The book discusses the thermal distribution principle and nonlinear optimal control for HVAC water systems in large public buildings. Firstly, the models of the main components in HVAC water systems are introduced, serving as the foundation for subsequent nonlinear optimal control. Then, the most unfavorable loop and thermodynamic stability are examined concerning the thermal distribution principle. To enhance control at the most unfavorable loop and system thermodynamic stability, a differential pressure-based optimal control strategy is presented. Furthermore, the book systematically covers the hysteresis and nonlinear characteristics of the HVAC water system, followed by an exploration of global optimization methods and intelligent optimization algorithms through experimental research.