Absorption Chillers
From Swikipedia
Introduction
Absorption chillers are thermally driven chillers using a liquid refrigerant / sorbent solution and a heat source to provide cooling.
They provide cooling to buildings by using heat. 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. These 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.
Brief Description
Application of Absorption Chiller:
Absorption systems fit well into cooling, heating, and power (CHP) schemes. When used with a micro-turbine or engine-driven generator, they can take waste heat from these components and use it as power, while producing useful cooling for space conditioning. Absorption chillers can change a building’s thermal and electric profile by shifting cooling from an electric load to a thermal load.
Good applications for absorption chillers have the following characteristics:
o High demand charges
o Coincident need for air conditioning and heating
o Maintenance and service requirements are acceptable to building owner
Types of Absorption Chillers:
Absorption chillers are generally classified as direct- or indirect-fired, and as single, double - or triple effect.
o Single Effect: The single-effect “cycle” refers to the transfer of fluids through the four major components of refrigeration machine - evaporator, absorber, generator and condenser.
o Double Effect: The desire for higher efficiencies in absorption chillers led to the development of double-effect LiBr/H2O systems. The double-effect chiller differs from the single-effect in that there are two condensers and two generators to allow for more refrigerant boil-off from the absorbent solution.
o Triple Effect: The triple-effect cycles are the next logical improvement over the double-effect. Triple-effect absorption chillers are under development, as the next step in the evolution of absorption technology.
Advantages of Absorption Chillers:
o Elimination of the use of CFC and HCFC refrigerants
o Quiet, vibration-free operation
o Lower pressure systems with no large rotating components
o High reliability
o Low maintenance
Limitations of Absorption Chillers:
o Cost is the primary constraint on the widespread adoption of absorption chiller systems
o The low thermal efficiency of single-effect absorption systems has made them non-competitive with readily available free waste heat.
o Absorption systems also require greater pump energy than electric chillers.
o Absorption chillers require larger cooling tower capacity than electric chillers, due to the larger volume of water.
References:
http://www.eere.energy.gov/de/pdfs/thermally_activated_absorption_chillers.pdf
http://www.newbuildings.org/downloads/guidelines/AbsorptionChillerGuideline.pdf
