This book focuses on the integration of air conditioning and heating as a form of demand response into modern power system operation and planning. It presents an in-depth study on air conditioner aggregation, and examines various models of air conditioner aggregation and corresponding control methods in detail. Moreover, the book offers a comprehensive and systematic treatment of incorporating flexible heating demand into integrated energy systems, making it particularly well suited for readers who are interested in learning about methods and solutions for demand response in smart grids. It offers a valuable resource for researchers, engineers, and graduate students in the fields of electrical and electronic engineering, control engineering, and computer engineering.