Ventilation is a set of measures and devices used in organizing air exchange to ensure a given state of the air environment in rooms and at workplaces in accordance with Construction Norms and Regulations (Construction Norms).

Ventilation systems ensure the maintenance of permissible meteorological parameters in rooms for various purposes.

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

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

Natural ventilation.

Air movement in natural ventilation systems occurs:

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

Aeration is used in workshops with significant heat if the concentration of dust and harmful gases in the supply air does not exceed 30% of the maximum permissible in the working area. Aeration is not used if, under the conditions of the production technology, preliminary treatment of the supply air is required or if the influx of external air causes the formation of fog or condensate.

In rooms with large excesses of 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, air circulation occurs in the enclosed space of the room, 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 difference in pressure of the air column, the minimum difference in height between the level of air intake from the room and its discharge through the deflector must be at least 3 m. Moreover, the recommended length of the horizontal sections of the air ducts should not be more 3 m, and the air speed in the ducts - not exceed 1 m / s.

The effect of wind pressure is expressed in the fact that on the windward (facing the wind) sides of the building an increased pressure is formed, and on the leeward sides, and sometimes on the roof, a reduced pressure (rarefaction) is formed.

If the fencing of the building has openings, then from the windward side the atmospheric air enters the room, and from the windward side it leaves it, and the speed of air movement in the openings depends on the speed of the wind blowing the building, and accordingly on the magnitude of the resulting pressure differences.

Natural ventilation systems are simple and do not require complicated expensive equipment and the consumption of electrical energy. However, the dependence of the effectiveness of these systems on variable factors (air temperature, direction and wind speed), as well as the small disposable pressure, do not make it possible to solve all complex and diverse problems in the field of ventilation with their help.

Mechanical ventilation.

Mechanical ventilation systems use equipment and instruments (fans, electric motors, air heaters, dust collectors, automation, etc.) that allow air to be transported 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 quantity, regardless of the changing environmental conditions. If necessary, the air is subjected to various types of processing (cleaning, heating, humidification, etc.), which is almost impossible in systems with natural motivation.

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

Each specific project determines which type of ventilation is the best in sanitary and hygienic terms, as well as economically and technically more rational.

Forced ventilation.

Supply systems are used to supply clean air to the ventilated rooms instead of the remote. Supply air, if necessary, is subjected to special treatment (cleaning, heating, humidification, etc.).

Exhaust ventilation.

Exhaust ventilation removes contaminated or heated exhaust air from the room (workshop, building).

In the general case, both supply and exhaust systems are provided in the room. Their performance should be balanced taking into account the possibility of air entering into adjacent rooms or from adjacent rooms. Indoors, only an exhaust system or only a supply system can be provided. In this case, 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 supply and exhaust ventilation can be arranged at the workplace (local) or for the entire room (general exchange).

Local ventilation

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

Local ventilation.

Local supply ventilation includes air showers (concentrated air flow at increased speed). They must supply clean air to permanent workplaces, lower the ambient temperature in their area, and blow workers exposed to intense heat radiation.

Local oversized ventilation includes air oases - sections of rooms fenced off from the rest of the room by mobile partitions 2–2.5 m high, into which air with low temperature is pumped.

Local ventilation is also used in the form of air curtains (at the gates, stoves, etc.), which create, as it were, air partitions or change the direction of air flows. Local ventilation is less expensive than general ventilation. In industrial premises, when emitting harmful substances (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.

Local exhaust ventilation is used when the places of hazardous emissions in the room are localized and their spread throughout the room can be prevented.

Local exhaust ventilation in industrial premises provides for the capture and removal of harmful emissions: gases, smoke, dust and partially generated heat from the equipment. To remove hazards, local suction is used (shelters in the form of cabinets, umbrellas, side suction, curtains, shelters in the form of casings for machine tools, etc.). The 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 labor 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 upward, cold heavy gases and dust - downward).
• The designs of local suction are conventionally divided into three groups:
• Semi-open exhausts (fume hoods, umbrellas, see Fig. 1). Air volumes are determined by calculation.
• Open type (side suction). The removal of harmful emissions is achieved only with large volumes of aspirated air (Fig. 2).

The system with local suction is shown in Fig. 3.

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

When using local exhaust ventilation to capture dust emissions, the air removed from the workshop must be cleaned of dust before being discharged into the atmosphere. The most complex exhaust systems are those in which they provide a very high degree of dust cleaning with the installation of two or even three dust collectors (filters) in series.

Local exhaust systems, as a rule, are very effective, since they allow you to remove harmful substances directly from the place of their formation or excretion, 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 air removed.

However, local systems cannot solve all the problems facing ventilation. Not all harmful secretions can be localized by these systems. For example, when noxious emissions are dispersed over a significant area or volume; air supply to certain areas of the room cannot provide the necessary conditions for the air environment, the same if the work is carried out on the entire area of \u200b\u200bthe room or its nature is associated with movement, etc.

