Building a fridge from scratch

[Bowdrie]

Originally Posted by wholybee

The common use right now (or not so long ago) was building shipping boxes to keep COVID vaccines at sub-zero temps during shipping.

but I am a solar powered boat. No generator, no charging from the engine. I want the icebox to be as efficient as possible.

Yeah, about 35 years ago we were experimenting with vacuum panels for refrigeration use at an outfit I worked for.
They were flexible plastic, filled with "Aerosil", (like you add to epoxy to thicken it,) then the plastic was sealed while in a vacuum chamber.
The main user of them was for shipping whole blood and were only available in a few sizes.
No generator? No engine charging?
"Sailing Uma"?

[wholybee]

Originally Posted by Bowdrie

Yeah, about 35 years ago we were experimenting with vacuum panels for refrigeration use at an outfit I worked for.
They were flexible plastic, filled with "Aerosil", (like you add to epoxy to thicken it,) then the plastic was sealed while in a vacuum chamber.
The main user of them was for shipping whole blood and were only available in a few sizes.
No generator? No engine charging?
"Sailing Uma"?

I have an engine, I just don't use or want to use it for charging. I want to be able to sit at anchor forever, or make a 30-day passage, and not run a loud smelly engine, or need to buy fuel.

Here are some that are available at R60 per inch. Using Styrofoam to protect it, you could have 4" of insulation that was R130.

https://www.digikey.com/en/product-h...ulation-panels

[jordanbigel]

For my freezer, I went with a combination of aerogel and regular foam to get to R40 (2 sides and top and bottom) and R55 on outboard side (facing hull) and R25 on the side facing the fridge. I had constraints on most sides and top of 4", and that was after already reducing box size from 10cuft down to 8cuft.

I installed a Technautics CoolBlue and it runs about 45% duty cycle (2 hours on/2+ hours off) and keeps the box at around 10F. For this, my power usage is about 40ah per day.

I expect when we leave California for the tropics, duty cycle will increase with commensurate power usage increase.

Next to the freezer is the fridge which is about 6.5cuft. It is insulated using standard insulation, not Aerogel, to R24 on all sides. I have a second CoolBlue compressor installed for the reefer box and it runs only 3 hours per day and consumes a total of about 15ah. That's it, once per day.

My total power consumption is about 55ah/day.

WRT Vacuum panels, I priced them out, both as a total solution (ie making an actual inner box out of FRP encased vacuum panels) and a partial solution (ie. embed panels only on some of the sides) - either way, the cost was way higher than the cost of Aerogel, and, I was scared off of VIP because of "horror stories" of punctured panels going from R20 to R1 overnight.

[wholybee]

Originally Posted by jordanbigel

For my freezer, I went with a combination of aerogel and regular foam to get to R40 (2 sides and top and bottom) and R55 on outboard side (facing hull) and R25 on the side facing the fridge. I had constraints on most sides and top of 4", and that was after already reducing box size from 10cuft down to 8cuft.

I installed a Technautics CoolBlue and it runs about 45% duty cycle (2 hours on/2+ hours off) and keeps the box at around 10F. For this, my power usage is about 40ah per day.

I expect when we leave California for the tropics, duty cycle will increase with commensurate power usage increase.

Next to the freezer is the fridge which is about 6.5cuft. It is insulated using standard insulation, not Aerogel, to R24 on all sides. I have a second CoolBlue compressor installed for the reefer box and it runs only 3 hours per day and consumes a total of about 15ah. That's it, once per day.

My total power consumption is about 55ah/day.

WRT Vacuum panels, I priced them out, both as a total solution (ie making an actual inner box out of FRP encased vacuum panels) and a partial solution (ie. embed panels only on some of the sides) - either way, the cost was way higher than the cost of Aerogel, and, I was scared off of VIP because of "horror stories" of punctured panels going from R20 to R1 overnight.

Where did you source your aerogel?

My construction thought if I use VIP panels is a 4 inch composite. I would rough in the box with 4 inches of Styrofoam (4 1" panels), but not glue any of it. Then for the middle 2 layers of foam, I would cut out squares and rectangles to fit the VIP panels and insert them in the foam. Fill voids with expanding foam. Then stack and glue the Styrofoam panels into a 4 in composite panel, with the VIP inside, unable to move and completely sealed. If something DID happen, VIP panels that are damaged are R5, so the result would be the same as if I had 4" of Styrofoam. But I don't see anyway that could happen, unless they fail due to age.

Anyway, I am undecided, and they are *really* expensive. So, I am curious what I could expect in performance of R30 vs R100ish. And Aerogel is also very attractive, but it seems harder to find.

[jordanbigel]

Originally Posted by wholybee

Where did you source your aerogel?

My construction thought if I use VIP panels is a 4 inch composite. I would rough in the box with 4 inches of Styrofoam (4 1" panels), but not glue any of it. Then for the middle 2 layers of foam, I would cut out squares and rectangles to fit the VIP panels and insert them in the foam. Fill voids with expanding foam. Then stack and glue the Styrofoam panels into a 4 in composite panel, with the VIP inside, unable to move and completely sealed. If something DID happen, VIP panels that are damaged are R5, so the result would be the same as if I had 4" of Styrofoam. But I don't see anyway that could happen, unless they fail due to age.

