Abstract:
An energy transfer wilt suitable for a geothermal heating system is formed from a plurality of modules. Each module has a frusto conical baffle overlying a heat exchange core to direct fluid radial across the core. A chimney is provided centrally in the baffle to promote radial flow. The modules may be located within a housing and ports are provide to allow flow in to the housing adjacent each of the cores.

Description:
CROSS-REFERENCE 
       [0001]    This application claims priority from U.S. Provisional Patent Application No. 61/536,331 filed Sep. 19, 2011. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to an energy transfer unit and a method of constructing such an energy transfer unit. 
       SUMMARY OF THE INVENTION  
       [0003]    Energy transfer units are well known and commonly used to transfer energy in the form of heat from one medium to another. As such they are generally referred to as heat exchangers. Such units are used in many industrial and commercial processes and are designed to meet the particular operating conditions of those processes. 
         [0004]    Energy transfer units are used extensively in HVAC (heating, ventilating and it conditioning) applications where they must operate at high efficiencies and at the same time be relatively economical to produce. One particular HVAC application arises in geothermal heating and cooling systems in which a heat exchanger is an integral part of exchanging energy between a ground source and a fluid circulating between the ground source and a heat pump. The ground source is a thermal reservoir that may be a body of water, such as at lake, river or stream, or may be the ground itself at a depth that provides a substantially uniform temperature. 
         [0005]    The heat exchangers presently used in geothermal applications may be as simple as a pipe buried within the ground or submerged in a lake, or may be a mesh of smaller pipes interconnected to a manifold. The effectiveness of the heat exchanger determines to a lame extent to the overall efficiency of the heating and cooling system, but the form of the heat exchanger has been maintained as inexpensive as possible despite e inefficiencies that such an arrangement introduces. 
         [0006]    In the Applicant&#39;s co pending application, International Application No. PCT/CA2011/000846, published as WO 2012/009802, there is disclosed an arrangement of energy transfer unit in which heat exchange cores formed from spirally wound small bore tubing, referred to as capillaries, are located within an external housing and a flow of water induced through the housing to increase the efficiency of the heat transfer. This arrangement has proven highly effective and has introduced significant efficiencies to the overall system. The efficiencies within the energy transfer unit have made increased thermal capacities possible within a compact overall envelope. However, such increased capacity has in turn made the control of flow within the housing more complex over a range of operating conditions. The manufacturer of the heat exchange core itself is however labour intensive and therefore relatively expensive. 
         [0007]    It is an object of the present invention to provide an energy transfer unit in which the above disadvantages are obviated or mitigated. 
         [0008]    In general terms, one aspect of the present invention provides an energy transfer nun having one or more modules. Each of the modules has a support structure to support a capillary spirally wound between an inlet header and an outlet header. The modules may be stacked one above the other, with the headers interconnected to provide a common inlet and a common outlet for the modules. The capillaries are arranged in parallel between the inlet and outlet. The heat exchanger may be sized to the particular requirements by selecting the appropriate number of modules. 
         [0009]    Preferably, each module has a frusto conical shell with a support structure integrated with the shell to support spirally wound capillaries. The frusto conical shells may be stacked one above the other in spaced relationship to provide a passage between adjacent shells and to promote flow between the shells and over the capillaries retained between the shells. 
         [0010]    In another aspect there is provide an energy transfer unit having a heat exchange core and a baffle juxtaposed over the core to direct fluid from a heat source radially relative to the core. 
         [0011]    Preferably, the baffle in inclined to the direction of flow of fluid, and as a further preference, the baffle directs the fluid to a chimney. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0012]    Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which: 
           [0013]      FIG. 1  is front elevation of an energy transfer unit; 
           [0014]      FIG. 2  is a section on the line II-II of  FIG. 1 ; 
           [0015]      FIG. 3  is an enlarged view of a portion of the energy transfer unit shown in  FIG. 2 ; 
           [0016]      FIG. 4  is a further enlarged view of a portion of the structure shown in  FIG. 3 ; 
           [0017]      FIG. 5  is a view on the line V-V of  FIG. 3 ; 
           [0018]      FIG. 6  is a plan view of the energy transfer unit shown in  FIG. 1  according to an example embodiment; 
           [0019]      FIG. 7  is a plan view of the energy transfer unit shown in  FIG. 1  according to another example embodiment; 
           [0020]      FIG. 8  is a schematic representation showing the assembly of energy transfer unit of  FIG. 1 . 
