Refrigerator

Refrigerator

Overview

A refrigerator is a common household appliance that consists of a thermally insulated
Thermal insulation
Thermal insulation is the reduction of the effects of the various processes of heat transfer between objects in thermal contact or in range of radiative influence. Heat transfer is the transfer of thermal energy between objects of differing temperature...

 compartment and a heat pump
Heat pump
A heat pump is a machine or device that effectively "moves" thermal energy from one location called the "source," which is at a lower temperature, to another location called the "sink" or "heat sink", which is at a higher temperature. An air conditioner is a particular type of heat pump, but the...

 (mechanical, electronic, or chemical) that transfers heat from the inside of the fridge to its external environment so that the inside of the fridge is cooled to a temperature below the ambient temperature of the room. Cooling is a popular food storage technique
Food preservation
Food preservation is the process of treating and handling food to stop or slow down spoilage and thus allow for longer storage....

 in developed countries and works by decreasing or even arresting the reproduction rate of bacteria.
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Encyclopedia

A refrigerator is a common household appliance that consists of a thermally insulated
Thermal insulation
Thermal insulation is the reduction of the effects of the various processes of heat transfer between objects in thermal contact or in range of radiative influence. Heat transfer is the transfer of thermal energy between objects of differing temperature...

 compartment and a heat pump
Heat pump
A heat pump is a machine or device that effectively "moves" thermal energy from one location called the "source," which is at a lower temperature, to another location called the "sink" or "heat sink", which is at a higher temperature. An air conditioner is a particular type of heat pump, but the...

 (mechanical, electronic, or chemical) that transfers heat from the inside of the fridge to its external environment so that the inside of the fridge is cooled to a temperature below the ambient temperature of the room. Cooling is a popular food storage technique
Food preservation
Food preservation is the process of treating and handling food to stop or slow down spoilage and thus allow for longer storage....

 in developed countries and works by decreasing or even arresting the reproduction rate of bacteria. The device is thus used to reduce the rate of spoilage of foodstuffs.

A refrigerator maintains a temperature a few degrees above the freezing point
Freezing Point
Freezing Point is a news journal in the People's Republic of China which has been the subject of controversy over its criticism of Communist Party officials and the sympathetic ear it lent to a Chinese historian who had criticized official history textbooks...

 of water. Optimum temperature range for perishable food storage is 3 to 5 °C (37 to 41 °F). 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
Icebox
An icebox is a compact non-mechanical refrigerator which was a common kitchen appliance before the development of safe powered refrigeration devices.- Design :...

, 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.

Freezer


Freezer units are used in households and in industry and commerce. Most household freezers maintain temperatures from -10 to 0 °F (-23 to -18 °C), although some freezer-only units can achieve −30 °F (−34 °C), and lower. Refrigerators generally do not achieve lower than -10 °F (-23 °C), since the same coolant loop serves both compartments: Lowering the freezer compartment temperature excessively causes difficulties in maintaining above-freezing temperature in the refrigerator compartment. 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.

Commercial and domestic refrigerators


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 anhydrous ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

 (R-717) or sulfur dioxide
Sulfur dioxide
Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...

 (R-764), which occasionally leaked, making them unsafe for home use and industrial purposes. Practical household refrigerators were introduced in 1915 and gained wider acceptance in the United States in the 1930s as prices fell and non-toxic, non-flammable synthetic refrigerant
Refrigerant
A refrigerant is a substance used in a heat cycle usually including, for enhanced efficiency, a reversible phase change from a liquid to a gas. Traditionally, fluorocarbons, especially chlorofluorocarbons, were used as refrigerants, but they are being phased out because of their ozone depletion...

s such as Freon-12
Dichlorodifluoromethane
Dichlorodifluoromethane , is a colorless gas, and usually sold under the brand name Freon-12, is a chlorofluorocarbon halomethane , used as a refrigerant and aerosol spray propellant. Complying with the Montreal Protocol, its manufacture was banned in the United States along with many other...

® (R-12) were introduced. The replacement for R-12, R-134a (tetrafluoroethane), has only been in common use since 1990.

Styles of refrigerators


Most households use the freezer on top and refrigerator on bottom style, which has been the basic style since the 1940s.
  • Traditional style — 1940s to present. Freezer top/refrigerator bottom (although most of the earlier models, some of the cheaper later models, and still some mini-fridges use the "freezer chest", or what is known as the "freezer in the fridge"). A separate freezer compartment — not located within the larger refrigerator compartment — became the industry standard during the early- to mid-1960s.
  • Side by side style — introduced by Amana
    Amana Corporation
    The Amana Corporation is an American brand of household appliances. It was founded in 1934 by George Foerstner as The Electrical Equipment Co. in Middle Amana, Iowa to manufacture commercial walk-in coolers. The business was later owned by the Amana Society and became known as Amana Refrigeration,...

     in 1949 but not popular until 1965–present; left side is freezer and the right is refrigerator.
  • Top refrigerator/bottom freezer style — mid-1950s to present.
  • French door style — late 1990s-present. Two French doors for refrigerator and bottom freezer.


In the early-1950s, most refrigerators were white, but from the mid-1950s through present day, designers and manufacturers put color into refrigerators. In the late-1950s/early-1960s, colors like turquoise and pink were popular, brushed chrome plating (similar to stainless finish) was available on some models from different brands. In the 1970s, common colors were Harvest Gold
Gold (color)
Gold, also called golden, is one of a variety of orange-yellow color blends used to give the impression of the color of the element gold....

