Note: Descriptions are shown in the official language in which they were submitted.
CA 02626219 2008-04-03
SPECIFICATIONS
FIELD OF THE INVENTION
Patent applications 2,559,296; 2,611,709; 2,583,161 by the present inventor
are also
drainpipe heat exchangers.
The present invention is a drainpipe heat exchanger for drainwater heat
recovery (DHR)
from a building's regular drainpipe plumbing system. It includes a cold-
drainwater-protected
heat storage reservoir. Also disclosed is a one- and two-piece heat exchanger
design that can
be installed over existing drainpipes while they remain in full operation. The
heat storage
reservoir uses the thermosiphon principle and makes DHR available from both
continuous
plumbing fixture/appliance drain flows, such as a shower or running sink, and
batch drain
flows, such as from a dishwasher or filled sink. Thermosiphon is a well-known
method of
passive heat exchange based on natural convection. (See, for example,
thermosiphon at
Wikipedia.com.)
BACKGROUND OF THE INVENTION
The traditional drainwater heat recovery (DHR) heat exchanger comprises a
large diameter
central copper tube (as used for drainpipes) wrapped with a small diameter
cold water tube
also of copper. It is based on the long-known Falling Film principle of heat
transfer. 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 12/15/2000, 10.1007/s00897000445a, CO 2001 Springer-
Verlag New
York, Inc., and, US patent # 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
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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 while drainwater is `falling' down the inside tube and transferring
its heat to the
cold water in the outer coil. Thus showering and sink rinsing are the
principal appliances/
fixtures where such heat exchangers can work 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.
However the traditional DHR design is not very cost effective because their
payback time
or return on investment (ROI) is too long in comparison to other energy saving
strategies.
This can be attributed to:
1. Too little use of the expensive heat transfer material, which is usually
copper, is actually
used for heat transfer. For example thermal contact is limited to a narrow
spiral contact strip
between the outer coil's (conduit) contact surface with the inner tube's wall.
Because heat
transfer is a direct function of surface area, this limitation reduces
performance which
negatively affects ROI. This limitation is so greatly increased when it is
laid horizontally
which is often necessary (i.e., buildings without basements), that horizontal
use is not
recommended. Also, in regards the outer coil, the greatest part of the of its
total surface area
is not used for heat transfer. Only that small inner portion of the
circumference actually
contacts the drainpipe wall, the remaining, larger, outer portion of the
circumference does not
do heat transfer at all.
In the instant invention, instead of a coiled tube conduit, sheet copper is
used and is
formed into a hollow jacket that serves as the cold water `tube' or conduit.
This dramatically
lowers cost, while increasing thermal contact area to nearly 100%. For
example, a 5 foot
long, 4 inch diameter drainpipe, requires only 2/3 the weight of copper for
the cold water
exchanger; plus sheet-form copper is less expensive by weight than tube-form
copper, and, a
much higher percentage of that copper is used for heat transfer. Further, the
instant invention
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allows for very compact, small diameter DHR (i.e., for a 11/a 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
has offers a shorter ROI allowing for wider use in all size buildings.
2. Lack of heat storage. The traditional DHR only works when both the
drainwater and the
cold water are flowing simultaneously, such as in showering or running sinks.
This referred to
as `continuous' hot water use. It cannot recover heat from `batch' hot water
use such as from
appliances/fixtures including wash machines and filled sinks and tubs, since
there is nowhere
for any meaningful amount of recovered heat to be stored. As a result, only
about 40% of the
total used hot drainwater (continuous use) is available for DHR with
traditional non-storage
DHR. And what little heat is stored in the outer coil is lost immediately to
any cold
drainwater which may flow at any time.
The instant design uses a separate reservoir to receive and store heat from
100% of a
building's drainwater no matter if it is from a continuous- or batch use
source. This remote
heat storage reservoir is mounted above the DHR so as to thermosiphon with the
cold water
jacket or conduit when hotter drainwater is flowing creating a thermal
differential with the
reservoir water. No moving parts or controls are required. Further,
thermosiphoning provides
automatic protection from heat loss to colder drainwater because
thermosiphoning stops
when the temperature differential is reversed. This further reduces the ROI.
3. 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. This then requires either larger, more expensive
tubing and/or a
manifold arrangement of two or more coils to have multiple, parallel flow,
tube coils which
again adds cost and negatively affects the ROI.
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In the instant invention, the jacket offers a direct flow path from inlet to
outlet and the
passage can be as small or as large as needed. This eliminates pressure drop
and reduces
manufacturing cost.
