Does the A/C reduce mileage?

[Bob64]

Or there is the lesser-known "4th" option of using "ice-gel" packs in a heatsink + fan + ice cooler configuration. (Or wear an ice-vest)

Less convenient, but for all us hypermiler-wannabes, we're used to a little inconvenience :P


Also, I think that your battery statement that the battery fan goes on high is a bit exaggerated. According to a battery presentation from Wayne, I'm lead to believe that the batteries of the prius II are much more efficient at dissipating heat and that the fan rarely goes high speed.

[member]

<div class='quotetop'>QUOTE(dallas2727 @ Oct 4 2007, 07:23 PM) [snapback]521477[/snapback]</div>

I've driven entire tanks with AC on (set to auto) during temps in the 90s, and I've done tanks with it off. I didn't see a lick off difference in MPG, and I pay close attention.
[/b]

Finally, the perpetual energy machine we've all been searching for! I hope you isolate and patent this process ASAP!

[JimboK]

As for highway driving, the MPG Simulator that Evan mentions above reveals the following at 55 MPH:

85F OAT, no AC: 61 MPG
85F OAT, AC set to 76F: 59 MPG
85F OAT, AC set to 70F: 57 MPG
95F OAT, no AC: 63 MPG
95F OAT, AC set to 76F: 59 MPG
95F OAT, AC set to 70F: 57 MPG

This assumes all windows closed. When you start opening windows at 55 MPH and 85F (no AC):

2 diagonally opposed windows down 1": 60 MPG
2 windows half way down: 57 MPG
All windows down: 53 MPG

All scenarios assume no wind and smooth, dry pavement.

[efusco]

<div class='quotetop'>QUOTE(Bob64 @ Oct 5 2007, 08:06 AM) [snapback]521666[/snapback]</div>

Also, I think that your battery statement that the battery fan goes on high is a bit exaggerated. According to a battery presentation from Wayne, I'm lead to believe that the batteries of the prius II are much more efficient at dissipating heat and that the fan rarely goes high speed. [/b]

If you think about the parameters I gave (100F outside temp windows up) we're talking about a cabin temp in the 120-140F range on a sunny day...the battery will get very hot and the fan will come on to max temp....guarantee it. I'm not saying that it will use a tremendous amount of energy to run the fan, but probably an equivalent amount to what the AC fan would use. Add to that the loss in efficiency of the battery as it balances against what the AC would use and the relative loss in FE for using the AC gets pretty small.

[qbee42]

<div class='quotetop'>QUOTE(hyo silver @ Oct 4 2007, 09:50 PM) [snapback]521502[/snapback]</div>

Hadn't we come to the conclusion in a previous thread that windows up/cool air on used less gas at highway speeds?
[/b]

Yes, but the OP didn't ask that question. The OP wanted to know if using A/C hurts mileage, which of course has to be true since A/C uses energy and the energy comes from fuel. The short answer is that anything that directly or indirectly burns fuel without moving the car hurts mileage. The longer answer is that in many cases using A/C is better than the alternative of open windows or roasting the battery.

Tom

[hycamguy07]

<div class='quotetop'>QUOTE(dallas2727 @ Oct 4 2007, 09:23 PM) [snapback]521477[/snapback]</div>

I've driven entire tanks with AC on (set to auto) during temps in the 90s, and I've done tanks with it off. I didn't see a lick off difference in MPG, and I pay close attention.
[/b]

I too have heard of this.... I never saw a difference in the milage either...

On a typical ICE yes there is a difference in MPG. and you have to leave the car running to use the ac.

On my 04' Prius it was great I would leave the ac on norm (med fan) set to 15* cooler than the outside temp (I had a thermometer in the a/c duct for setting the temp) , and when sitting still the ICE would turn on every 30 min and run for 10 then shut off. Again I had to use a prius for a year at work, I would average 350 - 400 mile per tank. Im in Florida and the outside temps hover around 85*- 102*

But again the opinion of most on PC. is that running the ac does effect your MPG's.

[qbee42]

<div class='quotetop'>QUOTE(hycamguy07 @ Oct 5 2007, 11:51 AM) [snapback]521762[/snapback]</div>

But again the opinion of most on PC. is that running the ac does effect your MPG's.
[/b]

Using A/C does effect mileage. It has to. Very basic thermodynamics will tell you that there is no free lunch. If you use energy, it has to come from somewhere, and in the Prius, that means burning gas.

What many of the posters have discovered is that the Prius A/C is very efficient. Compared to ordinary automobile A/C, it uses very little power. In many cases the power loss is too little to notice.

Tom

[efusco]

For those who haven't noticed a difference in MPG...
Let me add that we're talking about small percentage drops that you'll observe. It would be easy to see the difference if you could drive a route such as that simulated by Wayne's Prius simulator...but we're talking about a reduction of 1-3mpg over the course of a full tank at steady speed. That's what, 2-5%? Almost impossible to measure accurately on a single trip or even a single tank.

Some of us hypermiling nut-jobs can notice a significant drop...I can achieve 75-82mpg on my work commute (15 miles rolling rural roads and some city driving with around 10 stops over the distance of the drive, avg. speed about 30mpg). With AC there's no way I can get over 65mpg on that commute if used the whole way. I've found that there are strategic ways to use AC and times I can shut it off to take advantage of it's effects but not waste energy while I wait at lights and can get those numbers up closer to 70mpg or so and stay comfortable most of the trip.

By all means, when it's hot outside, turn on the A/C, the impact is small to unmeasurable for most drivers.

[David Beale]

Also, just to confirm windows open "wastes" energy, I've used it descending mountain passes to help hold my speed, just to see what the difference was between this and using "B". The difference was the "thumping" caused by the air pressure resonating at around 5 Hz in the cabin. Otherwise, the windows open would hold my speed almost as well as "B". So it does "waste" energy/is aerodynamically inefficient. Just like most other vehicles I've owned. Heck, the anti-Prius (2001 Pathfinder) owners manual recommended using A/C instead of having the windows open at highway speeds, stating it was more fuel efficient that way. And it was.

[dallas2727]

<div class='quotetop'>QUOTE(Display Name @ Oct 5 2007, 09:39 AM) [snapback]521679[/snapback]</div>

Finally, the perpetual energy machine we've all been searching for! I hope you isolate and patent this process ASAP!
[/b]

I'm not sure what you are getting at. I guess you were trying to be sarcastic and funny at the expense of me just factually reporting my experiance.