, Avocado Green
Green
Green is a color, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 520–570 nanometres. In the subtractive color system, it is not a primary color, but is created out of a mixture of yellow and blue, or yellow and cyan; it is considered...

 and almond. In the 1980s, black was viewed as luxurious. In the late 1990s, stainless steel
Stainless steel
In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....

 became stylish, and in 2009, one manufacturer introduced multi-color designs.

Many refrigerators can be blended into the cabinetry of the kitchen with panels that can slide over the doors for a built-in look.

Most home refrigerators weigh between 200 pounds (90.7 kg) and 450 pounds (204.1 kg), with some models weighing up to 875 pounds (396.9 kg).

History



Before the invention of the refrigerator, icehouses
Icehouse (building)
Ice houses were buildings used to store ice throughout the year, prior to the invention of the refrigerator. Some were underground chambers, usually man-made, close to natural sources of winter ice such as freshwater lakes, but many were buildings with various types of insulation.During the...

 were used to provide cool storage for most of the year. Placed near freshwater lakes or packed with snow and ice during the winter, they were once very common. Natural means are still used to cool foods today. On mountainsides, runoff from melting snow is a convenient way to cool drinks, and during the winter one can keep milk fresh much longer just by keeping it outdoors.

In the 11th century, the Muslim physicist and chemist
Alchemy and chemistry in medieval Islam
Alchemy and chemistry in Islam refers to the study of both traditional alchemy and early practical chemistry by scholars in the medieval Islamic world. The word alchemy was derived from the Arabic word كيمياء or kīmīāʾ...

 Ibn Sina
Avicenna
Abū ʿAlī al-Ḥusayn ibn ʿAbd Allāh ibn Sīnā , commonly known as Ibn Sīnā or by his Latinized name Avicenna, was a Persian polymath, who wrote almost 450 treatises on a wide range of subjects, of which around 240 have survived...

 (latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

ized name: Avicenna
Avicenna
Abū ʿAlī al-Ḥusayn ibn ʿAbd Allāh ibn Sīnā , commonly known as Ibn Sīnā or by his Latinized name Avicenna, was a Persian polymath, who wrote almost 450 treatises on a wide range of subjects, of which around 240 have survived...

) invented the refrigerated coil
Condenser (laboratory)
In a laboratory a condenser is a piece of laboratory glassware used to cool hot vapors or liquids. A condenser usually consists of a large glass tube containing a smaller glass tube running its entire length, within which the hot fluids pass....

, which condenses aromatic
Aromaticity
In organic chemistry, Aromaticity is a chemical property in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibit a stabilization stronger than would be expected by the stabilization of conjugation alone. The earliest use of the term was in an article by August...

 vapours. This was a breakthrough in distillation
Distillation
Distillation is a method of separating mixtures based on differences in volatilities of components in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction....

 technology and he made use of it in his steam distillation
Steam distillation
Steam distillation is a special type of distillation for temperature sensitive materials like natural aromatic compounds....

 process, which requires refrigerated tubing, to produce essential oil
Essential oil
An essential oil is a concentrated hydrophobic liquid containing volatile aroma compounds from plants. Essential oils are also known as volatile oils, ethereal oils or aetherolea, or simply as the "oil of" the plant from which they were extracted, such as oil of clove...

s.


The first known artificial refrigeration was demonstrated by William Cullen
William Cullen
William Cullen FRS FRSE FRCPE FPSG was a Scottish physician, chemist and agriculturalist, and one of the most important professors at the Edinburgh Medical School, during its heyday as the leading center of medical education in the English-speaking world.Cullen was also a central figure in the...

 at the University of Glasgow
University of Glasgow
The University of Glasgow is the fourth-oldest university in the English-speaking world and one of Scotland's four ancient universities. Located in Glasgow, the university was founded in 1451 and is presently one of seventeen British higher education institutions ranked amongst the top 100 of the...

 in 1748. The American inventor Oliver Evans
Oliver Evans
Oliver Evans was an American inventor. Evans was born in Newport, Delaware to a family of Welsh settlers. At the age of 14 he was apprenticed to a wheelwright....

, acclaimed as the "father of refrigeration," invented the vapor-compression refrigeration
Vapor-compression refrigeration
Vapor-compression refrigeration is one of the many refrigeration cycles available for use. It has been and is the most widely used method for air-conditioning of large public buildings, offices, private residences, hotels, hospitals, theaters, restaurants and automobiles...

 machine in 1805. Heat would be removed from the environment by recycling vaporized refrigerant, where it would move through a compressor
Gas compressor
A gas compressor is a mechanical device that increases the pressure of a gas by reducing its volume.Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe. As gases are compressible, the compressor also reduces the volume of a gas...

 and condenser, where it would eventually revert back to a liquid form in order to repeat the refrigeration process over again. However, no such refrigeration unit was built by Evans. In 1834, Jacob Perkins
Jacob Perkins
Jacob Perkins was an Anglo-American inventor, mechanical engineer and physicist. Born in Newburyport, Massachusetts, Perkins was apprenticed to a goldsmith...

 modified Evans' original design, building the world's first refrigerator and filing the first legal patent for refrigeration using vapor-compression. John Gorrie
John Gorrie
John Gorrie , physician, scientist, inventor, and humanitarian, is considered the father of refrigeration and air conditioning. He was born on the Island of Nevis to Scottish parents on October 3, 1802, and spent his childhood in South Carolina...

