Does Using Air Conditioning Consume More Fuel or Rolling Down the Windows?
2 Answers
At low speeds, using air conditioning consumes more fuel, while at high speeds, rolling down the windows consumes more fuel. When a car is driving on the highway, the faster the speed, the greater the wind resistance, and the car's fuel consumption is mainly used to overcome this wind resistance. Only when all the car windows are closed is the car's drag coefficient at its lowest. During aerodynamic design, cars undergo wind tunnel testing with all windows closed. Opening the windows disrupts the car's aerodynamic integrity, increasing the drag coefficient and reducing fuel efficiency. Tips for fuel-efficient driving: Maintain good driving habits. When accelerating, the engine must increase power output, and every time you brake, the energy generated by this power is lost as heat. Therefore, it's important to anticipate traffic conditions in advance, avoid congested routes whenever possible, and minimize stop-and-go situations. Reduce unnecessary weight on the car. The heavier the vehicle, the more fuel it consumes. Thus, unnecessary items such as roof boxes, roof rails, and bike racks should be removed when not in use. These not only add weight but also alter the airflow around the car, increasing air resistance.
I remember discussing this topic with friends last time, and we talked for a long time. Turning on the AC does consume more fuel because the compressor is directly driven by the engine, adding extra load—like carrying a small additional weight. In comparison, opening the windows increases aerodynamic drag. At low speeds, the drag is minimal and has little impact on fuel consumption, but at high speeds, the drag increases significantly, potentially making it even less fuel-efficient than using the AC. From my observation, opening the windows is more fuel-efficient below 60 km/h, while using the AC becomes more economical above 80 km/h. Vehicle design also plays a role—SUVs, for example, have higher aerodynamic drag, making open windows more likely to increase fuel consumption. My suggestion is to use open windows more often on city roads to save some fuel costs, but on highways, it's better to just turn on the AC to avoid higher fuel consumption. In fact, test data shows that using the AC increases fuel consumption by about 10% at average speeds, while open windows save fuel at low speeds but increase consumption by up to 15% at high speeds. Weighing these factors, it’s quite practical advice.
