, as they allow to remove harmful substances directly from the place of their formation or discharge, preventing them from spreading indoors. Due to the significant concentration of harmful substances (vapors, gases, dust), it is usually possible to achieve a good sanitary and hygienic effect with a small amount of exhaust air.

However, local systems can not solve all the problems facing the ventilation. Not all harmful secretions can be localized by these systems. For example, when harmful emissions are dispersed over a large area or in volume; air supply to certain areas of the room cannot provide the necessary conditions of the air environment, the same if the work is performed on the whole area of ​​the room or its nature is connected with movement, etc.

General exchange ventilation systems, both inflow and exhaust, are intended for ventilation in a room as a whole or in a significant part of it.

General exchange exhaust systems relatively evenly remove air from the entire serviced room, and general exchange supply systems supply air and distribute it throughout the entire volume of the ventilated room.

General ventilation.

General trade inlet ventilation is arranged to assimilate excess heat and moisture, dilute harmful concentrations of vapors and gases not removed by local and general exchange exhaust ventilation, as well as to ensure the calculated sanitary and hygienic standards and free breathing of a person in the working area.

With a negative heat balance, i.e. with a lack of heat, general exchange ventilation is arranged with a mechanical impulse and with heating of the entire amount of intake air. As a rule, before supplying the air is cleaned from dust.

When harmful emissions enter the air in the workshop, the amount of supply air must fully compensate for general exchange and local exhaust ventilation.

General exhaust ventilation.

The simplest type of general exhaust ventilation is a separate fan (usually of axial type) with an electric motor on the same axis (Fig. 4), located in a window or in a wall opening. Such installation removes air from the closest to the fan area of ​​the room, carrying out only general air exchange.

In some cases, the installation has an extended exhaust duct. If the length of the exhaust duct exceeds 30–40 m and, accordingly, the pressure loss in the network is more than 30–40 kg / m2, then a centrifugal fan is installed instead of an axial fan.

When harmful gases in the workshop are heavy gases or dust and there is no heat generation from the equipment, exhaust air ducts are laid on the floor of the workshop or carried out in the form of underground channels.

In industrial buildings, where there are diverse hazardous emissions (heat, moisture, gases, vapors, dust, etc.) and their entry into the room occurs in different conditions (concentrated, dispersed, at different levels, etc.), often It is impossible to do with any one system, for example, local or general exchange.

In such rooms to remove harmful emissions that can not be localized and enter the room air, apply general exchange exhaust systems.

In certain cases, in industrial premises, along with mechanical ventilation systems, systems with natural motivation are used, for example, aeration systems.

Channel and channelless ventilation.

Ventilation systems have an extensive network of air ducts for moving air (duct systems) or ducts (ducts) may be absent, for example, when fans are installed in the wall, in the ceiling, with natural ventilation, etc. (channel-free systems).

Thus, any ventilation system can be characterized according to the above four characteristics: by purpose, service area, method of mixing air and design.

Ventilation systems include groups of various equipment:

1. Fans.

• axial fans;
• radial fans;
• diametrical fans.

2. Fan units.

• channel;
• roof.

3. Ventilation systems:

• intake;
• exhaust;
• forced-air and exhaust.

4. Air-thermal curtains.

5. Sound attenuators.

6. Air filters.

7. Air heaters:

• electrical;
• water.

8. Air ducts:

• metal;
• metal-plastic;
• non-metallic.
• flexible and semi-flexible;

9. Shut-off and control devices:

• air valves;
• diaphragm;
• check valves.

10. Air distributors and air removal control devices:

• lattices;
• slotted air distribution devices;
• plafonds;
• nozzles with nozzles;
• perforated panels.

Mechanical ventilation systems are used where there is insufficient natural ventilation. Mechanical systems use equipment and appliances (fans, filters, air heaters, etc.) to move, clean and heat the air. Such ventilation systems can remove or supply air to ventilated rooms regardless of environmental conditions.

Mechanical ventilation systems can also be ductless and ductless. The most common channel systems. The cost of electricity for their work can be quite large. Such systems can supply and remove air from the local areas of the room in the required amount, regardless of the changing conditions of the surrounding air environment.

The advantage of mechanical ventilation over natural is the ability to ensure stable required air exchange regardless of the season, outdoor meteorological conditions, as well as wind speed and direction. It allows you to process the air supplied to the premises, bringing its meteorological parameters to the values ​​required by the standard, and purify the air from harmful impurities before being released into the atmosphere. The disadvantages of the mechanical ventilation system can be attributed to the high cost of electricity, but these costs quickly pay for themselves.

