A/C efficiency penalty quantified

[Frank Lee]

by our own National Renewable Energy Laboratory:

Vehicle air conditioning (A/C) systems represent the major auxiliary load on the engines of light-duty passenger vehicles, sport-utility vehicles (SUV), and heavy-duty vehicles and have a dramatic effect on fuel consumption and exhaust emissions in conventional vehicles and hybrid electric vehicles (HEV). Recent studies (paper is from about 2000?- Frank) have shown that, during the SC03 drive cycle, the average impact of the A/C system over a range of light-duty vehicles was to increase 1) fuel consumption by 28%, 2) carbon monoxide emissions by 71%, 3) nitrogen oxide emissions by 81%, and 4) non-methane hydrocarbons by 30%. Recent tests on hybrid electric vehicles (i.e., Toyota Prius / Honda Insight) at NREL [2] have shown that HEV fuel economy decreases by 30%-35% when the A/C operates.

And:

About 7 billion gallons of fuel—about 5.5% of total national light-duty vehicle fuel use—are used annually just to cool light-duty vehicles in the United States.

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

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

[mcrews]

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

(it was at 69!)

[Old Tele man]

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

[mcrews]

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)

[Daox]

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.

[Frank Lee]

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.

[mort]

Originally Posted by Daox

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.

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

[euromodder]

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

[drmiller100]

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.

[Old Mechanic]

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