General exchange ventilation systems - both supply and exhaust, are intended for ventilation in the 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 exchange forced ventilation.

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

With a negative heat balance, i.e., with a lack of heat, general exchange supply ventilation is arranged with mechanical motivation and with heating the entire volume of supply air. As a rule, air is cleaned of dust before being fed.

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

General exchange exhaust ventilation.

The simplest type of general exchange exhaust ventilation is a separate fan (usually axial type) with an electric motor on one axis (Fig. 4), located in a window or in a wall opening. Such an installation removes air from the area of \u200b\u200bthe room closest to the fan, providing 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 the axial fan.

When the harmful emissions in the workshop are heavy gases or dust and there is no heat emission from the equipment, exhaust ducts are laid along the floor of the workshop or are made in the form of underground channels.

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

In such rooms, general-exchange exhaust systems are used to remove harmful emissions that cannot be localized and enter the air of the room.

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

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 installing fans in a wall, in a ceiling, with natural ventilation, etc. (channelless systems).

Thus, any ventilation system can be characterized by 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:

• inflow;
• exhaust;
• supply and exhaust.

4. Air-curtains.

5. Mufflers.

6. Air filters.

7. Air heaters:

• electric;
• water.

8. Ducts:

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

9. Locking and regulating devices:

• air valves;
• apertures;
• check valves.

10. Air diffusers and air exhaust control devices:

• gratings;
• slotted air distribution devices;
• shades;
• nozzles with nozzles;
• perforated panels.

Under ventilation should be understood a whole range of measures and units designed to provide the required level of air exchange in the serviced rooms. That is, the main function of all ventilation systems is to support meteorological parameters at an acceptable level. Any of the existing ventilation systems can be described by four main characteristics: its purpose, the method of moving the air masses, the service area and the main structural features. And the study of existing systems should begin with a consideration of the purpose of ventilation.

Basic information on the purpose of air exchange

The main purpose of ventilation systems is to replace air in various rooms. In residential, domestic, household and industrial premises, air is constantly polluted. Pollutants can be completely different: from virtually harmless house dust to hazardous gases. In addition, moisture and excessive heat “pollute” it.

Four basic schemes for organizing air exchange during general ventilation: a - from top to bottom, b - from top to top, c - from bottom to top, d - from bottom to bottom.

It is important to study the purpose of air exchange systems and choose the most suitable for specific conditions. If the choice is made incorrectly and ventilation is not enough or a lot, this will lead to equipment failure, damage to property in the room and, of course, will negatively affect human health.

Currently, there are quite a few different in their design, purpose and other features of ventilation systems. According to the method of air exchange, existing structures can be divided into supply and exhaust type designs. Depending on the service area, they are divided into local and general exchange. And according to the design features, ventilation units are channelless and channel.

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Purpose and main features of natural ventilation

Natural ventilation is arranged in almost every residential and utility room. Most often it is used in city apartments, cottages and other places where there is no need for the installation of ventilation systems of higher power. In such air exchange systems, air moves without the use of additional mechanisms. This occurs under the influence of various factors:

1. Due to the different air temperature in the serviced room and outside it.
2. Due to the different pressure in the served room and the installation site of the corresponding exhaust device, which is usually located on the roof.
3. Under the influence of "wind" pressure.

Natural ventilation can be disorganized and organized. A feature of unorganized systems is that the replacement of old air with new air occurs due to the different pressure of the external and internal air, as well as the action of the wind. The air leaves and comes through the leaks and crevices of the window and door structures, as well as when they open.

A feature of organized systems is that air exchange occurs due to the difference in pressure of the air masses outside and inside the room, but in this case, appropriate openings are arranged for air exchange with the ability to control the degree of opening. If necessary, the system is additionally equipped with a deflector designed to reduce pressure in the air channel.

The advantage of a natural type of air exchange is that such systems are as simple as possible to design and install, have an affordable price and do not require the use of additional devices and connect to the mains. But they can only be used where constant ventilation performance is not needed, because the operation of such systems is completely dependent on various external factors such as temperature, wind speed, etc. Additionally, the possibility of using such systems limits the relatively low available pressure.

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Main features and purpose of mechanical air exchange

For the operation of such systems, special instruments and equipment are used, thanks to which air can move over fairly large distances. Such systems are usually installed at production sites and in other places where constant high-performance ventilation is needed. Installing such a system at home is usually pointless. Such air exchange consumes quite a lot of electricity.

The great advantage of mechanical air exchange is that, thanks to it, it is possible to establish a constant autonomous supply and removal of air in the required volumes, regardless of external weather conditions.

