MINISTRY OF EDUCATION AND SCIENCE OF UKRAINE

KRASNODON MINING TECHNIQUE

Abstract on the subject “SAFETY

TECHNOLOGICAL

PROCESSES AND PRODUCTION"

on the topic: “INDUSTRIAL VENTILATION »

Student of group 1EP-06

Uryupov Oleg

Checked by: Drokina T.M.

Krasnodon 2010

Ventilation is a complex of interconnected devices and processes for creating the required air exchange in production premises. The main purpose of ventilation is to remove contaminated or overheated air from the working area and supply clean air, as a result of which the necessary conditions are created in the working area. favorable conditions air environment. One of the main tasks that arises when installing ventilation is determining the air exchange, i.e. the amount ventilation air necessary to ensure an optimal sanitary and hygienic level of the indoor air environment.

Depending on the method of air movement in industrial premises, ventilation is divided into natural and artificial (mechanical).

The use of ventilation must be justified by calculations that take into account temperature, air humidity, release of harmful substances, and excess heat generation. If there are no harmful emissions in the room, then ventilation should provide an air exchange of at least 30 m 3 / h for each worker (for rooms with a volume of up to 20 m 3 per worker). When harmful substances are released into the air of the working area, the necessary air exchange is determined based on the conditions of their dilution to the maximum permissible concentration, and in the presence of thermal excess - from the conditions of maintaining permissible temperature in the work area.

Natural ventilation production premises is carried out due to the temperature difference in the room from the outside air (thermal pressure) or the action of wind (wind pressure). Natural ventilation can be organized or unorganized.

With unorganized natural ventilation air exchange is carried out by displacing internal thermal air with external cold air through windows, vents, transoms and doors. Organized natural ventilation, or aeration, provides air exchange in pre-calculated volumes and adjustable in accordance with meteorological conditions. Channelless aeration is carried out using openings in the walls and ceiling and is recommended in large rooms with significant excess heat. To obtain the calculated air exchange, ventilation openings in the walls, as well as in the roof of the building (aeration skylights) are equipped with transoms that open and close from the floor of the room. By manipulating the transoms, you can regulate air exchange when the outside air temperature or wind speed changes (Fig. 4.1). The area of ​​ventilation openings and skylights is calculated depending on the required air exchange.

Rice. 4.1. Scheme of natural ventilation of the building: A- when there is no wind; b- in the wind; 1 - exhaust and supply openings; 2 - fuel generating unit

In small industrial premises, as well as in premises located in multi-storey industrial buildings, channel aeration is used, in which contaminated air is removed through ventilation ducts in the walls. To enhance the exhaust, deflectors are installed at the exit from the ducts on the roof of the building - devices that create draft when the wind blows on them. In this case, the wind flow, hitting the deflector and flowing around it, creates a vacuum around most of its perimeter, which ensures air suction from the channel. The most widely used deflectors are the TsAGI type (Fig. 4.2), which are a cylindrical shell mounted above the exhaust pipe. To improve air suction by wind pressure, the pipe ends in a smooth expansion - a diffuser. A cap is provided to prevent rain from entering the deflector.

Rice. 4.2. TsAGI type deflector diagram: 1 - diffuser; 2 - cone; 3 - legs holding the cap and shell; 4 - shell; 5 - cap

Calculation of the deflector comes down to determining the diameter of its pipe. Approximate diameter of the pipe d TsAGI type deflector can be calculated using the formula:

,

Where L- volume of ventilation air, m 3 / h; - air speed in the pipe, m/s.

The air speed (m/s) in the pipe, taking into account only the pressure created by the action of the wind, is found using the formula

,

where is wind speed, m/s; - the sum of the local resistance coefficients of the exhaust air duct in its absence e = 0.5 (at the entrance to the branch pipe); l - length of the branch pipe or exhaust air duct, m.

