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Discussion in 'Gen 2 Prius Main Forum' started by JustDrooling4Now, Sep 4, 2007.

  1. JustDrooling4Now

    JustDrooling4Now New Member

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    My husband asked me a question. I don't know the answer . Here is the question.
    Dose the air conditioner effect gas milage when gliding or running off battery?
    I am not even sure how the air conditioner affects the gas milage in the car.
    Hope someone can give me the run down on the this.
    Just wondering.
    Sue
     
    #1 JustDrooling4Now, Sep 4, 2007
  2. hyo silver

    hyo silver Awaaaaay

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    Yes, using the air conditioner (cooling and heating) will affect your mileage. The power in the batteries came from the energy in the gas, so in effect you're still using gas, even if the screen says you're not. But don't let that keep you from using the air conditioner. On a long drive, it's a safety feature that will keep you more alert. At highway speeds, using the cool air and leaving the windows up is more efficient. It's also important not to let the batteries get too hot or too cold, and if you're uncomfortable, they're not operating at peak efficiency either.
     
    #2 hyo silver, Sep 4, 2007
  3. efusco

    efusco Moderator Emeritus
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    You don't know it, but you've opened a small can of worms.
    The A/C requires energy...all the energy for your car comes from gas...even the energy in the battery must be generated from gas.

    So yes if the A/C is running it will impact your FE and will use extra gas, ultimately. That said, the impact can be pretty minor and it may be MORE efficient to use the A/C at times.

    Confused...you should be if you're reading.
    When it is hot outside the traction battery temp. can get quite high...when it gets high it's less efficient. So using the A/C, since the air to cool the battery comes from the cabin, can help the battery stay a little cooler and run more efficiently decreasing the negative impact of the A/C relative to not using it.

    Also, if your alternative is driving with the windows down the comparative impact of wind resistance from having the windows down compared to windows up with A/C on is pretty comparable and may be more FE to use the A/C than to drive with the windows down.

    So, many of us who are FE freaks tend to avoid A/C use up to outside temps around 80 degrees F or so. The battery will stay cool, just using a 'vent' setting on the climate control can often keep enough air flow to remain fairly comfortable. Once temps climb higher I tend to set my A/C to "on" at around 78-80 degrees F. This keeps the cabin temp tolerable if not cold, keeps the battery cool, but avoids aggressive A/C use which puts a higher demand on the battery (and ultimately the gas use). In addition, and this is getting a little more picky, I turn off the AC about 1/4 mile before getting to my destination, then I tend to drive with the windows down when I'm first starting off and AC off until the initial warm-up phase is over then I'll turn the A/C on at 80F, put the windows up and go on my way.

    Still confused? I hope not too bad. The bottom line is use the A/C at a level that keeps you comfortable...it will impact your FE, but it will have positive benefits as well and it's worth it unless you become FE obscessed like me!
     
    #3 efusco, Sep 4, 2007
  4. a priori

    a priori Canonus Curiosus

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    <div class='quotetop'>QUOTE(efusco @ Sep 4 2007, 01:48 PM) [snapback]506863[/snapback]</div>
    I suppose this is another great can of worms, as you've said. I've heard it said many times over (and applying to "other" cars, as well as to the Prius) that it is more fuel efficient to run the A/C when driving at highway speed. That is, instead of rolling down the windows to cool off, you should run the A/C with the windows closed.

    In this distinguished group of tinkerers, diagnositicians and FE enthusiasts, I'm certain someone has run the data to support this statement. Right? Is there a cut-off speed? A cut-off temperature? Bueller? Anyone?

    a priori
     
    #4 a priori, Sep 4, 2007
  5. jtmhog

    jtmhog Member

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    <div class='quotetop'>QUOTE(efusco @ Sep 4 2007, 02:48 PM) [snapback]506863[/snapback]</div>
    The FE is higher at highway speeds (say, 55 MPH and above) with the windows up. At highway speeds, the air drag on the car increases exponentially with the speed of the car. With the windows down, the air enters the car and slams into the hatch and thus, trying to slow down the car. In town (35 MPH and below) FE is higher with the windows down and A/C off. Between 35-55 MPH, it's probably a coin flip. Ther are many other posts on this subject.
     
