Abstract:
A system for heating two independent water supplies having a water storage tank adapted to contain a first, potable water supply and a coiled heat exchange tube mounted within the tank to contain and conduct a second, non-potable water supply. The tank has a top, bottom, wall, and flue communicating between the top and bottom. The tube is in communication with the exterior of the tank and with a circulatory space heating system. The tube has a double wall to protect against the mixing of the potable and non-potable water supplies, and the ends of the tube terminate at the surface of the water storage tank at a dielectric fitting which maintains electrical isolation between dissimilar metals otherwise exposed to the water.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a combined water heating system For domestic or commercial use which is capable of heating water for consumption as well as for space heating. The system heats potable water for consumption while exchanging heat to a recycling water-based space heating system. The combined water heating system provides this function while maintaining separation between the potable and non-potable water supplies. 
     FIELD OF THE INVENTION 
     There has long been a need for compact appliances to be installed within living areas in single and multi-family dwellings as well as in commercial establishments. Stackable washer and dryer units, combination cooktop and oven units, and other compact appliances have been developed to satisfy this need. 
     Several attempts have been made to provide a combined water and space heating appliance to satisfy the need for a compact system for supplying hot water. For example, U.S. Pat. No. 1,070,175, issued to Ponninghaus, discloses a boiler having a coil to conduct water to be used for such purposes as heating rooms or the like. The &#39;175 system, however, cannot be used with a standard glass-lined water heater system, and degradation of the &#39;175 system may lead to the mixing of potable and non-potable water supplies. These drawbacks are also inherent in U.S. Pat. Nos. 2,704,188; 3,793,992; and 3,828,847. 
     All traditional combined water heating systems exhibit one or more of several critical shortcomings. The lack of protection against the mixing of potable and non-potable water creates a significant hazard to consumers of water heated in such systems. Moreover, traditional combined water heating systems accelerate the decay of the water heater system, thereby increasing maintenance requirements and reducing the cost effectiveness of such systems. Traditional combined water heating system designs are also inappropriate for use with standard glass-lined water heaters. Lastly, traditional combined water heating systems are inefficient and are not capable of practical use. 
     Accordingly, there is a long-standing and thus far unsatisfied need for a compact, inexpensive and efficient water heater system capable of providing hot potable water simultaneously with heated water for space heating. 
     OBJECTS OF THE INVENTION 
     It is an object of this invention to provide a combined water heating system for domestic or commercial use capable of heating water for consumption as well as for space heating. 
     It is another object of this invention to provide a combined water heating system that is compact in size so as to be useful for both residential and commercial use. 
     It is another object of this invention to provide a combined water heating system that utilizes standard glass-lined, direct-fired gas water heaters. 
     It is still another object of this invention to provide a combined water heating system which prevents the mixing of potable and non-potable water supplies. 
     It is a further object of this invention to provide a combined water heating system with a dual heating capability without degrading water heater performance or compromising water heater longevity. 
     It is another object of this invention to provide a combined water heating system utilizing a dielectric fitting to prevent the exposure of dissimilar metals to water and the accelerated corrosion associated therewith. 
     Finally, another object of this invention is to provide a combined water heating system characterized by both low manufacturing costs and maintenance costs. 
     Other objects and advantages of the present invention will become apparent to those skilled in the art from the drawings, the detailed description of preferred embodiments and the appended claims. 
     SUMMARY OF THE INVENTION 
     The combined water heating system comprises a heat exchanger incorporated into a standard, glass-lined water heater system which utilizes a direct-firing burner and a flue to heat potable water for domestic consumption. The heat exchanger has a coiled construction which surrounds the water heater flue, entering and exiting the water heater water storage tank through the wall, top and/or bottom of the water storage tank. The heat exchanger coil passes through the potable water contained within the water heater tank so that heat is transferred for remote space heating. The heat exchanger coil has a quantity of coils based on the space heating load of the heating system. 
     The heat exchanger coil has a double-wall construction, having a non-metallic outer wall surrounding a metallic inner wall. The double-wall construction protects the potable water supply from contamination. If either the inner or outer wall leaks, the potable system will not be contaminated by the recycling space heater water supply. The non-metallic outer wall also permits dielectric mounting of the heat exchanger coil within the glass-lined water storage tank to prevent the accelerated corrosion which occurs when water is exposed to dissimilar metals. The inner wall&#39;s metallic construction provides increased heat transfer by increasing conductive heat transfer. The inner wall also provides strength to, and facilitates the formation of, the heat exchanger coil. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a side view of one embodiment of the combined water heating system with a portion of the water storage tank wall removed. 