If the heat, moisture, gases, dust, odors or vapors of liquids released in the room go directly into the air of the whole room, then general ventilation is installed. General exchange exhaust systems relatively evenly remove air from the entire serviced room, and general exchange supply systems supply air and distribute it throughout the entire volume of the ventilated room. In this case, the volume of exhaust air is calculated in such a way that after it is replaced with fresh air, the air pollution will drop to the maximum permissible concentration (MAC).

Usually, the same amount of air is extracted from the room as is supplied to it. However, there are cases when the total air flow is not equal to the exhaust. So, for example, more air is extracted from rooms in which odorous substances or toxic gases are emitted than is supplied through the intake system so that harmful gases and odors do not spread throughout the building. The missing volume of air is pumped through open apertures of external fences or from neighboring rooms with cleaner air.

General ventilation

The inlet systems serve to supply clean air to the ventilated premises instead of the remote one. When necessary, the supply air is subjected to special treatment (cleaning, heating, humidification, etc.).

The scheme of mechanical ventilation (Fig. 1) includes: air intake device 1; air filter 2 ; air heater (heater) 3; fan 5; duct network 4 and inlets with nozzles 6 . If there is no need to heat the supply air, then it is passed directly to the production premises through the bypass channel 7.

Spaces can only be equipped with fresh air ventilation systems. In such cases, a calculated amount of air is supplied to the room. Air removal can occur unorganized through leaks in building fences or through specially provided openings.

Fig. 1. The scheme of ventilation

In the steady state, the amount of intake air is always equal to the amount of exhaust air, regardless of the total area of ​​leaks or holes in building structures. The most cleaned rooms, as a rule, are equipped with intake systems, since the air moves out of these rooms, and not vice versa.

Local ventilation

Local ventilation systems supply fresh air directly to the workplace or to a place of rest. In the area of ​​the system, conditions are created that differ from those in the entire room and meet the requirements. Air showers and oases belong to local ventilation. Air shower is a local, directed at the person air flow. In the air shower zone, conditions are created that are different from the conditions in the entire volume of the room. With the help of air showers such parameters as: human mobility can be changed; temperature; humidity; concentration of one or another hazard. Most often, air showers are used in hot shops exposed to thermal radiation in workplaces.

Air oases, areas of the premises fenced from the rest of the premises by movable partitions with a height of 2.0 - 2.5 meters, into which air with a lower temperature is forced, also belong to local ventilation.

Local ventilation is less expensive than general ventilation.

General exhaust ventilation

Exhaust ventilation is used to remove polluted or heated exhaust air from a production or dwelling (workshop, building). In the case of room equipment only exhaust ventilation system is organized by removing air from the premises. The inflow is carried out unorganized or through leakages in building structures, or through holes specially provided for these purposes.

Exhaust ventilation (Fig. 2) consists of a cleaning device 1, a fan 2, a central 3 and suction ducts 4.

Unlike inlet ventilation systems, in rooms that have exhaust systems only, the pressure is set below atmospheric or lower than in neighboring rooms.

If there is only an exhaust ventilation system in the room, as well as in the case of forced ventilation, air flows from the high pressure area to the lowered one. Thus, the movement of air in the opposite direction is prevented or obstructed. Exhaust ventilation systems are equipped with the most “dirty” rooms, when it is necessary to prevent or reduce the spread of air from them to neighboring rooms.

Fig. 2. Diagram of exhaust ventilation system

Local exhaust ventilation

Local exhaust ventilation is used in a situation when the places of hazard release in the room are localized and it is possible to prevent their distribution throughout the room. Local exhaust ventilation in industrial premises provides for trapping and removal of harmful emissions: gases, smoke, dust, suspensions, and partially the heat generated from the equipment. To remove the hazards used local suction (shelters in the form of cabinets, umbrellas, side suction, shelters in the form of casings at the machines, etc.).

Basic requirements that they must meet:

the place of formation of harmful emissions should be completely covered if possible;

the design of the local suction should be such that the suction does not interfere with normal operation and does not reduce productivity;

harmful emissions must be removed from the place of their formation in the direction of their natural movement (hot gases and vapors must be removed up, cold heavy gases and dust - down).

The air removed from the room during local exhaust ventilation must be cleaned of dust before it is released into the atmosphere. The most complex exhaust systems are those in which they provide for a very high degree of air purification from dust with the installation of two or even three dust collectors in series (filters).

