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

Consider the main methods:

Thermal insulation;

Heat shields;

Air showering;

Air curtains;

Aerial oases.

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

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

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

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

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

Ionic composition of air

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

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

Ventilation. natural ventilation systems

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

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

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

The method of moving air distinguishes:

Natural ventilation systems.

Mechanical ventilation systems.

Figure 7.1 - Ventilation systems.

Natural ventilation

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

The pressure difference is due to the difference in the densities of the external and internal air (gravitational pressure, or thermal head ∆Р Т) and wind pressure ∆Р В acting on the building.

Natural ventilation is divided into:

Unorganized natural ventilation;

Organized natural ventilation.

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

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

Organized natural ventilation  may be:

Exhaust, without organized air flow (duct)

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

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

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

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

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

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

To group sanitary measures   The use of collective protective equipment includes: Localization of heat generation, Thermal insulation of hot surfaces, shielding of sources or workplaces, air showering, air curtains, air oases, general ventilation or air conditioning.

Localization of heat

Reducing heat input to the workshop is facilitated by measures that ensure the tightness of equipment. Tightly fitting doors, shutters, blocking the closure of technological holes with the operation of the equipment - all this significantly reduces the heat generation from open sources. In each case, the choice of heat-shielding means should be carried out according to maximum values ​​of efficiency, taking into account the requirements of ergonomics, technical aesthetics, safety for a given process or type of work, and a feasibility study.

Heat-shielding means should provide irradiation at workplaces of no more than 350 W / m 2 and equipment surface temperature not higher than 308 K (35 ° C) at a temperature inside the source up to 373 K (100 ° C) and not higher than 318 K (45 ° C) at temperatures inside the source above 373 K (100 ° C).

Thermal insulation of hot surfaces

Thermal insulation of the surfaces of radiation sources (furnaces, vessels and pipelines with hot gases and liquids) lowers the temperature of the radiating surface and reduces both the total heat and radiation.

In addition to improving working conditions, thermal insulation reduces the heat loss of equipment, reduces fuel consumption (electricity, steam) and leads to an increase in the performance of units. It should be borne in mind that thermal insulation, increasing the operating temperature of insulated elements, can dramatically reduce their service life, especially in cases where insulated structures are in temperature conditions close to the upper allowable limit for this material. In such cases, the decision on thermal insulation should be checked by calculating the operating temperature of the insulated elements. If it turns out to be above the maximum permissible, protection against thermal radiation should be carried out in other ways.

Structurally, thermal insulation can be (see Fig. 3.1) mastic, wrapping, filling, piece goods and mixed.

Mastic   isolation is carried out by applying mastic (plaster mortar with heat-insulating filler) on the hot surface of the insulated object. This insulation can be used on objects of any configuration.

Wrapping   the insulation is made of fibrous materials - asbestos fabric, mineral wool, felt, etc. The device for wrapping insulation is simpler than mastic, but it is more difficult to fix it on objects of complex configuration. The most suitable wrapping insulation for pipelines.

Backfill   insulation is used less often, since it is necessary to install a casing around the insulated object. This insulation is used mainly when laying pipelines in channels and ducts, where a large thickness of the insulating layer is required, or in the manufacture of heat-insulating panels.

Mixed   insulation consists of several different layers. Piece products are usually installed in the first layer. The outer layer is made of mastic or wrapping insulation. It is advisable to arrange aluminum casings outside the insulation. The cost of housing the shells quickly pays off due to the reduction of heat loss by radiation and increase the durability of the insulation under the shell.

When choosing a material for insulation, it is necessary to take into account the mechanical properties of the materials, as well as their ability to withstand high temperatures. Usually, materials with a thermal conductivity coefficient of less than 0.2 W / (m o C) at temperatures of 50-100 ° C are used for insulation. Asbestos, mica, peat, earth are used as heat-insulating materials in their

natural state, But most thermal insulation materials are obtained as a result of special processing of natural materials, they are various mixtures.

At high temperatures of the insulated object, multilayer insulation is used: first they put a material that can withstand high temperatures (high-temperature layer), and then a more effective material with thermal insulation properties.

Screening sources or jobs

Heat shields are used to localize sources of radiant heat, reduce irradiation in the workplace, and lower the temperature of the surfaces surrounding the workplace. The weakening of the heat flux behind the screen is due to its absorption and reflectivity. Depending on which ability of the screen is more pronounced, heat-reflecting, heat-absorbing and heat-removing screens are distinguished (see Fig. 3.1),

By the degree of transparency, screens are divided into three classes:

1) opaque;

2) translucent;

3) transparent.

