BJD ventilation and air conditioning systems. Industrial ventilation and air conditioning. Natural lighting systems

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

Ventilation is achieved by removing contaminated or heated air from a room and supplying it with fresh air.

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 excreted harmful substances fresh air 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 required parameters are maintained air environment in 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 is installed (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. To this end technological equipment, which is a source of release 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 exchange, it requires significantly lower costs for device 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).

Ventilation called - organized air exchange, which involves removing polluted air from the working area and supplying fresh air into it.

Type classification ventilation systems produced on the basis of the following main characteristics:

By the method of air movement: natural or artificial system ventilation

By purpose: supply or exhaust ventilation system

By service area: local or general ventilation system

By design: stacked or monoblock ventilation system

Natural ventilation is created without the use of electrical equipment (fans, electric motors) and occurs due to natural factors - air temperature differences, pressure changes depending on height, wind pressure. Advantages natural systems The main advantages of ventilation are low cost, ease of installation and reliability due to the absence of electrical equipment and moving parts

The downside of the low cost of natural ventilation systems is the strong dependence of their effectiveness on external factors- air temperature, wind direction and speed, etc.

Artificial or mechanical ventilation used where natural is not enough. IN mechanical systems equipment and devices are used (fans, filters, air heaters, etc.) to move, purify and heat air.

Supply system ventilation serves to supply fresh air to the premises. If necessary, the supplied air is heated and cleaned of dust.

Exhaust ventilation, on the contrary, removes polluted or heated air from the room. Typically, both supply and exhaust ventilation are installed in the room.

Local ventilation designed to supply fresh air to certain places (local supply ventilation) or to remove contaminated air from places where harmful emissions are formed (local exhaust ventilation).

General ventilation, unlike local, is designed to provide ventilation throughout the entire room.

Stacked ventilation system assembled from individual components - fan, muffler, filter, automation system, etc. Such a system is usually located in a separate one. The advantage of typesetting systems is the ability to ventilate any premises - from small apartments and offices to supermarket trading floors and entire buildings. The disadvantage is the need for professional calculations and design, as well as large dimensions.

In a monoblock system ventilation, all components are housed in a single sound-insulated housing. Monoblock systems come in supply and supply and exhaust systems. Supply and exhaust monoblock units can have a built-in recuperator to save energy.

Design features local system ventilation

Ventilation systems have an extensive network of air ducts to move air ( duct systems), or channels (air ducts) may be absent, for example, during aeration - natural ventilation, saturation with air, oxygen (organized natural air exchange), when installing fans in the wall, in the ceiling, etc. ( ductless systems).

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. It creates air conditions that are the same 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.

Significant impact on air parameters in work area provide the correct organization and arrangement of supply and exhaust systems.

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, removing 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 >40m 3 and subject to availability 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.

Air exchange rate production 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.

Under normal conditions, a person emits about 18 liters of carbon dioxide per hour. Excess, as well as deficiency, of carbon dioxide has a harmful effect on the human condition. The permissible values ​​of carbon dioxide concentration in the room are: 0.03-0.07% - for the stay of children and patients; 0.07-0.1% – for long-term stay of people.

When designing ventilation and air conditioning systems, technical solutions are provided that ensure the normalized parameters of the air environment listed above. Specific requirements for the air environment for objects for various purposes are set out in building codes and regulations. The list of basic standards in the field of ventilation and air conditioning in force in Ukraine is given in Appendix 1.

1.2. Classification of ventilation systems.

There is no standard classification of SLE, but in practice and in the technical literature certain terminology and classification have developed, which we will adhere to.

Depending on the method of causing air movement, ventilation systems are divided into natural (gravitational) and artificial (with mechanical propulsion).

By purpose - for supply, exhaust and mixed.

By service area - general exchange and local.

By design– for ducted and ductless.

Air exchange during natural ventilation (aeration) occurs due to the difference in densities of indoor and outdoor air or the difference in temperatures between atmospheric air and indoor air.

In rooms with large heat releases, the air is always warmer than the outside air. Heavier outside air, entering the room, displaces less dense air from it. As a result, air circulation occurs in the room, similar to that artificially created by a fan.

On systems with natural ventilation , in which air movement is created due to the difference in pressure of the air column, the minimum difference in height between the level of air intake from the room and its release through the deflector must be at least 3 m. In this case, the recommended length of horizontal sections should not exceed 3 m, and the air speed in air ducts – 1 m/s.

Aeration is used in workshops if the concentration of dust and harmful gases in the supply air does not exceed 30% of the maximum permissible in the work area. If pre-treatment of the supply air is required, aeration is not used.

