MPG in Hybrid Mode

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

  1. CEJ

    CEJ Member

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    Great stuff, thanks again. Can you review for me a couple of points (some of these have probably come up before):
    1. Does the HP run at all in HV mode (for heating) or does all the warmth come from the engine coolant?
    2. Does all air conditioning come from the HP?
    3. When you refer to the electric compressor are you referring to the HP or is there a separate compressor from the HP also supplying AC?
    Comment: If one wants air to recirculate in the cabin and pushes that button, I find that this button has to be pushed again after every restart, which seems strange since the other climate control settings remain the same on restart. Have you observed this?
     
  2. Salamander_King

    Salamander_King Senior Member

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    Unfortunately, my rudimentary understanding of the HVAC system especially of heat pump does not allow a definitive answer to any of your questions. If I have to guess, my answers would be.
    1. If the heat from ICE and coolant is available, then the heat pump would not run at all. Thus during HV, no heat-pump generated cabin heat.
    2. Air conditioning (cooling) is just another mode for the HVAC system which is different from heat-pump mode but uses the same components. What I don't know is if the ambient air is used for cooling at all or not. Say when cabin temp is 100F (parked in sun in summer) and the ambient temp is cool enough 75F. And if I set AUTO 75F, does it use air conditioning alone or use some ambient air to cool the cabin? I don't know.
    3. My understanding is that there is only one electric compressor used for all modes of the HVAC system in PRIME.

    According to this article, How does the heat pump work in a Toyota Prius Prime plug-in hybrid?, there are six different HVAC modes: cabin cooling, cabin heating, serial dehumidification, parallel dehumidification, defrosting, and heat-pump generated cabin heat. The term "heat-pump" applies to only the last mode, and I think this "gas-injected heat pump" is used only in EV mode.

    As for your observation on the recirculate button, I have not used that button ever in my car. I will have to try it myself to see how it behaves and what effect it has on cabin temp and humidity. During fall to early winter when temp stays between 30-50F, I can comfortably drive my car without any heat, but If I totally shut off HVAC, the humidity in the cabin makes all windows to fog up very quickly. One easy way to avoid fogging is to open the window, but I have been trying to find the best setting to avoid fogging with minimal HVAC use without opening windows.
     
  3. jerrymildred

    jerrymildred Senior Member

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    I think I can help with this one

    In recirc, it is recirculating the air. Thus it is pulling cabin air into the heat exchanger, cooling it by the amount the system is able to pull out the heat (I'll use 25F for example), and blowing it back into the cabin. So it will take the 140F cabin air in and blow out 115F air (which will actually feel cool by comparison). As the cabin air cools, the AC vent air will get chillier.

    In outside air mode, it's using the 90F outside air, cooling it to perhaps 65F and blowing it into the cabin. So, this is much more efficient until the cabin air comes down to the same temperature as the outside air.

    You can feel the difference if you get in a really hot car and start the AC in recirc. Then hold your hand in front of the vent and switch to fresh air.
     
  4. Salamander_King

    Salamander_King Senior Member

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    Thanks Jerry, but I think @CEJ is asking if all air conditioning (cooling) come from the HP (electric compressor)? The temperature outside and inside would definitely affect the efficiency of cooling function whither recirculated or outside air modes are used. But the main question asked is this: During cooling function, is the electric compressor always being used? I don't know the answer to this.
     
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  5. vvillovv

    vvillovv Active Member

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    I hope someone knows the answer to the main question in question, I sure don't either.
    But, I'm glad JerryMildred posted his experience with fresh vs recirculated air. It clears up another issue for me about how this Enigma thing called a Prime functions.
     
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  6. MTN

    MTN Member

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    Most modern cars that I know of, automatically reset to outside air, as you've noticed. This helps prevent window fogging upon restart and using the HVAC and is why you need to switch back to recirc if you want to use it.
     
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  7. jerrymildred

    jerrymildred Senior Member

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    As I understand it, not being a professional, the compressor is always used for cooling as long as it's set to AC. But unlike a conventional car, the compressor speed will vary according to the cooling demand. If you turn off AC, then the compressor stops and you're just using the fan to circulate air. This would be interesting to investigate using techstream or a phone app.

    My Prime always starts up in recirc mode. If I want fresh air intake, like when it's really hot in the cabin, I have to wait for the stupid 11" screen to finish booting so I can change it. This initial mode can be set in the settings screen on the MID screen. It's page 227 in my 2017 manual. I changed it so long ago that I had to look it up to be sure I actually changed it. :D
     
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  8. Salamander_King

    Salamander_King Senior Member

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    I think A/C switch ON is sure thing that the compressor is ON whither for cooling or for de-humidification. One thing I don't know is when the A/C switch is OFF, is the compressor really OFF? If you ever check the state of compressor in various HVAC setting, please let me know what you find out in the situation described in my comment #345, when AUTO (climate) OFF with A/C turned OFF, and air flow direction WINDOW, (FAN running at level 2). What I find interesting is that even with A/C switch OFF, if you direct the flow of air to the WINDOW, I see the power directed from the traction battery to HVAC fan on the energy flow diagram. This happens on EV or HV. I was doing this in ambient temp that did not require cooling, (temp set at 70F and both inside and outside was cooler). I don't think it is for heating, for the same setting but direction of air flow to front or down (or both) will show no energy from the traction battery. So, my guess is that with air flow aimed at WINDOW (both in AUTO setting or MANUAL setting), the car automatically turns on the compressor to de-humidify (and NOT for heating) even if you manually set the A/C OFF.

