CA2745590C

CA2745590C - Hybrid horizontal drainpipe heat exchanger

Info

Publication number: CA2745590C
Application number: CA2745590A
Authority: CA
Inventors: Winston Mackelvie
Original assignee: Individual
Current assignee: Individual
Priority date: 2011-06-28
Filing date: 2011-06-28
Publication date: 2015-06-23
Anticipated expiration: 2031-06-28
Also published as: CA2745590A1

Abstract

The present invention is low-cost hybrid horizontal drainpipe heat exchanger that has a large internal diameter and that is best suited for long length application. Several embodiments are disclosed for drainwater heat recovery including a first to ambient air, a second to water with a single-wall-of-separation to the water, and a third having a double-wall-of-separation along with a vent to the ambient. All are based on a hybrid tube wherein a relatively narrow concave copper strip (a tube segment) is engaged in matching curved recesses in a large bore plastic tube segment. In the drainwater-to- fresh water embodiments a pressure chamber for the water supply is created beneath the concave copper strip by means of a thick, elongated gasket that seals against it and against the inner wall of a second plastic tube segment. Inlet and outlet fittings connect between a building's cold water supply and a hot water heater or a faucet. Socket fittings on each end of the hybrid tube heat exchanger provide connection means to standard drainpipe. Because of the low cost and where the length cannot be long, multiple units can be run in parallel or in series or in a zig-zag arrangement.

Description

SPECIFICATIONS
FIELD OF THE INVENTION
The present invention is in the field of heat exchangers and is ideally suited for drainwater heat recovery in homes and buildings. The large-bore potential means that all drainwater including toilet effluent can pass through. It has low cost so long lengths of large diameter can be used for cost-effective energy savings.
BACKGROUND OF THE INVENTION
Horizontal drainpipe heat exchangers for heat recovery and energy savings are uncommon and even less common where toilet effluent is part of the drainwater composition.
Although it may be used in numerous heat transfer applications, including heating and cooling, the description that follows will be focused on its use for heat recovery from drainwater (used hot water) in a home or building from the final drainpipe.
Three main embodiments are disclosed for: drainwater-to air; drainwater-to-water with a single wall of separation; and drainwater-to-water with double wall separation and vent to the ambient.
SUMMARY OF THE INVENTION
In a first embodiment a unique hybrid heat exchanger is used to transfer drainwater heat to the surrounding air. The hybrid tube comprises two or more tube segments. A tube segment is a straight tube of some suitable diameter with a wide open gap along its length, that is, a tube missing a full length longitudinal strip. This gap of course can be of any width such that the resulting tube segment has a lesser or greater circumference. For the purposes of this disclosure the term "tube segment or tube segments" will be used to refer to: a concave strip; an open-gap tube segment; a semi-cylinder; a horizontal cylindrical segment; or a tube segment.
In its simplest form the hybrid heat exchanger has a first lower tube segment and a second upper tube segment. The two tube segments are joined together to form a complete tube or cylinder.
The lower, elongate tube segment is for heat transfer and is preferably made from a strip of sheet copper, formed to a specific diameter. Uniquely, this tube segment can be kept as short as needed to match the depth of flowing drainwater. Minimizing the copper requirement in this way, keeps the final cost of the instant heat exchanger down without affecting performance.
The upper, elongate tube segment is of approximately the same diameter and length. It is preferably made from plastic. It may be custom extruded so as to have the required inside recesses along the gap, or, it may be assembled from two plastic tube segments arranged concentrically and having different gap widths, with the smaller gap being inside to thereby create the required internal recesses.
In either design, the lower tube segment seals into the recesses and bridges the gap in the upper tube segment(s) such that a substantial portion of copper is exposed below.
In this way a hybrid tube is created.
In the first embodiment of the instant heat exchanger the ends of this hybrid tube are connected to the drainage system leaving the majority central portion for heat transfer.
When the temperature of flowing drainwater is different from the surrounding ambient air, heat transfers by conduction through the copper to heat or cool the surrounding air.

