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Efficient ventilation mode?

Discussion in 'Gen 4 Prius Technical Discussion' started by Jeppefinn, Apr 7, 2018.

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  1. alanclarkeau

    alanclarkeau Senior Member

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    So it looks like yours is the same as ours - but reversed - almost, the FRONT & REAR Demist aren't reversed completely, just translated to the other side:
    upload_2018-4-9_22-51-28.png
     
    #21 alanclarkeau, Apr 9, 2018
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  2. Prodigyplace

    Prodigyplace 2025 Camry XLE FWD

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    Yours isn't upside down? ;) :LOL:
     
    #22 Prodigyplace, Apr 9, 2018
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  3. Jeppefinn

    Jeppefinn Active Member

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    Yup. I can confirm that's exactly what it does on my car.
    Today it was the first warm day of spring (+15C) and my car was parked in the sun (inside it was propably 25C or so).
    A/C button on, Auto/Fast/Eco setting was eco and drive mode was eco, temp setting at 21C.
    It turned recirc on automatically when car started and then it turned off automatically after a couple of kilometers.
    It only does this to cool the car and I bet only when A/C button is on.

    Many thanks, now I know.
     
    #23 Jeppefinn, Apr 9, 2018
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  4. pilotgrrl

    pilotgrrl Senior Member

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    You are a very optimistic person!

    We have similar sorts in my world, too.

    However, they are customers of an extremely low-budget carrier that provides bare-bones service, the minimum wage staff that company hires and fails to train, and the misinformation provided by same.

    So, they come to us with misconceptions and preconceived notions that are hard to dispel.

    Often, they give up on us when they find out how badly their carrier lied to them.

    Accepting help and following instructions are both good things.

    Posted via the PriusChat mobile app.
     
    #24 pilotgrrl, Apr 9, 2018
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  5. sam spade 2

    sam spade 2 Senior Member

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    Because it is a FACT, at least when first starting a vehicle that has been sitting.
    It sometimes even becomes a problem after the car has "warmed up" if there is an unusual source of moisture inside.......like wet floor mats or 4 or more people breathing.

    IF.....you lived in an area where very high humidity AND moderately cold temps both occur together on a regular basis you would know that too.

    And the new account is necessary because my other one apparently was damaged in the recent "attack"........and experience tells me that getting the old one fixed would be near to impossible. I posted that fact but I think that post was deleted. I don't know why that happened.
     
    #25 sam spade 2, Apr 9, 2018
  6. sam spade 2

    sam spade 2 Senior Member

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    NOT if the conditions are such that the outside air has an absolute humidity level close to ZERO it won't.
     
    #26 sam spade 2, Apr 9, 2018
  7. Jeppefinn

    Jeppefinn Active Member

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    What does the ECO
    I think you're both right. A/C on does remove moisture of course (although not sure how much if it's really cold, if at all.).

    But let me paint a picture from here where it's really cold.
    You go to your car in the morning and it's -20C.
    Your hair is wet from the shower you took and a couple of kids get to the car through the snow (dragging their feet) and you put them in the back.
    There always a little water on the floor mats from the snow on your/kids shoes.
    I think you could drive around for 1 day with recirc on if you wanted, no problem (although I've never tried that).

    But the next day? :D
    Your car looks like the inside of a refrigerator that has not been melted in a decade.
    And not only do you have to scrape the outside of the windows but the inside too.

    Trust me, recirc not an option in the wintertime.
    If you drive only short trips you want as much of the fresh/cold dry air in as possible all winter in order to try to keep the car dry and push the moisture out.

    But still I usually keep A/C on unless there's a cold spell (-4C or colder all day/night for a few days) only then I shut A/C off completely for longer periods.
    If it's something like +4C and a slushy wet snowy day IMO A/C helps to keep the car dry. But all that changes around 0 degrees celsius.

    This is just my opinion though, I bet some scientist here knows exactly how this works.
     
    #27 Jeppefinn, Apr 9, 2018
  8. RCO

    RCO Senior Member

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    Extreme climatic circumstances may necessitate changing, but should not be considered as the regular practice for the majority of cases in temperate climates. However, if you live in such an extreme clime them your choice will be whatever you feel works best for you. (y)
     
    #28 RCO, Apr 9, 2018
    Last edited: Apr 9, 2018
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  9. alanclarkeau

    alanclarkeau Senior Member

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    OK - that's a climate situation I've never encountered.

    At the lowest here, it's 40% "relative" - but where I've needed and experienced demisting is in drizzle+foggy nights with a relative humidity in the 90%+ range - opening the vent just added to the moisture load. Hence - Recirc+heat+a/c just peels the fog off the windscreen - here.
     
    #29 alanclarkeau, Apr 9, 2018
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  10. alanclarkeau

    alanclarkeau Senior Member

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    OK - different scene - a cold morning here is +10C, maybe +3C rarely. And snow - I've never seen it - though 2 of my VOLVOs had snow mats.

    But our humidity is always fairly consistently high and temperatures more like Florida, cooler on some of the mountain range areas. I run either an a/c or dehumidifyer in my home almost all year to keep it at reasonable levels [I've a large grand piano which prefers it to be about 50% - and more-so, I do too !!!]
     
    #30 alanclarkeau, Apr 9, 2018
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  11. Tideland Prius

    Tideland Prius Moderator of the North
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    Ahh ok. That Eco mode is the same as our ECO Heat/Cool then. It's just combined with the AUTO button.

