Installation, starting and adjustment of ventilation and air conditioning systems A Guide
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Production processes may be accompanied by the release of harmful gases and vapors to humans into the air of the working area of the premises, the amount of which depends on the characteristics of the technological process, the degree of sealing of equipment, etc. The content of harmful gases and vapors in the air of the working area should not exceed the maximum permissible concentration (MPC). The maximum permissible concentration is the maximum possible amount of a harmful substance, mg/m3, per unit volume of air, which during the entire working experience does not cause diseases or abnormalities in the health of people working in these conditions, and does not affect subsequent generations. In addition, a large amount of heat, as well as moisture and dust can come from the process equipment. The person involved in the production process is a generator of heat, moisture and carbon dioxide. The heat output of one worker to the environment is 150–300 Watts or more. Every hour from 60 to 400 g of water vapor evaporates from the surface of the human body. Respiratory system produces from 20 to 40 liters of carbon dioxide.
These hazards in the form of excess heat, moisture, harmful gases and vapors enter the surrounding air and blendes in, while its temperature, moisture content, gas content, dustiness increase. This involves changes in the chemical composition and physical properties of the air.
In order to maintain normal air parameters in the premises that meet sanitary and hygienic and technological requirements, we implement ventilation, which creates an organized air exchange-removes polluted air and supplies treated (heated or cooled, humidified or drained) fresh and clean air instead.
Ventilation in most cases can provide only acceptable sanitary and hygienic conditions in the premises. The air parameters, strictly defined by temperature and relative humidity, including optimal ones, can be reached by using air conditioning systems.
Classification of ventilation systems
Ventilation systems are divided into supply systems that supply fresh air to the premises, exhaust systems that remove dirty air from the premises, and air or air-heat curtains that prevent the penetration of cold air through the entrance or doors of buildings during the cold season.
Both supply and exhaust ventilation systems can be general and local type. General exchange systems are designed to supply and remove air evenly throughout the serviced room, to create an air environment with approximately the same parameters throughout the entire volume of the working area. Local exhaust systems remove the air in the places of formation of hazards from technological equipment, preventing the hazards from spreading throughout the entire volume of the room, polluting the entire air of the workshop. Local supply systems supply fresh air near workplaces, create an air shower or oasis – a restricted area in the production room where the parameters of the air environment meet sanitary and hygienic requirements.
Local exhaust ventilation is much more effective than central or general exchange ventilation, since it removes air from the places of formation of hazards with a higher concentration of them, does not allow the hazards to spread freely throughout the room, but such ventilation is not always feasible.
According to the method of air movement, all ventilation systems are either natural or mechanical.
In natural ventilation systems, air movement occurs due to the difference in densities of internal (heated and lighter) and external (colder and heavier) air.
In mechanical ventilation systems, air is moved by a fan or other equipment (a smoke pump, a blower, an ejector, etc.) driven by an electric motor. Mechanical systems are used much more often than natural ones, since the area of action of mechanical systems is much larger, and the cross sections of air ducts are smaller than in natural ventilation systems of the same capacity, due to higher air velocity. So, in the air ducts of natural ventilation systems, the air velocity is 0.5–2 m/s, and in the air ducts of mechanical systems 4–20 m/s.
During the operation of ventilation of any kind in the room, the air is forced to be changed. The ratio of the amount of fresh air supplied to the room for 1 hour to the internal volume of the room is called the multiplicity of air exchange. In real conditions, the multiplicity of air exchange can vary from 0.5 to 20 or more.
In addition to the designed air exchange carried out by ventilation systems, air can enter the premises by infiltration through leaks of windows, walls, doors, gates, etc. due to gravitational (natural) pressure and due to wind pressure. In the same way, air can be removed from the room.
If there are no harmful emissions in the room, then the supply ventilation systems are carried out in such a way that they take part of the air from the outside, and part from the room. This secondary use of air from the room for supply systems is called recirculation. It allows you to reduce the temperature difference between the supply air and the indoor air during the cold season, increase the relative humidity of the air and, most importantly, save heat (in winter) or cold (in summer).
Installation of ventilation systems
Natural ventilation systems can be ductless if air passes only through open apertures in external fences, or are ducted when air moves through ducts.
The operation of natural ventilation largely depends on the action of the wind. The wind, running into the building, creates an overpressure zone on the windward side, and a negative pressure zone on the leeward side. Controlled natural air exchange in the workshops of industrial buildings is called aeration. Such buildings are equipped with lanterns with shutters (transoms) that can be opened manually or by special mechanisms. The same opening valves are provided with window openings in the outer walls. By opening them partially or completely, you can create the required air exchange. Aeration is calculated only for the effect of gravitational pressure, since wind pressure is episodic and, as a rule, increases air exchange. Aeration is usually provided in industrial buildings with significant heat emissions.
The advantage of aeration is that air exchange is created without the help of fans, without consuming electricity. However, aeration provides only general exchange ventilation and does not provide cleaning of supply and exhaust air.
Mechanical ventilation systems can provide local ventilation.
The supply systems of mechanical ventilation supply purified air with a set temperature and, in some cases, humidity to the working area of the workshop to ensure the required sanitary and hygienic conditions for people and equipment inside the building. Mechanical ventilation exhaust systems remove dusty and polluted air, purifying it if necessary before being released into the atmosphere.