Basic Absorption Principles

 I have an old 5.5 cu/ft propane (3-way) refrigerator that has a small (1/3
cu/ft) freezer.  I would like to convert this to a freezer only or at least
mostly a freezer.  What I was thinking was to build a new highly-insulated
cabinet and move all the stuff to the new cabinet.  I would like to get at
least 1 cu/ft of freezer space (more would be better).

Last summer I checked the temps and got the following:

Refrigerator (just below the freezer): 36 F.
Freezer: 13 F.

I tried removing the freezer door to increase the cooling in the
refrigerator.  The thermometer read about 36 F.

I tried removing the entire freezer compartment.  The thermometer read about
36 F.

I tried attaching a sheet of aluminum where the freezer box was previously
attached and it still didn't get any colder in the refrigerator section.

I'm thinking that the aluminum needs to be a continuous box and it is needed
to conduct the cold from the coils but my experiments are inconclusive (or
at least I don't like the conclusion).  If I was to build a new cabinet with
a bigger freezer is it likely that this will work and get down to, say, at
least 20 F?  Anyone know if I need to use a specific grade or gauge of
aluminum?  I'm planning on insulating the new freezer box a little better
than the old one currently is (sheet styrofoam).

Thanks.

  Ulysses brought forth on stone tablets:

Seems like the magic temp is 36.  Is the refrigerator temperature the
controlling temp?  If so (and it probably is),  then what happens in the
unmodified unit is that the refrigerator temp is controlled to 36
degrees, and the freezer gets gets however cold it gets.  By removing
the partition between the freezer and the refer, you *warmed* the
freezer without changing the refer, which is still temp controlled at 36
degrees.

I would guess that you need (in addition to adding insulation and
removing the partitioning between refer and freezer) to
replace/bypass/supplant the existing temperature control with one that
reaches down to a temperature you like.

bob
s/v Eolian
Seattle

 

highly-insulated

previously

Yes, the temperature sensor is in the refrigerator section.  That makes
sense.  Thanks.

 Insulate it from the cold section and drill a small hole in the outer
case to fool it into thinking it is warmer. Like the function of a
soft butter keeper.

 Sounds like that unit has a thermostat somewhere that's set to 36 deg :-)

My RV's refrigerator would bring the cabinet down into the teens if I turned the
knob
all the way.  I never measured the freezer part.  Alas, the stinky fluids leaked
out
and I replaced the thing with an efficient electric unit running on an inverter.

Building a larger cabinet with more insulation is a straightforward approach so
it
should work well.  I don't know what the ultimate temperature limit is for an
absorption unit but it should be well below zero.

Given the low efficiency of absorption refrigeration and the prevailing price of
propane at the moment, have you considered just replacing it with a high
efficiency
electric?  

I have two of these:

http://www.advrv.com/engel/engel_45.htm

The energy consumption borders on hard to believe.  I'd probably not believe my
numbers had I not recorded them myself.  I don't have the specifics at hand but
I can
say that the two, one set at 32 deg and the other at -5, will run for over 2
days on
one 120ah AGM battery.  Throw two or three batteries at them and you could
probably
get by with recharging once a week.

BTW, Advanced RV is a great place to buy 'em.  The actual price is considerably
cheaper than on the web page - he's about to retire and never updates the web
site
anymore.

John



John De Armond
See my website for my current email address
http://www.neon-john.com
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Tellico Plains, Occupied TN
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