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     ICE BOX TO REFRIGERATION CONVERSION

It is always nice to get out for the weekend, to go cruising. We typically have to take 3 to 4 bags of ice to make through the entire weekend. I decided to do a little research on converting it to a Freon assisted Ice Box. I still wanted to have ice for drinks, but just not have most or all it melts The Cal 9.2 has the icebox drain to the bilge which I quickly changed to a pump-out system with a blaster pump. This helped to remove the water as the ice melted, but in doing so also removed "cold" BTU's as well. 

How good is the insulation on the Ice Box?
It measures out to be about 2.5 cubic ft. With 3" of insulation the thermal leakage should be in the range of 18 watts/hr. Check out the reference  (http://www.frigoboat.com/infocenter/consumptionguide.html ).   To freeze 1 lb of water it takes 144Btu's. So an 8lb bag of ice contains at least  1152 Btu's. Thermal leakage of the icebox indicates that a bag of ice should last only 4.5 hrs.  If 3 bags lasted me for 36hrs with a little still frozen, then the thermal leakage is closer to 10 Watts or 100 Btu's loss per hour. foam insulation
How many BTU's / Watts are available to cool?
Simple physics  assisted in determining  the overall performance of a system. The EER  of a refrigeration system is usually between 8 and 12.
An EER is a measure of Btu's per 1 Watt hour. I wanted a system that would extend the life of the ice that I brought on board without being a big power monger.  The smallest and least expensive system that I could find was a Sawafuji  compressor system. I found the guts to a Norcold on Ebay for $45.00. It turns out that they also make a system that allows for do-it-yourselfers that can be found at West Marine. It goes for about $700.00

sawafuji system It is comprised of a Sawafuji compressor, condenser coils, U bent evaporator plate, and 12volt to 20VAC driver. It is a capillary tube system where the capillary tube separates the high pressure side from the low pressure side. It was a R134 system which allows for aftermarket Freon conversions to increase its efficiency about 10-20%.
I  played with it at different charge levels to measure the amount of current draw. At 12.5 volts it draws about 2 amps or 25 watts. With the EER rating  guessed to be 10 for argument sake, the BTU's per hour would be in the ballpark of  250 BTU's per hour.
With 250-100(loss) = 150 Btu's available for cooling.
   If it is used to cool water from 80F to 40F that would be a delta of 40F. If I had a pound of water it would take 40 Btu's to do so.   To keep every thing is perspective, a 6-pack  is about 4 lbs of fluids. If a hot 80F 6-pack is placed in a cold icebox at 40F, it would take 40F*4lbs=160 Btu's to cool it. With 150 Btu's/hr available, it would take a little over an hour to cool it down.
In true life we are not that fortunate, physics plays mean tricks on us. Cooling turns out to be a differential equation with higher efficiency with the higher thermal delta, and reduced heat transfer capability as the delta is reduced. It turns out to be an asymptotic function. The lesson for us to learn is precool items going into the ice box. ( also less thermal load)

3d model of icebox

One of the difficulties will be to get the evaporator plate inside the icebox. The opening is 13.5"x13.5" which will allow the evaporator to slide through, my first thoughts were to place the opening in the panel towards the back wall to allow minimal of the  Feon lines in the icebox.. The solid crossover will cut the box into two sections with the front section only being about 8" wide by 11" . That should hold  3x4 or 12 cans per layer or 2 layers for about 24 total. Another option would be to place a few bags of ice in this area. The back or main section will be 11"x15" by 15" tall for the rest of the food.

The other alternative would be to unbend the end of the panel  where the line come into it and just install it like a  true U panel, not dividing the ice-box into 2 sections.  
I believe that it may be easier to install it the first way, so that the panel can cool food on both sides, dividing the box into 2 compartments. The disadvantage may be loss of volume due to inefficient design. The slanted side of the cooler would be waisted space and the supports would be more difficult to fabricate.
I ordered 2 sets of  refrigeration connection fittings. Only one set has arrived. When the other arrives, I will break one of the units into the laserette side for the condenser and compressor  and icebox side for the evaporator panel.

I also have to establish where the through hole will go to connect the refrigeration lines. I drilled a small pilot hole 1/8" to check for clearance and before the BIG hole was drilled. (1" to 1.5" diameter) 
I decided to go with the 1.5" hole, just large enough to line to prevent moisture infiltration of the foam and still pass the connections and thermal sensors through. I wanted it high enough in the refrigeration compartment to protect it and to route the refrigeration line efficiently. The hole is about 3" from the top in the center so it just clears the compresor on the lazerette side mounting plate.

evaporator plate in icebox

I was concerned over the amount of usable space due to the evaporator panel getting in the way so I fired up ProE and did a 3D model to evaluate which installation method would be best. I was planning to utilize the first, pushing the evaporator to the back wall. as depicted in the jpg to the right.




re-bent evaporator plate

Another option would be to rebend the evaporator plate to fit the vertical walls and be open to the slanted side along the hull. I tried to re-bend the evaporator plate and it was very difficult.

