Water-using operations in the process industry have demands for water usually both on water quality and temperature

and the existing mathematical models of heat exchange networks cannot guarantee the energy performance of a water network optimal.In this paper

the effects of non-isothermal merging on energy performance of water allocation networks are analyzed

which include utility consumption

total heat exchange load

and number of heat exchange matches.Three principles are proposed to express the effects of non-isothermal merging on energy performance of water allocation networks.A rule of non-isothermal merging without increasing utility consumption is deduced.And an approach to improve energy performance of water allocation network is presented. A case study is given to demonstrate the method.