, an American doctor from Florida
Florida
Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...

, invented the first mechanical refrigeration unit in 1841, based on Evans' original invention to make ice in order to cool the air for yellow fever
Yellow fever
Yellow fever is an acute viral hemorrhagic disease. The virus is a 40 to 50 nm enveloped RNA virus with positive sense of the Flaviviridae family....

 patients. Gorrie's mechanical refrigeration unit was issued a patent in 1851. American professor Alexander C. Twining of Cleveland, Ohio patented an early vapor-compression refrigerator in 1853 that was fully capable of producing a ton of ice per day.

In 1856, James Harrison
James Harrison (engineer)
James Harrison was an Australian newspaper printer, journalist, politician, and pioneer in the field of mechanical refrigeration.-Early life:...

, an imigrant from Scotland
Scotland
Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...

 living in Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

, developed an ice making machine using ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

 and an ether compressor. It was used in the brewing and meat packing industries of Geelong, Victoria. Ferdinand Carré
Ferdinand Carré
Ferdinand Philippe Edouard Carré was a French engineer, born at Moislains on 11 March 1824. Carré is best known as the inventor of refrigeration equipment used to produce ice...

 of France developed a somewhat more complex system in 1859. Unlike earlier compression-compression machines, which used air as a coolant, Carré's equipment contained rapidly expanding ammonia. In 1913, refrigerators for home and domestic use were invented by Fred W. Wolf of Fort Wayne, Indiana with models consisting of a unit that was mounted on top of an ice box. A self-contained refrigerator, with a compressor on the bottom of the cabinet was invented by Alfred Mellowes in 1916. Mellowes produced this refrigerator commercially but was bought out by William C. Durant
William C. Durant
William Crapo "Billy" Durant was a leading pioneer of the United States automobile industry, the founder of General Motors and Chevrolet who created the system of multi-brand holding companies with different lines of cars....

 in 1918, who started the Frigidaire Company in order to begin the first mass-production of refrigerators. The absorption refrigerator
Absorption refrigerator
An absorption refrigerator is a refrigerator that uses a heat source to provide the energy needed to drive the cooling system...

 was invented by Baltzar von Platen and Carl Munters
Carl Munters
Carl Georg Munters was a Swedish inventor, most known for inventing together with Baltzar von Platen the gas absorption refrigerator now sold by Electrolux...

 from Sweden
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....

 in 1922, while they were still students at the Royal Institute of Technology
Royal Institute of Technology
The Royal Institute of Technology is a university in Stockholm, Sweden. KTH was founded in 1827 as Sweden's first polytechnic and is one of Scandinavia's largest institutions of higher education in technology. KTH accounts for one-third of Sweden’s technical research and engineering education...

 in Stockholm. It became a worldwide success and was commercialized by Electrolux
Electrolux
The Electrolux Group is a Swedish appliance maker.As of 2010 the 2nd largest home appliance manufacturer in the world after Whirlpool, its products sell under a variety of brand names including its own and are primarily major appliances and vacuum cleaners...

. Other pioneers included Charles Tellier
Charles Tellier
Charles Tellier was a French engineer, born in Amiens. He early made a study of motors and compressed air. In 1868 he began experiments in refrigeration, which resulted ultimately in the refrigerating plant as used on ocean vessels, to preserve meats and other perishable food...

, David Boyle, and Raoul Pictet
Raoul Pictet
Raoul-Pierre Pictet was a Swiss physicist and the first person to liquefy nitrogen. He was born in Geneva and served as professor in the university of that city...

. Carl von Linde
Carl von Linde
Professor Doctor Carl Paul Gottfried von Linde was a German engineer who developed refrigeration and gas separation technologies...

 was the first to patent and make a practical and compact refrigerator.


These home units usually required the installation of the mechanical parts, motor and compressor, in the basement or an adjacent room while the cold box was located in the kitchen. There was a 1922 model that consisted of a wooden cold box, water-cooled
Watercooling
Water cooling is a method of heat removal from components and industrial equipment. As opposed to air cooling, water is used as the heat conductor. Water cooling is commonly used for cooling automobile internal combustion engines and large industrial facilities such as steam electric power plants,...

 compressor, an ice cube
Ice cube
Ice cubes are small, roughly cube-shaped pieces of ice, conventionally used to cool beverages. Ice cubes are often preferred over crushed ice because they melt more slowly; they are standard in mixed drinks that call for ice, in which case the drink is said to be "on the rocks."Ice cubes are...

 tray and a 9 cubic foot (0.254851623 m³) compartment, and cost $714. (A 1922 Model-T Ford cost about $450.) In 1923 Frigidaire introduced the first self-contained unit. About this same time porcelain-covered metal cabinets began to appear. Ice cube trays were introduced more and more during the 1920s; up to this time freezing was not an auxiliary function of the modern refrigerator.

The first refrigerator to see widespread use was the General Electric "Monitor-Top" refrigerator introduced in 1927, so-called because of its resemblance to the gun turret on the ironclad warship USS Monitor
USS Monitor
USS Monitor was the first ironclad warship commissioned by the United States Navy during the American Civil War. She is most famous for her participation in the Battle of Hampton Roads on March 9, 1862, the first-ever battle fought between two ironclads...

 of the 1860s. The compressor assembly, which emitted a great deal of heat, was placed above the cabinet, and surrounded with a decorative ring. Over a million units were produced. As the refrigerating medium, these refrigerators used either sulfur dioxide
Sulfur dioxide
Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...

