Which consumes more fuel, the car's internal circulation or external circulation?

[VanAdrian]

Using internal circulation is more fuel-efficient than external circulation, but in practical use, the difference is negligible. Relevant explanations are as follows: 1. When external circulation is on, the hot air drawn from outside the car is cooled by the air conditioning evaporator before entering the car. The temperature of the outside hot air remains relatively constant before passing through the evaporator and does not change with the duration of air conditioning use. Therefore, this cooling process is relatively slow, requiring a longer time to reduce the car's interior temperature to the set value. 2. When internal circulation is on, 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 decreases, the temperature of the air drawn by the fan also gradually lowers. With a constant air conditioning cooling capacity, the temperature of the cooled air blown out from the vents will be lower, creating a positive feedback loop that quickly reduces the car's interior temperature to the set value.

[VonLeila]

Speaking of this issue, I've been driving for over a decade and have always been thinking about how to save some money on fuel. Between the car's internal and external air circulation, which one consumes more fuel? I think it's the external circulation that uses more fuel. Because internal circulation only reuses the air inside the car, the air conditioning system doesn't have to work as hard to process the hot or cold air coming from outside, making it easier on the engine and thus lowering fuel consumption. Although the difference in cost isn't huge, small savings add up over time. When I'm stuck in city traffic, I use internal circulation, which allows the air conditioning to cool down quickly, and I feel like I'm saving a bit of fuel. Of course, don't keep the internal circulation on all the time, as it can lead to stale air and affect health. Occasionally switching to external circulation for fresh air, especially on highways or in less polluted areas, allows you to breathe fresh air without consuming too much fuel. From a daily perspective, switching between them appropriately is the most cost-effective strategy, saving money while staying comfortable.

[DiRiver]

As someone who enjoys studying cars, I often test the impact of air conditioning systems on fuel consumption. Simply put, using recirculation mode is more fuel-efficient than fresh air mode. The reason is that fresh air mode requires drawing external air into the cabin and then heating or cooling it, which forces the compressor to work harder, increasing engine load and slightly raising fuel consumption. Recirculation mode only processes the air already inside the cabin, resulting in lower load and naturally better fuel efficiency. However, this isn't absolute—for example, in dusty areas or places with unpleasant odors, fresh air mode may consume slightly more fuel but filters out dirty air, making it more important for health. I've also noticed that when setting higher AC temperatures, using recirculation mode cools the cabin faster, while in winter, it helps warm air circulate more efficiently, saving both time and fuel. Overall, fuel savings are a minor advantage, but they add up nicely during long-distance driving. Choosing between modes depends on the environment—finding the right balance is the smartest approach.

[SanJuliana]

I have extensive experience driving trucks for transportation, and fuel consumption is a daily concern. Between recirculation mode and fresh air mode, the latter definitely consumes more fuel. In the past, when I used fresh air mode, the fuel gauge would always spike, especially during hot summer days when the air conditioning had to process the hot outside air, putting more strain on the engine. Switching back to recirculation mode speeds up air circulation and reduces fuel consumption a bit. However, I suggest not focusing solely on saving money—ventilation is crucial. For example, when the truck is fully loaded and recirculation mode is used for too long, the air can become stale, possibly causing dizziness. On highways, I often use fresh air mode to ventilate, accepting slightly higher fuel consumption for safety. In summary, recirculation mode wins in terms of fuel efficiency, but safety comes first.

[OEmery]

As an environmentally conscious individual, I pay close attention to energy efficiency. Using the car's air conditioning in recirculation mode is generally more fuel-efficient than fresh air mode. This is because it reduces the energy required to process outside air, lowering the load on the AC system and allowing the engine to operate more efficiently, resulting in slightly lower fuel consumption. This helps reduce your carbon footprint and is more eco-friendly. However, don't overlook health factors – while fresh air mode consumes slightly more fuel, it introduces fresh air to prevent CO₂ buildup. I recommend using recirculation mode more often in urban traffic jams or during heatwaves to save fuel; switch to fresh air mode in mountainous areas or clean environments. Small habits like this can contribute to energy conservation and emission reduction, helping both the planet and your wallet – a win-win situation.