Geothermal waters, hot enough to provide direct heating, are available in many parts of the world. Some are exploited already but many more are only now being considered, as planners begin to recognize the environmental benefits of this unfamiliar energy resource. The relative economic benefits are more marginal, however, and a successful scheme requires careful design and optimization. The nature of geothermal resources imposes special conditions which may be unfamiliar to many plant engineers. In addition, many different approaches are possible, depending on the characteristics of the...