The impact of A/C on MPG

I only just bought my vee less than a week ago, so I really can't comment. However, I have definitely noticed that the gas mileage on my '12 Lincoln MKZ Hybrid has gone down considerably since I've had the AC on this summer.

 

I agree, i have yet to notice any change in MPG with the A/C on.

 

Guys, girls,
I was googling to find out typical A/C load, thanks for the numbers!
I'm british, we don't have the same need for a/c here and it's not that common. On the few hot days we do have, other measures are needed.
I have an NC fiancee. On my first visit out there, I was a bit shocked at how a 'green' family would prep their car before driving.
You know how it goes, it's 95+ outside, the car is parked in the sun. It could probably bake bread.
They'd go out start it, then go back inside the house for 15 minutes while it cooled down.
Now, at my suggestion, they go out, open every door, then go back in the house for 15 minutes. It's drops down to near ambient in that time, the a/c only needs a few more minutes to get it comfortable, if it's 95-100, you can just start it, shut the doors and it's tolerable if you point the vents at you and cool in a few minutes.

 

My approach is the same as it has always been. I get in the car and drive with the windows open until I get to where I will drive over 45mph. At that point I close the windows and turn on the a/c to a temperature that is as high as I am comfortable with, generally 77-80°F depending on where the Sun is. I don't find a huge hit in mpg and I don't see the fan speed staying about 2 bars very long. I think the key is to let the car get most of the way to ambient as fast as possible on its own. Shade would help, but I'd still do what I do now.

 

I want to remind you all, the HV battery is in the cabin with you because it NEEDS to stay cool. (Early prototypes could not cope with high heat with the battery in the trunk) When you feel hot, your battery 'feels' hot and hot batteries are short lived batteries. Run the A/C and have a trouble free Prius.

Yes, my Summer MPG is not as good as Spring/Fall, but I am happier and my battery is happier.

 

I agree with Jimbo - keep the battery cool!

How a/c affect mileage is quite simple really. The a/c draws it's power from the battery so the ICE has to replenish it. On first start up after the ICE has cooled and the interior has been baking in the sun, the battery is providing most of the power to the drive wheels while the ICE is warming up, AND it's providing power to the a/c system. This results in quite a bit of drain on the battery. In warm weather, the ICE doesn't take long to warm-up, but with the double load on the battery, it doesn't take long to drain it down. Then once the ICE has warmed up, it spends the next several miles or so providing power to the drive wheels AND replenishing the battery. Results are low mpgs during the first 3-5 miles. Once the ICE is fully warmed up and the battery is fully charged again, the a/c impact on mpg is negligible, unless of course you get stuck in stop/go traffic and the a/c then drains the battery again while you're not moving. It seems you can't win! But I temporarily switch to ECO mode to minimize the a/c load and it seems to help.

 

We have a winner!
First ventilate to approach ambient, then
Use AC moderately.

And of course do what is possible to keep the cabin from turning into an oven when parked:

1. Look for shade
2. Use a sun screen opposite the sun
3. Crack open windows

In my hot but dry climate summers I lose about 1-2% of my fuel economy on drives over ~ 10 miles.

 

Use of the A/C in 90+ weather costs me all of about 2 MPG. I think I can deal with that.

I get my best MPG in weather around 75-85', with the A/C on all the time.

 

Are the batteries affected negativly when the car is parked in the heat? Or just when the car is on in the heat?

 

It's reasonable trade-off for comfort.

 

No and no.

 

The ICE has to generate all the power to run the AC compressor, but it is a very efficient system. Instead of the compressor running at full output all the time, the Prius uses a 3 phase electric motor to run the compressor. On July 4 we were waiting in the Prius in a parking lot, waiting for a celebration to start.
I have always wondered if the Prius electric compressor was constant speed or if it uses a variable frequency drive to run the compressor only fast enough to supply the asked for level of cooling ?
My brother had the Prius in ready mode with the ICE off. I was on the passenger side with the window down so I could hear the compressor run. I turned the AC on with the blower speed low. The AC compressor ran at full speed until the AC evaporator cooled down. As the evaporator cooled , the ac compressor began stepping down it's speed in what sounded like about 30-50 rpm steps until it settled down to about 1/2 speed. I then set the blower speed at full speed so the warm air would lose heat to the cool AC evaporator. As the evaporator sensed it was getting warmer, it began stepping the compressor speed back up to maintain the evaporator cool temperature in spite of the warm air blowing through it. I turned the blower to minimum to slow the warm air flow through the evaporator. After a few seconds, the evaporator reached the low temp limit and again begain stepping the compressor speed down to a speed that just maintained the desired temp.
A very slick and efficient system . Me impressed.

 

My Scan Guage II never shows a MPG drop when the A/C is on. I do not know what setup you are using - dashboard readings?

 

Does your car have that amazing 'zero point energy' first shown in 'The Incredibles' ?

 

Here in the UK, damp cold climate, would leaving the AC on with heat, to demist, make any difference to mpg ?

 

No.

 

What rdgrimes meant was that the difference would be small, potentially not measurable.

And a heck of a lot better than they alternative of having an obstructed windscreen and a soggy car, right?

I think people get completely torqued up about a/c with the Prius. Using it uses energy. So? I wouldn't sit in the car for 10 minutes with it blasting and then drive around with the temp set to 64 (18C) in the summer. But at the same time, I'm not going to sweat using it either. (Two puns in one paragraph, go nsfbr!)

The thing to keep in mind is that Toyota has done several really smart things to reduce, and I'd say nearly minimize how much energy the a/c system uses. First, it is small, usually car a/c systems are way oversized. Like house oversized. Second, it is an electric system, rather than a belt / pulley system. So when it is off, it is really off, and when it is on, it doesn't affect the efficient operation of the HDS. It is more like driving on a grade that is very, very slightly more uphill.

I happen to think that the a/c in the Prius is one of the nicest aspects of the car's design. So use it, just use it smart.

 

Had I read this post I wouldn't have bothered my much less detailed one. Great explanation!

 

Huh? What's non-linear about an mpg scale? If you want gpm, all you have to do is invert, but that's a linear transform.