Drainpipe heat exchanger
The present invention is a jacket-type heat exchanger which may, for example, be used to replace or fit over a section of drainpipe to heat fresh cold water using the waste heat in the drainwater. Normal cold water pressure is used to create an internal-expanding force on the inner thermal contact wall of the jacket, which, in turn, creates an enormous heat-transfer clamping force on the drainpipe for fast heat transfer. A longitudinal gap in the jacket (or a two-piece jacket) enables clamping movement. An external sleeve with clamps resists bulging of the outer jacket wall. The heated cold water is plumbed to a faucet or water heater so as to reduce hot water use, which, in turn, reduces energy use and related environmental damage. Double-wall construction and venting for visible leak detection satisfies plumbing code requirements. A horizontal embodiment discloses a two-piece plastic-copper drainwater heat exchanger. Use on vehicular exhaust pipes is also contemplated for providing instant interior heat and/or motor warm-up.
This patent application follows on from provisional application 60/998,670.
FIELD OF THE INVENTIONA drainpipe heat exchanger for use on drain- or exhaust pipes for waste heat recovery including from any building's drainpipe. It can be made small enough for use with individual plumbing fixtures such as sinks, or for exhaust pipes of cars and trucks. It can also be used over existing drainpipes and exhaust pipes that cannot have their flow interrupted by their temporary removal/replacement. For example large diameter ones are difficult and expensive to remove and reinstall.
Heating cold water to make hot water for cleaning and then discarding the heat along with the dirty hot water is expensive, wasteful and environmentally damaging. It is estimated that in North America some $15 billion dollars is spent annually on fuel to heat water. The fuel's exhaust and the discarded heat in the used hot water contribute doubly to global warming and a lower standard of living. Speeding up heating of vehicle occupants using waste exhaust heat is also contemplated.
BACKGROUND OF THE INVENTIONA shortcoming of traditional drainwater heat recovery (DHR) heat exchangers is their cost effectiveness. This can be partly attributed to the poor use of the expensive heat transfer surface area. Even more so if laid horizontally which is often necessary.
Copper tubing for cold water coiled around a vertical copper drainpipe makes a simple but expensive DHR heat exchanger. It is based on the long-known Falling Film principle.
In Falling Film heat exchangers, a liquid is ideally made to overflow into the top of a straight, large bore, vertical tube. The flow is meant to be circumferential, flowing down in an even, falling film clinging to the entire inner vertical tube wall, from top to bottom. (More information on falling film heat exchangers can be found at: The Chemical Educator, Vol. 6, No. 1, published on Web Dec. 15, 2000, 10.1007/s00897000445a, © 2001 Springer-Verlag New York, Inc., and, U.S. Pat. No. 4,619,311 to Vasile which discloses a equal flow Falling Film DHR heat exchanger.)
The falling film DHR is, in many ways, ideal because it is not blocked by large solids and other matter contained in a building's drainwater. In operation, cold, ground water feeding a water heater first passes through the outer coil of tubing on its way to the heater. At the same time, drainwater is ‘falling’ down the inside tube, transferring heat to the cold water. Thus showering and sink rinsing are the principal appliances/fixtures for such heat exchangers because only then is cold water flowing into the hot water heater exactly while the drain is flowing with the now-dirty used hot water.
One of the weaknesses of such heat exchangers is the narrow spiral contact patch between the coil's inner surface and the tube's outer wall. Because heat transfer is a direct function of surface area, the less than full contact area reduces performance from high cost materials. Further, the long length of the coil tube (up to 100 feet long) and the fact that it flattens somewhat as it is wound, creates internal resistance to flow and an unwanted drop in water pressure for the heater.
In the instant invention, instead of tubing, sheet copper is used for the cold water. This dramatically lowers cost, increases contact area, and eliminates pressure drop. For example, in a 5 foot long, 4 inch diameter drainpipe, only ⅔ the weight of copper is needed for the cold water exchanger and, a much higher percentage of that copper surface is used for heat transfer. Further, the instant invention allows for very compact, small diameter DHR (i.e., a 1¼ inch diameter sink drainpipe) for individual fixtures and appliances which is not practical with wrapped tube designs due to the bend radius limitation of suitably sized outer tubing. Thus with the instant invention, DHR is made significantly more cost effective and more widely usable.
SUMMARY OF THE INVENTIONIn one embodiment of the instant heat exchanger invention, sheet copper is formed into a hollow, tubular, sealed chamber or jacket having spaced inner and outer walls forming a cavity and where the inner wall matches the shape or form of the drainpipe to which the exchanger is to be attached. A longitudinal gap, slit or opening is provided where the inner and outer walls converge giving the chamber or jacket a “C” shape. This gap allows contraction of the inner wall tightly onto a circular drain tube when the exterior wall is clamped using band clamps acting on a stiff outer sleeve (for clamp force distribution). Thus an intimate contact between the thermal transfer surfaces, namely, the chamber or jacket inner wall and the drainpipe outer wall is made possible and yet the jacket can be easily slid onto the drainpipe from one end. In addition, normal mains cold water supply pressurizes the inside of the jacket. This pressure adds to the thermal contact force with the drainpipe thereby to maximize thermal conduction and so, the all important rate of heat transfer.
