On Aug 25, 1:51 pm, "Steve Lusardi" wrote:
I wish to use a single large compressor to service 3 cold plates and 3 air
conditioning evaporators, but I am not a refrigeration expert, so if my
thinking is incorrect please let me know. Each one of these (users) will
have their own mechanical temperature controlled evaporator valve. I assume
the compressor should be cycled by head pressure with an overtemp sensor for
safety. I would like to use a salt water cooled condensor on the high
pressure side and a freon gas that changes state around -40 C. Please
advise. Do I need an accumulator of some description on either side? If so,
what? Each one of the users have 3/8" in/out tubes. How do I size the
compressor? Any tips or books on this subject would be welcome.
Steve

No, the compressor should NOT be cycled on head pressure, only safety
devices for over pressure and under pressure should be used for head
pressure.
Also it can be done mixing air conditioning and refrigeration/freezer
evaporators in one system, but you will need many more controls and
mechanical systems. You want to have 2 compressors and keep the air
conditioning separate from your cold plate application. This is
because what ever working fluid you use (R22/502/134A) the evaporator
boiling point is a function of suction pressure. For freezer
applications, you will cause the air condition coils to freeze, or for
air conditioning you will never get the cold plates to freeze.
If you are hell bent on this, you will need to control the input
refrigerant to the evaporators with electric solenoid valves, I assume
you have a 12 volt battery system on your boat, I've seen 12 volt
valves. Also I assume you are connecting the compressor(s) to a
diesel engine. The output of the condenser will go into a receiver
(not an accumulator). There are suction accumulators, which are used
to prevent liquid slugging into the compressor. To control air
conditioning suction pressure on such a system (one compressor) you
will need to use pilot operated suction valves for the air
conditioning evaporators, in the output of the evaporator so the
suction pressure will not be at the same pressure as the cold plates.

The last time I was sailing on a Moorings bare boat charter, the cold
plate system was replaced with a +12 compressor, and this worked so
much better then the cold plate of previous sails, it would keep ice
cream frozen, where the cold plate would totally defrost between
engine recharge cycles, or be one frozen mass of sh*t.
ignator