Taking into account the pressure created by the wind and thermal pressure, the air speed in the nozzle is calculated using the formula

,

Where - thermal pressure Pa; here is the height of the deflector, m; - density, respectively, of outdoor air and indoor air, kg/m3.

The speed of air movement in the pipe is approximately 0.2...0.4 wind speed, i.e. . If the deflector is installed without exhaust pipe directly in the ceiling, then the air speed is slightly higher.

Aeration is used for ventilation of large industrial premises. Natural air exchange is carried out through windows, skylights using heat and wind pressure (Fig. 4.3). Thermal pressure, as a result of which air enters and leaves the room, is formed due to the temperature difference between the external and internal air and is regulated by varying degrees of opening of the transoms and lanterns. The difference between these pressures at the same level is called internal excess pressure. It can be both positive and negative.

Rice. 4.3. Building aeration scheme

At negative value(exceeding external pressure over internal) air enters the room, and when positive value(internal pressure exceeds external pressure) air leaves the room. At = 0 there will be no air movement through the holes in the outer fence. The neutral zone in the room (where = 0) can only exist under the influence of excess heat alone; when there is wind with excess heat, it sharply shifts upward and disappears. The distances of the neutral zone from the middle of the exhaust and supply openings are inversely proportional to the squares of the areas of the openings. At , where are the areas, respectively, of the inlet and outlet openings, m 2 ; -height of the level of equal pressures, respectively, from the inlet to the outlet, m.

Air flow G, which flows through a hole having an area F, calculated by the formula:

Where G- massive second consumption air, t/s; m is the flow coefficient depending on the outflow conditions; r - air density in the initial state, kg/m3; - pressure difference inside and outside the room in a given hole, Pa.

The approximate amount of air leaving the room through 1 m2 of opening area, taking into account only thermal pressure and provided that the areas of the holes in the walls and lanterns are equal and the flow coefficient m = 0.6, can be determined using a simplified formula:

Where L- amount of air, m 3 / h; N- distance between the centers of the lower and upper holes, m; - temperature difference: average (altitude) indoors and outdoor, ° C.

Aeration using wind pressure is based on the fact that excess pressure occurs on the windward surfaces of the building, and rarefaction occurs on the windward sides. Wind pressure on the surface of the fence is found by the formula:

Where k- aerodynamic coefficient, showing what proportion of the dynamic wind pressure is converted into pressure in a given section of the fence or roof. This coefficient can be taken on average equal to + 0.6 for the windward side, and -0.3 for the leeward side.

Natural ventilation is cheap and easy to operate. Its main disadvantage is that the supply air is introduced into the room without preliminary cleaning and heating, and the exhaust air is not cleaned and pollutes the atmosphere. Natural ventilation is applicable where there are no large emissions of harmful substances into the work area.

Artificial (mechanical) ventilation eliminates the shortcomings of natural ventilation. At mechanical ventilation air exchange is carried out due to air pressure created by fans (axial and centrifugal); air in winter time It is heated, cooled in the summer and, in addition, cleaned of contaminants (dust and harmful vapors and gases). Mechanical ventilation can be supply, exhaust, supply and exhaust, and according to the place of action - general and local.

At supply ventilation system(Fig. 4.4, A) air is taken from the outside using a fan through a heater, where the air is heated and, if necessary, humidified, and then supplied to the room. The amount of air supplied is controlled by valves or dampers installed in the branches. Polluted air comes out unpurified through doors, windows, lanterns and cracks.

At exhaust ventilation system(Fig. 4.4, b) polluted and overheated air is removed from the room through a network of air ducts using a fan. Polluted air is cleaned before being released into the atmosphere. Fresh air is sucked in through windows, doors, and structural leaks.

Supply and exhaust ventilation system(Fig. 4.4, V) consists of two separate systems - supply and exhaust, which simultaneously supply clean air into the room and remove polluted air from it. Supply ventilation systems also replace air removed by local suction and spent on technological needs: fire processes, compressor units, pneumatic transport, etc.

