Session 1B: Low Temperature/Direct Use

Geothermal district energy systems (DES) with ambient-temperature loops, also known as thermal energy networks, are one option for decarbonizing space heating and cooling loads. Geothermal fifth-generation DES include an “ambient” temperature thermal loop that connects heat pumps at each building with thermal balancing sources such as geothermal borehole fields. Heating and cooling are provided via a water-source heat pump at each end-user. This project seeks to analyze the nationwide potential for ambient-temperature loop districts by creating a new module within the Distributed Geothermal Market Demand Model (dGeo). dGeo is an agent-based modeling tool for distributed geothermal resources; it can investigate potential on a nationwide or statewide scale using geospatial data for all 50 states and thermal demands for existing buildings. This process allows for high-level estimates of technical and economic potential for ambient-temperature loop districts across the United States. A lookup table was created using GHEDesigner to size borehole fields for different thermal loads and ground conditions experienced across the country. A cost and financing structure, along with incentives, were applied. Cost estimates include costs for the distribution network, borehole field installation and operation, and circulation pump operation, while savings are calculated based on energy bills for building owners (agents). This newly developed module can be used for assessing which areas of the country have the highest potential for agent benefits from ambient-temperature loop installation and assess the impact of future cost and price scenarios. Initial results for statewide analysis (for Vermont) and nationwide (for United States) are provided. Future work includes expanding the module to consider mixed residential and commercial districts as well as evaluating multiple cost scenarios.

Geothermal district heating (GDH) in North America has a history dating back to the 1800’s. Although North American GDH systems have been around almost as long as the steam networks of New York, they have not enjoyed large scale commercial expansion. There are several reasons for this. Low enthalpy geothermal systems historically develop around surface manifestations. Early production from these surface manifestations is often a matter of trial and error. Few low enthalpy geothermal systems undergo rigorous exploration, geologic investigation, or wellfield planning prior to drilling. In many cases, this leads to unnecessary contamination of distribution lines in the GDH, decreases in equipment lifetimes, and overall declines in reservoir temperatures and pressures. Despite the lack of deliberate development procedures for most North American GDH systems, they tend to save communities millions of dollars over the lifetime of operation, decrease the carbon footprints of building space conditioning, and provide jobs in sustainable energy. This paper explores the direct uses of geothermal, including GDH, in the Town of Lakeview, Oregon, highlighting early exploration, recent development activity, and recommendations for the future. To other GDH system operators, or those considering their own developments, the case of Lakeview can serve as a lesson, a tale of continuous improvement, and a success story.

District energy geoexchange systems are emerging as a promising solution for efficient, low-carbon heating and cooling in communities. This paper explores the implementation strategies and real-world applications of these systems, focusing on 4th and 5th generation district energy (DE) configurations. We present a comprehensive comparison of these two generations, highlighting their respective benefits and drawbacks in various contexts.

Two case studies are examined in detail: the Etobicoke Civic Centre Precinct, utilizing a 4th generation DE geoexchange system, and the Springwater Single Family Home community, using a 5th generation system. These cases illustrate the practical considerations and decision-making processes involved in selecting and implementing district energy geoexchange solutions.

Our analysis reveals that the choice between 4th and 5th generation systems depends on factors such as load aggregation benefits, operational complexity, space constraints, and end-user preferences. The 4th generation systems excel in scenarios where centralizing thermal energy generation offers significant advantages, while 5th generation systems prove beneficial in distributed, smaller-scale applications.

This research contributes to the growing interest in sustainable community energy systems and provides valuable insights for planners, developers, and policymakers considering district energy geoexchange solutions.

Building heating and cooling took center stage in the European Union’s 2023 Energy Efficiency Directive update, released in September of the same year. There were more than 350 mentions of heat, largely relating to the decarbonization of current combustion processes, including those in individual building systems. One of the pillars of decarbonizing building stock in the plan calls for a near doubling of existing district heating and cooling networks by 2050. The same calls for building stock decarbonization are being heard in North America, though the organization of regulation is much more disparate. Lessons from similar European initiatives suggest that local utility planning for city-scale projects is an effective way to attract investments in sustainable heat. In the context of geoexchange heating and cooling, that using the earth as a modulating mechanism for stable fluid temperatures, 5th generation district heating and cooling systems are useful in every geologic province of the continent. These 5th generation district heating and cooling systems are more frequently referred to as thermal energy networks (TEN) in North America, with the ability to operate at ambient or near-ambient ground temperatures using a spectrum of central through distributed water-source heat pumps. While front end engineering and design of the systems rely on detailed transient simulation, prefeasibility is an important first step in providing sufficient technical and economic data to support the development of networks that may contain a few dozen, or even a few thousand structures. City-scale sustainable heat planning, therefore, requires city-scale simulation capabilities. In this desktop study, a downtown section of Boulder, Colorado serves as an exploratory example of which metrics are important to consider before proceeding with production level engineering on a TEN. Geographic information system simulation tools enable the designer to quickly iterate through optimal pipe routing pathways, bills of materials, electrical ramping requirements of heat pumps, among other technical outputs, creating a method of global sensitivity analysis in the earliest stages of design while respecting the variable entering and exiting fluid temperatures of closed loop borehole arrays.

