what percentage does running the a/c decrease mileage and why?

bagwell · 05-12-2006, 03:06 PM

I find I lose a significant amount of MPG on my daily commute with the a/c on in the hot afternoons versus in the morning when I don't turn on the a/c and wondered if the compressor is just an old fashioned drag on the ICE or is it sucking up electricity from the hybrid battery which would leave less juice for the elelctric motor.

anyone know?

**efusco** · 05-12-2006, 03:33 PM

Well, it runs directly off of the HV battery, but the ICE still needs to run more to recharge the energy drained from the battery.

I can't give a % number too you. Too many variables. Outside temp, direct sun or cloudy, AC temp, fan speed, speed of travel, wind direction (determines how hard the car must work to maintain that speed), weight in vehicle, number of people in the vehicle (more people create more heat).

Charles Suitt · 05-12-2006, 03:38 PM

<_< Lawyers would term this an "imponderable." Such as "High high is the sky?"

There are far too many variables involved for a definitive response: Temperature, hills, road surface, varying speeds, use of brakeing, wind direction & velocity, percentage of ethanol in the fuel, how much coasting, type of accelleration, etc. etc.

Perhaps some forum members can share their experiences and W.A.G. information. Sorry, I have no data to assist. Personally, I can't tell any appreciable difference with/without the compressor unit running. Also, this would be in warmer or hot weather which would frequently tend to increase the MPG's compared to cold weather in which the ICE might well run more to provide warmth thus reducing MPG's.

Have to laugh at myself... All that text, and I really didn't say anything. And.... I'm not a lawyer or politician.

NuShrike · 05-12-2006, 04:17 PM

<div class='quotetop'>QUOTE(bagwell @ May 12 2006, 12:06 PM) [snapback]254254[/snapback]</div>

Quote:

I find I lose a significant amount of MPG on my daily commute with the a/c on in the hot afternoons versus in the morning when I don't turn on the a/c and wondered if the compressor is just an old fashioned drag on the ICE or is it sucking up electricity from the hybrid battery which would leave less juice for the elelctric motor.

anyone know?[/b]

What are the temperatures outside, and are you using AUTO? Generally, if it's not too warm outside with something like 90-100Fs, then AUTO and keeping your temperature around 78-80F will keep you cool enough and not impact mpg. Good IR tint also helps.

qbee42 · 05-12-2006, 04:38 PM

It takes power to run an A/C compressor. It makes no major difference whether the power comes directly from the engine as in a conventional car, or from electricity as it does on the Prius. Either way it is sucking up power and reducing your MPG. With thermodynamics, there is no free lunch: you want to move heat from the inside of the car to the outside, you gotta pay for it. Technology can produce more efficient compressors, but it can't defy the laws of thermodynamics.

Tom

tomdeimos · 05-12-2006, 06:07 PM

AC runs on electricity. This comes from the gasoliine so it is costly as in any car. But the extra cost from running it can be anywhere from 1 mpg to 50 or whatever your normal mpg is without it.

It is especially bad for short commuting after the car has beeen sitting in the sun. it takes lots of power to cool the car down.
Other than that the cost depends on the amount of sun, the temperatures outside, what you set the inside temperature at, and how fast you are going. In a traffic jam at 0 mph 100% of your gasoline goes to cooling and you get 0 mpg when you aren't moving.

So the added cost from AC generally gets less the faster you drive. With minimal use on a long trip, and going over 70 mph you can get to the 1 mpg cost level.

darelldd · 05-12-2006, 07:50 PM

<div class='quotetop'>QUOTE(tomdeimos @ May 12 2006, 03:07 PM) [snapback]254385[/snapback]</div>

Quote:

AC runs on electricity. This comes from the gasoliine so it is costly as in any car. [/b]

Sorry... by now you all know that I have no self control.

The "cost" of AC in the Prius is NOT the same as in any car. Maybe the same as in any traditional/gasoline car. But when I use AC in my electric Rav4, all the power for it comes from my batteries which are charged from my roof-mounted PV system - so just like with traction power, the energy for my AC is basically free at this point. It sure as heck doesn't come from gasoline. (as a data point, the AC in the Rav can reduce the range by about 2-5%. But it sure doesn't decrease the gas Mileage. )

Obviously I know exactly what you meant... but hate to miss an oportunity to show that we could and *should* have options to powering everything with gasoline.

But back to the discussion....

EricGo · 05-12-2006, 08:34 PM

I had to stop reading your posts to my wife, Darrell. She says you are a snot.
Ah well. I'll just enjoy them quietly.

