HYBRID DRAINPIPE HEAT EXCHANGER

ECHANGEUR DE CHALEUR A TUYAU DE VIDANGE HYBRIDE

English Abstract

The present invention is low-cost hybrid heat exchanger that uses sheet copper and rigid plastic tubing. Copper is used only where actual heat transfer takes place, adjacent the drainpipe wall. All other components are plastic. Its low cost makes it ideal for use as a drainpipe heat exchanger in a building where it can cost-effectively supply pre-heated water to a water heater, such as when showering. The heat exchanger comprises an inner copper conduit or drainpipe, a rolled sheet copper cylinder, an outer plastic tube and manifolds, and O-ring. On assembly, inserting the drainpipe results in the O- ring being compressed between the copper cylinder and the plastic tube. The result is a sealed water chamber wherein heat transfer takes place. The ends of the plastic tube have radially spaced water distribution holes into the chamber and inlet and outlet manifolds, each with water connections to the building's cold water supply. A method of recovering heat from non-shower hot water uses using a separate reservoir is also disclosed.

French Abstract

La présente invention est un échangeur de chaleur hybride peu coûteux comportant du cuivre en feuille et un tube en plastique rigide. Le cuivre est utilisé uniquement là où le transfert thermique réel a lieu, adjacent à la paroi d'un conduit d'évacuation. Toutes les autres composantes sont en plastique. Son faible coût le rend idéal comme échangeur de chaleur de conduit d'évacuation dans un immeuble où il peut alimenter de l'eau préchauffée à un chauffe-eau de manière rentable, comme l'eau d'une douche. L'échangeur de chaleur comprend un conduit ou ou conduit d'évacuation interne en cuivre, un cylindre fait d'une feuille de cuivre roulée, un tube en plastique extérieur et des collecteurs, et un joint torique. À l'installation, l'insertion du conduit d'évacuation entraîne la compression du joint torique entre le cylindre de cuivre et le tube en plastique. Le résultat est une chambre d'eau étanche où le transfert de chaleur se produit. Les extrémités du tube en plastique ont des trous de distribution d'eau espacés radialement dans la chambre et des collecteurs d'entrée et de sortie, chacun ayant un raccord d'eau à l'alimentation en eau froide de l'immeuble. Une méthode de récupération de la chaleur de l'eau chaude hors douche à l'aide d'un réservoir séparé est également présentée.

Claims

The embodiments of an invention in which an exclusive property or privilege is
claimed is defined as follows:
1. A heat exchanger comprising:
an inner conduit connected to a supply of a first fluid for heat transfer
therewith;
a cylinder formed to substantially enclose said conduit and having a
longitudinal
gap;
an outer tube substantially enclosing said cylinder and defining a space
therebetween, said outer tube having first and second end portions;
said first and second enc portions having respective first and second fluid
openings
therethrough;
a gasket in said space where said gasket is formed to seal along a marginal
area of
the perimeter of cylinder;
said cylinder and said outer tube and said gasket defining a chamber and where
said
chamber has said first and second fluid openings terminating therein;
at least one inlet manifold having an internal channel communicating with said
first
fluid openings, and with at least one inlet fluid fitting connected to a
second fluid for heat
transfer therewith;
at least one outlet manifold having an internal channel communicating with
said
second fluid openings, and with at least one outlet fluid fitting connected to
a fluid using
device;
said at least two manifolds being sealed proximate said ends of said outer
tube;
the arrangement being such that within said chamber, said first and second
fluids
transfer heat.
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2. The improvement to a building where said building has a fresh water
supply, at least
an intermittent used water supply, and at least one water using device, the
improvement
comprising the heat exchanger of Claim 1 where said inner conduit is connected
to said at
least intermittent used water supply and said at least one inlet fluid fitting
is connected to
at said fresh water supply and said at least one outlet fitting is connected
to said at least
one water using device.
3. The improvement of Claim 2 where said water using device is a water
heater.
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Description

