I tossed the holding plate/evaporator question around for several years
before settling on evaporators. Holding plates do have an advantage in that
they only have to be frozen down once or twice a day but that can also be a
disadvantage because it ties you to the boat. Evaporators are more or less
self maintaining so with a large enough battery bank and some alternate
energy sources we will be able to venture ashore for longer periods and fly
home for a week or so to visit the grandchildren without having to worry
about the refrigerator. Evaporators also tend to hold a more constant box
temperature and you are not limited to the single temperature that a holding
plate is designed for.

I also like ice in my drinks and remote undeveloped anchorages (if you can
find one anymore) and evaporators do a better job of making ice.

When I started looking evaporators were the cheaper alternative and holding
plates were the energy champs. That is not totally true anymore. The
little Danfoss compressors and controls have gotten a lot more efficient
over the past 5 or 6 years and with a couple of solar panels, bigger banks,
and the charging system they require a well designed evaporator system can
actually cost more.

I have attempted to set my systems up so that in normal use I can charge
batteries and make water for about 90 minutes every other day. Time will
tell how well it works out but evaporators just turned out to be the better
option for the way we plan to use the boat.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"Wayne.B" wrote in message
...
On Sun, 12 Mar 2006 11:45:50 -0500, "Glenn Ashmore"
wrote:

I have probably spent to much time working with PID and fuzzy logic
controllers. :-) There is so many sophisticated off the shelf industrial
process controllers these days I can see the day when we will see a marine
refrigeration controller that will do a lot more than we can think of.

Glenn, following along in this discussion, it sounds like you picked
an evaporater unit instead of a holding plate system. If so, I'm
curious why you did that. Perhaps my situation is different because I
have a large generator available, but I really like the idea of only
needing to run the compressors for a few hours per day.

Years ago I was shown a system that supposedly optimized efficiency by
monitoring the line from the condenser to the compressor and keeping the
refrigerant's phase change as close to the compressor as possible without
trying to pump liquid. We were working with fixed speed compressors
(on/off) so it wasn't practical for our use. Have you seen that scheme?

Roger

http://home.insightbb.com/~derbyrm

wrote in message
ups.com...

The reason we want to control compressor speed is to use the lowest
amount of daily onboard power and maintain the box temperature we want
at all times. We by a compressor that can produce the results we want
and generally more capacity output most of the time. Cutting down on
capacity by lowering compressor speed improves SCOP (System Coefficient
Of Performance). Whenever the box temperature can be maintained at the
compressors slower speeds and still have it cycle off the end result
will be fewer daily amp-hrs consumed. What all three of these speed
controllers do is compensate for day night and seasonal temperature
changes. They all will change speed but slowly when warm product is
added to the box. The SSC and ASU both can be set to manual to speed up
the cooling process. I believe only the SSC will provide actual
compressor speeds at the panel. All of these units change the milliamp
flow in the thermostat circuit to control compressor speed.