On Sat, 22 Mar 2008 09:19:58 -0400, "Roger Long"
wrote:

With a small engine like mine and modest electric loads otherwise, wouldn't
it me more efficient to put the largest compressor that a toothed belt pully
and engine PTO limitations would permit on the front end of the engine?
Then have a large cold plate in the box and draw it down as quickly as
possible keeping the engine under maximum load. It wouldn't give you the
fine temperature control of a constantly running 12 V. fridge system but
would be as good as ice. Drawing down the cold plate would be like buying
ice (and probably nearly as expensive at next year's fuel costs).

The conversion from fuel to electricity to charging and back to motive force
has got to use up more fuel than just running the compressor directly.

Most of the boats I see here use exactly that system. The more
up-market ones have a duel system with both engine driven and A.C.
powered compressors for use at sea and in the marina.

If you really want to get into it find a copy of Nigel Calder's book
on refrigeration systems (he is a fellow Mainiac. It is down to earth
and really teaches you how to build a system.


Bruce-in-Bangkok
(correct email address for reply)

Bruce in Bangkok wrote in
:

On Sat, 22 Mar 2008 09:19:58 -0400, "Roger Long"
wrote:

With a small engine like mine and modest electric loads otherwise,
wouldn't it me more efficient to put the largest compressor that a
toothed belt pully and engine PTO limitations would permit on the
front end of the engine? Then have a large cold plate in the box and
draw it down as quickly as possible keeping the engine under maximum
load. It wouldn't give you the fine temperature control of a
constantly running 12 V. fridge system but would be as good as ice.
Drawing down the cold plate would be like buying ice (and probably
nearly as expensive at next year's fuel costs).

The conversion from fuel to electricity to charging and back to motive
force has got to use up more fuel than just running the compressor
directly.

Most of the boats I see here use exactly that system. The more
up-market ones have a duel system with both engine driven and A.C.
powered compressors for use at sea and in the marina.

If you really want to get into it find a copy of Nigel Calder's book
on refrigeration systems (he is a fellow Mainiac. It is down to earth
and really teaches you how to build a system.


Bruce-in-Bangkok
(correct email address for reply)

I used to have a dual-coil system and ripped it out because it had
terrible performance. It started out having both an engine drive
compressor and an AC compressor. I replaced the AC compressor with a DC
driven compressor (1/2 HP motor driving a Bitzer IIY compressor) which
is basically what Glacier Bay utilized.

I wasn't happy at all with the performance. I then realized that the
problem was with the dual coils in the cold plate. Imagine a cold plate
that's about 2" thick. The front half of the plate had coils cooled by
the engine compressor and the back half had coils cooled by the DC
compressor.

In order to freeze the entire plate, either compressor has to freeze the
eutectic solution in the other half of the plate where it doesn't have
coils. This leads to very long run times.

The engine drive system did a great job of freezing the plates, but that
was rarely used. I suppose that if I ran the engine to charge the
batteries, this would be acceptable, but I rely on wind/solar and a
generator when the first 2 don't produce enough.

I ripped out the engine drive system and combined the 2 coils into 1
loop and after a lot of fine tuning, got the system to where it utilizes
about 85 Ah in the Caribbean. I don't have the measurements here, but
this includes a 3 cf freezer with it's own plate that's kept at about 4F
and a 4-5 cf refrigerator that maintains 40F. The addition of
electronic controls was very important also as it allowed me to
precisely control the on/off set-points.

I also installed run hour meters on the both the refrigeration and
freezer sides of the system, so I can closely monitor the system for
performance issues. I log the results in a spreadsheet on a regular
basis to make sure that everything is working OK.

I extensively used the Calder book and to say that "It is down to earth
and really teaches you how to build a system." is being very kind. It
provides you with a lot of information and you really have to study it
and other sources to determine how you really design a system. It's a
much better debugging guide than a design guide.

