Patent Publication Number: US-2006011149-A1

Title: Water heater/cooler

Description:
This invention relates to a water heater/cooler, and relates particularly, though not exclusively, to a solar boosted heat pump water heater and method of manufacture thereof.  
      In Australian Patent Nos. 582,291 and 603,510 there is described a solar boosted heat pump water heater where the water tank of the water heater is encircled along a substantial part of its length by a tube mechanically fixed by welded saddles and fused solder. The tube carries a refrigerant fluid to heat the surface of the water tank to thereby heat the water contained within the water tank. The tube about the water tank is held under tension during bonding to reduce the likelihood of the heat-conductive bonding material breaking during expansion and contraction of the tube and tank during use. A tin/lead/flux-acid solder paste is applied to the tube during its attachment to the water tank and the water tank is subsequently heated in an oven to melt the solder to complete the heat transfer bond between the tube and the water tank. The prewinding processes involving the grinding of the outer cylindrical surface to remove scale; a priming wash and a final wash with a copper sulphate solution to aid tinning and maintaining the tube under tension slows the manufacturing cycle and the post heating of the complete water tank to melt the solder results in further production time losses. The gas required to heat the tank mass to solder fusion temperature and the resultant cooling time adds considerable expense and time to the manufacturing process. Further time delays and costs occur as the tank must be washed down to remove residual soldering acid and treated with a bitumous anti-corrosion treatment. In addition the manufacturing process has the tube deforming/tensioning device about 600 mm from the tank when the tube is being applied which allows the tube to be randomly twisted as it leaves the rollers and may lead to loss of contact between the water tank and the tube.  
      It is therefore an object of the present invention to provide a water heater that improves on the concepts described in Australian Patent Nos. 582,291 and 603,510.  
      A further object of the present invention is to provide a water heater that is simpler to construct than that described in Australian Patent Nos. 582,291 and 603,510.  
      With these objects in view the present invention provides in one aspect a water heater/cooler including a water tank having a wall formed from material having heat transfer properties, a tube adapted to carry, in use, a refrigerant fluid, is applied externally about said tank wall, a heat-conductive material is coextensive with the length of said tube to allow said tube to be in said in heat-conductive contact with said tank wall and at least one layer of material tightly wrapped about said tank wall and said tube.  
      Preferably said tube is compressed against said tank wall and said compression is maintained by said at least one layer of material. Preferably said tube is of circular cross-section and during compression against said tank wall is deformed into a D-shape in cross-section. Alternatively said tube is of circular cross-section and during compression against said tank wall is deformed into a bi-lobular profile. In a preferred embodiment said at least one layer of material includes at least one layer of stretch wrap film and at least one layer of a heat reflective material thereover. Preferably at least a further layer of stretch wrap film is applied over said at least one layer of heat reflective material.  
      Preferably said stretch wrap film is polythene based. In a further embodiment said heat conductive material is a non-setting heat conductive paste. In yet a further embodiment said at least one layer of stretch wrap film surrounds said heat conductive material in an airtight manner. Preferably said tube extends over at least 85% of the length of said tank.  
      In a further aspect of the invention there is provided a method of forming a water heater/cooler, said method including the steps of winding a tube around the wall of a water tank under which a heat-conductive material coextensive with the length of said tube has been applied to either said tube or said wall of said water tank to allow said tube to be in heat-conductive contact with said tank wall and tightly wrapping at least one layer of material about said tank wall and said tube.  
      Preferably beads of heat-conductive material are applied to said tank wall on either side of said tube and said beads are formed into a join fillet to, in use, increase the heat transfer of said tube with said tank wall. 
    
    
      In order that the invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawing, in which:— 
       FIG. 1  is a perspective view of water heater made in accordance with a preferred embodiment of the invention;  
       FIG. 2  is a cross-sectional view of the water heater shown by the area circled “2” in  FIG. 1 ;  
       FIG. 3  is an enlarged view shown by the area circled “3” in  FIG. 2 ;  
       FIG. 4  is a sequence of steps to apply the tube to the water tank to make the water heater shown in  FIG. 1 ; and  
       FIG. 5  is a variation of the profile shown in  FIG. 3  without the wrappings. 
    