    I guess we did eventually solve the "Efficient Ventilation Mode" feature between this post and my previous one.

    Ahh I see. Ok well it appears we have solved the mystery of that setting :)
     
    #31 Tideland Prius, Apr 10, 2018
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  12. sam spade 2

    sam spade 2 Senior Member

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    I think you explained it pretty good.

    And, as I've been trying to explain, the conditions don't have to be that extreme for it to become a problem.

    For a discussion like this, relative humidity doesn't mean too much unless you also specify the temperature.

    At 0F, a 40% relative humidity indicates almost NO moisture in the air. As you warm it up the relative goes toward zero rapidly.
     
    #32 sam spade 2, Apr 10, 2018
    Last edited by a moderator: Apr 10, 2018
  13. RCO

    RCO Senior Member

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    40% RH is still 40% regardless of temperature and definitely not less! See below:-

    Relative humidity - Wikipedia

    The dew point is the association with which RH condensation causes the screen fogging etc.

     
    #33 RCO, Apr 10, 2018
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  14. RCO

    RCO Senior Member

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    Incidentally, re #33. The meteorological office only uses distilled, or de-ionised water in the Wet Bulb Reservoir.
     
    #34 RCO, Apr 11, 2018
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  15. Jeppefinn

    Jeppefinn Active Member

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    Yes. I would imagine in mountains or in a rainstorm in Florida recirc + A/C might be a very good option.
    At least if you want cooling and getting rid of moisture at the same time.

    It's a tricky thing, I tried looking it up.
    "The relative humidity [​IMG] or [​IMG] of an air-water mixture is defined as the ratio of the "partial pressure" of water vapor."

    I guess during high pressure (sunshine) relative humidity is lower and in low pressure (rain) higher :D, not hard to believe that.
    And cold air can hold less water than warm. The air is most dry during a sunny day somewhere in Siberia when it's -50C, I guess.

    The pressure thing does go over my head though.

    I have a heat pump in my house too, but I use it mainly to warm the house (Toshiba Arctic 35 RAS-35G2APV-ND is the model, ND=nordic). These winter models can both cool and heat and I guess the nordic ones have some added melting cycles and heaters on the outside radiator in order to get rid of the ice.

    I use it to remove moisture during summer thunderstorms too.

    In winter the air is so dry people do the opposite, here they use humidifiers.
    I have a humidity sensor inside my house and during a cold spell in winter (-15C to -25C outside) the humidity inside is below 30% at normal room temperature 21-22C.
    Your piano might do the opposite here, crack its finish due to drying up too much. :D .

    Doesn't the Prius Prime have a 2-mode heat pump like this? That can also heat not just cool air. The system can be reversed in order to heat or cool?
     
    #35 Jeppefinn, Apr 13, 2018
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  16. Jeppefinn

    Jeppefinn Active Member

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    Hey I found this that explains a lot (sorry it's in Finnish).
    On the left vertical axis there is amount of water vapour in air grams/cubic meter.
    Bottom horizontal axis temperature in celsius.
    Right vertical axis is realative humidity as a percentage.

    At +30C air can hold 32 grams of water vapour per cubic meter at 100% humidity.
    At -10C air can hold only 2,5 grams of water vapour per cubic meter at 100% humidity.
     
    #36 Jeppefinn, Apr 15, 2018
    Last edited: Apr 15, 2018
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  17. jerrymildred

    jerrymildred Senior Member

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    Nice find. That explains a lot.
     
    #37 jerrymildred, Apr 15, 2018
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  18. Jeppefinn

    Jeppefinn Active Member

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    Hey, I think got it now (I'm 47 but still can think) why fogging happens so easily in the cold.
    It takes very little added water vapour to reach the dew point when it's cold.

    Let's say my car is -10C inside in the morning and the relative humidity is at let's say 60% same as outside.
    When I get in it only takes a few grams of water vapour inside the car to reach the dew point.

    At -10C it takes only a few breaths (or grams of water vapour) to reach the dew point.
    At -10C it takes 1 gram of water vapour and at +10C it takes 4 grams of added water vapour in order for the air to reach the dew point.

    That's why when you breath out in the cold the there's a vapour cloud, the air reaches dew point so fast that a small cloud forms.

    No? Yes?
     
    #38 Jeppefinn, Apr 15, 2018
    Last edited: Apr 15, 2018
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  19. jerrymildred

    jerrymildred Senior Member

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    And that's why, when I had passengers when we lived up north, I'd ask them to hold their breath in the car. :LOL:
     
    #39 jerrymildred, Apr 15, 2018
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  20. alanclarkeau

    alanclarkeau Senior Member

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    Probably yes - I can't demonstrate -10C unless I climb into my freezer. But on a humid day (eg30C + 86%), I have noticed that if I'm shuffling stuff in my freezer there will be a slight cloud in there. Leave the door open for long on a hot humid day and there must be dew in the freezer as there will quickly develop a fluffy icy coating on the food packets. Being a FrostFree freezer, that icy coating will disappear over a few hours/days depending on how much there is.

    For what it's worth - at the moment at 05:30am, the internet tells me that my Temp is 14.4C and Dew Point is 12.1C - with Relative Humidity 86. Looking outside, there is a little dew on the grass - but I suspect the temp at grass level might be lower than the air temperature.
     
    #40 alanclarkeau, Apr 15, 2018
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