To determine the required air exchange, it is necessary to have the following initial data: the amount of harmful emissions (heat, moisture, gases and vapors) in 1 hour, the maximum permissible amount (MAC) of harmful substances in 1 m 3 of air supplied to the room.

Rice. 4.4. Scheme of supply, exhaust and supply and exhaust mechanical ventilation: A- supply; 6 - exhaust; V- supply and exhaust; 1 - air intake for intake of clean air; 2 - air ducts; 3 - filter for air purification from dust; 4 - air heaters; 5 - fans; 6 - air distribution devices (nozzles); 7 - exhaust pipes for releasing exhaust air into the atmosphere; 8 - devices for cleaning exhaust air; 9 - air intake openings for exhaust air; 10 - valves for regulating the amount of fresh secondary recirculation and exhaust air; 11 - a room served by supply and exhaust ventilation; 12 - air duct for the recirculation system

For rooms with the release of harmful substances, the required air exchange L, m 3 / h, is determined from the condition of the balance of harmful substances entering it and diluting them to acceptable concentrations. Balance conditions are expressed by the formula:

Where G- rate of release of harmful substances from technological installation, mg/h; Getc- rate of entry of harmful substances with air flow into the work area, mg/h; G beat- the rate of removal of harmful substances diluted to permissible concentrations from the work area, mg/h.

Replacing in expression Getc And G beat by the product and , where and are, respectively, the concentrations (mg/m 3) of harmful substances in the supply and removed air, a and the volume of supply and removed air in m 3 per 1 hour, we obtain

To maintain normal pressure in the working area, the equality must be satisfied, then

The necessary air exchange, based on the content of water vapor in the air, is determined by the formula:

,

where is the amount of removed or supply air indoors, m 3 / h; GP- mass of water vapor released in the room, g/h; - moisture content of removed air, g/kg, dry air; - moisture content of supply air, g/kg, dry air; r - density of supply air, kg/m3.

where are the masses (g) of water vapor and dry air, respectively. It must be borne in mind that the values ​​and are taken from tables of physical characteristics of air depending on the value of the standardized relative humidity exhaust air.

To determine the volume of ventilation air based on excess heat, it is necessary to know the amount of heat entering the room from various sources (heat gain), , and the amount of heat spent to compensate for losses through the building enclosures and other purposes, , difference and expresses the amount of heat that goes into heating the air in the room and which must be taken into account when calculating air exchange.

The air exchange required to remove excess heat is calculated using the formula:

where is the excess amount of heat, J/s, is the temperature of the removed air, ° K; - supply air temperature, ° K; WITH- specific heat capacity of air, J/(kg×K); r - air density at 293° K, kg/m3.

Local ventilation Is there an exhaust or supply? Exhaust ventilation is used when pollution can be captured directly at the point of its origin. For this purpose, fume hoods, umbrellas, curtains, side suction at bathtubs, casings, suction at machine tools, etc. are used. TO supply ventilation include air showers, curtains, oases.

Fume hoods work with natural or mechanical exhaust. To remove excess heat from a cabinet or harmful impurities naturally requires the presence of a lifting force, which occurs when the temperature of the air in the cabinet exceeds the temperature of the air in the room. The exhaust air must have sufficient energy to overcome aerodynamic resistance on the way from the entrance to the cabinet to the point of release into the atmosphere.

Volumetric flow rate of air removed from the fume hood during natural exhaust (Fig. 4.5), (m 3 / h)

Where h- height of the open cabinet opening, m; Q- amount of heat generated in the cabinet, kcal/h; F - area of ​​the open (working) opening of the cabinet, m2.

Rice. 4.5. Scheme of a fume hood with natural exhaust: 1 - level zero pressure; 2 - diagram of pressure distribution in the working hole; T 1- room air temperature; T 2 - gas temperature inside the cabinet

Required exhaust pipe height (m)

,

where is the sum of all resistances of a straight pipe along the path of air movement; d- straight pipe diameter, m (preset).