I will also point out that Richard Kollmann, the OP, has 2 good books on
marine refrigeration. See http://www.kollmann-marine.com/

-- Geoff
www.GeoffSchultz.org

Actually, with the introduction of the higher powered and more efficient
Danfoss 50 and 80 compressors Nigel has seen the light and come over to the
DC evaporator side. He wrote a good article in Ocean Navigator a few months
back explaining the trade offs between constant cycling evaporators and
engine driven holding plate systems.

--
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

"Bruce in Bangkok" wrote in message
...
On Sat, 22 Mar 2008 09:19:58 -0400, "Roger Long"
wrote:

With a small engine like mine and modest electric loads otherwise,
wouldn't
it me more efficient to put the largest compressor that a toothed belt
pully
and engine PTO limitations would permit on the front end of the engine?
Then have a large cold plate in the box and draw it down as quickly as
possible keeping the engine under maximum load. It wouldn't give you the
fine temperature control of a constantly running 12 V. fridge system but
would be as good as ice. Drawing down the cold plate would be like
buying
ice (and probably nearly as expensive at next year's fuel costs).

The conversion from fuel to electricity to charging and back to motive
force
has got to use up more fuel than just running the compressor directly.

Most of the boats I see here use exactly that system. The more
up-market ones have a duel system with both engine driven and A.C.
powered compressors for use at sea and in the marina.

If you really want to get into it find a copy of Nigel Calder's book
on refrigeration systems (he is a fellow Mainiac. It is down to earth
and really teaches you how to build a system.


Bruce-in-Bangkok
(correct email address for reply)

Post on equipment performance

For those persons who did not read the complete thread this is about
onboard energy. How many DC amp-hours per day is too many? If you
want a wide range response to a question about cruising boats and any
components performance ask your question on this cruisers Forum. I try
to follow all web posts relating to information about boat
refrigeration and equipment needed to support refrigeration. Most of
the time I am looking for factual quantified answers to questions. If
you have read this thread closely discounting opinions and theories
there may be valuable information you can use in making your own
decision about boat refrigeration.

Refrigeration on boats is expensive and is a luxury and is not
required by every boater.

If a boat is equipped 12 Volt refrigeration it will be the largest
consumer of electrical energy on a cruising sailboat.

How large of a refrigerator/freezer can a boat's DC electrical system
support without an onboard gen-set? I Believe 100 amp-hrs per day is
too much others seem to manage much higher DC usage, as much as 200
amp-hrs per day. Boats cruising with 12 volt refrigeration above
Latitude 36N in this country may consume 50% less energy for
refrigeration than those cruising south of 36N.

When electrical energy is not available 24 hours a day then holdover
plates can be used to store energy.

If refrigerated boxes are too large to be supported from electrical
energy then engine driven compressor refrigeration or a gen-set power
would be the answer.

Info quotes from Forums:

I don't have any experience with the 2000, but have found the Honda
specs to be pretty accurate with the 1000. I run it a 45 amp charger
with it.

Anyway, I think we have a close enough ballbark on fuel consumption
and output for planning/comparison purposes.

15 hours on 1.1 gallons at 500 watts might be stretching reality a
bit, but
it's not far off. I own EU1000i and EU3000is. The 1000 is uncanny.

40A at 14.2V = 568 watts plus some charger in efficiency so that would
be
around 600 to 650 watts so Skip's observations are very close.
But we consume mass quantities of ice, about a 10# block of ice every
couple of days during a Chesapeake summer. Cubes go faster, but their
primary purpose is to cool my Admiral's drinks. Would love to have a
fridge, but
we can buy quite a few years' supply of ice for the upfront cost and
backside power requirements.

In my case, easy to say bigger alternator and larger battery bank but
we're
talking about a 20 hp engine and very limited space and weight
capacity for
additional batteries.

