Recommendations for building spill over freezer/reeder box?

[mrybas]

I will use my boat for full time cruising in the tropics. I plan to build a box 5.3 cubic feet insulated to R-30. I will use space loft (aerogel) as the insulation material as I would be left with a very small interior volume if used lower R value insulation. I would like to have a freezer and fridge space. What is the best way to design/build the spill over style box?
What mechanicals would you recommend for my system?
Thanks,

[ColdEh Marine]

Originally Posted by mrybas

I will use my boat for full time cruising in the tropics. I plan to build a box 5.3 cubic feet insulated to R-30. I will use space loft (aerogel) as the insulation material as I would be left with a very small interior volume if used lower R value insulation. I would like to have a freezer and fridge space. What is the best way to design/build the spill over style box?
What mechanicals would you recommend for my system?
Thanks,

Hi Mrybas.
2/3 fridge and 1/3 freezer is the usual size for a spill over system. All ice boxes are different but I usually recommend an R10 insulation wall between the fridge and freezer. Better off to have to much insulation in the separator then too little. You can use a 2 inch piece of blue board or one inch of Aerogel. Make sure you cover that insulation with something like an acrylic board . Once you get the system up and running you can then see how the temperatures are on the two sides , you may have to make a couple of holes in the divider to get the fridge a little colder or maybe even a little fan that is controlled by a thermostat to pull cold air into your fridge side. Or you may find that it works just fine as is . The problem is if you don't put enough insulation between the compartments , its hard to add once you have finished the box. You can use two smaller plates in the freezer side or just one . Its always better to surround the food then it is to have just one cold spot .
Since you are using a good amount of insulation (R value) in a smaller box you should be able to reach refrigeration Nirvana with out to much difficulty.

Regards John.

[mrybas]

Is it possible to have the spillover setup with a top loading fridge and a freezer drawer below? Maybe a pvc tube on both ends from the freezer to the top of the fridge would allow the cool air from the freezer to pass to the fridge without being blocked by fridge contents?

[ColdEh Marine]

A drawer in a deep freeze may be a bad Idea . Freezers in the tropics are all about insulation, insulation. If you are using Aerogel you would still need 4 inches to get to R40 for a good freezer , that makes for a very thick drawer door and how to get a good seal is also a challenge. Freezers sweat in the tropics if poorly insulated.

For ultimate efficiency I would stay with the old tried and true side by side set up. If you don't have the space you could go to a bin evaporator , or even build an entirely separate box with its own system somewhere else on the boat.

Hope this helps a little

Regards John.

[mrybas]

Here's the old box. It must have been expensive to build. The cold plates are built into the stainless box. It only had 2" of blue board insulation though.

[ColdEh Marine]

Originally Posted by mrybas

Here's the old box. It must have been expensive to build. The cold plates are built into the stainless box. It only had 2" of blue board insulation though.
Attachment 148368Attachment 148369

I like it ! Thats the way to do something right . Get that junk out of there.

With 2 inches of blueboard insulation in the tropics you will never reach refrigeration "nirvana" R10 will just not work .

I did a similar job on a deep freeze when I was Typhoon in this thread . I took the stainless liner out with a cut off saw and left the cabinetry intact . By the looks at your stainless box and the way it was constructed , this would not have been possible.

Great Job !

Freezer Build

I can help you if you have questions about how to lay up the new liner .


Regards John.

[ColdEh Marine]

Just a few pics of building a box liner .

Note that this liner had to be cut in half to facilitate installation under the cabinetry and them glassed together in place,

Regards John.

[mrybas]

Here's the space after the old box was removed. The square part measures 36"x18"x33" before insulation. The polygon shape at the end adds another 12" of length but I'm not sure if I'll include this space for the box, or see if I can fit the compressor here.
I'll insulate with 3" of aerogel for R-30 insulation.
For construction of the box, I was planning on using thin plywood or fiberglass sheet to make a temporary shape of the box. There is a part for the bridge deck that is a radius that I'll square off and I need to leave a chase behind the box to run power and water lines. Once I am happy with the box shape, I'll wax it (mold release) and glass it essentially using the raw space as a female mold for the exterior of the liner.
I can now take the liner off the boat and build the box working from the outer liner.

Construction: outer fiberglass liner - 3" areogel insulation - plastic vapor barrier - inner fiberglass liner

The old box had reflective radiant foil on the exterior of the insulation, is this necessary? Is the vapor barrier necessary if the inner and outer liner are fiberglass? If it is necessary, does the vapor barrier go inside or outside the insulation or both?

[ColdEh Marine]

Don't wast your time with the shiny foil , it adds nothing in R value . If anything it will add in thermal bridging . You don't want that .

As for Aerogel , doing a whole box with it, is expensive, have you done the math? Its great stuff and the way to go if you don't mind the hole it is going to put in your wallet . If you give up a few inches you could go with Polyisocyanurate insulation. At R6 an inch its not bad .

As for vapor barrier , the more the merrier , Ideally you want to encapsulate the entire insulation envelope, you don't want any air moving around in there. Air carries moisture and will condensate on the colder points inside you insulation and water log it . Adds up over the years to a big mess. Fiberglass does not make for a great vapor barrier so you should barrier the inside wall as well before you put the liner in .


Regards John.

[mrybas]

Forgot to add that I'll be moving the electrical panel, so a lot of the wiring will disappear.

[mrybas]

I already bought the aerogel. I think it was $1300 for 262sf of 10 mil. I know it's stupid expensive, but it's not a large space and I wanted to maximize volume.

[ColdEh Marine]

Originally Posted by mrybas

Forgot to add that I'll be moving the electrical panel, so a lot of the wiring will disappear.

That would be a great idea, you could jam that space with more insulation,

Regards John.

[ColdEh Marine]

Originally Posted by mrybas

I already bought the aerogel. I think it was $1300 for 262sf of 10 mil. I know it's stupid expensive, but it's not a large space and I wanted to maximize volume.

Excellent , you are ready . Will 262 sf give you the R value you are looking for all around the box ?

Regards John.

[mrybas]

Originally Posted by ColdEh Marine

Don't wast your time with the shiny foil , it adds nothing in R value . If anything it will add in thermal bridging . You don't want that .

As for Aerogel , doing a whole box with it, is expensive, have you done the math? Its great stuff and the way to go if you don't mind the hole it is going to put in your wallet . If you give up a few inches you could go with Polyisocyanurate insulation. At R6 an inch its not bad .

As for vapor barrier , the more the merrier , Ideally you want to encapsulate the entire insulation envelope, you don't want any air moving around in there. Air carries moisture and will condensate on the colder points inside you insulation and water log it . Adds up over the years to a big mess. Fiberglass does not make for a great vapor barrier so you should barrier the inside wall as well before you put the liner in .


Regards John.

I was going to use 4-6 mil plastic from HomeDepot/Lowes for a vapor barrier. That looks like what you used in the box on your boat?

[ColdEh Marine]

Originally Posted by mrybas

I was going to use 4-6 mil plastic from HomeDepot/Lowes for a vapor barrier. That looks like what you used in the box on your boat?

Yep 6mm , you can even heat shrink it to form complicated corners and it the heat sticks it together as well. Great stuff.

Regards John