           [0021]      FIG. 9  is a section of an alternative embodiment of the energy transfer unit of  FIG. 2 , and 
           [0022]      FIG. 10  is an enlarged view of the embodiment of  FIG. 9 . 
           [0023]      FIG. 11  is a sectional view of a further embodiment of energy transfer unit. 
           [0024]      FIG. 12  is a view from below of one of the modules shown in  FIG. 11 . 
           [0025]      FIG. 13  is a perspective view of a further embodiment of an energy transfer unit. 
           [0026]      FIG. 14  is a perspective view of an energy transfer unit used within the unit of  FIG. 13 . 
           [0027]      FIG. 15  is a view on the line XV-XV of  FIG. 14 . 
           [0028]      FIG. 16  is a side elevation in the direction of the arrow A of  FIG. 14 . 
           [0029]      FIG. 17  is a plan view of the unit shown in  FIG. 14 . 
           [0030]      FIG. 18  is an under view of the unit shown in  FIG. 14 . 
           [0031]      FIG. 19  is the enlarged view of a component utilized in the energy transfer unit of  FIG. 15 . 
           [0032]      FIG. 20  is the section on an enlarged scale on the line XX-XX of  FIG. 14 , and 
           [0033]      FIG. 21  is a schematic illustration of the installation of the heat exchange unit shown in  FIG. 13  within a body of water. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0034]    Referring therefore to  FIG. 1 , an energy transfer unit, generally indicated at  10 , has a fluid inlet  12  and a fluid outlet  14 . The inlet  12  and outlet  14  are connected to respective pipes  16 ,  18  that in turn are connected to a heat pump in a known manner. One example of such an arrangement is shown in  FIG. 1  and the accompanying description of PCT publication WO 2012/009802, the contents of which are incorporated herein by reference. A particularly beneficial way of connecting the energy transfer unit  10  to a heat pump is shown in co pending application, U.S. Provisional Application No. 61/523,698, the contents of which are incorporated herein by reference. 
         [0035]    The energy transfer unit  10  is formed from a number of modules  20 , indicated individually as  20   a,    20   b,    20   c,    20   d,  that are stacked one above the other to provide a multi layered body to the energy transfer unit  10 . A base  22  extends across the lower most of the modules  20   d  and a tether assembly  24  is secured to the base  22 . The tether assembly  24  includes a ballast  26  and a pair of the lines  28  that allow the energy transfer unit  10  to be secured in location in a heat source, for example in a body of water. A flared collar  29 , is secured to the upper module  20   a  to promote flow through the heat exchanger  10 . 
         [0036]    Each of the modules  20  is of similar design and therefore only one will be described in detail. Each of the modules  20  has a frusto conical shell  30  formed from plastics, such as polyethylene or similar material. Headers  32  are integrally formed at spaced intervals about the outer periphery  31  of the shell  30  and the shell  30  terminates at its upper edge at a central aperture  34 . The shell has a half angle α in the order of 45° with the lower most portion adjacent the radially outer periphery flared to provide a shallow skirt  36 . The half angle β of the flared skirt is in the order of 25° and smoothly blends with the balance of the shell  30 . 
         [0037]    The shell  30  is integrally moulded with spars  40  that extend from the header  32  to the aperture  34 . Each of the spars  40  depends downwardly from the shell  30  and has a lower edge that is formed with v shaped notches  42 . Flanks  44 ,  46  of the notches  42  are formed with part circular recesses  48  to receive tubing  50 . A heat exchange core is provided by an array of tubing  50  that extends from an inlet header to an outlet header. Preferably, the tubing  50 , as can best be seen in  FIGS. 6 and 7 , is spirally wound from a radially outer location to a radially inner location and back to a radially outer location. Each run of tubing  50  is connected to a respective nipple  52  formed on the header  32  so that each run extends from an inlet header  32  to a diametrically opposed outlet header  32 . As shown in the embodiment of  FIGS. 1-8 , four headers  32  are uniformly spaced about the periphery  31  of the shell  30 , allowing two runs of tubing  50 , indicated by solid and dashed lines in  FIG. 6 , to be interlaced and extend spirally inwardly and subsequently spirally outwardly between the respective headers  32 . 
         [0038]    The diameter of the recesses  48  is selected such that the tubing  50  is a press fit within the recess  48  and thereby retained on the spar  40 . The press fit is such that the interior diameter of the tubing  50  is not reduced to avoid restrictions along the length of the tubing  50 . 
