WOW, that's more then I expected. Maybe those guys looking at solar cells should wire them to the A/C unit.

During the summer, I ran the A/C Auto much of the time and found that if I kept it set at 72 that it had no effect at all on mileage. Sounds like another goofy-assed test where the "testers" have no idea what the hell they're doing.

Hmmm... HybridVigor's down in Phoenix and he's reported a drop of a few MPG in 110 deg heat with the AC on full. <_< Furthermore, my MFD vs Manual Calc numbers have never been anywhere near that far off except with it's really cold out and the bladder has shrunk. Where do they get that number? <_< I believe the MFD more than the manual calc because of the bladder and differences in the autocutoff theshhold of different gas pumps. There are just too many variables there to be really confident of those numbers. They're a good sanity check though.

I'm in Dallas and I do see a small decrease in mpg with A/C on. See my graph of mpg vs average tank temperature at the bottom of Paul's Prius Web Page. I'm only seeing about a 3-4% penalty.

Cold weather has a much larger negative impact.

I ran the AC almost all summer too, the impact is negligible, IMHO.

View my results here: http://www.w8kc.com/priusmileage.htm

BUT... the HEATER is the REAL MPG killer.

Tripp has a good point. How did they measure fuel economy, and was the method of measurement consistant in each test vehicle?

The Prius system employs an electric motor to exclusively power the AC compressor. I would have thought that this would enable an air-conditioned environment without using engine power, and as a result would not decrease MPG.

On an opposite side of this discussion, what impact does the the electric motor have on providing quick heated air to the cabin? If the Prius does not have an adequate supply of heated water from the engine cooling system (i.e, Prius running off motor and not from engine) it seems like it would take longer than an acceptable amount of time to provide ready heat to the cabin. I do not own a Prius yet (Feb delivery) so maybe someone could comment on this.

Chris A.

I think the hit comes because the ICE has to charge the HV Battery more often because of the drain the the climate control places on the battery.

Also, the chart in the article is interesting because the GEN I and GEN II Prii got nearly identical mileage in their study. The HAH got worse mileage than the Escape. I know that the HAH is more of a performance hybrid, but still.

BTW, how low can you set the climate control? I haven't really used it much. Perhaps these guys have it set on -40F so that they can simulate winter driving at the same time.

Since all the Prius's energy ultimately comes from burning gasoline, heating and cooling must necessarily reduce MPG.
By how much is the real question.

Doesn't running the air conditioning lower the fuel economy of ANY car?

And I might add I NEVER crank the air conditioning up to the highest level. I don't run it at the chilliest temp and I don't run it at the highest fan and I certainly don't do both at the same time.

Then again....I don't live in Phoenix.

I found this significant:

" The testing also dispelled a persistent myth that the rechargeable batteries need to be frequently replaced. Francfort originally thought their battery evaluations would "go to 100,00 miles because that's how long the batteries are under warranty. The batteries were working so well, we thought we'd go further." They finally settled on 160,000 miles. Evaluations showed that the rechargeable batteries lasted to 160,000 miles with no effect on fuel economy."

I also found this interesting but would like to know how they proved it:

"Francfort and his team also determined that the computer dashboard readings for fuel economy—which most drivers use to base their judgment rather than manually calculating the actual mpg—inflates mileage numbers by somewhere between 10 to 20 percent."

yeah. I wonder what kinda impact it has? You'd think more because the alternator supplies the juice (this is correct, right?) and it's a belt driven system. Belt driven systems have a lot of mechanical loss involved in their operation.

Yeah, I found it lame that they didn't state how they measured their fuel consumption so that their work could be replicated or at least inspected. Seems like a specious argument to me.

just like every other vehicle on the road.

Hmm. We had a week of highs in the teens and single digits a couple of weeks ago and I didn't notice a huge hit. I lost about 5 MPG (~51 to ~46). I did get my block heater installed just in time. I have a short (5 mile) commute that takes about 10 minutes and I do a couple of other routine trips (lunch time hockey) a couple of times a week that are more like 20 mi round trip. On a cold night (0 F) when I had just filled up my tank I had to drive about 20 mi on the freeway and I still got right about 46 MPG starting with a fairly cold engine and no block heater.

Tag, how much of a hit are you taking? Just curious.

I ran my air conditioner continually during the (Los Angeles) spring, summer, and autumn and found the only time mileage was affected was in very heavy traffic, when the AC drained the battery and the ICE had to recharge it. Now that I'm not running AC I find the gain in fuel economy is only about 1-2 mpg.

Living in South Florida the weather here is usually hot and humid. Over the last several weeks the temps have been in the 60's so there has been no need for A/C.

I have noticed a 3-4 MPG improvement in my 2005 in gas mileage due to not running the A/C.


Thanks!!

Brian
BT Tech
305-652-3115

Which uses more energy at highway speeds in the Prius, or any car with a low CD, windows open and AC off or windows up AC on? Did they take things like this into account during their test?

I hear ya. I'm still in that no surrender stage. When it's cold here I bundle up and wear gloves. I only run the heater when I'm coming back from a hockey game and the car's all steamed up. Then I run the defrost its only in pulses to clear the window. Then I shut it off and the AC too. We'll see if I'm this stubborn in a year.