Ventilation of the lungs and pulmonary volumes The amount of pulmonary ventilation is determined by the depth of breathing and the frequency of respiratory movements. A quantitative characteristic of pulmonary ventilation is the minute volume of breathing (MVR) - the volume of air passing through the lungs in 1 minute.

An effective means of ensuring proper cleanliness and acceptable air microclimate parameters working area is industrial ventilation. Ventilation is an organized and regulated air exchange that ensures the removal of polluted air from a room and the supply of fresh air in its place.

Based on the method of air movement, natural and mechanical ventilation systems are distinguished. A ventilation system in which the movement of air masses is carried out due to the resulting pressure difference outside and inside the building is called natural ventilation. The pressure difference is caused by the difference in the densities of the external and internal air (gravitational pressure, or thermal pressure? Рт) and the wind pressure? Рв acting on the building. Calculated thermal pressure (Pa)

RT = gh(n - v),

where g is the acceleration of free fall, m/s2; h-vertical distance between the centers of the supply and exhaust openings, m; pni p^ - density of external and internal air, kg/m.

When the wind acts on the surfaces of a building on the leeward side, excess pressure is formed, and on the windward side - a vacuum. The distribution of pressure over the surface of buildings and their magnitude depend on the direction and strength of the wind, as well as on the relative position of the buildings. Wind pressure (Pa)

where kn„ is the aerodynamic drag coefficient of the building; the value of kn does not depend on the wind flow, is determined empirically and remains constant for geometrically similar buildings; WВ - wind flow speed, m/s.

Unorganized natural ventilation - infiltration, or natural ventilation - is carried out by changing the air in rooms through leaks in fences and elements building structures due to the difference in pressure outside and inside the room. Such air exchange depends on random factors - wind strength and direction, air temperature inside and outside the building, type of fencing and quality 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.

For constant air exchange required by the conditions for maintaining clean air in the room, organized ventilation is necessary. Organized natural ventilation can be exhaust without an organized air flow (duct) and supply and exhaust with an organized air flow (duct and non-duct aeration). Duct natural exhaust ventilation without organized air flow (Fig. 1.6) is widely used in residential and administrative buildings. The calculated gravitational pressure of such ventilation systems is determined at an outside air temperature of +5? C, assuming that all the pressure drops in the exhaust duct, while the resistance to air entry into the building is not taken into account. When calculating a network of air ducts, first of all, an approximate selection of their sections is made based on the permissible speeds of air movement in the channels top floor 0.5...0.8 m/s, in channels ground 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 available pressure in systems natural ventilation At the mouth of the exhaust shafts, deflector nozzles are installed (Fig. 1.7). The increase in thrust occurs due to the vacuum that occurs when flowing around the TsAGI deflector. The vacuum created by the deflector and the amount of air removed depend on the wind speed and can be determined using nomograms.

Fig.1.8. Aeration scheme for an industrial building

Aeration is the organized natural general ventilation of rooms as a result of the entry and removal of air through opening transoms of windows and lanterns. Air exchange in the room is regulated by varying degrees of opening of the transoms (depending on the outside temperature, wind speed and direction). As a method of ventilation, aeration has found wide application in industrial buildings, characterized by technological processes with large heat releases (rolling shops, foundries, forges). The supply of outside air to the workshop cold period years are organized so that cold air did not enter the work area. To do this, outside air is supplied into the room through openings located at least 4.5 m from the floor (Fig. 1.8); during the warm season, the influx of outside air is oriented through the lower tier of window openings (A = 1.5...2 m) .

When calculating aeration, determine the required cross-sectional area of ​​openings and aeration lanterns for supply and removal required quantity air. The initial data are the design dimensions of the rooms, openings and lanterns, the amount of heat production in the room, and the parameters of the outside air. According to SNiP 2.04.05-91, it is recommended to perform calculations under the influence of gravitational pressure. Wind pressure should be taken into account only when deciding on the protection of ventilation openings from blowing in. When calculating aeration, the material (air) and heat balance of the room is made up:

where Gnpi and Gouti are the mass of incoming and outgoing air with heat capacity Cp and temperature t.

The main advantage of aeration is the ability to carry out large air exchanges at no cost mechanical energy. The disadvantages of aeration include the fact that in the warm season the efficiency of aeration can drop significantly due to an increase in the temperature of the outside air and, in addition, the air entering the room is not cleaned or cooled.

Ventilation, by which air is supplied to or removed from production premises through systems ventilation ducts using special mechanical stimuli for this is called mechanical ventilation.

