Mainly ventilators are classified according to their power source, drive mechanism and cycle mechanism. Ventilation systems may be classified based on their ability to supply and withdraw air from the rooms ventilated. The below are the various principles on which ventilators are classified.
The Shortcut Principles: The ventilation system is “short cut” when the make up air is withdrawn from the room before it has been in the people operating zones. Short cut principles generally reduce the efficiency of the ventilators.
Mixed Principles: With a ventilation system based on the mixed principle, make up air is supplied to the room with high speed, and/or local fans are used to mix the air in the room to obtain a homogenous mass. The mixed principles are:
- Suited in general for ventilation, cooling and heating.
- Where homogenous temperature in the room are required.
- Where homogenous pollution concentration in the room are required.
Displacement principles: With the displacement principle heat and pollution is transferred from the residence zone close to the floor, up to the ceiling where it is sent out through the outlet system. Make up air is supplied with low velocity very close to the floor. The supply air is normally colder than the average air in the residence zone. The evacuated air close to the ceiling is warmer than the average air in the residence zone. The displacement principles are
- Heat and pollutants are transferred throughout the room.
- Heat supplied under the ceiling have limited influence on the temperature of the room.
- The cooling temperature of the air suppliers are limited to some degree.
- Under the temperature in the residence zone.the level of pollution in the residence zone is less.
The displacement ventilation system is suited for ventilation and cooling system.
Position principles: In a ventilation system based on the piston principle, the supply air moves through the room with piston. The piston principle can be regarded as an extreme variant of the displacement of the system with a minimum of turbulence in the air flow through the room.
The above are the major principles on which ventilators are classified.