Building a fridge from scratch

[hd002e]

I am looking to build a fridge into one of the galley cabinets on a boat that has only had a mobile selfcontained dometic fridge before. I want to put the compressor unit about 5-6 feet away into the lazarette to keep the hot air away from the cabin in the summer. I have about 130L of space in the cabinet but after accounting for insulation I expect for the inner volume of my fridge to be about 65L. I am planning to have a stainless box made and then glue layers of insulation foam between the stainless box and the interior walls of my wooden galley cabinets. The access will be from the top.

Other considerations are for a drain hole in the bottom for easy cleaning. Hole for wiring a door open sensor and LED light. Tray supports so I can have a shelf.

I have spoken to some technical people at industrial fridge manufacturers here in Turkey but my engineer’s mind is still craving more information especially around best practices and design considerations. Are there any resources you guys would recommend me to read up?

I would also love to hear from anyone who has gone through building such a thing themselves and what you yave learned, what would you differently?

Thank you!

[Mexican Hat]

Haven't built a fridge from scratch though I did do some research. Too many other mission-critical things had to be done instead so I bought a very efficient one. I think I'd look into vacuum panels as an addition to some foam. Easy enough to buy if there's anyone still well enough to be making them in China, but you can make your own. Save you a lot of space.

I don't have enough data for a broad comparison but my current 100L top loading fridge with 100mm of foam insulation and a good double lid seal uses 1/3 less power than the 50L front opening with the allegedly super-efficient swing compressor it replaced. This includes a tropical summer with heat indices over 105 for months. Which is to say that insulation and a really good compressor go a long way. As a further example of insulation, I found that I could put ice in a cheap pre-chilled Walmart gallon vacuum jug and it would stay frozen for a week if left undisturbed in the fridge. I have seen data suggesting that above 100mm the rate of improvement decreases but vacuum panels are about 10x as effective as the best foam. No-one seems to make large double wall vacuum containers suitable for building into a fridge... Shouldn't be too hard to make one if you have the time and resources.
I'd add a way to separate things on shelves or in crates for ease of organization, make it easy to drain and easy to clean. Cold air is more dense so put lots of insulation at the bottom and make sure the lid is very well sealed, preferably with a double seal. I think a hinged lid with a prop of some kind is better than a lift-off when space is already limited. If you wanted a fridge and freezer you could potentially wall off a portion at the bottom with an insulated layer and install the temperature sensor there, then use a fan to duct cold air to the rest of the fridge, using a separate temp sensor to trigger the fan.

My fridge needs at least three inches of free air space around it for efficient heat transfer but if you have the workings installed remotely that shouldn't be an issue. People have reported condensation at the boundary between hull and insulation and it might be good to look into this and think about some air gap around the cooler box.

[Bill O]

Made our fridge box out of SS and insulated similar to how you are describing your planned build. Ours has a front opening door with a magnetic seal.

The magnetic seal is the way to go, but wouldn't do the SS insert with a flange again. Even though we added extra insulation between the door frame (for the magnetic seal), the SS flange still is cold enough to condense water in humid conditions. It's not too bad, but we need it wipe up the condensation from time to time.

As mentioned, this is a front opening fridge that is 6 cu ft.. In the heat of the summer, we use ~35-40ah to keep it at ~35F. Here is a link for more details. (We now use a digital thermostat instead of a mechanical)

Since we installed the fridge, we made a top load 3.5 cu ft. freezer with a magnetic seal for the door. This time the box was made with Coosa and lined with f/g and white food grade epoxy (lesson learned, no SS box). The Frigoboat refrigeration system was similar to the fridge with a digital thermostat.

For the freezer, we used ~6" of pink board on the sides/top and >8" on the bottom (non usable space due to the shape of the hull). This amount of insulation along with the magnetic seal on the door produced a super efficient freezer. Again tested in the summer heat, we were able to keep the freezer at 4-6F and only use 22ah.


My bottom line:
Although it is easy to clean, no SS box unless it doesn't have any protruding flanges.

Use a digital thermostat which are easily made with an Inkbird (or similar device).

Use a magnetically sealed gasket. We purchased a custom one online to fit our door dimensions and it wasn't expensive.

Add as much insulation as possible to increase energy efficiency.

[GILow]

It sounds like you’d like some reference data.

I built my 220 litre fridge/freezer box from fibreglass.

