Mechanical Ventilation System Fans: Types, Components & Working Principles

In this article, I will share the types of fans used in mechanical ventilation systems, their main components and their working principles.


If you are left behind and don’t know how ventilation systems work then you should read the article below.


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Mechanical ventilation systems make pretty good use of the fans to either forced air into the building or extract it.


You have to know that we have natural ventilation and mechanical ventilation systems.


The natural ventilation system doesn’t use fans but it depends on the leeward and windward sides, while the mechanical ventilation system makes use of fans.


For you to understand how natural and mechanical ventilation systems work you should consider reading more about that topic.


Now that you are aware that mechanical ventilation system uses fans, let me enlighten you more about them.


Types of fans used in mechanical ventilation systems;

There are three types of fans that I will discuss in this article namely;

  • Propeller fan.
  • Axial fan.
  • Centrifugal fan.


Propeller fan: main components and working principles

The main components of this fan are these;

  • Impellers.
  • Electric Motor.
  • Casing with fixing points.



Propeller fans are usually placed at free openings of windows or walls to either push air within a building or extract it out.


It is usually used in low-pressure applications in a mechanical ventilation system.


Propeller fan is NOT usually employed for ducted ventilation systems because of their capacity.


They can’t handle a large volume of air since they are used in low-pressure application areas.


This fan won’t have the power to supply or extract air from a ducted system thus leading to ineffective ventilation within a space to be conditioned.


If they are to be used in a ducted ventilation system then it has to be ducts of a very short length.


Propeller fans can only develop a pressure of about 12.5 Pa and that is why propeller fans can’t be used in long ducted ventilation systems.


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Propeller fans have two types of blades which are namely; broad curved blades and narrow blades.


If you want a propeller fan that can move air and it’s very quiet then you should think of using broad curved blades.


This is because the broad curved blades provide a large surface area to handle the air compared to narrow blades propeller fans with the same diameter.


The other thing that you should know about propeller fans is that they operate up to 50% efficiency.


The advantage of using propeller fans is that; they have cheap installation costs, they are easy to install and they can remove a large volume of air.


Centrifugal fan: Main components and working principle.

You should not confuse a centrifugal fan with a centrifugal pump or compressor.


We are talking about a fan.


The main components of a centrifugal fan are these;

  1. Impeller blades (paddle blades)
  2. Electric motor.
  3. Scroll-shaped casing.
  4. Pulley.
  5. Inlet and Outlet.


The impeller blades revolve inside the scroll-shaped casing creating a suction that draws the air within the fan through the inlet. When the air enters the casing, it’s forced out by the blades rotating at high speed.


The pressure of the air is developed by reducing the velocity of air using the diffuser within the casing thus leaving the casing through the outlet under very high pressure.


The working principle of a centrifugal fan is quite similar to that of a centrifugal compressor.


The blades of the centrifugal fan can either be forward or backwards curved with a constant thickness or aerofoil section.


The forward blade is suitable for constant air resistance while the backward blade is suitable for variable air resistance.


Centrifugal fans can develop a very high pressure of about 760 Pa and that is why they are very appropriate in long ducted ventilation systems.


They are also quiet when operating which is an advantage but they are bulky, this is one thing that when choosing to install them one has to think about.


Centrifugal fans have higher efficiencies compared to propeller fan which ranges from 45 to 85%


The volume of air and the pressure that can be supplied by this fan can be varied by changing the speed of the motor or being coupled to a bolt drive which permits the change of pulley size to suit the fan’s speed.


The centrifugal fan comes with difficult to install because the inlet is 900 to the outlet, to make the installation easier, the only thing that one will have to do is to align the ducts the same way as the fan, which we all know it won’t work in most cases.


Axial fan: Main components and working principles.

The main components of an axial fan are these;

  1. Impellers.
  2. Duct flange.
  3. Electric motor.
  4. Cylindrical casing.


The fan consists of blades with an aerofoil section which draws air inside the duct systems and supplies it to the needed areas.


Axial fans can develop a pressure of about 1500 Pa which is a little bit higher compared to centrifugal fans.


This type of fan is usually fitted inside the ductwork of the ventilation or air conditioning systems.


This fan is mostly in place of a centrifugal fan because it’s easier when it comes to its installation.


The axial fan also deals with a large volume of air just like a centrifugal fan, which means that it supplies a large volume of air to the required space.


Axial fan offers two types of fans, which are axial fan flow and bifurcated axial fan flow.


Bifurcated axial fan flow extracts hot air from foundries and flue gasses in chimneys.


Final thoughts.

You have to understand that each fan works differently in the area of application depending on the work that it’s supposed to do.

Before you choose a specific type of fan to use in your ventilation system you have to understand its capacity.

If you select a fan with a greater capacity then you are likely to have a good ventilation system since the effectiveness of these systems depends mainly on the extraction and supply of air.

Ensure to do your research effectively before you choose any type of fan depending on the information you have obtained from this article.

Thanks so much for reading, if you have any questions you should leave your comment.


See you in my next article.

  1. Factors To Consider When Choosing Air Conditioning System
  2. Air Conditioning Systems (All-water & All-air system)
  3. Two-Stage Refrigeration Cycle Using A Flash Chamber: Working Principle
  4. Refrigeration Condensers: Functions, Types & Maintenance

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