Dynamic Model for Small-Scale Ammonia-Water Absorption Chiller

Optimization of the performance of absorption systems during transient operations such as start-up and shut-down to minimize lifetime costs is particularly important for small-capacity chillers and heat pumps. Most dynamic models in the literature have analyzed the transient response for a step change in a single parameter, but few have explored entire start-up and shut-down processes and control strategies. An accurate and robust model for simulating the transient behavior of an absorption chiller was developed here. The individual heat exchangers in the absorption system were analyzed using detailed segmental models. In components with significant mass transfer effects, reduced-order models are employed to decrease computational costs while also maintaining accurate system responses. System parameters such as heat exchanger size, solution flow rates, coupling fluid temperatures and flow rates used in the model are representative of a practical absorption chiller under development by the authors. This analysis can be used to minimize start-up times and also enhance steady state performance. The model can also be used for devising and testing control strategies in commercial applications