CA 02742075 2014-02-06
HYBRID DRAINPIPE HEAT EXCHANGER
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.
BACKGROUND OF THE INVENTION
Inefficient use of expensive copper in traditional drainpipe heat exchangers
has
prevented widespread use of drainwater heat recovery from becoming mainstream
in spite
of the vast energy saving potential in every habitable building. The instant
invention
greatly reduces the amount of copper required by using copper only where heat
transfer
takes place. All other surfaces are low-cost plastic.
SUMMARY OF THE INVENTION
While it may be used in a variety of heat transfer applications, instant heat
exchanger's use in heat recovery from a building's wastewater drainpipe will
be described
in detail herein. The instant heat exchanger is suitable for both vertical and
horizontal
installations.
When installed vertically it operates as a falling film heat exchanger where
the
drainwater flows circumferentially on the inner wall which maximizes the
wetter surface
area needed for heat transfer. Typically, vertical installations are limited
in length by
ceiling-to-floor dimensions in buildings which, in turn, limits the wetted
surface area.
By moving the relative locations of its plumbing fittings, it can be used
horizontally,
where it is preferably made as long as possible to maximize wetted surface
area for heat
transfer which directly affects performance and cost-effectiveness.
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CA 02742075 2011-05-31
The heat exchanger comprises a set of concentric cylindrical components. At
the center
is a conduit such as a standard drainpipe made of copper or other thermally
conductive
material.
Around it is a shorter cylinder of sheet copper (or other thermally conductive
material).
This cylinder is open along its length to define a small gap. Concentric with
the cylinder
and spaced from it (i.e., of larger diameter) is a outer tube of plastic or
other rigid, low-
cost material, which has a ring of spaced holes that are covered by a manifold
at each end.
Next is a unique gasket-spacer. such as a common 0-ring, that follows the
perimeter of
the copper cylinder and thereby defines the boundary of a sealed chamber one
wall of
which is the cylinder and the other the plastic tube. The inner openings of
the ring of
holes are also enclosed by the gasket.
The short cylindrical plastic manifolds are sealed to the outside of the
plastic tube and
have has an internal circumferential groove and a water fitting. The fitting
opens into the
groove within which the outer openings of the ring of hole are located.
Thus water (or other fluid) for heat transfer with the central drainpipe,
enters the sealed
chamber at one end and exits at the opposite end of the outer tube.
Heat transfer takes place in the chamber, either heating or cooling, depending
on the
relative temperatures of the drainwater and the fresh water. For most uses
heating of the
freshwater will be the goal. However, for example, a drinking fountain can use
the instant
invention to cool the delivered water using draining cold water to cool fresh
incoming
warmer water.
The diametric dimensions of the components ensures that upon final assembly of
the
components, the first described drainpipe, which is inserted last, is a press
fit into the
cylinder which causes the 0-ring to compress sealing the chamber.
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CA 02742075 2011-05-31
Inside the chamber, the building's normal water pressure exerts enormous force
on the
cylinder close the gap slightly to create an extremely tight clamping action
around the
drainpipe for maximum thermal conductivity. For example with water pressure of
50 psi
and a cylinder area of 200 square inches, the circumferential clamping force
onto the
drainpipe is 10,000 pounds.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a cross-section of the heat exchanger also showing the water flow
through the
fittings, manifolds and chamber;
Figure 2 is an exploded view of the outer tube and the manifolds;
Figure 3 shows how the 0-ring is shaped with its hoop ends and straight runs
when
installed adjacent the inner wall of the outer tube, and the two opposing 0-
ring
rods located on the opposite wall of the outer tube;
Figure 4 shows the central drainpipe and surrounding cylinder with its
longitudinal gap;
Figure 5 shows the relationship between the drainpipe, cylinder and 0-ring and
a
representation of how the pins work to hold the 0-ring. The pins actually
protrude
through the wall of the outer tube;
