CA2927158C - Horizontal drainpipe heat exchanger - Google Patents

Abstract

A horizontal drainpipe heat exchanger has a composite drainpipe inside a shorter tubular housing with an annular space between and inlet and outlet for a second fluid such as potable water. The drainpipe comprises a plastic tube segment with a gap and recesses along both edges. A concave metal strip bridges the gap and is sealed into the recesses. A second strip can be nested against it. A one-piece compressible gasket in the annular space co-contacts the perimeter margin of the strip and the housing enclosing the inlet and outlet thereby creating upper and lower arcuate spaces. A compression shoe is forced into the upper space compressing the gasket and sealing the lower space creating a conduit for the potable water. Second strip has vents open to the ambient for leak detection. Flow distribution and turbulence generation within the conduit arc also disclosed.

Description

HORIZONTAL DRAINPIPE HEAT EXCHANGER
DESCRIPTION
FIELD OF THE INVENTION
The present invention is in the field of energy savings by use of a big bore, straight-through drainpipe heat exchangers for drainwater (which may contain large solids) and fresh water to be tempered. They flow separately through the exchanger to exchange heat thereby pre-tempering the water before final tempering in a heater or chiller.
BACKGROUND OF THE INVENTION
Using hygienic hot water as an example, heating the cold supply water requires vast amounts of money (in USA+Canada $77 billion/year) and energy (-1.7 million MW/year), and releases equivalent amounts of pollution, city smog, and causes climate change and habitat destruction. Virtually all of the used hot water is simply drained away wasting its valuable heat energy and directly adding to global warming.
The instant invention is a low cost horizontal drainpipe heat exchanger that requires no power, no maintenance, is non-blocking, and can pre-heat (or pre-cool) fresh cold water supply without danger of cross-contamination.
SUMMARY OF THE INVENTION
The instant heat exchanger has a plastic tubular housing with inlet and outlet orifices for water. Inside, a smaller and longer composite drainpipe for drainwater extends from each end.
The annular space between has a sealed conduit for the potable water to flow and be tempered.

The drainpipe is a composite of plastic and copper. A long segment plastic tube with gap has recesses along the gap. A concave copper first strip bridges the gap and is sealed into the recesses. A copper second strip nests against the first strip. A stretched 0-ring in the annular space contacts the exposed perimeter margin of the strip and co-contacts the housing thereby defining an open upper arcuate space and a smaller enclosed lower arcuate space including inlet and outlet. The gasket also off-sets the drainpipe upwards.
An arcuate plastic compression shoe is forced into the narrower upper space to urge the drainpipe downwards compressing the gasket and sealing the resulting conduit.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 shows a cross sectional end view of the outer housing with composite drainpipe inside and annular space between;
Figure Is shows the same view as Fig I but with the missing elements added including, second metal strip, compression shoe, conduit, water orifice, gasket, turbulator, flow distributor, recess seal and vias;
Figure 2 is an end view of the drainpipe element with separated components to show in more detail the upper outer portion wall with longitudinal recesses, lower concave metal strips with inner one in recesses and outer strip having bendable tabs to restrain the gasket after assembly;
Figure 3 how the concave metal strips can be formed from a single wider piece of folded in half lengthwise. and how it can be impacted to produce a localized dents and dimples to create turbulent flows in both the drain water and the conduit water;
Figure 4 is a partial section side view showing the details of a manifold at an end of the

2 housing and how the drainpipe extends outwardly for plumbing to;
Figure 5 shows a partial sectional side view and how the heat exchanger connects into a drainage system;
Figure 6 is a section end view of the composite drainpipe and an end view of the shorter housing, compression show and gasket, and how the gasket contacts the perimeter margins of the strip and the end margin of the housing.;
Figure 7 shows a tool that has a chamfered end to pre-compress the gasket so as to ease entry of the compression shoe into the narrow upper annular space. The tool is pushed through and out the opposite by the shoe;
Figure 8 shows how the end of the housing can be notched to hold gasket accurately during assembly. After the shoe is installed, the loop ends are disengaged and forced into place between the housing inner wall and the drainpipe with the help of a lubricant;
Figure 9 shows a perspective of the cradle-shaped elongated or stretched gasket, in this case an 0-ring, when in its final location below between drainpipe and housing;
Figure 10 a perspective of mesh-type turbulators inserted in the conduit between flow distributors to generate turbulent flow through the conduit for faster heat exchange;
Figure 11 is a perspective view of a flow distributor for the conduit having an crescent shape that spreads out flow from a single central inlet into a sheet-like flow across and along the copper strip for faster heat exchange with the drainwater.
DETAILED DESCRIPTION
Referring to the drawings, although shown horizontal, in use such a drainpipe heat exchanger would be properly angled. Any two liquids can be used in exchanger 200 however for

