Ventilation and air conditioning. Moscow State University of Printing. BZD parameters of mechanical ventilation

Ventilation is an organized air exchange, during which dusty, gas-polluted or highly heated air is removed from the room and fresh, clean air is supplied in its place.

The ventilation system is a complex of architectural, structural and special engineering solutions, which, when correct operation provides the necessary air exchange in the room.

The ventilation system is engineering design, which has a certain functional purpose(inflow, exhaust, local suction, etc.) and is an element of the ventilation system.

Ventilation systems create conditions for ensuring the technological process or maintaining specified values in the room climatic conditions for highly productive human work. In the first case, the ventilation system will be called technological, and in the second - comfortable.

Technological ventilation provides a given air composition, temperature, humidity, and mobility in a room in accordance with the requirements of the technological process. These requirements are especially high in the workshops of such industries as radio engineering, electric vacuum, textile, chemical and pharmaceutical industries, storage facilities for agricultural products, archives, and premises where historical values are stored.

Comfortable ventilation should provide favorable sanitary hygienic conditions for people working in these premises.

The required meteorological conditions in the premises must be ensured in work area premises or workplaces. The working area of the premises is taken to be a space 2 m high from the level of the floor or platform on which it is located. workplace. Design parameters air - temperature, relative humidity and air mobility - for various workshops and production premises, depending on the category of human work and the conditions of the technological process.

The purpose of room ventilation is to maintain a favorable condition for humans. air environment in accordance with its standardized characteristics.

The chemical composition of indoor air depends on the length of time people stay in them and the operation of technological gas-emitting equipment. The maximum permissible content (concentration) of various harmful gases and vapors (MPC) established by research is given in GOST 12.1 005 76.

Depending on the chosen method, which determines the principle of operation of the systems and their design, ventilation is distinguished: general exchange, local and localizing.

At general ventilation harmful substances are diluted throughout the entire volume of the room due to the influx fresh air, which, passing through the room, assimilates the released harmful substances and is then thrown out.

Quantity supplied ventilation air(air exchange) is calculated to dilute the released harmful substances to concentrations acceptable in the workplace.

The main indicator for choosing this method is the location of people and possible sources of hazardous emissions throughout the entire or large area of the premises. The disadvantage of this method is the uneven sanitary and hygienic conditions of the air environment in different places premises, as well as the possibility of their unacceptable deterioration near sources of hazardous emissions or places where air is exhausted from premises.

The latter must be taken into account and, if possible, eliminated by the appropriate location and purpose of the required number of devices for distribution and exhaust of ventilation air.

General ventilation is installed in residential and public buildings. In rooms where the release of heat and moisture causes the natural rise of air, exhaust is usually carried out from the upper zone. ventilation fire hazard material radiation

It is advisable to supply the supply air so that it reaches people as clean and fresh as possible, without disturbing comfortable conditions.

Classification of ventilation systems by purpose

Ventilation systems can be divided according to their purpose into supply and exhaust. Supply systems serve to supply clean air to ventilated rooms to replace polluted air. In this case, if necessary, the supply air can be subjected to processing, for example, cleaning, heating and humidification.

The supply ventilation system consists of an air intake device, a supply chamber, a network of air ducts and devices for supplying air to the room.

Rice.

1. Fence installation.
2. Cleaning device.
3. Air duct system.
4. Fan.
5. Feeding device for work. place.

Local supply ventilation devices include air showers, air curtains and air heating.

An air shower is a device in a local supply ventilation system that provides a concentrated air flow. The supplied air creates air conditions in the zone of direct influence of this flow on a person that meet hygienic requirements.

Air and air-thermal curtains are installed in order to cold air V winter time did not penetrate through open doors V public buildings through open doors to public buildings and through gates to production areas of industrial buildings. Air curtain- this is a flat stream of air that is supplied from the sides of the gate or doors at a certain angle towards the outside cold air. For an air-thermal curtain, the air supplied by the fan is additionally heated.

In systems air heating the air is heated in air heaters to certain temperature, and then served into the room. In air heaters, the air is heated by hot or superheated water, steam or hot gases.

Exhaust ventilation serves to remove contaminated or heated exhaust air from the room. To exhaust ventilation systems industrial ventilation include aspiration or pneumatic conveying systems bulk materials, as well as production waste - dust, shavings, sawdust, etc. These materials are moved through pipes and channels by air flow.

Rice.

1. Air removal device.
2. Fan.
3. Air duct system.
4. Dust and gas collection devices.
5. Filters.
6. Air release device.