150 mm of XPS foam for the lower face, 100 mm for the sides, 50 mm for the lid. This equates to R30, R20 and R10 respectively. (Divide these by 5.678 for their SI equivalents)

Box is about 1200 mm long x 500 mm deep x 400 mm wide

30/70 split for the hinged lid (allows you to get the milk out without opening the whole lid) and a 75 mm XPS foam divider panel with PC muffin fan to run the spillover. The panel can be moved allowing me to vary the freezer to fridge ratio from 70/30 to 30/70 or anywhere in between. (I seem to need about 40/60 most of the time.)

Fridge system is a dual plate eutectic by Ozefridge.

Freezer side runs at around -10C with the plates running between -22C and -14C. The spillover controller keeps the fridge side within 0.1C of 4C.

In our warm latitude 35 summers it draws about 50 amp hours@12v every 24 hours, equating to around a 30% duty cycle of the compressor.

During a recent winter in Tasmania I saw a duty cycle of less than 10%, but there were mornings where the interior of the fridge was actually warmer than the interior of the boat.

I hope some of this helps.

Matt

[Madehn]

1) i put 6 inches of insulation on the bottom- worth it
2) drain - definitely yes- even put a little external pump on the freezer because it is deep
3) brackets welded into internal box that can support adjustable sliding shelves
4) shelves were made from easy to clean 1/2 inch polycorbonate- shelves all have pattern of holes drilled into them to facilitate air circulation
5) both fridge and freezer have two large holding plates in each-- these take up a lot of room along with accompanying piping which is inside box
6) digital thermostat- yes-- also get one with an alarm and remote temp readout
7) used 2 part foam to seal in cracks and areas that i could not get to- nasty stuff to work with but effective--- put at least 6 inches of insulation on side of box facing outside hull particularly in hot climate
8) VERY IMPORTANT- i have an air pipe with a small computer fan that circulates air top to bottom in my large fridge box-- keeps temps uniform and greatly improved performance and utility- it runs continuously as power draw is minimal
9) my unit draws around 6 amps at 12 volts DC and runs at about a 50% duty cycle keeping food at 15 degrees F in freezer and 36 degrees in fridge- i have separate compressors in each
10) agree with hinged hatch as well as making sure you have excellent seal on top -- door/hatch insulation should be at least 4 inches
11) highly recommend cool blue technautics as a source for parts- no affiliation they just did a great job for me
12) system running on easily replaceable 134a ( easy to source and to carry extra gas on board
13) i fabricated a cutting board that fitted over the hatch to provide even more insulation and seal- be sure to put a rim around hatch at the top if counter can get wet to prevent water from draining into box
14) if i had to do over again, i might put a water tank on one side with an external insulated tap so that i could get cold water without opening the box- may do that yet
15) oversize wiring to compressor to prevent voltage drops - compressors must be well ventilated (mine are air cooled, i would not want water cooled due to power draw and more complexity)- locate compressors where you can clean the heat exchange portion easily
16) freezer and fridges may well have different solutions in holding plates if separate boxes
17) a removeable basket at the top may be as easier than top shelves
good luck

[SVTatia]

Originally Posted by hd002e

I am looking to build a fridge into one of the galley cabinets on a boat that has only had a mobile selfcontained dometic fridge before. I want to put the compressor unit about 5-6 feet away into the lazarette to keep the hot air away from the cabin in the summer. I have about 130L of space in the cabinet but after accounting for insulation I expect for the inner volume of my fridge to be about 65L. I am planning to have a stainless box made and then glue layers of insulation foam between the stainless box and the interior walls of my wooden galley cabinets. The access will be from the top.



Other considerations are for a drain hole in the bottom for easy cleaning. Hole for wiring a door open sensor and LED light. Tray supports so I can have a shelf.



I have spoken to some technical people at industrial fridge manufacturers here in Turkey but my engineer’s mind is still craving more information especially around best practices and design considerations. Are there any resources you guys would recommend me to read up?



I would also love to hear from anyone who has gone through building such a thing themselves and what you yave learned, what would you differently?



Thank you!

