Abstract:
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.

Description:
[0001]    This patent application follows on from provisional application 60/998,670. 
     
    
     FIELD OF THE INVENTION 
       [0002]    A drainpipe heat exchanger for use on drain- or exhaust pipes for waste heat recovery including from any building&#39;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. 
         [0003]    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&#39;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 INVENTION 
       [0004]    A 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. 
         [0005]    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. 
         [0006]    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.) 
         [0007]    The falling film DHR is, in many ways, ideal because it is not blocked by large solids and other matter contained in a building&#39;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. 
         [0008]    One of the weaknesses of such heat exchangers is the narrow spiral contact patch between the coil&#39;s inner surface and the tube&#39;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. 
         [0009]    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 INVENTION 
       [0010]    In 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. 
         [0011]    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. 
         [0012]    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. 
         [0013]    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. 
         [0014]    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. 
         [0015]    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. 
         [0016]    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! 
         [0017]    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 
         [0018]    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. 
         [0019]    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&#39;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. 
         [0020]    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. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  shows a partial section end view a middle portion of one embodiment of the drainpipe heat exchanger having an upper conduit for drainwater and a lower conduit for cold water with forced thermal contact all along their flat surfaces; 
           [0022]      FIGS. 2 ,  3 ,  4  show the same embodiment in a sequence of forming steps to squeeze-close and solder-seal the two end portions of the lower exchanger; 
           [0023]      FIG. 5  shows the same embodiment in side view showing the sealed ends of the cold water heat exchanger, its lower fittings, and, the adapted ends of the upper conduit that connect to regular round drainpipes, and where the right end is shown to have an added adaptor while the left end is shown to have been formed into a short cylindrical shape, in both cases the flow path is flush such that there is no ‘step-up’ to impede drainwater flow in or out; 
           [0024]      FIG. 6  shows an adaptor for the drainwater heat exchanger formed, for example, from a suitable plastic material; 
           [0025]      FIG. 7  shows an end view of another embodiment where the drainwater heat exchanger&#39;s end&#39;s are formed to rectangular sockets to receive rectangular solder-type plumbing fittings and a plug, and where the excess material is closed off to be sealed by soldering at the same time that the fitting is inserted, and showing an internal fluid distribution tube enclosed therein; 
           [0026]      FIG. 8  shows a copper solder-type fitting having one end formed to a rectangular shape for insertion into the end socket; 
           [0027]      FIG. 9  shows a copper plug to be soldered in unused socket openings; 
           [0028]      FIG. 10  shows a side view of the same embodiment as  FIG. 7  showing the end location of the drainwater heat exchanger fittings; 
           [0029]      FIG. 11  shows a top view in section of a cylindrical, jacket-style heat exchanger having a longitudinal gap to allow clamping motion, which would be slid over a drainpipe/exhaust pipe; 
           [0030]      FIG. 12  shows a top section view of a two-piece design for clamping about an in-use drainpipe/exhaust pipe; 
           [0031]      FIG. 13  shows a side view of the embodiment in  FIG. 11  showing the outer sleeve and band clamps and showing the fluid fittings and the location of the end sealing members; 
           [0032]      FIG. 14  shows a top view of the sealing ring member made from tube or rod although a stamped sheet design may be more economical in production; 
           [0033]      FIG. 15  show a side view of the sealing member; 
           [0034]      FIG. 16  shows a possible use of the joint flange where it has various notches to distribute the fluid flow evenly over the jacket&#39;s inner wall so as to maximize heat transfer by maintaining the best temperature differential; 
           [0035]      FIG. 17  shows a thin, flat cold water (or other fluid) conduit clamped against the flat lower surface of the drainwater conduit; 
           [0036]      FIG. 18  is a cross section of the same embodiment and showing one internal baffle in the cold water exchanger to prevent bulging; 
           [0037]      FIG. 19  is a cross section showing how the drainwater heat exchanger may be a two piece design with the upper, non-heat transfer portion in plastic and the lower heat transfer portion in sheet copper, bonded together along the length, and, with tension walls of sheet copper to transmit the internal pressure in the cold water exchanger to the external clamping member; 
           [0038]      FIG. 20  is a side view of the same embodiment showing how the drainwater flow may be made to enter from the top at the inlet end and to collect in a cross tube outlet arrangement at the exit end; 
           [0039]      FIG. 21  shows a perspective view of the outlet fitting of the embodiment; 
           [0040]      FIG. 22  is a top view looking into the vertical heat exchanger where the cold water is made to flow past a distribution gap formed adjacent an annular ring and the jacket&#39;s inner wall so as to sweep the entire surface along its vertical length; 
           [0041]      FIG. 23  is a cross section side view of the same embodiment showing how the cold water inlet is located between the sealing end cap and the annular ring with the single-sided arrows representing the resulting sheet-like flow; 
           [0042]      FIG. 24  is an end view of an embodiment of a upper conduit having a lower surface with a gully-shape along flow path, to resist upward bulging from the force of contact generated by the internal pressure in the shaped cold water jacket below; 
           [0043]      FIG. 25  shows the same embodiment but with an oval shaped lower flow surface. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0044]    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. 