The first class includes metal water-cooled and lined asbestos, alfolium, aluminum screens; the second - screens made of metal mesh, chain curtains, screens made of glass reinforced with metal mesh; All of these screens can be irrigated with water film. The third class consists of screens made of various glasses: silicate, quartz and organic, colorless, painted and metallized, film water curtains, free and flowing down the glass, water-dispersed curtains.

Air shower

When exposed to a working thermal radiation with an intensity of 0.35 kW / m 2 or more, as well as 0.175 - 0.35 kW / m 2 with an area of ​​radiating surfaces within the workplace of more than 0.2 m 2, air drowning is used (air supply in the form air stream directed to the workplace). Air showering is also arranged for production processes with the release of harmful gases or vapors, and if it is impossible to arrange local shelters.

The cooling effect of air showering depends on the temperature difference between the working body and the air flow, as well as on the speed of air flow around the cooled body. To ensure the set temperatures and air velocities at the workplace, the axis of the air flow is directed horizontally or at an angle of 45 ° to the human chest, and to ensure acceptable concentrations of harmful substances it is sent to the breathing zone horizontally or from above at an angle of 45 °.

Air curtains

Air curtains are designed to protect against the breakthrough of cold air into the room through the openings of the building (gates, doors, etc.). An air curtain is an air stream directed at an angle towards the cold air stream. It acts as an air gate, reducing the breakthrough of cold air through openings. Air curtains must be installed at the openings of heated rooms that open at least once an hour or for 40 minutes. at a temperature of -15 ° C and below.

The amount and temperature of air for a curtain is determined by calculation, and the temperature of air heating for air curtains with water is taken no more than 70 ° C, for doors - no more than 50 ° C.

Air oases

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

General ventilation or air conditioning

General ventilation has a limited role - bringing working conditions to acceptable with minimal operating costs. We will consider this issue in detail in the following sections.

Local ventilation is designed to capture the hazards at the places of their allocation and prevent them from mixing with the air in the room. The hygienic significance of local ventilation lies in the fact that it completely eliminates or reduces the influx of harmful emissions into the breathing zone of workers. Its economic importance lies in the fact that harmful substances are discharged in higher concentrations than with general ventilation, and consequently, air exchange and the cost of preparing and cleaning the air are reduced.

Distinguish between local supply and local exhaust and, in some cases, local supply and exhaust ventilation.

Local ventilation systems include air showers, air curtains and air oases.

Air shower it is used when exposed to a working flow of radiation heat with an intensity of 350 W / m 2 or more, and if ventilation does not provide the specified parameters of the air at the workplace. Air showers are performed in the form of airflows directed to workers with specific parameters. Blowing speed is 1-3.5 m / s depending on the intensity of exposure. The action of the air flow is based on an increase in the return of heat by a person with an increase in the speed of movement of the blowing air.

Air shower units can be stationary (Fig. 5.6, but),  when air is supplied to a fixed workplace through a duct system with supply nozzles, and mobile (Fig. 5.6, b)  which use an axial fan. The effectiveness of such choking units increases when spraying water in a stream of air.

Air and air curtains  arrange for protection of workers from cooling by cold air penetrating the room through various openings (gates, doors, hatches, etc.). There are two types of air curtains: air curtains with air supply without heating and air-thermal curtains with air heating in air heaters.

The operation of the curtains is based on the fact that the air supplied to the openings through a special duct with a slit leaves at a high speed (up to 10-15 m / s) at a certain angle towards the cold flow, acting as an air gate.

Air curtains can be with lower air supply (Fig. 5.6, at)  and lateral feed (Fig. 5.6, d)  the height of the opening, the latter being the most common.

Air oases  allow to improve the meteorological conditions of the air in a limited area of ​​the premises, which, as a rule, is used to relax workers. This area is separated on all sides by movable partitions and filled with air with comfortable microclimatic parameters.

Fig. 5.6. Local ventilation: a, b  - air shower units; c, d - air curtains

The local exhaust localizing ventilation system is used to prevent the spread of secretions formed in individual sections of the process. The main method of combating harmful secretions is the device and organization of suction from shelters. Local suction structures may be fully enclosed, semi-open or open. The most effective are closed suction. These include enclosures, chambers, hermetically or tightly covering technological equipment.