Sometimes a phenomenon is used to organize air flow in a room wind pressure , which consists in the fact that an increased pressure is formed on the side of the building facing the wind, and a vacuum is formed on the opposite side.

Natural ventilation systems are simple and do not require complex expensive equipment or operating costs. However, the dependence of the effectiveness of these systems on external factors (outside air temperature, wind direction and speed), as well as low pressure, does not allow them to solve all complex and diverse problems in the field of ventilation. Therefore, systems with mechanical impulse.

Mechanically driven systems use equipment (fans) to move air to desired distances. If necessary, the air is subjected to various types processing: cleaning, heating, cooling, humidifying, drying. Mechanically driven ventilation can be divided into local And general exchange.

Local ventilation is called one that provides air supply to certain places (local supply ventilation) and polluted air is removed only from places where harmful emissions are formed (local exhaust ventilation).

Local ventilation provides air exchange only in the working area, and general exchange- throughout the room.

Local ventilation includes air showers (a concentrated flow of air from increased speed). They must supply clean air to permanent work areas, reduce the air temperature in their area and provide ventilation to workers exposed to heat.

TO local supply ventilation include air oases - areas of premises fenced off from the rest of the room by partitions 2-2.5 m high, into which air with a low temperature is pumped. Local supply ventilation is also used in the form of air curtains (at gates, entrances, stoves, etc.), which create air partitions or change the direction of air flows. Local ventilation requires less cost than general exchange. In industrial premises, in the presence of harmful emissions (gases, moisture, heat, etc.), a mixed ventilation system is usually used: general - to eliminate harmful emissions throughout the entire volume of the room and local (local suction and inflow) - to service workplaces.

Local exhaust ventilation is used when the places of harmful emissions in the room are localized and their spread throughout the room cannot be allowed. Local exhaust ventilation in industrial premises ensures the capture and removal of harmful emissions: gases, smoke, dust and heat. To remove harmful secretions, local suctions are used (shelters in the form of cabinets, umbrellas, boat suctions, etc.).

Harmful emissions must be removed from the place of formation in the direction of their natural movement: hot gases and vapors should be removed upward, and cold heavy gases and dust - downward. When installing local exhaust ventilation to capture dust emissions, the air removed from the room must be cleaned using filters before being released into the atmosphere. If local ventilation cannot meet sanitary, hygienic or technological requirements, use general ventilation systems .

General exhaust systems remove air evenly from the entire room, and general exchange inlet – supply air and distribute it throughout the entire volume of the ventilated room. When supply and exhaust ventilation operate simultaneously, they must be balanced in terms of air flow.

If the air supplied to a room is formed by mixing outside air and air taken from the room, then such a system is called supply and recirculation .

Ventilation systems that supply and remove air through channels or ducts are called duct , and those without channels – ductless .

A system designed to remove dust generated during technological processes is called aspiration .

Aspiration systems are divided into:

individual, when every workplace has a separate exhaust unit;

central , when one installation serves a group of workstations.

To move lightweight materials (wood shavings, textile waste, cotton, etc.), ventilation systems called by pneumatic transport.

1.2.1. Natural ventilation

Air exchange in industrial premises is carried out using natural ventilation or mechanical ventilation units.

Organized air exchange during natural ventilation (aeration) is ensured due to the difference in temperature (density) of the air, as well as as a result of wind pressure.

Under the influence of heat generated by machines and mechanisms, heated coal (during drying), people, as well as heated surfaces, the air temperature in production areas increases and becomes higher than the outside air temperature.

The heated air in production premises rises upward and goes outside through openings in the ceilings (roof).

Cold outside air enters the room through open openings in the lower or middle zones. As a result, natural air exchange is created, called thermal pressure.

The value of thermal pressure is determined by the formula

N m = h (ρ n – ρ V) g, N/m 2 , (1)

Where h – height between the centers of exhaust and supply openings, m; ρ n and ρ c – density of external and internal air, kg/m3; g– free fall acceleration equal to 9.81 m/s 2 .

Natural ventilation can be unorganized and organized. With unorganized ventilation, unknown volumes of air enter and are removed from the room, and the air exchange itself depends on random factors (direction and strength of the wind, temperature of external and internal air). Unorganized natural ventilation includes infiltration – air leakage through leaks in windows, doors, ceilings and ventilation, which occurs when windows and vents are opened.

Organized natural ventilation is called aeration. For aeration, holes are made in the walls of the building to allow in external air, and special devices (lanterns) are installed on the roof or in the upper part of the building to remove exhaust air. To regulate the supply and removal of air, the aeration holes and skylights are covered by the required amount. This is especially important during the cold season.

