Refrigerator on a sailing boat, the largest electricity spreader. Eighty percent of the electricity consumed on board is to maintain the cold in its gut. The principle of operation is simple. The so-called evaporator, or the cooling plate, takes the heat from inside the refrigerator and transports it to the outside, dissipating it into the sea using 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 cooling stops. From this moment on, the temperature starts to rise gradually and at a certain moment the thermostat starts the compressor again. But why does the temperature rise? Because when inside is colder than outside, heat gradually penetrates inward through the walls and the lid of the refrigerator. That is why so much heat insulating material is placed around the cooled volume. Thicker insulation - penetrates the heat more slowly, the refrigerator stays cold longer. If there was a perfect heat insulator, then the inside of the refrigerator, once cooled, in theory, would always remain cold, unless, of course, you open the lid.
Polyurethane foam serves as an insulator for refrigerators; it is an inert and lightweight material similar to polystyrene foam. Almost perfect insulator, but it ceases to be as soon as it absorbs moisture. To prevent this, polyurethane must be enclosed between two walls and perfectly sealed. If there is already a refrigerator on your boat and it is in good condition, it is better to leave everything as is. If the insulation is not in good condition, or you want to expand or modify it, there are two options.
First, buy from the manufacturer of marine refrigerators of suitable sizes, a ready-made, insulated refrigerating chamber 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 more difficult to find, but they are much more preferable than frontal ones, because they do not lose cold every time they open the door and they are not inclined to scatter their contents throughout the boat when they forget to lock the door when rolling, however, if the volume is in which you want to place the refrigerator has a strange shape, as often happens when the bottom of the box follows the hull lines, then you need to make the insulation yourself and here are the instructions:
The box is freed from all 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 in size and superimposed on the walls and bottom. Use a plate with a thickness of five centimeters, and if possible, even ten. Then again, two or three layers of glass, trying to ensure that the polyurethane was securely closed, because a small gap was enough for the moisture to slowly penetrate inside and then, after a few months, all the work would be in vain.
Next, you need to make a wooden cover, also isolate it with polyurethane foam and fiberglass and provide a gasket. To exit the pipes connecting the evaporator to the compressor, a hole is made in the wall, two to three centimeters in diameter. The hole is sealed with resin, and after the evaporator is installed, the hole must be completely closed with mastic or putty, not with silicone, otherwise it will be impossible to remove the pipes if necessary.
For the equipment of the internal volume of the refrigerator shelves can not be used screws, as they would break the insulation. But in its manufacture can be molded from fiberglass protrusions that will serve as supports for the shelves. In the end everything needs to be painted with food paint. At the bottom of the refrigerator you can make a hole for condensate drain, with all the above precautions. But even better not do it. Drainage, on the one hand, keeps the refrigerator dry, but cold air is constantly flowing through it. If there is no hole, you have to dry the bottom of the refrigerator every three to four days, but its effectiveness increases.
Since we equipped a refrigerator according to these principles on our boat, energy consumption has been halved.