While Nakahara started optimization control of HVAC nearly thirty years ago, due to poor capability of computer hardware, degree of optimization was basically limited to subsystem level. Optimization technologies in HVAC engineering have not made any remarkable advances, henceforth. Recently, however, the control and the data collection system which used open network, high performance micro computer and advanced simulation technology have become available and social demand for energy conservation is stronger as well. Authors overview the state of the art in the present paper.