The history of boat refrigeration is interesting as more innovative
new designs have failed than were successful. Most of the
refrigeration units designed for light duty in cool climates performed
poorly in warm climates or had major maintenance problems. Diaphragm
membrane oil free compressors driven by 12 volt motors were built by
two different companies in the eighties are all gone by now. Large 12
volt motors with belt and direct shaft driven compressors are a
disappointment do to noise, vibration and motor repairs. Ninety volt
motors driving a refrigeration compressor and powered by special
engine alternator failed to satisfy boaters because of their
electrical problems. Other hermetically sealed 12 volt compressors
motors with brushes from China and Italy were short lived mainly do to
non replaceable brushes wearing out.

There are five new unproven small mobile refrigeration systems
intended for boats that need to be evaluated by in-service experience,
variable speed DC compressors, CO2 refrigerant compressors, multi
voltage solar compressors, Masterflux 12 volt compressor systems and
even 12 volt air conditioning systems.
• Danfoss 12/24 volt variable speed compressors offer true efficiency
because compressor output capacity can be matched to other system
components as well as box size and climate heat load conditions. When
ice boxes were small or evaporators were undersized the old fixed
speed compressors cycled to often over powering evaporators by
exceeding their rate of heat transfer from food contents in
refrigerated box. When one of these new icebox refrigeration
conversion units is purchased the manufacturer will set the
compressor’s speed based on the type of gas, expansion device used and
evaporator temperature. Later it is possible in-service to change
compressor speed to improve efficiency as basic design conditions
change. The new Danfoss BD variable speed compressors are no longer
experimental as they now experienced more than 100,000 hours of
service. There are now at least ten manufacturers building
refrigeration systems for boats using the Danfoss BD35 and BD50
variable speed compressors.
• Carbon Dioxide (CO2) refrigerant is believed to be the replacement
refrigerant for all future high and medium temperature refrigeration
systems. In Europe and Australia there are industrial applications
using reciprocal and radial CO2 compressors now. AvXcel inc. did
produce an icebox conversion linear motor CO2 unit for boats and
demonstrated it at major boat shows. This ice box unit and a 0.88 cu
ft portable unit were sold under the name Tropikool. Tropikool’s units
use a free piston Stirling cooler oil free linear motor. It appears
AvXcel is no longer in business. The small portables are now available
at Wal-Mart under the Colman name.
• Danfoss has a new BD solar powered compressor that can handle a
voltage range from 10 to 45 volts DC. I know of no company building a
system using Danfoss’s solar compressor and module but there is a
complete application guide on their web site for the DIY person or job
shops looking for a new product line.
• Glacier Bay has another unit, the Micro HPS has been around for
three or four years but I know of none in service. I recently received
a question asking about the Micro HSP on this refrigeration forum and
answered it as best I could. I would like to hear from cruisers that
have one of these units in their boat. What I look for is actual
running hours per year and problems experienced with system in actual
warm cruising areas. I talked to a representative of GB about the
Micro unit and they are reorganizing and are not concentrating on boat
refrigeration at this time.
• Twelve volt air conditioning, is it practical on a sailboat? There
are 12 volt AC units developed for the trucking industry but the
performance figures I have seen are unbelievably high. Amp-hrs
consumed at night when boat hull is in seawater temps above 78 degrees
or higher indicates to me these units are not practical. First if air
conditioning is intended for creature comfort removing the moisture
from the air is just as important as cooling the air. Air can be
cooled quickly but dehumidifying air takes hours of system running
time. I sometimes think engineers that live in moderate climates
design refrigeration and AC for only the weather climate they are
familiar with.

I am interested in your comments.