Such air exchange is more effective than natural, also due to the fact that, if necessary, the supplied air can be pre-cleaned and brought to the desired humidity and temperature. Mechanical air exchange systems operate using various equipment and devices, such as electric motors, fans, dust collectors, noise suppressors, etc.

You need to choose the most suitable type of air exchange for a particular room at the design stage. At the same time, sanitary and hygienic standards and technical and economic requirements must be taken into account.

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Features of supply and exhaust systems

The purpose of exhaust and supply air exchange is clear from their names. Local ventilation is created for the flow of clean air to the required places. Usually it is preheated and cleaned. An exhaust system is needed to divert contaminated air from certain places. An example of such an air exchange is a kitchen hood. It takes air from the most polluted place - an electric or gas stove. Most often, such systems are organized at industrial sites.

Exhaust and supply systems are used in combination. Their performance must be balanced and tuned taking into account the possibility of air entering other adjacent rooms. In some situations, only an exhaust system or only a supply air exchange system is installed. To supply clean air to the room from the outside, special openings are organized or supply equipment is installed. There is the possibility of organizing general exchange exhaust and supply ventilation, which will serve the entire room, and local, due to which the air will change in a particular place.

When organizing a local system, air will be removed from the most polluted places and supplied to certain specified areas. This allows you to establish air exchange most effectively.

Local ventilation systems are usually divided into air oases and souls. The function of the shower is to supply fresh air to the workplace and reduce its temperature in the place of inflow. Under the air oasis should be understood such places serviced premises, which are fenced by partitions. They are supplied with chilled air.

In addition, air curtains can be arranged as local supply ventilation. They allow you to create a kind of air partitions or change the direction of air flow.

A local ventilation device requires much less money than a general exchange organization. At various production sites, in most cases, mixed-type air exchange is organized. So, for the removal of harmful emissions, general ventilation is established, and jobs are served using local systems.

The purpose of the local exhaust air exchange system is to remove harmful emissions and mechanisms of discharge from specific areas of the room. Suitable for situations where the spread of such secretions throughout the space of the room is excluded.

In industrial premises, thanks to a local exhaust hood, various harmful substances are captured and discharged. For this, special suction is used. In addition to harmful impurities, exhaust ventilation units remove some of the heat generated during operation of the equipment.

Such air exchange systems are very effective, because make it possible to remove harmful substances directly from the place of their formation and prevent the spread of such substances throughout the entire surrounding space. But they are not without flaws. For example, if harmful emissions are dispersed over a large volume or area, such a system will not be able to effectively remove them. In such situations, ventilation systems of the general exchange type are used.

Methods to reduce the adverse effects of the industrial microclimate are regulated by the “Sanitary Rules for the Organization of Technological Processes and Hygienic Requirements for Production Equipment” and are implemented by a complex of technological, sanitary, technical, organizational and medical and preventive measures.

Consider the main methods:

Thermal insulation;

Heat shields;

Air showering;

Air curtains;

Aerial oases.

Thermal insulation  surfaces of radiation sources reduces the temperature of the radiating surface and reduces both the total heat and radiation. Structurally, thermal insulation can be mastic, wrapping, filling, piece goods and mixed.

Heat shields used to localize sources of radiant heat, reduce irradiation in the workplace and reduce the temperature of the surfaces surrounding the workplace. The weakening of the heat flux behind the screen is due to its absorption and reflectivity. Depending on which ability of the screen is more pronounced, heat-reflecting, heat-absorbing and heat-removing screens are distinguished.

Air shower. The cooling effect of air showering depends on the temperature difference between the working body and the air flow, as well as on the speed of air flow around the cooled body. To ensure the specified temperature and air velocity at the workplace, the axis of the air flow is directed horizontally or at an angle of 45 ° to the human chest.

Air curtains  Designed to protect against the breakthrough of cold air into the room through the openings of the building (gates, doors, etc.). An air curtain is an air stream directed at an angle towards the cold air stream.

Air oases  designed to improve meteorological working conditions (more often recreation on a limited area). For this purpose, cab schemes with lightweight movable partitions, which are flooded with air with the appropriate parameters, have been developed.

Ionic composition of air

The aeroionic composition of the air has a significant impact on the well-being of the worker, and even deviating from the permissible concentration of ions in the inhaled air can even pose a threat to the health of workers. Both increased and decreased ionization are harmful physical factors and are therefore regulated by sanitary and hygienic standards. The ratio of negative and positive ions is also of great importance. The minimum required level of ionization of the air is 1000 ions in 1 cm 3 of air, of which there must be 400 positive ions and 600 negative.

For normalization of the ionic regime of the air, the supply and exhaust ventilation, group and individual ionizers, devices for automatic regulation of the ionic mode are used. As a group ionizer, a Chizhevsky chandelier has recently been used, which provides the optimal composition of aero ions. At most enterprises, this factor is not yet taken into account.