         [0039]    Each of the headers  32  is formed with an internal shoulder  60  at its upper end and an external shoulder  62  at its lower end. The shoulders  60 ,  62  facilitate the stacking of the headers  32  one above the other so that the shells  30  overlie one another in spaced relationship. The conical void between the adjacent shells accommodates the spirally wound tubing  50 . 
         [0040]    A pair or the headers  32  of the lower most module  20  is connected to the inlet  12  by conduits  70 ,  72  and the diametrically opposite headers  32  interconnected to the outlet  14  by conduits  74 ,  76  ( FIG. 1 ). The upper end the headers  32  of upper most module  20  is sealed by a cap  78  so that fluid entering the inlet  12  passes through the header  32 , along the tubing  50  to the outlet header  32  and back to the outlet  14 . The cap  78  occludes the volume between the upper most nipple  52  and the upper shoulder  60 , as shown in ghosted outline in  FIG. 5 , to inhibit accumulation of air within the headers  32 . 
         [0041]    The base  22  has a central aperture  23 , aligned with the aperture  34  but of smaller diameter, to create a central chimney through the energy transfer unit  10 . 
         [0042]    Each of the modules  20  may be assembled by feeding the tubing  50  in its spiral pattern on the underside of the shell  30 . The notches  42  present an open access to the recesses  48  thereby avoiding the need to thread the pipes  50  through the spars  40 . Once the tubing  50  is installed on the spars  40 , it may be connected to the nipples  52  to provide a self contained module  20  that provides a heat exchange core. 
         [0043]    The modules  20  may then be assembled by stacking one on the other until the requisite number of modules  20  has been assembled. The shoulders  60 ,  62  locate the headers  32  on one another and allow the modules to be secured by fusion welding or adhesive. The conduits  70 - 76  are then secured between the headers  32  and respective ones of the inlets and outlets  12 ,  14  and the base  22  secured to the lowermost module  20 . The tether  24  may then be connected. The headers  32  maintain the peripheral edges  31  of the shells  30  in spaced relationship to allow fluid to pass between the shells and around the tubing  50  arranged on the spars  40 . 
         [0044]    In use, the pipes  16 ,  18  are connected to the inlet  12  and outlet  14  respectively and the assembled heat exchanger  10  submersed within a body of water or other ground source that serves as a thermal reservoir. Heat exchange fluid is circulated through the pipes  16 ,  18  where it flows through the headers  32  and in to the tubing  50  to move between the inlet  16  and the outlet  18 . As the fluid flows, heat is transferred between the water surrounding the tubing  50  and the heat exchange fluid in the tubing  50 . The change in temperature of the fluid between the shells  30 , creates a density imbalance which imparts a flow of fluid between the shells  30  from the radially outer edge  31  to the aperture  34  in the case where heat is rejected to the body of water. The inclined surface of the shell  30  promotes the radial flow to the aperture  34 . The flow is enhanced by the skin  36 , which accelerates the flow radially inwardly between the shells  30  to enhance the circulation. The flow induced between the shells  30  enhances the heat transfer with the tubing  50 . The flared collar  29  promotes the flow of fluid out of the energy transfer unit  10 , and the aperture  23  in the base  22  promotes a chimney effect from the lower base  22  to the aperture  34  to further reinforce the flow through the shells. 
         [0045]    It will be noted that the runs of tubing  50  provide parallel paths between the inlet headers  32  and outlet headers  32  so that the pressure drop is maintained relatively small. 
         [0046]    The capacity of the energy transfer unit  10  may readily be adjusted by adding or subtracting the modules  20  and it will be noted that assembly of the modules may be performed prior to their assembly in to the energy transfer unit  10 . Of course, the energy transfer unit may consist of a single module, or may have multiple modules where an increased capacity is required. 
         [0047]    A further embodiment of modular heat exchanger is shown in  FIGS. 9 and 10 , in which like components will be identified by like reference numbers with a suffix “a” added for clarity. 
         [0048]    Referring to  FIGS. 9 and 10 , the shells  30   a  are paired to form a unit with tubes  50   a  spiraling from outside to inside on one of the pairs, and from inside to outside on the other of the pairs. Each shell  30   a  has a set of radial spars  40   a  with parallel sided notches  42   a  to receive the tubing  50   a.  The notches are sized to retain the tubing  50   a  without occluding the internal passage. 