With mechanical extraction

Where v- average suction speed in sections of an open opening, m/s.

Onboard suctions arranged near production baths for removal of harmful vapors and gases that are released from bath solutions. For bath widths up to 0.7 m, single-sided suction units are installed on one of its longitudinal sides. When the bath width is more than 0.7 m (up to 1 m), double-sided suction is used (Fig. 4.6).

The volumetric flow rate of air sucked from hot baths by single- and double-sided suction units is found using the formula:

,

Where L- volumetric air flow, m 3 / h, k 3 - safety factor equal to 1.5...1.75, for baths with special harmful solutions 1,75...2; kT- coefficient for taking into account air leaks from the ends of the bath, depending on the ratio of the width of the bath IN to its length l; for single-sided simple suction ; for double-sided - ; WITH- dimensionless characteristic equal to 0.35 for single-sided suction and 0.5 for double-sided suction; j is the angle between the suction boundaries (Fig. 4.7); (in calculations it has a value of 3.14); T in And T p- absolute temperatures, respectively, in the bath and air in the room, °K; g=9.81 m/s 2 .

Exhaust hoods used when the released harmful vapors and gases are lighter than the surrounding air and its mobility in the room is insignificant. Umbrellas can be either with natural or mechanical exhaust.

Rice. 4.6. Double-sided bath suction

With natural exhaust the initial volumetric air flow rate in the thermal jet rising above the source is determined by the formula:

,

Where Q- amount of convective heat, W; F- horizontal projection area of ​​the surface of the heat source, m 2 ; N- distance from the heat source to the edge of the umbrella, m.

With mechanical extraction the aerodynamic characteristic of the umbrella includes the speed along the axis of the umbrella, which depends on the angle of its opening; with increasing opening angle, the axial speed increases compared to the average. At an opening angle of 90°, the axial speed is l.65 v (v- average speed, m/s), with an opening angle of 60°, the speed along the axis and across the entire cross section is equal v.

In general, the flow rate of air removed by the umbrella is

Where v- average speed of air movement in the intake opening of the umbrella, m/s; when removing heat and moisture, the speed can be taken as 0.15...0.25 m/s; F- design cross-sectional area of ​​the umbrella, m2.

The receiving hole of the umbrella is located above the heat source; it must correspond to the configuration of the umbrella, and the dimensions are somewhat larger than the dimensions of the heat source in plan. Umbrellas are installed at a height of 1.7...1.9 m above the floor.

To remove dust from various machines, dust collection devices are used in the form of protective and dust removal casings, funnels, etc.

Rice. 4.7. The angle between the boundaries of the suction torch at different locations baths: A- near the wall (); b- next to the bathroom without suction (); V- separately (); 1 - bath with suction; 2 - bath without suction.

In calculations, take p = 3.14

Air volume flow L(m 3 / h), removed from sharpening, grinding and roughening machines, is calculated depending on the diameter of the circle dTop(mm), namely:

at< 250 мм L = 2,

at 250...600 mm L= 1,8 ;

at > 600 mm L = 1,6.

The air flow rate (m 3 /h) removed by the funnel is determined by the formula:

,

Where V H- initial speed of the exhaust torch (m/s), equal to speed transportation of dust in the air duct, accepted for heavy emery dust 14...16 m/s and for light mineral dust 10...12 m/s; l- working length of the exhaust torch, m; k- coefficient depending on the shape and aspect ratio of the funnel: for a round hole k= 7.7 for rectangular with aspect ratio from 1:1 to 1:3 k = 9,1; Vk- the required final speed of the exhaust torch at the circle, taken equal to 2 m/s.

LITERATURE

1. Life safety/Ed. Rusaka O.N.-S.-Pb.: LTA, 1996.

2. Belov S.V. Life safety is the science of survival in the technosphere. NMS materials on the discipline “Life Safety”. - M.: MSTU, 1996.

3. All-Russian monitoring of the social and labor sphere 1995. Statistical collection. - Ministry of Labor of the Russian Federation, M.: 1996.