1.2.2. Artificial ventilation.

Artificial (mechanical) ventilation, in contrast to natural ventilation, makes it possible to purify the air before releasing it into the atmosphere, trap harmful substances directly near the places of their formation, process the inflowing air (clean, heat, humidify), and more specifically supply air to the work area. In addition, mechanical ventilation makes it possible to organize air intake in the cleanest area of ​​the enterprise territory and even beyond it.

General exchange artificial ventilation.

General exchange ventilation ensures the creation of the necessary microclimate and clean air throughout the entire volume of the workroom. It is used to remove excess heat in the absence of toxic emissions, as well as in cases where the nature technological process and the features of production equipment exclude the possibility of using local exhaust ventilation.

There are four main schemes for organizing air exchange during general ventilation: top-down, top-up, bottom-up, bottom-down (Fig. 1).

Rice. 1 – Scheme of organizing air exchange during general ventilation

Schemes from top to bottom (Fig. 1a) and from top to top (Fig. 16 ) is advisable to use if the supply air in cold period year has a temperature lower than the room temperature. The supply air, before reaching the work area, is heated by the air in the room. The other two schemes (Fig. 1c And 1g) is recommended for use in cases where the supply air heats up during the cold season and its temperature is higher than the temperature of the internal air in the room.

If gases and vapors are emitted in industrial premises with a density that exceeds the density of air (for example, vapors of acids, gasoline, kerosene), then general ventilation should provide up to 60% of the air from the lower zone of the room and 40% – from the top.

If the density of gases is less than the density of air, then the removal of contaminated air is carried out in the upper zone.

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

Rice. 2 – Supply ventilation diagram

Air intake devices must be located in places where the air is not polluted by dust and gases. They must be located at least 2 m from the ground level, and from the exhaust ventilation exhaust ducts vertically – below 6 m and horizontally – no more than 25 m.

Supply air is supplied to the premises, as a rule, in a dispersed flow, for which special nozzles are used.

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

Rice. 3 – Exhaust ventilation diagram

Air after purification must be exhausted at a height of at least 1 m above the roof ridge. It is prohibited to make discharge holes directly in the windows.

In industrial production conditions, the most common is a supply and exhaust ventilation system with a general air flow into the work area and local exhaust of harmful substances directly from the places of formation.

In industrial premises where a significant amount of harmful gases, vapors and dust are emitted, the exhaust should be 10% more than the inflow, so that harmful substances are not displaced into adjacent rooms with less harmfulness.

In the supply and exhaust ventilation system, it is possible to use not only external air, but also the air of the premises itself after it has been purified. This reuse of indoor air is called recycling and is carried out during the cold season to save heat spent on heating the supply air. However, the possibility of recycling is determined by a number of sanitary, hygienic and fire safety requirements.

Local ventilation.

Local ventilation can be supply And exhaust.

Local supply ventilation , in which a concentrated presentation of supply air of specified parameters (temperature, humidity, speed of movement) is carried out, performed in the form of air showers, air and air-thermal curtains.

Air showers are used to prevent overheating of workers in hot shops, as well as to form so-called air oases (areas of the production zone that differ sharply in their physical and chemical characteristics from other premises).

Air and air-heat curtains are designed to prevent the entry of significant masses of cold outside air into the premises and the need for frequent opening of doors or gates. The air curtain is generated by a stream of air, which is supplied from a narrow long slit, D at a certain angle towards the flow of cold air. A channel with a slot is placed on the side or on top of the gate (door).

Local exhaust ventilation carried out using local exhaust hoods, suction panels, fume hoods, and on-board pumps (Fig. 4).

Rice. 2.5 - Examples of local exhaust ventilation:

A – exhaust hood, b – suction panel, V – fume hood with combined hood, G – onboard pump with blower.

The design of local exhaust ventilation should ensure maximum capture of harmful substances with a minimum amount of removed air. In addition, it should not be bulky and interfere service personnel work and supervise the technological process.

The main factors when choosing the type of local exhaust ventilation are the characteristics of harmful factors (temperature, density of gases and vapors, toxicity), the position of the worker when performing work, features of the technological process and equipment.

In cases where the source of production premises can be placed inside a spacious space limited by walls, local exhaust ventilation is arranged in the form of fume hoods, casings, and wind pumps. If, due to technology or service conditions, the source of the incident cannot be isolated, then an exhaust hood or suction panel is installed. In this case, the air flow that is removed should not pass through the worker’s breathing zone

A special case of local exhaust ventilation are on-board pumps that are used to equip baths (plating, pickling) or other containers with toxic liquids, since the need to use lifting and transport equipment when loading them makes it impossible to use exhaust hoods and suction panels. If the bathtub width is 1 m or more, it is necessary to install an on-board pump with blowing (Fig. 2.6d), in which air is sucked out on one side of the bathtub, and on the other – is being pumped up. In this case, the moving air seems to screen the surface of the evaporation of toxic liquid substances.

