Suggested summer cabin temperature to maximize MPG and battery life?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by StephenFromCT, Jul 26, 2019.

  1. schmuber

    schmuber Member

    Joined:
    Oct 9, 2018
    114
    81
    1
    Location:
    Georgia
    Vehicle:
    2010 Prius
    Model:
    N/A
    Sweatmiling. I've just coined it, invest while it's fresh.
     
    Threej, Mendel Leisk and Ed Beaty like this.
  2. fuzzy1

    fuzzy1 Senior Member

    Joined:
    Feb 26, 2009
    13,464
    7,067
    90
    Location:
    Western Washington
    Vehicle:
    2012 Prius
    Model:
    Three
    Perhaps we should remind readers that the 2010 Prius had the most energy-efficient AC system ever offered in a passenger car at that time. Somewhere around here is a thread describing this relatively new (then) and more efficient component, used in place of the traditional expansion valve, getting its first automotive use in the Gen3 Prius. Previously, it have been used only in some stationary applications.

    But I cannot find that thread right now, probably because I cannot remember the proper name of this device.

    I'd hope that the rest of the automotive market has been catching up.
     
    jerrymildred and The Electric Me like this.
  3. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    87,306
    38,848
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    the engine runs hotter than ambient too, but has a thermostat to keep it in range.

    the battery is similar. a multisided fan and cooling vents. testing in warmer climates would prove or disprove their effectiveness
     
  4. StephenFromCT

    StephenFromCT Junior Member

    Joined:
    Jul 17, 2019
    35
    10
    0
    Location:
    Connecticut
    Vehicle:
    2011 Prius
    Model:
    ----USA----
    Hello all,

    I am the original poster. Thanks for all the recent feedback on my original question.

    @Grit: I agree that to keep the HV battery at 80F the cabin temperature will need to be set to very cold. However, the 80F which I mentioned, and which @bisco describes are CABIN temperatures.

    @Rebound and @fuzzy1: This weekend I was talking to a friend who owns a 2010 prius, so also gen 3. I shared what I have read (on forums and in the manual) and viewed in vidoes, that the lowest two lines in the fuel meter may not be accurate and that waiting until the gas tank is almost empty is not recommended. Yes, I also told my friend that I do not know how the car determines the volume of fuel used, and I suggested using the calculations you described. The old math still works, even with hybrid technology.

    @fuzzy1: Thanks for sharing another way to use the Trip A and Trip B meters.

    @CR94: Thanks for sharing your observation that the HV battery temperature is roughly 25F higher than the cabin temperature. A good ball-park figure to know.

    Of course, the variable which I have not been considering is the outside temperature.

    @Grit: You describe an HV battery temperature of 80F when the cabin temperature set to just 76-78F. How long is your commute? What else do you do to keep the HV battery temperature only a few degrees higher than the cabin temperature?

    @Rebound: "What’s the term for driving with the cabin temp set to 80F with the windows rolled up to maximize mileage?" I was planning on calling myself a "frugal newbie". However, I like the name coined by @schmuber: "sweatmiler". Does the forum software make it easy to edit user names? @schmuber: If I have sweatmiler bumper stickers made where should I sent the royalty payments?

    @The Electric Me: The first automobile I remember my parents driving was a Volkswagen Transport, with a clutch and the "submarine-style windows". It had a four cylinder rear mounted air cooled engine. It did not have heating and it did not have AC. I do not move much when I am driving, so this weekend I was comfortable with the cabin set at 80F. I did not adjust the fan speed. During my next long trip I will set the cabin to 75F. I like the suggestion of lowering the cabin temperature just a few degrees and feeling more comfortable, even if fuel efficiency is slightly reduced.
     
    RMB and Rebound like this.
  5. Grit

    Grit Senior Member

    Joined:
    Aug 22, 2017
    3,403
    2,797
    1
    Location:
    NorCal (Non Bay Area)
    Vehicle:
    2012 Prius
    Model:
    Four
    My commute is an hour, up to 1hr 15min with bad traffic and about 100 miles round trip.

