This paper presents a systematic methodology for the synthesis of an entire energy system for chemical plants, which explores the interactions between the steam network and the heat recovery networks of process plants. The energy system is designed not only to meet the heating and power demands from an individual chemical process, but also to consider possibilities of energy transfer among holistic sites. In this paper, energy utilization across different plants is studied. Specifically, indirect and direct energy integration strategies are adopted for the design of the whole energy system to maximize the possible integration. With the energy integration strategies for the overall systems, the utility consumption can be reduced and the total annualized cost minimized. Case studies are presented to demonstrate the applicability and significant economic benefits of the proposed model when applied to industrial problems.