This article is part of the author’s personal search for understanding of why general relationships exist between chemical engineering design variables. His interest in hear exchanger energy optimization extends back to work done in support of a course for the AlChE Today Series on "Process Design For Energy Conservation" in 1976, which led to his recognition of the remarkably powerful set of relationships involving the balance between capital and energy, such as the "one-third rule." The generalization of the one-third rule from turbulent energy dissipation, slowly crystallized as a result of conversations with colleagues and rewrites of the chapter on "Process Energy Conservation" in the "Kirk-Othmer Encyclopedia of Technology." He recognizes that this article has too many equations for easy digestion, and suggests that it will be more accessible if the reader approaches it in this sequence : the figures and tables, then the two worked examples, then the text, and finally the equations.