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Homework Help: Room temperatures, please help

  1. Aug 26, 2007 #1
    room temperatures, please help!!!!!!!

    1. The problem statement, all variables and given/known data
    A room is initially at the outdoor temperature of 25C. Now a large fan that consumes 200W of electricity when running is turned on. The heat transfer rate between the room and the outdoor air is given as Q = UA(Ti - To) where U = 6 W/m^2^.oC is the overall heat transfer coefficient, A = 30 m^2 is the exposed surface area of the room, and Ti and To are the indoor and outdoor temperatures, respectively. Determine the indoor air temperature when steady operating conditions are established.

    2. Relevant equations
    Q = UA(Ti - To)

    3. The attempt at a solution

    Not really sure where to start with this problem.
  2. jcsd
  3. Aug 26, 2007 #2

    Doc Al

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    Staff: Mentor

    Hint: What happens to the 200 W of power "consumed" by the fan?
  4. Aug 27, 2007 #3
    I take it that only a percentage of the energy consumed is given off as heat the rest is transferred into other energy forms obeying the energy cannot be creasted or destroyed rule just transformed from one source to another.
  5. Aug 28, 2007 #4
    I know some of the energy used will be converted to heat and noise but can't seem to find an equation to work it out.

    I think the indoor temperature will be the initial 25^oC plus however much heat is given off by the fan. Not sure if I am correct in this assumption or not.
  6. Aug 28, 2007 #5


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    You have to assume that all the 200W is put out as heat.
    You probably also have to assume that this heat all goes into the room, otherwise there would be no point in telling you the value!
  7. Aug 28, 2007 #6
    Got it now. Energy in and out have to be equal. With the energy in being 200J, the same has to be said or energy out. Ti = To = 200.

    Just have to convert the equation so Ti is the unknown.

    Thanks for the help guys
  8. Aug 28, 2007 #7


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    Yes, but be careful, Ti/To are the temperatures not the energy.
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