Does Using Recirculated Air or Fresh Air Save More Fuel in a Car?

[DelStephen]

Using recirculated air is more fuel-efficient than using fresh air. The comparison between recirculated air and fresh air is as follows: 1. When using fresh air, hot air from outside the car is drawn in, cooled by the air conditioning evaporator, and then enters the car. The temperature of the outside hot air before passing through the evaporator is essentially constant and does not change based on how long the air conditioning has been running. Therefore, this cooling process is relatively slow, requiring a longer time to lower the interior temperature to the set value. 2. When using recirculated air, the fan directly draws air from inside the car, which is cooled by the air conditioning evaporator and then blown out through the vents. As the interior temperature drops, the temperature of the air drawn by the fan also gradually decreases. With a fixed cooling capacity of the air conditioning, the temperature of the cooled air blown out through the vents will be lower, creating a positive feedback loop that quickly lowers the interior temperature to the set value. 3. Once the interior temperature reaches the set value, the air conditioning compressor operates intermittently (or at reduced power), which reduces the engine load. Therefore, the faster the interior temperature is lowered to the set value, the sooner the engine load is reduced, leading to a decrease in fuel consumption.

[Juniper]

I've been driving for many years and have noticed that using the recirculation mode does save more fuel, especially during hot summer days. The air conditioner doesn't need to constantly process the hot air from outside, and the internal air circulation maintains a more stable temperature. With the compressor working less, fuel consumption naturally decreases. Once on the highway, I kept the outside air mode on, and the fuel gauge dropped rapidly. After switching to recirculation mode, it became much more stable. However, remember not to use recirculation mode all the time, as it can make the air inside the car stuffy. Just switch to outside air mode every few hours to refresh the air. This not only saves fuel but also makes driving more comfortable, especially in city traffic jams, where recirculation mode reduces the entry of external pollutants, significantly cutting down on fuel costs. I recommend giving it a try and observing the changes in fuel consumption to see the difference.