Ventilation of industrial premises: rules for the organization of air exchange
The main work performed by the ventilation of industrial premises is the removal of used air and the injection of fresh air. With its help, in the shops of the company create a comfortable air environment that meets regulatory requirements.
Only in such conditions can increase productivity be achieved.
Classification of ventilation systems
All existing ventilation systems are grouped in 4 ways:
- Depending on the way in which the air moves, ventilation is called natural, mechanical or artificial, combined, when both options are present at the same time.
- If we proceed from the direction of the air flow, the ventilation systems can be divided into inlet, exhaust or intake-exhaust systems.
- On such grounds as a venue, ventilation systems are combined into 3 groups: general exchange, local, and combined.
- Based on the appointment, allocate working and emergency systems.
The basis for the design of ventilation for workplaces in production are the norms prescribed in SNiP 41-01-2003. Natural and mechanical ventilation work according to different schemes.
While the processes occurring during natural ventilation depend on heat and wind pressure and are practically beyond the control of a person, forced air exchange is possible only with his active participation.
Scheme of action of natural ventilation
Ventilation of the premises, carried out in the first way, is nothing but simple ventilation. It occurs without human intervention and is possible when the barriers are not sufficiently dense, and allow air to enter the room, both from the outside and from the inside.
The direction is influenced by pressure. If its indicators have a higher value outside, then a way is open for penetration of clean air from the street into the room, otherwise the warm air from the room finds ways of going outside.Often, these processes occur in parallel.
Active natural ventilation occurs unorganized due to random circumstances. It is observed in conditions when the air temperature outside and inside the building differ sharply.
Contributes to this process and the emergence of individual sections with high and low pressure from the hull, intensively blown by the wind and its more protected side, respectively. In this situation, there is infiltration - the air enters the room from the windward side, and goes outside with the leeward side.
The air exchange coefficient, which characterizes the intensity of the process, with a natural method of ventilation does not exceed 0.5. Comfortable conditions for people who are in the production area and working equipment cannot provide an unorganized view of this type of ventilation.There must necessarily be specially designed systems.
Natural ventilation of an organized type is realized by aeration or with the help of deflectors. Both the supply and removal of air from the room takes place either through openings in the enclosing structures or through air vents. In the duct ventilation there is always a deflector.
Natural ventilation with aeration
In the workshops, where the technology provides for the formation of heat in large quantities, aeration involves air exchange, carried out through the lights and window openings under the influence of temperature and wind pressure. In cold workshops, air is assimilated only under wind pressure.
When aerating the device, it is necessary to take into account the wind rose, otherwise harmful emissions from pipes of neighboring enterprises may enter the production area. Nothing should interfere with the release of vapors, harmful gases through the lights.
The best conditions for ventilation are created by the location of the building on the windward side with respect to hazardous production. Opening and closing of the transom should be automated so that you can control them from the bottom.
Their different arrangement allows you to adjust the flow of fresh air.Aeration is a more suitable option for large-scale workshops where mechanical ventilation is not possible due to its high cost.
The recommended height of the air supply to the room with this type of ventilation is at least 0.3 and at most 1.8 m in the warm period and at least 4 m in the cold.
The best option is the vents of a special design on 3 levels. When warm, fresh air passes through the transom below, and dirty - goes through the top.
The middle row of vents provides airflow at a negative temperature. During that time, until the air mass reaches the level of the floor, it manages to warm up.
In small-scale production buildings, baffles are installed on ducts or pipes for exhausting. With their help, exhaust air is removed from workshops where there is a general exchange hood.
And also they are used for removal of heated gases from furnaces, presses, furnaces.When installing, they proceed from the trajectory of the dominant air flow.
Artificial or mechanical ventilation
Being more perfect, than natural, this type of ventilation, assumes considerable financial and operational investments. In such a system, there may be devices not only cleansing, but also ionizing, moisturizing, warming the air.
Mechanical ventilation can be either intake or exhaust or combined, i.e. forced-air and exhaust. Its advantages are obvious:
- It provides the intake of clean air, its processing - heating, drying, moistening.
- Moves air masses over long distances.
- It gives the opportunity to bring the delivery of clean air directly to the workplace.
- Allows you to remove the dirty air from any place and clean it.
- Her work is not affected by environmental conditions.
In general, exhaust and supply systems work together, but sometimes they recommend using only one of these two types.The task of fresh air ventilation is to provide the working space with air that is beneficial for people's health.
Apply it mainly where the production processes are accompanied by large heat, containing a small amount of harmful substances. Clean air entering through ducts is distributed to workplaces through the use of distribution nozzles.
Systems that remove air from the room containing various pollutants are called exhaust. This type of air exchange is used in industrial premises where there are no harmful emissions and the minimum value of such a parameter as the rate of air exchange is not excluded.
It can be warehouse, auxiliary, household premises. Air inflow is provided by infiltration.
In the case of the need for an active and reliable air exchange, supply and exhaust ventilation is used. In order to somehow protect the less polluted rooms from neighboring rooms with a high concentration of hazards, where pollutants are emitted in small quantities, they create a small pressure in the system.
At the stage of design work on the creation of a system of supply and exhaust ventilation, air flow is calculated, for which the formula is used:Lo = 3600FW.
Here F denotes the total area of openings in m², Wо - the average value of the speed at which air is drawn in. This parameter depends on the toxicity of the emissions and the type of operations performed.
Receiving exhaust devices may be at different heights. The main thing is that polluted air flows do not change their natural trajectory of movement. Emissions with a specific gravity greater than that of air are always in the lower zone, therefore devices for their intake should also be located there.
