2. Fundamentals of Absorption Heating Technologies

To improve the primary energy efficiencies of conventional heating systems, a cascade energy utilization principle is summarized for high-efficiency low-temperature heating systems. Absorption cycles are perfect examples of the cascade energy principle and are great options for energy-saving and emission reduction, owing to the exceptional advantages in the utilization of renewable energy and waste heat. Depending on the change in heat quantity or quality, the absorption heating technologies are classified into four main categories: heat increasing, heat shifting, temperature upgrading, and temperature adapting. The principles of various absorption heating technologies are introduced, the general characteristics of absorption working fluids are presented, the properties of the working fluids suitable for different applications are explained in detail, and the modeling methods of the absorption heating cycles are introduced, including the ideal equivalent model and the actual thermodynamic model. This chapter presents the fundamental aspects necessary to facilitate the understanding, design, analysis, and optimization of absorption heating technologies.