In one application the jacket is slid over and clamped onto the exterior of an existing drainpipe, in another it is pre-assembled with a drainpipe forming a complete DHR heat exchanger which then replaces a section of existing drainpipe. In a second embodiment, the instant invention is fabricated in two long half-cylindrical jackets (clam-shell like) which are assembled onto a operating drainpipe as described above.
A third embodiment, for horizontal installation, uses a somewhat flattened (D-shaped) drainpipe. The cold water conduit or chamber is in the form of a bar—a thin, flat, tube, or, in the form of a trough, located under the flat drainpipe and bound to it with clamps applied over a D-shaped shoe or shaped filler piece to even out the clamping force along the whole length. The clamping plus the internal water pressure provide high performance thermal contact therebetween.
In a fourth embodiment, the flattened, D-shaped drainpipe may be in two parts: an upper hemi-cylindrical plastic support portion bonded to a lower flat metal heat transfer portion, to lower costs.
In use, a sink or shower may have the heat exchanger lying horizontally beneath it such that cold water is pre-heated before reaching the cold water faucet. In this way less hot water is needed to mix with the now-warm cold water to achieve the desired temperature. Less hot water use saves energy and money and pollution, and, if electrically heated, lowers peak power demand.
During fabrication, the sheet copper should be slightly creased diagonally where thermal contact will occur to serve as a vent for visible leak detection (a drip path onto the floor). The sheet is then formed into an “outline C shape”, or, double walled hollow tube structure with a longitudinal gap. The outer wall of the jacket is punched to receive soldered-on pipe fittings for the cold water supply and the ends are sealed with “C” shaped rings of copper tubing, rod or twisted wire, dip-soldered into place at each end. Alternatively, the jacket ends may be squeezed-closed and soldered.
The unique, high-force hydraulic clamping action maximizes heat transfer which increases with contact pressure. For example, if the drainpipe is 3 inches in diameter and the jacket 48 inches long and the cold water is at 50 pounds per square inch pressure, the contact force will be approximately: 3.14(π)×3×48×50=22,000 pounds, or 11 tons of contact force!
Not only does such an enormous force provide excellent heat transfer but it does so evenly over its entire length. This would be extremely difficult or impossible to achieve by any mechanical clamping method
Where the instant invention is to be installed on an existing drainpipe already permanently in place, the jacket may be made in two halves (or hinged) with duplicate fittings to connect to the cold water supply. The outer plastic sleeve would also be in two halves (or hinged). In some cases only a lower, half-jacket may be appropriate to reduce cost when using it on a horizontal drainpipe, for example.
Use of the instant invention is also contemplated on vehicle exhaust pipes. So, for example, a stainless steel model, with a metallic outer retaining sleeve, may be fitted to an exhaust pipe of a car to provide double-walled-safe, hot air to the car interior in cold weather. The internal pressure-clamp feature may be duplicated using compressed air and flow restrictors, or internal fins/spacers to transmit the clamping force onto the inner wall of the jacket and onto the exhaust pipe. The recovered heat can be used to heat the vehicle's interior and/or its motor and/or a heat storage medium. Fresh air blown through the jacket becomes heated air for the vehicle interior.
In all embodiments, internal baffles, walls, dams (as in a weir) or fins can be incorporated to distribute fluid flow, optimize heat transfer and to distribute the external clamping force.
Two basic embodiments are disclosed, vertical heat exchanger 100, and horizontal heat exchanger 200. each has two conduits in thermal contact. One conduit is a straight pipe or tube that typically carries a waste fluid from which heat is to be recovered, and the second conduit is for the second fluid to which heat is to be transferred, although the heat transfer path could be reversed. Generally the conduits are metal and preferably copper if the temperature differential is small and therefore requires fast heat transfer. The two conduits are co-operatively shaped and tightly clamped together so as to provide optimal thermal contact and thus rapid heat transfer. In the horizontal embodiment the waste conduit is normally on top of the second conduit (waste fluid has heat to be recovered), while in the vertical embodiment the waste conduit is encircled by the second conduit.
One novel feature of the instant invention is the use of the internal water pressure in the colds water conduit to create very high thermal contact force with the drainwater conduit to provide fast heat transfer so as to maximize recovery of waste heat energy.