     FIG. 2 shows a side view of the coiled heat exchange tube used in the combined water heating system shown in FIG. 1. 
     FIG. 3 shows a top view of the coiled heat exchange tube used in the combined water heating system shown in FIG. 1. 
     FIG. 4 shows a side view of another embodiment of the combined water heating system with a portion of the water storage tank wall removed. 
     FIG. 5 shows a side view of the coiled heat exchange tube used in the combined water heating system shown in FIG. 4. 
     FIG. 6 shows a top view of the coiled heat exchange tube used in the combined water heating system show in FIG. 4. 
     FIG. 7 shows a side view of a portion of the heat exchange tube with a cut-away cross-sectional view of the coiled heat exchange tube&#39;s double-wall construction. 
     FIG. 8 shows a cross-sectional side view of the dielectric fitting assembly indicated by &#34;Detail A&#34; in FIG. 4, illustrating the termination and mounting of the coiled heat exchange tube. 
     FIG. 9 shows a side view of one end of the coiled heat exchange tube, illustrating the preparation of the coiled heat exchange tube for mounting in the dielectric fitting assembly shown in FIG. 8. 
     FIG. 10 shows a cross-sectional view of an embodiment of the coiled heat exchange tube shown in FIG. 7. 
     FIG. 11 shows a cross-sectional view of another embodiment of the coiled heat exchange tube shown in FIG. 7. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is intended to refer to the specific embodiments of this invention that are illustrated in the drawings. This description is not intended to define or limit the scope of the invention, which is defined separately in the claims that follow. 
     Referring to FIG. 1, the number 10 designates one embodiment of the combined water heating system. The combined water heating system 10 has a heat source 12 which heats potable water contained within a glass-lined water storage tank 14. The heat source 12 is preferably a direct-fired gas burner of the type traditionally used in standard water heaters. The water storage tank 14 has a bottom 16, top 18 and wall 24. The water storage tank top 18 has a cold water inlet port 20 through which water is introduced into the water storage tank 14. A hot water outlet port 22 is also provided in the water storage tank top 18 so that hot water may be drawn from the water storage tank 14 consumption. The wall 24 of the water storage tank 14 has a tank outlet port 26 in the top portion of the wall 24, and a tank inlet port 28 located toward the bottom of the wall 24. 
     A flue 30 runs between the water storage tank bottom 16 and the water storage tank top 18 to provide for the exhaust of combustion gases from the heat source 12. A coiled heat exchange tube 32 is mounted within the glass-lined water storage tank 14 so that it surrounds the flue 3{). The coiled heat exchange tube 32 terminates at a dielectric fitting assembly 34 at the tank outlet port 26 and also at a dielectric fitting assembly 34 located at the tank inlet port 28. Pipe section 36 runs from the dielectric fitting assembly 34 at the tank outlet port 26 to a space heating system, and pipe section 38 runs from the space heating system to the combined water heating system, terminating at the dielectric fitting assembly 34 located at the tank inlet port 28. 
     Referring to FIG. 2, the coiled heat exchange tube 32 has a plurality of coils inclined at an angle of incline α 1 . The coiled heat exchange tube 32 has an overall length L 1 , and terminates at an outlet portion 40 and an inlet portion 42. FIG. 3 illustrates the coiled heat exchange tube 32 as viewed from the top. The coiled heat exchange robe 32 has a coiled inner diameter D 1  larger than the diameter of the flue 30 shown in FIG. 1. The outlet portion 40 and inlet portion 42 of the coiled heat exchange tube 32 are radially separated by an angle α 2 . 
     Referring to FIG. 4, the number 50 designates another embodiment of the combined water heating system. The water heater system 50 has a heat source 52 and a glass-lined water storage tank 54. The water storage tank 54 has a bottom 56, a top 58 and a wall 66. The top 58 of the water heater system 50 has a hot water outlet port 60 as well as a cold water inlet port (not shown). The top 58 of the water heating system 50 also has a tank inlet port 62 and tank outlet port 64. A flue 68 extends between the tank bottom 56 and the tank top 58 to exhaust combustion gases from the heat source 52. A coiled heat exchange tube 70 surrounds the flue 68, terminating at a dielectric fitting assembly 72 located at the tank outlet port 64 and also terminating at a dielectric fitting assembly 72 located at the tank inlet port 62. 
