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White Roof?

Discussion in 'Model S: Interior & Exterior' started by tonybelding, Jun 7, 2007.

  1. tonybelding

    tonybelding Active Member

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    By way of Winding Road, I found this site. . .    http://metacool.typepad.com/metacool/2007/04/thoughts_on_a_c.html

    The argument for a white roof is that it reflects more sunlight away from the car, thus reducing the need for A/C in the cabin.  Sounds logical. . .   However, I'm not sure if anybody has crunched the numbers to show whether it really makes a significant difference.  My intuition is, probably not -- but I could be wrong.  Every little bit adds up.  (On Winding Road, somebody commented that if you really care about that, you'll just get a white car anyhow.)

    I did find this first photo striking. . .

    white_roof.jpg

    Can anybody identify what kind of car that is?

    It's interesting because it has a lot of efficiency cues.  Not only the white roof, but also the fastback shape which reduces aerodynamic base drag, and the covered wheel wells, which again reduces drag.  I also note the lack of sharp creases or "accent llines" on the body which would disrupt air flow.  It's obviously an older car, and the proportions are all wrong by today's standards (and the rocket nozzles are hilarious), but it's a curious thing to see these old designs where they were putting more thought into efficiency than today's cars.
     
  2. Kipernicus

    Kipernicus Model S Res#P1440

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    Back on topic:
    It's curious that Tesla offers a black roof option for Model S but not white. Two modern cars come to mind with white roofs: Mini and Toyota FJ Cruiser.
    It does stand to reason that, as white cars have recorded lower temps than black ones (source not available but I seem to remember reading that in one of the paint threads), that a white roofed car would be marginally cooler than a black roof one.

    Maybe if you could get a black car with a white roof people will think you're a cop and move over for you!
     
  3. Robert.Boston

    Robert.Boston Model S VIN P01536

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    My guess, @kipernicus, is this:

    The Model S was designed to have the pano roof. The solid roof was added later, partly to lower the base-model cost and partly to respond to client demand. When Elon and the designers looked at pictures with the solid roof, they shook their heads, saying "that doesn't look right. The roof should be black, like the pano roof!"

    Of course, Tesla does offer a white roof -- you just have to buy a white car. :wink:
     
  4. contaygious

    contaygious Member

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    Hmm mini looks a lot better with black roof IMO and so does tesla; benefits be damned!
     
  5. Doug_G

    Doug_G Lead Moderator

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  6. doug

    doug Administrator / Head Moderator

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    The Citroen stuff went here: Citroen
     
  7. Kipernicus

    Kipernicus Model S Res#P1440

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    I'm not sure I agree with that analysis, as they measured the temperature of the glass (an insulator) rather than interior temps.

    Mythbusters measured a 10 degree difference
    http://mythbustersresults.com/episode38

    - - - Updated - - -

    I liked this guy's analysis. The black car got hot faster (1/3 the time) than the white one but eventually both were just plain hot.

    http://jonathansantos.com/do-black-cars-get-hotter-white-cars
     
  8. doug

    doug Administrator / Head Moderator

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    Glass is an insulator of sorts, but it's more thermally conductive than air. I would think the figure of merit would be the interior air temperature.
     
  9. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    It's certainly the interior air temperature that makes you feel hot rather than the temperature of the glass (radiation through the glass is another story).
     
  10. olanmills

    olanmills Member

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    bird poop camouflage
     
  11. NEWDL

    NEWDL R#350 R#1323 Sig23 8136

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    I can tell you with a high level of certainty (as I sit at the MINI dealer behind a desk) that the roof color makes no difference in interior temperature. There is an air gap between the roof panel and the headliner. I believe this to act as a baffle and stops heat intrusion from the roof specifically.

    Interior material and color I believe makes a much more significant difference... Along with tint.
     
  12. rdunniii

    rdunniii Member

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    There are 3 ways energy (heat) is transmitted. Conduction, convection and radiation. Conduction is the way heat is transmitted from the exterior to the interior. Radiation is the primary way heat is transmitted to the exterior surface if there is little or no air motion. The amount of conduction between the exterior and the interior is dependent on the difference in the temperature of the outside piece and the interior temperature.

    So here a a test. Between 2-3PM of a summer day when the sun is out when there is little breeze. A breeze reduces the amount of radiative heat gain on the exterior because the convection of the surrounding ambient air temperature. Place your hand on a white roof and see how warm/hot it feels. Then do the same on a black roof and see if you feel a difference. I most certainly do.
     
