Windows down vs. AC

[CarpeCarne]

I've driven a PHEV for the last few years and really enjoy the gamification aspect of maximizing my efficiency. To that end I have an efficiency question for you physics geniuses in this group. I know from my PHEV how much of an impact climate control can have on battery drain. I also heard once that rolling the windows down can have a significant impact due to increased wind resistance. Anecdotally (or better yet if you know how to actually calculate the answer), does anyone have an idea at what speed it makes more sense to roll up the windows and turn on the AC? Thanks!

Sponsored

 

[Mach Tuch]

45 mphish. Myth Busters on discovery channel did exactly what your asking in as a controlled an experiment as they could. Windows up vs down. I’ll look for a link.

 

[Mach Tuch]

In aerodynamics if you double the airspeed you quadruple the drag. The formula escapes me but that’s about right.

 

[CarpeCarne]

45 mphish. Myth Busters on discovery channel did exactly what your asking in as a controlled an experiment as they could. Windows up vs down. I’ll look for a link.

Thanks!

 

[Mach Tuch]

 

[Guss-E 2021]

45 mphish. Myth Busters on discovery channel did exactly what your asking in as a controlled an experiment as they could. Windows up vs down. I’ll look for a link.

40 is my threshold not due to drag but noise. At 30-45 mph with the windows down, I'm still seeing well above 3 miles/kW.

 

[txaggies07]

45 mphish. Myth Busters on discovery channel did exactly what your asking in as a controlled an experiment as they could. Windows up vs down. I’ll look for a link.

Not sure that will apply in an EV. My guess is the answer would be much much lower speed since AC isn’t too much of a battery hog and air resistance is much more of a factor.

 

[Guss-E 2021]

Yeah but at 45 mph. They should try again at 65 mph+.

 

[River Rat]

I find the wind buffeting is bad with windows down over 30-40KMH. We need vent wings again

 

[Larry Paul]

Please keep in mind that every car has different aerodynamic profiles. There is nothing magical about 45MPH other than that they proved that what ever car they were test that was the crossover point.

The more aerodynamic the car the lower that crossover point is. I suspect it is closer to 30MPH for the MME if the windows are rolled down vs AC being on.

 

[Mach Tuch]

Yeah but at 45 mph. They should try again at 65 mph+.

I would like to have seen them figure out at what speed efficiency equaled but the would take a lot of laps around the track.

 

[daemonic3]

Shoot, I didn't think about this in the MME. I love efficiency and once the outside temps are reasonable, in my F150 I let air come in through the vents WITHOUT the A/C actively cooling, and adjust the rear cabin slider to open about 1 to 1.5". It is like a nice fresh breeze coming through and barely any noise.

Since there is no rear slider on the MME I just realized this won't work for me on spring and fall evenings. I'd have to crack the side windows and be subject to annoying Helmholz throbbing when hitting the resonant frequency. Guess I'll have to play with it when I cross that bridge.

Are you guys talking about OPEN windows or doing what I do and open the vents and barely crack a window(s)?

 

[Garbone]

I can run just vents with no heat or AC until it is above 80. At that point things start getting unpleasant. Worth about .3 on the miles per kw.

Have the vent visors but still only open the windows under 55mph.

 

[Mach Tuch]

Shoot, I didn't think about this in the MME. I love efficiency and once the outside temps are reasonable, in my F150 I let air come in through the vents WITHOUT the A/C actively cooling, and adjust the rear cabin slider to open about 1 to 1.5". It is like a nice fresh breeze coming through and barely any noise.

Since there is no rear slider on the MME I just realized this won't work for me on spring and fall evenings. I'd have to crack the side windows and be subject to annoying Helmholz throbbing when hitting the resonant frequency. Guess I'll have to play with it when I cross that bridge.

Are you guys talking about OPEN windows or doing what I do and open the vents and barely crack a window(s)?

Fully open.

 

[Mach1E]

I've driven a PHEV for the last few years and really enjoy the gamification aspect of maximizing my efficiency. To that end I have an efficiency question for you physics geniuses in this group. I know from my PHEV how much of an impact climate control can have on battery drain. I also heard once that rolling the windows down can have a significant impact due to increased wind resistance. Anecdotally (or better yet if you know how to actually calculate the answer), does anyone have an idea at what speed it makes more sense to roll up the windows and turn on the AC? Thanks!

It’s negligible.

If you don’t mind being miserable, you’ll save more energy opening the windows in your house and turning the HVAC off.

Sponsored