, which is corrosive to the eyes and may cause loss of vision, painful skin burns and lesions, or methyl formate
Methyl formate
Methyl formate, also called methyl methanoate, is the methyl ester of formic acid. The simplest example of an ester, it is a clear liquid with an ethereal odor, high vapor pressure, and low surface tension.-Production:...

, which is highly flammable, harmful to the eyes, and toxic if inhaled or ingested. Many of these units are still functional today. These cooling systems cannot legally be recharged with the hazardous original refrigerants if they leak or break down.

The introduction of Freon
Chlorofluorocarbon
A chlorofluorocarbon is an organic compound that contains carbon, chlorine, and fluorine, produced as a volatile derivative of methane and ethane. A common subclass are the hydrochlorofluorocarbons , which contain hydrogen, as well. They are also commonly known by the DuPont trade name Freon...

 in the 1920s expanded the refrigerator market during the 1930s and provided a safer, low-toxicity alternative to previously used refrigerants. Separate freezers became common during the 1940s, the popular term at the time for the unit was a "deep freeze". These devices, or "appliances", did not go into mass production for use in the home until after World War II. The 1950s and 1960s saw technical advances like automatic defrost
Defrost
Defrosting is a procedure, performed periodically on refrigerators and freezers to maintain their operating efficiency. Over time, as the door is opened and closed, letting in new air, water vapour from the air condenses on the cooling elements within the cabinet...

ing and automatic ice making. More efficient refrigerators were developed in the 1970s and 1980s, even though environmental issues
Ozone depletion
Ozone depletion describes two distinct but related phenomena observed since the late 1970s: a steady decline of about 4% per decade in the total volume of ozone in Earth's stratosphere , and a much larger springtime decrease in stratospheric ozone over Earth's polar regions. The latter phenomenon...

 led to the banning of very effective (Freon) refrigerants. Early refrigerator models (from 1916) had a cold compartment for ice cube trays. From the late 1920s fresh vegetables were successfully processed through freezing by the Postum Company (the forerunner of General Foods
General Foods
General Foods Corporation was a company whose direct predecessor was established in the USA by Charles William Post as the Postum Cereal Company in 1895. The name General Foods was adopted in 1929, after several corporate acquisitions...

), which had acquired the technology when it bought the rights to Clarence Birdseye
Clarence Birdseye
Clarence Frank Birdseye II was an American inventor who is considered the founder of the modern method of freezing food.- Early work :...

's successful fresh freezing methods.

The first successful application of frozen foods occurred when General Foods heiress Marjorie Merriweather Post
Marjorie Merriweather Post
-External links:******...

 (then wife of Joseph E. Davies
Joseph E. Davies
Joseph Edward Davies was appointed by President Wilson to be Commissioner of Corporations in 1912, and First Chairman of the Federal Trade Commission in 1915. He was the second Ambassador to represent the United States in the Soviet Union and U.S. Ambassador to Belgium and Luxembourg...

, United States Ambassador to the Soviet Union) deployed commercial-grade freezers in Spaso House, the US Embassy in Moscow, in advance of the Davies’ arrival. Post, fearful of the USSR's food processing safety standards, fully stocked the freezers with products from General Foods' Birdseye unit. The frozen food stores allowed the Davies to entertain lavishly and serve fresh frozen foods that would otherwise be out of season. Upon returning from Moscow, Post (who resumed her maiden name after divorcing Davies) directed General Foods to market frozen product to upscale restaurants.

Home freezers as separate compartments (larger than necessary just for ice cubes), or as separate units, were introduced in the United States in 1940. Frozen foods, previously a luxury item, began to be commonplace.

General technical explanation


A vapor compression cycle is used in most household refrigerators, refrigerator–freezers and freezers. In this cycle, a circulating refrigerant such as R134a enters a compressor as low-pressure vapor at or slightly above the temperature of the refrigerator interior. The vapor is compressed and exits the compressor as high-pressure superheated vapor. The superheated vapor travels under pressure through coils or tubes comprising "the condenser", which are passively cooled by exposure to air in the room. The condenser cools the vapor, which liquefies. As the refrigerant leaves the condenser, it is still under pressure but is now only slightly above room temperature. This liquid refrigerant is forced through a metering or throttling device, also known as an expansion valve (essentially a pin-hole sized constriction in the tubing) to an area of much lower pressure. The sudden decrease in pressure results in explosive-like flash evaporation of a portion (typically about half) of the liquid. The latent heat absorbed by this flash evaporation is drawn mostly from adjacent still-liquid refrigerant, a phenomenon known as "auto-refrigeration". This cold and partially vaporized refrigerant continues through the coils or tubes of the evaporator unit. A fan blows air from the refrigerator or freezer compartment ("box air") across these coils or tubes and the refrigerant completely vaporizes, drawing further latent heat from the box air. This cooled air is returned to the refrigerator or freezer compartment, and so keeps the box air cold. Note that the cool air in the refrigerator or freezer is still warmer than the refrigerant in the evaporator. Refrigerant leaves the evaporator, now fully vaporized and slightly heated, and returns to the compressor inlet to continue the cycle.

