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air conditioner and fuel economy

Discussion in 'Gen 2 Prius Fuel Economy' started by laceyandiris, Apr 14, 2004.

  1. laceyandiris

    laceyandiris New Member

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    how much effect have people noted on their fuel economy running the AC. I realized that the auto feature was on, and the AC was defogging, ? decr by 4mpg?
     
    #1 laceyandiris, Apr 14, 2004
  2. autoxic

    autoxic Commuter

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    Today, my mileage decreased from 50.5MPG to around 47MPG for the 10 miuntes while I had my AC on. I turned AC off and mileage jumped back up over 50MPG. Outside temp: 73F and sunny. AC set to 71, fan was on second lowest speed.
     
    #2 autoxic, Apr 19, 2004
  3. jimvitz

    jimvitz Junior Member

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    Sunday was our first really warm day here in the Chicago area (87
    F), and so I put on the air for the first time on a drive of about 40
    miles along the Chicago expressways and on several arterial streets,
    including some stop and go on the xway and heavy traffic on the
    streets. I set the temp at 76 F. I started out at 56.4 mpg at about
    360 miles on the tank, and ended at 56.3 and about 400 miles on the
    tank. So, I guess I'd have to say, having it on wasn't a factor. The
    biggest hit I took on mpg was when heading into the very strong winds
    we had yesterday, but gained it all back on the return trip with the
    wind at our backs.
     
    #3 jimvitz, Apr 21, 2004
  4. efusco

    efusco Moderator Emeritus
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    It depends on a lot of different things. If the OAT (outside air temperture) is 75 and you have the AC on 72 then the impact will be minimal. If the OAT is 95 and you're on 67 the impact will be dramatic. Likewise, any defroster use will have a larger impact.

    If you're a PDA owner/user you should install Wayne Brown's THSII Simulator and just play with the variables a bit--you can plug in your speed, OAT, AC on/off/temp, wind speed, road conditions, etc and see how much impact each variable has (via convenient sliders) on your overall mpg. It's pretty eye opening.

    http://www.seawell.net/Prius/PalmTHS2/THS2HiRes22.zip
     
    #4 efusco, Apr 21, 2004
  5. Wolfman

    Wolfman New Member

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    I've noticed little effect on my fuel economy, and my A/C is still engine driven.
     
    #5 Wolfman, Apr 22, 2004
  6. HTMLSpinnr

    HTMLSpinnr Super Moderator
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    In my classic, the A/C makes a huge hit in city driving since the ICE runs while stopped.

    In the '04, the hit is a bit more spread-out if the temp is set low since the ICE is working to generate the extra amps to run the compressor.
     
    #6 HTMLSpinnr, Apr 22, 2004
  7. Brian

    Brian Member

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    How does using the AC on the freeway help instead of a window open? I read it on John's site. I notice that the ICE runs and charges the battery. So using some of that energy is good?
     
    #7 Brian, Apr 22, 2004
  8. HTMLSpinnr

    HTMLSpinnr Super Moderator
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    The drag caused by the windows down is more parasitic than using some power to run the A/C compressor.

    This is usually the case at anything above 40mph I believe (that could be a number pulled out of my a$$, but at lower speeds, windows down is fine, at highway speeds, use the A/C instead).
     
    #8 HTMLSpinnr, Apr 22, 2004
  9. aarons12

    aarons12 New Member

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    i thought i read that the prius a/c runs on electric, not a belt on the ICE, and therefore should have a minimal impact on mileage.

    of course, i suppose in stop and go driving it would be more of an impact because the ICE would have to run more to keep the batteries charged
     
    #9 aarons12, Apr 22, 2004
  10. HTMLSpinnr

    HTMLSpinnr Super Moderator
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    The A/C is electric, however that electricity needs to come from somewhere.

    The advantage is that the A/C compressor can run at independant speeds, etc. which is more efficient than running off/on at engine speeds. There's also less of a direct drag on the engine while it's operating.

    HOWEVER - again, the electric power that runs it isn't free. It does drain the battery and/or put an additional load on MG1 (generator) while driving. The burning of gasoline within the ICE is the ultimate source of energy for this car, and since that energy is being converted to electricity, and electricity is being used for the A/C - more fuel will need to be used.

    The nice thing is that some of this energy can be stored in the battery so that the A/C can run for short periods (< 5-10 minues) of time w/o the engine running in stop and go situations. However, the next time the ICE kicks in, it will be working a bit harder to replenish that stored energy in the battery.

    The moral here is there is no such thing as free energy or a free ride. It all has to come from somewhere.

    Hope this helps,
    -Rick
     
    #10 HTMLSpinnr, Apr 22, 2004
  11. richard schumacher

    richard schumacher shortbus driver

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    The economy advantage of the Prius' AC over that of an ordinary car exists because the engine doesn't have to be running. True, there are conversion losses through the generator and the AC compressor motor, but these are outweighed by the benefit of leaving the engine off most of the time.
     
    #11 richard schumacher, Apr 22, 2004
  12. Ray Moore

    Ray Moore Active Member

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    Or as Dr. Joe says "There's no such thing as a free thermodynamic lunch."
    Ray
     
    #12 Ray Moore, Apr 22, 2004
  13. Medved

    Medved New Member

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    Is sun light free??
     
    #13 Medved, Apr 22, 2004
  14. bookrats

    bookrats New Member

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    Not for the sun. :D
     
    #14 bookrats, Apr 22, 2004
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