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Question - Thermodynamics/Heat Transfer

  1. Mar 24, 2013 #1
    I'm trying to explain to my roommate why I think it's better to leave my window open in the following scenario;

    It's 76F inside of the house except for my room (the room with the window in question) which is 82F. It's 78F outside. I believe I should leave my window open until my room cools down to at least 78F (since heat moves to equalize itself, thus the hot air in my room would move outside and lower the temperature in here).

    Am I correct? Is my roommate correct? If anyone has a quick little video to help explain the result that'd be great, since my roommate is kind of... thick. Thanks!
  2. jcsd
  3. Mar 24, 2013 #2
    There are a lot of possibilities and you forget to say about the sun radiation, equipaments, light, etc. You have to calculate the heat loads to give your friend a more accuracy answer
  4. Mar 24, 2013 #3
    Oh, uhmmm sorry. I don't know exactly what other specific info I can give you, I just want my friend to stop being a F*@KING moron and not yell at me when it's hotter outside than it is in the house, but much hotter in my room than either.

    I suppose no lights are on in the house and it's overcast outside. There's a ceiling fan running on full in my room, along with some electronics (TV & PC). Any other info you need? Also, the air is on (though only running when needed to keep the house at 76) so I suppose there's air flow coming in my room.
  5. Mar 24, 2013 #4
    If you have a temperature gradient and airflow probably your room will be cooler. Not always will be at the same outside temperature. You need to analyze whether the flow is sufficient to remove thermal loads.

    [itex]T_f=\frac{\dot{W}}{\dot{V}\times \rho \times c_p}+T_i[/itex]
  6. Mar 24, 2013 #5
    The only real point I'm trying to prove is that even if there was no air flow, then having my window open with those temperatures WOULDN'T be drawing in hot air. Is there a simple video (like Minute Physics) that can explain that concept?
  7. Mar 24, 2013 #6
    Without airflow it's impossible to expect your room be cooler because the convection has a higher efficiency to remove heat than conduction. It's impossible to doesn't have airflow due to the buoyancy force and other factors. Keeping your window open will help this situation but it's very hard to equalize.

    I dont know any video. Sorry
  8. Mar 24, 2013 #7
    Realistically there's air flow. There's ceiling fans and the A/C vent when it kicks on. But heat moves to equalize and even if it doesn't cool my room it won't heat the house. I need these idiots to realize that much. They're too dumb to read or learn when it comes to me being right and them being wrong, which is why I wanted a video. :/
  9. Mar 24, 2013 #8
    When you have a heat source like your body, computer, sun, etc you have to have airflow to romeve it. The complete equalization of a system occurs when you don't have any heat source. Look at the equation what happen when w=0 ?
  10. Mar 24, 2013 #9
    So.... who is right here? Me or them? My window open in that scenario = it's not heating up the house, right?
  11. Mar 24, 2013 #10
    You're right! Because you're softening the heat with airflow!
  12. Mar 24, 2013 #11
    This is not a general solution. Only works because the air outside is cooler.
  13. Mar 24, 2013 #12
    That's my whole argument with them, it's not heating up the house because the window has cooler air on the outside of it (since my room is normally 6-8 degrees hotter than the rest of the house)
  14. Mar 24, 2013 #13
    Easy solution.
    Buy a Thermo-Hygrometer and measure your room!!
  15. Mar 24, 2013 #14
    I dunno what that is but I have a thermometer in my room (that's how I got the temperature I used in my example).
  16. Mar 24, 2013 #15
    Show them your results! They cant argue with facts!
    Or they have been a bunch of ....... with you
  17. Mar 24, 2013 #16
    Uh that's the whole problem, they do argue with facts, that's what you get with high-school drop outs. Idiocy
  18. Mar 24, 2013 #17
    They think that A/C fires through my hot room and out the window (when its colder outside than in my room) like a goddamn howitzer through bread pudding.
  19. Mar 24, 2013 #18


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    Buy a fan and blow the hot air from your room into the rest of the apartment. :wink:
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