Ventilation

 

Topic -Ventilation

It is a process in which air is replaced or exchanged for a particular area to control moisture, odours, smoke, heat, dust airborne bacteria, carbon-di-oxide and maintaining oxygen level.

It has two types first one is

1)natural ventilation in which air is exchanged naturally, no external machine is used

2) the second one is forced Ventilation (Mechanical Ventilation) in which air is exchanged forcefully by means of fans.

Ex. Kitchens exhaust, Basement (car park) exhaust.





Types of ventilation Fan mostly used

1) Wall Mounted Propeller fan

In this type of fan air flows in parallel to the shaft.

A wall-mounted fan is a machine used to create flow within a system, typically a gas like air.

 It consists of a rotating arrangement of vanes or blade which act on the fluid. Usually, it is contained within some form of housing or case. This may direct the airflow or increase safety by preventing the object from contacting the fan blades.

Mostly these types of fan use in toilet, pantry for exhaust and fresh air purpose.






2) Inline Centrifugal fan

A centrifugal fan is a fan in which air flows in a radial or perpendicular direction relative to the fan shaft. This fan is specially designed to be connected to ductwork in direct line with discharge from housing.

 These fans contain scroll-shaped fan housing. it is available in circular and cabinet. It is mostly used for because it offers to speed controllable, maintenance-free, can be installed outside.





3) Axial Fan

It is mostly used for commercial application. It uses axial forces to achieve movement of air or gas, spinning a central hub with the blade extending radially from its outer diameter. The fluid moves parallel to the fan wheels shaft or its axis of rotation.

An axial fan consists of much fewer blades i.e., two to six, as compared to the ducted fan.

Axial fans operate at high specific speed i.e., high flow rate and low head and hence adding more blades will restrict the high flow rate required for its operation.

The axial fan wheel is often contained within a short section of cylindrical ductwork, to which inlet and outlet ducting can be connected.

Axial fan available of two type

Vane axial

These axial flow fans have a higher-pressure capability due to the presence of static vanes.

These fans highly efficient as compared to tube axial fan.

Tube axial

These are axial fan units with fan wheels located in cylindrical tubes, without inlet or outlet dampers. It has medium pressure, high flow capability.





4) Roof Mounted fan

Roof exhaust fan generally exhausts the air out of the building. It mostly called Roof Extractor.

It has a simple design and suitable for fixing on the inclined roof. The equipment contains one M.S. cowl for rain protection, Axial Flow Fan having cast aluminium alloy impeller of aerofoil design fitted on motor's shaft. It is better suited for relatively clean air systems, Roof exhaust fan suitable for commercial application like warehouses, hospitals, retails stores.





5) Jet fan

This type of fan develops for ventilation in tunnels and now it is widely used in basement car parking areas also. It works by propelling. A small jet of air at extremely high velocity which causes surrounding air to be entrained and in a confined space like a tunnel or car park. It is used to reduce ductwork and to drive the smoke toward extract fan to keep pollution within the acceptable limit.








Ventilation air quantity the calculation for fresh /Exhaust air

Fresh air

Formula(Q) -      N x V

N-Air change rate

V-Volume of room (m³)

Q-Fresh air quantity (CMH)

Air change Rate(N)

1.General space - 4ACPH

2.Auditorium - 8 to15 ACPH

3.Bakeries/Bars- 20 to 30 ACPH

4. Class Room-6 to 20 ACPH

5. Pump rooms-5 ACPH

6.Residential toilet-8 ACPH

7.Commercial kitchen & toilet-12 to 15 ACPH

8.Office-3 to 4 ACPH

9.Computer Room-15 to 20 ACPH

10. Warehouses-6 to 30 ACPH

11. Theaters- 8 to 15 ACPH

12.Substation, electric-5 to 10 ACPH

13. Museums-12 to 15 ACPH

14. Cafeterias-12 to 15 ACPH


Exhaust air

Formula(Q) - (N x A x H)/60

N-Air change rate

A-Area of room (SQFT)

Q-Exhaust air quantity (CMF)

H-Height of room (Ft)

Air change Rate(N)

1.Basement parking-15 to 30 ACPH

2.Commercial Kitchen & toilet-15 to 30 ACPH

3.Lab-6 to 12 ACHP

4.Warehouse-1 to 2 ACPH

5.Smoking room-10 to 15 ACPH

6.Residential toilet-10 to 15 ACPH

7.Classroom-3 to 4 ACPH

8.Smoke exhaust

Basement -30 ACPH &

Above Gr. Floor ACPH

 


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