Compressor Refrigerator - Fiberglass RV

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Old 11-16-2005, 01:11 AM   #1
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There was an interesting note on RV.NET the other day during a discussion of small 120VAC compressor reefers, like dorm reefers -- One poster mentioned that small chest FREEZERS are more efficient than reefers, hold the cold air in when opened and can have the thermostat set to function at reefer temps. I can see an arrangement where a small, under-counter chest freezer is set up to tip forward for access.

It was also mentioned that in the store, the freezers/reefers have a label stating the kilowatt usage per year for comparative efficiency purposes -- This number then includes starts, stops, down time and run time over a year (presumably in the ambient temps found in a home).

To find expected battery needs, take the annual KWh, divide by 365 (day use) , divide again by 10 (voltage conversion), and multiply by two (good battery practice is to not use more than 50% of amp hours before recharging) -- No estimate was given for inverter efficiency.

For a small Sears dorm reefer (1.7 cu-ft, $65), the annual number is 299 KWh, so 299,000/365/10 = 82 Amp Hours @ 12VDC; multipling by two means a 160 AH battery/battery string is needed for once a day charging. The UL label indicates 120VAC; 0.8A run consumption, or 96Watts, so a 300W inverter should handle this nicely.

Of course, a custom installation with plenty of insulation on bottom and sides, plus good circulation over heat exchange grid or plate, might reduce starts and run times (this is where chest box works really well because you don't dump out the cold air when you open the door).

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Old 11-17-2005, 12:07 PM   #2
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Pete --

I did some crazy thinking and calculating concerning a complete RV energy system (excluding primary propulsion) using a small gasoline engine. It was to be based on a 10 hp Honda 4=cycle outboard, turning a generator set.

Coolant water and exhause would provide hot water for space heating as well as hot water. Electricity would be provided for cooking, refrigeration, cooking, lighting, etc. Loads would be separated electrically and prioritized to avoid overloading the gen set. Automatic electric start would also be used. Since this would take the place of the propane system, the refrigerator would be compressor based.

I never got beyond the concept stage, decided the Keep It Simple, Stupid, idea should be controlling and just got a bigger propane tank. Is that smart? or stupid?

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Old 11-17-2005, 12:30 PM   #3
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(Is that smart? or stupid? )

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Old 11-18-2005, 06:27 AM   #4
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why not use a liquid cooled genset?

save yourself a couple of steps.
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Old 11-18-2005, 09:17 AM   #5
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At the time a friend of mine had dropped a 10 HP Honda off his boat while trailering. Most of what made the engine an outboard including the lower unit was toast. But it ran just fine clamped in a large vice. As I remember, it was almost free for the asking.
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