The Cold Shoulder

By

So here you are, a cruiser with enough experience to know that the rituals of organizing ice for the ice box are a pain. Last weekend's block is gone by the time you decide to embark on that impromptu midweek evening cruise. Those carefully husbanded last few beverages are now warm and sloshing about in 2-inches of smelly, stagnant meltwater along with the label from the skipper's reserve bottle of Chardonnay. Where did this mold come from? Did I really leave a jar of mayo in here too? Yikes! This cheese will definitely have to go. And damn, the gas dock is closed so no fresh ice. Well, the sunset won't wait, so you cast off and head out anyway with fizzy warm ones. Who said yachting was upper crust?
If you own a small cruiser, you probably don't have space for a refrigerator, yet you may not be aware that the luxury of refrigeration may be well within your grasp. As a reader of Mad Mariner’s DIY Boat Owner, you are no doubt an intrepid sort, possessing at least basic tools, moderate skills, a rudimentary knowledge of 12-volt electrics and plenty of determination. The most popular refrigeration systems are easy to install and within reach of most boaters' pocketbooks.

Let's assume you own a typical mid-size sailboat or powerboat equipped with a built-in icebox insulated with at least 2-inches of polyurethane foam all around, including the top and lid. A minimum of 4 inches is recommended. You have a 12-volt DC electrical system and inboard auxiliary engine with an alternator. You also have a 110-volt shore power system with an automatic battery charger and, ideally, separate house and engine starting batteries. If this sounds like your boat, you already have the fundamental system prerequisites for adding a 12-volt refrigeration system that can be left running while you are away from the boat.
If you don't have all of the infrastructure listed above, you may be able to run DC refrigeration as long as you can somehow provide the necessary 12-volt power (anywhere from 25 to 100 amp-hours a day). If you decide to drag the bar fridge from your basement on board your boat and plug it in with an extension cord or inverter, that's okay. Just don't leave the dock for long.
FUNDAMENTAL THERMODYNAMICS
All refrigeration systems consist of two separate components: an evaporator unit and a compressor/condenser unit. All that refrigeration does is remove heat from one location and, in this case, an insulated ice box; and release it somewhere else. This is accomplished by compressing a refrigerant gas and liquefying it, a process that concentrates heat in the liquid that is then cooled by air or water. The cooled liquid is then pumped to a remote location (the ice box) allowing the liquid to expand and suddenly evaporate within the confines of the evaporator. Gas is then sucked back to the compressor and the process starts again.
The physics of any fluid changing state from a liquid to a gas and vice versa (evaporation and condensation) dictates that the evaporating fluid will absorb heat from its surroundings. This latent heat is later released when the gas condenses into fluid. Find a gas or fluid that will change state in the right temperature range, then all you need is a mechanical fluid pump and clever plumbing and you've got refrigeration.
How efficiently a given system operates depends on how well the insulated ice box keeps the heat from leaking back in and how well the heat exchanger is able to shed heat at the other end by air or water cooling.
WHAT'S AVAILABLE
The most popular 12-volt ice box refrigeration systems are all based on the Danfoss compressor and "black box" controller. Various refrigeration manufacturers all over the world use these Danish-built components, renowned for their low power consumption, reliability, and ability to operate on a sailboat at 20 degrees of heel. In Canada, the best known manufacturers are E-Z Kold and Nova Kool Mfg. In the US, systems by Adler-Barbour (maker of the original ColdMachine) are popular, as are units by Crosby, the Italian-built Frigomatic, and Norcold (whose models operate with a different compressor). Prices range from $1,000 to $2,100.
The Nova Kool system is well known and fitted on thousands of boats. It consists of the typical frosted evaporator, installed in the ice box with room for two ice-cube trays. Compressor, cooling fan and control box all fit on a separate 12-inch by 18-inch by 10-inch chassis that mounts neatly in a cockpit locker. Nova Kool's Compucold thermostat also yields system and voltage information on an LED readout. All 12-volt systems deliver similar performance. Differences between manufacturers are in the design of condensing coils, fan structure and filters.
Some units, such as those from E-Z Kold, offer a similar frosted evaporator system but its forte is a holdover-plate system. The holdover plate, originally called a Dole plate, is a metal box containing a glycol solution that is frozen by internal evaporator plumbing. Holdover plates have tremendous cold-carrying capacity. This means you can run your fridge when power is available at dockside or while motoring, then shut it off for relatively long periods to conserve power. Holdover plates act in many ways like a permanent renewable block of ice. E-Z Kold custom fabricates these units to suit your ice box dimensions. This holdover-plate system is also thermostatically controlled so that it can be left plugged in at dockside. You will, however, have to rig your own ice-cube trays.
All this holdover-plate technology trickles down from the heavy-duty, engine-driven offshore systems offered by Sea Frost (used on 90 percent of charter boats in the Caribbean), Grunert, Glacier Bay, Technautics and others. The boat's engine drives the compressor which rapidly cools the ice box or freezer. Such systems use minimal fuel and are not dependent on a boat's battery supply. Most units have two systems: a holdover engine-drive system plus a 110-volt system when plugged into shore. They cool 10 times faster than a comparable 12-volt system and are more efficient. Refrigeration systems are rated in British Thermal Units (BTUs). Engine-driven units average 2,600 BTUs per hour versus 250 BTUs for 12-volt units.
If you are planning extended offshore cruising, these are the top-of-the-line systems but they are expensive. A complete system for a single ice box or two adjacent boxes, starts $2,600. Installation is somewhat complex and if you're in doubt you should contract a professional. You can save money by installing the plate and mounting the compressor on the engine yourself, then have a pro install the tubing. It takes about 20 to 30 hours to install a complete system. If completely owner installed, it must be leak tested and charged with refrigerant by a certified installer before use.
GETTING READY
