Window Fogging in Cold

Discussion in 'Prime Main Forum (2017-Current)' started by JJgrubs, Nov 14, 2019.

  1. JJgrubs

    JJgrubs New Member

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    Hello,
    My windshield and passenger windows are fogging on me in the interior in this cold weather. I do my entire commute electrically so I want to know how to keep everything clear without the Defogger (which turns the ICE).

    If I have the AC on (Auto and Eco and Recirculation all "on") it seems like it doesn't fog. I think it's because it serves to dehumidify? However, there's a point when I'm warm enough and when I turn off the AC (keeping Recirculation on), it begins to fog.

    Can you explain how to deal with this? When I turn off the AC, should I turn off recirculation also? Should recirculation be off when I have the AC on as well? I figured I should keep recirculation on all of the time to maintain the heat inside cabin.

    I'm very lost!
     
  2. Tideland Prius

    Tideland Prius Moderator of the North
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    Yes. Recirculation will recirculate the moist air (from your breath or any snow that is melting on the mats that you brought into the car).

    The A/C compressor is helping dehumidify the cabin. If you're warm enough, lower the temperature of the cabin. Sometimes, changing from recirc to fresh air may not be enough to keep the windows clear (especially if you're breathing out more moisture than the climate control is bringing in or if the outside air is humid anyway.
     
  3. Salamander_King

    Salamander_King Senior Member

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    Warmer humid air is condensing inside of the window when outside is cold. The quickest way to deal with fogging in this situation is to open a window a little bit to get fresh and usually drier air in and bring the temperature of the cabin lower.

    If you can't keep the window open, without turning on the front defroster, you can usually defog the front window if you set the direction of airflow to the window manually. You do not have to have A/C ON. Airflow to window automatically turns on the compressor.
     
  4. JJgrubs

    JJgrubs New Member

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    Ok great answers but now even more confused by the additional of manual stuff.

    Let me take a step back:
    1) If all climate control is OFF (click on Fan off button), is the heat still working? I read the heat pump works even with some stuff off based on the Temperature setpoint but here, the Temp setpoint is off 0_o
     
  5. JJgrubs

    JJgrubs New Member

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    And parallel to that question:
    2) If I want to heat the cabin in the winter but without fogging, which is more energy efficient/ more recommended:
    -Having recirculation ON (to keep warm air inside) and AC ON as well (to dehumidify said air and prevent fogging.
    OR
    -Turning Recirculation OFF (dry, cold air comes in) and just let the heat pump do its thing. AC would be OFF

    The latter seems more inneficient (always warming up cold, new air) but it would mean the compressor is off, so perhaps it IS more efficient after all.
     
  6. bisco

    bisco cookie crumbler

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    stop singing in the shower
     
  7. Wolfie52

    Wolfie52 Senior "Jr" Member

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    I have had a similar issue here is the south as the weather has changed.

    My Choice is ALWAYS SAFETY FIRST. Turn on the defroster--it works very quickly.

    It is not worth an accident to have an "all EV commute".
     
  8. fuzzy1

    fuzzy1 Senior Member

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    Your body and lungs always emit moisture as part of respiration, a necessity for life, boosting interior humidity. When the windows are colder than the dew point of the warmer interior air, you will get condensation.

    On top of this, it is possible that you have other unwanted moisture stored inside, in the form of wet floormats, or wet boots or coats or other clothing. These will add to the interior humidity problem.

    Lose the recirculation, at least when the A/C dehumidification is turned off. Bring in fresh outside air to push out the higher humidity interior air. This will help but is not always sufficient. If you have unwanted moisture stored inside, take it out. Remove wet clothing or towels. Take wet floormats out to dry in the house or garage. Wet carpets will need more effort to dry out, and may need fans and/or heat inside a garage. Use a desiccant (DampRid is one example).

    Or you may just need to use ICE heat to warm the windows.
     