An absorption refrigerator
Absorption refrigerator
An absorption refrigerator is a refrigerator that uses a heat source to provide the energy needed to drive the cooling system...

 works differently from a compressor refrigerator, using a source of heat
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...

, such as combustion
Combustion
Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...

 of liquefied petroleum gas, solar thermal energy
Solar thermal energy
Solar thermal energy is a technology for harnessing solar energy for thermal energy . Solar thermal collectors are classified by the United States Energy Information Administration as low-, medium-, or high-temperature collectors. Low-temperature collectors are flat plates generally used to heat...

 or an electric heating element. These heat sources are much quieter than the compressor motor in a typical refrigerator. A fan or pump might be the only mechanical moving parts; reliance on convection is considered impractical.

The Peltier effect uses electricity to pump heat directly; this type of refrigerator is sometimes used for camping, or where noise is not acceptable. They can be totally silent (if they don't include a fan for air circulation) but are less energy-efficient than other methods.

Other uses of an absorption refrigerator (or "chiller") include large systems used in office buildings or complexes such as hospitals and universities. These large systems are used to chill a brine solution that is circulated through the building.

Many modern refrigerator/freezers have the freezer on top and the refrigerator on the bottom. Many ask the question "How does the refrigerator stay cold if the motor doesn't start when I turn the refrigerator knob?" This question is answered easily. Most refrigerator/freezers, with the exception of manual defrost models and/or cheaper models utilize what appears to be two thermostats. Only the freezer compartment is properly temperature controlled. When the freezer gets too warm, the thermostat starts the refrigeration process and a fan also starts. The air is circulated around the freezer. During this time, the refrigerator is also getting colder. The refrigerator temperature control knob is doing nothing to "control" the temperature. This knob is only controlling the amount of air that actually flows into the refrigerator via a damper system. This means that the refrigerator may become too warm. However, because only enough air is diverted to the refrigerator compartment, the freezer usually re-acquires the set temperature quickly, unless the door is opened. When a door is opened, either in the refrigerator or the freezer, the fan in some units stops immediately to prevent excessive frost build up on the freezer's evaporator coil, because this coil is cooling two areas. When the freezer reaches temperature, the unit cycles off, no matter what the refrigerator temperature is. Some people recommend setting the refrigerator to maximum and the freezer to a point where one's refrigerated food won't freeze.

Modern computerized refrigerators do not use the damper system. The computer manages fan speed for both compartments, although air is still blown from the freezer.

Other alternatives to the vapor-compression cycle but not in current use include thermionic, vortex tube
Vortex tube
The vortex tube, also known as the Ranque-Hilsch vortex tube, is a mechanical device that separates a compressed gas into hot and cold streams. It has no moving parts....

, air cycle, magnetic cooling, Stirling cycle
Stirling engine
A Stirling engine is a heat engine operating by cyclic compression and expansion of air or other gas, the working fluid, at different temperature levels such that there is a net conversion of heat energy to mechanical work....

, Malone refrigeration, acoustic cooling, pulse tube
Pulse tube refrigerator
The pulse tube refrigerator or pulse tube cryocooler is a developing technology that emerged largely in the early 1980s with a series of other innovations in the broader field of thermoacoustics...

 and water cycle systems.

Features


Newer refrigerators may include:
  • Automatic defrosting;
  • A power failure warning, alerting the user by flashing a temperature display. The maximum temperature reached during the power failure may be displayed, along with information on whether the frozen food has defrosted or may contain harmful bacteria;
  • Chilled water and ice available from an in-door station, so that the door need not be opened;

Water and ice dispensing became available in the 1970s. Also, some refrigerators have ice makers built-in so, the user doesn't have to use ice trays. Some refrigerators have water chillers and water filtration systems.
  • Cabinet rollers that allow the refrigerator to be easily rolled around for easier cleaning;
  • Adjustable shelves and trays which can be repositioned to suit the user;
  • A status indicator to notify the user when it is time to change the water filter
    Filter (water)
    A water filter removes impurities from water by means of a fine physical barrier, a chemical process or a biological process. Filters cleanse water to various extents for irrigation, drinking water, aquariums, and swimming pools.-Methods of filtration:...

    ;
  • An in-door ice caddy, which relocates the ice-maker storage to the freezer door and saves approximately 60 litres (2 cu ft) of usable freezer space. It is also removable, and helps to prevent ice-maker clogging;
  • A cooling zone in the refrigerator door shelves. Air from the freezer section is diverted to the refrigerator door, to cool milk or juice stored in the door shelf.


Early freezer units accumulated ice crystals
Ice crystals
Ice crystals are a small crystalline form of ice including hexagonal columns, hexagonal plates, dendritic crystals, and diamond dust. The highly symmetric shapes are due to depositional growth, namely, direct deposition of water vapour onto the ice crystal...

 around the freezing units. This was a result of humidity introduced into the units when the doors to the freezer were opened condensing on the cold parts, then freezing. This frost buildup required periodic thawing ("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 (Freezer Chest) when a specific number of door openings had been made. The units were just a small timer combined with an electrical heater wire which heated 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.

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

An increasingly important environmental concern is the disposal of old refrigerators – initially because of the Freon coolant damaging the ozone layer
Ozone layer
The ozone layer is a layer in Earth's atmosphere which contains relatively high concentrations of ozone . This layer absorbs 97–99% of the Sun's high frequency ultraviolet light, which is potentially damaging to the life forms on Earth...

