Session 6C: Low-Temperature/Direct Use

Air source heat pumps (ASHPs) and ground source heat pumps (GSHPs) are the two most common types of electric-driven heat pumps in the marketplace to replace fossil fuel-based heating systems. However, the capacity and efficiency of ASHPs depend on the ambient air conditions. Therefore, ASHPs usually are equipped with electric resistance heaters to provide supplemental heating when the ambient temperature is low, and the heating demand is high. The electric resistance heaters could result in high power draws when they are turned on. On the other hand, due to the relatively steady temperature of the ground, GSHPs are more energy efficient than ASHP when providing space heating and cooling to the buildings. However, the adoption of GSHP is hindered by its high initial cost, mostly due to the cost of drilling boreholes for installing ground heat exchangers (GHE). To solve the above issues, our study integrates the performance and cost of a dual-source heat pump (DSHP). The DSHP will use ambient air when its temperature is favorable for the efficient operation of the heat pump. When the ambient temperature is too hot or too cold, the ground source will be utilized to retain the high-efficiency operation of the heat pump. Because the cumulative thermal load of the GHE is shared by the ambient air, the size of the GHE could be smaller than the conventional GSHPs. The study will model the DSHP and simulate its performance in providing heating and cooling for a typical single-family home in regions with hot, mild, or cold climates. In addition, the required GHE size of the DSHP system will be determined through annual simulations and compared with that of conventional GSHPs.

Geothermal networks, defined as networked ground-source heat pump systems, are a clean energy alternative to fossil fuels for heating and cooling buildings, and a scalable solution with the potential to decarbonize entire neighborhoods. The individual components used in these networks are well developed technologies, such as pipes, pumps, and geothermal heat pumps. Nevertheless, there is a knowledge gap regarding how to optimize design parameters for performance and costs for the entire system, to account for region-specific conditions and localized heating and cooling needs for the buildings within the network. Additionally, there is a current lack of standardized methods for comparing these systems.

This study introduces a systematic and quantitative approach to comparing geothermal networks and provides the first open-source database where the datasets can be accessed and analyzed. In the US, geothermal networks have been most commonly adopted in university campuses. Recently, geothermal networks gained widespread attention from gas utility companies, cities, and states, as a strategy to reach net-zero emissions goals. Massachusetts is one of the leaders in this space, with five approved demonstration projects, each at different stages. In order to facilitate the optimized adoption of these systems, it is necessary to compare them and apply lessons from existing installations to those in earlier feasibility or planning stages.

This paper selects and examines key parameters to be systematically measured and recorded before and after the installation of geothermal networks, allowing for a quantitative comparison of these systems, as well as optimization of future ones. These recorded parameters fall into three categories: thermal resources (borefields, boreholes, etc.), distribution (main pipe system), and end-users (buildings, weatherization, etc.). This categorization of parameters, paired with cost data, will allow for fair comparison of geothermal networks with other heating systems. The creation of this open-access database for geothermal networks will therefore inform and facilitate the development of these projects, enabling decarbonization of buildings on a wider scale.

Although geothermal technologies can provide stable, dispatchable, non-intermittent energy, it is often difficult to define them for the public and decision-makers. Even within the scope of district-scale geothermal technologies, there are multiple naming systems which are not clearly linked to the specific designs. In order to scale the provision of the different types of geothermal energy, technically accurate, clear, and standardized terminology needs to be adopted. This study proposes a taxonomy for geothermal energy networks, with a specific focus on thermal energy networks and geothermal networks, including different configurations of utility-scale heat pump deployments. We introduce a taxonomy rubric that connects geothermal network design choices to expected system outcomes. The proposed nomenclature is the product of extensive interviews and stakeholder engagement, with members of the geothermal community, as well as academic, industry, advocacy, workforce, customer, and environmental justice groups. As this industry grows, the link between technology components, system design, performance, and terminology needs to be made clear. State and federal regulatory agencies in charge of permitting and cost-benefit analysis of geothermal network projects can benefit from using this proposed taxonomy rubric as they develop a regulatory framework that supports these systems. This taxonomy framework will also be beneficial to the broader geothermal industry as it approaches the challenge of scaling up to meet city and state decarbonization goals.

Fuel based end-uses for residential, commercial, and industrial consumers require a technology change to achieve economy-wide decarbonization. Space heating accounts for 42% of residential and 32% of commercial energy demand, much of which is currently met through carbon emitting fuels. Industrial energy use is heavily fuel based with electricity currently representing 13% of energy demand. Geothermal heat pumps (GHPs) and geothermal direct use, can eliminate the need for CO2 emitting and simultaneously allow for more efficient electrification of end uses. Past work has assessed the impact on total energy costs and generation investments but did not identify specific grid services benefited. Energy usage in residential and commercial structures was assessed by leveraging data from ComStock and ResStock models. These models utilize housing attributes, occupancy patterns, weather data, and sophisticated energy simulations to generate hourly load profiles for individual buildings identified by unique IDs associated with their locations. Industrial sector energy use was evaluated using information from the Manufacturing Energy Consumption Survey (MECS) as well as plant utilization data from the US Census to estimate hourly plant operations. The change in end-use demand for electricity, natural gas, and other fuels was calculated for different technologies that could meet this need. Using the ReEDS capacity expansion model we produce regional price profiles that capture the grid benefit associated with the amount and timing of energy shifts in the power system from the adoption of geothermal systems relative to other technologies that could meet space heating, space cooling, and process heat requirements. We find that geothermal systems for meeting end-use demand add value to the energy system. In buildings where geothermal systems increase grid costs, these values are offset by reduced fuel costs and benefits to externalities including emissions and health impacts.

This paper seeks to addresses the significant gap in the literature regarding the installation and adoption of geothermal heat pump (GHP) systems in the United States. While the 2021 U.S. Geothermal Power Production and District Heating Market Report by the National Renewable Energy Laboratory (NREL) focused on direct-use geothermal district heating systems, it did not include an analysis of GHP installations. To bridge this gap, NREL has compiled a novel database currently containing 70,470 records of GHP installations, primarily sourced from state well permits and small-scale studies.
Our methodology emphasizes the collection, cleaning, and standardization of data, addressing challenges such as inconsistent reporting formats and privacy concerns. Despite limitations in data on capacity, costs, and performance, our preliminary geospatial analysis reveals insights into the distribution of GHP systems across urban and rural areas and climate zones.
The paper highlights the importance of publicly accessible data for advancing GHP technology adoption with a discussion of existing data sources and their limitations, advocating for improved collaboration between NREL and industry stakeholders.

A challenge of decarbonization and electrification of buildings has been the expense associated with converting the buildings to 130° piped heating networks for radiators and perimeter induction heating. New technologies in high temperature heat pumps can deliver 180°F plus temperatures to these buildings from 5th generation thermal energy networks.
This abstract will share new technologies (High temperature heat pumps) that are coming into The US that are simplifying the process of decarbonization and electrification of existing high temperature piped building circuits.