    #8 fuzzy1, Nov 14, 2019
    Last edited: Nov 14, 2019
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  9. bisco

    bisco cookie crumbler

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    i would think the heat pump and floor/defrost setting should be sufficient
     
  10. Mendel Leisk

    Mendel Leisk Titanic Social Director

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    Use fresh (outside) air. Set mode to heat/defog, crack windows slightly. Use AC if still fogging up.

    If one of the above kicks on the engine, just go with it?
     
  11. Salamander_King

    Salamander_King Senior Member

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    All the indication from the car, no warm air coming, or energy diagram not showing arrow from the battery to the HVAC seems to suggest the climate control OFF is no heat pump. In this setting, there is no fan running and your temperature setting is dimmed. However, I noticed if you have ICE running, you can feel the warm air from the vent without blowing. But under strict EV operation, I think you are getting just warm air.

    This is a hard call. My understanding it that for the six different modes of operation PRIME HVAC has, it can not perform gas injected heat pump AND electric compressor operated dehumidification at the same time. If you recirculate your cabin air, you are not going to get rid of humid air unless the compressor runs to dehumidify, but if recirculation if off, then colder fresh air from outside must be heated by the heat pump. Both situations demand more energy from the battery. I think it all depends on how humid and how cold the air is. And I think it is more case by case which operation is more efficient.
     
    #11 Salamander_King, Nov 15, 2019
    Last edited: Nov 15, 2019
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  12. JJgrubs

    JJgrubs New Member

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    Thank you for your response.

    Any chance you might know what's more efficient from my Q2 later in the thread?
     
  13. Tideland Prius

    Tideland Prius Moderator of the North
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    No but whatever air that flows through the vents (just from pressure differences.. depends on your speed) will still pick up the residual heat until that heat is gone.


    I don't have hard numbers to back that up so it's all speculation but...

    IF you are able to keep the windows clear by running it in FRESH AIR with the A/C compressor off, then that would use the least amount of energy.

    However, safety first and if you need defrosting, I would just run the climate control (with A/C on) and let the car do its thing. I'd imagine that constantly dehumidify (assuming the car windows are clear when you first start off) is better than cycling on and off the front defogger (Which will kick in the engine anyway).

    Recirculation will heat up the cabin faster because you're not constantly reheating cold outside air but of course that recirculated air needs to be dry so if it's moist, the A/C compressor will come on.

    Honestly, because there's more fan speed levels in AUTO mode than in manual, the computer is able to better fine tune the climate control so in most cases, I'd think AUTO works best. (the one case that I can think of that doesn't is when it's a cool fall or spring day where you can drive around without the A/C cooling or dehumidifying - then I'd run in AUTO with no A/C light on).

    @Skylis A did some tests if you're curious about energy uses but doesn't have your specific case.

    Estimated EV penalties for various heating cooling and lights | PriusChat

    Here's some reading on the heat pump

    How does the heat pump work in a Toyota Prius Prime plug-in hybrid? | PriusChat
     
  14. Tideland Prius

    Tideland Prius Moderator of the North
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    Hmm, so does it alternate or temporarily shut off the heat pump to dehumidify?
     
  15. Salamander_King

    Salamander_King Senior Member

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    That is my understanding. I will try to find the ref where I read this and post it if find it.

    But better yet, I contacted Linear Logic, a maker of ScanGuageII and got a suggestion for a X-gauge command to use to check what mode the HVAC is operating at any given moment on PRIME. Copied below is the command I supposed to use, but I am totally unfamiliar with X-gauge at moment. It will take sometime to play with the gauge and setting to get a meaningful data. 1-6 are the mode of operation. The comments in ( ) are mine. As you can see, mode 5, the gas injection heating (aka heat pump) is a different mode from the rest of HVAC modes. I believe 7 and 8 are Idle in which HVAC is OFF and Init which must be initialization when the system is turned on but not ready yet?