Figure 6 shows the concentric layout of the components without the manifolds
and
showing how pins protrude through the outer tube to engage the 0-ring until it
is
secured in place on final assembly;
Figure 7 shows how the cylinder could be made from a trapezoidal sheet to
provide an
angled gap;
Figure 8 is schematic drawing of how the instant heat exchanger having a third
centre
manifold can be used to recover heat during batch water use situations where
used
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CA 02742075 2011-05-31
hot water is draining from say, a dishwasher, but no cold water if flowing to
the
faucet or water heater. The separate reservoir will automatically thermosiphon
its
water supply through the heat exchanger thereby recovering heat from the
drainpipe.
DETAILED DESCRIPTION OF THE INVENTION
Referring to the drawings, Figs 1 shows a cross section of the drainpipe heat
exchanger
100. The central drainpipe 14 may be a common copper DWV (domestic waste vent)
tube
or pipe of any suitable diameter from, say, 2 to 6 inches. It may also be
rolled and seamed
from any suitable sheet material. In Figs 1 and 2 outer tube 1 may be of any
suitable still
material such as a PVC or ABS plastic tube or pipe capable of withstanding
pressure from
within and sized in accordance with the diameter of drainpipe 14. Outer tube 1
has fluid
openings adjacent each end preferably in the form of a ring of holes 9 through
the wall for
fluid distribution.
Inlet manifold 4 (lower) and outlet manifold 4a (upper) have inlet 5 and
outlet 6
fittings (inlet flow 15a, outlet flow 15b) and an internal circumferential
flow channels 10
that communicate with their respective distribution holes 9 in outer tube 1.
As shown in
Fig 2 the manifolds arrows indicate they are to be slid on over each end of
outer tube 1.
The distribution holes may be spaced and/or sized so as to optimize heat
transfer
performance. That is, more or bigger holes are better the further away they
are from the
fittings, 5, 6.
The manifolds 4 and 4a are orientated such that the inlet 5 and outlet 6 are
positioned
opposite to where the gasket 0-ring gap 3c will be located on assembly. For
horizontal
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CA 02742075 2011-05-31
operation, a third centralized manifold 4b may be added for the inlet 5 and
the two end
manifolds 4, 4a used collectively as outlet 6.
The manifolds can be fabricated from four parts: a short section of plastic
tube with
two spaced plastic rings 11 inside, and a plastic pipe fitting, all bonded
together and
defining a circumferential flow channel 10. Alternatively flow channel 10 may
be formed
internally by machining an internal groove in a piece of thick wall tube or
pipe. The
manifolds are bonded to secure and seal them to outer tube 1. The manifolds
may also be
fitted with 0-rings (not shown) that seal against the outer wall of outer tube
1. Of course
the flow channel 10 may be formed in the outer circumference of outer tube 1
instead of,
or, in addition to, its indicated location inside the manifolds 4, 4a (not
shown).
A third manifold 4b (dashed outline) of the same design may also be added
around the
middle of the outer tube inclosing a ring of distribution holes (not shown)
and with a
water fitting. Using manifold 4b as the water inlet the water flow therefrom
is both up and
down (or left and right if horizontal, with gasket gap 3d downwards). In this
way a
remote water tank or reservoir can be plumbed inline with the instant heat
exchanger to
enable thermosiphonic flow therebetween for heat exchange with batch water
flow.
Inlet manifold 4 may have a fluid pressure regulator fitted (not shown) to
limit the
internal pressure in chamber 15.
Cylinder 2 may be least expensively formed from sheet copper which remains
open
(un-seamed) along its length. Preferably it has at least one longitudinal
flange 2a shown
in Figs 4 and 6 that serves to index cylinder 2 in the 0-ring gap 3d (Fig 3)
and prevent its
unwanted rotation during assembly. Gap 7 enables cylinder 2 to clamp tightly
onto
drainpipe 14, first during assembly by means of the compression of 0-ring 3,
3a, 3b, 3c,
and then when installed, as a result of the enormous force created by the
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CA 02742075 2011-05-31
pressure. Gap 7 also serves the important function of providing a vent or
fluid path to the
ambient in the event of a leak developing in the heat exchanger between the
drainpipe 14
and cylinder 2 whereby a visible drip will signal a service requirement.
