Heating, Cooling, and Storage Technologies
Through research, NREL is exploring geothermal heating, cooling, and storage technologies including heat pumps and thermal energy networks.
Geothermal Heat Pumps
The ground temperature at about 30 feet below the Earth's surface remains a constant 40°F to 70°F in the United States. The relatively constant ground temperature throughout the year provides an excellent mechanism for heating and cooling applications, as excess heat can be transferred underground or vice versa with the Earth's shallow subsurface acting as a heat source or heat sink depending on the season. NREL researchers are analyzing various aspects of geothermal heat pumps, including the potential benefits to the electric grid that would come from incorporating geothermal heat pumps and other geothermal heating and cooling applications into everyday uses.
Geothermal heat pumps, also referred to as ground-source heat pumps or geo-exchange, can reduce energy use, carbon emissions, and peak electricity demand in buildings compared to traditional HVAC systems while satisfying space heating, space cooling, and domestic water heating needs. A GHP system consists of one or more water-source heat pumps, ground heat exchanger(s), circulating pump(s), and systems for air and water distribution. Fluid is circulated through the ground heat exchanger, installed in the relatively shallow subsurface to use the ground as a heat sink or source.
Leveraging high level analysis on heating and cooling demands, especially in residential and commercial buildings, NREL researchers are working to improve the widespread use of sustainable geothermal heat pump technologies for heating and cooling buildings to the benefit of the economy, society, and the environment. NREL capacities in techno-economic analysis, market modeling, and barriers analysis are contributing to the characterization and proliferation of geothermal heat pump technologies.
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Saqib Javed
Thermal Energy Networks Using Geothermal Heat Pumps
Connecting buildings through a thermal energy network (TEN) or a district heating and cooling (DHC) system create economies of scale that allow for the deployment of energy sources that are clean, resilient, and energy and cost efficient. Geothermal DHC systems and TENs typically use geothermal heat pumps to provide renewable and sustainable heating and cooling from a geothermal resource to buildings connected through a network of pipes. Geothermal DHC systems and TENs come in different configurations and designs and offer the potential to integrate with various other energy sources.
NREL is actively engaged in research on different aspects of geothermal TENs and DHC systems, including thermal, hydraulic, and control modelling; techno-economic and environmental analysis; integration of traditional, renewable, and waste energy sources; performance evaluation and optimization strategies; and the potential benefits to the electric grid, among others.
Contact
Saqib Javed
Geothermal Direct Use
Earth's naturally occurring heat exists everywhere beneath the surface, and it has been used for centuries for everything from cooking to space heating. District heating systems for schools, hospitals, and other facilities is one potential effective way of utilizing mediums to low enthalpy resources especially where such facilities are collocated and within reach. Using direct geothermal cooling for data centers and other institutional, commercial, and industrial applications in cold to moderate climates is another potential way of utilizing low enthalpy geothermal resources. Geothermal direct use deployment has huge benefits for the grid in reducing gas emissions and ensuring efficiency in energy utilization.
NREL is exploring the potential in the United States for specific types of resources especially in sedimentary basins and developing new, innovative ways to incorporate this heat into everyday uses across commercial, residential, industrial, and manufacturing sectors. Using our capabilities researchers are quantifying these resources while exploring opportunities for leveraging in other sectors. Repurposing oil and gas wells for producing heat for district heating for schools or commercial area is one such area NREL researchers are focusing on.
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Saqib Javed
Energy Storage
NREL researchers are exploring ways to use the Earth to store energy, including geothermal compressed air energy storage, borehole thermal energy storage, high-temperature storage, and reservoir thermal energy storage. Using national laboratory capabilities and leveraging geothermal technology as a large-scale thermal energy in boreholes and underground reservoirs, researchers are exploring ways to scale up and engineer subsurface heat energy storage, which can offer substantial cost savings compared to other energy storage technologies like batteries and molten salt as they require construction investment. Once identified and developed, geothermal deployment can be flexible over a range of storage hours, making it especially suitable for long-term energy storage.
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Capabilities
NREL's geothermal capabilities run the gamut from analysis to downhole tools and sensors and from reservoir modeling to full-scale field research validation. Learn more about these Geothermal Anywhere capabilities:
NREL is modeling fluid flow and heat transport in geothermal reservoirs to tackle the biggest question in next-generation geothermal: How do we develop geothermal anywhere?
From traditional hydrothermal sites to new reservoir designs such as enhanced geothermal systems and closed-loop advanced geothermal systems, NREL scientists are advancing the science behind geothermal heat exchange. New reservoir designs could significantly reduce upfront project risk and allow for the development of geothermal anywhere in the United States.
Our reservoir modeling team uses modeling tools for 3D static (structural) and dynamic (numerical) simulation, including thermal, hydrological, mechanical, and chemical properties. We engage our high-performance computing system to gain insights into the subsurface from well targeting to reservoir operations and from optimization to design of unconventional geothermal systems.
Publications
Techno-Economic Feasibility of Geothermal Energy Production Using Inactive Oil and Gas Wells for District Heating and Cooling Systems in Tuttle, Oklahoma, Energy Conversion and Management (2024)
An Embedded 3D Fracture Modeling Approach for Simulating Fracture Dominated Fluid Flow and Heat Transfer in Geothermal Reservoirs, Geothermics (2020)
Sedimentary Geothermal Resources in Nevada, Utah, Colorado, and Texas, NREL Technical Report (2020)
Code Modifications For Modeling Chemical Tracers and Embedded Natural Fractures at EGS Collab, Stanford Geothermal Workshop (2019)
Analysis of Geothermal Reservoir and Well Operational Conditions Using Monthly Production Reports From Nevada and California, Transactions (2017)
Slender-Body Theory for Transient Heat Conduction: Theoretical Basis, Numerical Implementation, and Case Studies, Proceedings of the Royal Society A (2015)
NREL works with government, municipal, industry, and university partners to find innovative yet effective ways to apply geothermal resources to meet residential, industrial, and commercial heating and cooling demands while reducing costs and carbon emissions.
NREL analysis including system modeling, techno-economic analysis, life cycle impact assessment, and performance measurements can help organizations meet their sustainability and decarbonization goals through demand-side analysis and management, resource assessment and optimization, storage potential evaluation and planning, and overall design and control strategy improvements.
Publications
Geospatial Characterization of Low-Temperature Heating and Cooling Demand in the United States, 48th Workshop on Geothermal Reservoir Engineering (2023)
Geothermal Deep Direct Use For Turbine Inlet Cooling in East Texas, NREL Technical Report (2020)
Desalination of Impaired Water Using Geothermal Energy, Geothermal Resources Council Transactions (2017)
Performance, Cost, and Financial Parameters of Geothermal District Heating Systems for Market Penetration Modeling Under Various Scenarios, 42nd Workshop on Geothermal Reservoir Engineering (2017)
Update on Geothermal Direct-Use Installations in the United States, 42nd Workshop on Geothermal Reservoir Engineering (2017)
Characterizing U.S. Heat Demand for Potential Application of Geothermal Direct Use, Transactions (2016)
Use of Low-Temperature Geothermal Energy for Desalination in the Western United States, NREL Technical Report (2015)
Industry Applications
NREL scientists work with industry partners to identify ways geothermal can meet their heat demands in economic and environmentally friendly ways. Industry applications use a large amount of energy each year for process heating and facility heating, ventilating, and air conditioning. With geothermal heat available throughout the U.S. and new closed-loop geothermal systems becoming more common, geothermal can help the United States meet its large heating demands reliably and cleanly. Integration with ground-source heat pumps or absorption chillers provides opportunity for cooling as well.
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