Publisher Summary This chapter discusses the design of an earth tube heat exchanger system for green houses. Greenhouses are primarily built to increase the air and plant temperatures, due to the so called greenhouse effect. Under certain circumstances, however, optimal plant production requires the greenhouse to be cooled. An earth tube heat exchanger-storage system is designed and installed in a polyethylene clad double wall greenhouse, to reduce under Western European summer conditions (the inside air temperature to 14–17°C). The thermal mass of the soil was used as a heat buffer. The system consisted of nonperforated corrugated plastic drainage pipes, 12 m in length and 20 cm in diameter, buried at a depth of 2 m underneath the greenhouse. Groups of five pipes are gathered in a collector equipped with a fan. In this way, the air can be circulated internally in the greenhouse—pipes system. The system allows one to transfer excessive heat from the greenhouse air to the soil during hot summer days and to protect the greenhouse plants from freezing during winter.