Refrigeration certainly is a desirable feature, but we're enjoying
the
simplicity of our systems. With less to break, we can enjoy the boat
more.
We've other reasons to go in for ice. The fresh water gets empty or
the
holding tank gets full at about the same time.

Most of the boats I see here use exactly that system. The more
up-market ones have a duel system with both engine driven and A.C.
powered compressors for use at sea and in the marina.

We are a family of four and are power hogs with kids DVD's and PC
use.
Our boat has a poorly insulated iceBox with a AB CU-200 system that
uses 5amps and typically runs maybe 10-15hrs/day.
Our 260W of solar and MPPT controler puts out about 60-70AH/day
Battery bank is 900AH
We use about 140-200AH/day
The engine alternator is a 105A unit and we are getting ready to
install a gen/water maker combo unit with an additional 105A
alternator that will burn about 1/6gal/hr of diesel.
My Honda 2000eu runs my Iota 75AMP battery charger, but I don't really
know fuel usage yet because we use it so infrequently. The honda stays
at load with the 75A charger.

Be patient Richard. You got my curiosity up about this last year and as
usual I have gone a bit overboard. Finished the vacuum insulated fridge
last month and have been running tests recirculating water through a 55
gallon barrel. I have one Hobo monitoring interior temps of the freezer,
fridge and ambient. The other Hobo is hooked up to hall effect sensors to
monitor amp draw of the two BD50s. I am running the compressors off a 90
amp 13.5V power supply as the batteries are not installed yet.

I can control almost all the variables but the ambient temp and so far it
has not been high enough to get any usable results. Right now, with an
average ambient of about 58F a basic ice melt test indicated R30 for both
the fridge and freezer. I am drawing 18AH/day on the fridge maintaining 34F
to 38F. The freezer is drawing 21AH maintaining 5F. You will have to
wait until June when I can get several days in the 90s to get any usable
numbers. Then I can give you a complete set of numbers for 3 or 4 days.

You will have to wait until this time next year to get actual at sea
numbers.

--
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

Power consumption for 12 volt refrigeration.

Glenn, I have developed a base line theory for projecting daily
electrical power consumption when planning for 12 volt refrigeration
on a boat. You may remember the Cruising World magazine article some
twenty years ago that GB is still proud of, in this article my boat
box heat load estimate was higher than the rest. I have found that
heat energy forces on small refrigerated boxes can be more important
in some cases than adding insulation R value. There are three factors
influencing daily refrigerator power consumption beyond that of R
value, most creative marketing people fail to point out, cruising
climate conditions, refrigerated product through put and the true
System COP of units purchased. In the past the installer or owner had
no control over matching system COP after installation but today with
Danfoss BD variable speed compressors they can adjust a system's
efficiency.
I usually recommend insulation R value of 30 for boat freezers as
they are not operated at box temperatures below zero degrees F.
My theory on amperage required per day is based on worst case actual
and simulated conditions. The base line conditions I work with are 90
degrees ambient air at midnight, seawater temp 86 degrees and three
inches of new polyurethane insulation. I use a standard box heat load
requiring 10 amp-hrs for each cu ft of refrigerator and 20 amp-hrs for
each cu ft of freezer per day, this is based on top loading boxes and
two p3eople on board. Once the worst case base line is established for
a given size box then it is possible to use the only stable factor in
this equation water temperature to adjust for less than tropical
conditions. For each degree of cooler seawater the energy usage can be
reduced by 2%. If a boat is now operated in seawater temperature of
61 degrees refrigerator power consumption projection can be reduced by
50%. If is easy to see why forum reports from west coast boaters seem
to get better performance figures than boats on the South East coast.

Danfoss does not recommend running BD compressors direct from a power
supply they have indicated that a battery is necessary to dampen
voltage spikes. The electrical module is Danfoss's weakest link and
the new three pin units seem to fail as frequently as their six
predecessors. Module failures seem to be related to improper size boat
wiring and not connecting power source direct to battery or main power
buss.