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post #115 of Old 01-04-2010
Cal 9.2 SilverSwan
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low cost refrigeration

One more for you, low cost refrigeration, The Sawafuji R134 unit was on Ebay for $45 so I had an idea that I could adapt it to the ice box. It appeared to be a factory replacement unit for the NORCOLD portable coolers. I cut a 1 1/2 hole for the lines to go through and cut evaporator panel supports out of starboard to mount the evaporator in the ice box. I had to unbend the evaporator and re-bend it. I bought a spare unit in case I needed a replacement. (it is destined to become a cooling system for home brewing lagers at controlled temps) The compressor was mounted on starboard to simplify the installation in the laserette. A thermal switch is not necessary, the unit is too small to freeze the contents unless used in the winter time. It measures out to be about 2.5 cubic ft. With 3" of insulation the thermal leakage should be in the range of 18 watts/hr. Check out the reference (Consumption Guide ). To freeze 1 lb of water it takes 144Btu's. So an 8lb bag of ice contains at least 1152 Btu's. Thermal leakage of the icebox indicates that a bag of ice should last only 4.5 hrs. If 3 bags lasted me for 36hrs with a little still frozen, then the thermal leakage is closer to 10 Watts or 100 Btu's loss per hour. If it is used to cool water from 80F to 40F that would be a delta of 40F. If I had a pound of water it would take 40 Btu's to do so. To keep every thing is perspective, a 6-pack is about 4 lbs of fluids. If a hot 80F 6-pack is placed in a cold icebox at 40F, it would take 40F*4lbs=160 Btu's to cool it. With 150 Btu's/hr available, it would take a little over an hour to cool it down.
In true life we are not that fortunate, physics plays mean tricks on us. Cooling turns out to be a differential equation with higher efficiency with the higher thermal delta, and reduced heat transfer capability as the delta is reduced. It turns out to be an asymptotic function to the true temp. The lesson for us to learn is pre-cool items going into the ice box. (also less thermal load)
Its been in operation for 3 yrs now and still can cool a 6pack with out ice, but for doing over-nighters I'll still take a bag of ice for my favorite beverages.
Power consumption is about 3-5amps, so your looking at 60 watts of power radiation, amount the same amount as a 100 watt light bulb. Running the engine put more heat in the laserette than the compressor /condenser. Other "commercial units" also use air cooling to keep the power consumption down.
Attached Images
File Type: jpg icebox2.jpg (26.4 KB, 1294 views)
File Type: jpg evap2.jpg (18.4 KB, 1286 views)
File Type: jpg evap1.jpg (72.9 KB, 1272 views)
File Type: jpg evap3.jpg (31.1 KB, 1267 views)
File Type: jpg comp.jpg (73.4 KB, 1267 views)

Cal 9.2 #19 SilverSwan

Last edited by roline; 01-04-2010 at 09:11 PM. Reason: added power/ heat considerations
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