Fig.1.9.

a - LB>Lnp. P1

Mechanical ventilation has a number of advantages over natural ventilation: a large radius of action due to the significant pressure created by the fan; the ability to change or maintain the required air exchange regardless of the outside temperature and wind speed; subject the air introduced into the room to pre-cleaning, drying or humidification, heating or cooling; organize optimal air distribution with air supply directly to workplaces; catch harmful emissions directly at the places of their formation and prevent their spread throughout the entire volume of the room, as well as the ability to purify polluted air before releasing it into the atmosphere. The disadvantages of mechanical ventilation include the significant cost of construction and operation and the need to take measures to combat noise.

Mechanical ventilation systems are divided into general, local, mixed, emergency and air conditioning systems.

General ventilation is designed to assimilate excess heat, moisture and harmful substances throughout the entire working area of ​​the premises. It is used if harmful emissions enter directly into the air of the room; workplaces are not fixed, but are located throughout the room. Typically, the volume of air Lpr supplied to the room during general ventilation is equal to the volume of air LB removed from the room. However, in a number of cases it becomes necessary to violate this equality (Fig. 1.9). Thus, in especially clean workshops of electric vacuum production, for which great importance has no dust, the volume of air inflow is greater than the volume of exhaust, due to which some excess pressure is created in the production room, which eliminates the ingress of dust from neighboring rooms. In general, the difference between the volumes of supply and exhaust air should not exceed 10...15%.

A significant influence on the parameters of the air environment in the work area is exerted by proper organization and installation of supply and exhaust systems.

Air exchange created in the room ventilation devices, is accompanied by the circulation of air masses several times larger than the volume of supplied or removed air. The resulting circulation is the main reason for the spread and mixing of harmful emissions and the creation of air zones of different concentrations and temperatures in the room. Thus, the supply jet, entering the room, draws the surrounding air masses into motion, as a result of which the mass of the jet in the direction of movement will increase and the speed will decrease. When flowing from a round hole (Fig. 1.10) at a distance of 15 diameters from the mouth, the jet speed will be 20% of the initial speed Vo, and the volume of moving air will increase by 4.6 times.

The rate of attenuation of air movement depends on the diameter of the outlet do: the larger do, the slower the attenuation. If you need to quickly reduce the speed of the supply jets, the supplied air must be divided into big number small jets.

The temperature of the supply air has a significant influence on the trajectory of the stream: if the temperature of the supply stream is higher than the room air temperature, then the axis bends upward; if lower, then downwards in an isothermal flow it coincides with the axis of the supply opening.

Air flows into the suction hole (exhaust ventilation) from all sides, as a result of which the drop in speed occurs very intensely (Fig. 1.11). Thus, the suction speed at a distance of one diameter from the hole round pipe equal to 5% Vo.

Air circulation in the room and, accordingly, the concentration of impurities and the distribution of microclimate parameters depend not only on the presence of supply and exhaust jets, but also on their relative position. There are four main schemes for organizing air exchange during general ventilation: top-up (Fig. 1.12, a); from top to top (Fig. 1.12, b); from bottom to top (Fig. 1.12, c); from below - down (Fig. 1.12, d). In addition to these schemes, combined ones are used. The most uniform air distribution is achieved when the inflow is uniform across the width of the room and the exhaust is concentrated.

When organizing air exchange in rooms, it is necessary to take into account the physical properties of harmful vapors and gases and, first of all, their density. If the density of gases is lower than the density of air, then the removal of contaminated air occurs in the upper zone, and the supply of fresh air directly to the working area. When gases with a density greater than the density of air are released, 60...70% of the polluted air is removed from the lower part of the room and 30...40% from the upper part. In rooms with significant moisture emissions, moist air is extracted in the upper zone, and fresh air is supplied in an amount of 60% to the work area and 40% to the upper zone.

Based on the method of supplying and removing air, there are four general ventilation schemes (Fig. 1.13): supply, exhaust, supply and exhaust, and systems with recirculation. Through the supply system, air is supplied to the room after it has been prepared in the supply chamber. This creates excess pressure in the room, due to which the air escapes outside through windows, doors or into other rooms. The supply system is used to ventilate rooms into which it is undesirable for polluted air from neighboring rooms or cold air from outside to enter.

Supply ventilation installations (Fig. 1.13, a) usually consist of the following elements: air intake device 1 for intake of clean air; air ducts 2 through which air is supplied to the room, filters 3 to clean the air from dust, air heaters 4 in which cold outside air is heated; motion stimulator 5, humidifier-dryer 6, supply openings or nozzles 7 through which air is distributed throughout the room. Air is removed from the room through leaks in the enclosing structures.