Local exhaust systems, as a rule, are very effective, as they allow to remove harmful substances directly from the place of their formation or discharge, preventing them from spreading indoors. Due to the significant concentration of harmful substances (vapors, gases, dust), it is usually possible with a small amount of exhaust air to achieve a good sanitary and hygienic effect.

Supply and exhaust ventilation

The system of exhaust ventilation is based on the creation of two opposing streams. Such a system can be created either on the basis of independent subsystems of inflow and exhaust of air - with its own fans, filters, etc., or on the basis of one appropriate installation operating both on the inflow and on the exhaust. The scheme of the supply and exhaust ventilation system is shown in Fig.3.

Fig. 3. The system of supply and exhaust ventilation: 1 - air distributors; 2 - air intake devices (grilles); 3 - dampers; 4 - fan (supply, exhaust); 5 - filter; 6 - air heater; 7 - the air valve; 8 - outer grille; 9 - exhaust umbrella; 10 - supply air duct; 11 - exhaust air duct

The convenience of such systems is not only to facilitate installation and installation, but also in operation, as well as in the additional properties of such systems. One of these properties is heat recovery - a process in which a partial increase in supply air temperature occurs due to the heat of the drawn out air. In this case, energy is spent only on the organization of air flows, i.e. not consumed for heating the incoming air. Heating of the incoming air due to the recovery can be supplemented with an electric or water heater. Supply and exhaust ventilation provides forced replacement of air in the room; produces the necessary air treatment (heating, purification); Some systems also provide for air humidification within certain limits.

Composition of ventilation systems

The composition of the ventilation system depends on its type. Ventilation artificial (mechanical) ventilation systems are the most complex and frequently used, therefore we will consider their composition.

Usually, a mechanical ventilation system consists of the following components (located in the direction of air movement, from the inlet to the outlet):

Air intake device. Air intake devices in mechanical ventilation systems are made in the form of holes in the fences of buildings, added or separate shafts (Fig.4).

When air is taken from above, the air intake devices are placed in the attic or the upper floor of the building, and the channels are output above the roof in the form of shafts.

The location and design of the air intake devices are selected taking into account the purity of the intake air and the satisfaction of architectural requirements. Thus, air intakes should not be located near sources of air pollution (emissions of polluted air or gases, chimneys, kitchens, etc.).

The height relative positioning of the inlet openings should be assigned taking into account the volume mass of the released pollutants. Holes for air intake should be placed at a height of more than 1 m from the level of stable snow cover, determined according to hydro meteorological stations or by calculation, but not less than 2 m from ground level.

Fig.4. Air intake devices: but  - in the outer wall; b  - at the outer wall; at  - on the roof

Architectural requirements are met by appropriate choice of the location of the holes and their design.

The outer walls of the exhaust ducts and shafts are insulated to avoid condensation of water vapor from the extracted moist air and the formation of frost.

The air velocity in the inlet channels and mines is assumed to be within 2–5 m / s, in the channels and mines of the emission devices - 4–8 m / s, but not less than 0.5 m / s, including for natural ventilation.

Air valve. To protect the premises from entering them through the ventilation ducts when the cold outside air is not working, the air intakes are equipped with multi-wing heat-insulated valves with manual or mechanical drive. In the latter case, the valve is blocked with a fan and closes the holes when it stops. With a low design outdoor air temperature, the valves are supplied with an electric heating system in order to protect their valves from freezing. Electric heating is switched on for 10-15 minutes before starting the fan.

Filter.  An air filter is a device in ventilation systems that serves to clean supply air and, in some cases, exhaust air. The filter is necessary to protect both the ventilation system itself and the ventilated premises from the ingress of various small particles, such as dust, insects, down, etc. The design of the air filter is determined by the nature of the dust (pollution) and the required cleanliness of the air.

Slipping coefficient (R,%) - characteristic of the filter or filter material, equal to the percentage of the concentration of particles after the filter WITH P WITH D

Efficiency (E,  %) - the characteristic of the filter or filtering material, equal to the percentage ratio of the concentration of particles to WITH D  and after filter C P  to particle concentration before filter WITH D

The size of the most penetrating particles is the particle size corresponding to the minimum efficiency of the filtering material.

Filter capacity (air flow) - air volume per unit of time passing through the filter.

Aerodynamic resistance (pressure drop across the filter) is the difference between the total pressures before and after the filter for a certain filter performance.

