Running your air conditioning at 50 percent capacity can consume an extra ten percent of fuel. Short trips will require more air conditioning power. For example, if you drive fifteen minutes to the bank on a hot day, you will have had the air conditioning on full blast to cool off your vehicle. It will have just cooled down by the time you reach the bank. Then you park your car for thirty minutes. In that time the interior car temperature will have risen again considerably. When you finish your errand, you must again have the air conditioning at full power to reduce the interior temperature. City driving with air conditioning will have the most significant effect on fuel efficiency and that affects a large majority of Singaporean. According to reports, if the vehicle has a small engine, the fuel consumption will be greater because the power draw from the air conditioner is relatively constant. This could explain why I experienced a 30% improvement in fuel economy with my aircon off as my car has a puny 1.4L engine. When the air conditioner is on, engine sounds louder and acceleration is less responsive as well.
I know it is tough in Singapore but do try to turn off the air conditioner whenever you can, if you wish to spare a though for your wallet and environment. Plan your trips or chores in the mornings or evenings when it is cooler, in order to reduce stress on the air conditioner. Lower the windows to get a cool breeze into the car when driving on the highway in the morning. While you might create a slight drag with opened windows that marginally lowers your fuel efficiency, this is offset by the much greater amount of gas an air conditioner would consume. You can also reduce your speed slightly on the highway to counteract the drag. If you are worried that your hairdo will be messed up at the end of the trip, I recommend lowering the set of windows on the passenger side (both front and back).
The price of crude oil has hit USD 102 per barrel recently. If you wish to save on fuel and are willing to forgo a little comfort, do try giving your aircon a break. Do share your findings on this blog!