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Old 05-03-2021, 15:53   #1
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Refrigerator Box insulation rebuild, Isotherm 2351

Iím rebuilding my boat box for the tropics. 100F air, 86F water,... been there and done it but not with the isotherm 2351. Itís a bin evaporator drain condenser system with bd35f compressor and energy saver controller Iím adding.
Iím using blue foam. Calder tested at R6.7 but at room temperature although itís labeled R5.
Isotherm says I can do 100mm(4in.) foam R3.5ish) for a 7 cubic ft. Box. Iím skeptical even though/inch thatís their numbers for tropics.
My numbers for insulation and box are:

For a 5 inches insulation (R25-R34.5) - 4.35 cu. ft. Box.
Or
For a 4inches insulation (R20-R27.4) - 6.37 cu. ft. Box

Iím looking for some real world input with one of these systems before I put it all together. I have 400w of solar and 400amphrs+ of fireflies to run it. If I go with the the thicker insulation the box is only going to be 16inches wide... is that extra inch of insulation necessary in the real tropical world?Click image for larger version

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Old 05-03-2021, 16:42   #2
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Re: Refrigerator Box insulation rebuild, Isotherm 2351

Vapour sealing, non conductive inner lining (not metal), soft 100% lid seal and adequate closed cell insulation are essential. Also add more insulation thickness to the base as it has the greatest rate of heat penetration (Heat rises!) Less thickness up top and add that to the base, so as to not reduce cabinet capacity.
If not water cooled or air water cooled, make sure the refrigeration unit is located where there is good flow through ventilation if going to the tropics.
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Old 05-03-2021, 17:19   #3
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Re: Refrigerator Box insulation rebuild, Isotherm 2351

Quote:
Originally Posted by OzeLouie View Post
Vapour sealing, non conductive inner lining (not metal), soft 100% lid seal and adequate closed cell insulation are essential. Also add more insulation thickness to the base as it has the greatest rate of heat penetration (Heat rises!) Less thickness up top and add that to the base, so as to not reduce cabinet capacity.
If not water cooled or air water cooled, make sure the refrigeration unit is located where there is good flow through ventilation if going to the tropics.


Itís water cooled. Iím just trying to figure out how much insulation is enough.
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Old 05-03-2021, 17:32   #4
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Re: Refrigerator Box insulation rebuild, Isotherm 2351

Inside surface area of the 2 options is:
6.37cubic ft. - 19.96 sq. ft.
4.35 cubic ft. - 16.88 sq. ft.
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Old 05-03-2021, 18:10   #5
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Re: Refrigerator Box insulation rebuild, Isotherm 2351

Quote:
Originally Posted by akopac View Post
Inside surface area of the 2 options is:
6.37cubic ft. - 19.96 sq. ft.
4.35 cubic ft. - 16.88 sq. ft.


Oops. Got those areas reversed
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Old 06-03-2021, 09:31   #6
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Re: Refrigerator Box insulation rebuild, Isotherm 2351

Here's an OzFridge insulation recommendation...
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Old 06-03-2021, 09:37   #7
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Re: Refrigerator Box insulation rebuild, Isotherm 2351

Not sure of the source of this document, but it goes into excellent details on the calculations for insulation...
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Old 06-03-2021, 09:38   #8
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Re: Refrigerator Box insulation rebuild, Isotherm 2351

What if itís just a fridge and not a freezer/fridge combo?
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Old 06-03-2021, 09:41   #9
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Re: Refrigerator Box insulation rebuild, Isotherm 2351

Quote:
Originally Posted by ayates View Post
Here's an OzFridge insulation recommendation...
To clarify, that is not an Oxefridge plan, but my own installation design with their equipment. Highly recommend Ozefridge
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Old 06-03-2021, 09:43   #10
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Re: Refrigerator Box insulation rebuild, Isotherm 2351

Quote:
Originally Posted by ayates View Post
Not sure of the source of this document, but it goes into excellent details on the calculations for insulation...