     In this embodiment of the invention, the coiled heat exchange tube 70 enters and exits the water storage tank 54 through the water storage tank top 58. Piping 74 extends from a space heating system and terminates at the dielectric fitting assembly 72 at the tank inlet port 62. Piping 76 runs from the dielectric fitting 72 located at the tank outlet port 64, and travels to the space heating system. 
     Referring to FIG. 5, the coiled heat exchange tube 70 has an overall length L 2  and a coiled length L3. The overall length L 2  is preferably about 34.5 =l inches, and the coiled length L 3  is preferably about 25.5 inches. A bend radius R 1  is provided near the outlet portion 71 of the coiled heat exchange tube 70 and at the bottom of the inlet portion 73 of the coil 70. The bend radius R 1  is preferably about 3 inches. 
     Referring to FIG. 6, the distance D 2  between the centerlines of the outlet and inlet portions 71 and 73 of the coil 70 is preferably about 11 inches. The coil inner diameter D 3  is preferably about 12.25 inches so that the flue 68 in the water heating system 50 shown in FIG. 4 can easily fit within the coiled heat exchange tube 70. For example, a flue 68 having an outside diameter of about 5 inches can easily fit within the coiled heat exchange tube 70. With the preferred dimensions provided above, the heat exchange tube will have an overall length of approximately 80 feet, and the coiled heat exchange tube 70 will have approximately 22.5 coils within the coiled length L 3 . This overall heat exchange tube length provides sufficient tube surface area for adequate heat transfer between water in the water storage tank 54 and water within the coiled heat exchange tube 70. 
     FIG. 7 illustrates the preferred double-wall construction of the coiled heat exchange tube 70. The heat exchange tube 70 has a tubing inner wall 78 having an inner wall thickness T 1  and an inner wall outside diameter D 4 . The tubing inner wall 78 is preferably formed from a soft metallic material such as copper or aluminum so that the coiled heat exchange tube 70 is provided with a means for support to prevent kinking while being soft enough to permit the formation of the coiled heat exchange tube 70 shown in FIG. 5. The metallic tubing inner wall 78 also provides conductive heat transfer to increase the output of the combined water heating system 50. The tubing inner wall 78 preferably has a thickness T 1  of about 0.035 inches and an outside diameter D 4  of about 0.625 inches. The tubing outer wall 80 fits snugly over the tubing inner wall 78 and has an outer wall thickness T 2  and an outside diameter D 5 . The tubing outer wall 80 is preferably formed from a non-metallic material such as high density polyethylene and may take the form of a co-extruded coating. The tubing outer wall 80 preferably has a thickness T 2  of approximately 0.020 inches, and the outside diameter D 5  of the tubing outer wall is preferably about 0.665 inches. 
     A strip or wire (not shown) may optionally be placed between the tubing inner and outer walls 78 and 80 of the heat exchange tubing 70. Referring to FIG. 10, A wire 100 is positioned between inner and outer walls 78 and 80. Alternatively, FIG 11 illustrates the use of a strip 102 between inner and outer walls 78 and 80. Such a strip or wire may be used to provide a path along which trapped potable or non-potable water can travel out of the system. The strip or wire can be applied axially or spirally to provide an axial or spiral water passage. 
     FIG. 8 provides a cross-sectional view of Detail &#34;A&#34; of the combined water heating system 50 shown in FIG. 4. The dielectric fitting assembly 72 provides a termination for the heat exchange tube 70 at both the tank inlet port 62 and tank outlet port 64 in the water storage tank top 58 shown in FIG. 4. The dielectric fitting assembly 72 provides a structural mounting for the coiled heat exchange tube 70 while maintaining isolation between the tube inner wall 78 and the wall 66 of the water storage tank 54. An O-ring 82 captured within a groove in the steel fitting 83 provides a seal against the outside surface of the outer wall 80 of the heat exchange tube 70. A second O-ring 84, also captured within the steel fitting 83, creates a seal around the outside surface of the inner wall 78 of the heat exchange tube 70. A relief hole 86 positioned between the first O-ring 82 and the second O-ring 84 provides a path for the escape of potable or non-potable water that may build-up in the annular region between the inner wall 78 of the heat exchange tube 70 and the inner surface of the steel fitting 83. The relief hole 86 will also provide an escape for potable or non-potable water that travels along the passageway formed by the optional strip or wire captured between the tubing inner and outer walls 78 and 80. 
