Internal circulation refers to the state of a car's air system where the air exchange channels between the inside and outside of the vehicle are closed. When the fan is off, the air inside the car does not circulate; when the fan is on, the airflow drawn in comes solely from within the vehicle, creating an internal air circulation loop. The primary function of internal circulation is to promptly and effectively prevent external dust and harmful gases from entering the car. It helps warm up the car faster in winter and cool it down more quickly in summer when the air conditioning is on. It can also be used during smoggy days. Essentially, internal circulation keeps the air inside the car recirculating, maintaining the interior temperature more effectively. While it aids in faster heating or cooling, it's important to note that internal circulation should not be used for extended periods while driving. The car cabin is a relatively sealed environment, and prolonged use of internal circulation can reduce oxygen levels inside, leading to fatigue and drowsiness, which can compromise driving safety. When to Choose Internal vs. External Circulation: Consider road conditions: On highways, use external circulation. Firstly, due to wind resistance and high speeds, opening windows is impractical. Prolonged use of internal circulation can cause brain hypoxia, impairing reaction times and judgment, which is highly dangerous. Secondly, air quality on highways is generally good, with low exhaust concentrations, making external circulation a viable option. In congested urban areas or during rush hours, where vehicle exhaust levels are high, it's advisable to switch to internal circulation. Consider the car's condition: New cars often contain higher concentrations of toxic gases like formaldehyde. For the first three to six months after purchasing a new car, it's recommended to use external circulation along with opening windows to enhance air circulation and dilute the toxic gas levels inside. Consider air quality: In regions where PM2.5 pollution is severe (PM2.5 levels above 50), and air quality is not good, it's best to use internal circulation to avoid inhaling excessive PM2.5 particles. The Role of External Circulation: External circulation ventilates the car, expelling stale, oxygen-depleted air and bringing in fresh air. In winter, if the heater is on, remember to switch to external circulation to prevent dizziness and chest tightness.
