[C38] Refrigeration

[tdtron at earthlink.net]

Hello Craig,

I'm surprised this idea of bilge cooling the refrigerant hasn't been explored more by the group.

You asked a very simple question but I'm gonna make you read some.

My refrigerator conversion used a medium sized dormitory sized refrigerator I got at Sam's club for just a little about $120.  I had a refrigerator in my boat from a similar refrigerator I bought used and the compressor finally wore out.  Sam's club had the exact same compressor I was trying to buy in one of their refrigerators and the whole refrigerator was $30 cheaper then just the compressor from a refrigeration dealer.  I took out the compressor  and controls and threw the rest of the brand new refrigerator, including the box,  into the dumpster at the dock.  You should have seen the faces on the other dock residents!

I also threw out the condenser that was attached to the back of the refrigerator.  On the earlier installation  on my boat I kept an air cooled condenser in series after the water cooled bilge condenser "just in case" but after I found out it was counter-productive, I kept it out on my second system and used only the bilge condenser.  The bilge condenser was so efficient that the refrigerant returning to the evaporator was actually cooler than the air in my sail locker where the compressor and air were installed.  The air cooled compressor was actually adding heat to the refrigerant as well as adding fluid resistance.  When I measured the temperatures of the return line, it was always cooler than the air temperature on a hot day and within only a few degrees of the sea temperature.  No air cooled condenser can ever get 100% efficiency so the return temperature will always be higher than the ambient air temperatures.

There is always at least a half inch of water in the Catalina 38 bilge because the bilge pumps can't pump down to lower than at least 1/2" which leave a little water to submerge the condenser line the entire perimeter of the bilge.

The benefit of this condenser system is that it gives a very efficient heat transfer from the refrigerant to the sea below with almost 100 efficiency and no pumps or through hulls needed.  I have even used this refrigeration system on the hard and there was no measurable difference in efficiency from when the hull was in water.  The big lead keel against the hull wicks out any heat from the bilge water.

I used common 1/4" soft copper from the compressor to the front of the bilge and back again to the capillary tube at the evaporator.  I used one long piece of copper to make sure I had no extra connections. The less connections, the better.

I measured out more copper tube than I thought I would need and bent in in a large radius in the middle and carried that bend up to the fore deck through the forward hatch.  I ran two different high strength nylon lines from the sail locker to the cabin and attached one string to each of the ends of the copper line.  I bent the last 1/2" of the copper ends so the string couldn't come off and taped the ends and string to better secure it and keep everything sanitary.

I then started pulling the copper tube aft by slowly pulling both strings lead through the sail locker.  Working alone, I used strings long enough to route back into the cabin so I could pull the strings as I fed the copper tube through the bilge.  I used the copper on the port side for my high temp and high pressure discharge side of the compressor connection and I used the starboard side of the bilge to carry the line going to the evaporator.

By keeping the cold and hot sides of the copper line apart using opposite sides of the bilge gives more efficiency by keeping the different temperatures as far apart as necessary.

When I had pulled the copper tube to the point that the ends of the copper were at the aft end of the bilge, I insulated the port side line, the high side, so that no heat from that line would dissipate until it reached the bilge.  I didn't want a hot copper line under my refrigerator.  One the line is in place, it would have been impossible to insulate the high side as well as doing it before you finish the pull to the compressor.

After the new condenser line was neatly placed around the perimeter of the bilge, I used small #8 screws and cable clips to secure the lines to the bottom of the bilge.  By pulling the two sides of the line into place from the fore deck kept the copper very kink free making for a better and easier installation.

You will need a refrigeration connection in the low pressure, cold return side before it returns to the evaporator.  You can use acid core lead solder for this but a much better and stronger weld will be from an oxy-acetylene torch using #15 silver solder.  You will also have to purge the system with an evacuation pump to remove all air and moisture.

It is illegal and I know we would never do this but I am going to tell you how really worthless scoundrels perform this operation without an evaporation pump.

They get everything in place and then purge the system with refrigerant but leaving a leak at one of the connections to allow the refrigerant to escape along with any air and moisture.  If this illegal procedure is repeated a couple of times and the leak is tightened before the refrigerant pressure is stopped, the system would be ready for a final charge of refrigerant.  The legal way is to pay an air conditioning tech to weld your system once everything is in place, evacuate the system, and charge both the system and YOU!

You may know someone at the dock who can help if you don't have the torch and evaporator pump.  Too bad you live so far from me, I would love to help if I could.

Charging is also something you don't want to mess up. Since you will have a home brew system, you will have no way to know how much refrigerant you will need.  I just charge slowly and keep readings of the temps of the evaporator in several places on the cold plate.  Once you get an even temp on the cold plate and it frosts evenly all over, you are probably as good as you are going to get it.

I have rattled on and I don't know how much of this is useful to you but if you already have a refrigerator, just cutting into the lines from your old condenser and replacing them with the lines described above from the bilge will greatly increase the efficiency of your existing system.

The commercial systems on the market that offer water cooling involve a 12v electric pump and a couple of through hulls to carry the water.  The extra energy loss of running that water pump negates most if not all of any gain you would have from water cooling.  My system is more efficient because of not needing that water pump.

Another debate is paying the high price for a 12v refrigerator.  I used the 120v AC type and could run it from an inverter or shore power.  The extra efficiency of running 120v allows enough power savings to power the inverter giving essentially the same total power load at a fraction of the expense.

You asked how much copper tube I felt was sufficient?  I have no idea.  I started with a 50' roll but I don't remember how much was trimmed off of the two ends after running it around the bilge.

I hope this helps but don't hesitate to give me a note if you have any questions.

Tom Troncalli
770-356-2223

----- Original Message ----- 
From: Craig 
To: Catalina 38 Listserve
Sent: 9/23/2011 9:28:18 AM 
Subject: [C38] Refrigeration


Tom, A While back you mentioned that you added cooling coils in your bilge to cool the refrigeration coils. How much line did you feel was required, and what did you use for a circulating pump?

Craig Steinkraus
“Wings” C-38  #280
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