The various techniques and systems for heat recovery in central air handling units are presented in detail with examples. Their characteristics, performance and efficiency ratings, as well as their application possibilities and economic viability are evaluated. Regulations, laws, standards, and guidelines that include requirements for heat recovery systems are introduced, including the European Ecodesign Directive for central air handling and climate control units that has been in effect since 2016. In an excursus, the author demonstrates how heat recovery, in conjunction with evaporative cooling, can also be used to generate ecological cooling capacity for air cooling. The book impressively illustrates the economic and ecological significance of heat recovery and shows the substantial contribution that heat recovery can make to the energy transition.