Another Fridge Rebuild

[RaymondR]

The image in Post 45 illustrates an expansion of the volume of the Ozyfridge eutectic tank by adding another tank on the back side of the Ozyfridge tank. I am now about to mix and fill the tanks to Ozyfridge instructions. Their recommendations are for a 10% ethylene glycol/water solution for a fridge and a 25% colution for a freezer.

This got me to pondering what if I gave myself a choice by using a 10% solution in the larger tank and a 25% in the smaller. This would provide the option of re-configuring this section of the enclosure as either a eutectic fridge or freezer merely by changing the thermostat setting.

Still pondering??

[RaymondR]

The Ozefridge eutectic tank has now been trial fitted into the side alcove.

However, because there have been a number of modifications to the original plan it would not fit within the plywood bulkhead which separated the forward and aft tanks and the bulkhead had to be removed leaving a nasty exposed edge which will now have to be re-coated.

In addition the DIY forward tank is now being modified to comply with some good advice from Ozypete.

One of the potential problems with these small installations is the retention of the compressor lubricating oil in the evaporator coils due to insufficient gas velocity not flushing the oil through the tubes and back into the compressor.

Ozypete suggested that I include a short section of 1/4" copper tube from the end of the lowest coil back up to the exit from the tank where it will join the 5/16" vapor return tube to the compressor. This will provide for a higher velocity to flush the oil up the vertical section between the lower end of the coil and the exit from the tank.

Having trial fitted the 1/4" tube in the return line and observing that the 1/4" tube fits much closer to the top of the tank than the 5/16" tube (Illustrated in Post 50) and will simplify it's installation into the alcove I will now also place a section in the liquid supply line.

[GILow]

Did you discuss the question of using a different concentration of coolant for fridge vs freezer with Pete?

I’ve always assumed either would work for either task and that it was just a case of one being more efficient than the other, but that’s just an assumption on my part.

I remember reading something about latent heat and state changes, but it didn’t really stick in my mind.

Coincidentally, I had the fridge mechanic on board the new boat yesterday, recommissioning my Ozifridge after moving it out of the Swanson. It went well and I learned a few tricks from the 80 year old mechanic in the process. Now THAT is a lot of experience.

[Bowdrie]

Pure water, in changing state from 32F ice to 32F water will absorb 144BTUs per pound.
Anything we add to the water to get it to freeze at a lower temp reduces that number.
Freezers already have a higher heat load than reefers, as well as a lower number of BTUs that their solutions can absorb upon melting, it generally behooves us to use the larger capacity holding plates for freezer application.
Of course, the volume of the reefer vs freezer is also part of the equation.
But generally, a freezer will require about twice the BTU capacity of a reefer, (given equal box volumes).
The total number of BTUs that must be removed each 24 hours is a given, the choice between freezing a solution or not will not change that number.
What freezing a solution does give you is a smaller number of start/stop cycles on the equipment.
As the starting current is greater than the running current on motors/compressors, the total energy consumption over a 24 hour period is less with a system that freezes its solution.
In a system that does not freeze its solution, the solution is basically acting as a buffer, or a "thermal shock absorber", if you will.

[RaymondR]

What I figure will happen is that the entire section of the tank with 10 percent will freeze then the section with 25 percent will freeze and the reverse when the condensing unit is off. That's in freezer mode. In fridge mode the 10 percent will freeze to do the holdover and the 25 percent never freeze.

[RaymondR]

The project has reached the stage where the refrigeration and electrical connections are being made. The image illustrates the silver soldered tubing connections of the old condensing unit to the DIY eutectic tank. The next step is to fill the tanks with fluid, mount them and then test run both systems.

It's cold here at my cyclone season haven so I'm also going sailing north to warmer climes on Friday so the project completion will be done "on the run".

[GILow]

Originally Posted by RaymondR

The project has reached the stage where the refrigeration and electrical connections are being made. The image illustrates the silver soldered tubing connections of the old condensing unit to the DIY eutectic tank. The next step is to fill the tanks with fluid, mount them and then test run both systems.

It's cold here at my cyclone season haven so I'm also going sailing north to warmer climes on Friday so the project completion will be done "on the run".Attachment 276014

Curious. Where is your cyclone haven?

[RaymondR]

Originally Posted by GILow

Curious. Where is your cyclone haven?

The Mary River at Maryborough. Cyclones going south of 25 degrees are very rare however about every ten years or so (La Nina years) the river floods which generally requires one to spend a few days down in the Great Sandy Straits.

I normally start north during April but have been delayed assisting the owner of the Mary River Marina replace piles which were broken off during last years floods. The piles are 18 m (60') long, 12" OD. 1/2" WT and we are using a gadget we built for the purpose after the previous floods in 2012. Interesting operation.