So you have checked your ice box dimensions, shopped around and purchased your new refrigeration system. Now unpack the boxes; in one is an assembly with a compressor, a cooling fan (if air cooled) and a black box voltage controller which is actually an inverter, converting AC power from the refrigeration unit to DC. In the other is either your frosted evaporator or a holdover plate that installs in the ice box. This will come with a coil of copper plumbing attached plus a thermostat. Handle this plumbing with care; it is pre-charged with refrigerant. There will also be installation instructions; follow these religiously. Before cutting any holes, plan the layout carefully and make sure that there is room for all components. Most installations are straightforward and require about a day to complete.
ICE BOX SET-UP
If you have a frosted-evaporator-type system, pick a convenient spot in the ice box, fasten the evaporator assembly to the inside of the ice box, drill a hole to feed the copper lines (refrigerant tubes) and connectors through to your compressor location and mount the thermostat. Seal the holes in the ice box by whatever means are convenient (an aerosol polyurethane foam works fine). If you are installing a holdover-plate system, consider subdividing the ice box into a freezer and fridge section, otherwise, the installation is much the same as above. Most units come prefilled with glycol from the manufacturer.
The cooling capability of a refrigeration system – BTU rating of the compressor- is only as good as the ice box. Insulation thickness and seals on lids or doors affect efficiency. Drains not equipped with a trap or valve funnel enormous amounts of cold air.
COMPRESSOR HOOK-UP
The compressor assembly sits in a tidy self-contained chassis that must be mounted within reach of the copper plumbing from the ice box. A typical location is on a well-secured shelf in a cockpit locker. If you don't have a shelf, you'll have to make one. Remember, the shelf must stay put in a knockdown when all the other stuff in the locker falls on top of it. Locate the compressor within easy reach of the refrigerant lines coming through from the ice box.
COOLING OPTIONS
A cockpit locker usually provides adequate ventilation in northern climates; however, if you cruise in southern climes or in temperatures above 25C (77F), or the compressor is mounted in a poorly ventilated locker, the unit will have to work very hard to shed all that heat removed from the ice box. In some cases, it may operate all day and all night, running your battery flat with a steady draw of 5.5 amps.
A better solution to the cooling problem is water cooling. It's more efficient – water is an eight times better heat exchanger than air – and is a necessity in southern boating areas. Water cooling is accomplished by the installation of a 12-volt water pump and an appropriate thru-hull fitting, to circulate water through a fridge compressor especially adapted for this purpose. Though this system is slightly more complicated, it should present no problems for a competent do-it-yourselfer. You may be tempted to connect the fridge pump to your existing engine seawater cooling intake. Don't do it. This short cut can result in your engine seawater pump sucking air through the fridge pump. The engine then overheats, quits and, well, you know the rest of the story. This turn of events will certainly annoy your insurance company, ruin your whole day/weekend/summer/marriage and create excellent repair opportunities for certain yards.
CONNECTING TUBING
Once the compressor is securely mounted and the copper refrigerant lines have been led neatly through from the ice box, you are now ready to connect evaporator to compressor. Special connector fittings are self-sealing and should screw together with no loss of gas. Both halves of the system are precharged and should now be ready to go. Be careful not to apply any torque to the soldered joint between the copper tubing and the connector ends. Any damage to the tubing joints or evaporator will release refrigerant gas and require professional repair and recharging.
ELECTRICAL HOOK-UP
You will need to provide a DC power supply cable; a minimum 10-gauge multi-strand type is recommended. Check installation instructions for specifics. Connect the fridge positive wire directly to the house battery using the fridge thermostat as the off-on switch or, alternatively, to a breaker on the main DC distribution panel. Install an in-line fuse in the feed wire. The negative ground connects to whatever negative common is available.
Alternatively, hook up the positive directly to the main panel. This latter option is easier to install and gives you better control – there's no need to mess with connectors on the battery terminals -but, take heed: You'll need larger wires and, when a battery charger is also connected, there's a risk you'll blow the inverter (black box) if the system does not receive pure DC power. Consult a professional installer on this one.
TEST RUN
Recheck your wiring connections, then turn the unit on. It should "gurgle" to life. Now check the ice box. The evaporator should soon get frosty. If it runs but does not cool, you have somehow managed to lose the refrigerant charge. If there is no sign of life, check the fuse in the unit and check to see that adequate voltage is being supplied. If the unit blows fuses continuously, call your dealer.
BATTERY MANAGEMENT
Cold beverages and unspoiled foods are dependent on plenty of 12-volt juice. Now that you have an operating fridge, you'll have to learn how to keep it running. Books have been written on the subject of battery management, but, to be brief, the engine starting battery should never be called on to supply power to the fridge. An engine that starts reliably is far more important than cold goodies. If you are using the traditional four-position master switch, which isolates the batteries, make sure you know which battery is for engine cranking and which is for house supply and the fridge. Refrigeration power requirements will exceed other items on board. For example, typical fridge power consumption in one day can be calculated as follows: 5-amp draw multiplied by 24 hours times the typical 50 percent duty cycle equals 60 amp hours per day.
You should have a good quality house battery capable of deep discharges without dam age; 12-volt batteries are surprisingly finicky devices. In addition, a battery should not be discharged past the 50 percent point if you want it to last. For example, if you have a 100-hour ampere battery (a typical 27 series or larger car battery) you should plan on its usable capacity to be 50-amp hours. Using the consumption rate outlined above, a battery this size will just suffice while cruising if charged once a day. Plan your daily energy budget taking into account your charging capabilities and the amount of power you consume. You may want to invest in high-quality monitoring equipment (Link 2000 or E-Meter), a high-output alternator or three-stage regulators if you plan more than overnight cruises. Remember: Batteries usually don't die; they are murdered.