4. Environmental hygiene./Ed. Sidorenko G.I..- M.: Medicine, 1985.

5. Occupational hygiene when exposed to electromagnetic fields./Ed. Kovshilo V.E.- M.: Medicine, 1983.

6. Zolotnitsky N.D., Pcheliniev V.A.. Occupational safety in construction. - M.: Higher School, 1978.

7. Kukin P.P., Lapin V.L., Popov V.M., Marchevsky L.E., Serdyuk N.I. Fundamentals of radiation safety in human life. - Kursk, KSTU, 1995.

8. Lapin V.L., Popov V.M., Ryzhkov F.N., Tomakov V.I. Safe human interaction with technical systems. - Kursk, KSTU, 1995.

9. Lapin V.L., Serdyuk N.I. Occupational safety in foundry production. M.: Mechanical Engineering, 1989.

10. Lapin V.L., Serdyuk N.I. Occupational safety management at an enterprise. - M.: MIGZH MATI, 1986.

11. Levochkin N.N. Engineering calculations for labor protection. Publishing house of Krasnoyarsk University, -1986.

12. Occupational safety in mechanical engineering./Ed. Yudina B.Ya., Belova S.V. M.: Mechanical Engineering, 1983.

13. Labor protection. Information and analytical bulletin. Vol. 5.- M.: Ministry of Labor of the Russian Federation, 1996.

14. Putin V.A., Sidorov A.I., Khashkovsky A.V. Occupational safety, part 1. - Chelyabinsk, ChTU, 1983.

15. Rakhmanov B.N., Chistov E.D. Safety during operation of laser installations. - M.: Mashinostroenie, 1981.

16. Saborno R.V., Seledtsov V.F., Pechkovsky V.I. Electrical safety at work. Methodological instructions. - Kyiv: Vishcha School, 1978.

17. Reference book on labor protection/Ed. Rusaka O.N., Shaidorova A.A.- Chisinau, Publishing House “Cartea Moldovenasca”, 1978.

18. Belov S.V., Kozyakov A.F., Partolin O.F. and others. Means of protection in mechanical engineering. Calculation and design. Directory/Ed. Belova S.V.-M.: Mechanical Engineering, 1989.

19. Titova G.N. Toxicity of chemicals. - L.: LTI, 1983.

20. Tolokontsev N.A. Fundamentals of general industrial toxicology. - M.: Medicine, 1978.

21. Yurtov E.V., Leikin Yu.L. Chemical toxicology. - M.: MHTI, 1989.

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 parameters The air microclimate of 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 schemes general ventilation :

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. Local system deletes harmful substances from casings and covers of machines. 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 exchange or local ventilation. 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.

One of the main means of collective protection of workers from negative impact harmful factors of the air environment (dust, gas contamination, increased heat and humidity) is ventilation.

Ventilation- is a complex of interconnected devices and processes designed to create organized air exchange necessary to remove contaminated or overheated (cooled) air from the production area with the supply of clean and cooled (heated) air instead, which makes it possible to create favorable air conditions in the work area.

The amount of air required to ensure the required air parameters in the work area is determined depending on the amount of harmful factors released in such a way as to ensure maximum permissible concentrations and levels.

Under ventilation system understand a set of ventilation units with different purposes that can serve a separate room or building. The classification of the main types of ventilation is presented in Fig. P1.9.

Depending on the method of air movement in work areas, ventilation is divided into artificial (mechanical), natural and combined.

With natural ventilation, air exchange is carried out in two ways:

Unorganized (ventilation and air infiltration through window, door openings, cracks and microcracks);

Organized (through aeration and using deflectors).

