The present paper analyzes the energy dynamics of networked process units. In such systems, the material recycle streams interconnecting the units take on the additional role of energy carriers. In the presence of large energy input and output flows, the process networks considered are shown to exhibit a dynamic behavior with multiple time scales, with the variables in the energy balance evolving over a short time horizon, and the variables in the material balance exhibiting both fast and slow transients. A singular perturbation analysis is employed for the derivation of reduced order models for the fast and slow dynamics, and a controller design framework that rationally accounts for this time scale separation is subsequently proposed. Finally, an illustrative example and numerical simulation results are presented.