Liquid Gold: Energy Savings Using Ground Source Heat Pumps
ESTCP is supporting two promising ground source heat pump technology demonstrations. While both projects feature conventional Ground Source Heat Pumps (GSHP), these demonstrations are centered around innovative approaches to obtain even better efficiencies than those found in most current GSHP systems.
The Subsurface Thermal Energy Storage (STES) system ( EW-201013) has been in operation now for nearly two years at the Marine Corps Air Station (MCAS) in Beaufort, South Carolina. This project, led by Dr. Ron Falta, is focused on the retrofit market for existing GSHP systems experiencing rising temperatures of the well field. As a result of the cooling-dominant conditions found at MCAS Beaufort and the rejection of summer heat into existing geothermal wells, well field temperatures have steadily been increasing over time, reducing the efficiency of the ground as a thermal exchange medium. The STES combines three 96-ton dry-fluid coolers equipped with variable speed fan drives and a traditional ground source heat pump system. The project is demonstrating that the problem of excessive summertime temperatures in the geothermal heat pump ground loop can be remedied by wintertime cooling of the loop. The cooler ground offers a greater temperature difference to serve as a heat exchanger in the summer, resulting in better operating efficiencies. Results are encouraging with summer working fluid loop temperatures dropping by 8 degrees compared to conditions before the dry fluid coolers went into operation. Operation of the coolers at low fan speeds during cold periods results in heat rejection with extremely high efficiency (Energy Efficiency Ratio of >1000 MBTUh/kW).
Another GSHP demonstration ( EW-201135), led by Mr. Chuck Hammock, introduces a new well field configuration to the United States Department of Defense. The Aquifer Thermal Energy Storage (ATES) system, which has been broadly adopted in Europe, will provide heating and cooling for a large headquarters building at Fort Benning, Georgia. This open loop system will use the extracted and injected aquifer water itself delivered into the underground unconsolidated geology to store “cold” thermal energy until it is needed for cooling the building. When the building is rejecting heat, thermal mass is transferred to another well field located at a distance from the “cool field,” to store a heated thermal mass of water. This heated thermal subsurface mass can then act as an efficient heating mechanism for the building in the winter. The ESTCP ATES project at Fort Benning will come online later this year.