[georgeniebling]

So I'm in Texas and that means my car is automatically 300° when I get in the car.

Is it more efficient to let the battery run the AC to cool it down or to roll the windows down and deal with the potential for extra drag

 

[JRRF]

I lived in TX for a number of years, and 460 AC will never compare to regular compressor AC. Whatever it costs in drag is worth it.

Actually, where I was it was so hot that even with the AC on full blast, I'd still be dizzy from the heat.

 

[Slotracer577]

Really depends on speed. From what I remember the cross over point for ac being more efficient is 45-50. I know myth busters has looked at this.

 

[flyingsherpa]

Mythbusters actually tested this years ago, you can probably find a discussion of it on their website. IIRC, using a/c was more efficient, especially as speed increased. Volt is going to run a/c to cool the battery anyway and that also comes into the cabin, nothing you can do about that, so you might as well close the windows and at least use that "free" a/c. In my experience, using a/c (unlike heat) doesn't have a very noticeable impact on range, but I don't live in TX so I don't crank it as much you'd need to.

 

[bjrosen]

My guess is that at highway speeds the AC will be more efficient, why don't you run the experiment and report the results. I live in New England where we have the opposite problem, summers are fairly mild so the AC has very little effect on MPGe, but in the winter the heater sucks electricity like there is no tomorrow so I rely on the seat warmers except on the coldest days where I run on the ICE instead of the batteries.

 

[mpmoore1979]

Use the a/c on ECO mode and you will not see much of a range change. Here in Phoenix I use the system in ECO mode and only see about 1 or 2 mile decrease in range. The a/c will run anyway above 85 degs or so to cool the battery so you might as well use it to cool off the cabin as well. In comfort mode, it uses a lot more power. You can see this if you put your screen in the hvac display and it will show you a percent number (gen 1) so you can see the difference between ECO and Comfort modes.

 

[telveer]

My suggestion for hot days: Roll down all your windows and let the car air for some time. Then close all windows and run AC. Start in Comfort, and once the car is comfortable, switch to Eco. Be Calm. You drive a Volt

If the temperatures are in mid 80s or lower, opening the windows works but who wants to inhale all that polluted air and deal with road noise? I roll down my windows f I am on a quite road with not much traffic, and road noise is bearable. I also have the buffering kit, which helps reduce wind buffeting.

 

[firehawk72]

When MythBusters tested this the answer was obvious. Put the windows down.

 

[El Dobro]

Hold the unlock button down on the remote and all the windows will drop together.

 

[Slotracer577]

When MythBusters tested this the answer was obvious. Put the windows down.

Depended on speed. At 45 windows down is more efficient, at 55 ac is more efficient, episode 38

 

[flyingsherpa]

When MythBusters tested this the answer was obvious. Put the windows down.

Not so fast... they tested this on two different episodes, 22 and 38. Their first, they said windows were more efficient (but did testing only at 45mph). Later testing using (IMHO) better methods, they showed above about 50mph (for their test vehicle anyway), it's more efficient to use a/c than windows. Certainly this crossover point will vary based on the exact vehicle driven, so take results with a grain of salt...

 

[firehawk72]

Depended on speed. At 45 windows down is more efficient, at 55 ac is more efficient, episode 38

Thanks for the input. I must have missed that episode, interesting.

 

[Dutch]

So....
I put a sunshield in the front window and a pop-up one in the drivers side window so I don't fry my butt. That tends to be a 10-18 degree drop right there.

Then windows down to dump the heated air while the A/C fires up

Then windows closed and a/c

Then again I live in VA where it doesn't get quite as hot, but the humidity will punish you.

 

[Bacardi]

The correct answer is we don't know yet...

Mythbusters even got it wrong the first time and had to do a follow-up "revisted" episode to correct their original mis-information that windows down was more efficent...What they found the second time around, in 2004 I might add, is with their test vehicle, when going 50mph+ was more efficient with the A/C on than it with the windows down...

However, their vehicle they used in 2004...
Doesn't have the same frontal area or Cd as the Gen2 Volt...
Doesn't use the same A/C system as the Gen2 Volt...
Doesn't a vehicle in which the batteries are more "sensitive" to ambient temperatures...

Then you have the variables...
What A/C temp set to?
A/C set to ECO?
What are you going speed?
How many windows were you putting down?
Are they open a crack and all the way down?
Ambient temperature?
Does elevation change the results?
If your route includes steep inclines or declines, will that change the results?

Unfortunately lots of testing and data points are needed, to parrot the 2004 mythbusters test that "50MPH is more efficient with the A/C on" isn't accurate...

 

[srmarti]

When MythBusters tested this the answer was obvious. Put the windows down.

No. At highway speeds there was a bigger penalty due to drag with windows down. A/C was better at highway speed. At low speeds where aero-drag isn't significant windows down and A/C off was better. Although A/C off and windows down might still be uncomfortably hot, make you choice... My SWAG is with the Volt's aerodynamics, drag is even more significant at highway speeds with the windows open.

 

[Taser54]

So I'm in Texas and that means my car is automatically 300° when I get in the car.

Is it more efficient to let the battery run the AC to cool it down or to roll the windows down and deal with the potential for extra drag

why not roll down the windows to remove the hotter than ambient air, then roll up the windows and use the a/c?

 

[canehdian]

1) hold unlock as you walk to the car (or if the car is really close, hit it before you leave your workarea/desk/office/whatever)
to roll down all windows and exhaust the hot air

2) if using A/C, initiate remote start once the windows have been down for a minute or so, if not, just get in and enjoy the breeze as you drive.

AC is better at highway speeds. But it's only about a 10% hit for freeway speeds with all 4 windows down. That may be worth it if you prefer the breeze and fresh air.

 

[freshcut]

I think the point to remember is that you can't really compare in this case due to the differing way in which the compressor is powered. If I recall the mythbusters segment they were comparing how much power is sapped from the engine and how much additional fuel is used to operate the compressor. Since the compressor is not directly driven off the engine it could be said that "zero" power is being used from propulsion. I personally have not yet noticed any significant decrease in mpg with or w/o the AC operating compared to a traditional ICE powertrain. I do a mix of both right now as we've had some great weather lately with temps in the 70's and lower 80's.

Also I think one should keep in mind that on extreme temp days the A/C will almost certainly be running for thermal maintenance on the battery anyway so even with the windows down and a/c off, you might still be running the compressor and losing additional power to drag as well due to BTM.

 

[Slotracer577]

Supposedly if you open a back door, then open and close the front door a few times to pump out the hot air it will help reduce the heat load at startup.

 

[snic]

My suggestion for hot days: Roll down all your windows and let the car air for some time. Then close all windows and run AC. Start in Comfort, and once the car is comfortable, switch to Eco.

My suggestion for hot days: turn the a/c on remotely 10 minutes before you leave. You will step into a comfortably cool car, and the hit on range will be tiny.

Supposedly if you open a back door, then open and close the front door a few times to pump out the hot air it will help reduce the heat load at startup.

After all that exercise, you will feel hot no matter how much you blast the a/c!