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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 Senior 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 Active 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 Active 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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  18. OptimalPrime

    OptimalPrime Member

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    I realize I'm late to this party by about 3 years, but will add my 2 cents worth for posterity.

    80MPG IS POSSIBLE, but......the example given was almost surely due to using some battery depletion.
    Regarding that 80mpg in HV mode on a long series of short trips, the key thing to pay attention to is whether or not the battery state of charge has changed during that series of trips, and whether or not you plugged in at all between those trips. No series of trips with any plugging in done at any time from start to finish, or with any drop in state of charge from the beginning to end of the series, is a valid test of HV mpg. It doesn't matter whether you thought that having it in HV mode meant it was all HV driving, it actually NEVER is all HV driving, but you can make it EQUIVALENT to all HV driving by ending your experiment at the exact same state of charge that the experiment began with, without having plugged in at all during that time.

    80% RULE....
    As to the significance of 80% state of charge (displayed %, which I realize is not on a true scale of fully discharged to fully charged battery, but just dividing up the subset of that range the car normally lets us use) it is simply the maximum level to which the car lets you use Charge Mode. Basically, above 80%, they need to limit how many times you rapidly charge the battery, it has a limited number of life cycles closer to resembling the number of times you'll plug in the car, than the number of times you could possibly charge it much more rapidly using Charge Mode. Charge Mode (as well as regenerative braking) can charge at much higher wattage than an L1 or L2 charger, so they basically are prohibiting you from rapid-charging when the battery is above 80%, except for the occasional mountain descent. When knowing a big mountain descent is ahead, I try to get the battery to around 20-50% before the descent starts. In good conditions (not freezing out, etc) you can descend several thousand feet of elevation with the car allowing all of it to go into the battery, if you stay in the lower or middle part of the battery range. The higher it gets charged, the more likely the car is to stop regen braking to protect the battery and put the load onto the friction brakes. In Arizona in 2018, I drove hard on an awesome road with huge ascents and descents, plus a large number of sharp turns following the terrain, and hairpin turns acting as switchbacks. By keeping the battery averaging around 50%, I never got shut out of regen braking. Therefore, I had so much more total braking energy absorption available without burning up the brakes, that the car was absolutely the king of the road, shocking some very fast cars that absolutely could not stop me from passing and running away from them. Those who tried, ended up with smoke billowing out of their wheel wells by the time they gave up. The Prius Prime is a better car on twisty roads, especially in serious mountains, than you'd expect. There were several stretches where for 5 minutes at a time, I was continuously either at full throttle or under maximum regen braking, only getting into the friction brakes to pass people just before a turn, by braking later than they could with their brakes already almost on fire.

    HV MODE DOESN'T GUARANTEE that battery state of charge won't change. It just generally aims to eventually get the state of charge back to what it was when HV Mode was entered. Say you enter HV Mode with it at 50%. If you descend a mountain, the state of charge will go up and up and up. Maybe 1% per 100-200 feet of elevation loss is a fair estimate, though it depends upon your speed, how steep it is, AC usage, weather, and many other things. On the other hand, if you enter HV mode at 50% and then creep along on level ground at 25mph, it will go down and down and down, knowing that EV usage in HV Mode is by far the most efficient thing to do. It will still know it's aiming for staying around 50%, but the super efficiency of keeping the ICE off while using almost no power to go 25mph, is just too good for it to pass up. If you want the ICE on in that situation, you need to force it on with Charge Mode, which there is rarely if ever a good decision in that sort of case where you're basically creeping along almost for free. When you eventually return to anything faster, or go up a hill, it will start recovering toward 50%, unless it finds yet another reason not to.

    So, HV Mode sometimes acts exactly like EV Mode, EXCEPT that while in HV Mode, the long-term target for state of charge is the number when you entered HV Mode. But if you were truly in EV mode, the "target if you go into HV mode" keeps changing. Say you crept along in HV Mode and charge went from 50% to 40%. The HV Mode target is still 50%. But if you don't want to go back to 50%, just switch into EV mode and back to HV mode. Two clicks, and now the HV Mode target is now the 40% you're currently at. And obviously, if you just stay in actual EV Mode, the "EV Mode target" is 0%, it's looking to use up the EV range ASAP, because it has no idea whether you're about to arrive at a charger in another moment.