If it is impossible to arrange such shelters according to the technology conditions, use suction with partial shelter or open: exhaust hoods, exhaust hoods, suction panels, airborne exhausts, etc.

Pull out drobe  (Fig. 5.7, but)  - The most effective device compared to other exhausts, as it almost completely covers the source of harmful emissions. It is a large-capacity cap with open openings through which air from the room enters the cabinet and works with sources of hazardous emissions.

Fig. 5.7. Local exhaust ventilation: but  - pull out drobe; b  - exhaust hood; at  - airborne suction (7 - one-way; 2   - bilateral); g  - activated side suction (blow)

The volumetric flow rate of air removed from the fume hood during mechanical extraction is determined by the formula

where V n  - average air speed in the open (working) opening of the cabinet, m / s; F n -  working opening area, m 2.

The value of the average air velocity in the working opening of the fume hood is taken depending on the type of hazardous emissions (m / s):

•   0.15-0.35 - with the release of non-toxic hazards (heat, moisture);
•   0.35-0.50 - with the release of toxic substances with a MPC of 100-1000 mg / m 3;
•   0.50-0.75 - with the release of toxic substances with a MPC of 10-100 mg / m 3;
•   0.75-1.0 - with the release of toxic substances with MPC 1 - 10 mg / m 3;
•   1.0-2.0 - with the release of toxic substances with a MPC of less than 1 mg / m 3.

  (Fig. 5.7, b)  It is used to remove harmful emissions rising up, such as heat and moisture, or harmful substances having a density lower than the surrounding air. Umbrellas are made open on all sides or partially open, and in cross-sectional shape - round or rectangular (Fig. 5.8). The receiving hole of the umbrella should be located directly above the source of hazardous emissions at a distance AND,  and its dimensions should be somewhat larger than the dimensions of the source in terms of:

where s, d  - respectively, the length and width of the source of hazardous emissions, m: And -  normal distance from the blocked source to the working opening of the umbrella, m

The opening angle of the umbrella φ is usually taken no more than 60 °, and the height of the side /? b - within 0.1-0.3 m.

Fig. 5.8.

In cases where the coaxial suction cannot be positioned low enough above the source or when it is necessary to deflect the flow of rising harmful emissions so that it does not pass through the breathing zone of a working person, apply exhaust(i suction) panels (Fig. 5.9). Such panels are widely used in welding and soldering areas.

Fig. 5.9.

The volume of air removed by an exhaust umbrella or exhaust panel during mechanical extraction is

where V  - average air velocity in the receiving hole of the umbrella (panel), m / s; F = ab -  the area of ​​the receiving hole of the umbrella (panel), m 2.

When removing heat and moisture, the air velocity in the inlet is taken equal V-  0.15-0.25 m / s, and when removing toxic substances - V-  0.5-1.25 m / s.

Side suction  (Fig. 5.7, at)  used when the space above the surface of the allocation of hazards should remain completely free, and the discharge does not heat up to such an extent as to create a steady upward flow.

The principle of operation of airborne exhausts, which are slit-shaped ducts with a slit height of 40-100 mm, is that the air drawn into the slit, moving above the surface of the bath, entrains harmful emissions, preventing them from spreading through the production room. Side suction can be one-sided when the suction slit is located along one of the long sides of the bath, and two-sided - when the suction slots are located on opposite sides of the bath (Fig. 5.10).

Fig. 5.10. Scheme of air suction from galvanic baths: about  - double-breasted; b  - single-sided

One-way suction is used with a bath width of not more than 0.7 m; bilateral - 0.7-1.0 m. These suction pumps are not used at high temperatures of emitted substances and significant volatility of the liquid, since the speed of these substances upward will be higher than the suction speed.

In practice, activated on-board suction pumps (blowouts) have also found application. Pereduv is a one-way suction activated by a flat jet directed from the supply air duct located on the opposite side of the suction (Fig. 5.7, d).  Under the action of the jet, the flow from the bath is directed to the exhaust slit at a high speed, which makes it possible to intensify the suction. In fig. 5.11 shows a multi-section activated side suction.