         [0049]    Four runs of tubing  50   a  extends from each of a pair of diametrically opposed headers  32   a  and are received in alternate notches  42   a  along the spars  40   a  of the uppermost shell  30   a.  The runs of tubing  50   a  are spaced apart vertically in each of the notches  42   a  and spiral inwardly to the central aperture  34   a.  At the radially inner extent of the spars  40   a,  the sets of tubing  50   a  are directed in to the lowermost shell  30   a  of the nun where they are received in the notches  42   a  as they spiral radially outwardly. The tubing  50   a  spirals in the same hand in the upper and lower shells  30   a  to minimise flow restriction in the tubes  50   a.  The tubing  50   a  of the lower shell  30   a  is connected to headers  32   a  located between the headers  32   a  of the upper shell to provide a circulation between inlet and outlet. 
         [0050]    The modules may be stacked one above the other as illustrated above to vary the capacity of the energy transfer unit  10   a  with the headers  32   a  nesting to provide a common inlet and outlet for each of the shells  30   a.  Again, only a single module may be required, although typically more than one module is provided. With the arrangement of  FIGS. 9 and 10 , the density of tubes in each shell is reduced, which promotes circulation across the tubing  50   a  from the periphery  31   a  to the central aperture  34   a,  whilst maintaining the modularity of the energy transfer unit. Assembly of the tubing  50   a  is facilitated by avoiding cross over between the ingoing and outgoing tubes and permits an ordered assembly of the shells  30   a.    
         [0051]    An alternate configuration of modular energy transfer unit is shown in  FIGS. 11 and 12 . Like components will be noted with like reference numerals with prefix “1” for clarity. 
         [0052]    Referring therefore to  FIG. 11 , the energy transfer unit  110  is formed from at least one shell  130 , each of which has a frusto conical central annular disk  131  with a peripheral downturned flange  136 . The disk  131  has a central aperture  134  that receives a central tube  80 . The tube  80  has ports  82  distributed about its circumference adjacent to the intersection with the intersection with the inner edge of shell  130 . 
         [0053]    The tube  80  locates a radially inner edge of a spar  140  that extends radially outwardly towards the flange  136 . The radially inner edge of each of the spars  140  is received within a groove  84  ( FIG. 12 ) formed on the outer surface of the tube  80 . 
         [0054]    Each of the spars  140  is formed from a sot of comb like strips indicated at  88 . Each of the edges of the strip  88  has a series of part circular recesses  148  to receive the capillary tubing  150 . When arranged edge to edge, the strips  88  locate the capillary tubing  150  between opposite edges of the strips to maintain a uniform spaced relationship. 
         [0055]    Headers  132  are provided at diametrically opposite locations on the shell  130 . Each of the headers  132  comprises a pair of tubes  90 . A row of spaced outlets  92  is provided along each of the tubes  90  facing in opposite directions for connection to the tubes  150 . The connection between the tubes  90  and the tubing  50  is typically performed by welding. 
         [0056]    The arrangement of the array of tubing  150  within the spars  140  is similar to that described above in that each is spirally wound and of opposite hand. A run of tubing  150  therefore proceeds from one of the tubes  90  through the spars  140  toward the central tube  80  and thereafter radially outwardly to terminate at the diametrically opposite tube  90 . 
         [0057]    To assemble the heat energy transfer unit  130 , the first strip  88  of the spar  140  is secured in each of the grooves  84  on the central tube  80 . The tubing  150  is then spirally wound and placed into the part circular grooves and is secured in situ by placement of the next of the strips  88 . The strips are preferably are the snap fit within the grooves  84  so as to securely hold these strips  88  in alignment. The strips  88  may extend radially outwardly to the flange  136  to provide extra rigidity or ma be joined to one another at the radially outer edge by a common channel or similar mechanical fastening device. 
         [0058]    The next spiral array of tubing  150  is located in the open set of recesses  148  and the next to the strips  88  then added. This continues until all of the strips  88  have been inserted to locate the tubing  150 . 
         [0059]    It will be appreciated that the arrangement of the spars  140  made from the individual strips could be replaced with a single rectangular spar with holes formed therein and the tuning threaded through those holes. Such an arrangement would require less individual components but would increase the complexity of threading of the tubing. 
         [0060]    Each of the central tubes  80  and the tubes  90  forming the headers  132  is formed with shoulders, as shown above with respect to  FIG. 5 , so that the tubes  80 ,  90  can be stacked one above the other into a unitary construction. Each module  120  may therefore be formed and then multiple modules assembled to provide an energy transfer united with the requisite capacity. 