Established in 1981 and later acquired by Reykjavik Energy in 2005, the Rangárveita District Heating Utility (RDHU) is one of seventeen geothermal district heating systems that Veitur operates. This utility plays a critical role in providing sustainable heating solutions across several communities in Iceland.
RDHU harnesses geothermal energy from four main production wells—LL-04 and LL-06 in Laugaland, boasting temperatures around 96°C, alongside KH-36 and KH-37 in Kaldárholt at approximately 67°C. Additionally, the GN-01 well serves both as a reinjection and occasional production source. This infrastructure supports heating for homes in Ásahreppur, Hella, Hvolsvöllur, Gunnarsholt, and areas along its 35 km main supply pipeline, delivering about 3 million cubic meters of hot water annually. With demand growing by roughly 1.3% each year the RDHU has a challenge to support regional heating needs.
As communities expand, Veitur is tasked with ensuring the scalability of its district heating systems to meet increasing demands. Accurate forecasting and strategic planning for resource expansion and pipeline enhancements are crucial. To this end, Veitur has launched "Resource for the Future" projects for each of its district heating systems, aiming to assess and plan for future needs effectively.
Investment decisions, particularly those concerning research and capacity expansion, are based on comprehensive analyses of potential hot water sources and their integration into the existing network. These long-term plans, spanning over 50 years, are informed by detailed evaluations, including AHP (Analytic Hierarchy Process) analysis. This process helps pinpoint optimal geothermal resource development opportunities and their alignment with current infrastructure, thereby guiding strategic investments.
The project presents a systematic exploration of geothermal resource development options for RDHU, assessed through AHP analysis to ensure their compatibility with existing transport pipelines. The findings serve as a crucial foundation for Veitur's investment strategies, ensuring that the utility's capacity to meet future heating demands remains robust and sustainable.

This study aims to assess the feasibility of utilizing open loop aquifer exchange for the Penn South Neighborhood of Manhattan, New York City. This neighborhood energy system will serve over 6.5 million square feet (60,400m2) of heated and cooled space. Aquifer thermal energy storage (ATES) was originally considered as part of a larger thermal energy network (TEN) to provide high peak load capacities (~44MWth) to meet extremes and to ameliorate saltwater intrusion. However, initial investigation produced serious concern that the shallow unconfined glacial till was not deep enough to avoid mixing oxygenated and anoxic waters. In particular, iron dissolved in anoxic water precipitates into iron oxide in oxygenated water. The Penn South neighborhood subsurface, however, does include favorable aquifers with high transmissivity for a properly designed open loop system. This study aims to build on the work done previously for the ATES model, but focuses on the utilization potential of an open loop geothermal and its associated risks, challenges, and benefits in the heavily populated New York neighborhood.

A 3D geologic model was developed to represent the phreatic glacial aquifer formation, weathered bedrock, and other minor sedimentary formations in the area. The simulations were conducted using TOUGH2 (EOS1) and visualized in PetraSim. Injection and extraction rates and accompanying enthalpies were matched and calculated to a preliminary load profile of the surrounding residential and commercial buildings to ensure that the model was representative and accurate. About 40% of the building energy load is exposed to the system while the remainder comes wastewater energy transfer and from the Hudson River to the west of the service area.

Some of the challenges with developing a geoexchange system of this magnitude include the depth to bedrock in the project area, management of the thermal plume, the presence of nearby dewatering wells, and building foundations that extend through the entirety of the target formation and into the bedrock. The depth to bedrock across the service area varies from about 20m to 92m. Since the thermal plume size is also a function of the screen length or thickness of the target formation, careful planning for well separation is necessary when storing up to 155,000GJ in the subsurface of a dense urban area. While many recharge zones for the phreatic aquifer are cut off because of civil engineering practices, a large volume of water arises from fractured bedrock. Nearby dewatering wells are common for building basement areas, subways, and utility corridors. In some cases, these dewatering wells may limit the potential thermal storage. The results of this study will help to quantify the potential for open aquifer exchange in the Penn South Neighborhood aquifers and inform the feasibility of implementing similar systems in other areas that target phreatic glacial aquifers for geothermal heating and cooling.