The volumetric flow rate of air sucked from the hot tubs by one- and two-sided airborne suction is found by the formula

where C s -  safety factor equal to 1.5-1.75 (for bathtubs with especially harmful solutions K s = 1,75-2); K t -  coefficient taking into account air inflow from the ends of the bath and depending on the ratio of the width of the bath AT  (m) to its length / (m) (for unilateral suction

; for bilateral -); C - no

Fig. 5.11.

• 7 - bathtub body; 2 - suction section; 3   - duct exhaust ventilation;
• 4 - air duct

dimensional characteristic, equal for one-sided suction 0,35; for bilateral 0.5; OS - the angle between the boundaries of the suction torch (in the calculations it is assumed that OS = 3.14); T  and T in  - absolute temperatures, respectively, of the solution in the bath and the air in the room, K; g =  9.81 m / s 2.

The efficiency of the onboard suction depends largely on the uniformity of air velocity along the entire length of the suction gap. Irregularity of speed is allowed no more than 10%. To ensure uniform air velocity in the suction gap, the following measures are used:

•   the length of the suction gap in the suction cover is no more than 1200 mm;
•   on long bathtubs, several suction sections are installed;
•   the narrowing of the casing at the base is not more than 60 °;
•   On each section of the suction provides an independent adjustment device.
• 5.5. EMERGENCY VENTILATION

Emergency ventilation is intended for intensive ventilation of the room in case of a sudden influx of large amounts of explosive or toxic emissions into it. 56

tat accident or disruption of the process, as well as to prevent the flow of harmful emissions into neighboring rooms. Emergency ventilation is an independent ventilation unit and is made only as an exhaust, in order to create a negative air balance in the room.

The emergency ventilation system should be activated automatically: by means of a sensor-detector, whose action begins when the concentration of an explosive substance in the air is 20% lower than the lower concentration limit of flame propagation, or when the detector-gas analyzer triggers when the maximum permissible concentration of the harmful substance is reached. In addition to automatic switching, local manual switching is provided, and sometimes remote switching on the control panel in the control room.

The performance of emergency ventilation systems is based on the total internal volume of the room. For pumping and compressor rooms, it is equal to 8 times air exchange, while for other production rooms at least 8 times air exchange is accepted, created by the combined action of emergency and main exhaust ventilation.

Air intake holes of emergency ventilation are located in areas of possible inflow of explosive and toxic gases and vapors, near the process equipment and near the deaf walls of the room; they should not be placed near opening windows and doors. For light gases with significant excess heat and for hydrogen, all air intake openings are located in the upper part of the room, for light gases with slight excess heat and for ammonia - 40% in the lower zone and 60% in the upper one; for heavy gases with any excess heat - only in the lower zone.

For emergency ventilation, centrifugal fans are used that are located outside the building on the foundations, platforms, ceilings of outdoor installations and on the building surfaces; emergency exhaust from the upper zone can be carried out by axial fans built into the roof or walls of a building. It should be possible to easily maintain these ventilation systems.

5.6. AIR CONDITIONING

To create optimal meteorological conditions in industrial premises, the most modern type of industrial ventilation is used - air conditioning. When air conditioning is automatically regulated, the air temperature, its relative humidity and the flow rate into the room, depending on the season, outdoor weather conditions and the nature of the process in the room.

In some cases, in addition to ensuring the sanitary standards of the microclimate, air in air conditioners undergoes special treatment: ionization, deodorization, ozonation, etc.

The schematic diagram of the air conditioner is shown in Fig. 5.12. Air conditioning operates according to the scheme of partial air circulation. Outside air and air drawn from the room (there is a vacuum in the air conditioner that occurs when the fan is running

8),   enters the mixing chamber. Next, the air mixture passes through the filter. 2.   At low ambient temperatures, it is heated in first-stage heaters. 4.   The amount of air passing through the heaters is regulated by valves 3.   In the irrigation chamber IIthe air is cleaned and humidified, which is achieved by spraying water with the nozzles 5. Droplet separators 7 are installed at the inlet and outlet of the irrigation chamber, after passing which air enters the temperature treatment chamber III,  where it is additionally heated or cooled using a heater or chiller 6,   followed by a fan 8   on the output channel 9   served in the room.

Fig. 5.12.

