EXTERNAL FLUE HEAT EXCHANGERS

Abstract

A heat exchanger is mounted external to a section of flue pipe or is an integral part of a section of flue pipe. The heat exchanger preheats a domestic hot water supply and boosts the return water temperature prior to reentry to the furnace coil. The heat exchanger reduces fuel use, pollution and wear of the furnace and burner. A typical heat exchanger installation includes an oil or gas burner located on a furnace or boiler having a flue pipe leading to a gaseous outlet, such as a masonry chimney. A short vertical flue section leads to a draft-regulating damper. The flue heat exchanger may be a coil of copper tubing wrapped around flue section, such that the tubing picks up heat from the heated flue gasses. The cold water source is coupled to a short length of convoluted flexible tubing with coupling flanges which couple the water through the flue mounted heat exchanger. Preheated water exits from the heat exchanger through flexible tubing having a safety pressure relief valve.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to heat exchangers, which are mounted external to a section of flue pipe or are an integral part of a section of flue pipe.

BACKGROUND OF THE INVENTION

[0002] Heat exchangers are known, which direct water in a pipe through a flue.

[0003] U.S. Pat. No. 4,122,801 of Burns describes a heat exchanger which first encircles water pipes in 2 circular rings around an exhaust flue, but then directs the water into coils within the exhaust flue. The external rings appear to be for positioning the water flow headers equally around the flue, not to preheat the water.

[0004] U.S. Pat. No. 4,211,187 of Farris discloses an energy conservation system for heaters that uses a heat exchanger in a furnace chamber or duct.

[0005] U.S. Pat. No. 4,136,731 of DeBoer discloses a heat transfer apparatus for supplementing a building heating and cooling system, using a heat exchanger in a furnace flue. DeBoer suggests an external heat exchanger, but provides no enabling details thereof.

[0006] U.S. Pat. No. 4,484,564 of Erickson disclose a water heater utilizing exhaust gases from furnaces or stoves, but the recovery is through a coil inside an exhaust flue.

[0007] U.S. Pat. No. 1,990,056 of Van Daam describes passing water through a spherical corrugated chamber.

[0008] U.S. Pat. No. 3,896,992 of Borovina and 2,521,462 of Kinzelmann both disclose water heaters that pass water through a spiral coil within an exhaust flue.

[0009] U.S. Pat. No. 4,037,567 of Torres proposes an exhaust flue over the water heater having a spiral coil for heating water therein.

[0010] U.S. Pat. No. 4,120,267 of Wood describe a tube and plate heat exchanger with water heating coils inside a chamber, such as a gas heat duct or flue.

[0011] Furthermore, U.S. Pat. No, 4,401,261 of Brown also discloses directing water coils inside of flues.

OBJECTS OF THE INVENTION

[0012] It is therefore an object of the present invention to provide a heater exchanger for domestic hot water with ease of installation, maintenance and removal.

[0013] It is a further object of the present invention to preheat a domestic hot water supply.

[0014] It is yet another object of the present invention to boost return water temperature in a hydronic heating installation prior to reentry to a furnace coil.

[0015] It is still another object of the present invention to reduce fuel use and to reduce pollution and wear of the furnace and burner.

[0016] It is yet another object of the present invention to improve over the disadvantages of the prior art.

SUMMARY OF THE INVENTION

[0017] In keeping with these objects and others, which may become apparent, the present invention includes heat exchangers mounted external to a section of flue pipe or as an integral part of a section of flue pipe. The heat exchanger preheats the domestic hot water supply and boosts the return water temperature in a hydronic heating installation prior to reentry to the furnace coil. The heat exchanger reduces fuel use and reduces pollution and wear of the furnace and burner.

[0018] A typical heat exchanger installation includes an oil or gas burner located on a furnace or boiler having a flue pipe leading to a gaseous outlet, such as a masonry chimney. A short vertical flue section leads to a draft-regulating damper. The flue heat exchanger may be a coil of copper tubing wrapped around the flue section, which picks up heat from the heated flue gasses. The cold water source is coupled to a short length of convoluted flexible tubing with coupling flanges thereby allowing water to travel to and from the flue mounted heat exchanger.

