How many joules of heat will be delivered to the room

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Homework Help Overview

The discussion revolves around a heat pump problem where heat is transferred from the outdoors to a room, with a focus on determining the amount of heat delivered for each joule of electrical energy consumed. The subject area includes thermodynamics and the concept of the coefficient of performance (COP) of heat pumps.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the use of the equation Q=mcT and question its applicability. There is an exploration of the coefficient of performance (COP) and its expression in terms of temperatures. Some participants express confusion about the input energy and how to approach the problem.

Discussion Status

Multiple interpretations of the problem are being explored, particularly regarding the correct equations to use and how to express the COP. Some participants have provided guidance on the correct expression for COP, while others are still seeking clarity on the concepts involved.

Contextual Notes

Participants note that the problem does not explicitly state an input, leading to confusion. There is also a mention of specific temperatures for the outdoor and indoor environments, which are relevant for calculating the COP.

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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.
 
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The question is asking for the coefficient of performance of the heat pump. Do you know the expression for COP?
 


Q/w correct? and if yes, what equation would i use to find heat, and how would i apporach the work?
 


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!
 


i found that Q=Winput+Qc
but the problem does not state an input.
 


name_ask17 said:
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.
 


to do that would i use Qh/Qh-Qc?
 


Where are the temperatures?
 


outside= 266K
and inside= 295K
so the hot would be the inside and cold would be the outside?
 
  • #10


im still a little confused
 
  • #11


Look up an expression for the coefficient of performance for a heat pump in terms of the temperatures.
 
  • #12


all i am finding is the hottemp-coldtemp/hottemp
is that not correct? it is not giving me the answer
 
  • #13


i am very lost.
 
  • #14


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 don't know how to get there. 63.6% is the answer. but why?
 

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