2 In a second embodiment of the instant heat exchanger, the hybrid tube is combined with a cold water chamber adjacent the exposed copper tube segment. This is accomplished by means of third plastic tube segment that is of larger diameter and concentric with the hybrid tube. It is shorter in length so that the ends of the hybrid tube remain exposed for connection to the drainage system. It has a water fittings:
an inlet near one end and outlet neat the other end. These fittings are through the bottom wall of this third plastic tube segment whereas its gap is opposite and uppermost. Spaced external clamps tighten around this tube segment.
Between the hybrid tube and the third plastic tube segment component is an elongate peripheral gasket of suitable thickness such that a chamber is defined therebetween. The gasket only seals around the central, heat transfer portion of the exposed copper tube segment, leaving end portions available connection as before. The gasket also encloses the water fittings. The gasket thus forms the wall of an elongate chamber such that when the external clamps are tightened, the gasket compresses so that pressurized cold water can flow via the fittings through the chamber adjacent the copper and transfer heat therewith. An auxiliary outer tube segment of steel may be used under the clamps to add strength. The water is directed to a faucet or water heater.
The third embodiment is very similar to the second but further includes a second elongate copper tube segment positioned between the gasket and the first copper tube segment. The gasket's compression and the internal water pressure in the chamber forces the two copper tube segments tightly together to maximize the rate of heat transfer. The second copper tube segment is narrower (and shorter) so that open paths are created along its edges. These paths are vents to the ambient so that in the event of failure, liquid leakage will visibly accumulate on the floor beneath the heat exchanger.

3 =
In the second and third embodiments yet another plastic tube segment can be introduced as a spacer between the hybrid tube and the third (outer) tube segment. Its purpose is to enable the exterior clamps to be heavily tightened so as to resist water pressure effects yet not over-compress the gasket. This tube segment can also serve to locate the gasket during assembly of the heat exchanger, and to affect the volume of the chamber by permitting a change in gasket thickness while holding the required compression under highly tightened clamps.
All embodiments are preferably made as long and as large a diameter as is convenient to maximize surface area for heat transfer which directly influences cost-effectiveness.
In the second and third embodiments copper tube segment may be formed with dimples or ridges to create turbulent flow which increases the rate of heat transfer. In the third embodiment, the two concave copper strips may be co-formed with such features are mirrored so as to maintain full thermal contact therebetween.
In certain plumbing installations it may be that using multiple hybrid drainpipe heat exchangers is preferable to a single long one. For example several shorter units (which may be of a standardized length) can be plumbed together in an end-to-end arrangement, or several may operate in parallel where a portion of the drainwater flows through each branch, or several may be arranged in a zig-zag fashion against a vertical wall in place of a vertical heat exchanger thereby offering more heat transfer surface area for higher performance.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a cross-section of the double-walled third embodiment showing the concentric arrangement of the various tube segments;

4 Figure 2 shows the two-tube segment are concentrically arranged and how the gap is bridged by the copper tube segment forming a hybrid tube of the first embodiment. Also shown are the next two concentric tube segments which are part of the second and third embodiments and where they are shorter leaving the hybrid tube end portion free for connecting to a building's drainage system;
Figure 3 shows a longitudinal view where the end portions have end connections, and how a series of exterior band clamps are arranged;
Figure 4 shows a close-up of part of Fig 1 (minus the outer plastic tube segment) detailing how the copper, heat transfer tube segment is held by the recesses created by two concentric, open-gap plastic tube segments (on the right), or by use of a single custom-formed tube segment (on the left). Also shown is the vent path, and how an 0-ring gasket is placed, and how the clamping forces cause tube segment compression at the recesses:
Figure 5 shows a partial phantom bottom view with the peripheral gasket against the second copper tube segment. The outer plastic tube segment is shown in dotted outline;
Figure 6 shows a top view of how several hybrid tube drainpipe heat exchangers can be manifolded together in parallel, each taking part of the drainwater flow which can increase performance in a short space;
Figure 7 shows a side view of a zig-zag series flow arrangement using multiple units as might be arranged on a wall, for example where there is sufficient vertical drop;
Figure 8 shows the second embodiment of a single wall heat exchanger having only one copper tube segment between the unpressurized drainwater and the pressurized fresh water;