    I may be the most OCD HV battery temp regulator on here. Ways I keep the HV battery pack cool is removing the back seat bench, the back seat back padding, trunk cover, plastic compartment cover & tanneu cover. Removing those items allow cooler outside air come in cool the battery pack down much quicker, if everything on the list above was still in the car, temp never went down because I believe they absorbed all the colder air. This morning, HV battery started at 89F, 30 minutes later w/o AC, temp was 78F so it works for me. I also use the hybrid assistant app to manually override the HV fan controller and set it to speed 6 spinning up the HV intake fan to full speed. With temps now over 100F, HV battery never goes above 80F with the application pictured below:

    IMG_0199.JPG
     
    #45 Grit, Jul 29, 2019
    Last edited: Jul 29, 2019
  6. fuzzy1

    fuzzy1 Senior Member

    Joined:
    Feb 26, 2009
    13,464
    7,067
    90
    Location:
    Western Washington
    Vehicle:
    2012 Prius
    Model:
    Three
    I started with a 2010 Prius. Its fuel gauge was far more 'accurate' than any prior car of mine, but the next-to-top bar was the most off (short). And the bottom bar was really just a half-bar until the low fuel blinking warning started. But bars 2 though 8 (bottom to top) were remarkably even. But that was just my particular unit, I wouldn't suggest that others are identical.

    Keep in mind that fuel gauges and distance-to-empty gauges are not meant to be sufficiently accurate that you can meaningfully use gauge reading and simple math to compute MPGs or reliable forecasts of remaining fuel distance. They are just general indicators. The top of the gauge is not at the real top of the tank, the bottom of the gauge is not at the real tank bottom, and the bars are not necessarily linear (consistent). Biases or errors are intentionally built in for 'customer expectation management' purposes, to eliminate angry calls to Customer Support such as "The fuel display said I had enough gas to get there, but it ran out too early and stranded me in a heavy downpour out in the boonies where there is no cell service!"

    As for running very low, or not, the Prius is not really different than other cars. Beware of the nearly religious disagreements between the fill-early crowd and the just-fine-to-run-low crowd. Pick your own view.

    My view: the warnings about condensation collecting inside tanks walls, and debris collection of the bottom of the tank just waiting to get sucked in the gas line pickup when fuel gets low, are overblown in this era. Modern tanks are reasonably well sealed against air flow-through, and the 10% ethanol blend fuels are like putting in several quarts of gas line drier at every refill. The fuel pickup is always near the bottom, so any debris should be getting picked up, and caught by the filter, all the time, not just when fuel gets low.

    One side has many people quite adamant about never letting fuel get below 1/4 or even 1/2 tank. This is a great idea for forgetful drivers who don't watch the gauge close enough, and for those who are less than fully able-bodied and are at a health risk if stranded. And for everyone in hazardous locations or weather. But not really necessary for everyone at other times.

    This is also a good approach in areas with fairly level fuel prices, i.e. lacking price gouging or 'convenience or 'tourist trap' pricing, so there is little to be saved by skipping the nearest stations and pushing on to better prices down the road. But I commonly travel in areas with large price differences.

    The other side has many people putting too much faith in the accuracy & linearity & consistency of their gauges, and lacking a real understanding of how variable fuel consumption really is. Short term consumption isn't nearly as consistent as many expect, but varies enormously with conditions. It changes considerably with speed, drops in winds or wet or slushy roads or foul driver moods, plummets on uphills, and each cold start eats up several extra miles of supply. Most of this gets hidden across whole tanks and consistent regular trips and routes, then pops up in a nasty way when trying to eke out the last few miles in an unfamiliar place or under adverse conditions. Don't ever do your first low-tank tests under hazardous conditions or when/where running out will cause a major problem. First tests should always be in a time and place and under conditions where a screw-up and major delay won't cause you any harm or to miss anything important.

