Industrial ventilation bzhd. Industrial ventilation and air conditioning. "Methods of organizing ventilation and

PRACTICAL LESSON No. 4

Subject

“CALCULATION OF REQUIRED AIR EXCHANGE DURING GENERAL VENTILATION”

Target: To become familiar with the methodology for calculating the required air exchange rate for designing general ventilation in industrial premises.

General information

In order to maintain in the workshops optimal conditions microclimate and prevention of emergency situations (mass poisonings, explosions), to remove harmful gases, dust and moisture is installed ventilation. Ventilation is an organized, controlled air exchange that ensures the removal of polluted air from a room and the supply of fresh air in its place. Depending on the method of air movement, ventilation can be natural or mechanical.

Natural – ventilation, the movement of air masses in which is carried out due to the resulting pressure difference outside and inside the building.

Mechanical– ventilation, with the help of which air is supplied to or removed from the production room through a system of ventilation ducts due to the operation of a fan. It allows you to maintain constant temperature and humidity in work areas.

Depending on the method of organizing air exchange, ventilation is divided into local, general exchange, mixed and emergency.

General ventilation – designed to remove excess heat, moisture and harmful substances throughout the entire working area of ​​the premises. She creates the conditions air environment, identical throughout the entire volume of the ventilated room, and is used if harmful emissions enter directly into the air of the room; workplaces are not fixed, but are located throughout the room.

Depending on production requirements and sanitary and hygienic rules, the supply air can be heated, cooled, humidified, and the air removed from the premises can be cleaned of dust and gas. Typically, the volume of air L in supplied to the room during general ventilation is equal to the volume of air L in removed from the room.

The proper organization and design of supply and exhaust systems has a significant impact on the parameters of the air environment in the work area.

1. Methodology for calculating the required air exchange during general ventilation.

With general ventilation, the required air exchange is determined from the conditions for removing excess heat, removing excess moisture, removal of poisonous and harmful gases, as well as dust.

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 considered to be such amounts in the process equipment, with the simultaneous release of which in the air of the room the concentration of harmful substances will not exceed the maximum permissible. At the same time, the maximum permissible concentrations of harmful and toxic substances in the air of the working area must comply with GOST 12.1.005 - 91.

If in a production room the volume of air for each worker is V pr i< 20м 3 , то расход воздуха L i должен быть не менее 30м 3 на каждого работающего. Если V пр i = 20 … 40м 3 , то L i ≥ 20м 3 / ч. В помещениях с V пр i >40m3 and in the presence of natural ventilation, air exchange is not calculated. In the absence of natural ventilation, the air flow per worker must be at least 60m3/h.

To qualitatively assess the efficiency of air exchange, the concept of air exchange rate K is adopted - the ratio of the volume of air entering the room per unit of time L (m 3 / h) to the free volume of the ventilated room V s (m 3). With proper organization of ventilation, the air exchange rate should be significantly greater than one.

Required air exchange for the entire production area as a whole:

L pp = n · L i ; (1)

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

In this practical work, we will calculate the required air exchange rate for cases of removing excess heat and removing harmful gases.

A. Necessary air exchange to remove excess heat .

Where L 1 is the air exchange necessary to remove excess heat (m 2 / h);

Q – excess amount of heat, (kJ/h);

c – heat capacity of air, (J / (kg 0 C), c = 1 kJ/kg K;

ρ – air density, (kg/m3);

(3)

Where tpr – temperature supply air, (0 C); It depends on the geographical location of the plant. For Moscow – is taken equal to 22.3 0 C.

Tух – the temperature of the air leaving the room is assumed to be equal to the air temperature in the work area, (0 C), which is taken to be 3 – 5 0 C higher than the calculated outside air temperature.

The excess amount of heat to be removed from the production premises is determined by the heat balance:

Q = Σ Q pr – Σ Q exp; (4)

Where Σ Q pr is the heat entering the room from various sources, (kJ/h);

Σ Q consumption - heat consumed by the walls of the building and leaving with heated materials, (kJ / h), is calculated according to the methodology set out in SNiP 2.04.05 - 86.