SUMMARY OF THE INVENTION
In a building, a first heat transfer fluid, referred to herein as drainwater,
flows through a
drainpipe. In the instant drainpipe heat exchanger invention, sheet copper is
formed into a
chamber or conduit. In one embodiment his chamber or conduit is in the form of
a jacket with
a longitudinal gap, to encircle a round, vertical drainpipe in the shape of a
letter "C" in
outline. In a second embodiment it is in the shape of a`bar' or beam or trough
that fits below
the flattened, `D' shaped, bottom portion of a horizontal drainpipe. In both,
the spaced inner
and outer walls are sealed at the ends and there are inlet and outlet fittings
for connection to a
second heat transfer fluid which may be under pressure such as the cold water
supply for a
water heater. The inner wall contacts the drainpipe and matches its shape so
as to maximize
the area of thermal contact. In the jacket, a longitudinal gap or slit is
provided where the inner
and outer walls U-bend back on themselves to create the chamber. This gap
allows
contraction of the heat exchanger's inner wall to clamp tightly onto a
circular drain tube. The
exterior wall has a stiff outer sleeve around which are several band clamps.
The outer still
sleeve provides clamping force distribution and heat insulation. The gap
allows for intimate
contact and easy sliding assembly onto the drainpipe. When connected to the
pressurized
water supply, the pressure adds to the thermal contact force much like a blood
pressure
measuring cuff, to further increase 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.
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In a third embodiment, the instant invention is fabricated in two long half-
cylindrical
jackets (clam-shell like) which are assembled onto a operating drainpipe
without disrupting
drainwater flow.
A the second flat embodiment, the instant invention is clamped between the
flattened
drainpipe and a shaped shoe or filler piece to spread the clamping force along
the entire
length. Again, the clamping plus the internal water pressure provide high
performance
thermal contact with the drainpipe.
In a fourth embodiment, for flattened, D-shaped drainpipes, the cold water
heat exchanger
may be in two parts: an upper hemi-cylindrical plastic sealing portion bonded
to a lower flat
sheet metal heat transfer portion. This would further lower costs to improve
the ROI.
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 too-hot
water is needed to mix with the now-warm-cold-water to achieve the desired
final
comfortable 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 on
the inner wall
to serve as a vent for visible leak detection (a drip or air-drop onto the
floor). The sheet is
then formed into a hollow structure either a tubular `C' shape or a flat bar
shape. The outer
wall of the jacket is pierced to receive soldered-on pipe fittings and the
ends are sealed with
appropriately shaped copper (tubing, rod or twisted wire), soldered into
place. Alternatively,
the jacket ends may be squeezed-closed and soldered shut.
The unique, high-force hydraulic clamping action maximizes heat transfer by
increasing
thermal contact force. 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 (at) x 3 x 48 x 50 = 22,000 pounds, or 1 I tons of
contact force!
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Not only does such an enormous force provide fast heat transfer over the
entire length, but
it forces intimate, conforming contact between the form-able sheet metal inner
wall and
drainpipe wall surfaces that may be imperfectly fitted. 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
inlet and outlet
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 large diameter, round, horizontal drainpipe, for example.
In a sixth embodiment a remote reservoir is part of the pressurized cold water
system and
is located above the instant vertical or horizontal drainpipe heat exchanger.
The reservoir is
connected with inlet and outlet tubes to the cold water heat exchanger jacket
or conduit. The
reservoir preferably has a high, horizontal orientation to provide maximum
thermosiphon
effect. One tube between the reservoir and heat exchanger terminates low in
the reservoir and
the other tube terminates above the first. Natural temperature gradients
(layering or
stratification) in the reservoir means that lower layers are always colder and
heavier that
upper layers. Thus whenever warm drainwater (first heat transfer fluid) heats
the cold water
(second heat transfer fluid) in the cold water heat exchanger, it will also be
made lighter and
will therefore automatically be displaced upward into the reservoir by the
heavier colder
reservoir water sinking downward. This circulation of reservoir water will
continue for as
long as a temperature difference exists. In that way the reservoir become
heated and the cold
water heat exchanger is cooled for best heat transfer.
When cold water is required by the water heater (hot water is being used) the
cold water
under pressure flows first into the center of the cold water heat exchanger,
then through the
connecting tubes at each end and into the reservoir, and then out of the
reservoir into the
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CA 02626219 2008-04-03
water heater. The outlet tube therefore can have two way flow depending on
whether
thermosiphon or pressure flow is occurring. By having these two flow paths any
heat received
from the flowing hot drainwater by the cold water conduit will either be
picked up directly
under forced flow (hot water being used) or by thermosiphonic action (no hot
water being
used). If cold water is flowing as, for example, in the case of replacing the
hot water being
used in a shower, it will directly be heated by the hot shower drainwater. If
no cold water is
flowing but hot drainwater is, the heat will automatically transfer by
thermosiphonic action
into the reservoir. Here, the heat is stored until some future hot water use
causes the now-pre-
heated cold water from the reservoir to flow into the water heater to reduce
energy use.
