Geothermal energy is the natural heat that is stored deep underground (about 1,500 feet down, in the case of the wells at Radcliffe). While the seasons change above ground in Cambridge, the temperature at this depth remains between 47 and 57 degrees Fahrenheit.

In winter, the energy from the rocks can be used as a source of heat for campus buildings, as water from deep wells brings warmth up to heat pumps at the surface.

In summer, the reverse takes place; the wells act as a heat sink, cooling the buildings.

Geothermal heating and cooling systems are environmentally friendly because they reduce the demand for fossil fuels.

Harvard has 12 geothermal wells on its Cambridge campus:

• 2 at 46 Blackstone St.
• 3 at 90 Mt. Auburn St.
• 2 for Radcliffe Gymnasium
• 5 for Byerly Hall