It did not bend where I wanted it to, and may not fit properly. The capilary tube is wrapped around the return tube as it was in the original design. To do so I had to extend the 1/4" return tube 3/4ths of the way around the outside of the plate with a "U" bend to return it to the back of the icebox. The connector is a 1/4" OD compression fitting that was tightened and soldered. re-bent evaporator plate


With all of the work it was taking to design and install this monster, reliability was important.

The wrapping of the capilary tube around the return tube acts as a pre-chiller cooling the compressed FREON liquid. The return tube is very cold and will be wasted when the tube exits the icebox. This helps to increase the system's overall efficiency. Also the extra 1/4" tubing that is wrapped around the outside of the evaporator plate can assist in cooling if the system is charged enough. If the tube frosts outside the icebox, the system is charged to full. Excessive FREON will return liquid to the compressor and result in excessive compressor load and inefficiency due to the return side pressure being too high. This prevents proper liquid to gas phase change that we need for thermal dynamics.
If this design version does not fit well, I could end up re-bending it again. I have one more spare unit if I totaly screw it up. I can just start over.
I designed an epoxy through tunnel to slide through the hole that I cut through the foam. I wanted to keep the foam sealed from the possibility of getting moisture trapped in it that would destroy its thermal insulation characteristics. I made a form from 11-17 sheet paper just rolled into a tube and taped. I put 4 wraps of plastic kitchen wrap over that and 4 layers of .5oz fiberglass cloth over the top. I had epoxy left over from the holding tank that I used to saturate the cloth. A couple days later I pealed the paper and plastic from the inside and I had a thin walled tube. For a grommet on the inside of the icebox, I used hole saws to cut out a donut of starboard material. I chucked it in a little lathe and rounded the exposed edges for a more functional look. I wanted to avoid sharp corners if possible to prevent kinking the freon lines that will pass through.


epoxy tunnel through the foam through hole sealed inside icebox
I had a little 4200 sealant left over from the keel bolt project and decided to use that to seal the icebox side. The components were cleaned with acetone, and then sealed and assembled. I will use a sharp knife to trim the excess off and peel off the masking tape. The tape was trimmed to match the OD of the grommet for a clean trim. The liner was installed with a slight down-hill run into the icebox. If the FREON lines sweat very much, it will drain back into the icebox.

I wanted the evaporator plate spaced from the side walls to increase the efficiency by improved circulation. The walls should have a slightly higher thermal transfer leakage to the insulation foam. The standoffs are cut out of 1/2" starboard with cut outs to clear the freon lines. I wanted to protect the lines from possible damage. evaporator plate mounted in the ice box

I also wanted to mount the evaporator plate up from the bottom so that the mounting screws could be above possible water level when the ice melts, should I decide to take some. Part of the original plan was to be able to cool without ice, but be able to carry ice for cooling our favorite beverages.

While checking out the system I noticed that the evaporator plate will frost over during operation. If you leave it on long enough it accumulates just like your old refrigerator at home. The manual defrost mode does melt the frost build up and it leaves a little water in the bottom. I will still leave the blaster pump connected to the ice box drain. It makes quick work of pumping it dry. The installation of the compressor and condenser coils was straight forward. I had planned the mounting plate and drilled the 1 1/2" hole when I drilled it in the icebox for perfect alignment. The compressor is mounted with 4 screws and the condenser coils are held in place with elastomeric lined metal cable clips. This was to keep down the vibrations from transfering to the boat.

The 1/4" OD tubing was sweat soldered to a T fitting with a fill fitting. The 3/16 OD pressure line was connected with a compression fitting that is sold for break lines. If you use a capilary tube system be sure to have a pre-filter between the condenser and the capilary line.



compressor mounted in the laserette The electrical requirements are under 5 Amps. The last breaker in the panel was connected to a Blaster pump that I used to drain the icebox, or as an axilery bilge pump. I installed a toggle switch to select the refrigeration system or the blaster pump.

I plan to utilize the refrigeration much more than the blaster pump. By connecting the blasterpump to a hose overboard, it is even a deck wash pump. The feed hoses were in the way of the compressor mounting plate, so they will have to be rerouted in a more sanitary method.


                                                                               
As with cutting, measure twice , cut once; this parable is plan twice and install once.

1-21-06 Eric Roline