  13. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    Agreed, but as far as the interior temperature is concerned what's the percentage transmitted through the windshield and other glass compared to the roof. My guess is that the roof transmits only a small percentage of the total.
     
  14. NEWDL

    NEWDL R#350 R#1323 Sig23 8136

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    #14 NEWDL, Sep 14, 2012
    Last edited: Sep 14, 2012
    If any at all. Like I said, if there was no material backing the roof of the vehicle then I can see how this feeling the roof would result in a valid point, but my point was obviously not that black and white roofs hold more/less heat. It was that it has (little to) no effect on the interior temperature of the vehicle.

    Look at why this glass sweats...
    6168690611_988deb3133_z.jpg

    But this one does not...
    pavinacooler.jpg

    On a side note, one of the best features on our BMWs/MINIs is the ability to roll down the windows from outside the vehicle. This allows you to exhaust all that hot air before getting into the vehicle.
     
  15. gg_got_a_tesla

    gg_got_a_tesla Model S: VIN P65513, Model 3 Res Holder

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    dadaleus confirmed that the Model S key fob does this too - one'd have to press and hold the 'roof' of the fob car.
     
  16. Doug_G

    Doug_G Lead Moderator

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    Oh great, I'll be pocket-dialing my windows all day. Better make sure I park it where I can see it.
     
  17. ElSupreme

    ElSupreme Model S 03182

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    Yes this is generally true. But with heat you really have to think things through because a lot of times the answer can be counter intuitive. Like you can over insulate things! If your black roof is conviently placed in the shade it could actually make the car cooler. If the roof gets warmer than the outside could easily radiate heat to the surroundings, if it isn't in direct sunlight.

    This is the real point. Glass is going to make your car hot. And interior color that is getting direct sunlight.

    When I was 10 or 11 I took an engineering summer camp at my local public school. Even then I had a pretty good understanding of how heat worked. We had to create a shoebox that would heat water inside a baby food jar. I sadly had 2 other teammates that were also allowed to put in design notes. Of the materials there was no clear substance to allow light through, but keep hot air in; well except for the plastic bag around the plastic cups we were allowed. I grabbed the clear plastic bag and sealed it over the shoe box. My teammates decided to put all aluminum foil, to my protest, on the inside of the box. We still won having our water at about 140F while the next best team was around 115F by just wrapping the baby jar in black paper. And this was in Tampa in July so it was 90F out with stupid strong direct sunlight for 2 hours (I think). The worst performers were the people who wrapped their boxes and baby jars in foil. So even with about the worst design, a single piece of clear plastic gave us a huge win. Windows are what make cars hot.

    Now some other interesting tidbits.

    Black absorbs heat the best. Black also gives off heat the best. The heat travels from the hotter to the colder. A mirror finish is pretty much the opposite. It reflects heat the best. But it also has a hard time giving it off.

    This is why your aluminum bits, and your seatbelts are so damn hot. All the black and colored items are continually giving off heat. Your shiny bits can't radiate the heat, so it has to convect or conduct off which is a bit slower.

    In the winter, to stay warm, you should wear white/reflective clothing. As you are warmer than your surroundings. Because of this you radiate heat, versus collect it. And white (versus black) is less radiative, and more reflective.

    You shouldn't insulate that hot water line to your sink. Sure it takes 2 minutes to get that hot water. But how often do you run it? Probably at dinner time. Maybe in the morning (although you should use cold water in your coffee maker). Even with insulation that water is going to cool off by the time you want it again. And if you have insulation on it. Not only do you have to push out all the cold water, and heat the pipe. Now you have to heat up that cold insulation, which means your first hot water isn't as hot. Intermittent lines always have this problem.

    Now lets say you have a hot water loop. We want 5 feet of insulation on that pipe to keep it warm. Well not quite. When dealing with pipe insulation there comes a point where the increased diameter of your insulation, which produces more surface area to the outside environment, will have a bigger effect than the thickness of the insulation, and act as a cooling fin. So for pipe insulation bigger isn't necessarily better.

    - - - Updated - - -

    I live in Atlanta. It can get quite hot here if you didn't know :wink:. At my last job the receptionist would go on the intercom, whenever it started raining between noon and when she left, and state that it was raining. This was so everyone could run to the parking lot and close their windows. There were even a few people who would leave their keys with her so she would do it.

    I kindof miss that. My cubical now is within sight of a window, but it has that frosted plastic film on it. So I can only really judge the weather by brightness. I have an HVAC duct directly above me so I can't really hear someone on the phone, much less some rain 20 feet away.
     

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