2.3. Basic requirements for ventilation systems.

Natural and artificial ventilation must meet the following sanitary and hygienic requirements:

– create normal climatic working conditions in the working area of ​​the premises (temperature, humidity and air speed);

– completely eliminate harmful gases, vapors, dust and aerosols from the premises or dilute them to maximum permissible concentrations;

– prevent the entry of polluted air into the premises from the outside or through the influx of polluted air from adjacent premises;

– do not create drafts or sudden cooling of air in the workplace;

– be available for management and repair during operation;

– do not create additional inconveniences during operation (for example, noise, vibrations, rain, snow).

Most fully meets the above requirements air conditioning system air, which is also widely used in enterprises. By using air conditioners the specified air parameters are created and automatically maintained in the production area. When deciding whether to use air conditioning, economic factors should also be taken into account.

It should be noted that a number of additional requirements are put forward for ventilation systems installed in fire and explosion hazardous areas, which are not discussed in this section.

1.3. Classification of air conditioning systems.

Air conditioning systems can be classified as follows:

1. According to the degree of ensuring meteorological conditions in the serviced premises, air conditioning systems are divided into three classes: first, second And third.

2. According to the pressure developed by the fans, – low (up to 1000 Pa), average (up to 3000 Pa) and high (over 3000 Pa) pressure.

3. According to the intended purpose of the object of use - comfortable And technological.

4. By the presence of sources of heat and cold - autonomous And non-autonomous.

5. According to the principle of location of the air conditioning system relative to the serviced object - central And local.

6. By the number of premises served – single-zone And multi-zone.

7. By type of objects served – household , semi-industrial And industrial .

Air conditioning systems first class provide the parameters required for the technological process in accordance with regulatory documents.

Systems second class provide sanitary and hygienic standards or required technological standards.

Systems third class provide acceptable standards if they cannot be provided with ventilation in the warm season without the use of artificial air cooling.

Optimal parameters air represent a set of conditions that are most favorable for the well-being of people (the area of ​​comfortable air conditioning), or conditions for the correct flow of the technological process (the area of ​​technological air conditioning). The optimal parameters of internal air in industrial enterprises are established based on the position that if the quantity and quality of products depends on compliance with the exact regime of the technological process, and not on the intensity of labor, then the determining factor is the requirements of the technological process. If the output of products is mainly influenced by the intensity labor, comfortable conditions are established for people working in the workshop.

Valid parameters air are installed in the case when technological requirements or for technical and economic reasons optimal standards are not provided ( SNiP 2.04.05-91).

Autonomous SCR They include a full range of equipment that allows for the necessary air treatment in accordance with regulatory requirements for cleaning, heating, cooling, drying, humidification, movement and distribution of air, as well as means of automatic and remote control and monitoring. To operate an autonomous SCR, only electrical energy must be supplied. Autonomous air conditioners include monoblock window, cabinet air conditioners, and split systems.

Non-autonomous hard currency do not have built-in units that are sources of heat and cold. These SCRs are supplied with cold or hot refrigerants (water, freons) from other sources of heat and cold supply.

Central hard currency They are non-autonomous air conditioners located outside the serviced premises, in which air is prepared and then distributed throughout the premises using air ducts. Modern central air conditioners are produced in sectional versions from unified standard models.

Local hard currency are produced on the basis of autonomous and non-autonomous air conditioners and are installed in the serviced premises.

Single-zone SCV are used to serve one room with a uniform distribution of heat and moisture, for example, exhibition halls, cinemas, etc.

Multi-zone SCR are used to service several rooms or rooms with uneven distribution of heat and moisture.

Household air conditioners Designed for installation in residential buildings, offices and similar facilities. A special feature of household air conditioners is that they are powered by single-phase network and power consumption no more than 3 kW. This is the power that standard electrical outlets installed in residential and administrative premises are allowed to consume. As a consequence of this. The cooling and heating capacity of domestic air conditioners does not exceed 7 kW.

AND conditioning air Task >> Life safety

The air microclimate of the working area is industrial ventilation. Ventilation called organized and controlled air exchange... the most advanced type is used ventilation conditioning air. Air conditioning air is called...

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 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 production premises, as well as in premises located in multi-storey buildings 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

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, 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- 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, 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 system ventilation(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 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 systems ventilation also replaces the 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 - 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, 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 special 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 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(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- 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; V k- the required final speed of the exhaust torch at the circle, taken equal to 2 m/s.

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