         [0045]    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. 
         [0046]    In  FIG. 1  horizontal heat exchanger  200  has an upper drainwater conduit  60  and a lower cold water conduit  50  held tightly together with clamping bands  12  ( FIGS. 5 and 10 ) around a suitable force distribution sleeve (not shown). Drainwater conduit  60  comprises wall  1  with drainwater A flowing along flattened bottom surface  1 ′ (of wall  1 ) to thereby form a hemicylinder that transfers heat to fluid B which enters and exists cold water conduit  50  via underside fittings  10 ,  11  or alternately, via end fittings  80 . 
         [0047]    In  FIG. 1-5 ,  7 ,  10 , cold water conduit  50  is shown being in the shape of a trough made from sheet copper and formed with longitudinal hems  4  that are solder joined to create a generally “C shaped” hemicylindrical conduit with flat surface  5 . Hem  4  also serves as a heat conductive fin and, as a result of the bend curvature  6 , provides a longitudinal vent to the ambient for leak detection. 
         [0048]    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  FIGS. 2 ,  3 ,  4  cold water conduit  50  is shown having a short end portion of hem  4  folded flat in preparation for sealing the ends. The wings  3  are pinched closed and excess metal is pulled into additional seams  3 ′. In  FIG. 4  is shown a dotted line  2  that represents the original cold water conduit  50  shape. 
         [0049]    In  FIG. 7  is shown an alternate way of sealing the ends of cold water conduit  50  so as to provide in-line connection sockets  33 ′,  34 ′. The two sockets at each end (4 in total) are formed on each side of hem  4  using an appropriate mandrel about which the remaining wall  3  and wing  2  are squeezed to bring them together as a seam to be soldered. Appropriate surfaces can be ‘tinned’ with solder prior to the forming in preparation for final soldering. 
         [0050]    In  FIG. 8 , fluid fitting  80  has rectangular end  33  inserted and soldered into socket  33 ′ or  34 ′ (at each end of cold water conduit  50 ), and has a round end  30  for connecting to standard plumbing. Fitting  80  may also be an end of a longer tube where installation conditions warrant. Alternatively one of the two rectangular shapes  33 ′ and  34 ′ may be blocked with a simple plug  34  as indicated in  FIG. 9 . Interior to cold water conduit  50  and inline with the socket  33 ′ and/or  34 ′ is a fluid distribution tube  35 ′ which extends full length and is closed at the far end and has cross apertures at intervals. The purpose of tube  35 ′ is to distribute fluid B (i.e., cold water) to cause a crossflow creating turbulence and evening out flow velocity across the width of cold water conduit  50 . 
         [0051]    In  FIG. 5  horizontal heat exchanger  200  is shown having the upper drainwater conduit  60  made from a flattened tube, and lower cold water conduit  50  (for, say, cold water) formed of sheet material bound together by exterior clamping bands  12 . In some uses the upper drainwater conduit  60  may also be formed from sheet to reduce cost. In either case the ends of drainwater conduit  60  can be adapted to connect with existing round drain pipes the right end of the drainwater conduit being shown having a separate, bonded-on adaptor  70 , while the left end  70 ′ is shown as having an integrally formed round end  20 ′. It is important that the drainwater conduit provides a flush flow path especially at the exit end so that solids in the drainwater will not hook and collect at the region of transition from flat to round. This can be achieved by forming a recess in the “D” shaped end of the bonded on adaptor equal to the thickness of the drainwater conduit material. The bonding region is shown at overlap  20 ′. 
