Measured effect of AC and Heater use

Discussion in 'Clarity' started by bpratt, Dec 8, 2018.

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  1. bpratt

    bpratt Active Member

    I live in Salt Lake City where our temperature can get above 100 F in the summer and into the single digits sometimes in the winter. My garage is partially conditioned so the temperature never exceeds 85 F in the summer and never below 50 F in the winter.
    Last summer after driving my car about 10 miles with the AC on, I parked in the sun on a 95 degree day, left the car on and measured a drop in EV miles of about .1 miles every 2 minutes. (or about 1 mile every 20 minutes).
    I did a similar test a few days ago after driving about 10 mile with the seat heat at 1 and the heat on set at 70 F. I parked in the shade on a 27 degree day, left the caon and measured a drop of EV miles of about .1 miles every 32 seconds. (about 1 mile every 5 minutes)
    One additional test I did is from Sept 1 until Nov 25 I drove my car with the climate system turned off, and no freeway driving, and kept track of EV miles based on temperature. From Nov 26 to Dec 5, I did the same test with the driver seat heat set at 1 and the climate system turned on heat at 70 degrees.
    Here are my findings:

    Month-----------Av EV range--------Actual EV--------Av High Temp------Av Low Temp

    September *1-------65------------------62--------------------77------------------55

    October *1-----------61------------------58--------------------63------------------44

    Nov 1-25 *1----------58------------------55--------------------48------------------32

    Nov 26-Dec 5 *2-----38------------------35--------------------38------------------22

    *1 Climate system off

    *2 Driver seat heat 1, Heat on temp at 70
    Last edited: Dec 8, 2018
    Kendalf, Texas22Step, KevinW and 7 others like this.
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  3. MNSteve

    MNSteve Well-Known Member

    Thank you. I find those numbers fascinating.
  4. bpratt

    bpratt Active Member

    Every AC in every car ever made is a heat pump. The evaporator inside the car removes heat and then it is expelled through the condenser in front of the radiator. Since the AC only uses 25% of the power of the resistive heater in our Clarity, it would make sense to me to use the AC to heat the inside of the car. All that has to be done is the fluid in the AC unit needs to flow the opposite direction, (a couple of flow control valves) a second expansion valve would need to be installed on the output of the condenser (which would become the input when it was set to heat mode) and a little computer programming would be all that needs to be done.
  5. David Towle

    David Towle Well-Known Member

    I'm pretty sure I read that Honda did that on the full electric Clarity so I'm sure the equipment exists, but it must be a cost adder that they didn't want to bear, although I can't imagine how it would cost more than $50 on the production line. But I guess that's a big number when it comes to mass production.
  6. David Towle

    David Towle Well-Known Member

    My recent EV run on the highway with heat at 70 was 27 miles, that costs $2.70 here, vs $1.75 in gas for the same miles. That's why I'm running EV only around town now and without heat as much as possible.
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  8. DaleL

    DaleL Active Member

    One issue to consider is that a heat pump becomes less efficient the colder it is. Below 25 degrees F a heat pump is not useful. The full electric Clarity is not marketed in cold climates. Turning the AC into a heat pump/AC unit would add complexity/cost and still not replace the need for resistance heating at temperatures below 25 degrees F.
    Texas22Step, Pegsie and KentuckyKen like this.
  9. David Towle

    David Towle Well-Known Member

    That was true in the past but they have home ones now that have a COP of 2 down to -10 F. I doubt this technology has been applied to cars yet though.
  10. Viking79

    Viking79 Well-Known Member

    Either way if you use a heat pump you still need a resistance heater, and if you have a combustion engine, you most likely have a heat exchanger in the car for it already (except on BMW i3, grrr) so a heat pump is added cost and weight whereas using engine heat is sort of free. Hyundai/Kia go to extreme and take away the electric heater as well to save costs and use only the engine.
  11. David Towle

    David Towle Well-Known Member

    Engine heat's fine for me, I'm mostly ignoring EV for the winter, but lots of folks on this forum want to drive further in EV mode.
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  13. michael shama

    michael shama New Member

    This helps a lot!! Thank you for doing this. My bottom line, is that 1 hr of EV driving with heat on will reduce EV range by about 15 miles compared to no heat on!! Im seeing about the same numbers, but this table takes it really easy to understand :)
  14. I’ve lost about 25% of my electric range running the heater and seat warmer during my 65 mile morning commute. I’m not going to freeze to save a dollar, lol.

    Average outdoor temp (morning) 34 degrees

    Temperature in car set to 75 degrees
  15. marshall

    marshall Well-Known Member

    The gas engine makes a very poor boiler. Plus it takes time the heat the engine, so it's ineffictive for short trips.
    MPower likes this.
  16. MPower

    MPower Well-Known Member

    That was certainly the case with my 2012 Prius Plugin which used the ICE for heating.

    I did not bother turning the heat on anytime I was just dubbing around town because generally I arrived before the ICE heated up especially since leaving my house is always downhill so I was always generating electricity instead of ICE heat. I used the heated seats instead which ran off the battery.

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