         [0061]    In operation, the heat transfer fluid is circulated through the inlet header  132  where it is discharged into the tubing  150  to flow in opposite directions to the outlet header  132 . The inlet  116  is provided from the lower point of the header  132  and the outlet  118  is taken from the highest point of the opposite header  132 . The transfer of heat to the surrounding water causes a radial flow of the water either from the flange  136  to the central tube  80  through the ports  82  where heat is being rejected to the cooling water or in the opposite direction when heat is being absorbed from the water. The inclination of the central disk  131  promotes the radial flow between the apertures  134  and the flange  136 . The inclination of the central disk  131  has a half angle between 65 and 75 degrees relative to the longitudinal axis of the tube  80  and the flange is radially outwardly inclined at a half angle of 10 degrees to the longitudinal axis. 
         [0062]    The stacking of the tubes  80  and the positioning of the ports  82  to control flow between the tube  80  and the space between adjacent shells  130  that accommodates the heat exchange tubing  150  provides a pronounced chimney effect along the longitudinal axis of the energy transfer unit. The chimney promotes the radial flow of fluid around the tubing and therefore increases the efficiency of the unit. 
         [0063]    The provision of the shell  130  and the chimney effect from the central tube  80  may also be utilized in an energy transfer unit located within a housing in a manner shown in PCT Publication WO 2012/009802. Such an arrangement is shown in  FIGS. 13 through 21 . 
         [0064]    Referring therefore to  FIG. 13 , an energy transfer unit  210  has a fluid inlet  212  and an outlet  214 . The inlet  212  and outlet  214  are connected to a heat exchange loop circulating through a heat pump in a conventional manner as referenced above. 
         [0065]    The energy transfer unit  210  has a housing  216  made from upper and lower shells  218  to  220  respectively. The shells  218  and  220  are connected to one another at an equator  222 . A number of inlet apertures  224  are provided on the equator around the periphery of the housing  216 . The upper shell  218  has a circular outlet  226  to receive a chimney described in greater detail below and the lower shell has a number of spaced apertures  223  ( FIG. 15 ) distributed about the lower surface of the shell  220  to permit the flow of water in to the housing  216 . 
         [0066]    The housing  216  contains a heat exchange unit  230  as best seen in  FIGS. 14 through 16 . The heat exchange unit  230  includes a pair of heat exchange cores  232  to  234 , each of which is formed from a pair of arrays of spirally wound tubing  236  that extends in opposite hands as described above. The tubing  236  is located on planar vanes  240  that are uniform ally distributed about the longitudinal axis of the energy transfer unit  210 . Each of the vanes contains a matrix of holes to receive the tubing  236 . As shown in  FIG. 15 , the runs of tubing  6  are arranged in a staggered fashion relative to one another although in certain circumstances, a rectilinear grid, as shown in  FIG. 19  is preferred. 
         [0067]    A central tube  244  extends through the housing  216  and projects though the aperture  226 . The lower end of the central tube  244  is sealed by a plate  246 . The inlet  212  and outlet  214  extends along the housing  210  at diametrically opposite sides of the tube  244 . The inlet  212  and outlet  214  respectively extend radially between the coils  232  to  234  to the radially outer periphery of the coils to a distribution conduit  248 . The distribution conduit  248  in turn is connected through a T-piece to a manifold  250  ( FIG. 14 ) winch supplies each of the coils  232  to  234 . Connection to the tubing  236  is provided through an elbow  252  that carries an apertured disk  254  ( FIG. 20 ). The disk  254  has apertures  256  to receive the end of each run of tubing  236  which are received in an aperture and welded to it to provide a secure fluid type connection. Each run of tubing flares outwardly from the disk  254  and through its spiral path to an opposite manifold connected to the outlet  214 . The supply of heat exchange fluid through the apertured disk  254  has been found to provide a more uniform distribution than is obtained through a vertical manifold. 
         [0068]    A conical baffle  260  is interposed between the coils  232  and  234 . The baffle  260  extends radially from the outer periphery of the coil  234  to the tube  244 . Ports  262  are provided in the tube  244  adjacent to the intersection of the baffle  260  with the tube. The ports  262  permit flow of fluid between the interior of the tube  244  and the underside of the baffle  260  with the inclination of the baffle promoting radially inward and upward flow of fluid. 
         [0069]    A similar baffle  264  is provided above the coil  236  which terminates at to collar which is concentric to the tube  244  to define an annulus. 
         [0070]    In use, the heat exchanger is located between the shells  218  and  220  of the housing  210  with the collar  268  projecting through the aperture  226 . The shells  218  to  220  are dimensioned to secure the heat exchangers within the housing  216  through engagement of abutments in the housing with the spars  240 . Such an arrangement is described in more detail in the PCT Publication noted above and need be described in greater detail at this time. 