[0019] In another embodiment two flue heat exchangers communicate with cold water entering the horizontal heat exchanger which is wrapped around a flue section having a mixture of hot flue gasses and some make-up ambient air from the draft regulating damper. This heat exchanger is plumbed in series with another heat exchanger wrapped around the vertical section of flue pipe below a damper. The second heat exchanger again increases the water temperature prior to entering the furnace 5 hot water coil.

[0020] In another embodiment a heat exchanger is prefabricated as a standard flue section and substitutes for a length of flue. This heat exchanger has a central flue pipe section with heat exchanger tubing wrapped around its periphery. A tubular shell encases the tubing with openings allowing for both the water inlet and water outlet coupling flanges. A highly conductive conformable material fills the empty spaces within the shell to increase heat transfer.

[0021] In another embodiment, a hydronic heating system is a hydronic loop circulated by circulator pump forcing water into heating coil inside a boiler or furnace. In this system, it first flows through heat exchanger where it picks up waste heat from the flue.

[0022] In a further preferred embodiment a preformed heat exchanger coil is wrapped around a cylindrically shaped sheet larger in diameter than a section of flue. This sheet is not totally enclosed, but it has a small gap along its length.

[0023] In yet another embodiment, two coiled heat exchanger conduits are interleaved together around a flue pipe.

[0024] Each embodiment of the heat exchanger may include a safety pressure relief valve through which preheated water may exit.

[0025] Often when two or more different types of metals contact each other, the metals deteriorate, corrode or weaken at the point of contact. Therefore, each embodiment of flue heat exchanger may also be constructed such that both the metal tubing and the section of flue piping that the metal tubing is wrapped around are made from the same type of metal, preferably copper. In addition, each embodiment that contains this variation may also include gaskets located at each end of this flue section (preferably copper), such that the gaskets prevent direct contact between this flue pipe section and the flue pipe section made from a different type of metal.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention can best be understood in conjunction with the accompanying drawings, in which:

[0027] FIG. 1 is a side elevation view of a flue heat exchanger installation of the present invention;

[0028] FIG. 2 is a side elevation view of an installation using two flue heat exchangers;

[0029] FIG. 3 is a perspective view of an alternate embodiment for a flue heat exchanger;

[0030] FIG. 3a is a perspective view of an alternate embodiment of a heat exchanger cover;

[0031] FIG. 4 is a side cross sectional view of the embodiment shown in FIG. 3;

[0032] FIG. 5 is a plumbing diagram of a flue heat exchanger used for hydronic heating;

[0033] FIG. 6 is a side elevation view of a preferred embodiment of a flue heat exchanger;

[0034] FIG. 7 is an end view of the embodiment shown in FIG. 6;

[0035] FIG. 8 is a side elevation view of an interleaved heat exchanger installation;

[0036] FIG. 9 is a perspective view of another embodiment of a flue heat exchanger; and

[0037] FIGS. 9A and 9B are respective end and cross sectional views of the embodiment shown in FIG. 9.

DETAILED DESCRIPTION OF THE INVENTION

[0038] For ease of installation, maintenance, and removal, the heat exchangers of this invention are mounted external to a section of flue pipe or are an integral part of a section of flue pipe.

[0039] Although the primary application is the preheating of a domestic hot water supply, a secondary application is the boosting of return water temperature in a hydronic heating installation prior to reentry to the furnace coil. In either case, the objectives are to reduce fuel use and to reduce pollution and wear of the furnace and burner.

