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Don Klipstein Don Klipstein is offline
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Default Energy savings of a ' fridge

In , Richard J Kinch wrote:
Don Klipstein writes:

You claimed 1.25 times as much energy to move the heat from the
kitchen to the outdoors as is consumed by the fridge in article
. You claimed in that
article $1 per day for the fridge and $1.25 again per day to move the
heat from the kitchen to the outdoors.


Simply an observation that if it cost $1 to pump some quantity of heat from
inside the refrigerator to the kitchen, it is going to cost about that much
to pump it again from the kitchen to outdoors, plus the additional heat
generated by the first pump.


However, essentially all of the net heat output from a fridge is from
the electrical energy consumed by the fridge. The heat being removed
the fridge is heat that went into it from the kitchen.

Hypothetically, put a fridge in a large black box. So now you have a
black box with a power cord coming out of it. The heat energy coming
out of this box will equal the electrical energy going through the power
cord. The law of conservation of energy does not care about what is
inside this black box.

What does that have to do with the 3:1 rule-of-thumb which I claimed
was for an air conditioner?


The 3:1 rule applies to one hop, moving heat from one place to another.
For an air conditioner you're sinking into the outside world on one
thermodynamic path, so it's one hop. A refrigerator has multiple paths,
and ultimately sinks into the room air, so the heat from making ice has
many hops, and the 3:1 rule does not apply. It can be worse if you're air
conditioning, or better if you're heating.


So a fridge consumes 1 KWH to pump either 3 KWH or some other quantity
of heat out - but the heat removed from the fridge is nearly entirely
heat that went into it from the kitchen.
The net heat output of the fridge during a time it has consumed 1 KWH of
electricity is going to be pretty close to 3414 BTU, which a good air
conditioner can pump from the kitchen to the outdoors with about 1/3 KWH
of electricity.

- Don Klipstein )