Did you check the drop ins? Since you are in Europe, Dometic makes a SS drop in box with a compressor that can be mounted 1.5 meters away, such as the one below sold in the US.

https://www.defender.com/category.jsp?id=2276230

[Bowdrie]

For built-in boxes, stainless steel has largely gone the way of the Dodo bird.
In all of the retrofits I've done, (installing refrigeration in an existing stainless box,) very few times have I come across one in which the insulation was hermetically sealed against the metal.
In general, metal boxes are excellent producers of condensation, and repairs, (like patching an un-needed hole or a leaking seam,) are almost futile.
Simply trying to glue insulation against the metal without any air space(s) is a "hope-and-a-prayer" situation.
If the box can be turned upside down, a dam built around it, and liquid foam poured all over and around the box then a reasonable chance of success can be achieved.
The liquid must be poured directly on the metal and allowed to expand outward, you cannot just pour the foam in such a way as to allow the foam to expand against the metal.
Also, expect that if you drop a frozen "something" of much weight into the box the metal could flex and compromise the insulation bond in that spot, (foam doesn't like to flex).
A process that was used in the old days was to "glue" the foam panels to the stainless with tar, applied hot, and the foam panel(s) stuck on to the tar before it hardened.
Really, a well laid-up/thick fiberglass box is superior for a DIY project.
The need for zero air space between box and insulation still applies.

[wsmurdoch]

Keep an eye out for the four books I know of on the subject. Unfortunately, all are 20 years or more old. It is a shame that there is little currently in print on the subject. Someone ought to...

Refrigeration for Pleasure Boats - Installation, Maintenance, and Repair, Nigel Calder, 1991.

Do-It-Yourself Boat Refrigeration, R. L. Kollmann, 2000.

12 & 24 Volt Refrigeration Manual, Richard L. Kollmann, 2003.

The Perfect Box: Thirty-Nine Ways to Improve Your Boat's Ice Box, Edgar J. Beyn, 1989.

A Yeti V cooler is $800 for 24.75” L x 16.625” W x 17.37” H all with the risk of sudden and complete failure if the vessel is breached and the vacuum is lost.

[s/v Jedi]

Originally Posted by wsmurdoch

Keep an eye out for the four books I know of on the subject. Unfortunately, all are 20 years or more old. It is a shame that there is little currently in print on the subject. Someone ought to...

Refrigeration for Pleasure Boats - Installation, Maintenance, and Repair, Nigel Calder, 1991.

Do-It-Yourself Boat Refrigeration, R. L. Kollmann, 2000.

12 & 24 Volt Refrigeration Manual, Richard L. Kollmann, 2003.

The Perfect Box: Thirty-Nine Ways to Improve Your Boat's Ice Box, Edgar J. Beyn, 1989.

A Yeti V cooler is $800 for 24.75” L x 16.625” W x 17.37” H all with the risk of sudden and complete failure if the vessel is breached and the vacuum is lost.

I used that first book from Nigel Calder and can second it. Worked out really well and calculations were spot on.

BTW, I recommend against using stainless steel and against using a drain. Not only is it a big hit on efficiency, it’s also a source of condensation in the bilge.

[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.

[jordanbigel]

Originally Posted by s/v Jedi

I used that first book from Nigel Calder and can second it. Worked out really well and calculations were spot on.

BTW, I recommend against using stainless steel and against using a drain. Not only is it a big hit on efficiency, it’s also a source of condensation in the bilge.

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.

[wholybee]

I will be doing this next year and am in the planning stage. I'll probably try and get a copy of Nigel's book. A quick search and the others don't seem available.

I am curious on the construction of a top and doors for a top loading box. I've read of the need for magnetic seals, and a double seal. How do you build that?

Also, is it worth exploring the newer high tech insulating materials? Vacuum Insulation panels or Aero gel? I understand that there are diminishing returns with higher insulation, but 4" of Styrofoam is R20, and in that same 4" you could get R90 with 2 inches of VIP sandwiched between Styrofoam. Can you get to a point where if you don't open the box the compressor will only run once in 24 hrs?

[Bowdrie]

Originally Posted by wholybee

Can you get to a point where if you don't open the box the compressor will only run once in 24 hrs?

In theory, yes.
In actuality, yes, with massive cold/eutectic plates and a large condensing system, (like an engine drive unit).
With any of the typical 12V evaporator systems, not a snowballs chance.

[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 ?

[wholybee]

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.

Anyone ?

That is basically what a Vacuum insulated panel is. A 1" panel, manufactured to the size/shape you need because you can't cut it, with a vacuum pulled inside. 1" of it is R40. The common use right now (or not so long ago) was building shipping boxes to keep COVID vaccines at sub-zero temps during shipping.

There are construction difficulties, it is very delicate, and if damaged loses its insulating properties. But R80 - R90 is achievable. I have to believe that would make a significant difference in efficiency over a typical R20 insulated box.

I'm not interested in more room, but I am a solar powered boat. No generator, no charging from the engine. I want the icebox to be as efficient as possible.