Aspiration systems use special fans, cleaning devices, dust collectors and other equipment. Aspiration systems are widely used at woodworking enterprises to remove shavings and sawdust from machines, at elevators for loading grain into vehicles, at cement factories when loading cement, in foundries for transporting sand and burnt earth.

In general, both supply and exhaust systems are provided in the room. Their performance must be balanced taking into account the possibility of air flow into or from adjacent rooms. The premises may also have only an exhaust or only a supply system. In this case, air enters this room from the outside or from adjacent rooms through special openings, or is removed from this room to the outside, or flows into adjacent rooms.

An effective means of ensuring proper cleanliness and acceptable parameters The indoor air microclimate is controlled by ventilation. Ventilation called organized and regulated air exchange, ensuring the removal of polluted air from the room and the supply of fresh air in its place.

According to the method of air movement, systems are distinguished between natural and mechanical ventilation. A ventilation system in which the movement of air masses is carried out due to the resulting pressure difference outside and inside the building is called natural ventilation.

Unorganized natural ventilation - infiltration, or natural ventilation, carried out by changing the air in the premises through leaks in fences and elements building structures due to the difference in pressure outside and inside the room. Such air exchange depends on random factors: wind strength and direction, air temperature inside and outside the building, type of fencing and quality construction work. Infiltration can be significant for residential buildings and reach 0.5-0.75 room volume per hour, and for industrial enterprises- up to 1-1.5 hours.

For constant air exchange required by the conditions for maintaining clean air in the room, organized ventilation (aeration) is necessary.

Aeration called organized natural general ventilation of premises as a result of the entry and removal of air through opening transoms of windows and lanterns. Air exchange in the room is regulated by varying degrees of opening of the transoms depending on the outside temperature, wind speed and direction. As a method of ventilation, aeration has found wide application in industrial buildings, characterized technological processes with large heat releases (rolling, foundry, forging shops).

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

Ventilation, by which air moves through duct systems using stimulants, is called mechanical ventilation.

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

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

General ventilation designed to assimilate excess heat, moisture and harmful substances throughout the entire working area of the premises. It is used if harmful emissions enter directly into the air of the room; workplaces are not fixed, but are located throughout the room. Typically, the volume of air £pr supplied to the room during general ventilation is equal to the volume of air £v removed from the room. However, in a number of cases it becomes necessary to violate this equality (Fig. 4.1). So, in especially clean industries, for which great importance has no dust, the volume of air inflow is greater than the volume of the exhaust, due to which some excess pressure is created R in the production area, which prevents dust from entering from adjacent rooms. In general, the difference between the volumes of supply and exhaust air should not exceed 10-15%.

Rice. 4.1.

Air circulation in the room and, accordingly, the concentration of impurities and the distribution of microclimate parameters depend not only on the presence of supply and exhaust jets, but also on their relative position. There are four main schemes for organizing air exchange during general ventilation: from top to bottom (Fig. 4.2, i), from top to top (Fig. 4.2, b); from bottom to top (Fig. 4.2, V); from bottom to bottom (Fig. 4.2, G). In addition to these schemes, combined ones are used. The most uniform air distribution is achieved when the inflow is uniform across the width of the room and the exhaust is concentrated.

When organizing air exchange in rooms, it is necessary to take into account physical properties harmful vapors and gases, and primarily their density. If the gas density is lower than the air density, then the contaminated air is removed in the upper zone, and fresh air is supplied directly to the working area. When gases with a density greater than the density of air are released, 60-70% of contaminated air is removed from the lower part of the room and 30-40% from the upper part. In rooms with significant emissions

Rice. 4.2.

moisture extractor humid air is carried out in the upper zone, and fresh food is supplied in an amount of 60% to the working zone and 40% to the upper zone.

Based on the method of supplying and removing air, there are four general ventilation schemes (Fig. 4.3): supply, exhaust, supply and exhaust, and with a recirculation system.

By supply system air is supplied to the room after it has been prepared in the supply chamber. This creates excess pressure in the room, due to which the air escapes outside through windows, doors or into other rooms. The supply system is used to ventilate rooms into which it is undesirable for polluted air from neighboring rooms or cold air from outside to enter.

Supply ventilation units (Fig. 4.3, A) usually made up of the following elements: air intake device / for intake of clean air; 2 air ducts through which air is supplied to the room, filters 3 for cleaning air from dust, air heaters 4, in which the cold is heated outside air; motion stimulator 5, humidifier-dryer 6, supply openings or nozzles 7 through which air is distributed throughout the room.