Ventilation. natural ventilation systems

An effective means of ensuring proper cleanliness and acceptable microclimate parameters of the air of the working area is ventilation.

Ventilation called organized and regulated air exchange, which ensures the removal of contaminated air from the room and the supply of fresh air in its place.

From the point of view of aerodynamics, ventilation is an organized air exchange regulated by SNiP P-33-75 "Ventilation, heating and air conditioning" and GOST 12.4.021-75.

The method of moving air distinguishes:

Natural ventilation systems.

Mechanical ventilation systems.

Figure 7.1 - Ventilation systems.

Natural ventilation

Natural ventilation  called a ventilation system, the air in which is due to the resulting pressure difference outside and inside the building.

The pressure difference is due to the difference in the densities of the external and internal air (gravitational pressure, or heat head ∆P T) and the wind pressure ∆P B acting on the building.

Natural ventilation is divided into:

Unorganized natural ventilation;

Organized natural ventilation.

Unorganized natural ventilation  (infiltration or natural ventilation) is carried out by changing the air in the rooms through leaks in the fencing and structural elements due to the pressure difference outside and inside the room.

Such air exchange depends on random factors - the strength and direction of the wind, the air temperature inside and outside the building, the type of fencing and the quality of construction work. Infiltration can be significant for residential buildings and reach 0.5 ... 0.75 room volume per hour, and for industrial enterprises up to 1 ... 1.5 h -1.

Organized natural ventilation  may be:

Exhaust, without organized air flow (duct)

Supply and exhaust, with an organized flow of air (channel and non-channel aeration).

Duct natural exhaust ventilationwithout organized air flow is widely used in residential and administrative buildings. The estimated gravitational pressure of such ventilation systems is determined at an outdoor temperature of +5 0 С, assuming that all pressure falls in the exhaust duct path, while the resistance to air inlet to the building is not taken into account. When calculating the network of ducts, first of all, an approximate selection of their sections is carried out based on the allowable air velocities in the channels of the upper floor of 0.5 ... 0.8 m / s, in the channels of the lower floor and prefabricated channels of the upper floor 1.0 m / s and in the exhaust shaft 1 ... 1.5 m / s.

To increase the pressure in natural ventilation systems, nozzles - deflectors are installed at the mouth of the exhaust shafts. Strengthening traction occurs due to the rarefaction that occurs during the flow around the deflector.

Aerationcalled organized natural general ventilation of the premises as a result of the intake and removal of air through the opening transoms of windows and lamps. The air exchange in the room is regulated by varying degrees of opening of transoms (depending on the outdoor temperature, wind speed and direction).

As a way of ventilation, aeration has found wide application in industrial buildings, characterized by technological processes with large heat emissions (rolling shops, foundries, blacksmiths). The supply of external air to the workshop during the cold season is organized so that cold air does not enter the work area. To do this, the outdoor air is supplied into the room through openings located at least 4.5 m from the floor, in the warm season, the flow of external air is oriented through the lower tier of the window openings (A \u003d 1.5 ... 2 m).

The main advantage of aeration is the ability to carry out large air exchanges without the cost of mechanical energy. The disadvantages of aeration include the fact that in the warm season, the aeration efficiency can significantly decrease due to an increase in the temperature of the outside air and, in addition, the air entering the room is not cleaned or cooled.

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Air oasis (aeration)

Air oasis (aeration)

An air oasis (aeration) is an organized natural air exchange in rooms, carried out due to the difference in the densities of the external and internal air and the effect of wind on the external fencing of the building in order to create the necessary microclimate in the room. Aeration is widely used in industrial plants (forging, foundry, rolling, etc.) with significant excess heat.

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

Devices for providing an air oasis:

1) supply transoms;

2) deflectors;

3) non-inflated lights;

4) exhaust shafts.

Several designs of supply transoms are known:

1) single upper suspension transoms with a rotation on the upper axis of not more than 45 °. They are used, as a rule, for the inflow and exhaust of air;

2) single mid-hanging transoms with rotation on the middle axis at an angle of no more than 90 °;

3) top-hung transoms made with double frames installed in the workshops; in the warm season, direct the hot outdoor air down to the floor where it cools;

4) transoms, mounted on the lower axis, open in the cold season at an angle of no more than 30 ° so that the cold air entering the building is heated, moving up, and warm down, down into the room;

5) transoms installed at a distance of two meters from the floor, having opened, are fixed for ventilation with a rail.

Air is removed from buildings, usually through transoms rotating on the upper axis.

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

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

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

An inflated flashlight is a device in which a vacuum occurs between the walls of the flashlight and the wind protection shields, due to which air is drawn from the room.

Exhaust shafts are devices installed in the ceilings of industrial buildings, the operation of which is due to natural pressure arising from the difference in temperature inside the shaft and outside the building.