The Technology

Absorption chillers provide cooling to buildings by using waste heat. This paradoxical but highly efficient technology is most cost-effective in large facilities with significant heat loads.

Absorption chillers not only use less energy than conventional equipment, they also cool buildings without the use of ozone-depleting chlorofluorocarbons (CFCs). Unlike conventional electric chillers, which use mechanical energy in a vapor compression process to provide refrigeration, absorption chillers primarily use heat energy with limited mechanical energy for pumping.

Chillers can be powered by natural gas, steam, or waste heat. An absorption chiller transfers thermal energy from the heat source to the heat sink through an absorbent fluid and a refrigerant. The absorption chiller accomplishes its refrigerative effect by absorbing and then releasing water vapor into and out of a lithium bromide solution.

The process begins as heat is applied at the generator, with water vapor driven off to a condenser.

The cooled water vapor then passes through an expansion valve where the pressure reduces. The low-pressure water vapor then enters an evaporator, where ambient heat is added from a load and the actual cooling takes place.

The heated, low-pressure vapor returns to the absorber, where it recombines with the lithium bromide and becomes a low-pressure liquid. This low-pressure solution is pumped to a higher pressure and into the generator to repeat the process.

Absorption chiller systems are classified by single- and double-effects, which indicate the number of generators in the given system. The greater the number of stages, the higher the overall efficiency.