building a drop in freezer/refrigerator box

[RobPatterson]

Originally Posted by coopec43

Don't you believe you should be removing heat by convection?

Heat flows from higher temperature to lower.
Water flows downhill
Electricity flows from high voltage to low.

The refrigerated space "box" needs to be insulated. Convection of warm air around this box will heat up the beer.

The equipment "box" with the compressor and condenser needs to be ventilated. Convection around the condenser will heat move heat out of the refrigerant.

[skipgundlach]

Snippets from others:

Originally Posted by tml

We built our box without a gap at the hull using the pink foam panels to 8" for an R 40 value. No problems that we have noticed. Using an infared thermometer don't see any temp differential even in full sunlight.
Talk to Cleve at Seafrost, his DC air cooled units have worked for us and many others.
If you have limited wall thickness look at aerogel insulation. We used it to beef up the R value where the cabinetry limited us to four inches or less insulation space. It is expensive but it does work.
We found the insulation in the tropics was likely more important than which refrigeration unit used.
Good luck
Tom

Good advice. We now have a Seafrost, which cannot approach what our smaller (50 vs 80 danfoss) Frigoboat accomplished with a much smaller amp load. Cleave is a good guy but - I learned as he and I chased a problem recently - he is highly dyslexic. Call, rather than write, to him. Their system has a ducted fan box, meaning that the compressor is cooled by the air pulled or pushed over it on the way past the condenser.

However, in tropical conditions, likely you'd need to add water cooling (unless you mount it in some very cool space; ours, like many others', is in the engine room), which is the bane of my existence, for reasons anyone with water cooling will understand; you REALLY don't want to go there unless you use the FW tank dodge to avoid clogging tubing and endless disassembly to deal with it. If you do, however, put copper stuff (cut up scrubbies, cut-off tubing segments, whatever) in your incoming water line and filter (both) to limit the critters growing; you'd still have to deal with grass and mud, if applicable. As to the hull-box gap, we very carefully filled it with 2-part (from tanks and combiner gun) polyurethane, with 13" at the top and ~5" at the bottom. When the boat was out of the water, in summer humidity, you could see condensation on the hull at the point of that insulation, so despite the depth, there was still heat transfer. Even with the lengths to which I went, mentioned below...

Onward:

Originally Posted by Madehn

i dont think you gain anything by the airgap except a place for water to condense- would fill it if possible- also a little concerned about lining with the FRP- i like the idea of using it from an ease of fabrication BUT what are you mounting your cold plates ( whatever form you are using) on? the FRP will not be sturdy enough to hold it and with 6 inch foam area before you get to any other substance then i think you will have issues- i would think about fiberglassing a 1/2 inch piece of foamboard with multiple layers of cloth on both sides then epoxying that piece by piece inside the box- use thickened epoxy as fillets in the corners and joins inside then gelcoat. I am in the process of doing that with my box right now. good luck!

We built our box from extruded polystyrene in 4 and 2 inch sizes (6" total). Do make a sturdy interior, as anything you'd want to hang on it (evaporator, shelf brackets, etc.) will rely on that to hang.

Expanding 2-part foam is, as others have noted, fraught with difficulties or potential disaster. If you have the access, blue/pink board is better, or some of the more esoteric insulators...

Onward

Originally Posted by jhulmer

Personally I like this plan. But only if you can get at least 5-6" of insulation all around. Test your resin on the blue board, in my case the epoxy worked no problem but polyester dissolved it.

