note on Refrigerator.

“A refrigerator is a common household appliance that consists of a thermally insulated compartment and a heat pump that transfer heat from the inside of the fridge to its external environment”.

Freezer:

Freezer units are used in households and in industry and commerce. Food stored at or below −18 °C (0 °F) is safe indefinitely. Most household freezers maintain temperatures from −23 to −18 °C (−9 to 0 °F), although some freezer-only units can achieve −34 °C (−29 °F) and lower.

Commercial and domestic Freezer/Refrigerator:

Commercial refrigerator and freezer units, which go by many other names, were in use for almost 40 years prior to the common home models. They used gas systems such as ammonia (R-717) or sulfur dioxide (R-764), which occasionally leaked, making them unsafe for home use.

Types of domestic refrigerators

• Compressor refrigerators are by far the most common type; they make a noticeable noise.
• Absorption refrigerators or thermo-electric Peltier units are used where quiet running is required; Peltier coolers are used in the smallest refrigerators as they have no bulky mechanism.
• Compressor and  Peltier refrigerators are powered by electricity. Absorption units can be designed to get power from any heat source. A noticeable difference between the two types is the absence of refrigerant with Peltier coolers (these use a different method of cooling). But Peltier coolers use more electricity because they are thermodynamically inefficient.
• Oil, gas (natural gas or propane) and dual power gas/electricity units are also available (typically found in RV's).
• Solar refrigerators and Thermal mass refrigerators are designed to reduce electrical consumption. Solar refrigerators have the added advantage that they do not use refrigerants that are harmful to the environment or flammable. Typical solar designs are absorption refrigerators that use ammonia as the working gas, and employ large mirrors to concentrate sufficient sunlight to reach the temperature required to free gaseous ammonia from the solvent. Most thermal mass refrigerators are designed to use electricity intermittently. As these units are heavily insulated, cooling load is limited primarily to heat introduced by new items to be refrigerated, and ambient air transfer when the unit is open. Very little power is therefore required if opened infrequently. Refrigeration units for commercial and industrial applications can be made in various size, shape or style to fit customer needs.

Other specialized cooling mechanisms may be used for cooling, but have not been applied to domestic refrigerators.

• Magnetic refrigerators are refrigerators that work on the magneto caloric effect. The cooling effect is triggered by placing a metal alloy in a magnetic field.
• Acoustic refrigerators are refrigerators that use resonant linear reciprocating motors/alternators to generate a sound that is converted to heat and cold using compressed helium gas. The heat is discarded and the cold is routed to the refrigerator

Temperature zones and ratings

• −18 °C (0 °F) (freezer)
• 0 °C (32 °F) (meat zone)
• 5 °C (41 °F) (cooling zone)
• 10 °C (50 °F) (crisper)

In Mexico, the Federal Government created the program Cambia Tu Viejo Por Uno Nuevo — Change Your Old One for A New One. The old refrigerators are recycled to recover their components — refrigerant gas, copper, glass, iron, etc.