Fridge Install with Stainless Liner & Pour-in Foam

[swinsail]

I am nearing the end (is there ever a real end) of a very long yacht construction project. A number of years ago I had a fridge / freezer system put together by a now defunct local mobile refrigeration company, “Refrigeration Research” (based in Mount Barker, South Australia). The system comprised of a stainless steel liner where evaporator coils were attached to the outside of the liner, in effect making the inside surface of the liner one big evaporator plate. This liner is designed to be installed using pour-in polyurethane foam for insulation. The basic specs of the system are a 37 litre (1.3 ft^3) freezer section and a 77 litre (2.7ft^3) fridge sections. The evaporator coils are located at the freezer end of the liner, with a thermostatically controlled fan moving cold air to the fridge section across a spill-over type internal divider. There will be 4” of foam all around the liner. The unit is powered by a Mitsubishi SSR120 Rotary Compressor. The Liner is manufactured from 0.7mm (22 gauge) Stainless Steel Patterned Sheet and has been fabricated by soldering all joints. The fridge needs to be suitable for live aboard use in the tropics.
As you can see from the attached photos I have a lid system that just requires final painting, and the cabinetry in the boat is ready to accept the fridge. There is obviously a lot of work been done to get to this point but I am questioning whether this system will give efficient performance in the long run. It seems that there are some questions about the use of pour-in foam with regard to water absorption degrading its thermal performance. There is also the question of the liner separating away from the poured in foam once there are a few bumps happening with goods loaded into the fridge.
It seems to me the options are . . .
1) Proceed ahead and install as designed. Are there any better types of pour-in foam that doesn’t absorb water? Any special encapsulation techniques? Anyone have experience with liner separating from foam?
2) Use the liner but glue blue board insulation to the outer skin.
3) Construct a new liner from fiberglass sheet with blue board insulation on the outer and with an internal plate evaporator.
As is often stated with the posts that have been made regarding fridge installation . . . I only want to have to do this once! Any advice would be much appreciated.

[senormechanico]

Congratulations on good work.
Do a search on CF for Aerogel.
Several people (including me) have used it and are very happy with the results.
You can even buy it on eBay.

[mikereed100]

I would keep the stainless liner but glue as much 'blue board' as you can to the the outside, being very careful to avoid air spaces that will allow condensation. If there are any voids left after gluing on the blue board you could fill them with urethane pour foam, again making sure there are no voids. Pour foam is closed cell and will not absorb water in the short term, but after long exposure to water it can break down and absorb water. The heavier foams are less likely to do this (4lbs/ft2 +) but care still needs to be taken to keep it dry.
That's a beautiful installation, best of luck!

[Terra Nova]

Foam of not greater than 2lbs/' is what you want for a reefer/freezer. Any air gaps between the insulation and stainless liner are likely to cause condensation to develop.

[Richard Kollmann]

Swinsail, Interesting project concept but leaves me with several concerns:

1. Box of 4 cubic ft to be used as a freezer refrigerator is small for a 38 foot boat. Spillover fan should be able to run any time even when compressor stops. Size of spillover fan on this small of a box I recommend 10 Cfm. The divider between refrigerator area and freezer should have at least an R value of 10 to provide a Delta T of 20 degrees. A 10 cfm one inch square fan hole in divider need not be larger than one inch. Twenty two gauge stainless steel box liner is pretty thin and easily damaged in normal use. This metal shell must be supported structurally sides and bottom to the boat.
2. Pour in place foam continues to expand for 24 hours with great force distorting walls and liners if they have strength than ½ inch plywood.
3. Soldered joints must be strong enough to withstand expansion and contraction of metal as it changes shape during temperature changes.
4. In order for heat conduction between evaporator coil and stainless liner to be efficient contact must be 100% and as much of tube circumference as possible touching steel liner. You might consider after attaching evaporator to liner using a thermo conducting past to increase heat transfer between the two surfaces.
5. I was unable to find any information on SSR120 Rotary compressors. Compressor Btu capacity must match capacity of evaporator with in reason if refrigeration is to efficient. This also means that size of tubing in evaporator be sized to provide adequate velocity need to prevent oil starvation at compressor.
6. Avoid any type insulation that has open cells this includes Aero Space and Vacuum Panels as well. Close cell pour in Polyurethane foam is generally closed cell but the problem with these foams in controlling the size (density) of the open cells. It is reported to help control foam density by mix small amounts and pour them in waiting before mixing the next batch.
Blue Board extruded Polystyrene is moisture resistant but has a lower R value than Polyurethane controlled density boards.
7. Over time most closed cell insulation ages allowing gas cells to open up and outgas leaving cavities for moist air to interior and exit each time compressor cycles. My experience using a radiation barrier of reflecting sun’s rays away on exterior of insulation greatly extends R value of insulation. I can not quantify this but aluminum foil is so inexpensive it might be worth doing.
8. I always recommend a moisture barrier seal on all insulation except when moisture resistant Blue Board is used.