The exhaust system is designed to remove air from the room. At the same time, a reduced pressure is created in it and the air from neighboring rooms or outside air enters this room. It is advisable to use an exhaust system if the harmful emissions of a given room should not spread to neighboring ones, for example, for hazardous workshops, chemical and biological laboratories.

Settings exhaust ventilation(Fig. 1.13.6) consist of exhaust holes or nozzles 8, through which air is removed from the room; movement stimulator 5; air ducts 2, devices for purifying air from dust or gases 9, installed to protect the atmosphere, and a device for releasing air 10, which is located at 1...1.5. m above the roof ridge. Fresh air enters the production premises through leaks in the enclosing structures, which is a disadvantage of this ventilation system, since an unorganized influx of cold air (drafts) can cause colds.

Supply and exhaust ventilation is the most common system in which air is supplied to the room by a supply system and removed by an exhaust system; systems operate simultaneously.

In some cases, to reduce operating costs for air heating, ventilation systems with partial recirculation are used (Fig. 1.13, c). In them, air drawn from the room is mixed with the air coming from outside. exhaust system. The amount of fresh and secondary air is controlled by valves 11 and 12. The fresh portion of air in such systems usually amounts to 20...10% of the total amount of supplied air. A ventilation system with recirculation is allowed to be used only for those rooms in which there are no emissions of harmful substances or the emitted substances belong to the 4th hazard class and their concentration in the air supplied to the room does not exceed 30% of the maximum permissible concentration. The use of recirculation is not allowed even if the air in the premises contains pathogenic bacteria, viruses or there are pronounced unpleasant odors.

Individual installations of general mechanical ventilation may not include all of the above elements. For example, supply systems are not always equipped with filters and devices for changing air humidity, and sometimes supply and exhaust units may not have a network of air ducts.

Calculation required air exchange with general ventilation, it is carried out based on production conditions and the presence of excess heat, moisture and harmful substances. To qualitatively assess the efficiency of air exchange, the concept of air exchange rate kb is used - the ratio of the volume of air entering the room per unit of time L (m3/h) to the volume of the ventilated room Vn (m3). When correct organized ventilation the air exchange rate should be significantly greater than unity.

In a normal microclimate and the absence of harmful emissions, the amount of air during general ventilation is taken depending on the volume of the room per worker. The absence of harmful emissions is such a quantity in the process equipment that, with the simultaneous release of which in the air of the room, the concentration of harmful substances will not exceed the maximum permissible. IN production premises with air volume for each working Vni<20 м3 расход воздуха на одного работающего Li должен быть не менее 30 м /ч. В помещении с Vпi ==20...40 м3 L пi - 20 м3/4. В помещениях с Vni>40 m3 and in the presence of natural ventilation, air exchange is not calculated. In the absence of natural ventilation (sealed cabins), the air flow per worker must be at least 60 m3/h.

Necessary air exchange for the entire production area as a whole

where n is the number of workers in a given room.

When determining the required air exchange to combat excess heat, a balance of sensible heat in the room is drawn up:

Qizb + Gprctpr + Gvcrtuh = 0,

Where? Qexcess sensible heat of the entire room, kW; GprСрtр and GBCptyx - heat content of supply and exhaust air, kW; Ср - specific heat capacity of air, kJ/(kg °C); tnp and tух - temperature of supply and exhaust air, °C.

In summer, all the heat that enters the room is the sum of excess heat. During the cold season, part of the heat generated in the room is spent to compensate for heat loss

where b t - heat release in the room, kW; Z b sweat heat loss through external fences, kW.

The outside air temperature in the warm period of the year is assumed to be equal to the average temperature of the hottest month at 13 o'clock. The calculated temperatures for the warm and cold periods of the year are given in SNiP 2.04.05-91. Temperature of air removed from the room

where tрз is the air temperature in the working area, °C; a - temperature gradient along the height of the room, °C/m; for rooms with qi<23 Вт/м3 можно применять а = 0,5 °С/м. Для «горячих» цехов с qя>23 W/m3 - a = 0.7...1.5 °C/m; N - distance from the floor to the center of the exhaust openings, m.

Based on the sensible heat balance of the room, the required air exchange (°C/h) is determined to assimilate excess heat

where?pr - density of supply air, kg/m3.

When determining the necessary air exchange to combat harmful vapors and gases, an equation is drawn up for the material balance of harmful emissions in the room over time d? (With):

where GBPd? is the mass of harmful emissions in the room caused by the operation of technological equipment, mg; LnpCnp d? - mass of harmful emissions entering the room along with the supply air, mg; LBCBd? - mass of harmful emissions removed from the room along with the exhaust air, mg; Vпdc d? c is the mass of harmful vapors or gases accumulated in the room during time d?; Spr and St - concentration of harmful substances in the supply and exhaust air, mg/m3.