/ - mixing chamber; II  - irrigation chamber; III - temperature treatment chamber; 1,3   - air supply control valves; 2   - filter; 4 - heater; 5 - nozzles; b - heater or chiller; 7 - drift eliminators; 8   - fan; 9 - output channel

During temperature treatment in winter, the air is heated partially due to the temperature of the water entering the nozzles 5, and partly when passing through the heaters. 3   and 6.   In summer, the air is cooled partially by feeding into the chamber. II  chilled (artesian) water, and mainly due to the operation of the refrigerating machine 6.

The operation of the air conditioner is automated. Automatic devices (thermo- and moisture controllers), when changing the set parameters of the air in the room (temperature and humidity), actuate valves that regulate the mixing of external and recirculating air, heat or cool the air, and supply cold water to the nozzles.

Air conditioning requires, as compared with ventilation, large one-time and maintenance costs, but these costs quickly pay for themselves by increasing labor productivity, reducing morbidity, reducing rejects, improving product quality, etc. It should also be noted that air conditioning plays a significant role not only in ensuring optimal microclimate conditions in industrial premises, but also in carrying out a number of technological processes when fluctuations in temperature and humidity are not allowed (for example, in radio electronics, high-purity materials, etc. .).

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

Basic information about the appointment of air circulation

The main purpose of ventilation systems is to replace the air in various rooms. In residential, domestic, household and industrial premises the air is constantly polluted. Contaminants can be completely different: from practically innocuous house dust to hazardous gases. In addition, it is "polluted" by moisture and excessive heat.

Four basic air circulation arrangements for general ventilation: a - top to bottom, b - top up, c - bottom up, g - bottom down.

It is important to study the purpose of the air exchange systems and select the most suitable for specific conditions. If the choice is made incorrectly and ventilation is insufficient or a lot, it will lead to equipment failure, damage to property in the room and, of course, a negative impact on human health.

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

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Purpose and main features of natural ventilation

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

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

Natural ventilation is unorganized and organized. A feature of unorganized systems is that the replacement of old air with new occurs due to the different pressure of the outside and inside air, as well as the action of the wind. The air leaves and comes through leaks and cracks of window and door structures, as well as when they are opened.

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

The advantage of a natural type of air exchange is that such systems are as simple as possible in design and installation, have an affordable price and do not require the use of additional devices and connection to the power grid. But they can be used only where constant ventilation performance is not needed, since the operation of such systems depends entirely on various external factors like temperature, wind speed, etc. Additionally, the possibility of using such systems limits the relatively small available pressure.

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The main features and purpose of mechanical ventilation

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

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

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

To choose the most suitable type of air exchange for a particular room is needed at the design stage. In this case, sanitary and hygienic standards and technical and economic requirements must be taken into account.

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Features of supply and exhaust systems

The purpose of exhaust and intake ventilation is clear from their names. Local ventilation is provided for the inflow of clean air to the required places. It is usually preheated and cleaned. Exhaust system is needed for discharge from certain places of polluted air. As an example of such an air exchange can result in a kitchen hood. It removes air from the most polluted place - an electric or gas stove. Most often such systems are organized on industrial sites.

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

When organizing a local system, air will be removed from the most polluted sites and fed to certain designated areas. This allows you to adjust the air exchange most effectively.

Local intake ventilation systems can be divided into air oases and showers. The function of the shower is to supply fresh air to the workplace and reduce its temperature at the location of the inflow. Under the air oasis should be understood such places serviced premises, which are fenced with partitions. They are cooled air.

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

The device of local ventilation requires much less cash investment than the organization of general exchange. At various production sites, in most cases, mixed air exchange is organized. So, for the removal of harmful emissions, general exchange ventilation is established, and workplaces are serviced using local systems.

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

In the production premises, thanks to the local exhaust, the capture and discharge of various harmful substances is ensured. To do this, use special suction. In addition to harmful impurities, exhaust ventilation systems divert some of the heat generated during operation of the equipment.

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

In the cold period of the year, heating should be provided in the production premises. Heating devices are placed, as a rule, under the light apertures in places accessible for inspection, repair and cleaning. The length of the heater is chosen from the purpose of the room. For example, in schools, hospitals, the length of the heater should be, as a rule, at least 75% of the length of the light opening.

By appointment, heating, in addition to the main, can be local and on duty.

Local heating  it is provided, for example, in unheated premises to maintain the air temperature that meets the technological requirements in individual rooms and zones, as well as in temporary workplaces during adjustment and repair of equipment.

