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Homework Help: Heat capacity of a room

  1. Jan 26, 2006 #1
    I have a room that is V m3. If I heat up the room a certain temp, then let it cool, and I measure the temp drop rate to be i.e. 10K in 2 hours. Then I use the following equation:

    \dot Q = C_P \cdot V \cdot \rho \cdot \dot T

    This gives me Watt value, but I'm not excactly sure what it tells me. Perhaps the value for the temp drop should be negative, so that it tells me that it would require so many Watts to cool the room 10K in 2 hours :confused: If someone can verify this it would be great.

    Also, if there are several items in the room that have different heat capacity, can I then just add these together or how would that work?
  2. jcsd
  3. Jan 26, 2006 #2
    In order to measure the room's heat capacity you need to heat it to a certain temperature, make sure the entire content of the room is at the same temperature, both before and after heating, and then divide the energy by the temperature difference.
  4. Jan 26, 2006 #3
    But is my thought on the equation correct? Does this Watt-value denote how much effect it would take to cool the room 10 degrees in 2 hours?
  5. Jan 26, 2006 #4


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    No, it just tells you how much heat is escaping from your room (leakage to the outside world). It tells you how much power you must spend to keep your room at a constant temperature (power like from an electric heater).

    If you stop the leak, somehow, and you want to create an artificial leak with an airco, then you will need to evacuate the same quantity of heat. But you do not need so much electrical power ; an airco needs less power than the heat it "pumps", which depends on the ratio of the inside and outside temperature (if the outside temperature is LOWER, it goes all by itself, as when opening a window), and on the quality of the airco.
    Last edited: Jan 26, 2006
  6. Jan 27, 2006 #5
    Aha, thx. This "leakage" would be a combination of transmission loss and infiltration loss right? Can I somehow measure (or calculate) how much is due to which? Then I would really be getting somewhere...
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