First in the Sustainability Series, the book “Understanding Geothermal Systems” is a comprehensive study and resource manual that serves as a best-practices guide for the design, installation, and maintenance of geothermal systems. The text, written by Jeff Persons, CM, covers geothermal systems and controls from their widespread introduction to the U.S. market in the early 1970s to the multi-stage ultra high-efficiency systems of today. Study topics include open-loop and closed-loop applications, subsurface geology, loop design, water chemistry, antifreeze solutions, system installation, and controls. Emphasis is placed on identifying common installation and service mistakes, and on learning from those mistakes.