The working of a ventilation system is broadly explained based on two phenomenon in the system i.e. inlet and outlet of air inside the work place and the circulation of the air inside the work place. These two will decide the working of the system. For different kinds of ventilation systems, the operations may not be the same.
Inlet and Outlet of air in the Ventilation System
- The removal of contaminated air and the inlet of fresh air is the main use of the ventilation system. This can be done by the aid of fans and tubes. When the fans are in action, they will change the direction of air or let the motion of the air to be fast.
- Then the air with the motion is allowed to pass through the series of tubes where it is moved out of the working environment as in case of local exhaust or it is mixed with the fresh air in order to make the contaminated air less toxic in the working environment.
- The inlet and outlet movement of the gas or the contaminated air is done by fans and the gases are captured due to the presence of a small nozzle type arrangement called as hood which will not allow the gases to exit from the tubes.
- Take the case of dilution system, in which the inlet air is let into the ventilation system and just made to move from one side of the working place to the other place where it is let out of the tubes by the aid of the exhaust fans.
- Similarly, take the case of the local exhaust system, in which the air is let in at a place and just let out from the other place. Air in the local exhaust system is also subjected to air cleaning.
Circulation of air inside the building
- The circulation of air is to be done in dilution type of ventilation system. The circulation just reduces the concentration of the toxic air inside the working area.
- Circulation of air also involves heat recovery system which maintains nominal temperature in the working area. The circulation is also done by the aid of a blower which will allow the air, in more concentrated area to move to the area in the lower contaminated air or fresh air.
- The main advantage of air circulation is, we need not take fresh air every time from the surroundings and liberate the contaminated air outside. It also saves the excess work.
- Circulation is also performed by creating low pressure region within the working environment so that the contaminated air can be mixed together attaining equilibrium of the pressure.
In a ventilation system, we can either circulate air inside or move the contaminated air completely outside the work place or we can have both in a single system.
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Every mechanical system has parts that make the working easier. In ventilation system too there are certain parts which make a complete system.
Mechanical parts of the ventilation systems
The mechanical systems consists of the series of tubes, air cleaner, blower etc. The mechanical arrangement for a dilution type ventilation is different that of the local exhaust system.
- The system must have tubes as it will cause the air to move from one place to another place.
- They can be made of different materials and different sizes depending upon the requirement of the industry.
- The tubes may also get corroded as they may be exposed to the toxic gases present in the working area when they are made of any kind of a metal.
- These tubes have perforations on their surface area in order to inhale the gases or the contaminated air.
- Air cleaner
- Air cleaner is usually used in the local exhaust type in order to remove the contaminated air which is taken by the ventilation at the very source.
- This usually requires a electric power in order to run the air cleaner. Size of the air cleaner may be determined by the type of the industry.
- In case of industry with toxic gases liberation the chemical process such as oxidation and hydration is carried to remove the gases from the air.
- In case of material contaminated air a centrifuge is used in order to remove the materials.
- When a centrifuge is implied, it rotates the contaminated air so that higher weight particles will be settled down.
- Blower is sometimes used in order to forcibly make a change in the direction of the air.
- This is used with the dilution type, in order to make the contaminated air mix with the non-contaminated air.
The ventilation system consists of different types of fans such as tube pressurizing fan and exhaust fan.
- Tube Pressurizing Fans
- This tube is usually present at the beginning of the source where it takes the contaminated air into it.
- This fan creates low pressure inside the tube so that the gases will travel quickly inside the tube.
- These can be made of either iron based alloy and aluminum alloys.
- Their working is very easy, they just create a low pressure in a region so that the air present around it will be inhaled creating an equilibrium.
- The surroundings of the pressurizing fan are to be fitted tight, in order to prevent the leakage of contaminated air.
- Exhaust Fans
- These fans are usually placed nearer to the outside environment.
- The exhaust fans just let the contaminated air go outside the working environment.
- These are similarly made of alloy steel or an aluminum alloy.
- Exhaust fans are used to create a high pressure so that the contaminated air will be exhaled out to attain the equilibrium.
- The exhaust fans surrounding are also to be air tight in order to prevent the leakage of air into the workplace.
There are many other parts in the ventilation system such as hoods, shutters, air filter etc which also play an important role in the working of the ventilation system.
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The ventilation system is mainly classified into two types depending upon the movement of air flow inside the work place. These two kinds have their own advantages and disadvantages. The two kinds are – dilution type ventilation system and the local exhaust type ventilation system. The local exhaust system is a bit costly system than the dilution ventilation system.
- As the term says ‘dilution’, the air inside the working area is mixed with the fresh air in order to make the contaminated air less polluting to the people inside the working area.
- This type of ventilation system is generally used when the working area is less and the polluted air is not chemically toxic.
- The working of this type is very simple. It uses a simple exhaust fan which directs the air to flow from one direction to another direction i.e. from the more polluted side of the work place to the less polluted side.
- One of the limitations of the dilution ventilation system is that the contaminants are not completely removed from the work area. This may have an effect on the people when they have long term exposure to the moderately contaminated air.
- So, it may not be effective in industries which deal with poisonous gases. As the system uses a simple exhaust fan to blow the air, it may not direct the air completely inside the work area.
- It also requires large amount of fresh air that has to be circulated inside the work area.
Local Exhaust Type
- In local exhaust type, the ventilation system is fixed at the beginning of the source of contaminated air where it completely sucks the polluted air and discharges it outside.
- In this type, the contaminated air is replaced with the fresh air. It uses a series of tubes, a hood which absorbs the contaminated air, an air cleaner, and a couple of fans.
- Local exhaust type is usually used when the contaminated gases are more toxic that may cause series of health problems with minute exposure to the gas. In most of the pharmaceutical industries this kind of ventilation system is used in order to remove the contaminated air in the work place.
- Some limitations of this type are that it is of high cost and maintenance should be done regularly.
- A skilled person is required for cleaning the parts of the system and for its maintenance.
- As the parts of the system are exposed to the toxic gases, they may get corroded. Installation is a bit difficult when compared to the dilution type.
Depending on the work place and the level of contamination in the industry, a right ventilation system has to be installed.
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