Since the difference in air temperatures inside and outside the building during the warm period of the year is small (3 - 5), when calculating air exchange based on excess heat generation, heat loss through building structures can be ignored. And a slightly increased air exchange will have a beneficial effect on the microclimate of the working room on the hottest days.

The main sources of heat generation in industrial premises are:

Hot surfaces (ovens, drying chambers, heating systems, etc.);

Cooled masses (metal, oils, water, etc.);

Equipment driven by electric motors;

Solar radiation;

Personnel working indoors.

To simplify calculations in this practical work, the excess amount of heat is determined only taking into account the heat generated by electrical equipment and operating personnel.

Thus: Q = ΣQ pr; (5)

ΣQ pr = Q e.o. + Q p; (6)

Where Q e.o. – heat generated during operation of equipment driven by electric motors, (kJ/h);

Q р – heat generated by working personnel, (kJ/h).

(7)

Where β is a coefficient that takes into account the equipment load, the simultaneity of its operation, and the operating mode. Taken equal to 0.25 ... 0.35;

N – total installed power of electric motors, (kW);

Q р – is determined by the formula: Q р = n · q р (8)

300 kJ/h – for light work;

400 kJ/h – when working avg. heaviness;

500 kJ/h – for heavy work.

q р – heat released by one

person, (kJ/h);

b. Necessary air exchange to maintain the concentration of harmful substances within specified limits.

When ventilation is operating, when there is equality in the masses of supply and exhaust air, it can be assumed that harmful substances do not accumulate in the production area. Consequently, the concentration of harmful substances in the air removed from the room q beat should not exceed the maximum permissible concentration.

The supply air flow rate, m 3 h, required to maintain the concentration of harmful substances within specified limits is calculated by the formula:
,(9)

Where G– amount of harmful substances released, mg/h, q beat– concentration of harmful substances in the removed air, which should not exceed the maximum permissible, mg/m3, i.e. q beat  q maximum permissible concentration ; q etc– concentration of harmful substances in the supply air, mg/m3. The concentration of harmful substances in the supply air should not exceed 30% of the maximum permissible concentration, i.e. q etc  0,3q beat

V. Determining the required air exchange rate.

The value showing how many times the required air exchange is greater than the volume of air in the production room (determining the air change rate) is called the required air exchange rate. It is calculated by the formula:

K = L / V s; (10)

Where K is the required air exchange rate;

L – required air exchange, (m 3 / h). Determined by comparing the values ​​of L 1 and L 2 and choosing the largest of them;

V с – internal free volume of the room, (m 3). It is defined as the difference between the volume of the room and the volume occupied by the production equipment. If the free volume of the room cannot be determined, then it can be assumed to be conditionally equal to 80% of the geometric volume of the room.

The air exchange rate of industrial premises usually ranges from 1 to 10 (higher values ​​for rooms with significant emissions of heat, harmful substances or small in volume). For foundry, forging and pressing, thermal, welding, and chemical production shops, the air exchange rate is 2-10, for mechanical engineering and instrument making shops – 1-3.

3. VENTILATION AND AIR CONDITIONING.

Microclimate parameters have a direct impact on a person’s thermal well-being and performance.

To maintain microclimate parameters at the level necessary to ensure comfort and vital activity, ventilation of the premises where a person carries out his activities is used. Optimal microclimate parameters are provided by air conditioning systems, and acceptable parameters are provided by conventional ventilation and heating systems.

The ventilation system is a set of devices that provide air exchange in the room, i.e. removal from the premises of contaminated, heated, humid air and supplying fresh, clean air to the room. According to the area of ​​action, ventilation can be general exchange, in which air exchange covers the entire room, and local, when air exchange is carried out in a limited area of ​​the room. 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.

For constant air exchange required by the conditions for maintaining clean air in the room, it is necessary organized ventilation, or aeration. 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 doors. Air exchange in the room is regulated by varying degrees of opening of the transoms (depending on the outside temperature, wind speed and direction).

The main advantage of natural ventilation is the ability to carry out large air exchanges without the expenditure of mechanical energy. Natural ventilation, as a means of maintaining microclimate parameters and improving the indoor air environment, is used for non-industrial premises - domestic (apartments) and premises in which, as a result of human work, no harmful substances, excess moisture or heat are released.

