Absorption Chillers
Absorption chillers differ from mechanical vapor compression chillers in that they utilize a thermal or chemical process to produce the refrigeration effect necessary to provide chilled water. There is no mechanical compression of the refrigerant taking place within the machine as occurs within more traditional vapor compression type chillers (centrifugal, screw, reciprocating, scroll). Most commercial absorption chillers utilize lithium bromide (a salt) and water as the fluid pair; lithium bromide being the absorbent, water being the refrigerant. In order to produce the refrigeration effect necessary to make, for example, 44F chilled water, the shellside of the machine must be maintained in a deep vacuum to allow the refrigerant (water) to boil at approximately 40F. The lithium bromide solution absorbs the vaporized refrigerant, diluting it before it is pumped to the generator section of the machine where heat is added to reconcentrate the dilute solution. The water vapor boiled off in the generator is then condensed, returning to the evaporator as liquid. The reconcentrated lithium bromide returns to the absorber section as strong solution to begin the cycle again.