Final answer:
The two main methods used for air ventilation are natural ventilation and mechanical ventilation. Natural ventilation occurs when air moves through opened windows and doors, while mechanical ventilation involves the use of fans and air-handling systems.
Step-by-step explanation:
The two main methods used for air ventilation are natural ventilation and mechanical ventilation. Natural ventilation occurs when air moves through opened windows and doors. This type of ventilation is caused by temperature differences between indoors and outdoors and by wind. Mechanical ventilation, on the other hand, utilizes devices such as fans and air handling systems to actively remove indoor air and bring in filtered and conditioned outdoor air. The rate at which outdoor air replaces indoor air is known as the air exchange rate.