How many joules of heat will be delivered to the room

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  • #1
name_ask17
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Homework Statement


In a heat pump, heat from the outdoors at -8.00 deg c is transferred to a room at 22 deg c, energy being supplied by an electrical motor. How mnay joules of heat will be delivered to the room for each joule of electrical energy consumed, ideally?


Homework Equations


Q=mcT?
im not sure about this one




The Attempt at a Solution


i tried the mcT, but that did not give the the correct answer. The answer should be 63.6% (answer given by instuctor) please help.
 

Answers and Replies

  • #2
rock.freak667
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The question is asking for the coefficient of performance of the heat pump. Do you know the expression for COP?
 
  • #3
name_ask17
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Q/w correct? and if yes, what equation would i use to find heat, and how would i apporach the work?
 
  • #4
Doc Al
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Yes, that's the correct expression. But how would you express the ideal coefficient of performance for a heat pump in terms of the temperatures. Look it up!
 
  • #5
name_ask17
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i found that Q=Winput+Qc
but the problem does not state an input.
 
  • #6
Doc Al
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i found that Q=Winput+Qc
but the problem does not state an input.
"...for each joule of electrical energy consumed" is the input. Find the coefficient using the temperatures.
 
  • #7
name_ask17
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to do that would i use Qh/Qh-Qc?
 
  • #8
Doc Al
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Where are the temperatures?
 
  • #9
name_ask17
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outside= 266K
and inside= 295K
so the hot would be the inside and cold would be the outside?
 
  • #10
name_ask17
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im still a little confused
 
  • #11
Doc Al
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Look up an expression for the coefficient of performance for a heat pump in terms of the temperatures.
 
  • #12
name_ask17
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all i am finding is the hottemp-coldtemp/hottemp
is that not correct? it is not giving me the answer
 
  • #13
name_ask17
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i am very lost.
 
  • #14
name_ask17
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i am not grasping the concept. can you please explain to me step by step what i am doing wrong. am i even using the right equation? if not, then i do not know what equation to use. i have to know this by tonight and i have the answer....just dont know how to get there. 63.6% is the answer. but why?
 

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