What he said. Our approach was to cut the board pieces, using stairsteps in the layers, to further limit the ability for convective transfer, first coating them in epoxy, and then epoxying (brush-on) the joints as they were laid. In our case we built the box first, then the top, for easier access. Front load reefer, top load freezer, with air gap (doorskin strips) to limit convective loss, reflective barrier (aluminum foil shiny side to heat) to limit radiant loss, and double "e" appearing foam weatherstripping at inside and outside of the 6" total foam to limit air loss. Interior was finished with a fiberglass layup; spillover gap/fan was 1/2" styrofoam on both sides of a 1/2" marine ply, all epoxied as above. In our case, it's a 4.5" computer style fan center, with the same square-inch pass on top - which in our construction worked out to exactly an inch. In practice, we've had to stuff that with some old cloth to limit the air flow during convective transfer; the divider intentionally wasn't as robust as the exterior, as the reefer gets its cold from the freezer anyway.

To the original, I know Rich Boren personally (Technautics and other refrigeration style stuff); like Cleave at SeaFrost, he's very accessible, but on the west coast of the US, for time zone issues. However, his site shows their system (air cooled only) easily operating in desert high temps conditions. Other than that he doesn't do evaporator (cold plates only, and I like my hysteresis to be within a couple of degrees) cooling, I'd have it instead. He and I have war-gamed how we might add condenser capacity to my system, as it's immensely amp-hungry and doesn't get within 10F of what my Frigoboat previously accomplished at half the amps.


If you don't mind wading through other projects' shots (I had not made subgalleries in the early days of our refit), the reefer project is here:

Pictures: Flying Pig Early Refit + Projects/Early_Major_Alterations_Work/00-2004-TheBeginning/12-04

L8R

Skip

[skipgundlach]

PS here's a look at the gaskets:

Pictures: Flying Pig 2013-2014 Shakedown/Refrigerator Gaskets

[akopac]

So I’m sticking with the dry deck air gap between hull and reflectix. I’m thinking if you have water and on one sided glass and foam. That’s not a good thing whether conductive or whatever transfer. It gives a 6mm air gap I think. I painted the entire cavity today (bulkheads and hull insides that are already glassed with epoxy)with 2 coats 2 part titanium dioxide epoxy paint. It’s pretty IR blocked, but will still run foul and reflective before foam. I’ll engineer some anchor points for the freezer bin as I move foreword to distribute and secure the load.
I just keep thinking to myself if watercooling is great in the tropics why would you not isolate almost 9 sq. Ft. Of area on the side of the box from the water too. Might as well.

[flyingfin]

Originally Posted by sailortype

"Don't make the mistake of filling the void between the box and the hull"
Is this a thing..? I have this job ahead of me this Spring and have never heard of leaving a gap between the insulated box and the hull. In addition to the practical difficulties in insulating and leaving such a gap... the space in that area is quite limited and I would have thought filling it with every last ounce of closed cell foam insulation would have been the best method.

Exactly! Air is an excellent insulator as long as it cannot escape or be replaced by new air,,,that is why foam (a cake with lots of air bubbles) is next in line. Water is excellent for transferring heat, followed solid metal. Read up on heat transfer, then decide how to proceed.

[akopac]

OK folks. Been doing some deep digging here. First off. It seems I can put radiant insulation all around the outside of my box including the top (a reflective blanket on counter like windshield reflector) without it being too coocky or obvious, except the bottom and hull side. When I say radiant heat insulation, I mean reflective with air space on outside toward heat source. After researching it seems that any radiant insulation whether it’s foil, reflectix, or whatever is almost useless without a 3/4” air gap toward the heat source. My initial thought of using dry deck is OK for the hull and bottom, but has a lot of contact with the radiant reflective layer. So I’m wondering if anybody has any thoughts on handling the bottom and hull side better? I was even thinking of putting windshield reflective film on the outside of the hull adjoining the fridge box. It’s the air gap thing that bothers me...