    ABOUT CHARGE MODE
    Different people have different experiences with Charge Mode, and either think it's worthless and just a way to waste gas, or they think it's the best thing since sliced bread. And I guess some are indifferent, or think it's pretty breakeven and just not worth dealing with. I get a lot of value out of Charge Mode, but it's not the solution to everything. Here are a few things it is great for. #1. It speeds up warming up the engine, if you're driving at low speed/power. That's useless if you're fully charged, because you can't enter Charge Mode until below 80%, and it cuts off when you get back up to 80%. But for instance, warming up the engine after a day at work without charging, can be sped up to possibly stop you from having to sit at a series of red lights with the ICE running due to not being warmed up yet. #2. It helps you get to and stay at super-efficient throttle settings, generally around the line in the middle. If you're on a local road that suddenly is a tiny bit downhill, you can choose between EV Mode, HV Mode running as EV, or this great third choice of Charge Mode getting you from almost no throttle, up to the perfect throttle position. ESPECIALLY WHEN #1 and #2 are BOTH TRUE, this is a no-brainer. If the ICE is already on, and is not warmed up (so refuses to run as EV when you get completely off the gas) and is way below optimal throttle, using Charge Mode to use more ICE power and get you near an efficient throttle setting, is a definite win.

    Under many conditions, such as 30-40mph driving, you'll find that on absolutely level ground, HV Mode itself switches back and forth from being EV vs being ICE, sometimes even acting like Charge Mode. But it doesn't know whether you'll be on terrain like this at speeds like this for hours, vs going 75mph starting a minute from now. It also doesn't know how level or hilly it is ahead. You might know those things. If you think it through, you can sometimes figure out a way to have efficient throttle settings when the ICE is on, and at the same time do all your downhill and low-speed stretches with the ICE off. Charge Mode gives you the ability to manually plan and control things almost perfectly, which HV Mode usually does well just by looking at the situation second by second, but lacks the clairvoyance to plan ahead perfectly for.

    While I don't disbelieve the people who claim that using EV mode at 60-65mph is part of the most efficient way of doing their particular commute, I feel that is the exception to the rule. The rule is:

    KEEPING THE ICE OFF FOR A LONG TIME IS A GOOD GOAL, because a certain amount of useless energy is wasted for each minute it runs, regardless of how much useful power above that overhead, you are getting out of it. Say you have a trip that is 46 miles, half at 23mph and half at 69mph. If you manage to make it 23 miles in EV Mode at 69mph for 20 minutes, you've squandered your entire EV capacity to save 23 minutes of ICE overhead. And there's a good chance you don't make it the 23 miles on EV due to your speed. On the other hand, if you use EV for the hour at 23mph, you've probably only used 1/2 or 2/3 at most, of your EV range, and totally avoided ICE overhead for an hour instead of for 20 minutes. Then you'll get some of the 69mph part done on EV, and the rest on ICE. So maybe you're only in HV Mode for 17 minutes instead of for 60 minutes. That's a tremendous amount of ICE overhead to overcome. Maybe all of the person's highway miles are downhill and lower speed legs are uphill, but I've found it to be extremely rare for using up EV range on level highway to be better than using it up at lower speeds or slight downhills.
     
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  19. Laura-Ann

    Laura-Ann Junior Member

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    It's hard to pin down accurate MPG numbers on a Prius Prime. The car is extremely sensitive to even small amounts of headwind or tailwind, speed, load, grade, temperature, and tire pressure. A few months ago, I did a 120 mile road trip on I-5, in a steady 20mph tailwind, at 55 mph. At the end of that 120 miles, the car had burned only about 0.85 gallons of gas, for an amazing 98 mpg. Other trips on this same stretch of road in a 10mph headwind, the car only got 52 mpg. The worst it's ever posted was 46 mpg, on a 520 mile road trip, heavily loaded, with a Thule cargo pod on the roof, and 200 miles of the trip was in mountainous terrain. Average at 55 mph, no wind, flat terrain, is about 63mpg, At 70mph under the same conditions, this drops to 53 mpg. The car's ICE and electric motors seem to be optimized for best efficiency between 35 and 50 mph, and every mph above that, efficiency drops off. At 75 mph or above, fuel consumption rises dramatically, to where the car is getting only about 40 mpg. In EV mode, on city streets at 30~35mph, I can get 6.5~7.0 miles per kilowatt hour (Have occasionally gotten 8!). At 55 mph, this falls to about 5 miles per kw-hr, and at 65 mph, 4.3 miles/kw-hr. But when planning a long road trip, it's risky to assume that you are going to get some specific MPG out of a Prius Prime. You might get 580 miles on a tank in nice weather. But if you get on the road and start running into an unexpected headwind, that 11 gallons of gas might get used up in only 480 miles.
     
  20. vvillovv

    vvillovv Senior Member

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    rain also effects my mileage and more than a dusting of snow on the road does also.
    @Laura-Ann I think you're post is an excellent description of what to expect from the Prime under various conditions.
     
    #380 vvillovv, Feb 10, 2023
    Last edited: Feb 10, 2023
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