How does Marine refrigeration work? The major parts of a DC refrigeration system include the refrigerant, a compressor, and a condenser, a cooling system for condenser, and a plate or plates inside the refrigeration box.
The compressor is part of a closed loop pumping refrigerant through the system and through the evaporator plate in the ice box. The compressor has two sides the High side or discharge side. The discharge side pumps refrigerant under pressure to the condenser. The suction side or low side and sucks refrigerant after it passes through the evaporator plate back to the compressor. The cold plates in the fridge space have either expansion valves or capillary tube that separate the low and high pressure sides of the refrigeration system.
The refrigerant in the compressor starts Marine Refrigeration and Freezers as a gas. The compressor compresses the refrigerant gas, from low pressure to high pressure between 100-150 psi. When the pressure is increased like this its temperature rises dramatically. This hot high pressure refrigerant is then fed to a condenser, where it is cooled and turned into a liquid. The condenser is cooled by either air or water. The refrigerant is now a cool high pressure liquid and is fed to an evaporator plate inside the boats refrigerator box.
The evaporator plate takes the refrigerant from the condenser and here it boils rapidly & evaporates back to a gas, at a very low temperature. This change of state absorbs vast amounts of sensible heat from the evaporator which in turn removes heat from the insulated refrigeration box, thereby lowering its temperature. The BTU is the measurement of heat removed. From the evaporator plate the refrigerant is returned to the low side of the compressor, to start the process again.
Evaporator or Holding Plates
Marine refrigeration systems use either an evaporator plate or a holding plate in the boats refrigeration space or freezer space. Each type of plate works differently in drawing heat from the boats refrigerator and ice box space.
Marine evaporator are just like the ones found in household refrigerators. They can get quite cold (thermostat setting) and many evaporators have the ability to make ice next to the evaporator plate or inside the evaporator box. Evaporators come in several shapes and sizes; they can be horizontal plate’s, vertical plates and rolled plates. Evaporators are constant cycling, or short cycle. Most use a Danfoss marine compressor with H134 refrigerant.
Thermostat controlled evaporator temperature. Turn to lower ice box temperature. Evaporator plates are less expensive, but need Constant power supply.
Marine Holding plates
Marine Refrigerator Holding Plates act like large blocks of ice and the cold temperature of the holding plate sucks heat out of the boats refrigeration box. Holding plates can keep ice boxes cold for long periods.
The main advantage of a holding plate over an evaporator is that they only need to be recharged 1 or 2 times per day. This charging can coincide with attaching to shore power, running the engine and so the refrigerator does not rely on the battery bank. When incorporated into a properly designed system, holdover plates can significantly reduce energy consumption. However DC holding plates are also possible. The holding plate is filled with a solution that has a freezing point below 23 degrees F. As the compressor runs, the refrigerant passes through the holding Plates coil, freezing the holding plate solution. The compressor turns of and as the holding plate thaws out, heat is removed from the box.