Thanks, I will check it out!

As noted in the afore mentioned site the RV industry type refer units use heat to cool.  For the record a normal RV refer will use about $20.00 of electric per month, the larger the unit the more it will cost.  The unit on the electrical side uses a heating element which is no more than a controled short.  If you are wondering about the high electrical bill it might pay you to consider to use propane to cool. 
Using propane in the unit is much more efficient, but with today prices you have to check it out for yourself.

RV refrigeraters operate by heating a liquid (ammonia) to expand through and orifice which cools on expansion which then takes the heat from your freezer and escapes through the return line to a large volume which is liquid.  These ammonia boilers work well as long as the gas travels easily through the system as designed.  The tubing in these systems is coated with metals that make the system efficient.  The more level ie the more in the orientation the system likes the better it works.  These can be powered by convention electric, battery, or gas although battery is not so much used anymore.

Modern refrigeration uses mechanical compressors which are much more efficient and accomodate very large volumes with relatively small systems.  You don't want to even think about how big a boiler it would take to cool you home 20+ cubic ft of refrigeration.  Also the boiler needs to be on an outside wall because the fluid is so toxic.  Not very flexible in a conventional home.

Similar technology is used in a gas fired heatpump which was popular in some parts of the country before compressors became so efficient because of modern machining techniques.

Just FYI and probably more than you ever wanted to know.

Larry

A key reason for the LPG refer is that they require very little electrical energy - usually only an amp or two at 12v and also require very little LPG (enough to keep a small candle sized flame going). Hence, you can boondock for a long long time with an LPG refer. There are super high efficiency 12v marine refers that don't find their way into RVs due to cost, but these will consume a fair amount of 12v thus limiting, but far from eliminating, their boondocking ability. And of course, the increasingly popular residential refers in RVs are power hogs requiring easily 10amps at full house 120v while running and can never be too far from a power pedestal or a running genset.

What do you give up with an LPG (i.e. ammonia/gas absorption) unit? They have low "heat capacity" in that it takes a lot longer to cool/freeze stuff than in a power house residential refer hence the tip to cool/freeze it before you stock it.

BTW: Not to split hairs, but LPG refers (a.k.a gas absorption refers) do NOT work by expansion through an orifice as that is how the mechanical compressor systems typically using Freon (i.e. your residential refer, a/c units) works, Rather, gas absorption units work on a chemical principle where certain compounds when mixed (absorbed) with another (typically ammonia, hydrogen, and water) causes cooling (due to a form of evaporation - a phase change). Heat is then applied to simply separate out the compounds and thus a continual process of combining/separation occurs causing the cooling effect. Pressure, in the form of compression/decompression, plays no role in these units. See the how things work link in the post way above for more boring details.


-- Edited by RVDude at 23:28, 2008-03-30