System and Method for Heat Exchange based on Shell Pipe

Abstract

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.

The invention claimed is: 
     
         1 . A system for exchanging thermal energy between a circulating fluid and a surrounding media, comprising:
 an elongate shell pipe having thermal conductivity greater than 5 W/m−° K; wherein said shell pipe is closed at the bottom end, is positioned approximately vertically in the media and is in intimate thermal contact with said surrounding media;   a first U-tube assembly positioned within said elongate shell pipe, comprising a down pipe, an up pipe, and a U-turn element wherein fluid may be serially conducted from inlet of said down pipe through said U-turn element to outlet of said up pipe with minimal flow restriction;   a thermally conductive filler positioned within the volume between inner radius of said elongate shell pipe and outer radii of said down pipe and said up pipe having thermal conductivity greater than 0.4 W/m−° K wherein said thermally conductive filler comprises a mixture of particulates, water, and antifreeze;   a closed loop comprising serial fluidic connection between at least said inlet of said down pipe, said outlet of said up pipe, a flow-through heat exchange element, a pump, and said inlet of said down pipe wherein said flow-through heat exchange element is either a source or sink of thermal energy; and   a heat exchange fluid circulating within said closed loop wherein said heat exchange fluid effects heat exchange with said surrounding media.   
     
     
         2 . The system of  claim 1  wherein said shell pipe has inner diameter less than about 160 mm and preferably about 60 mm and each of said down pipe and said up pipe has diameter less than half the inner diameter of the said shell pipe and preferably about 27 mm. 
     
     
         3 . The system of  claim 1  wherein each of said down pipe and said up pipe is formed from material having thermal conductivity greater than 5 W/m−° K. 
     
     
         4 . The system of  claim 1  wherein each of said down pipe and said up pipe is formed from plastic material, either HDPE or PEX-A. 
     
     
         5 . The system of  claim 1  wherein said U-tube assembly comprises one of said down pipe and said up pipe formed from copper, and the other of said down and said up pipe formed from plastic material, either HDPE or PEX-A material. 
     
     
         6 . The system of  claim 1  wherein said thermally conductive filler is a mixture of glycerin and water. 
     
     
         7 . The system of  claim 1  wherein said U-turn element is formed of material compatible with solder joining with said down pipe and said up pipe and has outer diameter at least 1.0 mm smaller than inner diameter of said elongate shell pipe. 
     
     
         8 . The system of  claim 1  further comprising a second U-tube assembly positioned within said elongate shell pipe, comprising a down pipe, an up pipe, and a U-turn element wherein fluid may be serially conducted from inlet of said down pipe through said U-turn element to outlet of said up pipe with minimal flow restriction. 
     
     
         9 . The system of  claim 1  wherein said elongate shell pipe comprises segments that are joined by slip fit and welded in a manner compatible with the direct push method. 
     
     
         10 . The system of  claim 1  wherein said thermally conductive filler occupies the volume between inner radius of said elongate shell pipe and outer radii of said down pipe excluding at least the top 1.5 meters measured from surface of said media and preferably excluding the top 4.0 meters from said surface of said media, is a mixture of glycerin and water, and is capped with at least 1 mm of oil or synthetic lubricant having low evaporation rate. 
     
     
         11 . A method for installing a heat exchange loop system comprising the steps of:
 directly pushing a first element of an elongate shell pipe portion of a vertical heat exchange loop system into the ground, wherein said shell pipe is sufficiently rigid to allow for direct insertion,
 has thermal conductivity greater than 5 W/m−° K, and 
 has diameter less than about 110 mm and preferably about 60 mm; 
   attaching a second element to said elongate shell pipe and continuing direct push into said ground;   continuing to add additional elements and directly pushing into said ground until a target total length of said elongate shell pipe is reached;   inserting within said elongate shell pipe either one or two U-tube assemblies, each comprising a down pipe, an up pipe, and a U-turn element wherein fluid may be serially conducted from inlet of said down pipe through said U-turn element to outlet of said up pipe with minimal flow restriction;   dispensing into the volume formed by inner radius of said elongate shell pipe and outer radii of said U-tube pipes a thermally conductive filler comprising a mixture of particulates, water, and antifreeze to complete the thermal path between a fluid circulating through the U-tube assembly and the surrounding ground, wherein said thermally conductive filler has thermal conductivity greater than 0.4 W/m−° K;   connecting the uppermost portion of said down pipe serially to at least a fluid pump and flow-through heat exchange apparatus and uppermost portion of said up pipe to complete a closed fluidic loop;   positioning means for measuring and recording both entering fluid temperature at uppermost portion of said down pipe and leaving fluid temperature at uppermost portion of said up pipe;   activating said fluid pump and said flow-through heat exchange apparatus to exchange heat with the surrounding ground.   
     
     
         12 . The method of  claim 11  wherein each of said down pipe and said up pipe is formed from material having thermal conductivity greater than 5 W/m−° K. 
     
     
         13 . The method of  claim 11  wherein each of said down pipe and said up pipe is formed from plastic material, either HDPE or PEX-A. 
     
     
         14 . The method of  claim 11  wherein one of said down pipe and said up pipe is formed of copper and the other of said down pipe and said up pipe is formed of plastic material, either HDPE or PEX-A. 
     
     
         15 . The method of  claim 11  wherein a pilot hole having diameter smaller than said elongate shell pipe is drilled prior to directly pushing a first element of a said elongate shell pipe portion of a vertical heat exchange loop system into the ground. 
     
     
         16 . The method of  claim 11  wherein the volume of said thermally conductive filler is less than 3,000 cubic centimeters per unit meter of length. 
     
     
         17 . The method of  claim 11  wherein said thermally conductive filler comprises glycerin, a less pure form of glycerol, and water. 
     
     
         18 . The method of  claim 11  wherein said thermally conductive filler comprises glycerin, a less pure form of glycerol, water and graphite particulates. 
     
     
         19 . A heat pump system, comprising:
 an indoor refrigerant-to-air heat exchanger;   a compressor both increasing pressure and temperature and forcing circulation of refrigerant;   an expansion valve for reducing refrigerant temperature;   an outdoor refrigerant-to-air heat exchanger;   a reversing valve to switch between heating and cooling modes;   a ground-based heat exchanger, further comprising an elongate shell pipe embedded in the ground;   a U-tube assembly inserted into said elongate shell pipe, said U-tube assembly comprising a down pipe, an up pipe, and a U-turn element;   thermally conductive filler positioned within the volume between inner radius of said elongate shell pipe and outer radii of said down pipe and said up pipe, said filler further comprising a mixture of particulates, water, and antifreeze having thermal conductivity greater than 0.4 W/m−° K; and   fluidic connections between said U-tube assembly, outdoor refrigerant-to-air heat exchanger, and expansion valve.   
     
     
         20 . The heat pump system of  claim 19  further comprising a plurality of valves selectively configurable to switch refrigerant flow from first direct path through said outdoor refrigerant-to-air heat exchanger to expansion valve to second longer path first through said outdoor refrigerant-to-air heat exchanger, next through said ground-based heat exchanger and then to expansion valve.