Refrigerating Machines
principle of a heat pump

Heat pumps and refrigerating machines (for example a refrigerator) are based on the same technological principle – yet with different purposes in mind. With heat pumps heat from the surrounding environment is raised to a useful temperature for heating purposes. With refrigerating machines the same process is used to produce colder temperatures by removing heat. The heat absorption occurs at an evaporator through a freezing agent that evaporates at a lower temperature.

A compressor does the required work of heat transformation from a low to a higher temperature level. It sucks the evaporated freezing agent and compresses it. This compression “raises” the freezing agent to a higher usable temperature level. Then the compressed freezing agent gives off its gained heat to another heat exchanger. If this occurs below the critical temperature of the freezing agent, then it condenses.

If, however, the freezing agent’s operating temperature lies above the critical temperature it will not condense to become liquid again. The freezing agent, under high pressure, is then expanded through a valve. Finally, it is led back to the compressor and the process repeats itself.

Text and illustration: BINE Information Service (BINE Informationsdienst), Subject Information Center Karlsruhe, Germany (Fachinformationszentrum),

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