Why mileage gets worse in winter

Discussion in 'Gen 3 Prius Fuel Economy' started by cwerdna, Oct 30, 2011.

  1. a priori

    a priori Canonus Curiosus

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    With a very powerful battery and a pair of electric motors, getting the ICE to turn over is not an issue at any temperature. The question is not whether a block heater is necessary to assure an easy start-up. The question is whether you can increase your fuel economy by using one. The simple answer is: Yes. The more complicated answer, hinted at in a couple of other posts above, is: Maybe.

    By increasing the temp of the engine block, it will be that much sooner before the ECU determines the ICE is warm enough to allow it to shut down unless it is actually needed to supply power. This is where fuel savings occurs. In a Gen III Prius, by choosing to run in ECO mode and utilizing a block heater, you'll be able to have the ICE turn off sooner and more frequently at the beginning of your cold morning drive. This will save gas and dollars.

    What makes it more complicated is that there is a cost to plugging the block heater into your wall socket. I used to plug it in right when I awoke, which was about 90 minutes before I left for work. It was very effective except on those exceptionally cold mornings. I never did measure the cost of the electricity, but that cost is what makes the more complicated answer a "Maybe."
     
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  2. markabele

    markabele owner of PiP, then Leaf, then Model 3

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    To me an EBH is a no brainer if you live in a cold climate and you have to park outdoors. It's probably also pretty smart if you live far north and your garage gets pretty chilly, too.
     
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  3. Corwyn

    Corwyn Energy Curmudgeon

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    Got any numbers to go with that "no-brainer"?
     
  4. markabele

    markabele owner of PiP, then Leaf, then Model 3

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    No but I think it is safe to assume that 55 mpg for a short to medium commute is much better than 40.
     
  5. Corwyn

    Corwyn Energy Curmudgeon

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    Only if you get the EBH for free, and the energy to run it, is both free and imposes no costs on others or the environment. Otherwise, you need to balance the decreased gasoline usage versus the increased electricity usage, and the cost of the block heater, and actually engage that brain. :)
     
  6. markabele

    markabele owner of PiP, then Leaf, then Model 3

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    I've always had hints of your egotism in other posts but you finally showed your true colors with that comment. The community would be better off without comments like this.
     
  7. Corwyn

    Corwyn Energy Curmudgeon

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    'Engaged brain' would seem to me to be the opposite of 'no brainer'. No offense intended. 'No brainer' was your choice of words, if you didn't wish to imply that you didn't think about it, perhaps another word choice would help.
     
  8. markabele

    markabele owner of PiP, then Leaf, then Model 3

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    There are tons of expressions in the world that have very different definitions than those of their literal ones.

    Back to the subject: Do you really think that people that park outside in cold winter climates and have morning commutes wouldn't benefit from an EBH?
     
  9. miscrms

    miscrms Plug Envious Member

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    FWIW the purpose of grill blocking and EBH are really different on the Prius than most vehicles, at least in how most folks here use them.

    Grill blocking helps immensely because the engine regularly shuts off during operation. As soon as it does, the cold airflow over the block cools it very quickly, and you're likely to have it restart just keep warm. Even here in Phoenix I notice the difference, and block the lower half pretty much all "winter." I keep it in until day time temps are routinely in the 70s. Without the block I find I get better mileage on the freeway in winter than on surface streets, as freeway driving keeps the ICE running most of the time. With the block, performance is similar to the rest of the year, when surface street driving usually yields the best overall mileage.

    EBH compliments this well by helping the engine get up to temp faster to start with, then the grill block helps keep it warm. The $ save on gas may very well not pay for the EBH and electricity used, but it will help you use less gas if that is your priority.
     
  10. walter Lee

    walter Lee Hypermiling Padawan

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    The EHB gives you an advantage on the ride to work but not from work because often there's no place to plug in your EHB while at work - so from the get go the EHB is only a partial solution. The EHB advantage is that it shortens the time and the amount of energy needed for the Prius ICE is trying to heat up the coolant/catalytic converter and in turn quickens the time when a Prius can do a full glide so it can help increase FE in that respect.

