Building a Custom Stainless Freezer Compartment

[zboss]

Hi all,

I am trying to understand the parts that are used when constructing a custom drop-in stainless fridge or freezer.

Specifically, I plan to yank out all the old fridge fiberglass and insulation and have a new stainless box welded in the size I need. The cooling and freezing capability will be mounted on the outside of the stainless box, like a normal refrigerator.

I currently have an frigoboat system that is nearly new and I want to be able to use as much of that system as possible.

What I don’t know is the terminology for the component I want wrapped around the outside of the box. Does the coil ( I suppose) come in direct contact with the sheet metal?

Any hints on how others may have completed a project like this would be welcome.

[Privilege]

Basically....you have a compressor which can mount anywhere...normally just outside of your fridge/freezer. That connects via a small tube to an evaporator plate which sits INSIDE of your cold box. They come in many shapes and can be bent as desired to fit. A chest-type freezer is better if you have the room as cold air sinks and will drop out of a door type fridge much quicker.

I made a fridge/freezer for my boat using a Danfoss 35 compressor. I made the box from fiberglass and 4" insulation all around. At fridge temperature of around 4 degrees, once the fridge reached temperature, I measured the consumption to be 17ah for a 24hr period. I can turn it up to freezer temperature by simply twisting the thermostat know on the compressor.

[zboss]

Originally Posted by Privilege

Basically....you have a compressor which can mount anywhere...normally just outside of your fridge/freezer. That connects via a small tube to an evaporator plate which sits INSIDE of your cold box. They come in many shapes and can be bent as desired to fit. A chest-type freezer is better if you have the room as cold air sinks and will drop out of a door type fridge much quicker.

I made a fridge/freezer for my boat using a Danfoss 35 compressor. I made the box from fiberglass and 4" insulation all around. At fridge temperature of around 4 degrees, once the fridge reached temperature, I measured the consumption to be 17ah for a 24hr period. I can turn it up to freezer temperature by simply twisting the thermostat know on the compressor.

No I understand the usual construction method. We have a sister vessel that refrigerates the interior of the stainless from the outside.

Scroll down here:

zeroXTE

[OzePete]

Originally Posted by zboss

No I understand the usual construction method. We have a sister vessel that refrigerates the interior of the stainless from the outside.

Scroll down here:

zeroXTE

Like has been done in the project shown at the link. A few things, it is called the evaporator tubing and best if soldered to the stainless at each bend and heat transfer past applied to the tubing so as to increase the tube to stainless heat transfer then cover with aluminium tape as in the pics. Suggest using two mix urethane for insulation but do read this attachment first, it is tricky and can go pear shaped very easily.

Click on pic to expand..


Cheers OzePete Ozefridge | 12 Volt Refrigeration Systems

[zboss]

Thanks...

Is there general guidance on how much tubing to cubic feet? What diameter tubing and length? It looks like he just put tubing on the freezer side and maybe put some sort of spillover into the fridge side.

This seems like this is sort of an ideal solution - you never have to worry about puncturing and evaporator and you don't lose the space to an evaporator standoff.

Also, it seems like if you are running copper tubing against stainless sheet there is some potential for galvanic corrosion. I suppose you could use copper sheeting instead of stainless.

[Dougtiff]

Better to not build the new box out of stainless steel, because it will conduct way more heat than say fiberglass, its easy to build a fiberglass box, also if you are going to have the evaporator tubing between the box liner and the insulation, with fiberglass there will be no electrolysis issues.

[Richard Kollmann]

[QUOTE=zboss;2696003]Thanks...

Is there general guidance on how much tubing to cubic feet? What diameter tubing and length? It looks like he just put tubing on the freezer side and maybe put some sort of spillover into the fridge side.

This seems like this is sort of an ideal solution - you never have to worry about puncturing and evaporator and you don't lose the space to an evaporator standoff.

Also, it seems like if you are running copper tubing against stainless sheet there is some potential for galvanic corrosion. I suppose you could use copper sheeting instead of stainless.[/QUOTE

As to the size of evaporator tubing it is the compressor's refrigerant return line size that determines evaporator coil. It compressor is a Danfoss BD model 1/4 inch OD copper tubing is recommended 25 to 35 feet in length.

I have had to repair three of this type evaporators hidden behind stainless liners. Still do not know why they failed but my fix was taking a fifty foot roll of refrigerant and cutting it in half without unrolling it. I then clamped the half roll as is using screws to either one wall or to the top of box.

Soldering copper to stainless is not easy and this length of evaporator I would not try. Cleave at SeaFrost and Rob at Frigoboat USA both use stainless steel to cover and protect copper evaporator coils they may be able to advise you on tubing behind stainless liners.

Marine Ice makers cabinets use an aluminum heat conducting past between evaporator and ice maker that might be a solution for a behind the liner evaporator.

Home Depot also has a super aluminum heating and AC tape that might be the best solution, it is strong and seems to hold forever.

[zboss]

Thanks Richard.... we currently have a 2 year old frigoboat keel and air cooled. So you basically just wrap the fridge coil around the stainless, attach by whatever method you decide, and then solder the appropriate ends and route to the compressor? Does output of the compressor have to go to the top of the coil or the bottom? Does the coil have to slope steady up (or down) and not have any hills and valleys? Does that 25 or so feet include the run to and from the compressor or just the length of coil to be wrapped around the fridge?

[Terra Nova]

Stainless steel makes an excellent reefer/freezer liner. The evaporator is mounted inside the enclosure using 1"-long plastic spacers to allow air flow on all surfaces of the evaporator.