[akopac]

Everything is dry fit. I’m making FRP panels now and blocking to hold it all in place while it dries after I lay it up.
What do you laminate your foam sheets with?
Epoxy? With or without filler? Caulk? Spray foam?
How about sheet joints?
Attachment 1

[skipgundlach]

Originally Posted by akopac

Everything is dry fit. I’m making FRP panels now and blocking to hold it all in place while it dries after I lay it up.
What do you laminate your foam sheets with?
Epoxy? With or without filler? Caulk? Spray foam?
How about sheet joints?
Attachment 238504Attachment 238505Attachment 1Attachment 238507

If you are using extruded polystyrene (pink and blue/Owens Corning and Dow) - "styrofoam" - is sensitive to poly but not to epoxy. Coating with poly will attack the foam blocks...

I coated the blocks (after a dry fit) entirely with epoxy before setting, and then went over any joints/corners again, all before the fiberglass layer...

If you're anal about it you could use all 2" material and stairstep each joint, or just one each 2" and 4"; the 'stairstep' will minimize any potential vapor passage potential.

That curved portion will be a bear to do well; I had enough space that I didn't include ours (filled that void between the two bulkheads and the end of the box next to the hull curve with polystyrene 2-part foam - two canisters, combined trigger from feed lines - VERY carefully, to avoid over-expansion) so it was fully rectangular.

One heads-up; my freezer section had a smaller-than-the-box lid; my original evaporator was large enough to wrap around all 3 non-spillover sides. I had to destroy it to get it out (which meant, also, that there was no way, dangit!, to get a replacement in there). Allow for future replacement, whether under yours or a future owner's watch, of whatever you install...

Good luck with your project. Looks pretty good from here!

[akopac]

Do I need to add thickener to the epoxy for between sheets?

It’s all stair-stepped. Bin evaporator will go at end with 3/4” clearance on sides and wall. I was able to shape the first layer of foam to fit the hull curve using a angle grinder with flapper sanding disk. Min. 6” blue foam bottom, hull and side behind bin evaporator opposite hull side. 5” blue for and aft bulkhead/walls.

[skipgundlach]

Originally Posted by akopac

Do I need to add thickener to the epoxy for between sheets?

It’s all stair-stepped. Bin evaporator will go at end with 3/4” clearance on sides and wall. I was able to shape the first layer of foam to fit the hull curve using a angle grinder with flapper sanding disk. Min. 6” blue foam bottom, hull and side behind bin evaporator opposite hull side. 5” blue for and aft bulkhead/walls.

Sounds like you're on the right track.

If your material is thick extrusions you shouldn't likely need thickener between layers.

My coating was to provide another layer of moisture protection to already-excellent water-exclusion insulation. If both layers are wet at the time of setting I expect the bond will be ample.

In our case, the aft bulkhead is the engine room. It makes a difference, especially as our air-and-water condensing is in that space.

As you probably know the practical boundary of effectiveness is 6" for your and my insulation, but anything I can do to minimize (without making my space unusably small) heat transfer is a good thing.

Ours is a spillover system; I no longer recall how you're handling the two spaces, if it was mentioned. I put 6" everywhere except the spillover panel; it has a 5" fan central, in any case (and in periods of particularly good freezing, will manage merely with convection in our ~3.5/6.5CF space).

For that panel, I used a 1/2" ply panel faced with 1/2" styrofoam (both sides) and finished with fiberglass like the rest of it.

And, give some thought to the possibility of repair or replacement; as noted, my top-load freezer (where the plate was, and the new plates are) lid was too small to remove/replace the large wrap-around evaporator when I had to. Putting it in when the top wasn't yet on was easy, but the potential for future work wasn't on my mental horizon!!

[akopac]

Final layup. Need to cleanup fillet areas and fillet. Upper top will need 4 moor inches glass to bring in to point where it will meet shelf top face. Will be adding 1 more inch of foam on sink side fridge wall.
Took 3 hours to layup as continuous process.
Radiant barrier all round
Bottom, hull side, and sink side will be 6 inch
For and aft bulkheads 5. Inch
Total of 36 foam and laminate pieces and 1 gallon epoxy went into lay
Used leftover scrap foam to proactively make compressive fill pieces for interior for while epoxy layer up overnight.