Natural unorganized air exchange in a room is caused by the action of two factors: thermal air movement and wind pressure. Thermal movement is created by the difference in the weight of air columns outside and inside the room. Thus, a pressure difference occurs, which causes air exchange. Wind pressure is caused by the action of the wind, due to which excess pressure occurs on the windward surfaces of the building, and rarefaction occurs on the leeward sides. The resulting pressure difference causes air to enter from the windward side of the building and exit through openings on the opposite windward side. In some cases, unorganized air exchange is not enough to remove harmful emissions from the room, so a special device is used - a deflector (see Fig. A1.10). The deflector is the end of a pipe designed to remove air from the upper zone of the room. The wind flow, hitting the deflector and flowing around it, creates a vacuum that ensures air suction from the room through the deflector channel. Aeration is organized natural air exchange, carried out in pre-calculated volumes and regulated in accordance with external meteorological conditions.

The advantage of natural ventilation is the simplicity of the devices and minimal operating costs. The disadvantage is the influence of natural factors (wind, ambient temperature) on its effectiveness, as well as the fact that air is supplied and removed from the room that has not undergone special treatment (not cleared of dust and other harmful impurities, not cooled or not heated). Therefore, natural ventilation is used mainly where there are no significant emissions of harmful factors.

At artificial ventilation air movement is activated mechanical devices. The classification of mechanical ventilation is shown in Fig. P1.11.

According to the nature of the room coverage ventilation systems can be general exchange, local (local) and combined.

With general ventilation, air change occurs throughout the entire volume of the room. This type of ventilation can be carried out either naturally (aeration) or mechanically.

The purpose of local ventilation is to localize harmful emissions in places of formation and remove them from the room. It can be carried out mechanically with the help of fans and naturally with the help of deflectors.

With a combined system, simultaneously with the general air exchange, the individual most intense sources of emissions are also localized.

Local ventilation can be supply or exhaust.

The supply air is provided for the purpose of supplying clean air to the work area to create a microclimate in individual places (air showers, curtains and oases). An air shower is a stream of air directed at a person. The air curtain prevents penetration into manufacture building through the cold air gate in winter. Air oases improve weather conditions for limited area room, which for this purpose is separated on all sides by light partitions and flooded with air that is colder and cleaner than the air in the room.

Exhaust ventilation is installed in places where harmful emissions are formed in the form of cabinets, umbrellas, suction from various equipment, vacuum cleaners, dust collectors, ejection units, individual suction units, and so on.

General mechanical ventilation can be supply, exhaust, supply and exhaust, and can also be carried out using air conditioners. With forced-air general ventilation, fresh air is taken from places outside the building and distributed throughout the entire volume of the room. Polluted air is displaced by fresh air through doors, windows, lights and cracks building structures. Supply ventilation is used in the presence of heat emissions and the absence of gas emissions.

Exhaust general ventilation allows you to remove contaminated and overheated air from the entire volume of the room. To replace the removed air, clean air is sucked in from the outside through doors, windows, and cracks in building structures.

Supply and exhaust general exchange mechanical ventilation consists of two separate units. Through one, clean air is supplied, through the other, contaminated air is removed.

Air conditioning is ventilation unit, which, using automatic control devices, maintains the specified air parameters in the room.

There are two types of air conditioners: full air conditioning units, which ensure constancy of temperature, relative humidity, air speed and air purity, as well as incomplete air conditioning units, which ensure the constancy of only part of these parameters or one parameter, most often temperature.

Depending on the method of refrigeration supply, air conditioners are divided into autonomous and non-autonomous. In stand-alone air conditioners, the cold is produced by its own built-in refrigeration units. Non-autonomous air conditioners are supplied with coolants centrally.

According to the method of preparing and distributing air, air conditioners are divided into central and local. The design of central air conditioners provides for the preparation of air outside the serviced premises and its distribution through the air duct system. In local air conditioners, air is prepared directly in the premises served; the air is distributed concentratedly, without air ducts.

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 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 the premises through leaks in fences and elements of 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 natural ventilation systems, deflector nozzles are installed at the mouth of exhaust shafts (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.

