A good isolated fridge
Refrigerator on a sailboat, the biggest waster of electricity. Eighty percent of the electricity consumed on board is used to keep it cold inside. The principle of operation is simple. The so-called evaporator, or cooling plate, takes heat from inside the refrigerator and transports it outside, dissipating it into the sea with the help of a heat exchanger. As the evaporator works, the temperature inside the refrigerator drops. When it cools down enough, the thermostat gives a signal, the compressor stops and the refrigerationis cancelled. From this point on, the temperature begins to gradually rise and at a certain moment the thermostat starts the compressor again. But why is the temperature rising? Because when it is colder inside than outside, heat gradually penetrates inside through the walls and lid of the refrigerator. That is why so much heat-insulating material is placed around the cooled volume. Thicker insulation - heat penetrates more slowly, the refrigerator stays cold longer. If there were an ideal heat insulator, then the insides of hothe lodilnik, once cooled, in theory, would always remain cold, unless, of course, you open the lid.
The insulator for refrigerators is polyurethane foam, which is an inert and lightweight material similar to polystyrene foam. An almost perfect insulator, but it ceases to be so as soon as it absorbs moisture. To prevent this from happening, the polyurethane must be enclosed between two walls and perfectly sealed. If your boat already has a refrigerator and it is in good condition, it is best to leave everything as it is. If the insulation is not in good condition, or you want to expand or modify it, there are two options.
The first is to buy a prefabricated, insulated cold room from a suitably sized marine refrigerator manufacturer and install it as it is. Thus, you can be sure of the quality of thermal insulation. When choosing, keep in mind that top-opening refrigerators are harder to find, but they are much more preferable than front-facing ones, because they do not lose cold every time the door is opened and do not tend to scatter their contents all over the boat when they forget to fix the door when rocking. However, if the volume in which you want toto replace the refrigerator, it has a strange shape, as often happens when the bottom of the box follows the contours of the case, then the insulation must be done by yourself and here are the instructions:
The box is emptied of everything unnecessary, the walls are sealed with resin and everything, including the bottom, is covered with two or three layers of fiberglass. Polyurethane foam plates are cut to size and superimposed on the walls and bottom. Use a plate five centimeters thick, and if possible, ten. Then again two or three layers of glass, trying to ensure that the polyurethane was securely closed, because a small gap is enough for moisture to slowly begin to penetrate inside and then, after a few months, all the work would be in vain.
Next, you need to make a wooden cover, also insulate it with polyurethane foam and fiberglass and provide it with a gasket. To exit the pipes connecting the evaporator to the compressor, a hole is made in the wall with a diameter of two to three centimeters. The hole made is sealed with resin, and after the evaporator is installed, the hole must be completely closed with mastic or putty, but not silicone, otherwise it will not be possible to remove the pipes if necessary.
Screws must not be used to equip the interior of the refrigerator with shelves, as they would break the insulation. But in its manufacture, it is possible to mold ledges from fiberglass, which will serve as supports for the shelves. In the end, everything needs to be painted with food coloring. A hole can be made in the bottom of the refrigerator to drain the condensate, with all the precautions described above. But it's even better not to do it. Drainage, on the one hand, keeps the refrigerator dry, but cold air constantly escapes through it. If there is no hole, you have tosew the bottom of the refrigerator every three to four days, but its effectiveness increases.
Since our boat was equipped with a refrigerator according to these principles, energy consumption has been halved.