A finite time thermodynamic model of an absorption chiller was developed. The effects of irreversibilities due to finite rate heat transfer in the heat exchangers are modeled by using the standard UA formulation with the absorber and condenser lumped as one heat exchanger. In order to match experimental data within 20%, the UA of the generator was modeled as a linear function of the heating fluid flow rate. A constant entropy production due to internal processes was included to model reduction in performance at off design conditions. The UA parameters and internal entropy production constant form a set of five fitting parameters with physical meaning. This is fewer parameters than the non-physical curve fit used in the industry standard Energy Plus model. The model was validated within 20% against data sets from two different systems.

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