Rice. 4.3.

A - forced ventilation(PV); b - exhaust ventilation (VV); V - supply and exhaust ventilation with recirculation

Air is removed from the room through leaks in the enclosing structures.

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

Settings exhaust ventilation(Fig. 4.3, b) consist of exhaust openings or nozzles 8, through which air is removed from the room; motion stimulator 5, air ducts 2; devices for air purification from dust or gases 9, installed to protect the atmosphere, and air release devices 10, which is located 1 - 1.5 m above the roof ridge. Fresh air enters the production premises through leaks in the enclosing structures, which is a disadvantage of this ventilation system, since an unorganized influx of cold air (drafts) can cause colds.

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

In some cases, to reduce air heating costs, they use ventilation systems with partial recirculation (Fig. 4.3, V). In them, air drawn from the room is mixed with the air coming from outside. II exhaust system. The amount of fresh and secondary air is controlled by valves 11 n 12. Fresh air in such systems usually accounts for 20-10% of the total amount of supplied air. A ventilation system with recirculation is allowed to be used only for those rooms in which there are no emissions of harmful substances or the emitted substances belong to the 4th hazard class (see paragraph 3.2 of Table 3.4) and their concentration in the air supplied to the room does not exceed 30% maximum permissible concentration (MPC) - The use of recirculation is not allowed if the air in the premises contains pathogenic bacteria, viruses or there are pronounced unpleasant odors.

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

The calculation of the required air exchange during general ventilation is made based on production conditions and the presence of excess heat, moisture and harmful substances. To qualitatively assess the efficiency of air exchange, the concept of air exchange rate is used Ka - the ratio of the amount of air entering the room per unit time b (m3/h), to the volume of the ventilated room V, (m3). When correct organized ventilation the air exchange rate should be significantly greater than unity.

In a normal microclimate and the absence of harmful emissions, the amount of air for general ventilation is used depending on the volume of the room per worker. The absence of harmful secretions is the amount of them in technological equipment, with the simultaneous release of which in the air of the room the concentration of harmful substances will not exceed the maximum permissible. In industrial premises with a volume of air for each worker Un1< 20 м3 расход воздуха на одного работающего bx must be at least 30 m3/h. In a room with Ki1 = 20-40 m3I, > 20 m2/h. In rooms with UpH > 40 m3 and if available natural ventilation air exchange is not calculated. In the absence of natural ventilation (sealed cabins), the air flow per worker must be at least 60 m3/h. Necessary air exchange for everything production premises overall equal

Where P - the number of workers in this room.

When determining the required air exchange to combat excess heat, a balance of sensible heat of the room is drawn up, based on which the volume of air for excess heat is calculated D<2из6:

where rdr is the density of the supply air, kg/m; £ух, £р - temperature of outgoing and supply air, °С; ср - specific heat capacity, kJ/kg-m3;

where bvr is the intensity of formation of harmful substances, mg/h; StsdK, S"r - concentrations of harmful substances within the maximum permissible concentration and in supply air.

The concentration of harmful substances in the supply air should be as minimal as possible and not exceed 30% of the maximum permissible concentration.

The necessary air exchange to remove excess moisture is determined based on the material moisture balance and in the absence of local suction in the production area according to the formula

where (gvp is the amount of water vapor released into the room, g/h; p"p is the density of the air entering the room, kg/m; yuh is the permissible content of water vapor in the air of the room at standard temperature and relative humidity, g/ kg; s!pr - moisture content of supply air, g/kg.

When harmful substances that do not have a unidirectional effect on the human body, for example, heat and moisture, are simultaneously released into the work area, the necessary air exchange is assessed by the largest amount of air obtained in calculations for each type of emissions produced.

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

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

The designs of local suction can be completely closed, semi-open or open (Fig. 4.4). Closed suctions are the most effective. These include casings and chambers that hermetically or tightly cover technological equipment (Fig. 4.4, A). If it is impossible to arrange such shelters, then exhaust systems with partial shelter or open ones are used: exhaust zones, suction panels, fume hoods, side exhausts, etc.

One of the simplest types of local suction is an exhaust hood (Fig. 4.4, and). It serves to trap harmful substances that have a lower density than the surrounding air. Umbrellas are installed above baths for various purposes, electric and induction furnaces, and above openings for releasing metal and slag from cupola furnaces. Umbrellas are made open on all sides and partially open on one, two and three sides. The efficiency of an exhaust hood depends on the size, height of the suspension and its opening angle. The larger the size and the lower the umbrella is installed above the place where substances are released, the more effective it is. The most uniform suction is ensured when the umbrella opening angle is at least 60°.

