Nonlinear Model Predictive Control (NMPC) of a Heat-Exchanger Network (HEN) is studied. For this purpose, an optimal retrofit design of the HEN is; accomplished, and thus, bypasses as control variables are placed in order to satisfy steady-state hard/soft target-temperature constraints. The NMPC scheme, in which the nonlinear distributed-parameter HEN model is salved sequentially by referring to an algebraic steady-state-optimization model, satisfies the temporal and steady-state hard/soft constraints imposed on the target temperatures of the retrofit HEN.