Our family cottage in Michigan is not heated. We store things in the
refrigerator we do not want to freeze. Why don't things freeze in
winter even when the temperature is below 0? Things DO freeze if the
power goes out. A typical refrigerator- as far as I know- is only able
to generate cold air, not warm air, so why don't things freeze unless
the power goes out? This has been mystifying our family for ages.

Thanks for asking!

Refrigerators are designed to keep contents at a controlled
temperature, usually 40-45F. The CFC (chlorofluorocarbons) in the
refrigerator coils "boils" at approximately -27F to produce a cool air
heat exchange. That's likely even colder than the air inside your
cabin.

A refrigerator space, from floor to ceiling is a microhabitat of its
very own. The outside coils produce radiant heat. The motor and
compressor also produce heat, which rises, surrounding the insulated
inside box, providing an air layer between the inside refrigerator
air, and the outside air. The insulation also traps, or holds, heat
from the motor. In addition to the compressor, most modern frost free
refrigerators also have a pair of small (motorized) fans, which
circulate air around the coils, both inside and outside of the
refrigerator.


The Refrigeration Cycle
-----------------------

The compressor compresses the coolant gas (CFC), which heats up as it
is pressurized. The gas is pumped under pressure through the
refrigerator coils, cooling, and condensing into a liquid.

The liquid flows through an expansion valve. The expansion valve is a
very small doorway between two different pressure environments, high
pressure on one side, low pressure on the other. The compressor
"pulls" the coolant gas creating low pressure in the section of coils
inside the refrigerator. As the coolant passes through the expansion
valve, it immediately boils and vaporizes. Its temperature drops to
27F, which is enough to cool the inside of the refrigerator. The now
cold gas is sucked into the compressor and the cycle repeats.

In cold weather the refrigerator cycles on and off less often, thanks
to cooler surrounding air temperatures, but its own heat is sufficient
to make the cooling necessary.

If electricity is lost, the refrigerator motors stop producing heat.
If the surrounding air temperature is below the freezing point (32F)
then the contents will eventually freeze. Once frozen, they're well
insulated against thawing, even if the electricity comes back on.
Remember how long it takes a 12lb turkey to thaw (in the fridge)
enough to pull out the giblets. I put my Thanksgiving bird in the
fridge on Sunday for Thursday.
 

How Stuff Works offers a nicely illustrated article about the secret
lives of our refrigerators.

How Refrigerators Work, by Marshall Brain
http://home.howstuffworks.com/refrigerator.htm

Illustrated Refrigeration Cycle
http://home.howstuffworks.com/refrigerator4.htm  

Also see:

How a Frost-free Refrigerator Works
http://home.howstuffworks.com/question144.htm


Google Search Terms:
----------------------------------------------------------------------
how refrigerators work
"heat pump" compressor


I hope this clears up the mystery for you. If you have any questions,
or if you (egads!) discover a broken link, please let me know. I'll
make it right. :)

---larre

---

Clarification of Answer by larre-ga on 22 Aug 2003 23:35 PDT

'Scuse me, cottage, not cabin. I should know better. My dad was a
Michigander. He spent boyhood summers at a cottage on the Canadian
side of Lake Erie.

---l

---

Request for Answer Clarification by greenlake-ga on 25 Aug 2003 18:20 PDT

As you may have noticed, there was a comment attached to your answer
that also occured to me. Would a refrigerator turn on often enough in
very cold weather to prevent the contents from freezing? Or do you
suspect as snsh suggested in his response that it might be the frost
free feature of the unit?

Thanks,

Lee

PS Thanks for the quick response to my question.

---

Clarification of Answer by larre-ga on 25 Aug 2003 20:36 PDT

You ask... "Would a refrigerator turn on often enough in very cold
weather to prevent the contents from freezing? Or do you suspect as
snsh suggested in his response that it might be the frost free feature
of the unit?"

I'm pretty confident that the regular cycle of the refrigerator is
enough to keep things from freezing. I have an older, non-frost-free
refrigerator sitting outside under a snow roof. We have about two
months of sub-freezing weather here. The fridge is shaded during the
winter (northern exposure) and on its own electricity line. The
electric bills for it are virually the same, summer and winter. I need
to manually defrost the small freezer. The contents of the
refrigerator do not freeze even in sub-zero weather. Also, my outdoor
cat sleeps next to the grille, a sure sign that it's a warm place.

The frost free feature will certainly contribute to the total heat
generated by the appliance motors, and therefore the need to cool the
inside air space. Remember, however, the freezer coils in question are
only slowly heated up to 32F to melt any condensation on those coils.
The defrosting process is only loosely related to the need to cool the
refrigerator portion.

---larre

I appreciated the quick response and thorough answers to both the
original question and the follow-up question. I also enjoyed the
respondant's combination of factual and annecdotal information, sense
of humor and links to other sites.

I don't think the compressor has much to do with it -- just the frost
free feature, and possibly the "reduce exterior moisture feature". 
The compressor may never switch on in the winter, but the heating
coils will still go through the defrost cycle every hour or so.

Thank you! ---l