A system (30), methods, and user-friendly program product (51) to optimize energy recovery for a process or cluster of processes under all possible combinations of given process changes and stream-specific minimum temperature approach values without enumeration, are provided. The systems (30), methods, and program product (51) can include steps/operations to synthesize multiple heat exchanger network designs according to different process variations schemes, analyze the impact of process variations on each heat exchanger network, and identify which design provides a more optimal heat exchanger network design and which process variation scheme represents a more optimal flexibility index.