Ground heat exchanger

Abstract

A geothermal system includes an outer vessel having a sidewall that is in contact with surrounding ground material. A geothermal pile is disposed within an interior volume of the outer vessel, wherein a first heat conducting liquid at least partially fills a space between an inner surface of the sidewall of the outer vessel and an outer surface of the geothermal pile when in an installed condition. A conduit disposed within an interior space of the geothermal pile conducts a second heat conducting liquid along a flow path within the geothermal pile toward a bottom end thereof and then back to an outlet at a top end thereof. During operation, heat is transferred from the surrounding ground to the second heat conducting liquid via the first heat conducting liquid within the space between the inner surface of the sidewall of the outer vessel and the outer surface of the geothermal pile.

What is claimed is: 
     
         1 . A geothermal system for extracting heat energy from the ground, comprising:
 an outer vessel having a diameter d 2 , the outer vessel disposed within the ground and having a sidewall with an outer surface that is in contact with surrounding ground material when the geothermal system is in an installed condition, and the outer vessel having an inner surface defining an interior volume of the outer vessel;   a geothermal pile having a diameter d 3  that is less than d 2  and being disposed within the interior volume when the geothermal system is in the installed condition; and   a first heat conducting liquid at least partially filling a space between the inner surface of the sidewall of the outer vessel and an outer surface of the geothermal pile when the geothermal system is in the installed condition,   wherein the geothermal pile comprises a conduit contained within an interior space thereof for conducting a second heat conducting liquid into the geothermal pile at a top end thereof and along a flow path within the geothermal pile toward a bottom end of the geothermal pile and then back to an outlet at the top end thereof, and wherein during operation heat is transferred from the surrounding ground to the second heat conducting liquid via the first heat conducting liquid within the space between the inner surface of the sidewall of the outer vessel and the outer surface of the geothermal pile.   
     
     
         2 . The geothermal system of  claim 1 , wherein the outer vessel has a closed bottom end for containing the first heat conducting liquid within the interior volume thereof. 
     
     
         3 . The geothermal system of  claim 1 , wherein the closed bottom end is closed by a baseplate that is welded to the sidewall or by a plug of concrete into which the sidewall is embedded. 
     
     
         4 . The geothermal system of  claim 1 , wherein the outer vessel has an open bottom end that abuts against an impermeable subsurface layer in the ground. 
     
     
         5 . The geothermal system of  claim 2 , wherein the outer vessel is disposed in a borehole in the ground having a diameter d 1 , wherein d 2  substantially conforms to d 1  so as to provide a contact-fit between the outer surface of the sidewall of the outer vessel and the surrounding ground material. 
     
     
         6 . The geothermal system of  claim 1 , wherein the first heat conducting liquid fills the space between the inner surface of the sidewall of the outer vessel and the outer surface of the geothermal pile to a height that is sufficient to cover less than ¾ of the length of the geothermal pile. 
     
     
         7 . The geothermal system  claim 1 , wherein the conduit within the geothermal pile has an upper portion that is insulated or double-jacketed. 
     
     
         8 . The geothermal system of  claim 7 , wherein the conduit within the geothermal pile has a lower portion that is fabricated from a material having a higher heat conductivity relative to a material of the upper portion of the conduit. 
     
     
         9 . The geothermal system  claim 1 , further comprising means for inducing a convective liquid current within the first heat conducting liquid. 
     
     
         10 . The geothermal system  claim 1 , further comprising gravel or sand disposed within at least a portion of the space between the inner surface of the sidewall of the outer vessel and the outer surface of the geothermal pile. 
     
     
         11 . The geothermal system  claim 1 , wherein the second heat conducting liquid flowing along the flow path within the conduit does not mix with the first heat conducting liquid. 
     
     
         12 . The geothermal system  claim 1 , comprising a flow control valve for controlling a pumped flow of the first heat conducting liquid into the space between the inner surface of the sidewall of the outer vessel and the outer surface of the geothermal pile. 
     
     
         13 . The geothermal system  claim 1 , further comprising a circulating pump or an impeller arranged to increase turbulence of the first heat conducting liquid within the space between the inner surface of the sidewall of the outer vessel and the outer surface of the geothermal pile. 
     
     
         14 . The geothermal system  claim 1 , wherein the first heat conducting liquid is water. 
     
     
         15 . A method of constructing a heat exchange system in the ground, comprising:
 providing a borehole in the ground having a first diameter d 1 ;   providing an outer vessel, having a diameter d 2  that is less than or equal to d 1 , within the borehole;   arranging a geothermal pile having an internal conduit extending along a length thereof within the outer vessel;   at least partially filling a space between an inner sidewall surface of the outer vessel and an outer surface of the geothermal pile with a first heat conducting liquid; and   coupling an inlet port and an outlet port of the conduit to a liquid circuit for a second heat conducting liquid.   
     
     
         16 . The method of  claim 15 , wherein providing the borehole in the ground comprises forming a concrete plug at the bottom of the borehole, and wherein the sidewall of the outer vessel is embedded within the concrete plug prior to full curing thereof. 
     
     
         17 . The method of  claim 15 , wherein providing the borehole in the ground comprises exposing an impermeable subsurface layer at the base of the borehole, and wherein the sidewall of the outer vessel abuts against the impermeable subsurface layer. 
     
     
         18 . The method of  claim 17 , wherein providing the borehole in the ground further comprises boring into the impermeable layer to form an opening having a diameter less than a diameter d 1  and less than the diameter d 2  of the outer vessel, and wherein the diameter of the opening is greater than a diameter d 3  of the geothermal pile. 
     
     
         19 . The method of  claim 18 , wherein arranging the geothermal pile within the outer vessel comprises disposing a bottom end of the geothermal pile within the opening that is formed into the impermeable layer, wherein a length L 1  of the geothermal pile is greater than a length L 2  of the outer vessel. 
     
     
         20 . The method of  claim 18 , further comprising disposing gravel or sand within the space between the inner surface of the sidewall of the outer vessel and the outer surface of the geothermal pile, so as to cover at least a portion of a length L 1  of the geothermal pile. 
     
     
         21 . The method of  claim 18 , wherein the first heat conducting liquid fills the space between the inner surface of the sidewall of the outer vessel and the outer surface of the geothermal pile to a height H that is sufficient to cover less than ¾ of a length L 1  of the geothermal pile.