Designing a Modular Geothermal System for a Net-Zero House; The Intermittency Dilemma: Is Green Hydrogen the Answer?

Mulford, Isaac, School of Engineering and Applied Science, University of Virginia
Chelliah, Harsha, EN-Mech/Aero Engr Dept, University of Virginia
Earle, Joshua, EN-Engineering and Society, University of Virginia

The sound of a parent or guardian shouting unintelligibly about left-on light switches echoes in the memories of countless Americans. Due to the financial burden of keeping household utilities and vehicles running, energy conservation is engrained in the habits and practices of families across the country. Investigating novel ways of alleviating this burden while minimizing negative environmental externalities is the overarching goal of this research and experimentation.

An increasingly popular solution for homeowners looking for a reduction in costly grid dependence lies in the utilization of geothermal energy. Heating and cooling accounts for a significant portion of energy consumption, and geothermal ground source heat pumps (GSHPs) provide a cost-effective, sustainable, and environmentally friendly alternative to conventional gas or oil furnaces. Closed loop geothermal systems cycle refrigerant through a buried polyethylene ground loop which acts as a heat exchanger to transfer thermodynamic energy to or from the ground. Open loop systems are the most cost-effective, but they are often not feasible since they rely on access to groundwater. Thus, increasing closed loop efficiency and minimizing upfront installation costs is key to making geothermal more desirable and accessible for the average consumer.

As part of a multi-team net-zero residential design initiative, the technical portion of this work details exploration by the heating and cooling team of the effect of ground loop design on the performance of a closed loop geothermal system. Preliminary flow simulation and analysis was performed in Ansys to compare four potential loop configurations. Simulation results provided temperature and pressure drop values per unit length, and these key performance factors along with ease of installation considerations were evaluated via a decision matrix. A horizontal slinky configuration was selected as the experimental design to be implemented in a small-scale ground loop system. Physical trials were conducted using a sandbox heat sink, and thermocouples placed throughout the loop gathered temperature data to be processed in LabView. The team’s subsequent analysis and conclusions are recorded in the design report.

The success of these and other net-zero endeavors depend heavily on the energy generation and storage systems, which in turn rely on renewable energy sources such as wind or solar. One major challenge with renewables is intermittency, or the unavailability of the energy source at certain times (e.g., solar power at night). Potentially viable solutions often involve storing surplus renewable energy for later use to supplement existing grid capacity, with storage devices taking forms such as batteries or gas compression systems. Finding a cheap, clean, and effective solution to energy storage could be the push that renewable energy needs to become globally implemented and overcome fossil fuels as the world’s leading energy source.

An emerging energy storage technology that offers reason for optimism involves the use of “green” hydrogen. Unlike “blue” or “gray” hydrogen, which are derived from natural gas and produce harmful byproducts, green hydrogen is obtained through the clean process of water electrolysis. However, relatively high costs and sociopolitical barriers have hindered implementation of these technologies in much of the world and led to questions regarding their role in the push for renewables. “The Intermittency Dilemma: Is Green Hydrogen the Answer?” attempts to answer these questions through qualitative analysis of these barriers alongside research-based predictions of green hydrogen’s technological and sociological plausibility.

BS (Bachelor of Science)
Green Hydrogen, Renewable Energy, Geothermal, Net-Zero, Intermittency

School of Engineering and Applied Science

Bachelor of Science in Mechanical Engineering

Technical Advisor: Harsha Chelliah

STS Advisor: Joshua Earle

Technical Team Members: Lucas Daugherty, Alex Davis, Kara Koopman

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