My Boat Refrigeration System is the

 best for you. True or False?

 
 
In the last three months there is a lot of activity on the Internet from boat owners asking for help in
selecting a refrigeration unit. This question got the wildest responses, “Any opinions or experience on
choosing a system from the selection of the latest refrigeration equipment would be  helpful”.
Other questions about what refrigeration is best got the same responses such as:
     "Who needs refrigeration on a boat! I like my Frigoboat unit.  My Isotherm unit works good, etc." 
     Just about every system made was liked by someone. What was missing from the responses was: 
 
  • How cold did it get?
  • Did it work in the tropics?
  • How big was the box?
  • How much insulation did the box have?
 Of the many boat refrigeration types and models I am sure there is an application that will fit each unit. 
What must be remembered is that one type or model will not fit all applications.
There are four categories of refrigeration on boats:
 
1.       A COOLER - The average temperature of the box is 50°F. suitable to prevent spoilage
of some meats, fish and milk products for one day maybe.
2.      REFRIGERATOR - In the coldest area of the box a temperature of 32 to 35°F. can be maintained 
           for sensitive foods extending their freshness far as much as a week.
3.      HIGH TEMPERATURE FREEZER - Great for making a tray or two of ice cubes daily.
           The freezing area is maintained between 20 to 30° F. Meats will not stay frozen solid at these
            temperatures and these boxes are considered short-term storage freezers two to three weeks.
4.     LOW TEMPERATURE FREEZERS - These low temperature Freezers
            are rarely found in commercially manufactured boats because they need a well-insulated box and the energy
            to keep it cold.


 SELECTING A REFRIGERATION CONVERSION

Which refrigeration is best? There are 15 to 20 manufactures to choose from with each offering different options 
for their basic units. There are many systems available to convert an icebox to a refrigerator, but matching up the 
equipment to the boat and box is the trick. 
 COMPRESSOR -The selection of the compressor is the first step in putting together the correct refrigeration system. 
The compressor's output in btu’s must be greater than the box's daily heat load. The second step is the 
EVAPORATOR or HOLDING PLATE
 Other component selection will not affect the sizing but could improve the efficiency, electronic controls, pumped
 water-cooling, and better air-cooling and direct water-cooling without a pump.

 INSULATION - A well-insulated refrigerator needs 3 to 4 inches; a freezer needs 4 to 6 inches of quality foam.
 Standard insulation delivered with a new boat is rarely over 2 ½ inches. Boxes operating as freezers with standard 
insulation will have exterior condensation problems.

 THE CORRECT SIZE COMPRESSOR IS THE KEY - Beginning with the smallest compressor, this is 
a rough idea of how to match a compressor to a boat and icebox to be converted. Keep in mind that the boat
 must be equipped to produce the power to operate the refrigeration system you select.

 Compressors available for refrigeration are:

The  Swing 12-volt compressors

 USED IN NORTHERN CLIMATES the smallest conversion unit can turn a well-insulated six cubic foot 
box into a refrigerator. With standard insulation the box would be a cooler.

USED IN TROPICAL CLIMATES the box size should be limited to no larger than three cubic ft.

The key to a refrigerator's performance and efficiency is to match the compressor and evaporator to 
the heat load of the box. The Engel 45 ( shown below) is a good example of this.
The thermostat can be set to work as a Cooler or set down to a Low Temp. Freezer.
 

 
Danfoss BD35F 12/24-volt Compressors 

 More of Danfoss's older model BD2,2.5 and 3 compressors are used in boat refrigeration than other compressor.
These new improved models are capable of running at several different speeds. Manufacturers of refrigeration 
systems can set the speed to match the compressors output to the heat load to the evaporator.
When the BD35F is operated at high-speed 3500RPM its output is about the same as the older less efficient BD3. 
The following recommendations are based on the compressor operating daily 50% to 70% of the time.

 BD35F COMPRESSORS USED IN NORTHERN CLIMATES - Most of the system manufacturers using 
these compressors are designing for the small boxes in the northern climates with standard insulation.
Some Manufactures further degrade the compressors speed and output to be able to reduce power consumption. 
If the compressor is operated at high speed with a matching evaporator and the condensing unit is in a 
well-ventilated area it can be used in combination boxes up to 6 cubic ft. with standard insulation. 
Compressors operated at high speed can be used for well-insulated freezers up to 3 cubic ft.

 BD35F COMPRESSORS USED IN TROPICAL CLIMATES - At reduced speed the
 BD35F can handle a 1 ½ to 2 cubic ft. refrigerator box and at high speed the same size freezer 
with standard insulation. At high speed in the tropics and a well-insulated box the BD35F can handle
 top loading combination refrigerator/freezers up to 6 cubic ft.

 Danfoss BD50F 12/24-volt Compressors

 The BD50F has from 5% to 25% more pumping capacity than the BD35F and is a better choice for the tropics.

 BD50F COMPRESSORS USED IN NORTHERN CLIMATES- If the compressor is operated at high speed 
with a matching evaporator and the condensing unit is in a well-ventilated area it can be used in 
combination boxes up to 8 cubic ft. with standard insulation. It could also operate a 12 cubic ft. cooler. 
In a well-insulated box it can handle a 4 cubic ft. freezer.

BD50F COMPRESSORS USED IN THE TROPICS - In a well insulated box with the heat of the 
condensing unit properly exhausted the BD50F will handle a 6 cubic ft. combination refrigerator/freezer.
 A 4 cubic ft. well built freezer tested with 6 inches of foam maintained temperatures of
 less than +10 degrees F., under tropical conditions, on 56 amp-hr. per day.
Two compressors are best when dealing with separate refrigerator and freezer compartments.

Component enhancements for the BD compressors
 Several manufactures have come up with different methods of controlling the 
compressors speed in an effort to store more energy when batteries are being charged. 
Isotherms ASU (Automatic Speed Up) controller can increase compressor speed based on temperature 
or when a positive charge voltage is present. BD compressors connected to holding plate evaporators
 can now store more energy when solar or wind power is available if switched on when batteries are charging.
 Two new energy saving components are available for the BD compressors a Keel-cooler and a through-hull 
condenser that eliminates the need for a water-pump on water-cooled models.
Alternating current 1/6 horse power compressors.

The 1/6 horse power compressors were popular in the past to supply refrigerant to holding plates
 when connected to shore power, the same plates were then powered by an engine driven system when at sea. 

Alternating current 1/4 and 1/3 horse power compressors.

The 1/3 and 1/4 horse power compressors are used in applications where continuous electrical power
 is available from a generator.

Alternating current 1/2 horse power compressors

A 1/2 horse power low backpressure alternating current compressor connected to holding plates is a great boat refrigeration system
 but it does require a 2KW+ reliable generator.

Engine driven compressors

If the boxes to be refrigerated are too large for the boats direct current power distribution system and the boat is not equipped 
with a generator an engine driven refrigeration system may be the answer. An engine drive system is still the favorite of the
 larger cruising boats. 

Large 12/24-volt compressors  

Large belt driven or direct drive 12/24 volt DC compressors are an alternative to the engine drive refrigeration system and do not

require a backup system when connected to shore power.

 

BACK