Refrigerator
Refrigerators are found in virtually every American home, and vary greatly in terms of size, quality, look, and price. This site will explain the differences in refrigerators, explain their history, how they work, and show you where to purchase.
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Refrigerator - Basics
A refrigerator (often shortened to fridge) is an electrical or gas appliance that uses refrigeration to help preserve food. A domestic refrigerator is present in 99.5% of American homes. It works using phase change heat pumps operating in a refrigeration cycle. An industrial refrigerator is simply a refrigerator used in an industrial setting, usually in a restaurant or supermarket.
They may consist of either a cooling compartment only (a larger refrigerator) or a freezing compartment only (a freezer) or contain both. The dual compartment was introduced commercially by General Electric in 1939. Some refrigerators are now divided into four zones for the storage of different types of food:
-18°C (0°F) (freezer)
0°C (32°F) (meats)
4°C (40°F) (refrigerator)
10°C (50°F) (vegetables)
The capacity of a refrigerator is measured in liters (or cubic feet). Typically the freezer volume is 100 liters (this will vary) and the refrigerator 140 liters.
History of refrigerators
Although ice houses have been used for thousands of years to provide a source of ice in summer, the first common domestic refrigeration was in the form of ice boxes in the latter years of the 19th Century. As the ice melted it was replaced with ice bought from commercial manufacturers.
In 1856, using the principle of vapor compression, Australian James Harrison produced the world's first practical refrigerator. He was commissioned by a brewery to build a machine that cooled beer.
In 1857, the first refrigerated railway car was introduced by the Chicago meatpacking industry, to prevent spoilage during shipping. In 1866, the first refrigerated railway car to carry fruit was built by Parker Earle of Illinois. The car was used to ship strawberries on the Illinois Central Railroad.
The first domestic refrigerator was apparently manufactured in 1913 by Fred W. Wolf Jr. in Chicago, and called the DOMELRE (DOMestic ELectric REfrigerator). It was not commercially successful, that distinction apparently going to the Kelvinator Company. This company was formed in May 1916 as the Electro-Automatic Refrigerating Company by Edmund J. Copeland and an industrialist, Arnold H. Gross. The company was renamed within two months to the Kelvinator Company and produced their first model shortly afterwards. Like most of their modern descendants, this refrigerator cooled using a phase change heat pump.
The first refrigerators were of the "remote" type, essentially an upgrade of an existing ice box with the installation of a cooling unit in it, but the motor, compressor and condenser installed either beside it or in the basement. The first self-contained refrigerators were not manufactured until 1925.
The earliest units used toxic refrigerants, typically ammonia (R-717), sulfur dioxide (R-764), or methyl chloride (R-40) as their refrigerant.
The first refrigerator to see widespread use was the General Electric "Monitor-Top" refrigerator introduced in 1927. The compressor assembly, which produced substantial heat, was placed above the cabinet, and surrounded with a decorative ring. Over 1,000,000 units were produced. This refrigerator used sulfur dioxide refrigerant. Many units are still functional today.
In the early 1920s the industry grew considerably, with some other manufacturers using absorption of ammonia in water instead of liquefying a gas through compression to achieve the phase change. A similar design, the Einstein refrigerator, used butane as a refrigerant and ammonia as a pressure-equalizing fluid. However, these were not very successful, largely because of public prejudice against ammonia as a refrigerant. Today they are used in homes that are not connected to the electric grid, and in recreational vehicles because they can be efficiently powered using a heat source rather than an electric motor.
It was not until 1931 that Dupont produced commercial quantities of R-12, the first refrigerant which was neither toxic nor flammable.
Types of Refrigerators
Freestanding
Counter/cabinet depth: a refrigerator can be approximately 30 inches deep as opposed to approximately 35 inches deep like a normal refrigerator. This allows the unit to be more flush with surrounding cabinets. A counter depth refrigerator tends to come at a steep price premium despite providing less capacity.
Built under: refrigerators and freezers which can be installed under the counter top. Often known as a Bar Fridge it is used in personal bars as a means to cool beverages.
Integrated.
In-Column refrigerators or freezers: these are built into a tall cabinet in your kitchen furniture. The appliance is built into your kitchen so that it looks like a normal cupboard. Getting the right size refrigerator is very important when choosing integrated.
Door situation
Eye level freezer refrigerator (or top mount).
Bottom freezer refrigerator (or bottom mount). The freezer is generally bigger and the refrigerator has two independent motor-compressors.
French door (or trio). Similar to bottom freezer, but the refrigerator (top) section has two doors that swing outward like a kitchen pantry.
Side-by-side. The unit is divided into two tall compartments, with the freezer on the left and the refrigerator on the right.
Wide-by-side. Similar to side-by-side, but the refrigerator compartment is wider at eye level and becomes narrow at the bottom. Allows the convenience of a side-by-side, but able to fit wider items in the refrigerator.
Single door. Originally, most units featured only one door, with the freezer compartment located within the larger refrigerator compartment. Beginning in the early 1960s manufactures began offering units with separate freezer compartments, which gradually took over the market. One-door models, though still manufactured, are now rare in full size. This style is still common with small half-size refrigerators.
Features
Some newer refrigerators may feature:
An LCD suggesting what types of food should be stored at what temperatures and the expiration date of the food stored.
Filter Status Indicator tells you when it's time for a change.