Suction panels (Fig. 4.4, V) used to remove secretions carried away by convective currents during manual operations such as electric welding, soldering, gas welding, metal cutting, etc. Fume hoods (Fig. 4.4, e) - the most effective device compared to other suction systems, since it almost completely covers the source of the release of harmful substances. Only the service openings remain uncovered in the cabinets, through which air from the room enters the cabinet. The shape of the opening is chosen depending on the nature of the technological operations.

The required air exchange in local exhaust ventilation devices is calculated based on the localization conditions of impurities released from the source of formation. The required hourly volume of sucked air is determined as the product of the area of the suction intake openings P (m2) and the air speed in them. Air speed in the suction opening

Rice. 4.4.

A - shelter box; b - onboard suctions (1 - single-sided, 2 - double-sided); V - side blowjobs (1 - unilateral, 2 - angular); G - suction from work tables; d - stained glass type suction;

e - fume hoods (1st upper suction, 2nd bottom suction, 3 - with combined suction); and - exhaust hoods (1 - straight, 2 - inclined)

V (m/s) depends on the hazard class of the substance and the type of local ventilation air intake (g) = 0.5^-5 m/s).

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

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

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

Air conditioners can be local (to serve individual rooms) and central (to serve several separate rooms). The circuit diagram of the air conditioner is shown in Fig. 4.5.

The outside air is cleaned of dust in the filter 2 and enters chamber I, where it is mixed with air from the room (during recirculation). Having passed through the stage of preliminary temperature treatment 4, the air enters chamber II, where it undergoes special treatment (air washing with water, ensuring the specified parameters of relative humidity, and air purification), and into chamber III (temperature treatment). During temperature treatment in winter, the air is heated partly due to the temperature of the water entering the nozzles 5, and partially, passing through heaters 4 And 7. In summer, the air is cooled partially by the supply of chilled (artesian) water to chamber II and, mainly, as a result of the operation of special refrigeration machines.

Air conditioning plays a significant role not only from the point of view of life safety, but is also necessary in many high-tech industries, so in recent years it has been increasingly used in industrial enterprises. The adverse effects of excess or lack of heat can be significantly reduced or eliminated by improving technical processes, using automation and mechanization, as well as using a number of sanitary, technical and organizational measures: localization of heat generation, thermal insulation of heating surfaces, shielding, air and water-air showering, air oases, air curtains, rational work and rest regime.

In any case, measures must ensure irradiation in workplaces of no more than 350 W/m2 and equipment surface temperature of no higher than 308 K (35 °C) at a temperature inside the source of up to 373 K (100 °C) and not higher than 318 K (45 °C ) at temperatures inside the source above 373 K (100 °C).

Rice. 4.5.

1 - intake duct; 2 - filter; 3 - connecting duct; 4 - heater; 5 - air humidifier nozzles; 6 - drip eliminator; 7 - second stage heater; 8 - fan; 9 - exhaust duct

For non-fixed workplaces and outdoor work in cold climates, special rooms for heating are organized. Under unfavorable meteorological conditions (air temperature -10 °C and below), heating breaks of 10-15 minutes every hour are required.

At outdoor temperatures (-30) - (-45) °C, 15-minute rest breaks are organized every 60 minutes from the start of the work shift and after lunch, and then every 45 minutes of work. It is necessary to provide the possibility of drinking hot tea in heating rooms.

3. VENTILATION AND AIR CONDITIONING.

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

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

The ventilation system is a set of devices that provide air exchange in the room, i.e. removal of polluted, heated, humid air from the room and supply of fresh, clean air to the room. According to the area of action, ventilation can be general exchange, in which air exchange covers the entire room, and local, when air exchange is carried out in a limited area of the room. Based on the method of air movement, natural and mechanical ventilation systems are distinguished.

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

For constant air exchange required by the conditions for maintaining indoor air purity, organized ventilation, or aeration, is necessary. Aeration is the organized natural general ventilation of rooms as a result of the entry and removal of air through opening transoms of windows and doors. Air exchange in the room is regulated by varying degrees of opening of the transoms (depending on the outside temperature, wind speed and direction).

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

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

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

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

4. Heating.

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

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

5. Lighting.

A necessary condition for ensuring human comfort and functioning is good lighting.

