Since the publication of the first edition in 1992, the HVAC industry has gone through enormous changes. Simple digital systems have given way to complex systems and the demand for information on how these systems work and how they are best applied has grown rapidly. This text is thoroughly updated and expanded to include coverage of the architecture of digital control systems, distributed intelligence in networked systems, DDC system network, communication protocols, digital controllers, application strategies, and designing and specifying control systems. Illustrations throughout help keep the subject accessible, and hardware, software, and systems applications are described. This second edition contains a new section on BACnet ™, a significant development in DDC. BACnet ™ is an ASHRAE standard adopted in 1996 which mandates that all components of a system, regardless of manufacturer, be able to communicate, thus creating interoperability . The text should be of interest to HVAC engineers; building owners; contractors; and consultants.