    The best post in all of Priuschat for how low a Gen3 will go until it runs out, is the base post of this too-long thread, originated by a member who ran his various cars out more than 50 times for sport, engineering curiosity, and a wide variety of fuel comparisons and other very interesting tests:

    [WARNING] Running out of gas (Gen III) | PriusChat

    OBDII-port monitors commonly use air flow as a proxy for fuel consumption (fuel used = stoichiometric fuel/air ratio * cylinder volume (derived from engine size & cylinder number) * number of power strokes (derived from RPM & time)), and allow the user to adjust a calibration factor. The car has access to better information, such as the amount of fuel actually injected at each stroke, but somehow the car makers prefer to keep the display intentionally 'optimistic', and not allow for user calibration. We know they could make it accurate, if they wanted to, because they have done so in the past. But several choose to not do so anymore.
     
    #46 fuzzy1, Jul 29, 2019
    Last edited: Jul 29, 2019
    SFO and CR94 like this.
  7. StephenFromCT

    StephenFromCT Junior Member

    Joined:
    Jul 17, 2019
    35
    10
    0
    Location:
    Connecticut
    Vehicle:
    2011 Prius
    Model:
    ----USA----
    @Grit,

    Thank you for sharing how you use a combination of increased fan speed plus greater exposure to keep your HV battery cooler. Your attention to details show that it is possible to keep the HV battery low. My speculation is that a cooler HV battery will last longer.

    I will look at the Hybrid Assistant app as a way to increase the HV battery fan speed.

    I also plan to look up the path the air takes after it leaves the fan and cools the HV battery. If there is no unimpeded way for the air, after it gets warmed up by the HV battery, to easily return to the cabin (where it can be cooled again by the AC compressor) then I am wondering if creating some type of vent above the 21V battery would facilitate the air circulation, and cooling.

    Of course, I would have to add a way to prevent small things from falling through the vent holes and landing on the 12V battery terminals.

    Any thoughts?
     
  8. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    87,306
    38,848
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    just drive it?:p
     
    Rebound, CR94 and Raytheeagle like this.
  9. fuzzy1

    fuzzy1 Senior Member

    Joined:
    Feb 26, 2009
    13,464
    7,067
    90
    Location:
    Western Washington
    Vehicle:
    2012 Prius
    Model:
    Three
    Doesn't most of the warmed battery air get dumped overboard through a vent?

    Posted via the PriusChat mobile app.
     
  10. Grit

    Grit Senior Member

    Joined:
    Aug 22, 2017
    3,403
    2,797
    1
    Location:
    NorCal (Non Bay Area)
    Vehicle:
    2012 Prius
    Model:
    Four
    And then what? Bam, battery overheat. Warped cells and wack-o-mole :p
     
    bisco likes this.
  11. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    87,306
    38,848
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    yes, but wouldn't rather keep recirculating and breathing it?:cool:
     
  12. Grit

    Grit Senior Member

    Joined:
    Aug 22, 2017
    3,403
    2,797
    1
    Location:
    NorCal (Non Bay Area)
    Vehicle:
    2012 Prius
    Model:
    Four
    Don't get cool battery fever though. I get the best mileage when HV battery is up in the 90F end. There's an ending stretch of my commute that drains my SOC from 60% to 42% when battery is below 80F. But if battery is above 80, on the same stretch, SOC goes from 60% to 50% so you don't want an HV battery too cold. If I blast my AC, HV battery temp can get cold as 70 degrees even when outside temp is 100F with my setup. By then you'll use too much electricity for the AC compressor and lose more MPGs. 80F-ish is the sweet spot for me, at times I'll even turn off the HV fan but keep the AC on for myself.
     
    RMB and Rebound like this.
  13. CR94

    CR94 Senior Member

    Joined:
    Dec 2, 2014
    1,747
    666
    0
    Location:
    Northwestern S.C.
    Vehicle:
    2011 Prius
    Model:
    Two
    It gets dumped in the spare-tire compartment. From there, it is free to exit the car or re-enter the interior or a combination of both (depending on other factors).
     
