EGEE 401
Energy in a Changing World

Refrigeration Cycle

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Air Conditioning and Heat Pumps

Air conditioners and heat pumps use a series of energy transformations to convert electricity to thermal energy, and none of them involve combustion! At the heart of these systems is a multi-step transformation process called the "refrigeration cycle" that transforms motion energy into thermal energy (heat).

Essentially, in the refrigeration cycle, a working fluid (refrigerant) moves through a series of stages where it goes from gas to liquid and back to gas. A compressor mechanically squeezes the gas until it is a hot, high pressure gas. From there, the gas goes to a condenser where it cools down (releasing heat to the surrounding air) until it becomes a liquid, still under high pressure. In the final stage, the liquid goes to an evaporator where the pressure drops and the liquid evaporates, becoming a gas again. When the liquid evaporates, it pulls heat in from the surrounding air.

Reading Assignment

To better understand, read through "How an Air Conditioner Works" and "What a Ton of Cooling Is" from the American Society of Heating, Refrigerating and Air-Conditioning Engineers.

Air conditioners and heat pumps use electricity to drive the compressor, fans, and air handling units.

According to the EIA, in 2014 about 13% of the electricity used in U.S. homes was used for space cooling. (We'll talk a lot more about electricity demand and consumption later in the course, but know for now that the multi-step refrigeration cycle is the transformation process that is at the heart of a significant portion of energy consumption in our country.)