Dynamic model for a small-capacity ammonia-water absorption chiller

Optimization of the performance of absorption systems during such transient operations as start-up and shut-down to minimize lifetime costs is particularly important for small-capacity chillers and heat pumps. Dynamic models in the literature have been used to study responses to step changes in single parameters, but more complex transient processes, such as system start-up, have not been studied in detail. A robust system-level model for simulating the transient behavior of an absorption chiller was developed here. Individual heat and mass exchangers were modeled using detailed segmental models. System parameters used in the model were representative of a 1-RT (3.5-kW cooling) absorption chiller currently under development. Representative simulations were performed for the full "cold start-up" process and for system responses to step changes in the desorber coupling-fluid temperature and valve settings. Results from this analysis can be used to optimize start-up and steady-state performances.