This paper describes the new applications of simulated annealing (SA) algorithm to three different domains: (1) design and modification of district heating pipe-networks, (2) sizing of the branch based CMOS (Complementary Metal-Oxide-Semiconductor) digital circuits, and (3) design of finite wordlength, parallel-structured filter banks. In each application, the appropriate cost function is described and justified. The modifications of the basic SA algorithm are introduced to adapt to each studied problem. Results show that the SA algorithm is general and gives satisfactory results in difficult optimization environment.