     The dielectric fitting assembly 72 is preferably capable of sealing against pressures approaching and even exceeding 300 psi. If both the inner and outer walls 78 and 80 of the tube 70 leak, the pressure within the water storage tank 54 will force potable water into the tube and will prevent the leakage of non-potable water into the water storage tank 54, thereby preventing the contamination of the potable water supply. 
     In order to prevent axial movement of the heat exchange tube 70 within the steel fitting 83, there are provided two plastic spacers which capture the inner wall 78 of the heat exchange tube 70. A first plastic spacer 88 forms an upper end of a groove in which the second O-ring 84 is seated. The first plastic spacer 88 also prevents movement of the heat exchange tube 70 into the water storage tank 54. A second plastic spacer 90 is positioned to prevent the axial movement of the heat exchange tube 70 outward from the water storage tank 54. The exposed end of the inner wall 78 of the heat exchange tube 70 terminates in a position remote from the inner surface of the steel fitting 83 so as to maintain dielectric isolation. A retaining ring 92 is positioned within a groove in the steel fitting 83 in such a way as to capture the first and second plastic spacers 88 and 90. 
     Male pipe threads 94 on the steel fitting 83 are provided to permit sealing engagement with the tank inlet and outlet ports 62 and 64, indicated with phantom lines in FIG. 8. The tank inlet and outlet ports 62 and 64 are attached to the wall 66 of the water storage tank 54 by means of welds 96. Female pipe threads 98 are provided at the opposite end of the steel fitting 83 to provide for sealing connection with piping components which lead to and from a space heating system so that water within the space heating system can be circulated to and from the water heating system 50. 
     FIG. 9 illustrates the manner in which the ends of the heat exchange tube 70 are prepared for mounting within the dielectric fitting assembly 72 shown in FIG. 8. So that a seal can be made against each of the inner and outer walls 78 and 80 of the heat exchange tube 70, the outer wall 80 is stripped from the inner wall 78 for a length L 4 . This strip length L 4  is preferably about 1.121 inches. 
     In order to allow for the mounting of the heat exchange tube 70 within the dielectric fitting assembly shown in FIG. 8, the end portion of the inner wall 78 must be flared so that the first and second plastic spacers 88 and 90 can capture the inner wall 78 to prevent axial movement. The inner wall 78 is flared over a length L 5  and at an angle α 3 . The flare length L 5  is preferably about 0.296 inches, and the angle α 3  is preferably greater than about 45°. 
     Referring to FIGS. 1 and 4, the operation of the combined water heating systems 10 and 50 will now be described. In the embodiment of the combined water heating system shown in FIG. 1, water from a spaced heating system enters the combined water heating system 10 through piping 38, a dielectric fitting assembly 28, and an inlet port 28. The water travels upwardly through the coiled heat exchange tube 32 aided by convection currents as it is heated by exposure to hot water within the water storage tank 14 and the flue 30. The water then exits the water storage tank 14 through an outlet port 26 and a dielectric fitting assembly 34 and travels to the space heating system through piping 36. This water is continuously circulated through the combined water heating system 10 and space heating system as needed. 
     Referring to FIG. 4, the combined water heating system 50 has a coiled heat exchange tube 70 which terminates at tank inlet and outlet ports 62 and 64 located in the top 58 of the water storage tank 54. The ends of the coiled heat exchange tube 70 are fixedly mounted in dielectric fitting assemblies 72. Water from a space heating system enters the combined water heating system 50 through piping 74, dielectric fitting assembly 72, and inlet port 62. The water travels downwardly toward the bottom 56 of the water storage tank 54 and then travels upwardly through the coiled heat exchange tube 70 aided by convection currents. The water is heated by exposure to hot water within the water storage tank 54 as well as the flue 68. The heated water then exits through the top 58 of the water storage tank 54 by passing through a dielectric fitting assembly 72 mounted at the tank outlet port 64. The water then travels towards the space heating system through piping 76. The vertical leg of the heat exchange tube 70 which extends from the tank inlet port 62 travels downwardly between the flue 68 and the coils of the heat exchange tube 70. 
