HVAC System Working Principle

HVAC is an important regulatory requirement for cleanrooms of pharmaceutical industries. HVAC stands for heating ventilation and air conditioning system and in this article we will discuss the working principle of HVAC meaning how HVAC works. 

HVAC works on the principle of air filtration/purification and circulation or recirculation. 

If you are not familiar with the basic structure and components of HVAC then must read the following article to have a brief overview of the HVAC structure function and components because this article will only discuss the working principle in detail.

HVAC or Heating Ventilation & Airconditioning System.

Working Principle

When the blower of the HVAC is on it draws the air from the environment & this air is passed through a series of filters to remove contaminants.

After filtration this air is passed through heating and cooling coils & finally delivered to the area or room after passing through HEPA filters.

HVAC working


The air from the environment is first of all filtered by the mesh filter to remove leaves,threads & larger particles & then this air is filtered through the bag filter to remove fine particles.When the air purification process is done then this filtered air pass through the heating coils or cooling coils & sometimes from both coils depending upon the requirements.

This filtered and treated air is supplied to the cleanrooms or area through the supply air duct (SAD).

This treated air passes through the HEPA filters installed at the end of the supply air duct to ensure the removal of very fine particles and microbes.

After passing through HEPA filters the air is supplied by diffusers to the area or cleanrooms.

The air from the cleanroom or area is supplied back to the AHU or air handling unit of HVAC through the return air duct or RAD.

Generally 10% of the return air is exhausted & 90% is taken for recirculation.The 10% exhausted air compensation is done by taking the fresh air from environment through fresh air duct or FAD.

Through RAD the air enters into the mixing box of AHU & again the cycle is repeated.

Depending upon the requirements for areas dealing with dangerous materials,all the air collected from the room is exhausted and 100% fresh air is taken from the environment for filtration and circulation.

Image Credit

Image Source – Google | Image By – Berkeley Lab

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