An in-door ice caddie, which relocates the icemaker storage to the freezer door and saves approximately 2 cubic feet (60 L) of usable freezer space. It is also removable, and helps to prevent icemaker clogging. In-door ice caddies are exclusive to side-by-side refrigerators.
A cooling zone in the refrigerator door shelves. Air from the freezer section is diverted to the refrigerator door, helping to keep milk or juice in the door shelf colder.
A power failure warning, alerting the user to the failure, usually by flashing the 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.
Frost-free operation. Over time atmospheric water vapor condenses onto the cooling coils as ice, which can eventually build up into a layer several centimeters thick. This can be removed by emptying the refrigerator and turning it off so that the ice melts. In a refrigerator equipped for frost-free operation, a heater and a thermostat are fitted around the cooling coils. The cooling is periodically switched off (varies between every 6 to 24 hours depending on model) and the heater turned on until the temperature around the coils slightly exceeds the freezing point of water, after which normal cooling is resumed. This melts any ice which has collected around the coils and prevents it from building up.
An increasingly important environmental concern is the disposal of old refrigerators - initially because of the freon coolant damaging the ozone layer, 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 (1,2,2,2-tetrafluoroethane) instead of freon, which has no ozone layer depleting properties.
Disposal of discarded refrigerators is very often strictly regulated by municipalities, by mandating the removal of doors, as many children playing hide-and-seek have been asphyxiated while hiding inside a discarded refrigerator.
Temperature Settings
Temperature settings for refrigerator and freezer compartments are given arbitrary numbers for example (1 through 9, warmest to coldest) by manufacturers, but generally 37 degrees F (3 degrees C) is ideal for the refrigerator compartment and 0 degrees F (-17 degrees C) for the freezer. If you suspect a problem, test the temperatures with a refrigerator or outdoor thermometer.
Parts of a refrigerator
The basic idea behind a refrigerator is very simple: It uses the evaporation of a liquid to absorb heat. You probably know that when you put water on your skin it makes you feel cool. As the water evaporates, it absorbs heat, creating that cool feeling. Rubbing alcohol feels even cooler because it evaporates at a lower temperature. The liquid, or refrigerant, used in a refrigerator evaporates at an extremely low temperature, so it can create freezing temperatures inside the refrigerator. If you place your refrigerator's refrigerant on your skin (definitely NOT a good idea), it will freeze your skin as it evaporates.
There are five basic parts to any refrigerator (or air-conditioning system):
Compressor
Heat-exchanging pipes - serpentine or coiled set of pipes outside the unit
Expansion valve
Heat-exchanging pipes - serpentine or coiled set of pipes inside the unit
Refrigerant - liquid that evaporates inside the refrigerator to create the cold temperatures
Many industrial installations use pure ammonia as the refrigerant. Pure ammonia evaporates at -27 degrees Fahrenheit (-32 degrees Celsius).
Cycles of Refrigeration
The refrigerator in your kitchen uses a cycle that is similar to the one described in the previous section. But in your refrigerator, the cycle is continuous. In the following example, we will assume that the refrigerant being used is pure ammonia, which boils at -27 degrees F. This is what happens to keep the refrigerator cool:
The compressor compresses the ammonia gas. The compressed gas heats up as it is pressurized (orange).
The coils on the back of the refrigerator let the hot ammonia gas dissipate its heat. The ammonia gas condenses into ammonia liquid (dark blue) at high pressure.
The high-pressure ammonia liquid flows through the expansion valve.
You can think of the expansion valve as a small hole. On one side of the hole is high-pressure ammonia liquid. On the other side of the hole is a low-pressure area (because the compressor is sucking gas out of that side).
The liquid ammonia immediately boils and vaporizes (light blue), its temperature dropping to -27 F. This makes the inside of the refrigerator cold.
The cold ammonia gas is sucked up by the compressor, and the cycle repeats.
By the way, if you have ever turned your car off on a hot summer day when you have had the air conditioner running, you may have heard a hissing noise under the hood. That noise is the sound of high-pressure liquid refrigerant flowing through the expansion valve.
Pure ammonia gas is highly toxic to people and would pose a threat if the refrigerator were to leak, so all home refrigerators don't use pure ammonia. You may have heard of refrigerants know as CFCs (chlorofluorocarbons), originally developed by Du Pont in the 1930s as a non-toxic replacement for ammonia. CFC-12 (dichlorodifluoromethane) has about the same boiling point as ammonia. However, CFC-12 is not toxic to humans, so it is safe to use in your kitchen. Many large industrial refrigerators still use ammonia.
In the 1970s, it was discovered that the CFCs then in use are harmful to the ozone layer, so as of the 1990s, all new refrigerators and air conditioners use refrigerants that are less harmful to the ozone layer.
Before You Buy
When you are buying a refrigerator, there are really two price tags. The initial purchase price can be thought of as the down payment. Sometimes, energy efficient models seem to be more expensive than less efficient units. Actually, these energy efficient models can be a better value. Recent design changes include better insulation and more efficient compressors.
The second price tag is the cost to operate the refrigerator over its lifetime. You'll be paying the second price tag on your monthly utility bill for about 15 years. Look to the yellow EnergyGuide label to find how much energy the refrigerator will use annually. Compare the energy use (in kWh) and cost to operate to other models of similar size and configuration. The more energy the refrigerator uses, the more it will cost you to operate it.
When you are comparing two models, be sure to compare both first and second price tags before you buy to figure out the true cost of buying and operating the refrigerator. You may find that although one appliance may cost more to purchase, it could end up costing you less over the lifetime of the unit.
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