Ventilation, by which air is supplied to or removed from rooms through systems of ventilation ducts, using special mechanical stimuli, is called mechanical ventilation. The most common ventilation system is supply and exhaust, in which air is supplied to the room by the supply system and removed by the exhaust system; systems operate simultaneously. The air supplied and removed by ventilation systems is usually subjected to processing - heating or cooling, humidification or removal of contaminants. If the air is too dusty or harmful substances are released in the room, then purification devices are built into the supply or exhaust system.

Mechanical ventilation has a number of advantages compared to 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; capture harmful emissions directly at the places of their formation and prevent their distribution 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 its construction and operation and the need to take measures to combat noise pollution.

To create optimal meteorological conditions, first of all, the most advanced type of ventilation – air conditioning – is used in industrial premises. 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 premises are automatically regulated depending on the time of year, external meteorological conditions and the nature of the technological process in the room. In some cases, special treatment can be carried out: ionization, deodorization, ozonation, etc. Air conditioners can be local - for servicing individual premises, rooms, and central - for servicing groups of premises, workshops and production facilities in general. Air conditioning is much more expensive than ventilation, but provides best conditions for human life and activity.

4. Heating.

The purpose of heating premises is to maintain them in cold period year of the given air temperature. Heating systems are divided into water, steam, air and combined. Water heating systems are widespread, they are efficient and convenient. In these systems, radiators and pipes are used as heating devices. Air system cooling is that the supplied air is preheated in heaters.

The presence of a sufficient amount of oxygen in the air is a necessary condition for ensuring the vital functions of the body. A decrease in oxygen content in the air can lead to oxygen starvation - hypoxia, the main symptoms of which are headache, dizziness, slow reaction, impairment normal operation organs of hearing and vision, metabolic disorders.

5. Lighting.

A necessary condition ensuring human comfort and vital activity is good lighting.

Poor lighting is one of the reasons for increased fatigue, especially during intense visual work. Prolonged work in low light conditions leads to decreased productivity and safety. Correctly designed and rationally executed lighting of industrial, educational and residential premises has a positive psychophysiological effect on humans, reduces fatigue and injuries, and helps to increase labor efficiency and human health, especially vision.

When organizing industrial lighting, it is necessary to ensure a uniform distribution of brightness across work surface and surrounding objects. Shifting your gaze from a brightly lit to a dimly lit surface forces the eye to adapt, which leads to visual fatigue.

Due to improper lighting, deep and sharp shadows and other unfavorable factors are formed, vision quickly becomes tired, which leads to discomfort and an increase in the danger of life (primarily, an increase in industrial injuries). The presence of sharp shadows distorts the size and shape of objects and thereby increases fatigue and reduces labor productivity. Shadows must be softened by using, for example, lamps with light-diffusing milky glass, and in natural light, use sun-protection devices (blinds, visors, etc.).

When lighting rooms they use daylight created by straight lines sun rays and diffused light of the sky and changing depending on geographical latitude, time of year and day, degree of cloudiness and transparency of the atmosphere. Natural light better than artificial, created by any light sources.

If there is a lack of illumination from natural light, use artificial lighting, created electrical sources light, and combined lighting, in which natural lighting, insufficient by standards, is supplemented with artificial lighting. According to its design, artificial lighting can be general or combined. With general lighting, all places in the room receive illumination from a common lighting installation. Combined lighting, along with general lighting, includes local lighting (local lamp, for example, desk lamp), focusing the light flux directly on the workplace. The use of local lighting alone is unacceptable, as there is a need for frequent readaptation of vision. A large difference in illumination in the workplace and in the rest of the room leads to rapid eye fatigue and gradual deterioration of vision. Therefore the share general lighting in the combined must be at least 10%.

The main task of industrial lighting is to maintain lighting in the workplace that matches the nature of the work. visual work. Increasing the illumination of the working surface improves the visibility of objects by increasing their brightness and increases the speed of distinguishing details.

To improve the visibility of objects in the worker’s field of vision, there should be no direct or reflected glare. Where possible, shiny surfaces should be replaced with matte ones.

