What are the functions of internal and external circulation?
3 Answers
Internal circulation refers to the recirculation of air inside the vehicle, which helps maintain the interior temperature more effectively. External circulation involves the exchange of air between the inside and outside of the vehicle, improving air quality. Internal and external circulation are two modes of air circulation in a car. Internal circulation means that air only circulates within the vehicle, with no exchange between the inside and outside air. This mode is commonly used when running the air conditioning in summer or the heater in winter, as it allows for quicker cooling or warming. It also effectively prevents dust and harmful gases from entering the cabin when outdoor air quality is poor or there are unpleasant odors outside, keeping the interior air clean and fresh. External circulation, in contrast, enables real-time air exchange between the inside and outside of the vehicle. Stale air inside the car is expelled, while fresh outside air is drawn in. When using the air conditioning in summer or the heater in winter, external circulation helps replenish fresh air, improving cabin air quality and increasing oxygen levels, thereby preventing driver drowsiness caused by prolonged use of internal circulation. External circulation is also frequently used for defrosting in winter and defogging on rainy summer days.
Having driven for over a decade, I frequently use the recirculation and fresh air modes to adapt to different road conditions. Recirculation mode keeps the interior air circulating without bringing in outside air, making it ideal for heavily polluted urban areas or traffic jams—it prevents exhaust fumes from entering the cabin, maintains AC cooling or heating efficiency faster, and helps save fuel costs. Fresh air mode, on the other hand, acts like opening a window for ventilation, drawing in outside air. It quickly defogs windows during rainy weather, ensuring clear visibility; in summer, switching to fresh air mode periodically prevents stale, stuffy air when using AC. The key is flexible timing: use fresh air mode on highways to stay alert and recirculation mode in tunnels to avoid smoke and dust. Remember not to keep recirculation on too long, as rising CO2 levels may cause dizziness and impair driving. Developing a habit of automatic adjustment ensures a more relaxed and confident drive.
I have some interest in automotive technology and have figured out the basic functions of the internal and external air circulation systems. Internal circulation is equivalent to the vehicle's air recirculation system, which does not draw in outside air, allowing for rapid cooling or heating, improving efficiency and saving fuel when using the air conditioning. External circulation draws in fresh air from outside, increasing oxygen supply, defogging and dehumidifying, and preventing odor buildup. The core purpose of these two functions is to regulate air quality: use internal circulation on smoggy days to avoid PM2.5, and switch to external circulation for a few minutes every hour during long drives to prevent carbon dioxide poisoning. Many cars also have an automatic mode that intelligently switches between the two, making it easy for novice users like me to simply press a button to set it up. This enhances driving comfort without requiring time to study complex mechanisms.
