Shell Pipe Heat Exchanger Reducing Borehole Thermal Resistance
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Solution Overview
Problem
Conventional ground-source heat pump systems face challenges in minimizing borehole thermal resistance (BTR) and ensuring uniform pipe spacing, leading to reduced heat exchange efficiency and increased costs, while also risking contamination of underground water sources during installation.
Innovation Solution
The use of a shell pipe with high thermal conductivity, directly pushed into the ground, and U-tube loops with a thermally-conductive filler to reduce BTR and prevent groundwater contamination, allowing for the use of more corrosion-susceptible materials and minimizing site disruption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional drilling methods are used to install U-tube loops, then boreholes can be formed to accommodate the loops, but borehole thermal resistance increases and heat exchange efficiency decreases
Solution Approach 1:
The patent implements a nested structure where the U-tube loop is placed inside a shell pipe, which is then inserted into a pre-formed borehole. The annular space between the shell pipe and borehole wall is filled with thermally-conductive grout. This nested configuration allows the shell pipe to serve as a thermal conduit, reducing the thermal resistance path from the ground to the U-tube loop, thereby improving heat exchange efficiency while maintaining a manageable borehole size.
2Ease of manufacture
If conventional drilling and grouting methods are used, then U-tube loops can be installed, but there is risk of contaminating underground water sources
Solution Approach 1:
The patent extracts the potential contamination risk by introducing a sealed shell pipe as an intermediate barrier between the drilling/grouting process and the underground water sources. The shell pipe acts as a protective enclosure that prevents grout and drilling materials from entering the groundwater, while still allowing thermal energy to transfer through the grout-filled annular space. This extraction of the harmful factor enables safe installation without compromising installation feasibility.
3Use of energy by moving object
If thinner pipe walls are used to reduce pressure drop, then pump horsepower requirements decrease, but pipe strength and resistance to impact forces during direct push installation decrease
Solution Approach 1:
The patent introduces the shell pipe as an intermediary structural element that bears the mechanical loads during direct push installation. The shell pipe, with its thicker walls, provides the necessary strength and rigidity to withstand impact forces and ground pressures. The U-tube loop inside can then use thinner walls since it is protected by the shell pipe, allowing reduced pump horsepower requirements while maintaining adequate pipe strength during installation.
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 significantly reduces BTR, enhances heat exchange efficiency, and minimizes the risk of groundwater contamination, resulting in a cost-effective and environmentally friendly ground-based heat exchange system.
Implementation Method 1
The shell pipe, preferably having 0.03-0.10 meter outer diameter, is placed into the media to which heat will be exchanged... made of metal, such as steel, which has high thermal conductivity... thermally-conductive filler within the remaining volume
Implementation Method 2
The bottom-most end of the shell pipe portion is closed by a conically-shaped head to prevent media from entering the pipe, wherein the head is sized to reduce friction during drive-in
Implementation Method 3
A slurry comprising a mixture of thermally-conductive particulates, water, and antifreeze is added into the volume between shell pipe and U-tube pipes to complete the thermal path
Data Source
AI summary
The invention is a heat exchange system and method relying on circulation of a fluid through a loop to exchange thermal energy with the ground. A metallic shell pipe, optionally inserted into the ground by the direct push method, is in intimate thermal contact with the ground and accommodates one or two U-tube loops placed internally followed by introduction of a thermally conductive filler to occupy remaining volume and to thermally connect the outer radii of the U-tube pipes to the inner radius of the shell pipe. The U-tube loops are formed of either metallic pipes for lowest thermal resistance or plastic pipes for lowest cost. Shell pipe volume is precisely known, allowing for precise metering of filler, either liquid or particulates suspended in a liquid. The semi-sealed shell pipe provides superior environmental protection, eliminating potential for ground water contamination and allowing use of corrosion-susceptible pipe materials such as copper.