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post #1 of Old 06-18-2002 Thread Starter
Sue & Larry
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Installing 12-Volt Refrigeration

Though installing your own refrigeration system may seem daunting at first, but the authors discovered that it's really a straightforward process. Here Larry ensures that the evaporator fits snuggly in the box.
Tired of lugging heavy, dripping bags of ice to the boat only to finally get them in the icebox and find that there's no room left for all the food and drink you planned for your cruise? Whether you're out for the weekend or on a long-term cruise, having refrigeration on board means always having a cold drink and never again having to rescue a soggy sandwich from the watery abyss at the bottom of your icebox.

While refitting Serengeti, our 1978 Formosa Peterson 46 cruising boat, Sue and I put proper refrigeration high on our list of priorities. We wanted the freedom to travel and stay away from docks and marinas for extended periods of time, but we didn't want to sacrifice the healthy benefits and enjoyment of fresh food. The system had to be one that we could rely on, didn't cost a trillion dollars, and hopefully would be simple enough that we could install and maintain it ourselves.

After researching our options, we concluded that 12-volt refrigeration systems provided just what we were looking for. The major components of a 12-volt refrigeration system include an icebox, a compressor, and an evaporator (the coils you see inside the icebox). The components available today are small, energy efficient, reliable, designed to be owner installed, and most require virtually zero maintenance. If you buy the right equipment, the compressor and evaporator come pre-charged with refrigerant so once you connect the two and provide power, you're just minutes away from an ice-cold drink.

"If your plan is to convert an existing icebox into your new refrigerator, you may need to do a bit of detective work to ensure that it's sufficiently insulated. At a minimum, you need at least four inches of insulation."
Before you can configure and purchase a system, you first need to confirm that you have an icebox that's up to the task. If your plan is to convert an existing icebox into your new refrigerator, you may need to do a bit of detective work to ensure that it's well insulated. Ideally you'd like to see four inches of foam insulation surrounding the box. If you're light on insulation, you can add to either the inside or outside of the box. Sheets of urethane foam, whicht are available at building supply stores, are easy to cut and shape. If you have larger spaces or maybe a cavity to fill and insulate, you can use a polyurethane two-part foam. When the two liquids are mixed, they expand to fill the space and then provide a solid block of insulating urethane. If you have cracks or crevices that need to be filled, Great Stuff, urethane foam in a can, is very easy to apply. In our own refrigeration refit of Serengeti, we installed new 12-volt refrigeration into an existing box, and built a second box from scratch that we surrounded by six inches of foam for use as a freezer. A 12-volt freezer uses virtually the same components as a refrigerator. The main difference is the sizing of the evaporator and the use of a different thermostat.

If you don't have an icebox, and you plan to build a box from scratch, you might want to pick up a copy of Refrigeration for Pleasureboats by Nigel Calder. This book covers icebox construction and many other aspects of refrigeration in great detail.

After you're sure you have a suitable box, the process of choosing a refrigeration system begins with correctly sizing a compressor and evaporator. Since the size of box you wish to cool is the primary determinant, you begin by measuring the height, width, and length of your box to ascertain its size in cubic feet. With this number, you'll be able to peruse the manufacturer's literature and correctly size a compressor and an evaporator for your installation.

The compressor and the evaporator—the guts of any 12-volt refrigeration system—await installation.
Compressors are generally either air-cooled or water-cooled. An air-cooled compressor is very much like your refrigerator at home. A fan blows air across coils transferring the heat removed from the box into the air. This installation is the easiest and requires no plumbing. If you mount an air-cooled compressor in a closed locker though, you may need to cut a couple of vent holes, or add some ducting to enhance the air's ability to circulate.

A water-cooled compressor uses seawater instead of air for cooling. This improves efficiency by around 20 percent, but is a little more difficult to install because you'll need a source for water, a strainer, and an electric pump to circulate the seawater through the unit. The added efficiency resulting from water-cooling decreases compressor running time, and reduces power consumption. If you sail in hotter climes or plan to cruise the tropics, water-cooling is truly your best option; but if you have to, an air-cooled system should suffice. Some manufacturers are making compressors that are both air and water-cooled. We think these are a very good idea since you always have air as a backup cooling method should a pump fail or strainer get clogged.

The system installation begins by choosing a mounting spot for the compressor. It must be close enough to the box so that the refrigeration lines from the evaporator will reach. These are between six and 12 feet long depending upon the manufacturer and the particular model you have selected. If your compressor is water-cooled, keep in mind that you'll want to locate it so that you have easy access to a seacock for seawater.

