The objective of this project is to demonstrate to the Department of Defense (DoD) community at-large that a Direct Chilled Water (DCW) Aquifer Thermal Energy Storage (ATES) system (aka a DCW-ATES system) can be successfully executed under a Utility Energy Service Contract (UESC) to significantly reduce Heating, Ventilation & Air-Conditioning (HVAC) energy and water consumption in a cost-effective manner. Furthermore, ESTCP’s before/after energy metering requirements and comprehensive Final Report will build additional confidence in the UESC-Utility and DoD-customer communities for this ultimate-in-efficiency-version of the underlying overall technology of Underground Thermal Energy Storage (UTES). The most efficient architecture of UTES is DCW-ATES because for warmer portions of the year, when air-side economizers are inadequate, the inherent air-conditioning(A/C) capability of DCW-ATES will be demonstrated to still be able to frequently cool the building without the use of refrigeration compressors. Compressors are the greatest energy consumer in an A/C system and with them off, DCW-ATES system have achieved an 80% reduction in HVAC energy during A/C operations in warm weather.

Technology Description

This project will be focused on a specific form of UTES that directly stores chilled water underground and is known as DCW-ATES. Though virtually unheard of in the United States (US), over 1000 of these systems are in use outside the US providing unprecedented levels of A/C system efficiency and still providing very high heating system (heat pump) efficiencies by also storing warm water underground. “Free” cooling (aka air-side economizers), or the ability to air-condition a building, without the use of compressors, has generally been limited to periods when the outside air was below 50-55F. During these periods, large volumes of outside air, sometimes of questionable air quality, would be introduced to “free” cool the building. With DCW-ATES, outside air and the building’s heating loads will be utilized to extract heat from the ground water and chill it down to 40-48F in late-fall/winter/early-spring to directly make “chilled water” (DCW), which will then be stored in the underground ATES. This chilled water will be extracted at times when the ambient air is typically above 55F and used, until it is exhausted, to “free cool” the building during the warmer months without the use of the refrigeration compressors.


Beyond being the first demonstration of a DCW-ATES system within DoD, this project will also demonstrate to the UESC/ESPC community at-large that it can add more innovative technologies like Direct Chilled Water ATES systems (DCW-ATES) to their portfolio of projects in a repeatable and successful manner. ESTCP’s previous “standard” (non-chill water) ATES system demonstrated under EW-201135 that ATES systems worked and that they can achieve significant (50%) HVAC energy (and water) saving and this DCW-ATES system will exceed the performance of that system and do so within the UESC framework (aka without the use of capital expenditures funded directly by DoD).