Ventilation Systems
Depending on different ventilation requirements, ventilation systems are generally divided into two types: (1) natural air flow system and (2) mechanical air movement (fans). Sometimes it is also combined to provide comfort to the chickens.
Natural air flow system
Ventilated shelters must be exposed to the wind, so place the building on a high site rather than in a low place at least 100 feet away from the side where the prevailing wind enters the building.
Winter Ventilation: Systems for cold weather are much more complicated than for warm weather because houses must be closed tightly for comfort and to conserve energy. Tight enclosures trap the gases, odors, humidity, etc. that must be dealt with continuously for the health of the birds.
Summer Ventilation: A natural air system is used for warm weather conditions in houses with side curtains. This system uses temperature differences and natural air movement to remove excess heat and moisture, and to supply oxygen. 

Mechanical ventilation system
Mechanical air movement is required to properly ventilate a house in all extreme climatic conditions.  They can be divided into two distinct types: (1) negative pressure and (2) positive pressure. 

Negative (Exhaust) System: In the negative pressure system, fans are arranged to expel air from the building.

Positive Pressure System: A positive pressure system uses fans to push air into the building and create a positive pressure.