Anyway, I am undecided, and they are *really* expensive. So, I am curious what I could expect in performance of R30 vs R100ish. And Aerogel is also very attractive, but it seems harder to find.

The aerogel came from buyaerogel.com - not fun to work with, but not that bad.

I think your plan to encapsulate the VIP panels sounds reasonable. Should work fine.

WRT the idea of R75 or R100 - it sounds like if you get the R value up high enough, then the only way any heat can enter the box is through the door when you open it! But, I have a feeling (for no reason at all) that there is a top end where adding more R-value begins to have diminishing effects. My instinct is that R-100 is probably no better than R-50, but I dont know what the math is on this, the guys from Technautics can probably address this question definitively.

[wholybee]

Originally Posted by jordanbigel

The aerogel came from buyaerogel.com - not fun to work with, but not that bad.

I think your plan to encapsulate the VIP panels sounds reasonable. Should work fine.

WRT the idea of R75 or R100 - it sounds like if you get the R value up high enough, then the only way any heat can enter the box is through the door when you open it! But, I have a feeling (for no reason at all) that there is a top end where adding more R-value begins to have diminishing effects. My instinct is that R-100 is probably no better than R-50, but I dont know what the math is on this, the guys from Technautics can probably address this question definitively.

I have read that going more than 4" of foam doesn't do much. But going from 4"-6" is only an increase of R10. I can understand that not doing much. The question is would a *huge* increase do much. Many things work logarithmically, such that noticeable increases happen with doubling of value. So, R5 to R10 is noticeable. R10 to R 20 is noticeable. The next noticeable jump would be R40, then R80. So, adding another inch or 2 of insulation wouldn't do anything. But adding R60 of a super insulator would. I am purely speculating.

I ordered Nigel's book. I'm sure it doesn't address high tech insulators and recommends not needing more that 4 or 6 inches of foam. But maybe the math is in there.

[Celestialsailor]

This is a thread that I started 10 years ago. Some of it might be of interest.


https://www.cruisersforum.com/forums...gel-75006.html

[s/v Jedi]

Originally Posted by jordanbigel

Agree strongly about not using a drain. I lived 20 years with drains and when I rebuilt them from scratch I omitted the drains. Nothing but a source of condensation and leakage. The small amount of water which sometimes accumulates in the fridge is dealt with during bi-monthly cleanup with rags. A drain in a freezer makes even less sense since any liquids would by definition be frozen. Now when you defrost your freezer, you will have to remove the meltwater but that is something done very rarely.

We have had a sponge on the lowest point for many years but have switched to a mini shopvac since, which works perfectly

About the vacuum panels being discussed: I have read many reports about these panels failing after only a short period, regardless of how protected they are. The extra insulation around them is all you get when this happens.

Unless you have no room for 6” regular insulation for a freezer, or 4” for a fridge, I would stick to regular insulation. Much more care should be given to preventing channels that conduct heat/cold like using spray foam as an adhesive for the insulation instead of other types of glue. Also, moisture barrier quality is very important because most wet insulation occurs around through holes for refrigerant tubing etc. Such holes should be lined to block water ingress.

[RaymondR]

"like using spray foam as an adhesive for the insulation instead of other types of glue"

My experience was that glues like contact did not give a good bond because it did not penetrate the highly porous surface of the polyurethane foam whereas pouring a bead of 2 pack polyurethane onto the surface and then quickly clamping the surfaces together whilst the foam expanded cause the expanding foam to penetrate the porous surfaces and consequently form bond stronger than the base material.

After fabricating the box and working inside it to fillet the corners I decided that if I ever built another box I would cut the pieces then fibre glass the working and inner surfaces, then bond the box together, then fillet the corners and glass them over using fibre glass tape.

I would also build the inner box from light marine ply using the nylon stitching technique, thoroughly seal the plywood with epoxy sealer,.then fit the polyurethane sheeting onto the outside and glass it over.

[s/v Jedi]

Originally Posted by RaymondR

"like using spray foam as an adhesive for the insulation instead of other types of glue"

My experience was that glues like contact did not give a good bond because it did not penetrate the highly porous surface of the polyurethane foam whereas pouring a bead of 2 pack polyurethane onto the surface and then quickly clamping the surfaces together whilst the foam expanded cause the expanding foam to penetrate the porous surfaces and consequently form bond stronger than the base material.

After fabricating the box and working inside it to fillet the corners I decided that if I ever built another box I would cut the pieces then fibre glass the working and inner surfaces, then bond the box together, then fillet the corners and glass them over using fibre glass tape.

I would also build the inner box from light marine ply using the nylon stitching technique, thoroughly seal the plywood with epoxy sealer,.then fit the polyurethane sheeting onto the outside and glass it over.

