Windows Down VS AC

When to Use AC

The Kenyan weather has been as unpredictable as ever so far, but as we gear up to enter a season where temperatures should be at a high, what’s really the best to keep cool in the car? In addition, the fuel prices have hit a historic high, so how can one save fuel and keep cool while they drive?

According to writer Brendan Koerner “The rule of thumb is to keep the windows down while on city streets, then resort to air conditioning when you hit the highway.”

Therefore, when cruising down the Southern Bypass, you might want to consider having your AC on to reduce the drag. It is important to note that this doesn’t mean that having the AC on would not consume more fuel, but considering how dusty our roads can get, it would benefit you to have the aircon on in this case.

Having your windows rolled down increases wind resistance, also known as drag, which slows your car down. As a result, it requires more fuel to run.

Size & Shape of Car

Your car already experiences a certain amount of drag (even if the windows are rolled up) based on its shape, height, and size, and having the windows rolled down can heighten that. However, if your car already experiences a lot of drag regardless of your windows (like an SUV or a truck, for example), having the windows down is unlikely to drastically affect your drag.

Over the years, engineers found that rolling down the windows in an SUV reduced fuel efficiency by only 8 percent, mainly because the SUV’s boxy shape was already creating significant drag.

But the more aerodynamic sedan had a 20 percent reduction in fuel efficiency. The study concluded that the more aerodynamic a vehicle, the greater the loss in fuel efficiency when windows were rolled down at higher speeds.

Pollution

The windows vs air con debate isn’t just about working out which is more fuel efficient. It is also worth considering your exposure to air pollution.

In hectic Nairobi traffic situations, it is probably best to avoid using air con or opening your windows. However, we know that in hot conditions that might be uncomfortable, so as a solution you could turn on the air con but close your air vents, so the air con merely recycles the cabin air rather than drawing the air from outside, where there is nose-to-tail line of traffic all belching out exhaust fumes.

There are old-fashioned ways you could consider to keep your car cooler, such as trying to park in the shade or opting for tinted windows or heat deflectors or just using a fan to keep cool.

In most driving conditions though, apart from on the highway, it’s likely that a crack in the window, will work better for you than turning on the AC

In the end, which is better? The answer is: it depends. Aspects such as vehicle size and aerodynamics, driving speed, Kenyan terrain and wind speeds will all play a role in determining your fuel efficiency and how you choose to cool your car. To know what’s the best for your vehicle, you might consider testing these theories yourself.