Carnegie Mellon University Website Home Page

Steam Driven Absorption Chiller

Absorption chillers are key components in a building cooling, heating, and power, BCHP, system to cool space in buildings. They generate chilled water to be used to provide a portion of a building's space cooling needs.  Conventional refrigeration chiller units use electricity to drive the water cooling. Absorption chillers are instead driven by thermal energy.

The source of the thermal energy may be heat recovered from various sources, including power generation equipment and solar receiving devices.  The combination of heat recovery equipment and heat driven absorption chillers provides significantly increased overall energy efficiency. Most of today’s heating and cooling technologies for buildings, however, are not designed to make use of rejected heat.

Overall building energy efficiency gains result from:

  • Waste heat recovery
  • Replacement of inefficient electrically powered chillers
  • Reduction of peak summer electrical requirements for room air conditioning.


The objective of the present project is to develop methods for the effective specification and evaluation of steam-driven absorption chiller components of overall BCHP systems that reduce energy consumption, decrease operational costs, and improve environmental benefits in residential and light commercial buildings. The developed methods would also provide the basis for optimizing the operational performance of installed absorption chiller systems.


In this project a microscale,,16 kW or 4.5 refrigeration tons, steam driven chiller was installed and integrated with the IWESS chilled water system that is used to provide a portion of the space cooling for the work area via a system of mullions around the area's periphery.  The selected chiller runs on the water-LiBr, lithium bromide, refrigeration cycle, and was provided by the Broad Air Conditioning Company.

The cycle is similar to a conventional refrigeration cycle, the refrigerant being water/steam.  In the condenser of this cycle waste heat is rejected to a separate cooling water stream.  After the expansion valve, a spray nozzle system,  in the evaporator a separate chilled water stream is cooled.  In the absorption cycle, the refrigerant “compressor” function is provided by an absorption solution system.  In it, the steam refrigeration fluid is absorbed in a concentrated LiBr-water solution.  Then the now dilute solution is delivered to a heat driven regenerator, to provide both the concentrated solution and the water for the refrigerant cycle.  The actual components and conditions required to achieve this simplified cycle description can be seen in a following, Flow Diagrams, section.

Peripheral systems have also been installed for characterization and testing of the absorber under more controlled conditions, independent of the building steam supply and building chilled water demand, when desired.  These include a steam boiler and a heat exchanger where building hot water heats the chilled water for return.  There is also a web based data acquisition and control system, integrated with the equipment of other projects.  Additional instrumentation were installed with both the chiller system and the overall system.

Installation, initial testing, as well as mathematical modeling for this chiller system were performed under an initial PhD program by Hongxi Yin. 

Additional information can be found in the thesis of Hongxi Yin "An Absorption Chiller in a Micro BCHP Application: Model based Design and Performance Analysis" (pdf) (Appendices 1A, 2A, 2B, 3A, 4A)


Hongxi Yin – PhD 2006.
Dennis Bachovchin
– Visiting Researcher