[0040] FIG. 1 shows a typical installation showing an oil or gas burner 6 on a furnace or boiler 5 with flue pipe section 2 leading to masonry chimney 3. A short vertical flue section 15 leads to a draft regulating damper 4. The flue heat exchanger 1 includes a coil of heat conductive tubing, such as copper tubing, which is wrapped around flue section 2. Flue heat exchanger picks up heat from the heated flue gasses within flue section 2. The cold water source 7 is coupled to a short length of convoluted flexible tubing 9 with coupling flanges 8 at either end, which couple the cold water through heat exchanger 1. The exit of preheated water from heat exchanger 1 is coupled to another short length of flexible tubing 9 and then coupled to a short length of pipe via coupling flanges 8.

[0041] This leads to a safety pressure relief valve 10 and isolation valve 11 (normally open) which couples the preheated water to a domestic supply pipe 12 (optional) and to the boiler 5 hot water coil intake 13. Pipe 14 is the normal domestic hot water supply line from the hot water coil.

[0042] The need for safety pressure relief valve 10 is predicated on rare events, which could conspire to cause boiling or excessive pressure in heat exchanger 1. While flue surface temperatures above 212 degrees F. are sometimes encountered, water at normal supply pressure (above 35 psig) requires a flue temperature over 280 degrees F. to present a danger of boiling. In the event of a defective well pump or control, the water pressure could be abnormally low. Likewise, an improperly adjusted fuel burner could produce abnormally high flue temperatures approaching 300 degrees F. The combination of such events may result in excessive pressures, hence the pressure relief valve. This danger is more pronounced in situations with a common boiler supplying heat and hot water since it would be more likely for the burner to be on while there is no call for domestic hot water; and there would be no cooling water flow through the heat exchanger.

[0043] FIG. 2 shows an installation using two flue heat exchangers 1 and 20 in a single installation. The coldest water enters the horizontal heat exchanger 1, which is wrapped around flue section 2 having a mixture of hot flue gasses and some make-up ambient air from draft regulating damper 4. Heat exchanger 1 is plumbed in series with heat exchanger 20, which is wrapped around the vertical section 2a of flue pipe below damper 4. This section of flue pipe 2a has a surface temperature higher than flue section 2 since it is closer to furnace 5 and only has hot flue gasses within. Therefore, heat exchanger 20 further boosts water temperature prior to entering the furnace 5 hot water coil.

[0044] FIGS. 3 and 4 show two views of an alternate embodiment 25 of the heat exchanger of this invention. This heat exchanger 25 is prefabricated as a standard flue section length L. It would be simply substituted for a length of flue. Heat exchanger 25 includes a central flue pipe section 26 with heat exchanger tubing 30 wrapped around its periphery. A tubular shell 31 with heat resistant end caps 32 encases the tubing 30 with openings for inlet 28 and outlet 27 extensions terminating in coupling flanges 29. A highly conductive conformable material 33 such as copper or aluminum wool is forced between flue 26 surface and coils 30 and generally fills the empty spaces within shell 31 to increase heat transfer. Further efficiency is achieved if shell 31 is a thermal insulator such as a fiberglass liner within a plastic hard shell.

[0045] FIG. 3a shows a removable embodiment of tubular shell 31 with openings for inlet 28 and outlet 27 extensions. A highly heat conductive conformable material 33 such as copper or aluminum wool is secured to the entire inner wall of tubular shell 31. Clasps 80 are placed along the outside of the surface of tubular shell 31 thereby allowing a means to secure the tubular shell around both flue pipe 26 and heat exchanger coil 30.

[0046] FIG. 5 shows the plumbing hook-up for the use of an external flue heat exchanger 1 in a hydronic heating system using fin tube heating elements 44. The basic circuit is a hydronic loop circulated by circulator pump 40 forcing water into heating coil 41 inside boiler (furnace) 5 then leading to expansion tank 42 and further to a parallel arrangement of zone valves 43 through fin tube sections (baseboard hot water room units) 44 and through return manifold 45. In systems without heat exchanger 1, this return flow would be directly plumbed to the intake of circulator pump 40. In this system, the return flow first flows through heat exchanger 1 where it picks up waste heat from the flue.

