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Cold Plates -
"You
should never have to run your engine or waste batteries
for your refrigeration system."
What
is a cold plate system?
Cold
Plate refrigeration systems take advantage of surplus power
created from a generator or running engine. Cold plates are
the most efficient way of storing energy for refrigeration.
An AC compressor system can freeze cold plates in a short
period of time.
Example:
A small 12-volt compressor removes two hundred BTUs of heat
per hour. In a cold plate system, a large compressor can remove
as much as 4000 BTUs per hour. The energy stored in cold plates
then provides cooling for 24 hours or more.
How do
cold plates work?
Cold
plates are stainless steel tanks mounted inside of refrigeration
or freezer units. These plates contain networks of refrigeration
tubing surrounded by a low temperature liquid solution that freezes
quickly. Our
objective is to make sure this solution freezes fast while
you have surplus power available. While running your generator
or engine for one to two hours a day (heating water, cooking
food, charging batteries, etc.), you are simultaneously freezing
your cold plates. A good cold plate system will save money
normally spent on battery replacements or running your
generator needlessly.
Refrigerants?
R134
is used in our Model SF 5000. It’s boiling point of -15°F
makes R134 ideal for refrigerators or warm temperature freezer
cold plates systems.
R404A,
with a boiling point of -50°F, is used in our three larger
models because of its excellent performance at low temperatures.
Freezing temperatures of -15 to -20 degrees are possible.
R404A increases the temperature differential between the solution
and refrigerant, increasing the freezing time 20-30% compared
to other refrigerants.
Cold
plate efficiency...
Surface
area of tubing inside a plate is critical to efficiency -
the more you have the faster the solution will freeze. Most
manufacturers use 1/2 inch or 5/8 inch outside diameter tubing.
We've found these sizes to be too large. In refrigeration
systems, refrigerant and oil continuously circulate through
the system. When tubing is large in diameter, refrigerant
moves slowly which makes the compressor work excessively.
To solve this problem and increase efficiency, we use a
distribution
system comprised of multiple passes of either 1/4 inch or 5/16
inch tubing plumbed in parallel. This method can double the
surface area of tubing inside the plate while maintaining
the proper velocity of refrigerant.
Water
cooled, air cooled or both?
We
build cold plate systems that use air, water or a combination
to remove heat from the plate.
- An
air-cooled compressor mounted in a well-ventilated area
perform quite well. Although running longer per day than
water-cooled models, they are less complex mechanisms and
therefore more trouble free.
- A
water-cooled compressor model offers outstanding performance
in a hot or non-ventilated compartment.
- A
combination air-and-water-cooled compressor provides excellent
performance and reliability.
Sizing
you compressor...
There
are two ways to calculate the size of your compressor: [1]
Run time per day or [2] by the amount of power available to
run your compressor.
Example:
You have one-hour per day to charge batteries and freeze your
cold plates. The first step then is to calculate the heat
loss on the box or boxes to be cooled. With that information,
determine how much cooling per day you require. For large
boxes or fast pull down, a large compressor may be required.
A problem with large compressors is that the starting current
draw may be 50 to 70 amps. Most inverters or dockside power
units can only support 20 to 25 amps. To accomplish a fast
freeze-up of large cold plates, we offer a double compressor
system that employs two small compressors starting at different
times, each drawing only 23 initial amps.
Picking
the right cold plate...
The
three factors to keep in mind when sizing cold plates:
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Surface area of the plate. This determines how many BTU's
per hour can be a removed.
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Thickness of the plate. This determines the length of time
the plate can maintain temperature.
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Temperature differential between the cold plate solution and
the box air temperature.
To
get the very best performance out of your system, cold plates
should be custom built for each job.
What
we need to do the job right....
To
design an efficient cold plate system we need to determine
the following:
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Inside or outside dimensions
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Amount of insulation
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Desired temperature inside the box
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Outside air temperature
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Desired run time per day
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Type(s) of power available
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Amount of ice or food to be refrigerated, if any
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