"If the soft copper tubing is bent too sharply, a hole in the sidewall may result, allowing the refrigerant to leak out, and then you've got real problems."
Once you've found a home for the compressor, the trickiest part of the installation begins—mounting the evaporator and running the copper refrigerant lines to the compressor. You'll definitely want to have a helper for this segment of the installation. Carefully uncoil the copper lines from the back of the evaporator, keeping in mind which way they will need to turn as they make their way to the compressor. These lines need to make gentle turns, not hard bends. If the soft copper tube is bent too sharply, a hole in the sidewall of the tubing may result.

While holding the evaporator, have your helper carefully feed the end of the refrigerant lines into the box and out a pre-drilled hole in the side of the box. Slowly feed the copper tubing into the box and out the hole while moving the evaporator down and into position in the box. As the evaporator is getting closer to the box, make sure that the end of the tubing is also getting closer to the compressor. If your lines are too long, add a gentle loop somewhere in the line to shorten it up. Attach the evaporator permanently to the box using stainless steel screws and making sure you bed them with a sealant. Mounting the evaporator and running the refrigerant lines is not a difficult process, but it is time-consuming and a bit sensitive regarding technique.

This dual control thermostat had to be mounted by the authors, but that portion of the installation was equally straightforward.
The thermostat for your refrigerator may or may not be already mounted on the evaporator itself. If it's not, slide the tip of the thermostat into the bracket provided. This will hold it firmly against the evaporator plate. Run the two conductor electrical wires from the thermostat control in the box to the compressor following the same path as the copper tubing. The wire from the thermostat plugs into the control box at the compressor. After running the thermostat wire, seal the exit hole in the box with compressed foam like Great Stuff.

With the refrigerant lines run to the compressor, it's time to make the connection between the compressor and evaporator. This is accomplished with gasketed, quick-connect fittings that come factory-installed on the end of the refrigerant lines. These are made specifically for owner-installed systems, and make it easy for us regular folks to interconnect two precharged halves of a system without losing refrigeration gases. The result is a perfectly charged and balanced system once mated.

"If your compressor is water-cooled, you'll also need to think about where you'll be gaining access to seawater."
If your compressor is water-cooled, you also need to think where you'll be gaining access to seawater. Although it's possible to use a T fitting into existing plumbing to access seawater, personal experience has taught us (the hard way) that it's best to install a dedicated thru-hull. We tried tapping into several different sources of existing plumbing for our cooling, but we always had trouble with air locks. Finally we installed a dedicated thru-hull and eliminated our problems. Locate the thru-hull and seacock as close to the center of the boat and as low as possible to eliminate air locks from forming in the line when the boat heels.

To complete the plumbing of your seawater cooling circuit you'll need a strainer, a small 12-volt water pump, the appropriate amount of hose, and an above-water thru-hull fitting for the discharge.

The final step in the installation is to provide power to the system. Today's 12-volt compressors are quite energy efficient, consuming between three-and-a-half and five amps when running, so their power requirements are fairly modest. Size your wiring according to the recommendations in the installation literature. Remember that wire size is a function of power draw and distance from the batteries. Also, be sure to add circuit protection by means of a dedicated circuit breaker.

Larry savors the fruits of his labor, indulging in a cold adult beverage topside.
We've had great luck with 12-volt refrigeration and it has consistently met all of our needs. Now we stock up with all kinds of wonderful fresh foods as we find them and eat as well on board as we did on shore. The addition of a 12-volt freezer has even further extended our freedom from the dock. It's wonderful to be able to prepare most of our meals in advance for an offshore passage and it means we don't have to overly gorge ourselves after catching a big fish or let any of it go to waste. Today, when friends come over to Serengeti for dinner, they're first impressed with the unexpected frosty mug for their beer; but we really bowl them over when we pull out the popsicles for dessert.

So, consider adding refrigeration to your boat this year and save some bucks by doing it yourself. If you're a cruiser, you may also want to consider the benefits of a freezer. With just a few simple components and a couple of days work, you'll soon leave your ice-toting, soggy-sandwich days behind you.

Suggested Reading:

Refrigeration by Tom Wood

Insulating an Icebox by SailNet

The Art of Ice-ing by Joy Smith

SailNet Store Section:   Refrigeration Systems

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