    Grill blocking helps the Prius retain heat that its already created so that when the engine gets to its thermally most fuel efficient temperature(180-190F) - it tends to stay there even when the ICE is turned off. this is important when the Prius is running at low speeds and the ICE is turned off frequently, e.g. in a P&G cycles, traffic jams. When the Prius is on the highway and constantly going over 60 mph, grill blocking can push the ICE temperature over 200 F and trigger the coolant fan to go on - making the Prius less FE. So grill blocking is for non-super highway driving. In cold suburban-urban stop and go driving environment, e.g. less than 48 F outside, if I start hypermiling the Prius from the very start - it may takes up to 40 minutes/12 miles before the Prius reaches its thermally optimal FE temperature and hence there are only a few miles left in my 15.8 mile commute when I notice grill blocking's FE bump. If my commute was longer - say 20 miles one way - I probably would see a bigger difference in the FE with grill blocking.
     
  11. NortTexSalv04Prius

    NortTexSalv04Prius Active Member

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    I guess some have to "ask" about no brainer. The EBH is a wise,plan ahead, dealer suggested, Prius chat listed, and smart idea. In the dead of winter with no garage with outside ambient temps at or below freezing(been known to break plumbing pipes in bldgs) why would you not consider a EBH,OPH, andBW all available in the marketplace. I agree EBH a no brainer .....if you want more warmer vehicle and less ICE run time in winterrr
     
  12. john1701a

    john1701a Prius Guru

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    That applies to total blocking, full upper & lower sealing.

    With my Gen3 (2010), the approach was full block of the lower and leaving the upper open entirely. That worked extremely well with temps in the low-50's to the extremes of Minnesota. Heat was retained for a very long time and the temperature didn't exceed the normal high of 195°F.

    Of course now, I have a plug-in. With the engine off for much longer durations and at higher speeds, the grille blocking will be more beneficial than ever.
     
  13. Corwyn

    Corwyn Energy Curmudgeon

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    Sure, that's why I asked if you had any other input you wanted to make on the subject.

    It depends on their individual circumstances. As I have said, for MY circumstances, after doing the math, it made neither money nor energy sense.
     
  14. TonyPSchaefer

    TonyPSchaefer Your Friendly Moderator
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    Hey guys. If anyone's interested, I just post charts of my per-tank average mileage at various temperatures. I park outside year-round so I installed the EBH in 2009 and you can see a little bump in the cold-weather mileage. I didn't do it in order to recoup any money; I did it to get better mileage and to heat the cabin faster. It did both. So perhaps I did recover some money in gas savings but it's not as though it was expensive compared to me being warmer when it's cold outside.

    Anyway, here's a link to the thread: Eight Years of Mileage Tracking and Pretty Charts | PriusChat
     
  15. Braddles.au

    Braddles.au DEFAnitely using an EBH

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    I agree that the maths doesn't make a compelling case. In Australia, where both petrol and electricity are expensive, it's about break even at best.
    I'm justifying my EBH purchase and use by the reduced emissions and wear and tear on the engine. These are much more difficult to quantify. My link to the DEFA technical manual (earlier in this thread) shows results of their testing or FC, emissions and wear. Perhaps we need to find similar, independent studies and settle it that way.
    Also consider that electricity can come from many sources and for "free", whereas petrol cannot.
     
  16. cproaudio

    cproaudio Speedlock Overrider

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    temp dropped quickly here. mid 60's. My mileage dropped from 59 to 54 over night. Grill blocked then temp dropped even more to high 50's but my mileage went back up to 59.
     
  17. a priori

    a priori Canonus Curiosus

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    I'm sorry if the question was asked before and you replied, but it would be helpful to me to see the math. It also would be a help to know the climate you're in and whether you park outside or in a garage.

    I had the EBH on my 2007, but I haven't installed one on my 2010. I'm thinking it might be a good idea to add the EBH, but I'll always want to consider dollar costs as well as other things. Your help would be appreciated.
     
  18. briank101

    briank101 Member

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    [/QUOTE]


    Regarding 2a, Can I debate this?. Please explain to me why more fuel mixes with the air in the winter. I thought the 14:1 was a mass ratio that is kept constant with a mass flow sensor regardless of temperature.

    Or stating this a different way, if there is a higher mass of air induced for a given volume, then that increase in the mass of air will be matched by the corresponding increase in the mass of fuel to maintain the mass ratio, which is same as the gas pedal being slightly pushed more, but the driver (or cruise control) controls the gas pedal depression amount to match the power demand, so how again does 2a above cause the fuel consumption increase?

    But I guess you said this is not debatable, it's plain and simple, and wait, it's also common knowledge :)
     
  19. OHHiker

    OHHiker Junior Member

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    I don't hear anyone saying they put their EBH on a timer so it only ran the hour or so before they started the engine.
     
  20. markabele

    markabele owner of PiP, then Leaf, then Model 3

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    I don't think there are a ton of people on this site that have an EBH.
     
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