Figure 9 shows a side view of the hybrid tube heat exchanger to be used for liquid-to-air heat exchange.
DETAILED DESCRIPTION OF THE INVENTION
Referring to the drawings, there are small gaps or spaces showing between some components in some figures. This is for clarity. Most components are tightly fitted and sealed to prevent leaks. Also, although shown dead horizontal, in use they would be installed at a slight downward angle to provide self drainage.
The first embodiment is shown in perspective in Fig 2 an in side view in Fig 9. It comprises two or three tube segments. A tube segment is herein defined as a cylinder, tube or pipe that is missing a longitudinal portion of its wall so as to have an open gap.
Fig 2 shows one end of a three tube segment hybrid tube 102 comprising two concentric plastic tube segments and a heat transfer tube segment in, say, copper. The left side of Fig 4 shows how a two tube segment hybrid tube is constructed from a custom, purpose-extruded tube segment 5a.
Tube segment 1 is largely used for heat transfer but has marginal portions 15a are for sealing. Internal tube segment 5 and tube segment 6 are engaged concentrically. Tube segment 5 has a wider gap and tube segment 6 a narrower gap. This creates recesses 15 into which marginal portions 15a of tube segment 1 locate and seal. Tube segment 1 therefore bridges the gap of second tube segment 6 creating a complete leak-proof tube 102 which is of one tubular diameter along its entire length. A linear gasket 4b may be used to augment sealing properties. Of importance in the design of the instant hybrid tube is the considerable compression that can be created in the recess 15 with tube segment 1, as shown as D in Fig 4, if an interference fit is used such that tube segments

5, 6 are at

6 least slightly spread apart by the insertion of tube segment 1. This compression D and resulting sealing effect can be further augmented by outside band clamps 9.
When in use, hybrid tube 102 has drainwater A inside and air outside. Thermal tube segment 1 (i.e., copper) conducts heat therebetween. If used for heat recovery, the outside ambient air is heated and moves by convection thereby providing drainwater heat recovery at low cost during, say, winter months (space heating months) to lower space heating costs. Obviously longer lengths of hybrid tube 102 will provide more heat recovery.
Embodiments two and three of the instant heat exchanger are for drainwater-to-water heat transfer and as such they have a pressurized water chamber through which a supply of cold water flows to be heated (or cooled).
Embodiment two 101 and embodiment three 100 each require, in addition to a hybrid tube 102, an enclosure 103 comprising two shorter tube segments: third plastic tube segment 7 and forth plastic tube segment 8. In Fig 2 these two additional tube segments are shown rearward to the open end of hybrid tube 102 and concentric therewith. Tube segment 7 is a spacer and tube segment 8 is the outer tube segment that seals a water chamber against tube segment 1.
Second embodiment 101 is a single-wall-of-separation design and is shown in cross section in Fig 8, where a single heat transfer tube segment 1 is used to transfer heat between drainwater and potable water. It may have dimples or ridges and the like formed thereon to create turbulence.
Third embodiment 100 is a double-wall-of-separation design identical to the second embodiment but further including a second tube segment 2 which is smaller in area (narrower and shorter) and lies adjacent the first tube segment 1 between recesses 15. A

7 small space along the longitudinal edges of this tube segment 2 provide a vent 10 or air filled path to the ambient. In the event of a failure liquid can pass along the vent 10 a drip visibly to the floor beneath. Vent 10 may also be additionally formed by gasket 4 that leaves a small space that it is unable to be squeezed into (Fig 4). Tube segment 1 and 2 are thermally conductive and as such are preferably made from a strip of sheet copper and formed into a concave shape herein referred to as a tube segment. They may also be further co-formed to have dimples, ridges and the like to create desirable turbulent liquid flow and remain in intimate thermal contact.
In second embodiment 101 and third embodiment 100 the water chamber is created from cooperating components rather than being a distinct article. The description that follows applies to both embodiments 101 and 100.
The internal volume of water chamber 3 is defined by a perimeter gasket 4 of elastomeric material of some appropriate thickness and in Fig 4 is shown to be an 0-ring.
Gasket 4 seals against tube segment 1 or tube segment 2 if present. Gasket 4 also seals against the inner wall of tube segment 8 which therefore must resist water pressure. It may be aided in this later function by an external tube segment of sheet steel, for example (not shown). Gasket 4 is protected from over compression (and resulting water volume reduction) by tube segment 7. Gasket 4 is compressed in place by outer clamping elements 9 Tube segment 8 has its gap on top and water fittings 12, 13 below, the water fittings communicating with the water chamber. The gap allows for diametric reduction from clamps 9. The water fitting 12, 13 connect between a water supply and a water use, such as a water heater or a faucet. Inlet fitting 12 may have an erosion plate 26 to prevent hard-