Fluctuations in illumination in the workplace, caused, for example, by a sharp change in network voltage, also cause re-adaptation of the eye, leading to significant fatigue. Constancy of illumination over time is achieved by stabilizing the floating voltage, rigidly mounting lamps, and using special switching circuits gas discharge lamps.

Noise pollution is also a negative factor affecting humans, major cities primarily related to transport. About 40-50% of their population lives in conditions of noise pollution, which has a negative psychophysiological effect on people. Reducing noise pollution environment– an important and complex task that requires an urgent solution today.

Conclusion.

On the one hand, increasing the level of comfort in people’s lives contributes to their security. But increasing comfort is only one of the consequences of economic development, which generates a number of acute problems along the way environmental problems, which in turn lead to increased negative impacts on humans. Consequently, to truly increase the level of security of people, it is necessary to ensure people’s livelihoods in accordance with the laws of nature.

Conclusion. The science of life sciences explores the world of dangers operating in the human environment, develops systems and methods for protecting people from dangers. In the modern understanding, the science of life safety studies the dangers of the industrial, domestic and urban environment, both in Everyday life, and in the event of an emergency of man-made or natural origin...

Managed and control systems, monitoring the progress of management organization, determining the effectiveness of the event, stimulating work. When choosing means of safety management, they distinguish ideological, physiological, psychological, social, educational, ergonomic, environmental, medical, technical, organizational and operational, legal and economic...

The environments turned out to be far from the acceptable requirements in terms of security. It should be noted that this is why in the last decade the doctrine of life safety in the technosphere has begun to actively develop, the main goal of which is to protect people in the technosphere from the negative impacts of anthropogenic and natural origin, achieving comfortable conditions life activity. ...

5. Rights and obligations of the employee. 6. Types of liability for misconduct and offenses in the field of labor protection. 1. The system of normative and legal acts in the field of life safety. The basis of normative and legal acts in the area of ​​safety and security is the Constitution of the Russian Federation, Labor Code Russian Federation, Code of the Russian Federation "On Administrative Offenses", Civil Code of the Russian Federation, Federal Law "On the Fundamentals of Labor Safety in the Russian Federation", Fundamentals...

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.

By way of air movement There are natural and mechanical ventilation systems.

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.

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.

Unorganized natural ventilation - infiltration , or natural ventilation - carried out by changing the air in the rooms through leaks in fences and elements building structures due to the difference in pressure outside and inside the room. 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.

For constant air exchange required by the conditions for maintaining clean air in the room, it is necessary organized ventilation. Organized natural ventilation can be:

Exhaust without organized air flow (duct);

Supply and exhaust with organized air flow (duct and non-duct aeration).

Channel natural exhaust ventilation without organized air flow is widely used in residential and administrative buildings

Aeration is called organized natural general ventilation of premises as a result of the entry and removal of air through opening transoms of windows and lanterns.

As a method of ventilation, aeration has found wide application in industrial buildings, characterized by technological processes with large heat releases. The supply of outside air during the cold season is organized so that cold air didn't get into work area. For this outside air served into the room through openings located at least 4.5 m from the floor. During the warm season, the influx of outside air is oriented through the lower tier of window openings.

When calculating aeration, the requirements of SNiP 2.04.05-91 are used.

The main advantage of aeration is the ability to carry out large air exchanges without the expenditure of mechanical energy.

To the disadvantages of aeration It should be noted that during the warm period of the year, 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 of ventilation ducts using special mechanical stimuli, is called mechanical ventilation .

Mechanical ventilation has a number of advantages:

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;

Capture 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.

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

Mechanical ventilation systems are divided into:

1. General exchange.

2. Local.

3. Mixed.

4. Emergency.

5. 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.

Based on the method of air supply and removal, four general ventilation schemes are distinguished:

Supply;

Exhaust;

Supply and exhaust;

Recirculation systems.

According to 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.

Exhaust system 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.

Supply and exhaust ventilation - the most common system in which air is supplied into the room by a supply system and removed by an exhaust system.

