Windows Down or Air Conditioning On?

[CheFlaco]

Im wondering if anyone knows which is better for fuel efficiency, windows down or air conditioning on as it pertains to EV driving and Hybrid Driving. Are they the same? Wondering if anyone has any input on the matter.

[wazer]

I say windows up and A/C on. It's more efficient at highway speeds, and also keeps you and your HVB cooler as the HVB is cooled with air from the cabin.

[Russael]

As someone who makes an annual 1028 mile round trip to Baltimore MD each year, and trying to squeeze every MPG possible out of a 1999 Expedition 4x4, I can say with authority, windows down @ 65MPH.  I've tried A/C a few times and I can see a substantial decrease in economy.  With windows down, I get >19MPG (yeah, awful numbers considering what the Fusion Energi gets), but with A/C... 16.5 to 17, a minimum 10% hit.

 

I usually drive with the stereo blaring so wind noise doesn't bother me.  Grew up without A/C in vehicles and I have a pretty wide range of temperature I can tolerate before I get uncomfortable.  However, once I start getting near Baltimore, the temps soar over 95 degrees almost every year I've been there (worst was 102) and yeah, I finally caved and turned the air conditioning on.

 

That trip happens to be coming up in short order too.  Again, I'll be driving my big, comfy Expo.  I love sitting up high and the captain's chairs in that thing are like driving a couch.  Plus 2 other people are coming along.

 

As far as it goes concerning the Fusion... the compressor is variable speed and can run more efficiently than the belt driven compressors of traditional gas vehicles.  If anybody could solidify numbers with that, it'd be Larryh. :)

[larryh]

I can't detect much difference in MPGe at 55 mph with the windows up vs. the windows down (at most 3%).  You will definitely detect a difference with the A/C on.  After it has cooled the car down, it consumes about 0.6 kW of power (only about 4% of the total power consumed).  However, until then, it consumes up to 5 kW of power.  That is more than the central AC for my house.  You will definitely see lower MPGe.   All you have to do is reset a trip odometer and monitor MPGe for AC vs. windows down. 

Edited July 26, 2014 at 09:12 PM by larryh

[Russael]

We had a cooker of a day here this past week... over 90 degrees.  I did run the A/C on the way home.  I pulled up the energy consumption gauge for climate and kept an eye on it.  Upon first power up, it consumed >5kw of energy which is typical.  However, once the temperature in the car reached the set temp, it stayed at about 2.5kw.  I had the temperature set at 72 degrees and kept recirculate turned on too.  When it's in the upper 70's outside, then I have also observed the A/C system sink under 1kw, at least until I start moving again.  MPGe sunk to about 114 for that trip home... I usually get 190 or higher.

[Griff]

My experience is based on a 34 mile trip with speeds averaging 60mph and ambient temps of 90 degrees. A/C on = 43mpg. Windows (partially) down = 56mpg. YMMV. :-) 

[jeff_h]

My experience is based on a 34 mile trip with speeds averaging 60mph and ambient temps of 90 degrees. A/C on = 43mpg. Windows (partially) down = 56mpg. YMMV. :-) 

 

This is more like I see in my driving with a commute 58-60 miles each way, but for me the difference gets more dramatic in DC traffic where there's a lot of stop-n-go driving - with AC on (and HVB getting diminished while you just sit there) the MPG for the trip is normally in the upper 60s to mid 70s (but 59 lowest I've had), with AC off (HVB largely unaffected while you sit there) MPG is normally 80s to 90s (and 120 best I've had).  So in my experiences I've had much better MPG with the windows down partially, but the trade-off is that it gets hot in the car, so if it's in the mid 80s or lower I will normally suck it up, but once over 85-90 it get more uncomfortable so I normally use the AC.

[rbort]

For me, in general windows cracked while driving on country roads at speeds of up to 45mph

Windows up on the highway otherwise too much noise.

 

AC ON if temps are above 75 degrees, otherwise just vent is OK with me.

If its cloudy out, I could tolerate vent at higher temps but somewhere around 80 you might have to draw the line and fire off the AC.

Most of the time at night its vent only.

 

In most cases I don't mind firing off the AC if I'm uncomfortable - its cheap in the cmax, 2500 max but 600w on average.  Its AC is less demanding than the Fusion AC.  I do however try my best not to use the heat in the winter when driving EV only.  That's expensive at 5000w+ down to maybe 2200-2500w at best to maintain the coolant temperature.  If I'm travelling long distance then once the engine is warmed up (not before) then I turn on the heat.  10 miles from home before I go EV only, I crank the heat to 85F to overheat the cabin (in the dead of winter) about 5 minutes before engine shutdown and then turn off the engine and heat and drive the last 10 miles on EV as an example.

 

-=>Raja.

Edited October 2, 2014 at 02:14 AM by rbort

[shaggy314]

Basically Windows down below 40-50 MPH, windows up and A/C on above that... Keeping in mind our a/c is more efficient than in the past. This was done in two different studies cited in the articles below, not anecdotal.

 

http://www.bankrate.com/finance/auto/will-rolling-down-windows-save-fuel-or-not.aspx

http://auto.howstuffworks.com/fuel-efficiency/hybrid-technology/driving-with-windows-down.htm

 

All that said 90%+ of the time I have the sunroof poped up in the back and about 3/4" on the rear passenger window cracked. In anything more than a drizzle, this is fine for a nice swirl air flow out the top. It's key to keep the sunshade only open about 4" so the air is sucked out the front of the car and not just the sunroof crack. No sunroof? there is a vent only trick option.

[Rexracer]

These articles are not specifically for an EV. I agree with them for a ICE car that is already running, so its the difference between the clutch engaged on the compressor vs the wind resistance. When in EV, this is much more difficult a question, as you are using up your EV range to get AC.

 

All in call, if im under 45-50mph and its not to hot, I go with windows, speeds over that I roll up the windows and run AC for noise, or if its just to hot out. I am not going to make my baby/wife or myself uncomfortable to get 1-2mpg better over the course of the year