         [0052]      FIG. 5  shows fluid B, such as cold water for a water heater, entering fitting  10  at the left to counterflow horizontally under the drainwater water conduit  60  and exit via fitting  11  on the right having absorbed (or given up) heat from warmer (or colder) drainwater. Drainwater A flows horizontally with a first temperature A′ at inlet on right side and a different temperature A″ at outlet on left side. 
         [0053]      FIG. 6  shows adaptor  70  having a “D” shaped first end  20 ′ for bonding to drainwater conduit  60  and a round end  20  for connecting to existing drainpipe. Adaptor  70  may also be made of molded rubber with a shaped shoe  22  (shown in dotted outline) under the flat portion  20 ′ to provide even clamping pressure for sealing. 
         [0054]    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. 
         [0055]    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. 
         [0056]    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. 
         [0057]    In  FIGS. 11-13  heat exchanger  100  is a jacket(s) comprising an inner heat transfer wall  5  and outer retaining wall  2  spaced apart for fluid flow therebetween with minimal resistance. This space may be, say, ¼ inch. The walls are contiguous and formed from a single piece of thin sheet metal (copper) using reversing bends  112  and lap joint  5 ′. This leaves a longitudinal opening or gap  111  between bends  112  to accommodate movement from external mechanical clamping forces and internal hydraulic clamping forces. The jacket may also be formed by extrusion in which case finning  115  (representative fins only, shown in  FIG. 11 ) and fluid control elements  114  may be easily included on the inner wall  5  and/or outer wall  2 . Outer clamping sleeve  116  with gap  113  closes tightly around and distributes clamping forces from band or hose clamps  12  to prevent expansion or bulging of outer wall  2  from the internal pressure of fluid B such as that from a building&#39;s cold water supply. Inner wall  1  is however free to expand every so slightly to provide a tight, intimate thermal contact with drainpipe  1  using that same internal pressure. 
         [0058]    In  FIGS. 11 ,  12  lap joint  5 ′ is a soldered and may include longitudinal joint flange  110  which can act as a fluid flow distributor and a stabilizer/spacer for aligning the sheet metal during soldering. Inlets(s)  10  and outlet(s)  11  are connections for fluid B (such as cold water) whose temperature is to be changed. Representative fluid control element  114  may be several in number and take various shapes such as mesh, rods, screen, angles, etc., that direct, for example, flow of fluid B over element  114  as indicated by dashed flow arrow  114 ′, to help effect best heat transfer from inner wall  5  by the fluid ‘sweeping’ the surface of the inner thermal contact wall as fully as possible. Element(s)  114  may also be used to create turbulent flow which is known to improve heat transfer. Element  114  may also be shaped and located to deflect fluid B inflow at inlet  10  to avoid erosion corrosion of the small area of the inner wall by the fluid impinging on it perpendicularly at full velocity over long years of daily use. 
         [0059]      FIG. 12  shows the hollow, tubular nature of the heat exchanger  100  as fitted onto a vertical drainpipe  1 . Sealing rings  34  are shown in dotted line and are soldered into the annular space between the inner and outer wall ends at top and bottom. Although a tubular shape is shown, other shapes such as oval are contemplated where, for example, fitting clearance is a concern. 
         [0060]      FIGS. 14 and 15  show the sealing member  34  which can be made from rolled rod, tube or twisted wire bundle to fit snugly into the annular space and have a gap  111 ′ to coordinate with gap  111 . They may be made by winding a long tube onto a mandrel of the correct diameter into the form of a coil spring and then sawing through the coil to free individual rings which are then made planar as in  FIG. 15 . Dip soldering is a fast method of construction. 
         [0061]      FIG. 16  shows a method of using the longitudinal joint flange  110  as a flow distributor by providing restriction to flow directly from fitting  10  such that fluid B is forced through spaced vias  120  to travel across inner wall  5  to reach outlet  11  thereby improving heat removal from drainpipe  1 . Flange  110  may also simply be more simply double-tapered (not shown) from full width at the center tapering to nil at each end to even out flow along its length, especially if the fittings  10  and  11  are positioned centrally and opposite one another. 
