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REFRIGERATION

Last Updated: 18 July 2010

Future Additions:
-Frigoboat Refrig System (being investigated)

12 Volt Refrigeration

Despite what some salesmen may lead you to believe, designing an efficient refrigeration system on a boat is a most complicated endeavor involving myriad decisions and a significant amount of research in order to get it right the first time around.   Most refrigeration experts agree that a quality high capacity 12 volt holding plate refrigeration system with well insulated boxes is the most convenient, reliable and efficient system for long term cruising with a big refrigerator and freezer.  Installing a system yourself for a reasonable amount of money that will cool large boxes for many years and that you can repair yourself is an entirely different thing from having a mechanic install an  off the shelf system that is guaranteed for a year or two.  The system described below is the former design.

My system has been on the boat now for 12 years using the same major components.   The compressor, a Tecumseh HG 1000 is now 30 years old and still going strong with only new seals and gaskets.  In comparison Danfoss compressor based evaporator plate systems, especially the air cooled ones, like those sold by Adler Barbour and others are  inefficient, easy to damage and have major components that cannot be repaired and must be replaced.  They are better suited for smaller boxes and short term cruising where you can replenish your refrigerated stores more often.  Because these less expensive systems do not use a holding plate with an eutectic solution they cannot take advantage of the significant energy savings made possible by freezing and thawing this solution.   They also are not set up with a receiver and valves for holding the refrigerant in the system while working on/replacing components, many of which are soldered into the system making removal difficult. 

A new holding plate system installed by a hired mechanic will easily cost $5K or more.  Or you can do it yourself for about $2K if you have the time, are willing to study/research and can learn some basic refrigeration skills.   This approach is not for everyone, but if you take this project on expect to spend several months at it.  Chances are real good you will need some of this knowledge and the skills anyway if you cruise long term to remote locations and with any refrigeration system.  The down side is that you won't have any of those refrigeration disaster stories to tell your friends.  The up side is you will always have ice for happy hour and you will have extra money to spend on ice cream when you reach port.

Below is a list of most of the parts and equipment you will need to build your own bullet proof refrigeration system as I have. Rparts is a good internet source and the numbers are from an old copy of their online catalog.  As they do not do phone business, some prior reading on your part will be necessary so you will know what you are looking for.  Two great references are the Glacier Bay website and Nigel Calder's book on Refrigeration.  Some of these parts are available from local refrigeration parts houses, like United Refrigeration, in major cities and also, of course, on the internet if you know what you are looking for.

You can buy the compressor rebuilt from Joe at Polar Bear in Ft Lauderdale for about $150 or new from Rparts on the internet for about $500 last time I checked.  This Tecumseh compressor has a cast iron block, is much more robust and will last much longer than any of the aluminum block models from York and others.  I rebuilt my original and then bought a rebuilt unit and spare gaskets/parts just in case.  The special ventilated compressor pulley is available from Blissfield, the company that now owns the rights to Tecumseh.  The Leeson motor is available new on the internet from multiple sources for about $250.  Buy the 3/4 HP model, not the 1/2 HP model which has no internal fan (see the Glacier Bay article on the 1/2 HP model on their website for a further explanation). 

If you have a large system with long tubing runs or don't use a generator while running the system you should slow the compressor down so the electrical draw is equal to about 1/2 HP by reducing the pulley size on the motor to 2".  The long tubing runs and many twists and turns are the limiting factor in how much refrigerant you can push around the system in an hour, not the compressor capacity.  This in turn limits the amount of BTUs that can be removed from the plates.  It is important to balance the maximum flow capacity of the system with the compressor output so that the compressor is not  working too hard against itself.  This also reduces the amp draw and thus improves the battery terminal voltage while the system is running.  In addition we net our solar panel output against the refrigeration motor electrical load thus reducing the load while running to around 20 amps or less if we have good sun.

PARTS FOR 12 V REFRIGERATION SYSTEM:
1 Tecumseh HG 1000 two cylinder compressor with double 8-1/2" pulley
1a Leeson 3/4 HP 12 volt motor with double 2" pulley
2 Suction accumulator Rparts 78-1001
3 Receiver 6 lb Rparts 75-0400
4 Condenser 1 ton Rparts 012-0523
5 Thermostats 2 ea Rparts 015-0288
6 Sight glass with moisture indicator, 3/8" flare Rparts 77-0200
7 Timer 60 minute Home Depot about $20
8 HP/LP cutout switch Rparts 015-1501
9 Drier 2.6"x6", 3/8" flare Rparts 020-0083
10 Freezer and Refrig holding plates Rparts custom made or used
11 Solenoid valve 12v 
12 Raw water pump March 809BR Rparts 072-8092
13 Expansion valve- refrigerator, Alco, 1/2 ton, 3/8x1/2 flare, internally equalized,
    RC, FWZ
14 Expansion valve- freezer, all same
15 Compressor/motor base damper feet 4 ea Rparts 026-0102
16 Staybright silver solder Rparts 079-0800
17 Stayclean paste flux Rparts 079-0806
18 Flaring tool kit, 45 degree, not automotive
19 Tube benders 1/2, 3/8, 1/4"
20 Portable pressure gauge set for R12
21 Installed pressure gauges Hp and Lp
22 Electronic Leak detector
23 Vacuum pump
24 Leak Lock
25 Tubing cutter
26 Deburring tool Home Depot
27 Isolation valves for closing off freezer when not in use
28 Copper refrigeration tubing 1/2", 3/8"
29 Numerous flare and sweat on fittings
30 Electrical components to run the Leeson motor and raw water pump using circuit breakers,
    solenoid, HP and LP cutoff switches and a timer (electrical diagram to follow when I have time).

