What is an Absorption Chiller?

Absorption chillers are not super easy or straightforward to understand.  Carrier has a great explanation on one of their product pages here:

“The refrigeration cycle for a conventional vapor compression chiller and an absorption chiller are similar in that both produce chilled water via the evaporation and condensation of a refrigerant at different pressures within the machine. However, a conventional chiller uses a mechanical means to compress and transport the refrigerant vapor to the condenser, while an absorption chiller depends on a thermo-chemical process involving lithium bromide and water to establish the pressure differential in lieu of mechanical compression. While most vapor compression chillers utilize electricity as its energy source to operate the machine, absorption chillers use heat, typically in the form of steam, hot water or through the direct combustion of natural gas.”

Because absorption chillers use waste heat as the driver for the process, they use significantly less electricity than conventional chillers.

When to use an Absorption Chiller

  1. Consider using an absorption chiller when your electricity costs are high, but your fuel costs are low.  This differential usually needs to be pretty large, as we’ll show in our example at the end.
  2. Consider using an absorption chiller when you have adequate low grade waste steam or hot water available—especially during the cooling season.  The key word here is “waste” heat.  If you’re producing more steam than you would otherwise use just for the purpose of supplying the chiller, it’s not waste steam.  You’re paying for the fuel to make it. Note that we have seen people fool themselves or be bamboozled by vendors because they did not understand this very key difference.
  3. Consider using an absorption chiller if you have adequate capacity on your low pressure heating systems to produce excess heat during the cooling season.   Make sure that items 1 or 2 also apply.


  1. The process can use either low grade steam or hot water heat to drive the absorption process.
  2. Absorption chillers have minimal moving parts. This means that they make less noise and have fewer vibrations than mechanical chillers.
  3. Absorption chillers typically only use 2 – 9% of the electricity that is usually required for mechanical chillers.  This means that facilities can avoid peak demand charges and high time-of-use electricity rates (if they are on that type of electric rate schedule).


  1. Absorption chillers have low efficiencies compared to mechanical chillers.  Single effect chillers, which tend to use lower-temperature heat, are less efficient than double-effect chillers, but double-effect chillers usually require steam, not hot water.
  2. It can be very difficult to cost effectively install new equipment, depending on the existing utility rates and estimated energy savings.
  3. Most facility staff and local equipment servicers are not as familiar with the maintenance for absorption chillers as they are with mechanical chillers.  We’ve heard more than one facility manager gripe about how they just “couldn’t get the thing to run right” and eventually gave up and started running the old mechanical chillers again.  You may need to rely on a maintenance contract with a big-name chiller manufacturer to regularly maintain your equipment.
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