         [0071]    Heat exchange fluid is provided trough the inlet  212  to the coils  232  to  234  and returned through the outlet  214 . The housing  216  is immersed within a body of water that provides a uniform temperature heat reservoir. If heat is being rejected to the water, i.e. as in the case where cooling is being affected b the associated heat pump, the temperature of the heat exchange fluids circulated through the inlet  212  and outlet  214  is higher than that of the surrounding water and heat is transferred to the water. The heating of the water causes a density imbalance that induces flow across the coils  234  to  232  so that fluid abuts against the underside of the baffles  260  and  264 . The inclination of the baffles  260 ,  264  causes a flow to move radially inwardly and, in the case of fluid passing over the lower through the ports  262 . The fluid then flows along the tube  244  and upwardly to the exterior of the housing  210 . 
         [0072]    Similarly fluid passing over the coil  236  is directed by the inclined baffle  264  to the annular between the collar  268  and tube  244  to emerge through the upper surface of the housing. 
         [0073]    The fluid lost through the tube  244  and collar  268  is replenished through ports  223  on the underside of the shell  220  and through the ports  224  provided around the equator of the housing  216 . The ports  224  are positioned above the baffle  260  so that a separate fluid inlet is provided for each of the coils. In this manner, a steady state of heat transfer between the heat exchange fluid provided through the inlet  212  and the surrounding water is accomplished. It will be appreciated that where more than two coils are provided within the housing  216 , a baffle is provided between each of the coils and set of ports provided in the housing to supply each of the coils, with a corresponding set of ports  262  in the tube  244 . In this manner, a modular arrangement is provided that can be adjusted to suit the particular installations. Where only a single core is required, flow may be provided from the ports  223  and the baffle is spaced from the top of the housing  216  to promote the radial flow. 
         [0074]    It will be appreciated that in a heat absorbing mode, that is when heat is being supplied through the heat pump, the temperature in the inlet  212  will be lower than that in the surrounding water and heat will be absorbed from the water. In this case the flow is in an opposite direction that is through the tube  244  and radially outwardly over the coils. 
         [0075]    The inclination of the baffles  260 ,  264  is typically in the range of 5° or 30° and preferably at 20°. 
         [0076]    As noted above, the tubing  236  is shown in  FIG. 15  in a staggered arrangement to increase the contact of the water with the tubes. It has however been found that in certain conditions, such as when the water is at its maximum density around 4 degrees Celsius, that the staggered arrangement of the tubing impedes the flow through the coils  234  and  236 . When operation in those circumstances is contemplated, the rectilinear array shown in  FIG. 19  is preferred so that the tubes  236  are aligned along the axis of the tube  244  and the flow of fluid enhanced. 
         [0077]    The flow of water across the coils is induced by the density imbalance caused by the heating of water. The chimney effect provided by the tube  244  acts to increase the flow through the lower heat exchange coil  234 . Moreover, the positioning of the collar  268  concentric to the tube  244  also increases the fluid flow across the coil  236  by inducing the flow under the baffle  264  where the tube and collar emerge. 
         [0078]    The provision of flow through the tube  244  and collar  268  also facilitates the installation of the heat exchange unit in a manner that avoids degradation of the heat source. As shown schematically in  FIG. 21 , a body of water such as a lake establish at a particular depth a thermocline beneath which the waters is at a relatively constant temperature. Above that layer, the water temperature may vary under different climatic conditions. The placement of a conventional heat exchanger within the thermocline layer increases the temperature in that zone thereby disturbing the cooler body of water. 
         [0079]    As shown in  FIG. 21 , the to  244  and collar  268  may be extended above the housing  216 . The housing  216  may then be located within the cooler body of water with the outlet at an elevated temperature in the surface or upper regions of the body of water. The elevated temperature water discharged from the chimney provided by the tube  244  and collar  268  does not return to the cool water below the thermacline, which is naturally replenished by the source of water, such as a stream or sprang that creates a lake or pond. A localised heating of the water at the surface can be observed that promotes heat loss due to evaporation and the maintenance of a steady state condition. 
         [0080]    This also permits the energy transfer unit to be utilized in an environment where the ground water provides the heat transfer medium to the surrounding earth. Conventional systems cause a thermal saturation of the ground water due to its limited flow and the lower thermal conductivity of the earth, but with the chimney provided by the tube  244  and collar  268 , the elevated temperature water is delivered to the surface where evaporation promotes the dispersion of the heat at a reduced flow rate.