The design of energy efficient water utilization systems becomes a recent research direction. However

even for utility targeting

the current models involve many variables and constraints and it takes much time to solve the problem. Furthermore

the resulting utility target relies on the assumption ofΔTmin=0℃

for treating both direct and indirect heat transfer in one transshipment model. This assumption may lead to ΔTmin violations in the following HEN construction. A new kind of NLP model for utility targeting underΔTmin=0℃ is presented which can reduce the number of variables greatly. Moreover

an improved design approach considering the specifiedΔTmin is generated. This approach

which treats the direct and indirect heat transfer separately

provides the information to construct the water utilization system as well as the corresponding heat exchanger network without anyΔTmin violation.