Filters are classified by purpose and performance on:

general purpose filters - coarse filters and fine filters;

filters that provide special requirements for clean air - high efficiency filters and ultra high efficiency filters.

Designations of classes of filters are specified in tab. one.

Table 1

Designations of classes of filters (GOST R 51251-99 )

The classification of general-purpose filters is given in table. 2

table 2

Classification of general-purpose filters on the efficiency of particles captured

Structurally, filters are subdivided into rolled (non-woven filtering material is used), cell-based (metal, viniplast mesh, foam rubber, special FPP type material are used).

Pocket type filters FyaK cleaning class G3-F9 are designed for air purification from dust of external recirculating air in the systems of inlet ventilation and air conditioning. Filters are manufactured according to TU 4863-015-04980426-2003, GOST R 51251-99. FyaK can be operated at a temperature of working medium from minus 40 ° С to plus 70 ° С. Environment and filtered air must not contain aggressive gases and vapors.

The filter (Fig. 1) consists of a metal frame 1 and a filter material sewn in the form of pockets 2.

Fig. 1. Pocket fak filter

Opposite surfaces of the pockets are tightened by stoppers, which prevents strong swelling and adhesion of adjacent pockets. At the end of the pockets there is a band 3, with the help of which the pockets are connected to each other and under the pressure of the air flow does not "fly away". Filter pockets are made of high quality synthetic filter material.

The dimensions of the pockets are chosen so that the air flow is uniform over the entire surface of the filter. The special shape of the pockets allows them to swell without touching each other, dust accumulates evenly over the entire surface of the pockets and every square centimeter of filtering material is optimally used.

Cellular corrugated filters of the type FyaG are designed for cleaning external and recirculating air in the systems of inlet ventilation and air conditioning for premises of various purposes for residential, administrative and industrial buildings. Filters FyaG (Fig. 2) consist of a frame (1), made of cardboard or galvanized steel, inside which is laid filtering material (2) in the form of a corrugation, supported from the air outlet side to a grid of corrugated (wavy) form (3).

Fig. 2. Filter circuit

To destroy unpleasant odors in residential premises, filters are used from a material with an ultramicroscopic structure, which allows the extraction of gases from the air. The most common absorber of gases, vapors and odors is activated carbon.

Great Encyclopedia of Technology The team of authors

Air oasis (aeration)

Air oasis (aeration)

Air oasis (aeration) is an organized natural air exchange in rooms, carried out due to the difference between the densities of outdoor and indoor air and the effect of wind on the external fences of the building in order to create the necessary microclimate in the room. Aeration is widely used in industrial workshops (forge, foundry, rolling, etc.) with significant excess heat.

To calculate an air oasis, it is necessary to take into account the dimensions of the building, the air pressure drops, the dimensions of the openings, the temperature in the working area, the location of heat sources, the temperature of the air exiting through the openings of the building, the outside air temperature, etc.

Devices for providing an air oasis:

1) inlet transoms;

2) deflectors;

3) non-inflatable lights;

4) exhaust shafts.

There are several constructions of inflow transoms:

1) single upper-hung transom with a rotation on the upper axis of not more than 45 °. Used, as a rule, for the inflow and exhaust air;

2) single podmusyh transom with rotation on the middle axis at an angle of not more than 90 °;

3) upper-hung transom, made with double frames, installed in the workshops; in the warm season, hot outside air is directed down to the floor, where it is cooled;

4) transom, fixed on the lower axis, open in the cold season at an angle of not more than 30 ° so that the cold air entering the building heats up, moving up, and warm down into the room;

5) transom installed at a distance of two meters from the floor, opening, fix for airing rail.

The air is removed from buildings, usually through transom, rotating on the upper axis.

Deflector - part of the exhaust device in the form of a nozzle on the exhaust pipe to enhance traction and eliminate the blowing of the wind into the exhaust channels.

Currently, the most frequently used deflectors of the system V. I. Khanzhonkov - TsAGI. The design of the TsAGI deflector provides for a nozzle with a cone-shaped diffuser, a shield for protection against wind blowing, an umbrella and a cylinder, which serve to protect the exhaust opening to which the deflector is fixed from precipitation.

Advantages: independence of the deflector from changing the direction of the wind and ensuring reliable protection of the exhaust shaft from precipitation.

Flashlight is a device in which there is a vacuum between the walls of the lamp and shields against wind, thereby extracting air from the room.

Exhaust mines are devices installed in the ceilings of industrial buildings, whose work is due to the natural pressure arising from the difference in temperature inside the mine and outside the building.