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In one embodiment, wall 2 of conduit 50 has wings 3 which contact the side of the drainwater conduit 60 to create additional surface for heat transfer. In
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In use, by connecting cold water conduit 50 to a pressurized fluid supply, an enormous thermal transfer contact force is created between the flat surfaces of conduits 50 and 60, restrained by bands 12 (over a stiff sleeve, not shown), to provide exceptional heat transfer therebetween. For example, with a 4 inch wide flat that is 50 inches long and with a pressure of 40 pounds per square inch, the contact force is some 8,000 pounds. This force custom forms typically imperfect flat surfaces 1′ and 5 into intimate contact.
With the instant invention, horizontally flowing drainwater, whose valuable heat energy is normally wasted, can be cooled by heat transfer to the cold water supply of the water heater to thereby shorten the time it takes to fully heat hot water which, in turn, saves energy and money and provides more hot water due to faster recovery. It may also be used to cool a flow of warmer water feeding, for example, an ice cube maker, using colder drainwater from a ice-filled sink.
In all figures the drainwater flow or exhaust gas inlet flow is indicated as A′ and A″ and the fluid whose temperature is to be changed is B and B′. Heat exchanger 200 may be used to heat or cool fluid B. Although gaps between surfaces are shown in the figures (for clarity) it is understood that there is intimate contact between heat transfer and clamping surfaces.
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Claims
1. A heat exchanger for heat transfer with a fluid within a conduit, said heat exchanger comprising: the arrangement being that said inner wall is tightened against said conduit by said attachment means.
- a chamber having a portion thereof for contacting at least a portion of said conduit, said chamber having spaced inner and outer walls defining a cavity therebetween;
- a fluid inlet to said cavity for a second fluid;
- a fluid outlet from said cavity for said second fluid;
- attachment means exterior of said outer wall for securing said chamber to said conduit;
2. The heat exchanger of claim 1 including flow directing means to direct said second fluid to flow over substantially the entire inner surface of said inner wall.
3. The heat exchanger of claim 1 where, when said second fluid is supplied under pressure said inner wall is further tightened against said conduit.
4. The heat exchanger of claim 2 wherein said portion is formed into a recess to receive at least a portion of said conduit.
5. The heat exchanger of claim 4 wherein said chamber has a substantially cylindrical configuration.
6. The heat exchanger of claim 5 wherein said portion comprises a passageway through said chamber.
7. The heat exchanger of claim 2 wherein said chamber has a C-shaped configuration.
8. The heat exchanger of claim 2 wherein said chamber has a U-shaped configuration.
9. The heat exchanger of claim 2 wherein said chamber has a bar-shaped configuration.
10. The heat exchanger of claim 7 wherein said cylindrical chamber has a gap to permit tightening of said inner wall onto said conduit.
11. In a building having a plumbing system including a hot water supply, a cold water supply and a drainage pipe, the improvement comprising a heat exchanger mounted about said drainage pipe, said heat exchanger comprising:
- a chamber having a portion thereof for receiving said drainage pipe, said chamber having spaced inner and outer walls defining a cavity, a fluid inlet connected to said cavity, said fluid inlet being connected to said cold water supply;
- a fluid outlet from said chamber being connected to a water fitting; and
- attachment means for securing said inner wall adjacent to said drainage pipe.
12. The improvement of claim 10 wherein said chamber has fluid directing means within said chamber being arranged to direct fluid flowing from said fluid inlet to cause maximum heat transfer between fluid in said chamber and fluid flowing through said drainage pipe.
13. The improvement of claim 11 wherein said drainage pipe has a horizontal portion, said chamber being secured to said horizontal portion.
14. The improvement of claim 11 wherein said drainage pipe has a vertical portion, said chamber being secured to said vertical portion.
15. The improvement of claim 12 wherein said chamber has a substantially cylindrical configuration, said chamber having a gap therein to permit tightening said inner wall onto said drainage pipe.
16. In a vehicle having an interior compartment requiring heat and an exhaust pipe through which flows hot exhaust gases, the improvement comprising a heat exchanger mounted about said exhaust pipe, said heat exchanger comprising:
- at least one chamber having a portion thereof for receiving said exhaust pipe, said chamber having spaced inner and outer walls defining a cavity, a fluid inlet to said cavity, said fluid inlet being connected to a fluid supply to be heated;
- a fluid outlet from said cavity being connected to said interior compartment, and
- attachment means for securing said inner wall adjacent to said exhaust pipe.
17. The improvement of claim 14 wherein said chamber has fluid directing means within said chamber arranged to maximize heat transfer between said fluid and said exhaust pipe;
18. The improvement of claim 14 wherein said chamber has a substantially cylindrical configuration, said chamber having a gap therein to permit tightening said inner wall onto said exhaust pipe.
Type: Application
Filed: Mar 11, 2008
Publication Date: Apr 16, 2009
Inventor: Winston MacKelvie (Knowlton)
Application Number: 12/075,394
International Classification: F28D 7/00 (20060101);