8 water particles from eroding tube segments 1 or 2 prematurely. It would rest against concave strip 2 but is shown floating for clarity Fig 2 shows how enclosing tube 103 comprises tube segments 7 and tube segment which are both shorter in length than hybrid tube 102 so as to only enclose heat exchanger portion 16 (Fig 3) and leave end portions 17 exposed and of a minimum diameter to receive hubs 22 for connection to standard drainage plumbing B.
Fig 4 also shows that third tube segment 7 may have bevelled gap edges to help retain gasket 4 during assembly.
In use a first liquid, drainwater A (shown with entrained solids), flows on tube segment 1 which is thereby heated if drainwater A is warmer. The cooled drainwater C
leads to a sewer connection (not shown). The second liquid enters chamber 3 via inlet fitting 12, flows against tube segment 1 or tube segment 2, transfers heat therewith, and leaves via outlet fitting 13 to the intended final use.
In all embodiments, the tube segments may be made of any suitable material.
Tube segments 1 and 2 being used for heat transfer may be made of copper or stainless steel for example. Tube segments 5, 6, 7, 8 are not for heat transfer and so may be of a low-cost material such as galvanized or painted steel, but preferably are made from water-safe plastic such as PVC or ABS and the like.
All embodiments have some form of connector or are able to connect in a leak-proof manner to the drainage tubes or pipes in the building where they are installed. There will be some small unavoidable cracks and crevices present at the connection end due to different thickness and rates of thetnial expansion. To seal the ends perfectly from septic drainwater leakage the following hubs are described.

9 In Fig 3 hubs 22 have seals 23, preferably square-section 0-rings, and holes 25 (one shown on right). Holes 25 are for an adhesive to be injected at final assembly to encase ends 17. The hubs 22 do not seal on their inner ends. A small gap 10a allows for any leakage from vent 10 to continue through to the ambient.
Using as an example heat recovery from, say, a shower or sink, upon opening a faucet (valve) hot water flows out in reaction to pressurized cold water flowing into the water heater. The resulting drainwater flows down the drain and through the instant hybrid horizontal drainpipe heat exchanger. The pressurized fresh cold water however, first flows through the heat exchanger where its temperature is raised by the heat of the drainwater.
This allows the water heater to reach 'hot' temperature faster increasing the useable hot water supply while less energy which saves money.
In certain plumbing installations, it may be that using multiple heat exchangers is preferable. For example, several shorter units can be joined end-to-end;
several may operate in Parallel (Fig 6) where a portion of the drainwater flows through each branch; or arranged in a zig-zag fashion (Fig 7) against a vertical wall in place of a vertical heat exchanger thereby offering more heat transfer surface area.
A common water pressure regulator (not shown) can be used to control too-high pressures.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A hybrid tube heat exchanger comprising:
a first heat transfer element comprising a tube segment of thermally conductive material and having an inner surface of a concave configuration and an outer surface of a convex configuration and longitudinal edges with marginal areas;
an enclosing element having inner and outer walls and a longitudinal gap oriented downwards and having recesses in said inner wall adjacent said longitudinal gap;
said marginal areas of said first heat transfer element sealingly engaged in said recesses thereby creating a fluid conduit;
the arrangement being that a first fluid flowing on said inner surface will transfer heat to a second fluid adjacent said outer surface.

2. The hybrid tube of Claim 1 where said enclosing element comprises second and third tube segments each with longitudinal gaps of different widths and concentrically arranged.

3. The hybrid tube of Claim 1 further including external clamping means.

4. The heat exchanger of Claims 1, 2 or 3 where said first heat transfer element is a tight fit between said recesses.

5. A heat exchanger comprising:
the hybrid tube of Claim 2 where, said hybrid tube has a central heat transfer portion and end portions;
said outer surface of said first heat transfer element having a peripheral margin area within said heat transfer portion;

a peripheral gasket contacting said peripheral margin area;
a fourth tube segment enclosing said central heat transfer portion and generally concentric therewith and having inner and outer walls;
said gasket contacting said inner wall thereby defining a chamber;
said fourth tube segment having inlet and outlet means to said chamber;
clamping means exterior to said outer walls;
the arrangement being that a first fluid flowing through said hybrid tube can transfer heat with a second fluid flowing through said chamber.

6. The heat exchanger of Claim 5 further including a fifth tube segment between said fourth tube segment and said third tube segment of said enclosing element.

7. The heat exchanger of Claim 5 further including:
a second heat transfer element having inner and outer surfaces;
said second heat transfer element located within said heat transfer portion;
said second heat transfer element located within said longitudinal gap such that at least one longitudinal vent is created therebetween;
said inner surface in thermal contact with said outer surface of said first heat transfer element;
said outer surface in contact with said peripheral gasket;
the arrangement being that heat transferred between said first and second fluids passes through both said heat transfer elements.