Clemson engineers to create model underground energy-storage facility

www.physorg.com
June 10, 2010

With a new twist on an old idea, two Clemson University environmental engineers are developing ways to store "waste" energy underground to cut heating and cooling costs and reduce carbon emissions. Ron Falta and Fred Molz have received a $991,000 grant from the US Department of Defense to create a Subsurface Thermal Energy Storage (STES) system that can be used as a model for energy efficiency. Five military bases are being considered for the pilot project, among them the Marine Corps Recruit Depot at Parris Island and the Marine Corps Air Station in Beaufort, as well as locations in California and Rhode Island.

"This technology has the potential to greatly reduce energy costs and greatly reduce carbon emissions," said Falta, a professor in Clemson's environmental engineering and Earth sciences department. "At the same time, it allows for the integration of renewable energy into the infrastructure of the base, and it provides a clear path for reducing base carbon emissions and carbon footprint."

Using the natural insulating properties of underground sediments to store hot and cold material is an old engineering concept. The new twist is using a conventional heat pump to move heat between buildings and the subsurface: moving heat from the ground to the building in the winter, then heat from the building to the ground in the summer.

The Subsurface Thermal Energy Storage system differs from conventional geothermal heat pump designs in that it takes advantage of waste energy - such as heat produced in power production or low-cost solar heat collectors - to create an artificially hot zone beneath the surface. It then takes advantage of natural winter chill to create an artificially cold subsurface zone. By using the hot water source in the winter and the cold water source in the summer, the geothermal heat-pump system can achieve higher heating and cooling efficiency than a conventional system.

"STES is a technology where low-cost or waste energy, heat or cold, is harvested when it is produced or when it is available, stored in the subsurface using borehole heat exchangers or water wells, and then used when the heat or cold is expensive or difficult to obtain," said Molz, an emeritus professor in the department. "This method of heating and cooling is far more efficient than conventional HVAC systems, and it could be 15 percent to 30 percent more efficient than current geothermal heat pump systems."