How to Reduce MPG loss Because of A/C Use

Discussion in 'Gen 2 Prius Fuel Economy' started by F8L, Sep 11, 2011.

  1. ProximalSuns

    ProximalSuns Senior Member

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    Air temperature, altitude are the only real environmental factors to control for the other stuff is irrelevant. All you want to know is the difference the air conditioning makes on fuel consumption at a controlled environment. Using the EPA dynamometer test sequence with AC on and AC off would be fine.

    It's amusing to see how many variables people want to control for in scientific dynamometer testing but have no objection to many wild cards in the anecdotal tests.
     
  2. markabele

    markabele Senior Member

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    A couple things: I am going to start monitoring battery temp and can include this in my logs. What temps do I need to stay below?

    Also, I need to buy a sun shade. Any cheap ones you guys recommend?
     
  3. 2009Prius

    2009Prius A Wimpy DIYer

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    Just pick up one of the shiny silver foldable shades from any of your local auto parts stores or grocery stores or whole sale stores.
     
  4. 2009Prius

    2009Prius A Wimpy DIYer

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    F8L likes this.
  5. dianeinreno

    dianeinreno Member

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    Apparently most sunshades you get in the auto store will not fit the Prius due to it's large windshield. I just bought this one from Amazon 33 bucks plus about 6 dollars shipping. It seemed to get reasonably good reviews.
     
  6. SageBrush

    SageBrush Senior Member

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    I like the type that folds accordion like, it takes just a few seconds to put away. I think ours are from Walmart.
     
  7. jdcollins5

    jdcollins5 Senior Member

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    What was your OAT when doing these tests and what is your commute like? The reason that I ask is that when I monitor the HV battery temp with the SGII I see quite an increase in battery temps on my afternoon commutes when I get in town with a lot of stop and go driving. The increase is quite rapid without AC and much slower with AC when the cabin temp is in the mid-70's after a highway drive home.
     
  8. 2009Prius

    2009Prius A Wimpy DIYer

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    Thanks for the comments. What was the magnitude of increase you saw? To answer your questions, OAT was already plotted in the graph (dotted dark red and purple curves). My drive is almost all one lane roads with speed limit ranging between 25 and 40 MPH, and usually not a lot of stop and goes.

    By the way the thermal mass of the battery is huge so its temperature shouldn't change quickly. If you do see rapid movement of the measured temperature then it may be that the sensor is not in good thermal contact with the battery and merely measures the air temperature.
     
  9. jdcollins5

    jdcollins5 Senior Member

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    I think the difference in our two commutes explains the differences that we are reporting. Yours is at more of a constant speed and mine has a lot of start/stop at the beginning and end. I do not see a lot of change in battery temps while driving a constant 60 mph either since the battery does not see much activity.

    I have a 26 mile commute with about 2 miles of stop/start at the beginning, 20 miles of 60 mph highway driving and then about 4 miles of start/stop at the end. In the afternoons after sitting in an open asphalt parking lot the battery temp is normally in the 95F range.

    I will see it rise to just short of 100F by the time I get to the highway. With AC on and running steady the battery temp will eventually drop to under 95F by the time I complete the 20 mile trip. Without AC it will usually remain constant or increase slightly.

    Once I get close to home and start/stop 45 mph traffic I will see it rise from 95 to 105-110 over the last 4 miles with AC and the cabin temp around 75. Without AC I have seen it rise as high as 120F. This is not a rapid jump but a steady increase with each regen stop and then the following restart.

    If I park at the house and then leave again to go to dinner about an hour later I have seen the temp as high as 125 to 130F as the battery temp continued to rise with the power off and the battery fan off.
     
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  10. SageBrush

    SageBrush Senior Member

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    Yep, this is why Seilerts warns against parking with a full battery on a hot day. Are the windows of your car open for ventilation when you have seen this temp spike ?

     
  11. jdcollins5

    jdcollins5 Senior Member

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    Yes, I have seen this same temp increase with the windows open and with closed. My battery is never fully charged when I get home since I drive a few blocks through our neighborhood mostly without the ICE.
     
  12. F8L

    F8L Protecting Habitat & AG Lands

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    ttt for newbies and a little more info on the cross-vent method. :)
     
  13. imOCD4a_prius

    imOCD4a_prius Member

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    Kindly define "ttt" please. I may be new yet I'm willing 2 learn as many acronyms as I can, germane to my PRIUS.
    Thanks, DJ 2pm 7-31-12
     
  14. briank101

    briank101 Member

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    Remember a regular car's mpg going from 31 mpg to 28 mpg with A/C use is a bigger $ and gasoline hit to your pocket than a Prius going from 60 mpg to 50 mpg. At $4/gallon the regular car A/C on cost is $1.38 per 100 miles, Prius cost is $1.33 per 100 miles if the mpg drops from 60 to 50 mpg, However it is likely the Prius A/C impact will be less as it is a more advanced and efficient design. Note if doing a long re-gen brake going down a hill, lowering the AC temp (and jumping out of ECO mode) while regen braking will more efficiently capture the available re-gen power eliminating some of the battery in/out storage losses and stresses. Also at higher speeds the A/C runs quite a bit more efficiently as air blowing through the condenser is removing heat at a far greater rate. So one should build up a store of cooler air (lower the temp) during the high speed portion of the trip if one is anticipating a slower portion later in the trip where they can then back off on the A/C (raise the temp setting) and go back into ECO mode. The occupants and the HV battery have by then cooled sufficiently to withstand slightly higher temps in the slower part of the trip. Also the obvious: make sure A/C is on recirculate, and a high fan speed with higher temp setting is more efficient that a low fan speed with low temp, and if the vents are facing you a windchill effect of the blowing air helps, but note the HV battery will not be as happy with this.
     
  15. markabele

    markabele Senior Member

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    As a general rule you won't have to worry too much about the traction battery temp unless you are doing a lot of stop and go and it is fairly hot in the car and very hot outside. That is, as long as the fan is working properly and nothing is clogged up.
     
  16. SageBrush

    SageBrush Senior Member

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    Actually, about the same amount -- to within 0.0001 gallon/mile
     
  17. Abdullah Jordan

    Abdullah Jordan Junior Member

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    nop , stop and go with AC will not make you happy at all , you will get 35 mpg max , and thats a big a problem i guess .
     
  18. briank101

    briank101 Member

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    Yes. I should said "is about the same as" instead of bigger. Overall point being of course that the numerical value change in mpg are not comparable if starting from different baselines. Many auto journalists (Consumer Reports) don't get this.
     
  19. dbcassidy

    dbcassidy Toyota Hybrid Nation, 8 Million Strong

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    I agree with your statement completely. better to have a little hit in mpgs than looking at a bill for traction battery replacement. Especially in your Prius is out of warranty! Desert environment dictates using the A/C for keeping the traction battery cool.

    Or, one could be penny wise and dollar foolish.

    DBCassidy
     
  20. dbcassidy

    dbcassidy Toyota Hybrid Nation, 8 Million Strong

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    Why not is this thread for dianeinreno? A poster has every right to comment in this thread on A/C use in the Prius.

    Are you against posters taking a opposing view? Are you offended by their view or the stand they take?

    If you do not see it that way, then, why did you start this thread in the first place?

    DBCassidy
     
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