Freezers, Refrigerators, Conversion Kits, 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:

  1. Surface area of the plate. This determines how many BTU's per hour can be a removed.
  2. Thickness of the plate. This determines the length of time the plate can maintain temperature.
  3. 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:

  • Inside or outside dimensions
  • Amount of insulation
  • Desired temperature inside the box
  • Outside air temperature
  • Desired run time per day
  • Type(s) of power availableAmount of ice or food to be refrigerated, if any