Multi-channel ground heat exchange unit and geothermal system
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Solution Overview
Problem
Current geothermal geo-exchange systems are costly to install and inefficient for smaller buildings, with high borehole drilling expenses and thermal resistance issues due to improper backfilling, leading to long cost recovery periods and suboptimal thermal energy transfer.
Innovation Solution
A subterranean heat exchange system using an elongate polymer block with multiple narrow channels (0.5 mm to 20 mm in diameter) for efficient heat transfer, connected to supply and return conduits, and employing a two-phase heat exchange fluid like carbon dioxide for direct expansion, reducing borehole size and depth requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional large-diameter boreholes (4 inches or greater) are drilled to 100-400 feet depth for geothermal heat exchange, then thermal energy transfer capability is improved, but installation cost increases prohibitively for residential applications
Solution Approach 1:
The heat exchange system is segmented into multiple smaller-diameter conduits (each less than 4 inches) rather than using a single large borehole. This allows installation through smaller, less expensive boreholes while maintaining thermal exchange capability through multiple parallel flow paths
Solution Approach 2:
The system transitions from a single large-diameter vertical borehole to multiple smaller conduits that can be arranged in various configurations (vertical, horizontal, or combination), adding dimensional flexibility to the installation approach and reducing drilling depth requirements
2Loss of energy
If boreholes are back-filled with material to secure loop positioning and improve thermal contact, then thermal resistance between fluid and ground is reduced, but improper backfilling creates voids that increase thermal resistance by up to 50%
Solution Approach 1:
The system uses flexible thermal interface materials or conformal sealing elements within the conduit assembly that adapt to irregular borehole surfaces, ensuring consistent thermal contact without requiring perfect backfilling. This eliminates void formation and maintains reliable thermal coupling
Solution Approach 2:
The conduit assembly includes pre-installed thermal interface materials or expansion elements that compensate for potential gaps or voids before backfilling occurs, ensuring consistent thermal contact is maintained regardless of backfilling quality
3Loss of energy
If multiple U-tubes are used in a borehole to improve heat exchange capacity, then thermal energy transfer is enhanced, but proper positioning of multiple loops becomes challenging and negative thermal interactions between loops occur
Solution Approach 1:
Multiple U-tube loops are merged into a single integrated conduit assembly with coordinated flow distribution. This unified structure eliminates positioning challenges between separate loops and prevents negative thermal interactions by ensuring proper spacing and thermal zoning within the single assembly
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
The system achieves a 40% reduction in energy consumption and a quarter of the installation costs compared to conventional systems, with improved thermal efficiency and reduced thermal resistance, making geothermal energy more viable for residential and small business applications.
Implementation Method 1
employing a two-phase heat exchange fluid like carbon dioxide for direct expansion
Implementation Method 2
employing a two-phase heat exchange fluid like carbon dioxide for direct expansion
Implementation Method 3
efficient heat transfer
Implementation Method 4
heat exchange fluid to and from the supply and return conduits
Data Source
AI summary
Geothermal energy is increasingly recognized as a useful energy source for both industrial and residential purposes. Disclosed herein are units for subterranean heat exchange comprising a polymer block with ‘mini-channels’ adapted and/or sized for highly efficient heat exchange. In some embodiments such units can, as needed, be manufactured off site, spooled for transport, and conveniently installed in boreholes. Other arrangements are also described for conduits located within a borehole for heat exchange, without a polymer block. Also disclosed are geothermal heat exchange systems including those that employ such units, for example with direct expansion of a two-phase heat-exchange fluid such as carbon dioxide.