Duty heating  it is provided for maintenance of air temperature in rooms of heated buildings, when they are not used, and during non-working hours. At the same time, the air temperature is taken below normalized, but not lower than 5 ° С, ensuring the restoration of the normalized temperature to the beginning of the use of the room or to the beginning of work. Special systems of on-duty heating are allowed to be designed at economic justification.

On constructive performance heating systems are water; steam; air; electrical; gas. The use of certain heating systems is determined by the purpose of the production premises.

Consider the advantages and disadvantages of these types of heating.

Merits stove heating  are: low cost of the heating device, low metal consumption, the possibility of using any local fuel, high thermal efficiency of modern furnace designs. Disadvantages - high fire danger, physical labor costs for the furnace of the furnace, large areas for storing fuel, large area of ​​the room occupied by the furnace, uneven temperature in the room during the day, the danger of carbon monoxide poisoning.

Merits water heatingthe following factors are considered: high heat capacity of the coolant (water), small cross-sectional area of ​​pipes, limited temperature of heating devices, uniform temperature inside the room, noiselessness and durability of the system. The disadvantages of this type of heating are: high metal consumption, significant hydrostatic pressure, inertia of heat transfer control, the ability to defrost (damage) the system when the heating medium is no longer heated.

Among the merits steam heatingcan be called: lightly moving coolant with low thermal inertia quickly heats the room, a small hydrostatic pressure in the heating system. The disadvantages are the high temperature of the heating devices (most often more than 100 ° C), high corrosion of the metal heating system, and large noise when steam is introduced into the heating system.

Merits air heatingare: the ability to quickly change the temperature in the room, the uniformity of temperature in the space of the room, fire safety, the combination of heating with the general ventilation of the room, the removal of heating devices from heated premises. The disadvantages are the large size of the air ducts, the increase in irrational heat losses due to the emission of air through the exhaust ventilation openings, the high consumption of heat-insulating materials when designing air ducts.

To the merits electric heatingthese include: low cost of the system, ease of energy transfer, high thermal efficiency, lack of devices for processing and use of fuel, ease of automation of heat transfer processes, no pollution of the atmosphere by the products of combustion of fuel. The disadvantages are the high cost of electrical energy, the high temperature of the heating elements and their fire hazard.

Gas heatingit can be used in steam and water boilers, as well as in furnace heating. The advantages of gas heating in some cases is the relatively low cost of combustible gas compared to other types of fuel.

Principles of heating calculation.The task of calculating the heating is to determine the balance of thermal power between the total heat produced in the room, including the heat of the heating appliances, and the total heat loss, including losses through the building’s external fences (walls, windows, floor, roof, etc.).

This balance can be expressed by the ratio

Q from ³Q å pot - Q å vyd, (3.6)

where Q  from - thermal power of heating devices, W;

Q å sweat - total heat loss in the room, W;

Q å выд - total heat emissions of heated equipment, appliances in industrial buildings, and in public buildings - people, watts.

The total heat release of heated equipment is usually determined from the technical documentation of the equipment or the process.

The most difficult is the calculation of possible heat loss through the enclosing surfaces of the premises (buildings, passenger rolling stock, control cabs, etc.).

Total heat losses through fences (walls, ceiling, window openings, etc.) are determined from the relationship:

(3.7)

where K heat i is the heat transfer coefficient of the material of the i-th enclosing structure, W / m 2 ° С or W / m 2 K;

t в, t н - respectively, the indoor temperature (determined according to GOST 12.1.005–88 or sanitary standards) and outside the building (determined as the average for the coldest month of the year from meteorological observations for a given area), ° С or К;

S i- area of ​​the i-th enclosing structure, m 2.

The required total surface of the heating devices F n. n is determined on the basis of heat balance (3.6):

, (3.8)

where K pr -  the heat transfer coefficient of the material of the thermal device (for metals To pr= 1), W / m 2 ° С;

t g -  temperature of the heating element of the heat source, material (for example, hot water), ° С;

t in- normalized indoor temperature, ° C;

b cooling down- coefficient of cooling water in pipelines.

Knowing the total area of ​​the required heating devices and the area of ​​the heating surface of one selected heating device for this production room, determine the total number of heating devices of the selected design.

Thermal insulation surfacesradiation sources (furnaces, vessels, pipelines with hot gases and liquids) reduce the temperature of the radiating surface and reduce both the total heat release and the radiation.

