Heating ventilation and air conditioning system is also called as HVAC.Heating ventilation and air conditioning systems play an important role in the air supply of any room, building or area.Installation of HVAC in pharmaceutical industries is the requirement of cGMP and other legal agencies.
H of HVAC represents heating. Heating is done either by electric heaters or by the use of circulating hot water.
V of HVAC is for ventilation. Ventilation is the process of replacing the room air with fresh or processed air, removing odour, gases or microbes from a room or building.
AC of HVAC is for air conditioning, it provides cooling and maintains the humidity of the room or building.
Key Points to Discuss
In this topic, we will discuss the following,
- Working Principle of HVAC
- Functions of HVAC
- Types of HVAC
- Components of HVAC
In components of HVAC, we will learn about
- Air Handling Unit or AHU
- Ducts
- Diffusers and Grills
In Air Handling Unit we will learn about all the parts of the air handling unit or AHU such as
- Metal Housing
- Mixing box or Mixing chamber
- Filters
- Cooling Coil
- Heating Coil
- Fan or blower
- Dehumidifier
- Humidifier
Working Principle of HVAC
HVAC usually works on the principle of purification and recirculation. Air from the environment is filtered, processed by heating or cooling and is supplied to the room or building through ducts called inlet ducts and this supplied air is removed from the area or room by the outlet ducts or return ducts. Some portion of this returned air usually 15-20% is exhausted in the environment and the remaining portion is again entered into the air handling unit for recirculation.
Some portion of the fresh air usually 15-20% enters into the air handling unit and is mixed with returned air in mixing box. It is again filtered, processed and is supplied to the room or building.
The return air of the areas dealing with poisonous substances or chemicals producing harmful fumes is fully exhausted to the environment by HVAC so no recirculation of air takes place in these areas because it may be harmful to the people who are working in those rooms or building.
Functions of HVAC
Main functions of heating ventilation and air conditioning system or HVAC are given as follow
- HVAC is used to purify the air.
- HVAC is used to control the temperature of the room or building.
- The humidity of the room is also maintained by HVAC.
- HVAC is used to create a pressure difference between two adjacent areas or rooms in pharmaceutical industries.
- HVAC is used in pharmaceuticals to prevent cross-contamination.
- HVAC is used to maintain air changes per hour of the room or area in pharmaceutical industries.
- It removes dust from processing rooms or areas.
Types of HVAC
There are two types of HVAC which are as follow
- Ducted HVAC
- Non-Ducted HVAC
Ducted HVAC
As the name indicates that the ducted system consists of ducts.
The air in this system is transferred through ducts.
It is of following two types
- Chilled Water System
- Dx System
Chilled Water System
In the Chilled water system, circulating chilled water is used to cool the air.
Dx System
In Dx system, refrigerating gases are used to cool the air.
Non-Ducted HVAC
As the name indicates that this system has no ducts and the air is supplied directly into the room or area by an indoor unit.
Example
Examples of the non-ducted system are as follow,
- Window AC
- Split AC
Components of HVAC
Following are the main components of HVAC or Heating ventilation and air conditioning system.
- Air Handling Unit or AHU
- Ducts
- Diffusers and Grills
Air Handling Unit or AHU
The air handling unit is a closed box which we see usually on the roof of buildings and in many pharmaceutical industries. It is the main component of HVAC and is also known as the respiratory system of HVAC or the lungs of heating ventilation and air conditioning system.
One side of the air handling unit is attached with the duct returning from the room or an area and the other side of AHU is attached to the duct which supplies air to the room or an area. Air handling unit consists of following main components.
- Metal Housing
- Mixing box or Mixing chamber
- Filters
- Cooling Coil
- Heating Coil
- Fan or blower
- Dehumidifier
- Humidifier
Metal Housing
The outer body of the air handling unit which contains all the components is called the housing of the air handling unit and it is made of metal.
Mixing box Or Mixing chamber
Returned air from a room or a building enters into the air handling unit through return duct and the fresh air from the environment enters into the air handling unit through fresh air duct. Both returned and fresh air are mixed in a chamber of AHU called mixing box or mixing chamber. It is called a mixing box because in this box both return and fresh air are mixed.
Filters
Filters are installed in the air handling unit and are of following types
- Standard Filters
- Aerosol Filters
1.Standard Filters
Standard filters or of following types,
- Coarse Filters
- Medium Filters
- Fine Filters
Coarse Filters
- Coarse filters are the first line of defence filters.
- Coarse filters are also known as primary filters or panel filters.
Coarse filters are classified as
- G1 Filters
- G2 Filters
- G3 Filters
- G4 Filters
Medium Filters
Medium filters are classified as
- M5 Filters
- M6 Filters
Fine Filters
Fine filters are classified as
- F7 Filters
- F8 Filters
- F9 Filters
Medium and fine filters include bag filters.
These are also known as the second line of defence filters or secondary filters.
