A vapor absorption chiller machine (VAM) is a machine that produces chilled water using a heat source rather than electrical input as in the more familiar vapor compression cycle. It seems unreasonable that cooling can be achieved with heat, but that is what occurs within an absorption chiller.
Both vapor compression and absorption refrigeration cycles accomplish the removal of heat through the evaporation of a refrigerant at a low pressure and the rejection of heat through the condensation of the refrigerant at a higher pressure.
The basic difference is that an electric chiller employs a mechanical compressor to create the pressure differences necessary to circulate the refrigerant whereas the absorption chillers use heat source and do not use a mechanical compressor.
The differences cause an absorption system to use little to no work input, but energy must be supplied in the form of heat. This makes the system very attractive when there is a cheap source of heat, such as solar heat or waste heat from electricity or heat generation.
Absorption chillers have recently gained widespread acceptance due to their capability of not only integrating with cogeneration systems but also because they can operate with industrial waste heat streams.
What is Absorption?
Comparing the absorption refrigeration cycle with the more familiar vapor compression refrigeration cycle is often an easy way to introduce it. The standard vapor compression refrigeration system is a condenser, evaporator, throttling valve, and a compressor. Figure below is a schematic of the components and flow arrangements for the vapor compression cycle.
Author: A. Bhatia