Knigh wrote
Interesting!!! I understand the point re: drag etc - but how on earth do you come to the answer that at 20 mph it is better to have the cc on and windows closed?
By grossly over-simplifying, of course
I did some searching and found some university projects that had adressed this issue, and one manufacturers research project which quoted numbers. From what I can tell, at about 25 C outside temp, aiming for 22 C cabin temp, their conclusion was that the drag rise from open windows crossed over the power consumed by the aircon compressor at about 20-30 mph. It does depend on the engine, as the aircon compressor power consumption (when it is on ) is dependent on engine rpm, not speed, so keeping in a high gear reduces the losses from aircon. The aircon power consumption is relatively flat and at motorway speeds is considerably less than the open-window drag. Ofcourse if you have aircon fitted then you are already paying a penalty for dragging around all that extra weight, so it makes sense to use it where it pays. Around town it is unlikely to make a lot of difference which you use.
Interesting!!! I understand the point re: drag etc - but how on earth do you come to the answer that at 20 mph it is better to have the cc on and windows closed?
By grossly over-simplifying, of course
I did some searching and found some university projects that had adressed this issue, and one manufacturers research project which quoted numbers. From what I can tell, at about 25 C outside temp, aiming for 22 C cabin temp, their conclusion was that the drag rise from open windows crossed over the power consumed by the aircon compressor at about 20-30 mph. It does depend on the engine, as the aircon compressor power consumption (when it is on
) is dependent on engine rpm, not speed, so keeping in a high gear reduces the losses from aircon. The aircon power consumption is relatively flat and at motorway speeds is considerably less than the open-window drag. Ofcourse if you have aircon fitted then you are already paying a penalty for dragging around all that extra weight, so it makes sense to use it where it pays. Around town it is unlikely to make a lot of difference which you use.
