MPG in Hybrid Mode

Discussion in 'Prime Technical Discussion' started by CEJ, May 13, 2019.

  1. john1701a

    john1701a Prius Guru

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    Actually, there is. Notice the battery-to-fan arrow in this video...

     
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  2. Salamander_King

    Salamander_King Senior Member

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    Is it an indicator of the heat pump being ON? Or it just means the battery power is used to run some component of the HVAC system in some way, such as running a fan? What happens to the arrow if the ICE heat is being used and the fan is still blowing heat?
     
  3. john1701a

    john1701a Prius Guru

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    It really does indicate heat-pump drawing electricity. Watch the coolant temp. Once the engine is warmed up and shuts off, that arrow ceases despite the heater still running.
     
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  4. Salamander_King

    Salamander_King Senior Member

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    COOL! This is very useful information to monitor how the heat is being generated in my car when I try HV/EV switches during this winter. For the past two winters, I have driven my car all HV on my way to work in the morning, the ambient temperature usually below 14F, and all EV on my way home in the afternoon usually above 14F. With this driving habit, I was getting ~3miles/kWh and ~25% AC load ratio.

    Thanks for sharing this info.
     
    #344 Salamander_King, Oct 9, 2019
    Last edited: Oct 9, 2019
  5. Salamander_King

    Salamander_King Senior Member

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    OK @john1701a , I checked this morning on my car and observed following. I can't tell in your video what Climate setting you had in your car, but for this morning commute in my car the battery-to-fan arrow would never turn off even after engine warmed up, in following three settings. Please note that I did not check the coolant temp.
    1. AUTO (climate) ON with A/C turned ON. (air flow direction LO, FAN running at level 2)
    2. AUTO (climate) OFF with A/C turned ON. (air flow direction LO, FAN running at level 2)
    3. AUTO (climate) OFF with A/C turned OFF, and air flow direction WINDOW. (FAN running at level 2)

    In contrast, for following setting, the battery-to-fan arrow turned off.
    4. Climate system is OFF (OFF switch was pushed) (air flow direction WINDOW, FAN was not running)
    5. AUTO (climate) ON with A/C turned OFF. (air flow direction LO, FAN running at level 2)
    6. AUTO (climate) OFF with A/C turned OFF. (air flow direction LO, FAN running at level 2)
    7. AUTO (climate) OFF with A/C turned OFF. (air flow direction LO/High, FAN running at level2)
    8. AUTO (climate) OFF with A/C turned OFF. (air flow direction High, FAN running at level 2)

    PRIME HVAC table.png

    In all the cases, the front and rear defrosts were both OFF, the ECO HEAT/COOL mode was ON, S-Flow was set to Driver priority, and Temperature setting was 72F while outside temp remained 50F and cabin temp never reached 72F while testing.

    My conclusion based on the fact that the battery-to-fan arrow stayed showing the energy flow from the battery to the fan even after engine was well warmed up seems to suggest it is not always showing the heat pump operation, but rather some other component of HVAC system that is associated with A/C switch regardless of air flow and to the WINDOW air flow when A/C switch is OFF. My guess is the compressor used for dehumidification, and this function is always ON if A/C switch is ON or WINDOW air flow is selected (even with A/C off). This matches the notion @Tideland Prius pointed out earlier.

    PRIME HVAC.png
     
    #345 Salamander_King, Oct 10, 2019
    Last edited: Oct 10, 2019
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  6. vvillovv

    vvillovv Active Member

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    I'm not sure it was the heat pump, but at 10 mph on a dead quiet night with below freezing temps I think I heard the heat pump switch on than switch off at 7 mph.
    I wasn't watching any animated graphics at the time either so could comment on that part of this discussion, sorry.
     
  7. Salamander_King

    Salamander_King Senior Member

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    To be honest, I have no idea what sound I should be hearing when the heat pump kicks on and off. I have been trying to figure out under what conditions heat pump switches on and off and utilize engine heat. All I know is that at or below 14F, ICE comes on to provide heat source, but don't know if heat pump has no function under those low temp? Similarly, when the ambient temp is ideal for the heat pump operation, say around 50F, but ICE is on, I don't know if the car use the wasted heat off ICE instead of using the heat pump.
     
  8. vvillovv

    vvillovv Active Member

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    I edited your quoted post so you'd know exactly what I'm talking about in my response.
    I've run our prime and 2014 PIP in EV mode with ambient temps below 14 F perconditioned.
    What the actual limits are have probably not yet been verified under every possible set of variables.
     
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  9. john1701a

    john1701a Prius Guru

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    The system will squeeze coolant heat out wherever possible, even in the most extreme conditions. Energy that would otherwise be wasted is always used first. That's why I include the coolant temp data. Even even cycled frequently, it is still an efficiency benefit.
     