     In any embodiment, the combined water heating system according to this invention confers many significant benefits. First, the combined water heating system provides a compact, economical, and durable appliance for use in both residential and commercial applications. The combined water heating system simultaneously provides hot potable water for consumption as well as heated water for use in radiant hot-water heating systems. The combined water heating system can be provided with standard glass-lined water heaters without compromising the longevity of the water heaters. 
     Also, the transfer of heat from potable water within the water storage tank to non-potable water circulated through a radiant hot-water heating system provides increased energy efficiency. Because space heating needs are sporadic and seasonal, constant heat transfer is not required. In a reversed system, heat transfer would have to be constant to meet hot potable water needs. 
     The dual heating capability of the water heating system is made possible by using a heat exchange tube having a double-wall construction. The outer wall of the coiled heat exchange tube when mounted in a dielectric fitting provides dielectric isolation, thereby preventing the accelerated corrosion associated with the exposure of dissimilar metals to water within water storage tanks. The inner wall is formed from a soft metallic material which provides strength and structure to the coiled heat exchange tube while providing for improved heat exchange and increased conductivity for improved heat exchange and malleability to facilitate coil formation. 
     The combined water heating system confers these benefits in any embodiment, and various modifications to the overall system or its various components can be made without reaching beyond the scope of this invention. For example, the tank inlet and outlet ports at which the coiled heat exchange tube ends terminate can be formed in the wall of a glass-lined water storage tank, in the top of a water storage tank, through the bottom of the water storage tank, or in any combination of the water storage tank surfaces. Water may enter the coiled heat exchange tube near the top of the water storage tank instead of near the bottom. The combined water heating system can be used in a gas water heater using a direct-firing burner or in an electric water heater without a flue, and the number of coils formed in the coiled heat exchange tube may be varied depending on the type of water heater and the load demands of the space heating system. 
     The double-wall heat exchange tube is preferably formed with a nonmetallic coating such as high density polyethylene, but can be formed from many other materials, including but not limited to polyethylene and polypropylene. The outer wall may optionally be co-extruded over the inner wall so as to maintain a uniform fit between the heat exchange tube&#39;s outer and inner walls. The outer wall may optionally be applied by employing materials such as heat shrink tubing. The outer wall may also be applied by means of a heat fit process wherein the outer wall is heated to cause its expansion, and the inner wall is placed within the outer wall so that, when the outer wall cools and contracts, there remains a close lit between the inner and outer walls. No matter how the outer wall is applied to the inner wall, it is preferable that a path remains between the walls to permit the drainage of trapped water. To ensure that such a path remains between the walls, a strip or wire may optionally be inserted in an axial, spiral or some other orientation between the walls. The inner wall is preferably formed from a malleable metallic material such as aluminum or copper, but may optionally be formed from any other suitable material, including but not limited to carbon and stainless steel. 
     The dimensions of the coiled heat exchange tube may vary depending on practical considerations or the load requirements of the space heating system. For example, an increase in the diameter of the coiled heat exchange tube will increase the surface area over which heat exchange may occur, thereby increasing the output of the system. Similarly, the wall thickness of the inner and outer walls can be increased or decreased to facilitate the co-extrusion and coiling processes, and when a nonmetallic, nonconductive material is used to form the outer wall, the thickness of the outer wall may be reduced to decrease its insulative effect. The thickness of the inner wall must be sufficient to avoid kinking of the heat exchange tube during the coiling process, and must be suitable to maintain the shape of a finally coiled heat exchange tube. 
     The dielectric fitting assembly may be structured in any way capable of maintaining dielectric isolation between the metallic inner wall of the heat exchange tube and the inside surface of the steel fitting, and the heat exchange tube can be mounted within the dielectric fitting assembly in any way which prevents substantial axial movement of the heat exchange tube within the dielectric fitting assembly. A plastic fitting may optionally be used to provide dielectric isolation between the metallic inner wall of the heat exchange tube and the inlet and outlet ports in the water storage tank. 
     The water storage tank within which the coiled heat exchange tube is mounted need not be directly heated. For example, the water storage tank may optionally be remote from the water heater, and hot water supplied to the remote water storage tank would heat the water circulated through the coiled heat exchange tube. 
     These and other modifications to the combined water heating system can be made without exceeding the scope and spirit of this invention. The scope of this invention is separately defined in the following claims.