A/C efficiency penalty quantified
 

by our own National Renewable Energy Laboratory:

And:
Probably doesn't include all the time spent idling in parking lots to "keep it cool" :mad: :rolleyes:

I ripped the compressor and condenser outta the Coupe a few days ago...

I'll raise the automatic temp setting to 73.........

(it was at 69!)

...if you'll pardon the obvious "pun", but "...let the HOT AIR roll..." (ha,ha).

There is a lose in aerodynamics with the windows open.

When I had my 1999 Vanden Plas 4 door Jag, I ran with the windows down on a route I was driving everyday. I ran at 60mph w/cruise set for 16 miles. When the windows were down there was a lose of 4mpg (running a scangauge) with the windows up and a/c on I got 26.2 mpg.
Is the report stating that there is a drain on the engine even with the a/c off? couldnt be more that 5% (imho)

Got a link?

Those numbers seem very high to me. I use the A/C in my Prius on the highway and where I normally get 50 mpg there is no way that is cut down to 35 mpg (30% loss) just by turning on the A/C. I suspect the truth will be told in their testing procedure.

NREL: Advanced Vehicles and Fuels Research - Vehicle Ancillary Loads Reduction

http://www.crtech.com/docs/papers/C599-061.pdf

Maybe the difference in your experience and their report is they are doing lots of start/stop vs. you cruising.

I think the numbers are high also, but here see page 17 and on. Same kind of results. In my car I see about a 5 mpg hit on hot days, but the cold weather hit is worse. My daily commute is amost exactly the EPA highway cycle.
-mort

Key words : during the SC03 drive cycle.

Real life : before I had CC installed, I couldn't even tell a difference in FC with or without A/C during steady state driving with an already cooled interior.
Sure it draws more power initially when it has to work hard to cool everything down, but it's nowhere near 28-35 % on average.

I wish it was, I'd see far better results from keeping the A/C off :o

I would really appreciate some real numbers from the real world from real members on this site.

For instance, vehicle weight, vehicle size, mileage with AC and without, and city or highway driving.
Thank you much.

It depends on how you use the AC. Start in my garage with the interior fairly cool to begin with, run it on recirculate and low fan, set the temp lever as high as you can stand it and it doesnt use to much fuel. On my old Insight it cost 10 MPG, on the Maxima probably not even 2.

regards
Mech

On my vehicle the fuel difference is about 0.5 ltr / 100 klm for air on and off.

Steady highway running is around 7.2 and with the air on it is around 7.7 l / 100 klms. (US mpg: from 7.2 (32.6) to 7.7 (30.5) so about 2 mpg) at around 90 kph (US 55 mph) which is just under the legal max of 100 kph (62 mph)

The car is a GM variant (Holden 2003 Acclaim sedan) with the 3.8 engine and the 4L60E trans. Weight is around 1600 kgs (3200 lbs US approx).

Peter.

I would really appreciate members posting there vehicles under their avitar.......

just sayin.....

I almost never run my A/C anymore, but when I did, I only noticed about a 2-3 mpg (10%) decrease.

At this point, I've mostly weened myself off of using the A/C. We've had a pretty mild year, and in addition, my car is white and most often parked in the shade. I'm thinking I might get a UV reflective tint at some point, but I haven't really needed it yet.

Should I drop a note to the lab telling them they are full of crap?

I don't use a/c enough to get any data.

Just did a big trip, about 3,000km, air con on all the time, 30-36C outside, virtually no change in the FE.
I think this is an issue that shows up more with smaller vehicles, mine is a big diesel 4x4, smaller vehicles still have the same needs for auxillary load, whether it be alternator, aircon etc., but as a percentage on the fuel economy it is much bigger on smaller vehicles than on a larger vehicle.
I could delete all my auxillaries and not see much change, but if I keep the weight down and streamline the box, I can get major improvements.

...I've "measured" drops in MPG ranging from 10% to 14% on my Vibe with A/C, but back-to-back A-B-A testing was NOT exactly 100% "repeatable"...LOT's of variation.

...hence, I 'rule-of-thumb' A/C at 10%-15% for my car...others will obviously get different values, but probably close.

Nah, it's just that the cycle during which they measure these differences, isn't representative of normal everyday driving.


The problem I have to filter out the AC use, is than I mostly use it under conditions that don't make up most of my normal driving.
When the AC is on, I'm usually also carrying passengers - and when carrying passengers, I'm usually also driving faster, both of which affect FC.

Tesla,
Thats is my thinking as well.

I remember my brother's Nissan Micra had aircon and you could have cool air or more performance...but not both at the same time.

Interestingly he traded to 4.0 litre Falcon and gets about the same economy.

I suspect he doesn't have to drive the Falcon nearly as hard.

Peter.

For really small four-pots and three-pots I've had and tested, it seems to be about a 10-15% penalty in traffic, depending on how weak the engine was and how big the compressor was.

We did this on the dyno (a hell of a long time ago) and got about a 10-15 horsepower drop on a standard 1.6 liter engine at idle... which just happened to have 400 horsepower and a turbocharger, but it's the same for most small engines... and the turbo didn't make boost at idle.

Worst I had was a compressor conversion when the Calsonic compressor clutch on my Nissan went kaput for the fourth time. Stuck a bigger compressor with an indestructible rubber clutch on it, instead... on there and you could feel about 25 to 30 ponies go south every time it turned on.