    What I really want to know is sure sign when the heat-pump mode of HVAC is engaged and/or disengaged. It is clear that the heat-pump does engage as a heater during EV mode even if the A/C is turned off. But I just don't know when it turns on and off.
     
    #368 Salamander_King, Nov 1, 2019
    Last edited: Nov 1, 2019
  9. MTN

    MTN Member

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    ^ either one of my previous cars or my wife's would always run the AC (I think it was my Saturn Vue) when the vent was directed to the windshield. Didn't matter that I had the AC off. I'm annoyed by cars that take away some of my choices. Sometimes I prefer to vent to go there and want the fan on, but don't need the AC compressor to run. The engineers think the owner is too stupid to realize that you need AC for dehumidifying (and I have to agree that 80% of owners probably don't realize this).
     
  10. CEJ

    CEJ Member

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    So it would seem to follow that it would be good to switch to recir after the cabin temp is lower than the outside temp.
     
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  11. CEJ

    CEJ Member

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    I have noticed that now that the weather is colder, the recir comes on automatically in auto mode. That I guess means the prime realizes the temp inside the cabin is higher than outside?
     
  12. jerrymildred

    jerrymildred Senior Member

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    Seems like a logical assumption.

    I've only driven mine in conditions like that a couple times and it was months ago. But it seems that I recall mine doing the same and notifying my with the AC ON indicator on the big screen. Just working from old memories here. We're still months from needing those settings here. They say we might get down to the upper 50s tomorrow morning. Almost perfect driving weather! :D
     
  13. lech auto air conditionin

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    Depending on the dewpoint of that day and the humidity when you turn off the air conditioning button the instant the AC stopped working your evaporator between the fins is totally loaded up with water droplets that were dripping down stuck between all of the fins in the bottom of the drip tray where the water settles before exiting through the drip tube. At this very moment while your blower is blowing through the evaporator fins now the air starts to pick up the water absorbing it becoming extremely humid on the other side as it leaves your ducts. And in the condition that your glass is physically cooler than the dewpoint which changes at different temperatures and different humidity that air will condensate on the inside of the glass.
    And depending on the ambient conditions temperature humidity and dew point this could be very drastic and sudden or slowly and mild in some situations not at all. But if you were to drive continuously with the fan blowing with outside air and the outside air humidity was low enough it would remove all the water and dry out the fins and the bottom of the pan The condensation on the inside of your glass would disappear because there’s no more water dripping from the wet evaporator or drain pan.
     
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  14. lech auto air conditionin

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    One way to determine if your heat pump is on or off from within your car is with a scanner. Not sure if any of the cheaper inexpensive third-party aftermarket scanners hook up to the new primes and give you this information yet if somebody can chime in on that and let us know. Then there is the physical way we are gifted with one of the greatest tools on earth are hands. If the compressor is running in what you call heat pump mode the condenser will be very cool to the touch because your condenser has now become the evaporator.
    And if you were a do it yourself mechanic and your ingenious for around $.99 you could get some thermistors wire them up to the inlet and outlet pipes of your condenser back to your cabin department or if you’re good with Arduino‘s and using Bluetooth wireless to your cabin department.
    Here’s an example let’s say it’s in air-conditioning mode for reference purposes only your temperature sensor on the inlet of your condenser on 80° day might be 115°. The discharge outlet line of your condenser with your temperature sensor hooked up maybe 88°.
    Now in heat pump mode comes on you may see 45° entering your condenser and maybe you see 75° leaving your condenser these are only examples not exact numbers but you can see where this is going.
     
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  15. CEJ

    CEJ Member

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    Change of subject: With HUD on, the speed is shown and also the HSI is displayed showing the GOM reading. But the latter switches from time to time to indicate the speed limit. When does it switch? When the speed limit changes? It doesn't seem to always do that.
     
  16. Tideland Prius

    Tideland Prius Moderator of the North
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    Supposedly when the speed limit changes.

    I know there are settings in the MID for speed limits (always, with caution and off) but I think they only affect the “Compass” MID screen and not the HUD.

    I can’t check since HUD speed limits only show up on US roads.
     
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  17. CEJ

    CEJ Member

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    Didn't know there were settings for the compass screen for getting speed limits. Thanks all the info!
     
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