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

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

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

When lighting rooms, natural lighting is used, created by direct sunlight and diffused light from the sky and varying depending on the geographic latitude, time of year and day, degree of cloudiness and transparency of the atmosphere. Natural light is better than artificial light created by any light sources.

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

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

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

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

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

Conclusion.

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

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

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

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

5. Rights and obligations of the employee. 6. Types of liability for misconduct and offenses in the field of labor protection. 1. The system of regulatory and legal acts in the field of safety and security. The basis of regulatory and legal acts in the field of safety and security is the Constitution of the Russian Federation, the Labor Code of the Russian Federation, the Code of the Russian Federation “On Administrative Offences”, the Civil Code of the Russian Federation, the federal law “On the Fundamentals of Labor Safety in the Russian Federation”, Basics...

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 air conditions are created in the working area. One of the main tasks that arises when installing ventilation is determining the air exchange, i.e., the amount of ventilation air necessary to ensure the 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 work 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 for maintaining the permissible temperature in the work area.

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

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

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

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

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

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

Where L- 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 an 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

With a negative value (the external pressure exceeds the internal one), air enters the room, and with a positive value (the internal pressure exceeds the external one), the air leaves the room. At = 0 there will be no air movement through the holes in the outer fence. The neutral zone in the room (where = 0) can only exist under the influence of excess heat alone; when there is wind with excess heat, it sharply shifts upward and disappears. The distances of the neutral zone from the middle of the exhaust and supply openings are inversely proportional to the squares of the areas of the openings. At, where are the areas, respectively, of the inlet and outlet openings, m2; -height of the level of equal pressures, respectively, from the inlet to the outlet, m.

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

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

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

Where L- amount of air, m3/h; N- distance between the centers of the lower and upper holes, m; - temperature difference: average (altitude) indoors and outdoor, ° C.

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

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

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

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

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

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

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

To determine the required air exchange, it is necessary to have the following initial data: the amount of harmful emissions (heat, moisture, gases and vapors) 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 the process unit, 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 tables of physical characteristics of air depending on the value of the standardized relative humidity of the 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 is used when pollution can be captured directly at the point of its origin. For this purpose, fume hoods, umbrellas, curtains, side suction at bathtubs, casings, suction at machine tools, etc. are used. Supply ventilation includes air showers, curtains, and oases.

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

Volumetric flow rate of air removed from the fume hood during natural exhaust (Fig. 4.5), (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 - zero pressure level; 2 - diagram of pressure distribution in the working hole; T1- room air temperature; T 2 - gas temperature inside the cabinet

Required exhaust pipe height (m)

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

With mechanical extraction

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

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

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

Where L- volumetric air flow, m3/h, k 3 - safety factor equal to 1.5...1.75, for baths with particularly harmful solutions 1.75...2; k T- coefficient for taking into account air leaks from the ends of the bath, depending on the ratio of the width of the bath IN to its length l; for single-sided simple suction; for double-sided - ; WITH- dimensionless characteristic equal to 0.35 for single-sided suction and 0.5 for double-sided suction; j is the angle between the suction boundaries (Fig. 4.7); (in calculations it has a value of 3.14); TV And Tp- absolute temperatures, respectively, in the bath and air in the room, °K; g=9.81 m/s2.

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

Rice. 4.6. Double-sided bath suction

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

Where Q- amount of convective heat, W; F- horizontal projection area of the heat source surface, m2; N- distance from the heat source to the edge of the umbrella, m.

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

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

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

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

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

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

In calculations, take p = 3.14

Air volume flow L(m3/h) removed from grinding, grinding and roughening machines is calculated depending on the diameter of the wheel d To p(mm), namely:

at< 250 мм L = 2,

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

at > 600 mm L = 1,6.

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

Where VH- 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.

LITERATURE

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.

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

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 >40m3 and in the presence of natural ventilation, air exchange is not calculated. In the absence of natural ventilation, the air flow per worker must be at least 60m3/h.

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

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

L pp = n · L i ; (1)

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

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

A. Necessary air exchange to remove excess heat .

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

Q – excess amount of heat, (kJ/h);

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

ρ – air density, (kg/m3);

(3)

Where tpr – supply air temperature, (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 – 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.

Where n is the number of working personnel, (persons);

q р – heat released by one

person, (kJ/h);

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

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

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

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

V. Determining the required air exchange rate.

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

K = L / V s; (10)

Where K is the required air exchange rate;

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

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

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

on the topic: “INDUSTRIAL VENTILATION »

Methodology for calculating the required air exchange during general ventilation.