The air exchange created in the room by 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, the hood humid air is carried out in the upper zone, and fresh food is supplied in an amount of 60% to the working 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. Clean air enters the production area 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 P by the exhaust system is mixed with the air coming from outside. 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 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 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). With properly organized ventilation, the air exchange rate should be significantly greater than one.

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 areas with air volume per worker 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 time 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

With the help of 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, chambers, hermetically or tightly covering 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 suction - 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 over openings for releasing metal and slag from cupola furnaces. Umbrellas are made open on all sides and partially open: on one, two and three sides. Efficiency 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 are 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 for those production premises in which a sudden entry into the air of a large amount of harmful or explosive substances is possible. 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 ensuring sanitary standards for the air microclimate, air conditioners undergo special treatment: ionization, deodorization, ozonation, etc.

Air conditioners can be local (to serve individual rooms) and central (to serve several separate rooms). 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 the point of view of life safety, 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.

The purpose of ventilation is to ensure clean air and specified meteorological conditions in production premises.

Ventilation is achieved by removing polluted or heated air from a room and introducing fresh air into it.

Depending on the method of air movement, ventilation can be natural or mechanical. It is also possible to combine natural and mechanical ventilation (mixed ventilation) in various options.

Depending on what the ventilation system is used for - to supply (supply) or remove (exhaust) air from the room or both at the same time, it is called supply, exhaust or supply and exhaust.

Depending on the location of action, ventilation can be general and local.

The action of general ventilation is based on the dilution of released harmful substances fresh air up to maximum permissible concentrations or temperatures. This ventilation system is most often used in cases where harmful substances are released evenly throughout the room. With such ventilation, the necessary parameters of the air environment are maintained throughout its entire volume (Fig. 2, a).

Rice. 2. Ventilation systems:

a, b, c - general exchange; g - general exchange and local; d — organization of air exchange: 1 — control panel room; 2 - local suctions

If the room is very large, and the number of people in it is small, and their location is fixed, it does not make sense (for economic reasons) to improve the health of the entire room completely, you can limit yourself to improving the air environment only in the places where people are. An example of such an organization of ventilation can be observation and control cabins in rolling shops in which local supply and exhaust ventilation(Fig. 2, d), workplaces in hot shops equipped with air showering units, etc.

Air exchange in a room can be significantly reduced if harmful substances are captured at the points of their release, preventing them from spreading throughout the room. For this purpose, technological equipment that is a source of emission of harmful substances is equipped with special devices from which polluted air is sucked out. Such ventilation is called local exhaust or localization (Fig. 2, d).

Local ventilation, compared to general ventilation, requires significantly lower costs for installation and operation.

In industrial premises in which large quantities of harmful vapors and gases may suddenly enter the air of the working area, emergency ventilation is provided.

In production they often arrange combined systems ventilation (general exchange with local, general exchange with emergency, etc.).

For successful work ventilation system, it is important that the following technical and sanitary-hygienic requirements are met even at the design stage.

1. The volume of air flow into the room Lnp must correspond to the exhaust volume Lext; the difference between these volumes should not exceed 10-15%.

In some cases, it is necessary to organize air exchange in such a way that one of the volumes is necessarily larger than the other. For example, when designing the ventilation of two adjacent rooms (Fig. 2, d), in one of which harmful substances are released (room I), the volume of exhaust from this room is greater than the volume of inflow, i.e. Lout > LnpI, resulting in This room creates a slight vacuum and harmless air from room II with slight overpressure LBblTII

There are also possible cases of organizing air exchange when excess pressure relative to atmospheric pressure is maintained throughout the room. For example, in electric vacuum production workshops, for which the absence of dust penetrating through various leaks in enclosures is especially important, the volume of air inflow is greater than the volume of exhaust, due to which a certain excess pressure is created (RPom > Patm).

2. Supply and exhaust systems in the room must be correctly placed.

Fresh air must be supplied to those parts of the room where the amount of harmful emissions is minimal (or none at all), and removed where the emissions are maximum (Fig. 2, b, c).