Closed-Loop Geothermal Heat Transfer via Induced Groundwater Flow
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Solution Overview
Problem
Closed loop geothermal systems are limited by the thermal conductivity of geological formations, requiring multiple and deep boreholes for adequate heat transfer, which increases capital costs and drilling expenses, while open loop systems face regulatory issues due to groundwater depletion and contamination risks.
Innovation Solution
The induced groundwater flow closed loop geothermal system separates a borehole into sections to induce groundwater flow, reducing thermal resistance and maintaining separation between groundwater, closed system fluid, and surface runoff, thus bypassing thermal conductivity limitations and regulatory concerns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If closed loop geothermal systems use traditional boreholes, then system safety and compliance are maintained, but heat transfer efficiency is limited by thermal conductivity requiring multiple deep boreholes
Solution Approach 1:
The borehole is divided into multiple sections with different permeability characteristics. Upper and lower sections have different gravel pack configurations that segment the groundwater flow path, allowing controlled induction of groundwater through the heat exchanger while maintaining system integrity and compliance
Solution Approach 2:
Groundwater is introduced as an intermediary medium to enhance heat transfer between the closed loop refrigerant and the geological formation. The groundwater flows through the gravel packs and heat exchanger, acting as a thermal conduit that overcomes the limitations of thermal conductivity in traditional closed loop systems
2Productivity
If multiple deep boreholes are drilled to overcome thermal conductivity limitations, then adequate heat transfer is achieved, but capital costs and drilling expenses increase
Solution Approach 1:
The system changes the thermal transfer parameters by introducing groundwater flow through permeable sections. This transforms the heat transfer mechanism from pure conduction through borehole walls to convection-enhanced transfer through moving groundwater, achieving higher efficiency in fewer, shallower boreholes
3Productivity
If open loop systems extract and discharge groundwater, then heat transfer efficiency improves, but regulatory issues arise due to groundwater depletion and contamination risks
Solution Approach 1:
The system nests the open loop groundwater flow mechanism within a closed loop structure. Groundwater is induced to flow through the heat exchanger but remains contained within the borehole system, combining the efficiency benefits of open loop systems with the safety and compliance of closed loop systems
Solution Approach 2:
The system converts what would normally be harmful uncontrolled groundwater discharge into a beneficial controlled flow through the heat exchanger. The groundwater that could potentially cause contamination is instead utilized as a thermal transfer medium and returned to its source, transforming a potential harm into a performance benefit
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances heat transfer efficiency while ensuring safety and compliance by maintaining separation of water sources, reducing the number and depth of boreholes needed, thereby lowering capital costs and improving market acceptance.
Implementation Method 1
The induced groundwater flow closed loop geothermal system utilizes groundwater flow to reduce the thermal resistance between the working fluid in the closed system and the geological formation
Implementation Method 2
The system includes a heat exchanger that receives the working fluid from the HVAC system and induces groundwater flow through the geologic formation from a first section to a second section
Data Source
AI summary
An induced groundwater flow closed loop geothermal system provides safety associated with closed loop geothermal systems (e.g., no mixing of surface water, closed system fluid, and groundwater) and efficiency associated with open loop geothermal systems (e.g., increased heat transfer provided by groundwater flow). A heat exchanger connected to an external system is located in a hole in a geological formation. The hole has a depth below where groundwater is located. A fluid from the external system is routed through the heat exchanger. A pump is utilized to induce groundwater flow from the geological formation, across the heat exchanger and back to the geological formation to enable thermal transfer between the fluid and the groundwater and the groundwater and the geological formation. A casing may be located in the hole to provide structural support and grouting materials may be used to fill space around the casing enabling a groundwater flow path.