Begreen · 05-12-2006, 09:40 PM

<div class='quotetop'>QUOTE(EricGo @ May 12 2006, 05:34 PM) [snapback]254448[/snapback]</div>

Quote:

I had to stop reading your posts to my wife, Darrell. She says you are a snot.
Ah well. I'll just enjoy them quietly. [/b]

Arogant and righteously proud maybe. But he is (s)not! Darrell points out that there is hope on the horizon.

kirbinster · 05-13-2006, 06:34 PM

Energy usage in for a/c in a new Prius (post '03) is strictly a functions of heat load. In a classic prius or any other non-electric a/c it is a function of heat load and vehicle speed. At low speed it puts a big strain on the engine and costs a lot, at high speed there is almost no strain on the engine and it is "almost" free.

05-12-2006, 03:38 PM	#3
Charles Suitt Senior Member Join Date: Oct 2004 Location: Dallas TX Posts: 1,622 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	<_< Lawyers would term this an "imponderable." Such as "High high is the sky?" There are far too many variables involved for a definitive response: Temperature, hills, road surface, varying speeds, use of brakeing, wind direction & velocity, percentage of ethanol in the fuel, how much coasting, type of accelleration, etc. etc. Perhaps some forum members can share their experiences and W.A.G. information. Sorry, I have no data to assist. Personally, I can't tell any appreciable difference with/without the compressor unit running. Also, this would be in warmer or hot weather which would frequently tend to increase the MPG's compared to cold weather in which the ICE might well run more to provide warmth thus reducing MPG's. Have to laugh at myself... All that text, and I really didn't say anything. And.... I'm not a lawyer or politician. __________________ Charles Suitt Dallas Texas 2007 Touring Edition (Former Prius: 2004)

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05-12-2006, 03:06 PM	#1
bagwell Member Join Date: Sep 2005 Location: the woodlands, tx Posts: 77 My Car: 2006 Prius Package: #3 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	I find I lose a significant amount of MPG on my daily commute with the a/c on in the hot afternoons versus in the morning when I don't turn on the a/c and wondered if the compressor is just an old fashioned drag on the ICE or is it sucking up electricity from the hybrid battery which would leave less juice for the elelctric motor. anyone know?

05-12-2006, 03:33 PM	#2
efusco Troll Slayer Join Date: Nov 2003 Location: Nixa, MO Posts: 14,050 My Car: 2004 Prius Package: #9 Nominated 1 Time in 1 Post TOTM Awards: 0 Friends: 23	Well, it runs directly off of the HV battery, but the ICE still needs to run more to recharge the energy drained from the battery. I can't give a % number too you. Too many variables. Outside temp, direct sun or cloudy, AC temp, fan speed, speed of travel, wind direction (determines how hard the car must work to maintain that speed), weight in vehicle, number of people in the vehicle (more people create more heat).

05-12-2006, 04:38 PM	#5
qbee42 Senior Member Join Date: Mar 2006 Location: Northern Michigan Posts: 5,555 My Car: 2006 Prius Package: #7 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 5	It takes power to run an A/C compressor. It makes no major difference whether the power comes directly from the engine as in a conventional car, or from electricity as it does on the Prius. Either way it is sucking up power and reducing your MPG. With thermodynamics, there is no free lunch: you want to move heat from the inside of the car to the outside, you gotta pay for it. Technology can produce more efficient compressors, but it can't defy the laws of thermodynamics. Tom

05-12-2006, 06:07 PM	#6
tomdeimos Join Date: Feb 2004 Location: Lexington, MA Posts: 995 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	AC runs on electricity. This comes from the gasoliine so it is costly as in any car. But the extra cost from running it can be anywhere from 1 mpg to 50 or whatever your normal mpg is without it. It is especially bad for short commuting after the car has beeen sitting in the sun. it takes lots of power to cool the car down. Other than that the cost depends on the amount of sun, the temperatures outside, what you set the inside temperature at, and how fast you are going. In a traffic jam at 0 mph 100% of your gasoline goes to cooling and you get 0 mpg when you aren't moving. So the added cost from AC generally gets less the faster you drive. With minimal use on a long trip, and going over 70 mph you can get to the 1 mpg cost level.

05-12-2006, 08:34 PM	#8
EricGo Three cats, one Prius, and assorted humans Join Date: Apr 2005 Location: Albuquerque, NM (SouthWest US) Posts: 1,810 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	I had to stop reading your posts to my wife, Darrell. She says you are a snot. Ah well. I'll just enjoy them quietly.

05-13-2006, 06:34 PM	#10
kirbinster Senior Member Join Date: Jun 2005 Location: Morris County - New Jersey Posts: 575 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	Energy usage in for a/c in a new Prius (post '03) is strictly a functions of heat load. In a classic prius or any other non-electric a/c it is a function of heat load and vehicle speed. At low speed it puts a big strain on the engine and costs a lot, at high speed there is almost no strain on the engine and it is "almost" free.