Fig 1 shows how a open plastic hoop 20 (dashed outline) can be implemented to
prevent erosion of the cylinder 2 from the jets of water that would otherwise
impinge
directly on the cylinder surface slowly eroding it.
Fig 3 shows the gasket-spacer component which operates in a marginal area
around the
perimeter of cylinder 2. An 0-ring may be used. It is slightly stretched to
hook over pins
16 (Figs 2, 5, 6) to create the end hoops 3a separated by the straights 3.
Pins 16 are
preferably inserted through the wall of outer tube 1 where one end protrudes
into chamber
15 and the other end terminates in flow channel 10. Alternately pins 16 may be
attached
to cylinder 2. Opposite the 0-ring straights 3 are two rear compensators 3c of
similar
gasket material that act as compression elements to ensure even compression of
straights
3 along the length on either side of gap 7 of cylinder 2.
Once assembled the 0-ring elements maintain a sealed spacing between cylinder
2 and
outer tube 1 which defines a chamber 15 (Fig 1) through which water flows for
heat
transfer therewith. Chamber 15 may have inserts to provide turbulent flow,
such as plastic
mesh, rings, beads and the like. Further this chamber 15 may be made to hold
more or
less water by altering the 0-ring diameter including using large bore tubing
or by adding
a shaped spacer under the the 0-ring and bonded to the interior wall of the
outer tube. In
this way a reservoir is formed to hold a quantity of water. This would be
advantageous in
applications such as below a sink where a supply of hot water is undesirable
due to
plumbing or operational costs, as, for example, in a restaurant. With enough
volume the
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CA 02742075 2011-05-31
instant heat exchanger can provide warm water at no cost and maintain a warm
flow by
using the draining used water to heat the incoming cold water.
Cylinder 2 may be fabricated with an angled gap 7a as shown in Fig 7 which
will avoid
an unbalanced inwards force that would exist along the otherwise axial gap 7
where no
water pressure is exerted.
Fig 6 shows how the components are arranged concentrically, how pins 16 engage
0-
ring 3,3a, how flange 2a engages the 0-ring gap 3d, and how the 0-ring is
compressed
between cylinder 2 and outer tube 1 defining chamber15 (Fig 1) and sealing
same.
In Fig 8 is shown how the instant heat exchanger 100 may be plumbed to include
a
separate reservoir 110 which is in turn, is plumbed to a water heater 120 (or
a faucet, not
shown) which supplies hot water via hot water branch 108. Mains water pipe 106
enters a
building and splits into two branches: cold water branch 101 and hot water
heater supply
branch 102. All drainwater leaves via sewer connection 107. Hot water heater
supply
branch 102 enters the center manifold of heat exchanger 100 and flows both up
and down
(dashed arrows) to exit via the two end manifolds. The end manifolds are
plumbed into
reservoir 110 at its top 103 and bottom 104. Due to the physical property of
fluids
including water, hotter water is lighter or less dense that colder water.
Therefore water in
reservoir 110 naturally stratifies with the coldest being at the bottom which
is continuous
with water contained in heat exchanger 100. Any heat in drainpipe 14 will heat
water in
chamber 15 making it lighter. By natural convection it will therefore be
displaced
upwards by the heavier, colder water entering below. This thermosiphonic
process
continues automatically as long as the water in the chamber 15 is warmer than
the water
at the bottom of reservoir 110, the end result being that the water in
reservoir 110
becomes warmer from the top down. Reservoir 110 is plumbed to hot water heater
120
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CA 02742075 2014-05-06
which will therefore receive that warmed water when the next demand for hot
water
causes cold water from mains 106 to push the warmed water in heat exchanger
100
and reservoir 100 into water heater 120 and finally into hot water branch 108
and out the
opened faucet (not shown).
Note that with this arrangement lower branch 104 can see two way flow at
different
times (double-ended arrows): if there is cold water flowing through branch
102, flow
through branch 104 (and branch 103) is to the left into reservoir 110; if only
used hot
water is draining, then the flow in branch 104 will be to the right into heat
exchanger 100
because of the above described thermosiphonic phenomena.
8

Representative Drawing