Refrigerators are heat movers, which move heat from a low temperature (inside the refrigerator) to a high temperature (outside the refrigerator into the kitchen). Heat movers do not produce any heat, but just move from one location to another. (Note: The animation has no audio.)
The principle of operation of a refrigerator is similar to an air conditioner. It moves the heat energy from inside to outside. There are four basic components in a refrigerator and their functions are as follows:
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Compressed liquid refrigerant passes through an expansion valve that reduces the pressure and, in turn, the temperature. The now cold liquid travels through a series of evaporator coils. As it travels through the coils, the liquid evaporates, drawing the heat energy needed for evaporation from the food in the fridge. This process leaves the food cold as the heat has been moved to the refrigerant.
The evaporated refrigerant passes through a compressor that raises the pressure and temperature of the refrigerant and turns it back into a liquid. The liquid dispenses the heat collected from inside the fridge through the condenser coils and then passes through the expansion valve again to repeat the process.
There are four types of refrigerators: top-freezer (or top-mount), bottom-freezer (or bottom-mount), side-by-side, and built-in (as shown below).
Refrigerators also come in four size categories: small (7 to 9.9 cubic feet), medium (10 to 13.9 cubic feet), large (14 to 19.9 cubic feet), and extra large (20 to 29 cubic feet).
Most of the energy used by a refrigerator is used to pump heat out of the cabinet. A small amount is used to keep the cabinet from sweating, to defrost the refrigerator, and to illuminate the interior.
The efficiency of a refrigerator is based on the energy consumed per year for a given size. The efficiency of a refrigerator is expressed in volume cooled per unit electric energy per day. Volume is measured in cubic feet and electrical energy is measured in kilowatt-hours.
Refrigerator Efficiency = Volume Cooled (ft3) / Unit Electrical Energy per day (KWh)
The energy efficiency of refrigerators and freezers has improved dramatically over the past three decades. For example, the energy bill for a typical new refrigerator with automatic defrost and top-mounted freezer will be about 55 dollars / year, whereas a typical model sold in 1973 will cost nearly 160 dollars / year (almost three times the energy consumption).
The Department of Energy (DOE) standards set maximum allowable annual energy consumption for different sizes and classes of refrigerators. These Federal efficiency standards first took effect in 1993, requiring new refrigerators and freezers to be more efficient than ever before. A new set of stricter standards took effect July 1, 2001.
Refrigerators now come with an EnergyGuide label that tells you in kilowatt-hours (kWh) how much electricity a particular model uses in a year. The smaller the number, the less energy the refrigerator uses and the less it will cost you to operate.
ENERGY STAR qualified refrigerators provide energy savings without sacrificing the features you want. ENERGY STAR–qualified models have
These models also use at least 15% less energy than required by current federal standards, and 40% less energy than the conventional models sold in 2001.
Many ENERGY STAR qualified models include automatic ice-maker and through-the-door ice dispensers. Qualified models are also available with top, bottom, and side-by-side freezers.
When selecting a refrigerator, remember the following:
The improvement in the energy efficiency over the past three decades is due to the: