120 vac or 12V Refridgeration

[john61ct]

Yes that's a crazy big fridge for off-grid use.

Make the box with 8+" insulation maybe doable, but will definitely require a very expensive custom setup, likely three compressors, maybe even worth designing a combination of powerful holding plates for when loading warm contents and burning dino juice, plus evaporators to help maintain temps in between charging cycles.

Originally Posted by Jammer

Typical inverters are around 90-95% efficient.

Maybe on the spec sheet, which cherry-picks the optimum load type and quantity, at ideal temperature etc

Real life averages are much lower.

[Richard Kollmann]

If you were to look back at the marine refrigeration industry supplying 40 ft sailboats with large twin iceboxes 30 years ago companies like Crosby, Grunert and a few others understood what a functional ice box conversion refrigerator freezer design needed to be. Large charter boat fleets were mainly responsible for development of refrigeration in 36 to 50 ft sailboats. Twelve volt icebox conversion refrigeration on boats with large iceboxes needing a refrigerator/freezer 30 years ago was not good then nor is it a good idea today. Large sailboat refrigeration systems with real low temperature freezers built by Crousby and Grunert were generally hybrid with two separate energy sourced engine driven and ¼ to ½ hp12 volt belt driven compressors. Sailboats in the fourth foot class that were delivered with generators usually had AC electric high capacity refrigeration compressors. The condensing unit designs by these companies used the same off the shelf components as super market refrigerator/freezers. The earlier large ice box twin compressor systems were described as eutectic holdover refrigeration with an extra shore power system and both systems connected to the same dual evaporator coil eutectic holding plates.

The real question in this forum post is how large a box can be refrigerated by a 12 volt DC hermetically sealed compressor? There are always comments suggesting the answer is to add insulation and not Btu capacity. Insulation has never been a solution if boat is to be a live aboard in the tropics unless adding insulation is to reduce size of area to be refrigerated.

Lifeofreilly57, Here are some solution options you may want to consider:

1. Keep the present system as is and with a divider separate large box into two areas for a 33 to 36 degree F refrigeration section and the other area to be used as a 40 to 55 degree F cooler. I would then purchase one or maybe two Engel 45 qt portable refrigerators to be used as zero degree freezers or by changing thermostat setting refrigerators.
2. Separate large box into a separate refrigerator freezer reducing size of each area to less than seven cubic feet by added moisture resistant insulation inside box. Not knowing location of holding plates and their solution’s freeze point I can only deal with this as a conceptual idea, if this create performance temperature problems they can be resolved. The present system would still be 110 volt AC and lack any redundancy if generator or refrigerator stopped running.
3. Keep present system as is and again separate large box into two separate areas of less than eight cubic feet. Then purchase two 12/24 volt refrigeration units with largest bin evaporators and Danfoss engineered BD50 compressors. One unit with freezer mechanical thermostat and the other with refrigerator mechanical thermostat. For dependable reliability I only recommend basic air cooled systems without unnecessary gadgets. For price and solid design I would recommend the Nova Kold BD50 units with their box bin evaporators and Adler Barbour vertical Ice cube trays The divider between Refrigerator and freezer section needs to be an R value of at least R10

[Typhoon]

You need to decide how much refrigerated/freezer space you really need . Most people have do with half the space you have combined .

For efficiency, insulation will be your best investment . It will serve you constantly and require no maintenance .

We have an 8 cubic foot fridge at R30 insulation and a 2.5 cubic foot deep freeze with R40 insulation. We run the fridge at 33F to 37f and the deep at 0F to 5F . Both are top loading and both have well insulated doors and good seals.

Each box has its own system ColdEh system with a BD35 . They have always been run at low speed. On the hottest days the systems combined have never used over 35 AHs in 24 hrs .

Spectacular results can be had with the right combination of insulation and equipment in the right sized boxes.

If you are coming to the Spring Annapolis boat show we will be there , also we are dropping our prices by a great deal. PM me with the details .

Regards John.

[Cheechako]

My mono in the Caribe was maybe 2 cu ft. Fridge. with rectangular evaporator/freezer. Enough for us two, be we weren't headed off the grid to Timbuktu either.
My Cat in the Caribe had a front door type freezer-refridge. It did ice up and need more defrost for sure. But bottom line, didnt seem to need any more engine running to replenish batteries than the little 2 cu ft top loader. Go figure. It likely held a lower avg temp throughout the day I suppose.
My 47 ft mono I installed a Grunert belt drive big compressor unit. I think it was 1/2 HP at 12V! That thing was terrible amp draw. You can read too much by tech types who love big chunks of cool machinery and write books! Being an engineer I fell for it.

Two of my boats had counter top , top loaders, but they had a front door also to reach the bottom. To me that was the perfect solution. I kept cold drinks on the bottom.

[lifeofreilly57]

Originally Posted by a64pilot

Just about everyone is running a 12V system, it’s the standard.
However tell us more about your fridge, what is it specifically?
We have a Mod that is running a 120V dorm fridge off of an inverter for thousands of dollars less than a 12V system, and is close to the same efficiency.
What is extremely important efficiency wise is insulation, it will make an inefficient compressor, efficient, and a very efficient compressor, inefficient, based on insulation, or lack there of.

I know that is obvious, just it can make more of a difference than you might think.

Right now it has a Grundfos 120vac compressor with a cold plate.
I have not drilled or cut into the insulation but feel it is well insulated, once the fridge is cooled down to temp it stays at about 38-40F when the compressor is run for one hour twice a day..
I'm considering dividing it into two sections, a small section as a freezer section and the larger portion as a regular fridge section.
If I'm doing this it means I'll have to reconfigure my refrigeration in general so while I'm at it.......

[lifeofreilly57]

Originally Posted by john61ct

Yes that's a crazy big fridge for off-grid use.

Make the box with 8+" insulation maybe doable, but will definitely require a very expensive custom setup, likely three compressors, maybe even worth designing a combination of powerful holding plates for when loading warm contents and burning dino juice, plus evaporators to help maintain temps in between charging cycles.

Maybe on the spec sheet, which cherry-picks the optimum load type and quantity, at ideal temperature etc

Real life averages are much lower.

My figuring may be a bit off, I have to measure it and figure it out. Since it is built into the side of the hull it's got a triangular shape with the curve of the hull on the back side.