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Old 08-21-2014, 02:30 PM   #1 (permalink)
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A/C vs MPG test: impact of air conditioning on fuel economy (2015 Nissan Micra)



Nothing ground-breaking here, but while I was test driving the new Micra, I decided to find out how much of an impact the A/C had on fuel consumption over a range of speeds.

(As an aside, these Micra results would also apply to the 1.6L Versa Note and Versa sedan. Same platform/drivetrain/components.)

I ran a bunch of bi-directional runs at 3 different speeds with the A/C on and off. The fan was left on the 2nd speed for all the runs, just toggling the A/C switch.

Results...

(Note: I graphed it for L/100 km, so those of you used to seeing graphs of "MPG" where the taller bar means better fuel economy, keep in mind it's reversed in this case.)




From: AC vs. MPG: impact of air conditioning on fuel economy tested - Micra-Forum.com


The average fuel consumption increase with A/C on vs. A/C off was 5.9%.

In retrospect, I wish I'd done a couple more 100 km/h runs, since it seemed to show that the A/C impact is smaller at higher speeds & engine loads. Though it makes sense that it would be, since you're covering more ground for a given power draw, plus the engine is probably sitting in a more efficient part of the BSFC map while it's providing that power to the compressor.

Code:
speed   AC      N.      S.      avg L/100 km*

60      off     4      4.1      4.05
        on      4.3    4.4      4.35
        on      4.3    4.5      4.37
        off     4.2    4.1      4.16
                        
80      off     5      4.5      4.75
        on      5.5    4.7      5.10
        off     5      4.5      4.75
                        
100     off     6.3    5.6      5.91
        on      6.6    5.8      6.15

(* Some of the averages are affected by rounded conversions of initial 
readings that were taken in MPG)

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Old 08-21-2014, 03:37 PM   #2 (permalink)
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At 62 mph, the AC loss drops to 4%. What's more significant to note is that increasing speed from 50 mph to 62 mph results in a 20% drop in mpg.

How were the nifty charts generated?
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Old 08-21-2014, 03:50 PM   #3 (permalink)
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Excel, then tarted up in Photoshop.

Quote:
What's more significant to note is that increasing speed from 50 mph to 62 mph results in a 20% drop in mpg.
Yessir. I also collected speed vs. mpg numbers for this car, and I'll get around to posting those as well one day.
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Old 08-21-2014, 04:33 PM   #4 (permalink)
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Now what everyone really wants to know, can you hypermile so you can have your cake and eat it? Is there a way to drive and have ac without effecting mpg?
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Old 08-21-2014, 04:38 PM   #5 (permalink)
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Quote:
Originally Posted by Cobb View Post
Now what everyone really wants to know, can you hypermile so you can have your cake and eat it? Is there a way to drive and have ac without effecting mpg?
Use the A/C only going downhill? I did that in a '97 Odyssey and got a record tank while remaining pretty comfortable.
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Old 08-21-2014, 06:11 PM   #6 (permalink)
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I lose about 3 mpg in my Bronco. I have been turning the A/C on for a couple minutes, then off for about 5 or until the heat gets to be too much. Seems to help MPG wise. Be nice to automate it with a time delay relay or something.
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Old 08-21-2014, 06:45 PM   #7 (permalink)
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Run the air just prior, during or instead of braking
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Old 08-21-2014, 08:17 PM   #8 (permalink)
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In my Tacoma with the v6 and my 09 scion xb I couldnt tell a diff with ac on or not. In my geo and insight it feels like such a load.

To make your home ac more efficient they have variable compressors. Of course most home ac runs at a constant speed and with enough extra capacity it cycles off and on. With a car its speed varies a hell of a lot and cycles as needed. Many newer cars use an ecu vs high and low psi sensors to cycle the compressor off and on. Plus it works the ac differently if you have the eco mode on or sport. My insight the ac is always colder with eco off and sport mode on addition to the settings. Eco off makes it 1 step colder, sport makes it another.
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Old 08-21-2014, 09:13 PM   #9 (permalink)
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5.9%? Hell, that's big enough a difference to drive a semi through, given most test results here.
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Old 08-21-2014, 09:54 PM   #10 (permalink)
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Quote:
Originally Posted by tyronasauras View Post
Run the air just prior, during or instead of braking
Quote:
Originally Posted by Gasoline Fumes View Post
Use the A/C only going downhill?
Yup! And yup!

Sounds like we need an Arduino type of project that uses accelerometers/inclinometers to automate the A/C switch.

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Ecodriving test: Manual vs. automatic transmission MPG showdown



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