In some cases, to reduce operating costs for air heating, ventilation systems with partial recirculation are used. In them, the air sucked from the room by the exhaust system is mixed with the air coming from outside. The amount of fresh and secondary air is controlled by valves . The ventilation system with recirculation is allowed to be used only for those rooms in which there are no emissions of harmful substances.

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.

Using local ventilation the necessary meteorological parameters are created at individual workplaces. Local exhaust ventilation is the most widely used. The main method of combating harmful secretions is to install and organize suction from shelters.

Local suction designs can be completely closed, semi-open or open.

Closed suctions are the most effective. These include casings and chambers that hermetically or tightly cover technological equipment .

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. It serves to trap harmful substances that have a lower density than the surrounding air.

The required air exchange in local exhaust ventilation devices is calculated based on the localization conditions of impurities released from the source of formation.

Mixed ventilation system is a combination of elements of local and general ventilation. Local system removes 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 entry into the air is possible large quantity harmful or explosive substances.

To create optimal meteorological conditions in industrial premises, the most advanced type of industrial ventilation is used - air conditioning.

Air conditioning is called its automatic processing in order to maintain predetermined meteorological conditions in production 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:

1. Local (for servicing individual premises).

2. Central (for servicing several separate premises).

Air conditioning plays an essential 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.

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 industrial 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 m3 / h for each worker (for rooms with a volume of up to 20 m3 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 the air exchange when changing outside temperature air or wind speed (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- ventilation air volume, m3/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 is 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

When the value is negative (the external pressure exceeds the internal pressure), 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, m2; -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- mass second air flow rate, 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, m3/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. With mechanical ventilation, air exchange is carried out due to the 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. Clean air is sucked in through windows, doors, and structural leaks.

Supply and exhaust system ventilation(Fig. 4.4, V) consists of two separate systems - supply and exhaust, which simultaneously supply the room fresh air and remove the contaminated material 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) per 1 hour, the maximum permissible amount (MAC) of harmful substances in 1 m3 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 - room served supply and exhaust ventilation; 12 - air duct for the recirculation system

For rooms with the release of harmful substances, the required air exchange L, m3 / 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; G etc- rate of entry of harmful substances with air flow into the work area, mg/h; Gud- the rate of removal of harmful substances diluted to permissible concentrations from the work area, mg/h.

Replacing in expression G etc And Gud by the product and, where and are, respectively, the concentration (mg/m3) of harmful substances in the supply and removed air, a and the volume of supply and removed air in m3 per 1 hour, we obtain

To maintain normal pressure in the working area, 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 exhaust or supply air in the room, m3 / h; G P- 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 the tables physical characteristics 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's enclosures and other purposes, the difference expresses the amount of heat that goes to heat the air indoors 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 are suitable 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. Supply ventilation includes air showers, curtains, and 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.

Volume flow rate of air removed from fume hood with natural exhaust (Fig. 4.5), (m3 / 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; T1- 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, m3/h, k 3 - safety factor equal to 1.5...1.75, for baths with particularly harmful solutions 1.75...2; k T- 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); TV And Tp- absolute temperatures, respectively, in the bath and air in the room, °K; g=9.81 m/s2.

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 heat source surface, m2; 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 for different bath locations: 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(m3/h) removed from grinding, grinding and roughening machines is calculated depending on the diameter of the wheel d To p(mm), namely:

at< 250 мм L = 2,

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

at > 600 mm L = 1,6.

The air flow rate (m3/h) removed by the funnel is determined by the formula:

Where VH- the initial speed of the exhaust torch (m/s), equal to the speed of dust transportation in the air duct, is assumed to be 14...16 m/s for heavy emery dust and 10...12 m/s for light mineral dust; 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; V k- the required final speed of the exhaust torch at the circle, taken equal to 2 m/s.

LITERATURE

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

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One of the main means of collective protection of workers from the negative effects of harmful factors in the air (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 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.

At 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. Air curtain helps prevent penetration into manufacture building through the cold air gate in winter. Air oases improve weather conditions in a limited area of ​​the room, which is separated on all sides for this purpose light partitions and is 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 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, lanterns and cracks in building structures. Forced ventilation used in the presence of heat emissions and 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.