Why is the air volume greater in car's internal circulation than external circulation?
2 Answers
Car's internal circulation has greater air volume than external circulation because internal circulation not only needs to cool but also dehumidify, hence requiring more airflow. Below are detailed explanations about car's internal and external circulation: 1. Differences: Generally, external circulation is used when outside air quality is good, while internal circulation is used when outside air quality is poor. Additionally, external circulation should be used on highways, and internal circulation should not be used for prolonged driving. 2. Precautions: Driving on highways often involves long-distance travel, requiring the use of external circulation due to extended driving time. If internal circulation is used, because the vehicle is sealed and air cannot exchange with the outside, oxygen inside the car is consumed by breathing, leading to decreased oxygen levels and making the driver more prone to fatigue.
I've pondered this question for quite some time and eventually realized it fundamentally comes down to different air sources. When using recirculation mode, the AC directly draws air from the cabin interior. Since the air is confined within the compact cabin space, the blower encounters almost no resistance when sucking it in, resulting in naturally strong and forceful airflow. However, fresh air mode requires drawing outside air - this process is much more laborious. The air must first break through the resistance of the front grille, then navigate through complex duct labyrinths, and finally get filtered by the cabin air filter like passing through a sieve. Each layer of obstruction reduces airflow volume, making the final output noticeably gentler. This is especially noticeable when using fresh air mode at highway speeds - you can distinctly feel the blower struggling against airflow resistance.
