baumgrenze
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Leaf Number: 16273
Location: Palo Alto, CA

Open Windows vs Air Conditioning

Mon May 07, 2012 10:00 pm

Has anyone tried to research the mileage hit one takes when driving with the driver and passenger front windows open and to compare it with the impact of running the AC?

Clearly opening the windows destroys some streamlining and adds to the drag. Conversely, the AC requires power to run the unit. In climates like mine, northern California, there are many summer days with temperatures in the 80's, hot enough for us to want some form of cooling. Which is more efficient?
Thanks,

baumgrenze

2012 Glacier Pearl

thejabrother
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Joined: Mon Dec 19, 2011 1:19 am
Delivery Date: 28 Dec 2011
Leaf Number: 9360
Location: Visalia, CA

Re: Open Windows vs Air Conditioning

Mon May 07, 2012 10:07 pm

I don't know the mathematical answer to this question, but here in the Central Valley where I live, it's been pushing 90 the last few days. Cranking on the climate control the mileage estimator only drops a few so it's worth it to me. Then when the temp is around 80 or less I've been running with the windows down, around town anyway. I would say if you're driving at around town speeds, or below like 50 mph, it's probably better to use the windows down approach, if you're on the highway going 55 or higher, it probably makes sense to run the climate control on warm days. Anyway, like I said, I don't have any hard facts but the climate control sure does work nicely in these cars!

kubel
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Re: Open Windows vs Air Conditioning

Mon May 07, 2012 10:13 pm

Mythbusters did an episode on this. They found that leaving your windows down is always the better option when it comes to fuel economy. But they weren't exactly driving vehicles that were heavily dependent on aero-efficiency. As I recall, they were F-150s.
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Herm
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Re: Open Windows vs Air Conditioning

Mon May 07, 2012 10:20 pm

Should be easy enough to test.. get on the hwy on a calm day, set the cruise control at 60mph and note the power consumption with the AC off and the windows open and closed..

cwerdna
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Re: Open Windows vs Air Conditioning

Tue May 08, 2012 12:17 am

^^^
Do find a level road (check Google Earth for elevation changes) or better yet, do a run in both directions to help cancel out effects of elevation change and wind. Do this with and w/o AC.

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LEAFfan
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Leaf Number: 1855
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Re: Open Windows vs Air Conditioning

Tue May 08, 2012 12:20 am

Someone in another thread posted about the most efficient way to use your A/C. They said to turn on the A/C, turn off 'Auto', lower it to 60, then use just your fan. It works great! So I want to thank them for posting that. After just a few minutes, it shows just a sliver of energy use and the mileage penalty goes to 1 and zero.
I drove the 151 miles on one charge yesterday with both my front windows all the way down (no A/C, 92 degrees, no wind), and both back ones partly down. At the lower speeds, I doubt there was that much drag, but at highway speeds, if you're only losing zero to one mile while using it, I would say use the A/C.
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padamson1
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Leaf Number: 9240
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Re: Open Windows vs Air Conditioning

Tue May 08, 2012 12:24 am

kubel wrote:Mythbusters did an episode on this. They found that leaving your windows down is always the better option when it comes to fuel economy. But they weren't exactly driving vehicles that were heavily dependent on aero-efficiency. As I recall, they were F-150s.
Hmm. My Dad did this same test with his Olds Cutlass and A/C won. He used cruise control (this was his 1st car that had it), filled the tank, drove a couple hundred miles with the windows opened a couple of inches to keep things cool, filled it up again, then drove with A/C. It was on Rt 95 between NJ and MA, so there wasn't too much elevation change, if anything the open windows portion had the advantage as there are more hills in CT & RI. As I remember it A/C won by a couple of mpg. I got that car in college, best mpg I ever got was 23 on the highway and it definitely wasn't as aerodynamic as a LEAF.

I don't have too many controlled chances to test this as the terrain varies too much for my travel, but I'll bet that the additional drag of open windows has more of a load than A/C with closed windows (the A/C load is nothing compared to the heater).

kovalb
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Re: Open Windows vs Air Conditioning

Tue May 08, 2012 1:47 am

The answer will depend upon a couple of variables.

Speed is one. Aero drag is much less at lower speeds so open windows may be better in that condition.

The other variable is whether the driver knows enough to set the climate control to 60 degrees. Setting it higher can click the heater on to re-heat the air conditioned air. That is very inefficient in an EV, unlike an ICE that uses waste heat from the engine. Once stabilized the A/C only draws around 200W, which is extremely efficient. FYI, this fact won't change for the 2013 model with the heat pump. You can't run the compressor in both A/C and heat pump modes at once.

Personally I just run the A/C and don't worry because the effect on range is negligable. Especially if I pre-cool the car using the timer or Carwings. Living in Phoenix A/C performance is near and dear to me, and the LEAF has the best A/C of any car I've driven in years.
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ztanos
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Re: Open Windows vs Air Conditioning

Tue May 08, 2012 7:11 am

The results of the aforementioned Mythbusters test was that anything higher than 55 and you should use AC. Anything lower and you should lower the windows. Granted their test wasn't exactly scientific, but rather it was lets drive two cars until empty and see which goes farther, so I'm not sure how they got an exact number with only doing 2 runs with 2 vehicles, but it seems reasonable that 55 would be close to the break even point on wind resistance.

adric22
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Re: Open Windows vs Air Conditioning

Tue May 08, 2012 7:27 am

I've been planning to test this when the Summer weather hits 100 degrees outside.

My thinking is that in 70 or 80 degree weather the A/C compressor will cycle on and off. But in 100 degree weather, it will run pretty much constantly. So I think that will be a factor to consider.

Personally, I always have the windows down on warm days unless the temperature is over 100 degrees and the sun is shining. At that point I can't take it anymore and have to run the A/C. But I've always been that way, even with gasoline cars. Seems like such a waste of energy.

The way I plan to do the test is to drive down a strip of highway at 65 miles per hour, and repeat this several times. I'll check the average kilowatts used for maintaining the speed. I'll do the test a few times with the windows down, and a few times with the A/C on. Then I'll see which one uses more power.
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