Underground Thermal Energy Storage (UTES) as a DoD facilities UESC Energy Conservation Measure
Christopher Hood | Gulf Power Company
The objective of this demonstration is to engineer, construct and extensively document a Department of Defense (DoD) Underground Thermal Energy Storage (UTES) system installation, funded via a Utility Energy Service Contract (UESC) contracting vehicle. Furthermore, through the extensive documentation, and before/after energy metering requirements of an Environmental Security Technology Certification Program (ESTCP) Demonstration Project, this project will build confidence in the underlying UTES technology, both in its Aquifer Thermal Energy Storage (ATES) configuration, and its closed-loop/borehole (BTES) counterpart configuration.
ATES is the higher performance version of “open loop” Geothermal Heat Pump (GHP) heating, ventilation, and air conditioning (HVAC) systems because it is “reversible”, as all wells are capable of operating as either supply or injection wells. Specifically, in the colder evenings or seasons (when the building in the heating mode and/or the ambient air is colder than the groundwater in the “warm wells”), water is extracted from the warm wells, where it is then used as the source of the buildings heating energy and, excess waste heat in the warm well is rejected to atmosphere (i.e. the groundwater is “chilled” for use in the cooling season). Conversely, in the warmer months, groundwater is extracted from the “cold wells” and used to efficiently cool the building while simultaneously capturing the buildings waste heat for use in the winter. The aquifer itself, which is nearly stationary, serves as the underground thermal storage vessel, retaining 80% or more of its acquired heat or “cold” for use by the building.
From an energy prospective, ATES will reduce the building’s HVAC energy consumption, conservatively speaking, by at least 30% vs. the existing HVAC system (under EW-201135, ATES savings exceeded 52%). It will also eliminate on-site carbon emissions of any natural gas equipped system as the building will now resiliently source its heating energy from its own inside-the-fence waste heat and the geology. Under the energy-water nexus perspective, UTES can use adiabatic dry-coolers (as was done under EW-201135) to reduce building HVAC water consumption by 80-100% or, via traditional cooling towers, have lower first cost and lower HVAC kwh usage than the former. ATES will conservatively achieve at least 10-20% reduction in first cost vs. conventional full closed-loop geothermal. This project will increase the resiliency and energy security of hurricane-vulnerable Hurlburt Field’s HVAC systems by placing the primary heating and cooling energy sources, pumps and storage “tanks” deep underground where they are immune to wind, flying debris and storm surge. From an ESTCP prospective, with EW-201135 only having demonstrated ATES at a small (35 ton) scale, this project will give DoD stakeholders a highly documented larger scale (in excess of 100 tons) ATES project that will give them confidence to execute this technology through a wide variety of Contracting Vehicles. With the demonstration of the majority of this physical UTES project being funded directly by the UESC contract vehicle, due to its extensive ESTCP-class documentation and tools (that will be delivered alongside the physical ATES system), UESC financiers will then have the confidence to embrace this ESTCP, now twice-demonstrated, technology. The toolkit and measured results that this project delivers, will de-risk the use of UTES to a comfort level needed to be widely deployed within DoD and beyond.