    #5 jtmhog, Sep 4, 2007
  6. richard schumacher

    richard schumacher shortbus driver

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    I never roll down the windows. The battery system uses inside air to cool itself; using outside air risks letting the battery get too hot and will more quickly coat all those hidden little cooling surfaces with dirt so that they cool less effectively. Subverting the design intent of the battery cooling system in order to gain at most a few percent in fuel economy seems to me to be a poor tradeoff.
     
    #6 richard schumacher, Sep 5, 2007
  7. PriuStorm

    PriuStorm Senior Member

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    Here's another question along the same line...

    We pulled into a gas station to get a soda one day last week when temps were in the hundreds. I put the car in park (ICE was off) and left the a/c fan running while my partner waited in the car.

    After I returned with the soda, I re-entered the car, but the a/c had been turned off and the car was hot again.

    I asked, 'Why'd you turn the a/c off?' She replied she didn't want to waste the battery/energy on a/c while parked.

    I said for such a short errand (few minutes), leaving the a/c on wouldn't matter because the battery can only charge itself so high... then any overflow charge going to the battery is lost. So if the battery is full when we park, leaving the a/c on running off the battery for a little while won't matter because once we start up and drive again, we'll be recharging...

    Am I way off base here? Thanks.
     
    #7 PriuStorm, Sep 5, 2007
  8. hill

    hill High Fiber Member

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    <div class='quotetop'>QUOTE(PriuStorm @ Sep 5 2007, 11:24 AM) [snapback]507316[/snapback]</div>
    My experiment from year 2004:
    On our '04 model (supposing 04 thru 08 are nearly the same battery systems), at an outside temp of 90 degrees, leaving AC on, and the thermostat set at 73 degrees, high fan speed w/ batteries up in the green, they will draw down to the purply red (last 2 pips) color zone in about 10 minutes. Your results may vary, so you can do the experiment yourself. And it'll probably take about the same length of time.
     
    #8 hill, Sep 5, 2007
  9. efusco

    efusco Moderator Emeritus
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    <div class='quotetop'>QUOTE(PriuStorm @ Sep 5 2007, 10:24 AM) [snapback]507316[/snapback]</div>
    Sorry to say...yes, you're off base. The computer maintains the battery charge and only in rare situations does the batter ever get so full as to spill off excess energy as waste...that's typically on long downhill braking situations where the battery capacity tops off. Otherwise the battery simply acts as a buffer.

    Now, that said, if you made the choice to leave the car in READY while you ran inside I would have left the A/C on..I'd turn the temp to about 80F...but if the Car is on I'm leaving the AC on. Depending upon how many "a few minutes" is I probably would turn off the car and roll down the windows (anything more than 5 minutes).
     
    #9 efusco, Sep 5, 2007
  10. hycamguy07

    hycamguy07 New Member

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    Layman terms: Yes using the a/c effects your gas milage. But you will use slightly more gas due to more wind resistance with the windows down.

    This was proven plausible on Mythbusters...
     
    #10 hycamguy07, Sep 5, 2007
  11. TonyPSchaefer

    TonyPSchaefer Your Friendly Moderator
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    <div class='quotetop'>QUOTE(hycamguy07 @ Sep 5 2007, 12:07 PM) [snapback]507369[/snapback]</div>
    CASE CLOSED!

    Mythbusters rule!
    (especially Kari)
     
    #11 TonyPSchaefer, Sep 5, 2007
  12. qbee42

    qbee42 My other car is a boat

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    <div class='quotetop'>QUOTE(TonyPSchaefer @ Sep 5 2007, 01:31 PM) [snapback]507388[/snapback]</div>
    (especially Kari).... <sigh>

    Tom
     
    #12 qbee42, Sep 5, 2007
  13. alanh

    alanh Active Member

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    As long as the car is at READY and in park, the engine will start as necessary to charge the battery if the A/C is running it down. Yes, this will use gas, but I'd rather not roast (it gets 110+ here).
     
    #13 alanh, Sep 5, 2007
  14. PriuStorm

    PriuStorm Senior Member

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    <div class='quotetop'>QUOTE(hill @ Sep 5 2007, 11:35 AM) [snapback]507351[/snapback]</div>
    Yeah, I will experiment... In our case, we had the fan on low and I was only gone for about 3 minutes... :)
     
    #14 PriuStorm, Sep 6, 2007
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