If the masses of supply and exhaust air are equal and assuming that, thanks to ventilation, harmful substances do not accumulate in the production area, i.e. dc/d? = 0 and St = Spdk, we get L=GBP/(Cpdk-Spr). The concentration of harmful substances in the removed air is equal to their concentration in the room air and should not exceed the maximum permissible concentration. The concentration of harmful substances in the supply air should be as minimal as possible and not exceed 30% of the maximum permissible concentration. Required air exchange for removal excess moisture determined based on the material balance for moisture

where GB^ is the mass of water vapor released into the room, g/s; ?pr - density of air entering the room, kg/m3; dyx - permissible content of water vapor in the indoor air at standard temperature and relative humidity, g/kg; dпp - moisture content of supply air, g/kg.

When harmful substances that do not have a unidirectional effect on the human body, such as heat and moisture, are simultaneously released into the work area, the required air exchange is taken according to the largest mass of air obtained in calculations for each type of industrial emissions.

When several harmful substances of unidirectional action are simultaneously released into the air of the working area (sulfur trioxide and dioxide; nitrogen oxide together with carbon monoxide, etc., see CH 245-71), the calculation of general ventilation should be made by summing the volumes of air required to dilute each substance separately up to its conditional maximum permissible concentrations, taking into account air pollution by other substances. These concentrations are less than the standard MPC and are determined from the equation?ni=1

By using local ventilation the necessary meteorological parameters are created at individual workplaces. For example, capturing harmful substances directly at the source, ventilation of observation booths, etc. Local exhaust ventilation is the most widely used. The main method of combating harmful secretions is to install and organize suction from shelters.

The designs of local suction can be completely closed, semi-open or open (Fig. 1.14). Closed suctions are the most effective. These include casings and chambers that hermetically or tightly cover technological equipment (Fig. 1.14, a). If it is impossible to arrange such shelters, then use suction with partial shelter or open: exhaust hoods, suction panels, fume hoods, side suction, etc.

One of the most simple types local suctions - exhaust hood(Fig. 1.14, g). It serves to trap harmful substances that have a lower density than the surrounding air. Umbrellas are installed over bathtubs for various purposes, electric and induction furnaces and above the holes for releasing metal and slag from cupola furnaces. Umbrellas are made open on all sides and partially open: on one, two and three sides. The efficiency of an exhaust hood depends on the size, height of the suspension and its opening angle. How larger sizes and the lower the umbrella is installed above the place where substances are released, the more effective it is. The most uniform suction is ensured when the umbrella opening angle is less than 60°.

Suction panels are used to remove harmful emissions carried away by convective currents during manual operations such as electric welding, soldering, gas welding, metal cutting, etc. Fume hoods- the most effective device compared to other suction systems, since they almost completely cover the source of the release of harmful substances. Only the service openings remain uncovered in the cabinets, through which air from the room enters the cabinet. The shape of the opening is chosen depending on the nature of the technological operations.

The required air exchange in local exhaust ventilation devices is calculated based on the localization conditions of impurities released from the source of formation. The required hourly volume of sucked air is determined as the product of the area of ​​the suction intake openings F(m2) and the air speed in them. The air speed in the suction opening v (m/s) depends on the hazard class of the substance and the type of local ventilation air intake (v = 0.5...5 m/s).

A mixed ventilation system is a combination of elements of local and general ventilation. The local system removes harmful substances from machine covers and covers. However, some harmful substances penetrate into the room through leaks in shelters. This part is removed by general ventilation.

Emergency ventilation is provided in those production premises in which a sudden entry into the air is possible. large quantity harmful or explosive substances. The performance of emergency ventilation is determined in accordance with the requirements regulatory documents in the technological part of the project. If such documents are missing, then the performance of emergency ventilation is accepted such that, together with the main ventilation, it provides at least eight air changes in the room per 1 hour. The emergency ventilation system should turn on automatically when the maximum permissible concentration of harmful emissions is reached or when one of the general or local ventilation systems is stopped . The release of air from emergency systems must be carried out taking into account the possibility of maximum dispersion of harmful and explosive substances in the atmosphere.