[0047] The preferred embodiment shown in FIGS. 6 and 7 shows a preformed heat exchanger coil 1 wrapped around a cylindrically shaped sheet (or sleeve) of metal 55 such as copper which is slightly larger in diameter than a section of flue. Sheet 55 is not totally enclosed, but it has a small gap along its length. The cylindrically shaped sheet is soldered or brazed to the copper tubing 1 for approximately three-quarters of its circumference to enhance heat transfer. The region indicated by 90 degrees in FIG. 7 is not bonded to tubing 1, thereby allowing the sleeve to open and enclose the flue. Three sets of clamping tabs 58 are located at each end and in the middle in a gap between adjacent coils of tubing 1. Bolts 56 and nuts 57 are used through tabs 58 to insure sheet 55 fits securely around a flue section 2.

[0048] An alternate embodiment specifically for dual-use boiler installations is shown in FIG. 8. An interleaved coil flue heat exchanger 70 is shown wrapped over flue pipe section 2. It consists of two separate conduits. Coil 71 plumbed into the domestic hot water return 13 and coil 72 plumbed into the hydronic heating return line 73. The method for forming this flue heat exchanger 70 is to coil two lengths of bendable tubing together resulting in the interleaved coils of sections 71 and 72. The plumbing is straightforward with the outlet end of coil 72 leading to circulator pump 40 through conduit 74 thus boosting the temperature of heating water that has been cooled by its flow through the various room hydronic heating units such as baseboard fin tube units or radiators. Similarly, the cold supply water at 7 uses the interleaved flue heat exchanger 70, a single section of flue pipe 2 can be used to recover waste heat year round regardless of whether the burner 6 is being fired to generate heat, hot water, or both. It is highly likely that circulator pump 40 will be running or that domestic hot water demand will occur while burner 6 is active or while flue pipe 2 is still hot from a recent firing. For dual-use installations, this maximizes the flue waste heat recover on a seasonal basis.

[0049] FIGS. 9, 9A and 9B show an alternate embodiment of a flue heat exchanger with particular gaskets 85, 86. This is because when two or more different types of metals contact each other, the metals may sometimes deteriorate, corrode or weaken at the point of contact. Therefore, while it is preferable that a flue heat exchanger may be constructed such that both the metal tubing 88 and the section 87 of flue piping that the metal tubing 88 is wrapped around are made from the same type of metal, preferably copper, modifications must be made if different metals are in contact with each other.

[0050] Therefore, FIGS. 9, 9A and 9B show a flue piping section 87 of a flue heat exchanger having metal tubing 88 wrapped around it, with flue piping section 87 having gaskets 85, 86 located at each end of flue piping section 87(preferably copper), such that the gaskets 85, 86 prevent direct contact between this flue pipe section 87 and the permanent flue pipe section which may be made from a different type of metal other than copper, to which flue pipe section 87 is attached.

[0051] It is further noted that other modifications may be made to the present invention, without departing from the scope of the invention, as noted in the appended Claims.

Claims

1. A heat exchanger for preheating domestic water comprising a hollow tubing having a water inlet end and a water outlet end, said hollow tubing external to and wrapped around a section of a flue pipe of a furnace.

2. The heat exchanger as in claim 1 further comprising a pressure relief valve coupling one end of said relief valve to the water outlet end of said hollow tubing.

3. The heat exchanger as in claim 2 further comprising an isolation valve coupling said relief valve to a boiler hot water coil intake.

4. The heat exchange as in claim 2 further comprising an automatic feeder coupling said relief valve to a boiler hot water coil intake.

5. The heat exchanger as in claim 1 wherein said heat exchanger further comprising a second heat exchanger connected in series therewith and wrapped around and external to another section of flue piping, further increasing water temperature prior to entering the furnace hot water coil.

6. The heat exchanger as in claim 1 wherein said heat exchanger is prefabricated as a standard flue section, which substitutes for a length of said flue pipe, said pre-fabricated heat exchanger having a central flue pipe section with heat exchanger tubing wrapped around its periphery, said pre-fabricated heat exchanger further having encasement over said heat exchanger tubing.

