Advanced Exergy Analysis for a Solar Double Stage Absorption Chiller

Solar driven absorption chiller technology as an alternative mechanism for cooling has been the focus of tremendous recent interest due to its potential advantages for energy conservation and the environment benefits. However, the comparatively lower coefficient of performance (COP) of these systems compared to the COP of the electric chillers has prevented more widespread applications.

In this dissertation, a novel comparison between an electric and an absorption chiller will be presented (Chapter 3), including a method for calculating the true solar energy requirement for fossil fuel (coal) formation. The same comparison is then extended to the exergy domain. Compared to an electric chiller, in order to provide the same amount of cooling, a solar driven absorption chiller actually consumes a much smaller amount of both solar energy and exergy.

Beyond demonstrating this lower level of actual energy/exergy consumption, it is still important to increase the efficiency of the solar chiller system. Therefore, a detailed exergy destruction analysis (Chapter 4 and 5) is performed in this dissertation, both for the solar collector, which includes pumping exergy loss, and for a two-stage lithium bromide (LiBr)-water absorption chiller. These analyses allow for a better understanding of the exergy destruction due to a component’s own inefficiency and/or due to the remaining components’ inefficiencies. Given the limits of current technology, the results show that the COP of a two-stage LiBr-water absorption chiller can be improved from 1.1 to 1.38, a 25% efficiency increase, by recovering the avoidable exergy destruction.

Finally, based on the contributions described above and the conclusions that can be drawn from them, a range of potential future work is presented. Other comparative systems are discussed, and the challenges in properly assessing the performance of those systems are described.