, but as the older generation of refrigerators disappears it is the destruction of CFC-bearing insulation which causes concern. Modern refrigerators usually use a refrigerant called HFC-134a (1,1,1,2-Tetrafluoroethane
1,1,1,2-Tetrafluoroethane
1,1,1,2-Tetrafluoroethane, R-134a, Genetron 134a, Suva 134a or HFC-134a, is a haloalkane refrigerant with thermodynamic properties similar to R-12 , but with less ozone depletion potential...

), which does not deplete the ozone layer, instead of Freon. A R-134a is now becoming very uncommon in Europe. Instead, newer refrigerants are being used instead. The main refrigerant now used is R-600a, or isobutane. This refrigerant is naturally occurring and therefore has a smaller effect on the atmosphere, if released. There have been some reports of refrigerators exploding, if the refrigerant leaks and comes into contact with a spark.

Disposal of discarded refrigerators is regulated, often mandating the removal of doors; children playing hide-and-seek have been asphyxiated while hiding inside discarded refrigerators, particularly older models with latching doors. Since August 2, 1956, under U.S. federal law, refrigerator doors are no longer permitted to lock from the inside. More modern units use a magnetic door gasket which holds the door sealed but can be pushed open from the inside. This gasket was invented by Herman C. Ells Sr.

Types of domestic refrigerators



Domestic refrigerators and freezers for food storage are made in a range of sizes. Among the smallest is a 4 L Peltier refrigerator advertised as being able to hold 6 cans of beer. A large domestic refrigerator stands as tall as a person and may be about 1 m wide with a capacity of 600 L. Some models for small household
Household
The household is "the basic residential unit in which economic production, consumption, inheritance, child rearing, and shelter are organized and carried out"; [the household] "may or may not be synonymous with family"....

s fit under kitchen work surfaces, usually about 86 cm high. Refrigerators may be combined with freezers, either stacked with refrigerator or freezer above, below, or side by side. A refrigerator without a frozen food storage compartment may have a small section just to make ice cubes. Freezers may have drawers to store food in, or they may have no divisions (chest freezers).

Refrigerators and freezers may be free-standing, or built into a kitchen.
  • Compressor refrigerators are by far the most common type; they make a noticeable noise.
  • Absorption refrigerator
    Absorption refrigerator
    An absorption refrigerator is a refrigerator that uses a heat source to provide the energy needed to drive the cooling system...

    s 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
    Thermoelectric cooling
    Thermoelectric cooling uses the Peltier effect to create a heat flux between the junction of two different types of materials. A Peltier cooler, heater, or thermoelectric heat pump is a solid-state active heat pump which transfers heat from one side of the device to the other side against the...

     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 (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 refrigerator
    Thermal mass
    Thermal mass is a concept in building design which describes how the mass of the building provides "inertia" against temperature fluctuations, sometimes known as the thermal flywheel effect...

    s 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 refrigerator
    Absorption refrigerator
    An absorption refrigerator is a refrigerator that uses a heat source to provide the energy needed to drive the cooling system...

    s 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 specialised cooling mechanisms may be used for cooling, but have not been applied to domestic refrigerators.
  • Magnetic refrigerator
    Magnetic refrigeration
    Magnetic refrigeration is a cooling technology based on the magnetocaloric effect. This technique can be used to attain extremely low temperatures , as well as the ranges used in common refrigerators, depending on the design of the system.The effect was first observed by the German physicist Emil...

    s are refrigerators that work on the magnetocaloric 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 which is then converted to heat and cold using compressed helium gas. The heat is discarded and the cold is routed to the refrigerator.

Energy efficiency


In the past, refrigerators consumed more energy than any other home appliance, but in the last twenty years progress has been made to design, manufacture, and encourage the sale of refrigerators with improved energy efficiency.{} In the early 1990s a competition was held among the major manufacturers to encourage energy efficiency.{Feist, et. al. Super Efficient Refrigerators: The Golden Carrot from Concept to Reality. ACEEE. 1994} Current models that are Energy Star
Energy Star
Energy Star is an international standard for energy efficient consumer products originated in the United States of America. It was first created as a United States government program during the early 1990s, but Australia, Canada, Japan, New Zealand, Taiwan and the European Union have also adopted...

 qualified use 50 percent less energy than the average models made in 1974. The most energy-efficient unit made in the US consumes about half a kilowatt-hour per day. But even ordinary units are quite efficient; some smaller units use less than 0.5 kilowatt-hour.
Larger units, especially those with large freezers and icemakers, may use as much as 4 kW·h per day.
The small "mini-fridge", or "bar fridge", is an example of bad design. Because these refrigerators are so small and lacking in large amounts of capacity, when the door is opened a large amount of the cool air escapes, leaving a large amount of warm, moist air for the unit to cool down. This means, if the unit is cycled off when the door is opened, it is likely the unit will start almost as soon as the door is shut.

Among the different styles of refrigerators, top-freezer models are more efficient than bottom-freezer models of the same capacity, which are in turn more efficient than side-freezer models. Models with through-the-door ice units are less efficient than those without. Dr. Tom Chalko in Australia has developed an external thermostat to convert any chest freezer into a chest refrigerator using only about 0.1kWh per day—the amount of energy used by a 100 watt light bulb in one hour. A similar device is manufactured by Johnson Controls. Scientists at Oxford University have reconstructed a refrigerator invented in 1930 by Leó Szilárd and Albert Einstein in their efforts to replace current technologies with energy efficient green technology. The Einstein refrigerator
Einstein refrigerator
The Einstein-Szilard or Einstein refrigerator is an absorption refrigerator which has no moving parts, operates at constant pressure, and requires only a heat source to operate...

 operates without electricity and uses no moving parts or greenhouse gases.