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  10. Salamander_King

    Salamander_King Senior Member

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    IIRC, @john1701a commented on other thread that he could run all EV with just heat pump as heat source down to 11F. I think this low temp limit for the heat pump thus the low temperature threshold for the ICE automatically turns on has some other factors beside ambient temperature playing role. @MSantos commented in another thread that he can run all EV without ICE kicking in down to -20C (-4F) no problem, while at that temperature my PRIME usually start ICE immediately after turning the car ON even if the climate control is set to OFF (and no front defroster either). The difference I found out was that his car stays in a garage while mine sit in cold outside. Beside from ambient temp, the coolant temp and battery temp must play a big role in whither the ICE turns on or not.
     
  11. CEJ

    CEJ Member

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    This morning I drove in EV first with everything off (except flow direction) and no visible temp setting. Outside was about 50 degrees or less and I am now convinced that the air coming in was just the ambient stuff, because the minute I turned the fan on (with everything else still off), the temp setting became visible and there was heat coming in. So as mentioned earlier in this thread, if you want ambient air and the fan, you should turn down the temp setting to ensure heat doesn't come on.
     
  12. Salamander_King

    Salamander_King Senior Member

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    That's good to know. Just curious, in what situation would you want to intake ambient air with the fan? I usually just roll down the window for that.
     
  13. walterm

    walterm Active Member

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    Driving at highway speeds I'd rather have a light breeze of ambient air through the vents than the noise/buffeting from having the windows open.
     
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  14. CEJ

    CEJ Member

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    I guess I thought there would be less air resistance compared to opening the windows and, hence, be more efficient. But, of course, energy is being used to drive the fan so I don't know how all that shakes out in terms of all-over efficiency. And there is the noise factor which has been mentioned.
     
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  15. CEJ

    CEJ Member

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    When in EV and auto climate control selects windshield airflow, what is going on? Is the heat pump then supplying heat to defrost just the front window or also the back window? Does the ICE come on if HP doesn't have enough heat to do the job?
     
  16. Salamander_King

    Salamander_King Senior Member

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    I don't know what AUTO mode does when it selects windshield. But with MANUAL mode, I discovered that windshield airflow selection automatically causes the power moving from the traction battery to AC. This happens even if with AC buttons turned off. See my post #345.

    I think when airflow to the windshield is selected electric compressor is automatically turned on. This requires power from the traction battery. As far as heat goes, if the heat is available from ICE, it is used as a heat source, otherwise, the heat pump is supplying heat if the temperature is set as such. And yes it's always true that if the heat pump does not provide sufficient heat, it may turn on ICE as in the case when the ambient temp drops below 14F. And rear window has no airflow heat source, IFAIK. You have to turn on the rear defogger switch for that.
     
  17. CEJ

    CEJ Member

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    Thanks, SK! Can always depend on you for perceptive and useful input!
     
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  18. Salamander_King

    Salamander_King Senior Member

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    You are welcome, as always. I am just starting to learn about those HVAC behavior in PRIME myself as well. Because I hated to use the 11.6 screen, for my first two years of driving, I always kept the HVAC setting at 70F AUTO, and did not change the setting for most part.This has caused sometimes over 30% A/C load during cold winter months. I started changing the HVAC setting manually this summer to see if that will improve the EV efficiency. At least for now in milder temperature, I can keep the HVAC use to minimal at A/C load % down in a single digit. I will see what happens when it really gets cold.

    BTW, you may already know this, the front defroster switch when turned on, even if you had your HVAC on low with A/C off, will cause the fan and A/C to run at max and this will start ICE if you are on EV mode. This will cause huge A/C load on EV mode. I have been switching to HV before I use the front defroster and turn the front defroster off before switching back to EV mode, this seems to minimize the A/C load on EV mode and increases EV efficiency (miles/kWh) thus results in higher number on EV range on GOM. I am still keeping my GOM at above 40 miles range with this technique. The problem is that it uses gas to switch the car into HV, so overall mpg is down. However, going into winter, this technique might actually make sense to save gas when I have to use HV to complete my daily commute.
     
  19. CEJ

    CEJ Member

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    Wow, that is interesting! Let me see if I understand. Assume you are in EV mode when you get the 30% load on AC? Is the AC on then for purposes of defrosting? (Maybe I am confused here.)
    Yeah, I have noticed turning defrost on in EV mode, kicks ICE into action. I saw the 999.9 mpg reading start dropping quickly.
     
  20. Salamander_King

    Salamander_King Senior Member

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    I had my HVAC set at 70F AUTO with A/C ON all the time for the last two winters. I had misunderstood the A/C button on the screen was for the heat pump (heating) as well as air conditioner (cooling), as in the case of what "A/C" meant on the fob. As it turned out, A/C on the screen seem to represent only electric compressor used for air conditioning (cooling) in summer, and dehumidifying in winter and not for heating. This setting was causing huge hit on EV efficiency. Of course, I was driving my car all EV until it runs out of the range and switching to HV, or forcing HV in the cold morning and saving EV range for afternoon commute back home. My thinking is if I distribute EV range over the morning and afternoon commute and utilize HV mode to generate as much heat as I need to defrost the windows and warm-up the cabin, I may get better EV efficiency and HV gas mileage due to longer EV range.
     
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