The general problem of heat and power integration in process networks is complex and to date not fully understood. The subject covers site combined heat and power, on-plant power generation, heat pumps, and refrigeration systems. This paper is the first of a two-part series and explains the concept of “appropriate” heat engine and heat pump placement in process networks based on a fundamental new insight. “Appropriate” placement takes advantage of integration opportunities with the remainder of the process and yields marginal efficiencies far greater than could be achieved through stand-alone heat engines. Conversely, “inappropriate” placement can never offer an advantage over stand-alone systems. Part II describes procedures for preliminary design, involving heat engine, and heat pump equipment selection and performance assessment.