Abstract

Absorption chillers and heat pumps exhibit high decarbonization potential in various sectors, but their slow response and complex controllability severely limit their application under dynamic conditions. Hence, this work sets out to deepen the understanding of the dynamic behavior of these systems. A physics-based absorption chiller dynamic model was developed, featuring a novel control volume architecture based on falling film chillers, which attained small errors up to 0.18 K in the outlet temperatures, compared to experimental data. The results focus on the transient response to ramp-type changes in a control variable-the hot water temperature and flow rate-studying the effect of the speed and magnitude of change on the response time and the transient performance loss (TPL), a novel metric representing the accumulated inefficiency product of system inertia. A general quasi-linear behavior in the absorption chiller's dynamic response was observed, in accordance with their well-known steady-state quasi-linear behavior represented by the characteristic equation. This insight inspired ad-hoc linear models representative of the cooling capacity and heat input dynamic responses, providing an analytical dimension to the analysis. As the key finding of this work, the quasi-linear chiller behavior proved the TPL of a transient response to be invariant with respect to the particular trajectory, depending only on the "distance" between the endpoint states, and thus interpretable as the intrinsic cost of changing the system state. Applying the developed tools in a simulated transient operation case, reduced the cooling TPL by 88% at the expense of 95% additional driving heat consumed.