[seasick]

I have nearly an identical installation. What jumps out at me is the minimal taper in your access hatches or lids.
I nearly throw my back out every time I go for a beer.
By all appearances a great system otherwise.

[swinsail]

Thanks for your replies . . . . much appreciated.

I would be interested to hear how similar your installation is to my proposed one Seasick. If you do have a stainless liner with pour-in foam are there any areas where the liner has separated from the foam? Don't like the sound of your install getting in the way of grabbing a beer from the fridge. Rectifying that must be near the top of your to-do list.

Thanks for your detailed reply Richard. You make may valid points. It seems that the pour-in foam would still be the best overall solution as it also provides the required structural support for the liner. The interior surfaces of the cabinetry that the foam would be poured into are epoxy coated timber and so along with the steel hull of the boat on the 4th side of the cavity would form a vapour barrier for the foam. I would therefore just need to create a vapour barrier for the top of the foam pour.

The specs that was originally given for the Mitsubishi Rotary Compressor is . . .

Model SR120 produces 390 BTU’s per hour of refrigeration at a minus 23°c evaporator temperature, (freezer operation), or 1305 BTU’s of refrigeration at zero°c evaporator temperature operating as a refrigerator.

The tubing consists of a 10 foot supply & return run in 1/4" OD copper between compressor and evaporator. There is approximately 40 feet of 1/4" OD tube coiled to the outside of the liner to form the evaporator. This is thermally bonded to the liner with thermal transfer paste. The capillary tube is 1.7mm OD. Do these numbers work out to a relatively balanced (efficient) system???

[Truemettle]

All very good advice, I would also make sure there is a water drain hat you can attach to a hand pump for any Beer can explosions and other normal spills. It also makes cleaning the fridge a joy, just flood it with soap and water, then pump it dry.
Nice work!

[Richard Kollmann]

Without knowing what refrigerant and capillary tube length you are using it is impossible to project superheat and flow efficiency. Capacity and line sizes are all correct, nice job. Forty ft of ¼ tubing in evaporator tube is smart. I might have used a refrigerant receiver and expansion valve to make superheat mechanically adjustable expanding its range over range of cap tube. This means superheat can only be controlled by adding or removing refrigerant.

One very important comment before pouring insulation in the interior of box liner and outside walls must be braced all sides with ½ inch plywood. Supports across interior strengthen plywood this is also very important. I have said liner must be supported for 24 hours on my web site and heard later that in all cases this was not long enough to prevent distortion of walls and liner.

[sainted]

Insulation is one of the most important aspects of refrigerator system design. Have you considered vacuum panels? They have an r value of 30 per inch, way more than pour in foam or blue board. Since your box has the evap tubes on the out side of the liner, you could get vacuum panels to line the refrigerator/freezer cavity and then use pour in foam to fill the void between the refer box and the vacuum panels. See rparts.com for info on vacuum panels.

[Richard Kollmann]

Sainted, I know of no manufacturer that has been able to produce VIP insulation that will stand up to the dynamics of pleasure boat refrigeration. My position is if you must use open cell insulation of any kind even in Vacuum Insulation Panels or so called spaace age insulation make sure it can easily be replaced when it fails. These open cell insulations will fail if and when moist ambient air has acess to move in and out of open cells. Application of open cell versus close cell insulation will not perform the same when keeping heat dry air in a box versus cold inside a box with warm moist air outside box.

[Dougtiff]

Having done marine refrigeration for many years, i noticed a couple of things not mentioned,first 4" of insulation is not sufficient for a freezer in the tropics,6" is minimum to keep the running time down,also as far as what kind of power system is to be used depends on a number of things,if your going to use the main engine to power the compressor it will be a waste of energy unless you are doing other things,i.e. charging batts,making water,etc. if not you should consider a 12 volt system, although you could power the compressor with a 12 volt motor,about insulation i agree using blue board and some pour in foam is the way to go,also using VACUME panels along with blue board gives you much more insulation,i use 1" blue board,1" VACUME panel and 1"blue board, the blue board on each side protects the VACUME panel,as you do not want to puncture it or you will lose the R value,again if you are going to use 12 volts i would consider not using the existing hold over design piping with the rotary pump, but remove the tubing[i know its a bummer to redo work already done but its old technology,needs to go away] the new generation of compressors are far superior to old ones,they monitor voltage have soft start up,etc. and are more efficient than the old hold over plates you can order the EVAPORATOR in various sizes and bend it to the configuration needed with a 1" stand off with out losing much need room and you can do this work your self as its all precharged,hope this helps.