Originally my refrigeration system was an engine driven Crosby holding plate system using the bullet proof Tecumseh HG 1000 compressor.  The boxes started as an over/under front loading refrigerator/freezer with 4" of insulation all around.  The interior liner of the unit was built in one piece with a separate front panel to hold the doors and a slide in divider shelf.  The divider shelf only had 1" of insulation and that was so badly deteriorated that it provided no insulation for the freezer.  That double box is now all a front loading refrigerator with over/under compartments.  The new freezer is separate and top loading built under the main cabin table.  The refrigerator is now 10 cubic feet and the freezer 3.  Both have heat loads of around 3000 BTUs a day, a little more if in the tropics with temps in the 90s, a little less if in temperate climates.  The heat loads of any box are easy to calculate if you have the cubic feet of the box and the average thickness of dry insulation.     The BTU capacity of a holding plate can also be calculated if you know the size of the plate in inches and the type of eutectic solution.  Use the heat load and holding plate charts available on the  Glacier Bay website or from other refrigeration companies like Sea Frost, Grunert and Technicold.  Crosby's brine plates are about 10 percent less efficient than glycol plates used by most companies these days but their freeze-thaw temps are much tighter.  This is more important in the refrigerator box than in the freezer.  So a brine plate in the refrig and glycol plates in the freezer would be optimum.  Used SS plates are often available on the internet or from owners installing new systems for less than $100 each-new plates are now well over $600 each.  If a used plate looks intact and is not leaking eutectic solution it is probably fine.  Mine are all used plates, some of which are original Crosby on the boat and most dating back to the late 1970s. 

And you can mix up your own glycol eutectic solutions which would allow you to use a freezer plate in a refrigerator and vice versa by just changing out the solution.  See Nigel Calder's refrigeration book or ask on the internet for the proper mix with water.  I used a 1 part Propylene Glycol to 5 parts distilled water mix for a 27 degree refrigeration plate and it seems to freeze at the right temp.  That was from Clive at Sea Frost who also told me that 1 part PG to 4 parts water gives a 0 degree plate.  Calder says 40/60 PG to H2O gives 0 degrees and 30/70 gives 26 degrees.  Richard Kohllman, a do it yourself guru on the internet, has another mix.  As with many things in refrigeration there is often disagreement among the experts. 

We run the entire system for about 1.5 hours in the morning and the freezer only in the late afternoon for about 20 minutes.  The daily current consumption is about 75 amp hours.  The refrigerator is able to hold over for 24 hours, the freezer for 18.  Because the freezer will only hold over for 18 hours we top it off in the late afternoon so it will hold over through the night.  If I could get more/better insulation around the freezer it would do much better.

The current refrigeration system, as of 2007, has the following modifications from what some of the pictures below show:
    -Leeson motor mounted with 2" pulley so that the compressor runs at about 415 RPM producing about .5 HP and drawing about 50 amps at startup (average 40 amps per hour during pull down).  Set up like this the motor runs MUCH cooler and the system is better flow balanced with the long refrigerant tubing runs I have.
    -Freezer now has two 2100 BTU glycol holding plates producing more even temps and holding over considerably longer.  The insulation consists of 2" of extruded polystyrene and 1" of NASA Heat Shield vacuum sealed.  Vacuum panels might be better but they are expensive, and the warranties are suspect since it would be easy to puncture one during installation and that is not covered.  Bruce Antognoni at Nautic-Kold, in Ft Lauderdale, who originally helped me rebuild my system, says that based on his side by side tests, the Glacier Bay vacuum panels were no better than vacuum sealed NASA Heat Shield.
    -Upper Refrig box has a single Crosby brine 3300 BTU holding plate while the lower refrig box has a single 1500 BTU glycol plate.  Since I had the glycol plate, and couldn't find a suitable brine plate for the lower refrig, I used what I had.  This setup, though not optimum, gives even refrig temps throughout the 10 cubic feet of refrigerated area, partly because of the spillover from the upper to lower boxes, and makes the best use of the 4" of insulation.
    -Permanently mounted and easily visible service gauges attached to the compressor.
    -Permanently mounted muffin fan to help cool the Leeson motor.  It can now run for the full 1.5 hours and still not be very hot to the touch.
    -Suction accumulator added to prevent drawing liquid refrigerant into the compressor by mistake and to allow excess refrigerant to be held in the system without damage.

Holding Plates

(Topica Post 02/08/2005)  Don't pitch your old holding plates! If it is original Crosby, it is a stainless steel brine plate with steel interior tubes. It has a capacity to remove about 3300 BTUs of heat an hour.  Today it would cost you more than $600 to replace. They have a very tight freeze-thaw temperature span and work very well in our large boxes. My refrig plate, which is the same size as the one you mentioned, is cooling our 10 cu foot refrigerator box for about 25 AH a day. (top)

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