All the pictures from my build are here: https://sv-jedi.smugmug.com/Projects...Refrigeration/

We don’t use these boxes anymore but the build was in 2004 and we used it until 2019 so 15 years

[Tupaia]

Originally Posted by Pizzazz

There isn't that much to marine fridge design. You need an insulated box and a compressor/evaporator. The easiest way is to get a residential fridge that fits your cabinet and a 12/24V truck portable fridge with a Danfoss compressor, then replace the 110/220V compressor with the DC compressor. The Danfoss control units (read the manual) have a number of settings where you can control the speed of the compressor to match the volume of your compartment. In my case, I found a residential fridge that fit my cabinet for $150 and a second hand truck fridge/Danfoss for $90. Much better than the $2,000+ marine units that would not even fit my space.

Using an off the shelf domestic fridge is not really possible any more unless you replace the complete gas circuit. All domestic refrigeration sold in Europe now uses R600 gas, which is flammable and unsuitable for mobile appliances. The evaporator plates are not compatible with R134 that should be used for mobile units.

[Bowdrie]

Originally Posted by RaymondR

I decided that if I ever built another box I would cut the pieces then fibre glass the working and inner surfaces, then bond the box together, then fillet the corners and glass them over using fibre glass tape.

^ This 100%.
Aside from laying-up a box over a male mold this is the way to go.
Giving the foam parts a coat or two of epoxy first, to seal the pores and harden the surface, and then doing the layup on the parts in a horizontal position gives so much better results.
And being able to properly use a squeegee on the layers of fiberglass gives a superior surface finish.
Bending over with your head and arms inside a box whilst trying to fiberglass large vertical surfaces is a most miserable job and seldom produces pro looking results.
For the layup work either the plastic or rubber squeegees work, (take your pick). For the corner coving, a rubber one, cut to ~1" radius and dipped in acetone at intervals gives a good finish.
Be fussy where 3 coves come together, (2 sides/bottom,) both with coves and fiberglass tape overlays.
Nothing so miserable as sanding an internal 3 corner joint.
Where hole(s) enter for refrigeration lines a piece of schedule 20 pvc pipe fitted in with thickened epoxy works well, allowing it to protrude into the box a 1/2" or so with a epoxy fillet around it.
After the tubing is installed a bit of squirt foam seals it up.

[dlj]

Originally Posted by Dave_S

Just a thought.

Vacuum flasks are more efficient than foam insulation. Maybe you could save some room / have more room, by making a tank inside a tank, air tight and braced so the walls don't collapse, then fit a connection so you could suck most of the air out between the walls with a hand pump.

How close to a vacuum does it need to be to outperform foam?

Anyone ?

The difficulty with vacuum is maintaining the vacuum. The second difficulty is the support structure. So you have this great insulation with nice heat port (connections). It's very difficult to design using vacuum for insulation. It's more commonly combined with other types of insulation. If you look at windows for example, they used to say they were vacuum but now they just fill with argon. Argon is a fairly heavy gas and does not diffuse out as easily and also does not move around as much meaning you don't get as must conduction of heat through convection.

There are three forms of heat transfer; radiation, conduction and convection. Radiation typically is only predominant in high temperatures. So you are really minimizing the transfer of heat through conduction and convection when you are looking at a frig/freezer.

At what level of vacuum do you need to achieve a "functional" level of insulation in this kind of application I don't really know the answer. Looking at the physics of it, I'd guess in the rough vacuum range of 10 to the minus 2 (10^2) or minus 3 (10^3) torr. The difficulty is that your vacuum will degrade due to a number of things that happen. Even if your seal is "perfect", there is the phenomena of adsorbed water that you can't get rid of at those vacuum levels that will make your vacuum degrade over time. Now if you could create that vacuum and then back will with argon, that would give you a number of years of reliable insulation. But in my opinion on a boat refrigerator system, better to go with more traditional insulation methods.

dj

[RaymondR]

On the extant fridge rebuild I did consider using polystyrene sheets in pieces vacuumed and sealed in plastic using my food vacuum and seal machine but abandoned the idea as impractical and went with cutting lots of holes in the plywood inner box and injecting two pack polyurethane foam with a big syringe I made from poly down pipe, then epoxying dowel into the holes to seal them. Very messy job but it worked.

[wholybee]

Thank you. I will probably skip the VIP.

What about the top/lid? How is that constructed with a double seal and magnetic seal? (Apart from buying a door)

Pictures of a sistership Icebox rebuild are herescroll down to see all the pictures in the thread)
https://www.morgan38.org/morgan38/in...rebuild.15257/

My plan is similar to that. Remove the top. Cut out the existing icebox. Clean up/remove the poor quality opencel foam. Apply a vapor barrier to plywood box. Add 4-6 inches of blue or pink foam board. Probably 8" on the bottom and against the hull to square the inside of the box. Fiberglass.(noting the recommendation to fiberglass before installing the foam) I would have a PVC pipe for the lines glassed in and sealed.

I plan on about a 1.5 cf freezer against the hull, where the box isn't as deep, and the rest of the box a fridge(probably about 3cf), in a spillover design.

Then I need to build and install the top. I would like to shoot for 3-4 inches of insulation on the top. But I'm not sure the best way to build the top/doors (2 doors, one for the freezer and one for fridge).