The design of computer rooms and telecommunications facilities is different in fundamental ways from the design of facilities used primarily for human occupancy. ASHRAE has not, until now, published a basic reference text to provide an overview of the special design needs of datacom facilities. As the power density of datacom equipment continues to increase, this need has grown more severe. This book covers basic design considerations for data and communications equipment centers. The book is divided into two parts. Part I, Datacom Facility Basics, includes chapters on datacom design criteria (temperature, temperature rate of change, relative humidity, dew point, and filtration), HVAC load, computer room cooling (including both air and liquid cooling), and air distribution. Part II of the book, Other Considerations, includes chapters on ancillary spaces (battery plants, emergency generator rooms, burn-in rooms and test labs, and spare parts rooms), contamination, acoustical noise emissions, structural and seismic design and testing, fire detection and suppression, commissioning, availability and redundancy, and energy efficiency. This book does not cover electrical or electronic systems design and distribution. The primary changes for this second edition center on the updated thermal envelope and relate to the recommended temperatures at the inlets of the equipment operating in datacom facilities. This book is the third in the ASHRAE Datacom Series, authored by ASHRAE Technical Committee 9.9, Mission Critical Facilities, Technology Spaces and Electronic Equipment. This series provides comprehensive treatment of datacom cooling and related subjects.