    RMB likes this.
  14. jerrymildred

    jerrymildred Senior Member

    Joined:
    Oct 28, 2016
    7,441
    9,147
    0
    Location:
    Tampa, FL
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Premium
    According the the Weber State teardown video, the Prime has two flapper door vents to the outside where the hot air can discharge. It's not a direct connection like in the regular Prius' single vent, though, so it is possible that a very small amount of hot air could leak back into the cabin but I don't know where that leak would be. It looks pretty tight to me.

    So the fans pull the cabin air through the openings in the back seat and draw it between the cells (an improvement over previous Prii), and dump it into the below-deck battery area. The positive air pressure there forces it out the flapper doors.
     
    fuzzy1 likes this.
  15. StephenFromCT

    StephenFromCT Junior Member

    Joined:
    Jul 17, 2019
    35
    10
    0
    Location:
    Connecticut
    Vehicle:
    2011 Prius
    Model:
    ----USA----
    @Grit, Thank you for sharing that an HV battery temperature of 80F-ish is your target for best mileage. This is consistent with the observation I have read that fuel economy is worse during cold winter days. If the ambient temperature is too low, then the HV battery temperature is below the optimal 80F-ish.

    @jerrymildred, the idea that the only way the warm air (post circulation through the HV) battery can return to the cabin (after being dumped into the space near the spare tire) is to slowly diffuse past the "flapper doors" is exactly why I was speculating whether adding a vent (above the 12V battery) would facilitate the cooling of both batteries during the summer. During a cold winter day, the HV battery will warm up faster (to the 80F-ish target used by @Grit) if warm air from the cabin pass through the fan and then over the HV battery (where the air is cooled by the cold HV battery). Then we want to warm up this cooled air by allowing it to easily mix with the cabin air which is heated. I am guessing the 12V battery will also benefit from the creation of a low resistance path for recombining the air with cabin air after air passes over the batteries (cooling during the summer and heating during the winter).

    I am impressed by all the improvements the Toyota engineers have added to the Prius during each generation. If they designed a plastic grill to cover the air intake for the HV battery cooling fan (with an aftermarket OEM screen to reduce pet hair from clogging the fan), why would they not add an easy way for the air to return to the cabin? Using an electrical circuit analogy, the "flapper doors" are acting like a large resistor.
     
  16. CR94

    CR94 Senior Member

    Joined:
    Dec 2, 2014
    1,747
    666
    0
    Location:
    Northwestern S.C.
    Vehicle:
    2011 Prius
    Model:
    Two
    Why worry about non-existent problems? There are enough real ones.
     
    Raytheeagle, bisco and Ed Beaty like this.
  17. jerrymildred

    jerrymildred Senior Member

    Joined:
    Oct 28, 2016
    7,441
    9,147
    0
    Location:
    Tampa, FL
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Premium
    There is no reason for any of that. The system works beautifully. Besides, if you take a look, you'll see that the intake to the cooling system is directly ducted from the cabin and the output is directly ducked to the discharge vent. It does not slowly diffuse out the flapper door. It blows out the door. "Flapper" being an important adjective. And the last thing you want is for that air to return to the cabin. What if the battery starts to leak?
     
    Ed Beaty and fuzzy1 like this.
  18. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    87,306
    38,848
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    isn't keeping the battery at the proper temp more important than your health?(n)
     
    fuzzy1 and jerrymildred like this.
  19. jerrymildred

    jerrymildred Senior Member

    Joined:
    Oct 28, 2016
    7,441
    9,147
    0
    Location:
    Tampa, FL
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Premium
    As Mike Rowe says, "Safety third!" :D
     
    bisco likes this.
  20. fuzzy1

    fuzzy1 Senior Member

    Joined:
    Feb 26, 2009
    13,464
    7,067
    90
    Location:
    Western Washington
    Vehicle:
    2012 Prius
    Model:
    Three
    The flappers doors are not to return anything back to cabin. These doors vent that air to the outside.
     
    jerrymildred likes this.
Loading...