To create optimal meteorological conditions in production premises, the most advanced type of industrial ventilation- air conditioning. Air conditioning is its automatic processing in order to maintain predetermined meteorological conditions in industrial premises, regardless of changes in external conditions and indoor conditions. When air conditioning, the air temperature, its relative humidity and the rate of supply to the room are automatically adjusted depending on the time of year, external meteorological conditions and the nature of the technological process in the room. Such strictly defined air parameters are created in special installations called air conditioners. In some cases, in addition to providing sanitary standards The air microclimate in air conditioners is subject to special treatment: ionization, deodorization, ozonation, etc.

Air conditioners can be local (for maintenance separate rooms) and central (for servicing several separate premises). Schematic diagram air conditioner is shown in Fig. 1.15. Outside air is cleared of dust in filter 2 and enters chamber I, where it is mixed with air from the room (during recirculation). Having passed through the stage of preliminary temperature treatment 4, the air enters chamber II, where it undergoes a special treatment (washing the air with water, providing the specified relative humidity parameters, and air purification), and into chamber III (temperature treatment). During temperature treatment in winter, the air is heated partly due to the temperature of the water entering the nozzles 5, and partly by passing through heaters 4 and 7. In summer, the air is cooled partly by supplying chilled (artesian) water to chamber II, and mainly as a result of the operation of special refrigeration machines .

Air conditioning plays a significant role not only from a life safety point of view, but also in many technological processes, in which fluctuations in air temperature and humidity are not allowed (especially in radio electronics). Therefore, air conditioning installations in last years are increasingly used in industrial enterprises.

Fig. 4.3. Air supply diagrams: diagrams a - from top to bottom; b - from top to top; c - from bottom to top; g - from bottom to bottom Rice. 4.2. Pressure distribution in a building Rice. 4.4. Supply ventilation diagram: 1 - device in the form of a channel or shaft; 2 - filter for air purification; 3 - bypass channel; 4 - air heater; 5 - air duct network; 6 - fan; 7 - supply pipes with nozzles Rice. 4.5. Schemes of supply nozzles: a, b - for vertical supply; c, d - for one-sided feeding at different angles; d - for concentrated inclined feed; f, g - for scattered horizontal feed Rice. 4.6. Exhaust ventilation diagram: 1 - air purification device; 2 - fan; 3 - central air duct; 4 - suction air ducts Rice. 4.7. Supply and exhaust ventilation: 1 - shaft; 2 - filter for air purification; 3 - bypass channel; 4 - air heater; 5 - air ducts; 6 - fan; 7 - supply pipes with nozzles Rice. 4.8. Supply and exhaust ventilation with recirculation: 1 - shaft; 2 - filter for air purification; 3 - bypass channel; 4 - air heater; 5 - air ducts; 6 - fan; 7 - supply pipes with nozzles; 8 - exhaust pipes with nozzles; 9 - valve Rice. 4.9. Air curtains: a - with bottom air supply; b - with lateral two-way air supply; c - with one-way air supply; d - detail of the slot; H, B - height and width of gates (doors), respectively; b - slot width Rice. 4.11. Fume hoods: a - with top suction; b - with lower suction; c, d - with combined suction Rice. 4.10. Local suctions: a - umbrella; b - overturned umbrella; c - suction panel Rice. 4.12. Onboard suction: a - to remove volatile vapors; b - to remove heavy vapors Rice. 4.13. Cyclone TsN-15 NIIOGAZ: 1 - bunker; 2 - metal cylinder; 3 - pipe; 4 - pipe

The state of the human body is greatly influenced by meteorological conditions (microclimate) in industrial premises.

In accordance with GOST 12.1.005-88 microclimate of industrial premises is determined by the combinations of temperature, humidity and air speed acting in them on the human body, as well as the temperature of the surrounding surfaces.

If work is carried out in open areas, then meteorological conditions are determined by climatic conditions and the season of the year.

Air temperature- a parameter characterizing its thermal state, i.e. kinetic energy of the gas molecules included in its composition. Temperature is measured in degrees Celsius or Kelvin.

The temperature regime of the room depends on the formula "src="http://hi-edu.ru/e-books/xbook908/files/tp, these two factors determine the convective and radiation heat exchange of a person and environment. To assess the influence of temperatures of heated surfaces, the concept of radiation temperature is introduced. Roughly it can be defined as follows:

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Joint influence formula" src="http://hi-edu.ru/e-books/xbook908/files/tp.gif" border="0" align="absmiddle" alt=".gif" border="0" align="absmiddle" alt="

In most cases, for ordinary premises the formula" src="http://hi-edu.ru/e-books/xbook908/files/tp.gif" border="0" align="absmiddle" alt=".gif" border="0" align="absmiddle" alt=".