3 simplicity the terms drainwater and potable water are used herein.
Fig 1 shows the two main components, the non-slit, continuous wall, tubular plastic housing 1 encircling a smaller, longer composite drainpipe 100.
The housing 1 has aligned inlet and outlet orifices 31 for the water supply to be tempered.
The inner surface of the housing has margins at each end and paths between margins, one on each side of the orifices.
In Fig 1 drainpipe 100 has an upper portion 12 and lower portion 7. Upper portion is a segment a plastic tube with gap that has recesses 6b along each side. Lower portion is a concave metal strip 7 nested in the recesses to which it is sealed and flush.
Additional components shown in Fig la are: lower metal strip 7 (copper) that bridges the gap and is sealed flush into recesses 6b and has a perimeter margin, a second strip 3 which nests against first strip 7 and has a perimeter margin, one-piece compressible gasket 5 shown contacting margin of second strip 3, orifices 31, fitting 23, compression shoe 12 , turbulator 52, and flow distributor 55. First strip 7 has vent flat 50 and second strip 7 has vent groove 51.
Second strip 3 provides double-wall protection from cross-contamination.
Crease or groove 51 along strip 3 vents any leak to the ambient for visual detection. A
vent can also be a flat 50 draw-filed or milled on strip 7. Additional vents 11 are naturally created in the void where the gasket cannot conform to the inherently sharp corners.
Vias 65 (Fig la) can be used to inject a solvent cement after assembly to bond the concentric plastic elements together.
Inlet and outlet 23,31 for for the water are located at opposite ends of housing 1. They can be single centred fittings 23a (Fig la) or multiple orifices 31 with associated manifold 20 (Figs 4,5) which can be rotated to have fitting 23 on top (Fig 4) to lower installation height and

4 to add protection from breakage.
When one-piece elongated gasket 5 is inserted, unequal upper and lower arcuate spaces are created. Gasket 5.contacts the perimeter margin of second strip 3 and complementary margins and paths on interior of housing 1. Gasket 5 also encloses the inlet and outlet thereby defining an arcuate conduit 12a for the water.
A arcuate compression shoe 12, a plastic tube segment, has a wall thickness equal to the target compressed thickness of gasket 5. Shoe 12 is forcibly inserted into the thinner upper annular space 12a which urges drainpipe 100 down against gasket 5 compressing it against the margins and paths thereby sealing conduit 12a.
Fig 4 shows exchanger 200 lengthwise in cross-section. Manifold 20 has 0-rings 22 in grooves 25 on either side of water flow path 21. Fitting 23 communicates with flow path 21.
Orifices 31 are shown at a severe angle to direct water 30 against gasket 5 ensuring heat transfer from the endmost portion and reduce erosion of strip 3. Manifold 20 is shown to have a flange 24 at the end to restrain gasket 5. Second fluid 30 is shown by linear arrows to be flowing through conduit 12a.
In Figs 1,11 flow distributor 55 (only one shown) prevents a direct, narrow linear flow between inlet and outlet by providing more flow restriction at the centre where inlet pressure at inlet 23 is highest, and proportionally diminishing restriction towards the extremities where water pressure is lowest thereby providing a wide, even, curtain-like flow along strip 3 or 7 for faster heat transfer.
Fig 3 shows a lower concave metal strip 40 formed from a wider copper strip folded in half lengthwise as shown at fold 40a to replace separate strips 3,7. With folded strip 40 there is no unwanted relative movement between strips 3,7 during handling and assembly.
Further, this design lends itself to the impact-punching of pits 60 (only one shown) which raises dimples 60a without interfering with the all-important thermal contact conductance. The pits and dimples create turbulence in both the drainwater and the fresh water which improves heat exchange. Also with folded strip 40, vents can be co-formed with wire inserts while forming and removed after.
Both nested strips 3,7 and folded strip 40 are held in intimate contact by the water pressure in the conduit.
In Fig 5 the connections to the instant drainpipe heat exchanger 200 are shown at both ends where a common drainpipe B carries drainwater A through coupling C with insertion stop ridge C'. Fluid fittings 23 are shown at different radial positions which can be useful for plumbing to the second fluid supply.
In Fig 6 housing I, shoe 12, safety layer 3, and gasket 5 are all shown in end view while the composite drainpipe 100 is shown in cross-section indicating it extends beyond housing 1 to provide a stub for pluming connection.
Insertion tool 102 with chamfered end 101 shown in Fig 7 can be used to wedge apart upper arcuate space. A second such tool 102 may be used at the other end to keep the drainpipe evenly positioned. Tool(s) 101 are pushed through and out by permanent shoe 12.
Fig 8 shows how notches 5a in the housing rim may be used to hold gasket 5 in place during insertion of drainpipe 100 after which the loop ends are released from the notches 5a and pushed into position between the housing I and strip 3. A food-safe lubricant such as K-Y jelly can be used. Strips 3,7 can have its tabbed ends Sc bent up (two shown in Fig 2) after assembly to prevent end loops of gasket 5 from being displaced from internal water pressure.
Fig 9 shows a perspective of how elongated 0-ring gasket 5 becomes cradle-shaped when in place and can be pre-formed to that shape.

