The overall objective of this project is to evaluate performance of the Darcy geothermal heat exchange (GHX) system compared to a conventional heating and cooling system at a demonstration site. Specifically, the project objectives are to evaluate whether the Darcy GHX system can deliver increased energy efficiency, reduced electrical grid load, and improved facility self-reliance compared to traditional heating and cooling systems with minimal impact on groundwater flow patterns and temperatures. In addition, the project will evaluate whether Darcy GHX systems are cost-effective, reliable, and scalable for a multi-building or district system at many Department of Defense (DoD) installations. 

The Darcy GHX system utilizes convection-based heat exchange with groundwater to provide energy-efficient building heating and cooling. The key feature of the Darcy GHX system is a heat exchanger positioned in an aquifer. A submersible pump is used to enhance groundwater flow across the heat exchanger to take advantage of the superior heat transfer benefits of flowing groundwater. A heat exchange fluid is pumped through a closed-loop system to transfer heat between the flowing groundwater and a building heating, ventilation, and air conditioning system. Darcy GHX systems can be retrofitted to existing buildings or designed and installed in newly constructed buildings. Each Darcy GHX well is designed to deliver 50-150 tons or more of heating/cooling capacity, making the Darcy GHX system suitable for larger buildings such as commercial and multi-unit residential buildings, and for urban areas or locations where a small footprint is required. 

As compared to air source heat pumps, the Darcy GHX system could deliver two to three times greater energy efficiency and a more consistent energy usage profile, mitigating the challenges of demand peaks. In addition, in climates with strongly cooling-dominated building loads, traditional geothermal systems can heat the subsurface, reducing the long-term efficiency of the geothermal system. The Darcy GHX system, however, is designed to take advantage of the capacity of flowing groundwater to dissipate heat away from the GHX well, sustaining relatively constant subsurface temperatures and long-term system efficiency. 

For this demonstration, building energy use, system maintenance, and groundwater temperature and level data will be collected for periods both before and during the Darcy GHX system operation to evaluate whether the Darcy GHX system performance compared to the building’s existing heating and cooling system. 

Successful demonstration of the Darcy GHX system will provide an energy-efficient and cost-effective heating and cooling solution for DoD buildings. The project will evaluate the viability of the convection-based Darcy GHX system and its reduced footprint for sites without access to large parcels of land, equipment flexibility for different types of building side pairing equipment, and the energy efficiency attributes over the course of time. Using the Darcy GHX system for building heating and cooling may enhance site independence by reducing the reliance on delivered fuels and/or electricity. It is anticipated that Darcy GHX systems will be widely applicable across DoD facilities in many regions of the U.S. as the necessary groundwater flow and aquifer conditions are relatively common in much of the U.S.