By Richard L. Kollmann
Selectingthe right refrigeration system for your boat is important. What works for your friend's boat may not work for you.
Also, product advertisements can mislead you. Consider statements such as "chosen by more boat owners than any others," or "we build the world's leading refrigeration system," or "our system is rated #1." All of these statements may contain some truth under certain applications, but they can also be misleading and lead to the installation of a system that will prove to be wholly inadequate for your needs.
The selection of a refrigeration system for an individual boat should be based on the following:
- Size of the box to be converted
- The amount and quality of insulation
- The amount of cooling required per day - Do you just need a replacement for ice of 40-60 degrees or do you need short or long term freezing?
- The size of the freezer
- Whether the boat will be used in the tropics or a more temperate climate
- Whether the boat has a generator
- The size of the alternator
- The total available house battery
- Whether the boat is used for weekend jaunts, short vacations of one to two weeks or extended cruising or liveaboard circumstances
- Your personal needs such as the need to cool a large amount of drinks per day for a charter, or do you need quick freezing for your fish catch.
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Once you have the above questions answered, you will need to consider the types of boat refrigeration systems available. I've listed the main ones below:
- The standard hermetic sealed 110-volt or 220-volt units that can be water or air cooled
- The hermetic sealed 12-volt brushless compressor that is air cooled only.
- The hermetic sealed 12-volt brushless compressor that is water cooled only.
- An engine drive, belt-driven system that is normally connected to holding plates.
- A belt-driven 12-volt unit.
- A hermetic sealed 12-volt unit with brushes.
- Gas and thermocycle electronic units are available but rarely used.
Fifty years ago belt-driven compressors were common in low temperature refrigeration, but they have been replaced by hermetic sealed units. Belt-driven units are less efficient and suffer from vibration and shaft seal leaks, and if they are driven by a 12-volt motor, it will last less than a year if used in the tropics. Since 12-volt hermetic sealed compressors are not available in 1/6-1/2 horsepower, there will be instances where the motor-driven belt units would be the only choice. For example, a person's refrigeration requirements were large and there was no room to mount the compressor on the motor.
Since all ice boxes have different amounts and quality of insulation and boats are used in all different climates, I have assumed, for the following examples on equipment selection, that the box has three inches of good quality insulation in the refrigerator and four inches in the freezer and that the boat will be operated in the tropics with 86º seawater and has a crew of two.
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Guides to equipment selection
Box A: Two boxes - An 8-cubic-foot refrigerator and a 4-cubic-foot freezer with a 9,000 BTU daily requirement.
Recommendations: There are a couple of options for this box.
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Three holding plates with a 110-volt 1/2 HP system. The boat would need to be equipped with a reliable auxiliary generator, and the generator would need to run 2 hours per day.
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Three holding plates connected to an engine drive system. The engine would need to be run 2 hours per day even when connected to shore power.
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Although a 12-volt system could be used, I would not recommend it as the daily energy drain would be too high. A small 12-volt unit would require 150 amp hours per day, and a belt-driven 12-volt unit would require 180 amp hours per day.
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A combination of 1 & 2 connected to the same holding plates (plates would need dual coils) would give greater flexibility.
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Box B: A single 6-cubic-foot box with a divider which allows for a 4-cubic-foot refrigerator and a 2-cubic-foot freezer. It would require 4,800 BTU per day.
Recommendations: There are several options.
- A small 12-volt unit that uses a Danfoss compressor (if the lid opening is large enough). I would recommend the Adler/Barbour air-cooled Cold Machine. It would require 80 amp hours per day. The boat should be equipped with the following:
- At least 500 amp hours of battery capacity
- A high output alternator and smart generator
- Some type of voltage monitor.
The engine would need to be run 2-1/2 hours per day. For the liveaboard at anchor, a wind generator could supply 30% of the energy requirement if in the tropics. For the more temperate climates it could supply almost 100% of the energy required.
- One or two holding plates connected to a 1/2 HP 110-volt system. I would only make this recommendation if the boar was equipped with a reliable auxiliary generator. The daily running time would be one hour.
- One of the holding plates could be connected to an engine drive system. The engine running time would be one hour per day.
- A hybrid system that would use a 12-volt and an engine drive system connected to the same holding plates (dual coils needed). The engine drive would do the bulk of the work while the 12-volt would add supplemental cooling as desired. This would also add redundancy in case one system fails.
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Box C: A single box of 4 cubic feet or smaller and its daily BTU requirements would be 2,400-3,000.
Recommendation: A small 12-volt Danfoss compressor such as the Adler/Barbour Cold Machine, if it will fit through the lid opening, which uses a large evaporator and requires 40-50 amp hours per day. The boat should also be equipped with at least a 70 amp alternator, smart voltage regulator, and have a 400 amp hour battery capacity.
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Box D: has two separate 4-cubic-foot boxes, one as a freezer and the other as a refrigerator. It would require 7,200 BTU per day.
Recommendation: One Danfoss unit for each box would provide adequate cooling The daily amp hour requirement would be 120.
The boat should be equipped with at least a 100 amp alternator and a smart regulator. The total battery capacity should be at least 500 amp hours.
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