Figs 1,10 show turbulator 52 used to generate turbulent flow in the conduit, especially if the conduit has considerable depth, that is, has a thick gasket 5. Fig 10 shows turbulator 52 as sheets of mesh. Punched tabs (not shown) can also be used. Fig 10 also shows how the turbulator is in sections to be inserted from one end between spaced flow distributors before the second end loop of gasket 5 is pressed into position finally sealing conduit 12a.
In certain plumbing installations it may be that using multiple heat exchangers 200 is preferable. For example several shorter standardized units can be joined end-to-end. 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 (with elbows between) and installed against a vertical wall in place of a vertical heat exchanger thereby offering more heat transfer surface area at lower cost due to elimination of an expensive vertical copper drainpipe.
If necessary a common water pressure regulator (not shown) can be used to control pressure in conduit 12a.
Although the invention has been shown and described it should be understood by those skilled in the art that various changes in form and detail may be made without departing from the spirit and the scope of the claimed invention.

Claims (10)

I Claim

1. A heat exchanger for first and second fluids comprising:
a tubular housing having a continuous wall, a length, an interior surface with margins at each end, linear paths between the margins, and orifices between the margins and between the paths;
a drainpipe longer than the housing and extending therethrough with an annular space therebetween;
the drainpipe comprising:
an arcuate wall with a gap with recesses along each edge of the gap;
a concave metal first strip bridging the gap and nested in the recesses and having an exterior perimeter margin;
a compressible gasket in the annular space contacting the paths and margins thereby defining an open arcuate space above the drainpipe and a enclosed arcuate space with orifices below the drainpipe;
a compression shoe forced through the open arcuate space so as to urge the drainpipe downwards compressing the gasket and sealing the enclosed arcuate space thereby creating a conduit through which the second fluid can flow and exchange heat with the first fluid.

2. The heat exchanger of Claim 1 further including a concave metal second strip nested against the first strip, the second strip having an outer perimeter margin onto which the gasket is compressed.

3. The heat exchanger of Claim 2 where first and/or the second metal strip has at least one vent to the ambient.

4. The heat exchanger of Claim 1 further including inlet and outlet manifolds.

5. The heat exchanger of Claims 1 and 2 further including at least one flow distributor in the conduit.

6. The heat exchanger of Claims 1 and 2 where at least one orifice is at an angle to the housing wall.

7. The heat exchanger of Claims 1 and 2 further including a turbulator within the conduit.

8. The heat exchanger of Claim 2 where the first and second strips are formed from a single folded strip.

9. The heat exchanger of Claims 1 and 2 where the concave metal strips are copper.

10. The heat exchanger of Clahn 2 where the first fluid is drainwater and the second fluid is potable water.