From the process design, demand for utilities can be estimated. The utility system is then designed with respect to the process design. Energy-integrated process design can be introduced at this stage to seek the design that requires the minimum energy, and the corresponding levels at which the utility should enter the process can also be determined. The interaction between process design and the utility system is a further step of energy integration. This step is usually considered after the process design is energy-integrated and targets for minimum hot and cold utilities identified. When hot and cold utilities are specified, it is possible to deal with these utilities as normal process streams to be presented on a grid diagram with the rest of the process streams. The objective of this simultaneous approach for the interaction between utilities and process design is to assign the most efficient way for the utility to be introduced to the process. Consequently, the synthesis of the heat-exchanger network design should become more effective, thereby resulting in a reduced demand for utility import.