In the autumn-winter period, the air supplied to the room must be heated. To reduce costs, use recycling, which involves heating part of the purified air and returning it to the room. At the same time 2 rules should be followed:
- At least 10% of fresh air enters from the outside, and the content of harmful substances in the back-fed air does not exceed 30% relative to the maximum permissible capacity.
- It is forbidden to use recycling in production, where explosive dust is present in the air mass, microorganisms that can cause various diseases, emissions belonging to 1-3 hazard classes.
The choice of type of ventilation at the site of action depends on the weight of emissions, their concentration, temperature. Generalized ventilation allows you to divert the entire volume of dirty air no matter from what points it stands out.
The most widespread channel option. Here, for the advancement of air through special air ducts, the presence of an ejector unit or a fan - centrifugal or axial - is provided for.
If there are no air ducts, then the system is called channelless. In this case, ventilation equipment is mounted directly in the wall or in the ceiling. The main condition - the presence of natural ventilation.
The possibility of emissions in the room with a high degree of explosion hazard does not allow non-explosive ventilation equipment to be installed on the duct air ducts, therefore ejectors are used in these cases.
The forced-air general ventilation system is often connected to central heating. Outside the building, air intakes are organized for fresh air intake.
The mines are located above the roof and above the ground. The main thing is that near the receivers there were no productions with harmful emissions. The air intake openings themselves must be at least 2 m from the ground, and if the production is located in the green zone, the minimum allowable distance from ground level to the lowest point of the opening must be 1 m.
The principle of operation of the general exchange ventilation is simple: the fan sucks the air masses through the heater, heating occurs here. Further, the air is humidified, and sometimes dried and enters the building through special air ducts.
The volume of incoming air is coordinated by valves or gates intended for this purpose.
General trade ventilation of the supply and exhaust type is open and closed.In the first case, these are 2 independent systems, one of which injects air, and the second in parallel removes the previously neutralized waste.
These systems are suitable for workshops where substances of the 1-2 classes of hazard are released, and the production itself falls into categories A, B, B.
In addition to working ventilation in potentially hazardous industrial premises, there must also be an emergency version of it. Do it mostly exhaust. For rooms belonging to categories A, B, E, the system is supplied with a mechanical drive.
All elements of the system must comply with the requirements of OES. In the workshops of category B, D, D, the presence of a natural inducement of ventilation is permissible if performance is ensured under the most adverse weather conditions.
The grilles and branch pipes of the emergency ventilation system are located in the places with the highest concentration of hazardous substances.
Umbrellas do not need to be installed on pipes and mines of emergency ventilation. Themselves holes should not be placed where people are constantly. This will worsen the local microclimate.
Emergency ventilation is installed in workshops where, in case of an emergency, there will be a release of vapors or gases that are lighter than air. Switching to emergency ventilation should occur automatically as soon as the usual system fails.
Local exhaust eliminates exhaust air in places where it is polluted. The set of production hoods include exhaust fans, pipelines, ventilation grilles.
Local ventilation, designed to remove from the equipment substances belonging to hazard classes 1 and 2, is arranged so that when the ventilation system is turned off, equipment start-up becomes impossible.
In some cases, provide backup fans and supply local suction automatic. Divide such ventilation into 2 types - forced-air and exhaust. The supply type of ventilation is carried out in the form of air curtains, air showers.
The openings that remain open for a long time (more than 40 m per shift) or open quite often (more than 5 times) contribute to hypothermia of people in the room. The work of drying plants that emit pollution also leads to negative consequences.
In these cases, air curtains are suitable. They act as a barrier to cold or very hot air. Air and air-heat screens are designed so that in cold time when opening the openings, the temperature in the workshops does not fall below the mark:
- 14⁰ - during the performance of work that does not require great physical effort;
- 12⁰ - when the work is classified as moderate;
- 8⁰ - when doing hard work.
If workplaces are located close to gates and technological openings, install screens or partitions. The air-thermal curtain near the doors that go outside must consist of air with a maximum temperature of 50⁰, and at the gate - no more than 70⁰.
Local exhaust with special suction
The local exhaust system with special suction first captures and then removes unhealthy impurities in the form of gases, smoke and dust.This is a kind of air shower, whose task is to inject fresh air at a fixed place and lower the temperature in the inflow zone.
It is used in production where workers are exposed to high temperatures and radiant energy with an intensity of more than 300 kcal / m² per hour emitted by heating and smelting furnaces. There are such installations both stationary and mobile. They should provide air velocity from 1 to 3.5 m / s.
There is such a thing as an air oasis, which is the same device included in the local ventilation system. It creates in a certain part of the production area a microclimate with the given parameters.
Purified air supplied to a given alienated zone is usually subjected to a special heat and moisture treatment.
If the local suction device is brought directly to the place of release of substances polluting the space, it will be possible to remove air containing a higher percentage of them than with general-type ventilation. Local ventilation can significantly reduce air circulation.
Air exchange calculation
If as a result of industrial activity no harmful substances are released, the amount of air required for ventilation is calculated by the formula:L = N x Ln.
N- this is the number of people usually in the room,Ln- the volume of air required for 1 person, measured in mᶾ / h. At a rate of between 20 and 60 mᶾ / h.
Using a parameter such as the rate of air exchange, the calculation is performed according to the formula:L = n x S x Hwheren- the frequency of air in the room. For production facilitiesn = 2.S- floor space in m², andH- its height in m.
Conclusions and useful video on the topic
Here is all about the intricacies of various ventilation systems:
Details of the installation of the system:
Whichever ventilation system is chosen, it must have two main properties: competent design and functionality.Only when these conditions are fulfilled in the production premises the microclimate is constantly maintained optimal for health.