July 28 2008

What is an Absorption Chiller?

An absorption chiller, also known as an absorption refrigerator, is a cooling system that uses a heat source, in lieu of electricity and a compressor, to drive the device. The systems are commonly used where excess heat is available and are considered a type of heat recovery device. Trigeneration, production of electricity, hot water, and air conditioning, is also possible because of the design of the system and the ease of which it can be integrated into other building systems. Absorption chillers use no moving parts and are powered by heat alone.


Absorption chillers use the process of evaporation, instead of Charles' Law (as in the case of compressor driven systems), to generate coolth. The process uses a heat source, a tubing and container system, three substances (ammonia, hydrogen gas, and water) and goes something like this (described below is a 'small ammonia' refrigeration cycle - for reference):

  • First - In the Evaporator, liquefied anhydrous (containing no water) ammonia enters a chamber filled with gaseous hydrogen. Hydrogen takes up space so the rest of the system stays pressurized, but per Dalton's Law the ammonia acts as though the pressure was decreased, and begins to boil. As the ammonia boils it absorbs heat and produces the coolth required by the chiller.
  • Second - The Absorber mixes water and the hydrogen/ammonia gases and the ammonia condenses into the water (hydrogen and water do not mix). Once the mixture reaches the bottom of the cascade of tubes the ammonia and water are thoroughly mixed and the hydrogen is free to circulate back to the evaporator .
  • Third - The Generator separates the water and ammonia by using the heat source to boil out the ammonia! Ammonia gas/water bubbles are generated and a Separator removes the water bubble from the gas it contains.
  • Fourth - A Condenser, or heat sink, removes excess heat from the system and brings the ammonia back down to room temperature.

Absorption Chiller Diagram_Image 01

Above is a reference diagram to help explain the process:

For more information please visit the original Wikipedia article.

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