[Richard Kollmann]

Originally Posted by zboss

Thanks Richard.... we currently have a 2 year old frigoboat keel and air cooled. So you basically just wrap the fridge coil around the stainless, attach by whatever method you decide, and then solder the appropriate ends and route to the compressor? Does output of the compressor have to go to the top of the coil or the bottom? Does the coil have to slope steady up (or down) and not have any hills and valleys? Does that 25 or so feet include the run to and from the compressor or just the length of coil to be wrapped around the fridge?

It is important that you end up with balanced components on your one of a kind refrigeration system that follows a normal design. If compressor is a BD35 I would use 25 feet as evaporator if BD50 then 35 ft. I assume the two condensers are connected in series so refrigerant Flows from compressor through both condensers and then to a Small liquid refrigerant receiver. From outlet of receiver to a 1/4 in Flare sight glass with 1/4 inch Flares on 032 filter dryer attached attached. From the filter dryer 1/4 inch copper tube to the correct size TXV valve flow control. I spent a lifetime in DIY instruction an in refrigeration I never suggest soldering these small lines there are refrigeration nuts that will never leak so from filter dryer to TXV and on to evaporator coil and back to compressor all refrigeration brass flare nuts and unions. The TXV temperature sense tube needs to be connected at end of evaporator. I did the best I could here you will need more information as you proceed so always asked for help. Do not change adjustment on TXV until advised to by a tech that understands TXV like Rich John or myself.

You asked about gravity assistance in evaporator coil Yes to connecting line at top and exiting at bottom. Of freezers where refrigerant flow is velocity is low at zero degrees F oil return is better using some gravity pull.

[OzePete]

Originally Posted by Terra Nova

Stainless steel makes an excellent reefer/freezer liner. The evaporator is mounted inside the enclosure using 1"-long plastic spacers to allow air flow on all surfaces of the evaporator.

It certainly does make make a nice clear walled cabinet interior. The stainless liner should have a 'lid exit area' thermal break so it doesn't exit the cabinet exposed to the 'outside world'
Soldering stainless steel is easy with the correct flux (Ezi weld 801). Soft solder using a very small flame or large soldering iron. Don't use copper as it is too soft besides it is not an approved material for food area cabinet interiors in some countries.

The liner evaporator's clear interior has several advantages but it is a little less power efficient than a 'stand off the wall evaporator, so their are positives and negatives either way to consider.
But the starting point of any 'one off refrigeration project is to establish the proposed cabinet's heat load etc. Only then can you proceed to select the appropriate equipment.

Cheers OzePete Ozefridge | 12 Volt Refrigeration Systems

[zboss]

Thanks very much everyone. If we decide to go forward with this project I intend on hiring a welder to weld the appropriate stainless boxes to our specifications, then find a professional to complete the mechanicals of the fridge/freezer conversion, do the prep and insulation myself, and a yard and counter fitter to update the counter with the appropriate lids.

I just needed information so I knew what kinds of questions to ask to start the conversation.

[stainless guy]

I make exactly what you have described, typically for restaraunt salad bars and countertop wine chillers

I typically use 3/8 copper and bend in a grid pattern on all 5 sides of the cooler, then weld studs to the outside walls of the cabinet and use stainless rectangles bent in a w to bolt the lines to the exterior of the cooler. After it is all bolted up gently bang the copper lines with a rubber mallet or dead blow hammer to eliminate gaps between the cooler and copper

The stuff you refer to as heat transfer paste is called "thermal mastic" and should be applied liberally to the lines trying to eliminate all air from between copper and stainless

Install the thermometer with the return line
Wrap and tape over the copper and thermal mastic with either foil back insulation or aerogel.product of choice
Build a secondary box for the cooler box to fit into and insulate the inside of this with 2.5" extruded polystyrene

Drop the cooler assembly into the insulated box (with hole for supply, return and thermometer line) fasten together you can use plastic strip 1/4" thick as a thermal break between the cooler liner and external shell body



Build a suitable lid, install where you want and plumb to your appropriately sized compressor

And as a side note I got side tracked into this thread on a search for different dive compressor setups. ..

[sailingunity]

Originally Posted by stainless guy

I make exactly what you have described, typically for restaraunt salad bars and countertop wine chillers

I typically use 3/8 copper and bend in a grid pattern on all 5 sides of the cooler, then weld studs to the outside walls of the cabinet and use stainless rectangles bent in a w to bolt the lines to the exterior of the cooler. After it is all bolted up gently bang the copper lines with a rubber mallet or dead blow hammer to eliminate gaps between the cooler and copper

The stuff you refer to as heat transfer paste is called "thermal mastic" and should be applied liberally to the lines trying to eliminate all air from between copper and stainless

Install the thermometer with the return line
Wrap and tape over the copper and thermal mastic with either foil back insulation or aerogel.product of choice
Build a secondary box for the cooler box to fit into and insulate the inside of this with 2.5" extruded polystyrene

Drop the cooler assembly into the insulated box (with hole for supply, return and thermometer line) fasten together you can use plastic strip 1/4" thick as a thermal break between the cooler liner and external shell body



Build a suitable lid, install where you want and plumb to your appropriately sized compressor

And as a side note I got side tracked into this thread on a search for different dive compressor setups. ..

Do you have pictures of said arrnagement? Sounds interesting...

[stainless guy]

Originally Posted by sailingunity

Do you have pictures of said arrnagement? Sounds interesting...

I probably do somewhere I will see I I can find and post them