A system using mechanical devices (pumps, fans, photovoltaic cells, etc.) that transfers collected heat to the storage medium or the end-use. Below is a more extensive glossary of terms that you might encounter in energy conscious design discussions. We have found them in Brown. G.Z.: Sun, Wind, and Light - Architectural Design Strategies. New York: John Wiley & Sons, 1985. ISBN: 0-471-895067