Under atmospheric pressure is understood as a quantity characterized by the pressure of a column of atmospheric air on a unit surface. Normal pressure is considered to be 1013.25 hPa (hectopascal, very rarely used in practice) or 760 mm. rt. Art. (1 hPa =
= 100 Pa = 3/4 mm. rt. Art.).

Atmospheric air consists of a mixture of dry gases and water vapor, i.e. we always deal with moist air or a steam-air mixture. Moreover, water vapor can be either in a superheated or saturated state. To characterize the moisture content in the air, the concepts of absolute and relative humidity are used.

Absolute air humidity is the mass of water vapor contained in 1 mark"> Air mobility. A person begins to feel the movement of air at a speed of approximately 0.1 m/s. At normal temperatures, light air movement, blowing away the steam-saturated and superheated layer of air enveloping a person, promotes good health. At the same time, in conditions low temperatures, high air speed causes an increase in heat loss by convection and evaporation and leads to severe cooling of the body.

All life processes in the human body are accompanied by the formation of heat, the amount of which varies from 80 J/s (at rest) to 700 J/s (when performing heavy physical work).

Despite the fact that the factors that determine the indoor microclimate can vary greatly within wide limits, the human body temperature remains, as a rule, at a constant level (36.6 mark "> Weather conditions, in which there are no unpleasant sensations and tension in the thermoregulatory system are called comfortable (optimal) conditions.

Meteorological conditions are perceived by a person as comfortable only when the amount of heat generated by the body is equal to the total heat transfer to the environment, i.e. while maintaining thermal balance.

Heat exchange organism with the environment can occur in various ways: convective transfer of heat to the surrounding air (in normal conditions up to 5% of all heat removed); radiant heat exchange with surrounding surfaces (40%); contact thermal conductivity through contacting surfaces (30%); evaporation of moisture from the surface of the skin (20%); due to heating of exhaled air (5%).

When the air temperature drops, to reduce heat transfer, the body reduces the temperature of the skin, reduces the moisture content of the skin, thereby reducing heat transfer. When the air temperature rises blood vessels the skin expands, there is an increased blood flow to the surface of the body, and heat transfer to the environment increases significantly..gif" border="0" align="absmiddle" alt="With significant thermal radiation from heated surfaces, the body's thermoregulation is disrupted. This can lead to overheating, especially if moisture loss approaches 5 liters per shift. In this case, there is increasing weakness, headache, tinnitus, distortion of color perception (everything turns red or green), nausea, vomiting, and increased body temperature. Breathing and pulse quicken, blood pressure first increases, then falls. In severe cases, heat stroke occurs. A convulsive disease is possible, which is a consequence of a violation of the water-salt balance and is characterized by weakness, headache, and sudden cramps of the limbs.

But further, if such painful conditions do not occur, overheating of the body greatly affects the state of the nervous system and human performance. It has been established that with a 5-hour stay in an area with an air temperature of 31 hint ">, neuritis, radiculitis, etc., as well as colds. Any degree of cooling is characterized by a decrease in heart rate and the development of inhibition processes in the cerebral cortex, which leads to a decrease In particularly severe cases, exposure to low temperatures can lead to frostbite and even death.

Different combinations of microclimate parameters, having a complex effect on a person, can cause the same thermal sensations. This is the basis for the introduction of the so-called effective and effective-equivalent temperatures. Effective temperature characterizes a person's sensations when exposed to temperature and air movement simultaneously. The effective equivalent temperature also takes into account air humidity. The effective temperature and comfort zone can be determined using a nomogram constructed empirically(Fig. 4.1 ).

Excess heat, moisture release, thermal radiation, and high air mobility worsen the microclimate of industrial premises, complicate thermoregulation, adversely affect the body of workers and contribute to a decrease in productivity and quality of work.

Air contaminated with harmful gases, vapors and dust poses a risk of poisoning or occupational diseases, causes increased fatigue, and, as a consequence, increases the risk of injury.

From a physiological point of view, air should be considered from two positions: as air inhaled by a person, and as a medium surrounding a person. The role of air, accordingly, is to supply the body with oxygen, remove moisture during exhalation and ensure heat exchange between a person and the environment. Air is also a working agent that removes dust, moisture, and harmful emissions from the room.

Sanitary standards establish the values ​​of optimal microclimate parameters in workplaces (Table 4.1).

Table 4.1

Optimal parameters microclimate 5 at workplaces
(SanPiN 2.2.4.548-96)

5 Relative humidity air for all seasons and categories

The optimal tool for ensuring standard cleanliness and the necessary required parameters of the air microclimate in the workplace is considered to be an industrial ventilation network, i.e. artificial and controlled, which aims to remove waste air mass from the working space and bring in fresh air. Industrial ventilation and air conditioning, BZD - the parameters of which are met in accordance with all standards, SNiP and occupational safety and health standards, creates conditions for normal work people, as well as the operation of equipment and tools.