Thank you. Thatís more what Iím looking for.
Still wondering about any real world experience with this isotherm unit. It only has a BD35f compressor and water cooling.
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Old 06-03-2021, 09:54   #11
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Re: Refrigerator Box insulation rebuild, Isotherm 2351

I went with more on the bottom and did not put in the drain plug again. My compartments are deep and it's still no big deal to defrost and sponge out the water.
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Old 06-03-2021, 10:31   #12
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Re: Refrigerator Box insulation rebuild, Isotherm 2351

I used vacuum panels in addition to 4" XPS when I rebuilt my box. Costs a lot and so far they seem to be still working OK after 20+ years. Expensive but R to thickness is exceptional compared to XPS boards. I also used a magnetic strip/ regular fridge sealing strip on the hatch which seems to work very well especially for ice buildup.

No drain, glass interior.
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Old 06-03-2021, 10:36   #13
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Smile Re: Refrigerator Box insulation rebuild, Isotherm 2351

Ayates Referenced a very technical paper (PDF) regarding calculations for tropical refrigerators and freezers. In it there is a link for a spreadsheet that looks to be really well put together. The link is broken, but I found the spreadsheet at:
http://www.swingcat.co.uk/what/fridg...zer_calcs.xlsx

Still looking for some real world input on the isotherm 2351 refrigeration and box construction experiences though. I'm doing some calculating now
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Old 06-03-2021, 11:19   #14
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Re: Refrigerator Box insulation rebuild, Isotherm 2351

It's easy to keep fridge temperatures with 3-4" but freezer temperatures are much harder. I would consider 6" there.

Consider using some aerogel (R10) or vacuum panels (R40). To keep the cost reasonable you could just pick a few sides to maximize space in the fridge and use foam on the others walls

Aerogel can be bought on Ebay. Be sure to get the US made Aspen brand. Comes in 10MM sheets. Just cut with hand scissors (do outside and wear a mask as it's dusty), stack the layers and wrap and tape in plastic sheet.

Inexpensive vacuum panels can be bought off the shelf from Rparts. You don't need a perfect size fit. Fill in the empty areas with aerogel.
https://www.rparts.com/index.php?cPa...5psfb3aqppt966
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Old 06-03-2021, 11:50   #15
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Re: Refrigerator Box insulation rebuild, Isotherm 2351

I have a 5cu ft box, 1/3 freezer, AB air cooled cold machine (DB50 probably), eutectic holding plate, no drain, R parts medium hatch, FRP interior w/ tinted epoxy coating, vacuum panels and between 3 to 6 inches of XPS. In tropical weather and living aboard a typical 24 hour period the fridge/freezer will use 45 to 60AH/day of juice. The 60 AH is if I motored a lot as one wall of the fridge shares the engine room space. My system is 540 AH gel, 120amp alternator, KISS wind generator and 300W solar. I wish I had more solar if not in the trades. If I am in decent winds the KISS and solar takes care of things. Before I rebuilt the box it was an average of 4" urethane and consumption with the same system less insulation used 80 to 95AH/day. More R is better if you can do it.

Your numbers look OK to me (but several "experts" on the forum will tell you I'm a clueless idiot which I may very well be) with the caveats that you could use more solar. Or run a wind generator or generator or charge by engine often. The 400AH bank maybe fine but how often you tolerate recharging is the question. Or more precisely your bank size should be sized to your usage. Your charging capacity should be sized to your bank and your style i.e. do you want to run the engine/genny twice a day or twice a week?

The more R value the better if you want less energy consumption. The more solar the better to some extent. 400W nominal solar may turn out in reality to be a LOT less than that. Depends on shading, etc. etc.

If you can swing it vacuum panels give you a lot of R for not a lot of thickness. I am not familiar with aerogel but it also looks like good insulation for not a lot of thickness but the price scares me away plus I did my box rebuild over 20 years ago and I don't recall anyone using aerogel at that time widely in boats. But that was then.
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