    Heat Pump Status (State)
    TXD: 07C4217A
    RXF: C461057A3000
    RXD: 2808
    MTH: 000100010000
    NAME: HPS

    1 = Cooling
    2 = Series Heating/dehumidification (40-60° F/4-16° C for serial)
    3 = Parallel Heating/dehumidification (32-40° F/0-4° C for parallel)
    4 = Heating (I believe this is conventional heating using ICE)
    5 = Gas Injection Heating (This must be the "heat pump")
    6 = Defrosting
    7 = Idle
    8 = Init
     
    #15 Salamander_King, Nov 15, 2019
    Last edited: Nov 15, 2019
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  16. Salamander_King

    Salamander_King Senior Member

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    This thread has some refs, I read. But none seems to explicitly state that Gas injection heating (aka Heat Pump) can not operate at the same time as dehumidification mode. My best guess is that by inference that six modes operate separately, and dehumidification modes are linked to three of them (Series, Parallel and Defrosting) but not with the gas injection heating mode.

    How does the heat pump work in a Toyota Prius Prime plug-in hybrid? | PriusChat
     
    #16 Salamander_King, Nov 15, 2019
    Last edited: Nov 15, 2019
  17. Tideland Prius

    Tideland Prius Moderator of the North
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    What about mode 3? Parallel heating and dehumidification?
     
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  18. Salamander_King

    Salamander_King Senior Member

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    I don't know the technical differences between mode 3 Parallel Heating/dehumidification and mode 5 Gas injection Heating. But ref seems to suggest the mode 3 works in temp range (32-40° F/0-4° C) whereas mode 5 works down to 14° F/-10° C. What I don't know is mode 3 heating is using the heat pump just not gas injected or without heat pump but using ICE generated heat.

    Even if mode 3 heating does involve a use of the heat pump, if the temp range is restricted to 32-40° F/0-4° C as stated, it is likely there is no dehumidification that can function below 32° F/0° C. So, if the temperature is below freezing down to 14° F/-10° C, the heat pump must be working alone in mode 5 without dehumidification.
     
    #18 Salamander_King, Nov 15, 2019
    Last edited: Nov 15, 2019
  19. JJgrubs

    JJgrubs New Member

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    Ok so to summarize in winter driving:

    The best is to click Auto, AC off and recirculation on. This will heat the cabin the most and, if the airflow is directed to the windows, will help with defogging a little. Also most efficient.

    However, if that's not enough to prevent fogging in general, better to turn the Recirculation off to use dry air from outside.

    And if that's still not good enough ( because outside or inside is too humid) then turn AC on to dehumidify.

    Of course the final back up being the Defogger itself. Clearly I will click this if needed but I prefer sticking to options above if they're good enough.

    Did I get this right?
     
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  20. Salamander_King

    Salamander_King Senior Member

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    Like @Tideland Prius, I don't have a hard number to support my claim, but AUTO ON, AC OFF may not be the most efficient. It certainly is the most convenient and worry free, since you don't have to change much of anything.

    When in AUTO, I don't think you can select the direction of flow of air or fun speed. They are automatically selected. To do that you have to select them manually, which cancels AUTO, I think? I may have to confirm this on my car, but that's what I can recall.

    Also, either in AUTO or Manual, if the direction of air flow is to WINDOW, the electric compressor turns on regardless of A/C setting. Thus I believe if all you need to defog is the front windshield not involving the side windows, A/C ON is not necessary.

    I have been successfully using following setting on my car down to 14F this winter to conserve battery SOC and keep the cabin comfortable and defogged. AUTO OFF, A/C OFF, Recirc OFF, ECO mode, S-Flow driver priority mode, set temp 70, set fun speed to minimal needed (usually 2 is enough to keep me comfortable and keep the windows defogged), and use selection of air flow to the cabin for heating only or to Window for defogging. But unlike you I do use HV mode to generate initial heating I need to conserve battery power for actual EV drive rather than for heating. So it may not work for all EV drive like you do, but it should be more efficient than AUTO ON for most part, and more importantly it will keep the front windshield clear.

    IMG_20191115_062649.jpg
     
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