7. The heat exchanger as in claim 6, wherein said encasement permanently encloses said tubing, said encasement has a cavity and heat resistant end caps, said encasement also having a plurality of openings sufficient for a water outlet and water inlet to protrude therefrom, said cavity having a highly heat conductive material packed therein.

8. The heat exchanger as in claim 6, wherein said encasement comprises a preformed semi-pliable sleeve, said sleeve having two edges having clasps that when brought together close said sleeve and enclose said tubing forming a plurality of holes sufficient for said water inlet and said water outlet to protrude therefrom.

9. The heat exchanger as in claim 7 wherein said encasement includes a thermal insulator between said encasement's inner surface and the heat conductive material.

10. The heat exchanger as in claim 9 wherein said thermal insulator is a fiberglass liner.

11. The heat exchanger as in claim 1 wherein said heat exchanger is a hydronic heating system using fin tube heating elements, said heat exchanger having a hydronic loop circulated by a circulator pump forcing water into a heating coil inside the boiler then leading to an expansion tank and further to an arrangement of zone valves through fin tube baseboard hot water room sections and then through a return manifold.

12. The heat exchanger as in claim 1 wherein said heat exchanger coil is wrapped around a cylindrically shaped sheet of conductive metal, said cylinder having three quarters of its circumference affixed to a corresponding area of coil, which said sheet is slightly larger in diameter than a section of said flue pipe, said sheet having a small gap along its length, said gap allowing said flue section to slide into said cylinder, said cylinder further comprising a locking means to secure said cylinder when said gap is closed.

13. The heat exchanger as in claim 12 wherein said cylindrical sheet is copper, said cylinder also having gaskets on the inner and outer periphery of said cylinder sufficient in size to prevent contact with flue pipe sections made from a different type of metal.

14. The heat exchanger as in claim 1 further comprising a pair of interleaved flue heat exchanger coils wrapped together around said flue pipe, said coils comprising two separate conduits for separate transfer of heated water therethrough.

15. The heat exchanger for a domestic source of heat having a flue pipe leading to a masonry chimney, comprising:

a coil of heat conductive tubing wrapped around a section of said flue, said coil picking up heat from the heated flue gasses wherein said flue section is made of copper, said flue section further having gaskets located on respective inner and an outer edge peripheries, thereby preventing direct contact with flue sections made from metal other than copper.

16. The heat exchanger as in claim 15 wherein a cold water source is coupled to a length of convoluted flexible tubing having coupling flanges at either end, wherein said coupling flanges allow water transport to and from said heat exchanger.

17. The heat exchanger as in claim 16 wherein the preheated water from said heat exchanger is coupled to a boiler hot water coil intake.

18. The heat exchanger as in claim 17, wherein the preheated water from said heat exchanger is also coupled to a domestic supply pipe.

19. The heat exchanger as in claim 15 further comprising a pressure relief valve.

20. A heat exchanger for preheating domestic water comprising a hollow tubing having a water inlet end and a water outlet end, said hollow tubing external to and wrapped around a section of a flue pipe of a furnace,

said heat exchanger is prefabricated as a standard flue section, which substitutes for a length of said flue pipe,

said pre-fabricated heat exchanger having a central flue pipe section with heat exchanger tubing wrapped around its periphery,

said pre-fabricated heat exchanger further having an encasement over said heat exchanger tubing, said encasement enclosing said tubing,

said encasement having a cavity and heat resistant end caps, said encasement also having a plurality of openings sufficient for a water outlet and water inlet to protrude therefrom, said cavity having a highly heat conductive material packed therein,

said encasement comprising a preformed semi-pliable sleeve, said sleeve having two edges having clasps that when brought together close said sleeve and enclose said tubing forming a plurality of holes sufficient for said water inlet and said water outlet to protrude therefrom, and,

said encasement including a thermal insulator between said encasement's inner surface and the heat conductive material.