    
      In the drawings there is shown a water heater  10  including a water tank  12  having a bottom wall  14 , typically concave or convex, a convex top wall  16  and a cylindrical sidewall  18 . Water tank  12  can be formed of any suitable thermal conductive or heat transfer material preferably metallic or alloy based. In the preferred embodiment the water tank is formed from glass lined steel, stainless steel, copper or other suitable material. A cold water inlet (not shown) will be installed adjacent bottom wall  14  and a hot water outlet (not shown) will be installed adjacent the top wall  16 . The water tank  12  is held in a cylindrical casing  20  sealed by lid  22 . Insulating foam (not shown) will fill the gaps between water tank  12  and cylindrical casing  20  and lid  22 . Tube  24  is wrapped about cylindrical sidewall  18  and has an inlet  26  and outlet  28 . Tube  24  is also formed of any suitable thermal conductive or heat transfer material preferably metallic or alloy based. In the preferred embodiment tube  24  is formed from copper in view of its pliability and corrosion resistance. Tube  24  will typically extend over 85% of the length of cylindrical sidewall  18 . Refrigerant (not shown), typically R22 and including R12 equivalents, is pumped through tube  24  to heat the cylindrical sidewall  18  and thus heat the water contained within water tank  12 . Tube  24  is part of a solar boosted heat pump water heating system, which is described in Australian Patent Nos. 582,291 and 603,510. In order to avoid duplication of description reference is made to Australian Patent Nos. 582,291 and 603,510, the contents of which are herein incorporated into this specification.  
      In  FIGS. 2 and 3  there is shown the application of tube  24  to cylindrical sidewall  18 . Tube  24  has a D-shape (as shown), oval shape or other closed shape with a flattened base  30  and is formed by deforming a circular cross-sectional tube prior to its application to, or by form roller compression as shown), against the cylindrical sidewall  18 . Tube  24  has a heat transfer paste  32  applied to the base  30  to maximise the heat transfer from tube  24  to cylindrical sidewall  18 . Tube  24  is applied under compression to cylindrical sidewall  18  and layers of material wrapped around water heater  10  to maintain the compression. Typically, two layers  34 ,  36  of a stretch wrap film are applied first. The stretch wrap film may be a polythene film of a suitable formulation. The next layer  38  is an aluminium foil and it will act as a reflector to turn back heat to water heater  10 . Finally, layer  38  is encased in a further four (4) layers  40 , 42 , 44 , 46  of stretch wrap film. The number, and interleaving of the layers of material, can be varied to suit requirements and are not restricted to the number and positioning of layers described. As the stretch wrap film is not exposed to ultraviolet light, denaturing of the film will not occur. The wrapping and compression of the layers will ensure the integrity of the heat transfer paste  32  and will seal the paste against the possibility of air or heat cycle drying. Without the wrapping, the heat transfer paste  32  would tend to dry out and become crumbly when exposed to air over time. The heat cycling would also hasten this disintegration. The crumbling would reduce the heat conductive contact between tubing  25  and sidewall  18 . The wrapping seals the paste  48  from air and avoids any drying or thickening effects.  
       FIG. 4  shows the sequential steps of applying tube  24  to cylindrical sidewall  18 . In this embodiment tube  24  is formed by roller compression. Firstly, a length of circular cross-sectional tubing  25 , for example of 10 mm diameter, is moved into position and held against cylindrical sidewall  18 . A bead, for example of 3 mm diameter, of heat transfer paste  48  is placed on the horizontally rotating water tank  12  from a dispenser (not shown) underneath where tubing  25  will be forced onto the cylindrical sidewall  18 . The heat transfer paste  48  used in this embodiment is known as Bostik heat transfer sealer #1128 or #5603. The heat transfer paste  48  in this embodiment is a grease-like material with no bonding properties but a bonding type material may also be used. Secondly, tubing  25  is compressed to a D-shape (as shown) or an oval shape against cylindrical sidewall  18  to flatten the bead of heat transfer paste  48  and allow a uniform thickness of paste to be applied to base  30  of tube  24 . Paste  48  will typically ooze out from underneath base  30 . Tubing  25  is deformed into the D-shaped or oval tube  24  by a compression roller  64  which rotates about axle  66  to compress and deform tubing  25  onto cylindrical sidewall  18 . Thirdly, a pair of parallel beads  50 , 52 , for example of 4 to 6 mm diameter, of heat transfer paste are applied to cylindrical sidewall  18  and opposing sides of tube  24 . This step will increase the size of the heat transfer footprint. The final step is to mould the beads  50 ,  52  into a filleted join  56  to maximise the heat transfer. Tube  24  is typically wound from the bottom to the top and is held, but not attached, to cylindrical sidewall  18  at both ends by a bracket (not shown), typically plastic, which clips onto tube  24 . The clips are held to cylindrical sidewall  18  by a non-stretch binding passing around the tank circumference and pulled tight. When the tube  24  reaches near the top wall  16  of water tank  12  the tube  24  is clipped to stabilise it while wrapping of the windings occurs. The windings of tube  24  are usually in a tighter spiral at the lower half  58  than at the upper half  60 . Other variations of windings may be used, for example, a progressive spiral increase with a variable pitch, two separate winding, one above the other or interleaved. To complete the construction of water heater  10  the layers  3446  are then applied as discussed with reference to  FIGS. 2 and 3 . Tube  24  is then bent across the wrapped windings to provide outlet  28 .  
       FIG. 5  shows a variation of the D-shaped profile of tube  24 . In this embodiment tube  24  is indented at  68  to provide a bi-lobular profile with lobes  70 ,  72 . This will increase the concentration of heat mass to the edges of tube  24  and into the paste fillets  56  to increase the refrigerant velocity in the areas of the tube where refrigerant oil accumulates to assist oil return and reliability.  
      The preferred embodiment discussed above simplifies construction of a water heater compared to the techniques disclosed in Australian Patent Nos. 582,291 and 603,510. In parallel testing the preferred embodiment shows a 28% increase in performance over the water heater shown in Australian Patent Nos. 582,291 and 603,510 and a reduction in the compressor/water temperature ratio of over 10% in the mid to high temperature range. These performance improvements will directly increase efficiency and compressor life and reduce noise output. The preferred embodiment had at least a 28% higher Coefficient of Performance. This value increased to a 38% increase when 24 hour heat losses and their subsequent recovery were taken into account.  
      Although the preferred embodiment has been described with reference to its use as a water heater, water tank  12  could hold cooled water by reverse cycle refrigeration where the refrigerant in tube  24  is cold rather than hot.  
      Throughout this specification, unless the context requires otherwise, the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers.  
      The invention will be understood to embrace many further modifications as will be readily apparent to persons skilled in the art and which will be deemed to reside within the broad scope and ambit of the invention, there having been set forth herein only the broad nature of the invention and a certain specific embodiment by way of example.