         [0062]      FIG. 12  shows the cold water conduit in two halves with inlets  10  and outlets  11  on each half. The outer sleeve  116  and clamps  12  of  FIG. 11  are not shown. The outer sleeve  112  would of course be in two pieces either separate or hinged for ease of assembly onto the drainpipe in a building while it remains in operation. The sealing rings  34  (not shown in  FIG. 12 ) would of course be four in number each being a half ring, one at each of the four ends. 
         [0063]      FIG. 17  shows another embodiment of horizontal heat exchanger  200  where the cold water conduit  2  comprises a sheet copper duct or tube in the form of a flat, rectangular hollow strip. It is sealed at each end and preferably has flow-formers to ensure that the cold water flows as a flat sheet of water across the entire width of the heat transfer surface so as to keep the surface as cool as possible, thereby maximizing delta T for faster heat transfer. 
         [0064]      FIG. 18  shows a cross section of the same embodiment where the drainwater conduit is shown to be a flattened, hemi-cylindrical tube I forced into intimate, conforming thermal contact with cold conduit  2  using shaped pressure distribution shoes  130 ,  131  and clamp bands  12 . 
         [0065]    In the embodiments shown in  FIGS. 18 and 19 , and all embodiments of the horizontal drainwater heat exchanger, the cold water conduit may have internal baffles  2 ″ comprising one or more flattened tubes soldered between the top and bottom surfaces that will prevent excessive bulging of the conduit in reaction to the water pressure inside. This will help maintain flat drainwater heat exchange surfaces. 
         [0066]    In  FIG. 19  drainwater conduit  1  is comprised of a trough-like lower portion in sheet copper through which heat transfer takes place and a U-shaped plastic upper portion bonded  1   b  thereto, the two creating a hybrid drainpipe of rounded rectangular or hemicylindrical form. This embodiment is for the lowest cost device. Interior longitudinal supports  1   c  act to transmit bulging force from cold water conduit  2  to shoe  130  and bands  12  thereby maintaining a flat profile for the trough. Supports  1   c  may be wavy to create a desirable turbulent flow. Supports  1   c  also act as fins to extend heat transfer surface area. Supports  1   c  may be eliminated and baffles  2 ″ in the cold water exchanger may be used to prevent pressure bulging of the flat surfaces. 
         [0067]      FIG. 20  shows the same embodiment with different drainpipe connection fittings. Inlet  200 ″ is a vertical right angle inlet centered on plastic top  1   a  and outlet  200 ′ is a horizontal right angle fitting shown in more detail in  FIG. 21 , having an end cap and a slot  201  which matches the shape of the end of heat exchanger  1 ,  1   a,    1   b  ( FIG. 19 ) and is bonded and sealed thereto. A slight slope to outlet  200 ′ carries away the final drainwater drips to leave drainwater conduit  1  dry. 
         [0068]    In  FIG. 22  vertical heat exchanger  100  has an inner wall  5  (heat transfer surface) and ring-shaped flow distributor  110 ′ which provides an even annular gap  120 ′ adjacent wall  5 . End seals  34  ( FIG. 23 ) and flow distributor  110 ′ are spaced apart vertically creating a circular chamber into which flows fluid B, which then must leave the chamber in a full curvilinear sheet flow B′ (half arrows) against inner wall  5  so as to sweep heated (or cooled) fluid towards the outlet, which is similarly configured. This ensures that a maximum temperature differential, or delta T, can be maintained to optimize heat transfer. This annular flow control arrangement may be used to advantage in all the aforementioned heat exchangers including the two-piece embodiment of  FIG. 12 . In the case of horizontal heat exchangers  200  the distributor would take the form of a rectangular bridge held a small distance below the heat transfer surface by stand-off elements. 
         [0069]      FIGS. 24 and 25  show variations on the profile of the flow surface  1 ′ of the drainwater conduit  1  with the purpose of stiffening the flow surface  1 ′ to resist upward bulging from the expansive potential of the pressurized cold conduit below. The cold water conduit  2  is shown to be conforming in shape so as to maintain maximum thermal contact.