Pressure tested my soldering job. 80 psi for 12 hours rock solid. I would have liked more pressure but don't have any nitrogen available. A half second vent resulted in a slight pressure drop inferring that there was no liquid refrigerant in the system so I'm calling it a valid test.

[RaymondR]

The temperature sensor for the electronic thermostat is an NTC resistor on the end of two core and needs a well in the tank. A piece of 5/16 copper tube, a 1/8 gas plug and a drop of silver solder produced one.

[RaymondR]

The fridge is designed with two complete eutectic systems to provide redundancy and the provision of a freezer section. I have designated these "the forward" and "the aft" systems.

Status of the forward System

The eutectic tank filling with a 10% pink glycol/water mixture and fixing into the alcove, and the plumbing and wiring, of the forward system with the DIY eutectic tank and old condensing unit, was completed and the system switched on. The fan started and then the LED on the compressor started blinking with a "locked rotor" warning.

I know the compressor was running when I did the trial fit and charged the system with refrigerant because I could hear the liquid refrigerant running into the coil. A solution is still pending and I have now switched over to finishing the installation of the Ozyfridge.

The Status of the Aft System

The ozyfridge eutectic tank has now been filled with eutectic fluid and installed and I will now switch over to completing the plumbing and wiring of the condensing unit in the lazarette. Not looking forward to fitting my 6'7'' stiff old body into there but someones got to do it.

The image illustrates the two eutectic tanks permanently fitted in the alcove.

[Salerosi]

Buenas
En lugar de fregaderos deslizantes, podrías utilizar las bandejas de barillas de inox de los lavavajillas, reformandolas a medida del espacio necesites, es fácil soldar este material con equipo eléctrico

[RaymondR]

Originally Posted by Salerosi

Buenas
En lugar de fregaderos deslizantes, podrías utilizar las bandejas de barillas de inox de los lavavajillas, reformandolas a medida del espacio necesites, es fácil soldar este material con equipo eléctrico

Both the tanks and sliding trays are actually the trays from steam table food serveries (bain marie) The tanks are made by using stainless steel sheet bolted onto the top flange of the bain marie trays.

The images in post #3 show the sliding trays in their suspension frames.

[RaymondR]

Progress has been made.

The DIY tank was filled with a 10% pink glycol eutectic solution and installed and it was found that the rails for the rolling trays would not now fit. It was also found to have a very slow leak and had to come out again so I switched over to completing installation of the Ozefridge unit.

The Ozefridge unit came with an instruction manual which has proved to have all the required information without being in any way obtuse or verbose and consequently has earned them another tick in the ease of use column.

Post number 11 illustrates the end of the condensing unit with the two service valves where the refrigerant supply and return tubes to the eutectic tank are connected. This is a significantly different arrangement to the O ring connectors usually utilized on these kit systems.

The eutectic tank comes with the flare tubing connections plugged and wound around the tank. The tubes are filled with refrigerant gas and the instructions in the manual require rapid removal of the plugs and connection to the service valves. Most of the refrigerant precharge is stored in the condensing unit and the instructions require the manipulation of the service valves to both minimize loss of refrigerant and exclude air from the system.

The Ozyfridges system works and the flare fittings should prove more reliable than the O ring type fittings more usually implemented on these kit systems. Another advantage being that their OD is much smaller and require a significantly smaller OD entry into the box.

A bit of electrical work and the system was turned on and rapidly started to pull down the eutectic tank temperature. This was a big relief as the part of the project utilizing the salvaged components from the old system is not going well.

The next step of the Ozefridge installation is to tune the system refrigerant volume via gas releases from one of the service valves.

Not wanting to again go cruising with a portable fridge sharing my TV watching seat in the saloon again I embarked upon my winter cruise without refrigeration, the weather being cool and the first section of the cruise have numerous re-supply points. Having done it a number of times I am aware that one can survive without refrigeration but even in a cool climate living without refrigeration, even for a relatively short period, is miserable.

Now, back to the troublesome DIY installation.

[RaymondR]

The tuning of the system proceeds slowly, I having to cram my 6'7" old body into the lazarette each time to let a little of the refrigerant out. This is an important step with these low refrigerant-volume, capillary-flow-control systems as one wants all the heat sinking to take place inside the eutectic tank cooling coils and not in the high ambient experiencing return lines and/or compressor housing.

The DIY tank is now leak free and refilled and ready to go back into the box.

This time I did what I should have done the first time and pressurized the tank with the shop vacuum cleaner and sprayed all the seams and screw holes with a strong detergent and water mix and checked for bubbles. There was one machine screw holding a mounting bracket which was not tight enough. The eutectic fluid leak did not show for a short term visual inspection but readily showed as an air leak.

[RaymondR]

Final release for the tune, before (frosted) and after (drips) images.