Many refrigerators made in the 1930s and 1940s were far more efficient than most that were made later. This is partly attributable to the addition of new features, such as auto-defrost, that reduced efficiency. Additionally, post World War 2, refrigerator style became more important than efficiency. This was especially true in the 1970s, when side by side models with ice dispensers and water chillers became popular. However, the reduction in efficiency also comes partly from cost cutting (less insulation). Due to the introduction of new energy requirements, refrigerators made today are much more efficient than those made in the 1930s; they consume the same amount of energy while being three times as large.

The efficiency of older refrigerators can be improved by defrosting (if the unit is manual defrost) and cleaning them regularly, replacing old and worn door seals with new ones, adjusting the thermostat to be appropriate to the actual contents (a refrigerator doesn't need to be colder than 4°C if it is storing drinks and non-perishable items only) and also replacing insulation, where applicable. Some sites recommend that you clean the condenser coils every month or so on units that have coils on the rear. It has been proved that this does very little for improving efficiency, however, the unit should be able to "breathe" with adequate spaces around the front, back, sides and above the unit. If the refrigerator uses a fan to keep the condenser cool, then this must be cleaned, at the very least, yearly.

Frost Free refrigerators and/or freezers utilize electric fans to cool the appropriate compartment. This could be referred to as a "Fan Forced" refrigerator, whereas manual defrost units rely on colder air lying at the bottom, versus the warm air at the top to achieve adequate cooling. The air is drawn in through an inlet duct and passed through the evaporator where it is cooled, the air is then circulated through-out the cabinet via a series of ducts and vents. Because the air passing the evaporator is supposedly warm and moist, frost begins to form on the evaporator (especially on a freezer's evaporator). In cheaper and/or older models, a defrost cycle was controlled via a mechanical timer. This timer was set to shut off the compressor and fan and energize a heating element located at the base of the evaporator for up to 30 minutes. This melted any frost or ice build up and allowed the refrigerator to work normally once more. It is believed that frost free units have a lower tolerance for frost, due to their air-conditioner like evaporator coils. Therefore, if a door is left open accidentally (especially the freezer), the defrost system may not remove all frost, in this case, the freezer (or refrigerator) must be defrosted.

If the defrosting system melts all the ice before the timed defrosting period ends, then a small device (called a Defrost Terminator) acts like a thermostat and shuts off the heating element to prevent too large a temperature fluctuation, it also prevents hot blasts of air when the system starts again, should it finish defrosting early. When the 30 minutes or so defrost is completed, the compressor and fan are allowed to cycle back on if necessary.

Single frost free refrigerator units that are frost free generally don't shut off their fans whilst defrosting. This allows consumers to leave food in the main refrigerator compartment uncovered, and also helps keep any vegetables some-what moist. This method also helps reduce energy consumption, because a refrigerator is above freeze point, the warmer than freezing air can be passed through the evaporator to aid the defrosting cycle. The less time the electric heater element is left on, the lower the energy consumption.

Regarding total life-cycle costs, many governments offer incentives to encourage recycling of old refrigerators. One example is the Phoenix refrigerator program launched in Australia. This government incentive picked up old refrigerators, paying their owners for "donating" the refrigerator. The refrigerator was then refurbished, with new door seals, a thorough cleaning and the removal of items, such as the cover that is strapped to the back of many older units. The resulting refrigerators, now over 10% more efficient, were then distributed to low income families.

Effect on lifestyle


The refrigerator allows the modern family to keep food fresh for longer than before. This, along with the modern supermarket, allows most families, without a sizable garden in which to grow vegetables and raise animals, a vastly more varied diet and improved health resulting from improved nutrition. Dairy products, meats, fish, poultry and vegetables can be kept refrigerated in the same space within the kitchen (although raw meat should be kept separate from other foodstuffs for reasons of hygiene
Hygiene
Hygiene refers to the set of practices perceived by a community to be associated with the preservation of health and healthy living. While in modern medical sciences there is a set of standards of hygiene recommended for different situations, what is considered hygienic or not can vary between...

).

The refrigerator lets people eat more salads, fresh fruits and vegetables, without having to own a garden or an orchard. Exotic foodstuffs from far-off countries that have been imported by means of refrigeration can be enjoyed in the home because of domestic refrigeration.

While allowing more healthy foods to be stored for longer times, more refrigerators and freezers are stocked with processed, quick-cook foods that are less healthy. Studies connecting the correlation between frozen (microwaved) foods and obesity have proven that access to easy meals has led to a general decline in overall health.

Freezers allow households to buy food in bulk: it can be eaten at leisure, and bulk purchase saves money
Economies of scale
Economies of scale, in microeconomics, refers to the cost advantages that an enterprise obtains due to expansion. There are factors that cause a producer’s average cost per unit to fall as the scale of output is increased. "Economies of scale" is a long run concept and refers to reductions in unit...