Depending on the method of movement and movement of air masses, ventilation networks in production can be grouped into two main classes:

1. Natural;
2. Mechanical.

Organization of natural ventilation

Natural ventilation

Provided that the movement of air flows will be carried out through door and window openings due to the pressure difference from outside and inside the operating room, we are talking about natural ventilation. This pressure difference is associated with different air densities, air temperatures, and the wind pressure that acts on the building. Natural, or as engineers say, unorganized ventilation is often determined by random, uncontrollable factors, such as:

1. Wind direction and strength;
2. External and internal temperature;
3. Type of fencing;
4. Type of window and door structures.

At the same time, unorganized ventilation, according to BZD standards, should reach 1-1.5 room volumes per hour. Such indicators are quite difficult to achieve using only natural air exchange channels. According to labor safety and safety standards, the speed of air flows with this type of ventilation should be 0.5-0.8 meters per second for the upper floor, and 1-1.5 meters per second for the lower level and exhaust shafts.

Air movement

Mechanical ventilation

For permanent (constant) exchange air flow, which is necessary in accordance with the requirements and conditional parameters of the level of atmospheric cleanliness, it is necessary to arrange a mechanical ventilation network that has a number of advantages in comparison with the previous type, namely:

1. Wide range of action, which is ensured by the use of fans;
2. The ability to maintain and control the required frequency of air mass exchange, regardless of temperature regime and pressure outside;
3. The ability to combine the ventilation function with the functions of drying systems, increasing humidity, cleaning, heating and cooling air;
4. The ability to arrange flow distribution in accordance with the layout of workplaces and the wishes of the customer;
5. Possibility of filtering exhaust air and minimizing harmful atmospheric emissions.

Schematic diagram of mechanical ventilation

BZD parameters of mechanical ventilation

For any equipment engineering device or a communications system, which may also include an air exchange system, is subject to certain requirements regarding life safety, occupational safety and health of personnel, and environmental protection. Respectively, mechanical ventilation also has a number of requirements and standards, compliance with which is a critical condition for its organization.

Excess heat

In an operating room where equipment is operating, it is natural for excess heat to develop. From this perspective, provided there are workstations located non-fixed throughout the room, the volume of supplied air should be equal to the volume of exhausted air. The maximum permissible deviation from this norm is 10-15% of the total mass.

To achieve such parameters, the flow speed must be quite high. This can be achieved by increasing the diameter of the duct and the spread between the inlet and outlet openings.

Industrial ventilation wiring

Concentration of harmful impurities

An important indicator of the air environment in a working or production space is also the presence of impurities in the atmosphere, both solid and gaseous. This can be either dust generated during production or harmful fumes - carbon dioxide or hydrogen sulfide.

It must be remembered that 60-70% of substances with a density higher than atmospheric are removed from the lower layers of the atmosphere of the room (i.e. such gases fall down) and only 30-40% - from the upper section. And vice versa, wet air accumulates in the upper part of the room, while the dry one falls down.

The designer must take into account the specifics of production and arrange ventilation equipment and air ducts accordingly.

Ventilation duct layout

The optimal solution for such enterprises or buildings would be air supply network installations, which, as a rule, are equipped as follows:

1. Purified air supply device;
2. Air ducts;
3. Filters;
4. Heaters;
5. Stimulators of flow;
6. Humidifiers or dehumidifiers;
7. Supply channels and grilles;
8. Nozzles for indoor wiring.

MPC of pollutants

For calculation required power ventilation in the presence of factors harmful effects The maximum permissible concentrations of such substances must be determined, as well as the amount of air required for their dilution.

An effective means of combating harmful fumes is the installation of local suction systems, such as casings, chambers, fume hoods, exhaust hoods and others. The power of such devices is determined by multiplying the area of ​​the exhaust opening by the speed of movement (accepted according to reference tables, depending on the substance being removed).

Exhaust hood

Air exchange rate

To calculate the multiplicity required for a particular room, it is necessary to know the volume of the room, the number of people working in it, and the air exchange rate per person. As a rule, when organizing industrial ventilation in production, the air exchange rate per person is 60 m3/hour.

If there is excess thermal radiation in the room, a more complex calculation formula is used, which also takes into account excess heat in kW, heat capacity in kg/0C, and input/output air temperature. In this case, the temperatures of external and internal air taken for such calculations are given in SNiP.

