Refrigerators and Freezers 101

A refrigerator, often called a "Fridge", is a cooling appliance comprising a thermally insulated compartment and a chemical or mechanical heat pump to transfer heat from it to the external environment, cooling the contents to a temperature below ambient.

A device described as a "refrigerator" maintains a temperature a few degrees above the freezing point of water; a similar device which maintains a temperature below the freezing point of water is called a Freezer.

The refrigerator is a relatively modern invention among kitchen appliances. It replaced the icebox, which had been a common household appliance for almost a century and a half prior. For this reason, a refrigerator is sometimes referred to as an icebox.

Domestic refrigerators and freezers for food storage are made in a range of sizes.

A large domestic fridge stands as tall as a person and may be about 1 m wide with a capacity of 600 L. Some models for small households fit Under Kitchen work surfaces, usually about 86 cm high.

Fridges may be combined with freezers, either stacked with fridge or freezer above, below, or side by side. A fridge without a frozen food storage compartment may have a small section just to make ice cubes.

Fridges and freezers may be free-standing, or built into a kitchen.

Compressor refrigerators are by far the most common type and are most noticeable for the noticeable hum they make.

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 be powered by any heat source. A noticeable difference between the two types is the absence of refrigerant with the Peltier coolers, but they use more electricity because they are thermodynamically inefficient.

Oil, gas (natural gas or propane) and dual power gas/electricity units are also available and most 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.

Magnetic refrigerators are refrigerators that work on the magnetocaloric effect. The cooling effect is triggered by placing a metal alloy in a magnetic field.

Freezer units are used in households and in industry and commerce. Most freezers operate around 0 °F (−18 °C).

Domestic freezers can be included as a separate compartment in a refrigerator, or can be a separate appliance.

Domestic freezers are generally upright units resembling refrigerators, or chests resembling upright units laid on their backs. Many upright modern freezers come with an ice dispenser built into their door.

Early freezer units accumulated ice crystals around the freezing units. This was a result of humidity introduced into the units when the doors to the freezer were opened.

This frost buildup required periodic thawing or defrosting of the units to maintain their efficiency. Manual Defrost, referred to as Cyclic, units are still available.

Advances in automatic defrosting eliminating the thawing task were introduced in the 1950s, but are not universal, due to energy performance and cost.

These units utilized a counter, that only defrosted the freezer compartment when a specific number of door openings had been made. The units were just a small timer combined with an electrical heater wire which heater the Freezer's walls for a short amount of time to remove all traces of frost/frosting.

Also, early units featured freezer compartments located within the larger refrigerator, and accessed by opening the Refrigerator Door, and then the smaller internal Freezer Door; units featuring an entirely separate freezer compartment were introduced in the early 1960s, becoming the industry standard by the middle of that decade.

These older freezer compartments were the main cooling body of the refrigerator, and only maintained a temperature of around -6°C, which is suitable for keeping food for a week.

Freezers may have drawers to store food in, or they may have no divisions as in Chest Freezers.

Later advances included automatic ice units and self compartmentalized freezing units.