Structurally, the insulation can be mastic, wrapping, filling, piece goods and mixed. Mastic insulation is carried out by applying mastic (plaster solution with insulating filler) on the hot surface of an insulated object. Obviously, this isolation can be applied on objects of any configuration. Wrapping insulation is made from fibrous materials: asbestos fabric, mineral wool, felt, etc. Wrapping insulation is most suitable for pipelines. Filling insulation is used when laying pipelines in ducts and ducts, where a large thickness of the insulation layer is required, or in the manufacture of insulation panels. Thermal insulation with piece sludge molded products, shells is used to facilitate the work. Mixed insulation consists of several different layers. In the first layer are usually set pieces. The outer layer is made of mastic or wrapping insulation.

Heat shieldsused to localize sources of radiant heat, reduce exposure to workplace and reduce the temperature of the surfaces surrounding the workplace. The weakening of the heat flux behind the screen due to its absorption and reflectivity. Depending on which screen capacity is more pronounced, heat-reflecting, heat-absorbing and heat-removing screens are distinguished. According to the degree of transparency, the screens are divided into three classes:

1)opaque:  metal water-cooled and lined asbestos, alfol, aluminum screens;

2) translucent: metal mesh screens, chain curtains, metal mesh reinforced glass screens (all these screens can be watered with a water film);

3) transparent: screens from various glasses (silicate, quartz and organic, colorless, painted and metallized), film water curtains.

Air shower- air supply in the form of an air jet aimed at the workplace - is used when exposed to operating heat exposure with an intensity of 0.35 kW / m 2 or more, as well as 0.175 ... 0.35 kW / m 2 when the area of ​​the radiating surfaces is within workplace more than 0.2 m 2. Air dushirovaniya suit also for production processes with the release of harmful gases or vapors and with the impossibility of the device of local shelters.

The cooling effect of air choking depends on the temperature difference between the body of the worker and the air flow, as well as on the rate of air flow around the cooled body. To ensure the workplace set temperatures and air velocities, the axis of the air flow is directed to the human chest horizontally or at an angle of 45 °, and to ensure acceptable concentrations of harmful substances it is sent to the breathing zone horizontally or from above at an angle of 45 °.

If possible, a uniform speed and the same temperature should be ensured in the air flow from the steam pipe.

The distance from the edge of the damping pipe to the workplace must be at least 1 m. The minimum diameter of the pipe shall be taken equal to 0.3 m; with fixed workplaces, the calculated width of the working site is assumed to be 1 m. With an irradiation intensity of over 2.1 kW / m 2, an air shower cannot provide the necessary cooling. In this case, it is necessary to provide for thermal insulation, shielding or air showering. For periodic cooling workers arrange radiation cabins, rest rooms.

Air curtainsdesigned to protect against the breakthrough of cold air into the room through the openings of the building (gates, doors, etc.). The air curtain is an air jet directed at an angle towards the cold air flow (Fig. 3.2). It plays the role of the air gate, reducing the breakthrough of air through the openings. According to SNiP 02.04.91, air curtains should be arranged at the openings of heated premises that open at least once per hour or for 40 minutes at a time at an outdoor temperature of minus 15 ° С and below. The quantity and temperature of air is determined by calculation.

Fig. 3.2. Air heat curtain

L 0,m 3 / s, penetrating into the room in the absence of a thermal curtain, is defined as

L 0 = HBV slow, (3.9)

where H, B -  height and width of the opening, m; V wet -  air speed (wind), m / s.

Amount of cold outdoor air L n ap, m 3 / s, penetrating into the room at the device air curtain, is determined by the formula

(3.10)

where the air curtain is adopted as a gate with height h.

In this case, the amount of air required for an air thermal curtain, m 3 / s:

(3.11)

where j- function depending on the angle of inclination of the jet and the coefficient of the turbulent structure; b- the width of the slot located below the opening.

The speed of the air jet from the gap V  W, m / s, is determined by the formula

(3.12)

Average air temperature t cf° C penetrating the room

(3.13)

where t vn t drug - temperature of internal and external air, ° С.

Apply several basic air curtain patterns. Curtains with bottom feed (Fig. 3.3 but) are the most economical in terms of air consumption and are recommended in the case when lowering the temperature near openings is unacceptable. For openings of small width, the scheme in fig. 3.3 b. Scheme with a two-sided direction of the jets (Fig. 3.3 at) used in cases where it is possible to stop transport doorways.