2.Aerosol Filters
Aerosol filters are classified as
- EPA Filters (Efficient particulate air filters)
- HEPA Filters (High-Efficiency particulate air filter)
- ULPA(Ultra-low particulate air filter)
Classification of Aerosol filters.
Aerosol filters are also known as the third line of defence filters or tertiary filters.HEPA filters can be installed in the air handling unit or terminally in the diffusers of supply air ducts.
Query:
HEPA filters are more effective when installed in AHU or in Diffusers?
Reply in the comments section below the post.
Note:
- Aerosol or tertiary filters are sensitive filters so primary and secondary filters protect the tertiary filters. If we do not use pre-filters or bag filters mean primary and secondary filters then all the dirt, debris of the outside air will block the HEPA filters in a short period.
- HEPA filters can not be washed but we can wash bag filters and pre-filters so the life of HEPA is increased by using pre-filters and bag filters.
Cooling Coils
Cooling coils are installed in HVAC to cool the air. Air after filtration is passed through the cooling coils and is cooled.
Types of cooling
There are two types of cooling which are as follow
- Indirect cooling
- Direct cooling
Indirect cooling
Indirect cooling is also known as chilled water cooling. It is called indirect cooling because in this type of cooling first of all water is chilled and then this chilled water is circulated with the help of pump in a coil of AHU and then this chilled water is used to cool the air.
The chilled water is cooled in the chiller and is supplied through pipelines to the cooling coils of AHU. It circulates in coils and when air comes in contact with the cold water it becomes cool. The chilled water enters in coils form one side and from another side it returns towards the chiller. The heat of the water in the chiller is removed by a tower where the heat in the water is removed and water comes down in chiller barrel and is again cooled and pumped to the AHU and this cyclic process goes on.
Advantages of Indirect cooling
Following are some advantages of the indirect cooling system
- It can easily be used for long-distance.
- Cost is less than the Dx type system.
Disadvantages of InDirect cooling
- Extra space is required for installation of the chiller.
- Long pipelines are required for transferring of chilled water to the cooling coils.
Direct cooling
Direct cooling is also known as Dx type cooling or direct expansion. In this system, the air is cooled by the refrigerating gases which circulate in pipes.
Advantages of Direct cooling
- It is more efficient because it directly cools the air.
- Long pipelines are not required.
- The chiller plant is not required.
Disadvantages of Direct cooling
- It is effective for a short distance.
- Leakage of gas may occur.
Heating Coils
Heating of air in air handling unit is done by two ways which are given as follow,
- Direct Heating
- Indirect Heating
Direct Heating
In direct heating, the air is heated with the help of heaters and heaters may be of two types which may either electric heaters or gas heaters.
Indirect Heating
In indirect heating hot water is produced by the boiler which is then circulated in the heating coils of air handling unit. When air passes through these coils then the air is heated by the hot water
Fan or blower
A fan or blower is installed in the air handling unit to supply the air after processing,to the room or building.
Dehumidifiers
The humidity of air can be removed in the air handling unit by using either a heating or cooling mechanism or by the use of a rotating silica beads wheel.
Rotating wheel contains silica beads which absorb moisture from the air when it passes through the wheel.
Humidifiers
In extremely cold conditions, the humidity of the air may be very low so it is required to add some humidity in the processed air and It is done by following,
- Using a shower of water.
- By evaporation of water.
2. Ducts
Ducts of HVAC are like the veins and arteries of the human body. Veins and arteries supply blood but ducts supply air. There are following types of ducts.
- Supply Air Ducts or SAD
- Return Air Ducts or RAD
- Fresh Air Ducts or FAD
Supply Air Ducts or SAD
Supply air ducts or SAD are like arteries. As we know that arteries carry clean blood in the same way, supply air ducts carry processed or cleaned air. Supply air ducts are used to supply the cleaned, processed air to the area or building.
Return Air Ducts or RAD
Return air ducts or RAD are like the veins of the human body. As we know that veins carry uncleaned blood in the same way return air ducts collect uncleaned air from the cleaned area or room and deliver it back to the AHU for cleaning and recirculation.
Fresh Air Ducts or FAD
Fresh air ducts are used for supplying the fresh air to the mixing chamber of the air handling unit.
Note:
- The volume of supply, return or fresh air is controlled by the dampers.
- We can increase or decrease the volume of air by changing the position of dampers.
3.0 Diffuser and Grills
Grills and diffusers are used at the end of supply ducts facing down inside the room or at the face of return ducts inside the room or area.
Diffusers
- Diffusers are installed at the end of inlet ducts or supply ducts, usually facing down inside the room.
- Diffusers are used to supply the conditioned air in a specific direction or pattern.
- Diffusers showers and spread the air in a wide area.
- When HEPA filters are used terminally then these are installed above the diffusers.
Following main types of diffusers are used,
- Swirl Diffusers
- Perforated Diffusers
- Plain Diffusers
- Jet Diffusers
Grills
Grills are installed inside the room or area at the face of return ducts.
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