Refrigerator power vs. dissipation

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Discussion Overview

The discussion revolves around the power consumption and heat dissipation of refrigerators, particularly comparing the energy taken from the wall to the heat removed from the contents inside. Participants explore concepts such as the coefficient of performance (CoP) and the efficiency of refrigerators and air conditioners.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions whether the power consumption of an 80-watt refrigerator corresponds to the heat removed from its contents.
  • Another participant suggests that a refrigerator functions by moving heat rather than producing it, indicating that the power consumed does not equal the heat removed.
  • A participant introduces the coefficient of performance (CoP) as a measure of refrigerator efficiency, noting that it typically ranges from 2 to 3 for refrigerators, meaning they can transfer 2 to 3 times as much heat as the energy input.
  • It is mentioned that refrigerator specifications often do not provide cooling capacity, while air conditioner specs typically do, providing a clearer understanding of efficiency through cooling power and energy consumption.
  • A specific example of an air conditioner is provided, detailing its cooling capacity and energy consumption, along with a calculated CoP of 3.2.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between power consumption and heat removal, with some clarifying concepts while others raise questions. The discussion does not reach a consensus on the implications of these measurements.

Contextual Notes

Participants note that the coefficient of performance is dependent on temperature differences and that the efficiency of refrigerators can vary. There is also mention of the complexity in comparing cooling power and energy input due to differing units.

Pengwuino
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OK someoone on a different forum said his refrigerator is an 80 watt refrigerator (small lil college fridge). As in it takes 80 watts from the wall. Isnt it true that this isn't the same amount of heat that can be taken out of the contents inside?

I remember someone talking about an airconditioner using 2000watts of power while dissipating like 2500 watts... any help would be ... helpful :D
 
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Just as with the air conditioner thread a week or so back, think of a refrigerator as a device which moves heat, rather than producing it.

The amount of power consumed to 'move' the heat from the refrigerator cabinet to the surroundings isn't necessarily equal to the amount of heat removed from the cabinet.

Just think of carrying a block of metal at 50000 degrees across a room. If you're wearing gloves, it doesn't matter that the block is hot. You're just moving heat.
 
Ok good.. thought so... didnt want to give these guys incorrect info.
 
Pengwuino said:
OK someoone on a different forum said his refrigerator is an 80 watt refrigerator (small lil college fridge). As in it takes 80 watts from the wall. Isnt it true that this isn't the same amount of heat that can be taken out of the contents inside?
A refrigerator performance is measured by the co-efficient of performance: Heat removed from the cold reservoir (ie inside) divided by the Work input:

[tex]CP_{ref} = \frac{Q_c}{W}[/tex]

The CP depends on the temperature difference but is typically about 2 or 3 for air conditioners and a little higher for refrigerators - ie. 2 or 3 times as much heat transferred as energy input.

Refrigerators are also rated in terms of 'cooling power' or heat removed / time divided by power input (x BTU/hr cooling/y watts input) but since the units are odd you can't really tell how efficient it is in terms of heat out/input.

AM
 
AFAIK, refrigerator specs don't give cooling capacity, but often times, air conditioner specs give both cooling capacity and electrical usage. http://www.sears.com/sr/javasr/prod...vertical=APPL&pid=04273055000&tab=spe#tablink is an example. It says it has a capacity of 5600 BTU/hr and consumes 510 watts of energy to provide it. There are 3.4 BTU per watt, so that's 1647 watts of cooling. The heat rejected out the back will be the sum of the two. Using A_M's formula, that's a CoP of 3.2.
 
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