The objective of this demonstration was to fully maximize the inherent advantages of the geology and hydrogeology accessed by means of Ground Heat Exchanger (GHX) with closed loop systems or via direct ground water use with open-loop systems, which conventional Geothermal Heat Pump (GHP) systems in the U.S. are not designed to achieve. Deliberately engineered Underground Thermal Energy Storage (UTES) systems not only allow for the waste heat of cooling systems and the waste cool of heating systems to be captured, but also allow for the out-of-season capture of the winter’s “cold” or summer’s “heat”, if needed, in cooling-dominated or heating-dominated buildings, respectively.

 Historically, conventional GHP HVAC systems are considered one of the most, if not the most efficient active HVAC systems. Most Department of Defense (DoD) (and non-DoD commercial) facilities in many geographic regions are cooling dominated due to the consistent presence of cooling loads associated with people, lights and equipment (computers, copiers, monitors, etc.). Furthermore, most HVAC systems used in the Southeastern (SE) US (the region where both Environmental Security Technology Certification Program [ESTCP] projects were accomplished), are significantly cooling dominated. Typically, DoD facilities have imbalanced cooling versus heating loads, which in some applications, can have annual cooling loads that are as much as 5-10 times more than the annual heating loads. For a conventional GHP system, this load imbalance, over time, can lead to higher supply water temperatures and cause the operating efficiencies of the water-cooled equipment to decrease. In extreme cases, the supply water temperatures can increase up to the point where the water-cooled equipment can fail/fault due to high refrigerant pressure safeties. HVAC systems with UTES capability do not necessarily have to reject (or extract when heating dominated) heat during peak conditions. In retrospect, since the Borehole Thermal Energy Storage System (BTES) installed at the Marine Corps Logistic Base in Albany Georgia (MCLB) and the Aquifer Thermal Energy Storage (ATES) installed at Ft. Benning Georgia (GA) both are capable of diurnal and seasonal storage, this project would more aptly be named simply Coupling GHPs with UTES.

This demonstration project involved the implementation of high-efficiency GHP systems, coupled with an UTES system, at two locations in the SE U.S. to provide infrastructure with higher energy savings than conventional geothermal systems, but with lower installation cost. The demonstration project at the Marine Corps Logistics Base Albany (MCLBA) coupled GHPs with a form of UTES commonly known within the international community as BTES. The demonstration project at Fort Benning, GA coupled GHPs with a form of UTES known internationally as ATES.

- BTES 

GHP’s were connected to closed loop system comprised of 306 conventional underground grouted vertical boreholes with high-density polyethylene (HDPE) u-bends, but has an active outdoor adiabatic dry cooler. The dry cooler is optimized, from a construction and control/operational perspective, to capture the cooling energy of winter and store this energy in the underground formation for use in the peak summer months. This style of USTES is commonly referred to as a Seasonal Borehole Thermal Energy Storage system or simply “BTES”. 

- ATES 

The ATES system at Fort Benning includes an outdoor adiabatic dry-cooler but utilizes an open loop system of four wells to directly extract/inject the native ground water from/to the local aquifer. The Fort Benning open loop is properly known as a seasonal Aquifer Thermal Energy Storage system or simply “ATES”.

As part of the demonstration project, several quantitative performance objectives were proposed and evaluated as part of the overall performance. All but one of the performance objectives were achieved as part of this demonstration project. Overall, the demonstration project illustrated a successful performance evaluation for the implemented technology and it is hoped it opens two new architectures of HVAC system that can create significant energy and water savings for DoD and others.

The objective of this project was to successfully demonstrate that a high-efficiency GHP System, coupled with an USTES system could provide infrastructure with higher energy savings than conventional geothermal systems, but with lower installation cost and thereby address DoD’s substantial building energy inefficiency issues in a widely deployable and more affordable manner. 

This project demonstrated a high-efficiency GHP System, coupled with an USTES system could provide infrastructure with higher energy savings than conventional geothermal systems, but with lower installation cost and thereby address DoD’s substantial building energy inefficiency issues in a widely deployable and more affordable manner.