Preface Fundamentals of Water System Design@ Second Edition is an entry level text for the principles and fundamentals of water@ or hydronic@ HVAC system design and calculations. It uses the ASHRAE Handbook@ and its related chapters on hydronics@ as well as various research projects@ ASHRAE documents@ and articles on hydronics. The text represents the fundamentals of design and is an equally sound footing for work in commissioning@ operation@ and troubleshooting. The manual has been evolving over thirty years under the sponsorship of ASHRAE and is supported by ASHRAE Technical Committee (TC) 6.1@ Hydronic and Steam System Design. For the majority of its history@ this writing effort was lead by Richard (Dick) A. Hegberg. Hydronic systems are a key foundation technology of HVAC system design. Hydronics provides an important tool in the designer??s toolbox of providing effective and efficient HVAC systems to buildings around the world. One can argue exactly when hydronics started to be used for heating buildings; however@ the modern application of hot-water systems may have started in the 1870s in the United States@ and the technology has been refined ever since. Of the many benefits that water plays as a heat transfer medium for heating or cooling@ fundamentally important is the ability to transport a lot of energy in the small area of a pipe (especially when compared to the equivalent size of an air duct). That benefit allowed for the development of central systems@ eliminating the necessity of a local heating production system for each heated zone. The advancement allowed us to exercise individuality in our own building zone comfort control and lead to widespread application of hydronic systems in HVAC. From the early days of gravity circulation hot-water heating systems to the most complex of district energy chilled-water systems that are used today@ the fundamentals presented here can be employed to successfully design the modern hydronic system.