Does the A/C reduce mileage?

<div class='quotetop'>QUOTE(efusco @ Oct 4 2007, 09:03 PM) [snapback]521465[/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.

 

In really basic terms...

The ulitmate source of all power in the Prius (and other automobiles) is the gasoline in the tank. Whether the air conditioner is run directly from the engine (as in a regular automobile from a belt connected to the crank shaft) or by electric motor (as in the Prius) attached to the electrical system, the ultimate source of power is still the gasoline engine.

The air conditioner requires a only a couple of horsepower which is a relatively small fraction of power required to make the car go. Consequently in most cases you will not see very much, if any, reduction in gas consumption. (I suspect that if you ran two identical Prius automobiles side by side (one with air conditioning on, and the other with air conditioning off and windows closed) over a long distance, you might see some evidence in increased fuel consumption by the vehicle using air conditioning .

Keith

 

No difference on the fuel economy if you're on the highway. Little difference if you're in the city, as long as you set it to 78?F/Low. That's sufficient to keep you cool even in the desert heat. If you set it to Max and full blast and drive in the city, I assume it would have a more noticeable impact on the MPG.
No A/C in a HOT day doesn't mean just torture for you, it also tortures the car. The battery needs to be cool to perform at its best.
So if you need the A/C turn it on at a comfortable setting (around 78?F and low fan) and enjoy your drive!

 

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

 

All I have to say is that the energy has to come from somewhere. Any amps going into the AC is less amps going into the MG's.

 

Great answer Doc! You really put it in perspective.

 

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


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.

 

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

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

 

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.

 

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

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

 

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

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.

 

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

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

 

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.

 

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

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.