. Ice cream, a popular commodity of the 20th century, could previously only be obtained by traveling long distances to where the product was made fresh, and had to be eaten on the spot. Now it is a common food item. Ice on demand not only adds to the enjoyment of cold drinks, but is useful for first-aid, and for cold packs that can be kept frozen for picnics or in case of emergency.

Temperature zones and ratings


Some refrigerators are now divided into four zones to store different types of food:
(freezer) (meats) (refrigerator) (vegetables)

The capacity of a refrigerator is measured in either litres or cubic feet. Typically the volume of a combined refrigerator-freezer is split to 100 litres (3.53 cubic feet) for the freezer and 140 litres (4.94 cubic feet) for the refrigerator, although these values are highly variable.

Temperature settings for refrigerator and freezer compartments are often given arbitrary numbers by manufacturers (for example, 1 through 9, warmest to coldest), but generally 3 to 5 °C (37.4 to 41 F) is ideal for the refrigerator compartment and -18 °C for the freezer. Some refrigerators are required to be within certain external temperature parameters to run properly. This can be an issue when placing units in an unfinished area such as a garage.

Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

an freezers, and refrigerators with a freezer compartment, have a four star rating system
Star (classification)
Stars are often used as symbols for classification purposes. They are used by reviewers for ranking things such as movies, TV shows, restaurants, and hotels. For example, one to five stars is commonly employed to categorize hotels.-Restaurant ratings:...

 to grade freezers.
  • [∗] : min temperature = -6 °C. Maximum storage time for (pre-frozen) food is 1 week
  • [∗∗] : min temperature = -12 °C. Maximum storage time for (pre-frozen) food is 1 month
  • [∗∗∗] : min temperature = -18 °C. Maximum storage time for (pre-frozen) food is between 3 and 12 months depending on type (meat, vegetables, fish, etc)
  • [∗[∗∗∗] : min temperature = -18 °C. Maximum storage time for pre-frozen or frozen-from-fresh food is between 3 and 12 months


Although both the three and four star ratings specify the same storage times and same minimum temperature of -18°C, only a four star freezer is intended to be used for freezing fresh food, and may include a "fast freeze" function (runs the compressor continually, down to as low as -26°C) to facilitate this. Three (or fewer) stars are used for frozen food compartments which are only suitable for storing frozen food; introducing fresh food into such a compartment is likely to result in unacceptable temperature rises. This difference in categorisation is shown in the design of the 4-star logo, where the "standard" three stars are displayed in a box using "positive" colours, denoting the same normal operation as a 3-star freezer, and the fourth star showing the additional fresh food/fast freeze function is prefixed to the box in "negative" colours or with other distinct formatting.

Most European refrigerators include a moist cold refrigerator section (which does require (automatic) defrosting at irregular intervals) and a (rarely frost free) freezer section.

Recycling


Old refrigerators have been adapted to create low cost passive solar water heating systems.
Also, many refrigerators have been refurbished for low-income families in eastern Australia via the Phoenix refrigerator program (see energy efficiency)

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

See also


  • Absorption refrigerator
    Absorption refrigerator
    An absorption refrigerator is a refrigerator that uses a heat source to provide the energy needed to drive the cooling system...

  • Energy Star
    Energy Star
    Energy Star is an international standard for energy efficient consumer products originated in the United States of America. It was first created as a United States government program during the early 1990s, but Australia, Canada, Japan, New Zealand, Taiwan and the European Union have also adopted...

  • Ice cream maker
    Ice cream maker
    A domestic ice cream maker or ice cream freezer is a machine used to make small quantities of ice cream at home. Ice cream makers may stir the mixture by hand-cranking or with an electric motor, and may chill the ice cream by using a freezing mixture, by pre-cooling the machine in a freezer, or by...

  • Magnetic refrigeration
    Magnetic refrigeration
    Magnetic refrigeration is a cooling technology based on the magnetocaloric effect. This technique can be used to attain extremely low temperatures , as well as the ranges used in common refrigerators, depending on the design of the system.The effect was first observed by the German physicist Emil...

  • Pot-in-pot refrigerator
    Pot-in-pot refrigerator
    The pot-in-pot refrigerator, also known as a Zeer الزير in Arabic, is a refrigeration device which keeps food cool without electricity by using evaporative cooling. A porous outer earthenware pot, lined with wet sand, contains an inner pot within which the food is placed...

  • Refrigerator magnet
    Refrigerator magnet
    A refrigerator magnet is an ornament, often whimsical, attached to a small magnet which is used to post items such as shopping lists or report cards on a refrigerator door, or which simply serves as decoration. Refrigerator magnets come in a wide variety of shapes and sizes, including but not...

  • Star rating
  • Thermoacoustics
    Thermoacoustic refrigeration
    Thermoacoustic engines are thermoacoustic devices which use high-amplitude sound waves to pump heat from one place to another, or conversely use a heat difference to induce high-amplitude sound waves. In general, thermoacoustic engines can be divided into standing wave and travelling wave devices...

  • Thermoelectric cooling
    Thermoelectric cooling
    Thermoelectric cooling uses the Peltier effect to create a heat flux between the junction of two different types of materials. A Peltier cooler, heater, or thermoelectric heat pump is a solid-state active heat pump which transfers heat from one side of the device to the other side against the...

  • Ice famine
    Ice famine
    An ice famine was a scarcity of commercial ice, usually during the hot summer months, common before the widespread use of the refrigerator. It often resulted in the widespread spoilage of food and medicines, and in some instances in death from heat stroke....



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