Emergency ventilation

At some enterprises, particularly hazardous and hazardous production facilities, emergency ventilation must also be installed in case of sudden emissions and for the purpose of their rapid removal. Such a system must provide at least 8 complete air changes in 1 hour.

Emergency system fan

Air conditioning

system industrial air exchange often combined with an air conditioning system. The purpose of this is to create optimal, required according to the norms and rules of the Belarusian Railways, climatic conditions at the workplace, in administrative building or production premises. The air conditioning system will, of course, regulate not only the temperature, but also the humidity of the air, ionize it, remove odors, saturate it with ozone, etc. It all depends on the needs and wishes of the client.

When organizing industrial ventilation, local or central air conditioners, heaters (for heating air in winter), filters and other equipment are usually used, selected depending on the required network functions.

Industrial air conditioning system

Climate control and air ventilation are an important component not only in relation to life safety, but also in many production processes, requiring stable temperature conditions, humidity or dryness, and air saturation.

Basics of operation of the supply and exhaust system

KF MSTU im. N.E. Bauman

Practical lesson in the discipline "BJD"

Lesson topic:

"Methods of organizing ventilation and

conditioning to create

favorable microclimatic

working conditions,

determining the required performance"

Time: 2 hours.

Department of FN2-KF

Providing comfortable living conditions.

1. Industrial ventilation and air conditioning.

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

Ventilation is an organized and regulated air exchange that ensures the removal of dirty air from a room and the supply of fresh air in its place.

Systems are classified according to the method of air movement. natural and mechanical ventilation.

A ventilation system in which the movement of air masses is carried out due to the resulting pressure difference between the outside and inside the building is called natural ventilation.

Ventilation, with the help of which air is supplied to or removed from production premises through systems of ventilation ducts using special mechanical stimuli for this purpose, is called mechanical ventilation.

Mechanical ventilation has a number of advantages over natural ventilation:

large radius of action due to the significant pressure created by the fan;

the ability to change or maintain the required air exchange regardless of the outside temperature and wind speed;

subject the air introduced into the room to pre-cleaning, drying or humidification, heating or cooling;

organize optimal air distribution with air supply directly to workplaces;

catch harmful emissions directly at the places of their formation and prevent their spread throughout the room;

purify polluted air before releasing it into the atmosphere.

Disadvantages of mechanical ventilation The significant cost of construction and operation and the need for noise control measures should be taken into account.

Mechanical ventilation systems are divided into for general exchange, local, mixed, emergency and air conditioning systems.

General ventilation designed to assimilate excess heat, moisture and harmful substances throughout the entire working area of ​​the premises.

It is used if harmful emissions enter directly into the air of the room; workplaces are not fixed, but are located throughout the room.

According to the method of supplying and removing air, they distinguish four general ventilation schemes :

supply;

exhaust;

supply and exhaust;

recirculation system.

Calculation of the required air exchange during general ventilation is made based on production conditions and the presence of excess heat, moisture and harmful substances.

To qualitatively assess the efficiency of air exchange, the concept of air exchange rate is used K V- the ratio of the amount of air entering the room per unit time L(m 3 / h), to the volume of the ventilated room V P(m 3). With properly organized ventilation, the air exchange rate should be significantly greater than one:

, Where K V >> 1 (1.1)

In a normal microclimate and the absence of harmful emissions, the amount of air during general ventilation is taken depending on the volume of the room per worker.

The absence of harmful emissions is such a quantity in the process equipment that, with the simultaneous release of which in the air of the room, the concentration of harmful substances will not exceed the maximum permissible.

In industrial premises with air volume per worker (V p1):

V p1< 20 м 3 расход воздуха на 1 работающего (L 1)

L 1 ≥30 m 3 /h

L 1 ≥ 20 m 3 /h

V p1 > 40 m 3 and in the presence of natural ventilation, air exchange is not calculated. In the absence of natural ventilation (sealed cabins), the air flow per worker must be at least 60 m 3 /h

Mixed ventilation system is a combination of local and general ventilation. The local system removes harmful substances from machine covers and covers. However, some harmful substances penetrate into the room through leaks in shelters. This part is removed by general ventilation.

Emergency ventilation is provided in those production premises in which a sudden release of a large amount of harmful or explosive substances into the air is possible. The performance of emergency ventilation is taken to be such that, together with the main ventilation, it provides at least eight air changes in the room per 1 hour. The emergency ventilation system should turn on automatically when the maximum permissible concentration of harmful emissions is reached or when one of the general or local ventilation systems is stopped. The release of air from emergency systems must be carried out taking into account the possibility of maximum dispersion of harmful and explosive substances in the atmosphere.