In a seventh embodiment the same remote reservoir concept is applied to a
horizontal
drainpipe heat exchanger. here the reservoir may be vertical or horizontal. In
the event that
the water heater is properly positioned with appropriate upper and lower water
connections,
(one somewhat above the other) this embodiment may be plumbed directly to the
heater
using, for example, T-fittings at the heater's inlet and outlet.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 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;
Figures 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;
Figure 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
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CA 02626219 2008-04-03
shape, in both cases the flow path is flush such that there is no `step-up' to
impede
drainwater flow in or out;
Figure 6 shows an adaptor for the drainwater heat exchanger formed, for
example, from a
suitable plastic material;
Figure 7 shows an end view of another embodiment where the drainwater heat
exchanger's
end'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;
Figure 8 shows a copper solder-type fitting having one end formed to a
rectangular shape for
insertion into the end socket;
Figure 9 shows a copper plug to be soldered in unused socket openings;
Figure 10 shows a side view of the same embodiment as figure 7 showing the end
location of
the drainwater heat exchanger fittings;
Figure 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;
Figure 12 shows a top section view of a two-piece design for clamping about an
in-use
drainpipe/exhaust pipe;
Figure 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;
Figure 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;
Figure 15 show a side view of the sealing member;
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Figure 16 shows a possible use of the joint flange where it has various
notches to distribute
the fluid flow evenly over the jacket's inner wall so as to maximize heat
transfer by
maintaining the best temperature differential;
Figure 17 shows a thin, flat cold water (or other fluid) conduit clamped
against the flat lower
surface of the drainwater conduit;
Figure 18 is a cross section of the same embodiment and showing one internal
stiffener in the
cold water exchanger to prevent bulging;
Figure 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;
Figure 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;
Figure 21 shows a perspective view of the outlet fitting of the embodiment;
Figure 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's inner
wall so as to sweep the entire surface along its vertical length;
Figure 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;
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Figure 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;
Figure 25 shows the same embodiment but with an oval shaped lower flow
surface;
Figure 26 shows another vertical embodiment with a remote heat storage
reservoir connected
with tubes for thermosiphoning with the cold water heat exchanger and central
feed
into the cold water heat exchanger;
Figure 27 shows a horizontal embodiment of a drainpipe heat exchanger with a
remote heat
storage reservoir;
Figure 28 shows the same embodiment in partial section;
Figure 29 shows the embodiment of Fig 12 but as would be used on a horizontal
drainpipe
where only a lower half is used (no exterior clamping shown);
Figure 30 shows the same embodiment having a plastic outer wall for fluid
containment
joined to a metal inner wall for fluid containment and for heat transfer.
DETAILED DESCRIPTION OF THE INVENTION
Vertical drainpipe heat exchangers and horizontal drainpipe heat exchangers
are disclosed
each with unique embodiments. 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 could be reversed for cooling). Generally the conduits are metal
and preferably
copper for fast heat transfer. The instant drainpipe heat exchangers may
comprise both
CA 02626219 2008-04-03
conduits as a single assembly or just the second conduit which can be fitted
to and existing
first conduit.
The two conduits are co-operatively shaped and tightly clamped together so as
to provide
maximum thermal contact area and high thermal contact force again for 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
cold water conduit to add to the thermal contact force to provide even faster
heat transfer.
Faster heat transfer makes DHR more cost effective.
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.
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.
In one embodiment, wa112 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
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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.
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.
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.
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
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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'.
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.
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.
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.
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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.
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,'/a 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's cold
water supply. Inner
wall 1 is however free to expand every so slightly to provide a tight,
intimate thermal contact
with drainpipe I using that same internal pressure.
In Fig 11, 121ap joint 5' is a soldered and may include longitudinal joint
flange 110 which
can act as a fluid flow distribution ring 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
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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.
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.
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.
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.
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.
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.
CA 02626219 2008-04-03
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.
Fig 18 shows a cross section of the same embodiment where the drainwater
conduit is
shown to be a flattened, hemi-cylindrical tube 1 forced into intimate,
conforming thermal
contact with cold conduit 2 using shaped pressure distribution shoes 130, 131
and clamp
bands 12.
In the embodiments shown in Fig 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.
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 lb
thereto, the two creating a hybrid drainpipe of rounded rectangular or
hemicylindrical form.
This embodiment is for the lowest cost device. Interior longitudinal supports
Ic 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 lc may be wavy to create a
desirable
turbulent flow. Supports lc also act as fins to extend heat transfer surface
area. Supports lc
may be eliminated and baffles 2" in the cold water exchanger may be used to
prevent
pressure bulging of the flat surfaces.
Fig 20 shows the same embodiment with different drainpipe connection fittings.
Inlet
200" is a vertical right angle inlet centered on plastic top la 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, la, lb (Fig 19) and is
bonded and sealed
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thereto. A slight slope to outlet 200' carries away the final drainwater drips
to leave
drainwater conduit I dry.
In Fig 22 vertical heat exchanger 100 has an inner wall 5 (heat transfer
surface) and ring-
shaped flow distribution ring 110' which provides an even annular gap 120'
adjacent wall 5.
End seals 34 (Fig 23) and flow distribution ring 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 distribution ring would take the form of a rectangular
bridge held a small
distance below the heat transfer surface by stand-off elements.
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.
Fig 26 shows a vertical drainpipe heat exchanger 500 having a remote heat
storage
reservoir 400 which is always pressurized with the cold water supply B and
lies in series with
the cold water flow into, say, a water heater. Outlet 11 connects to external
plumbing to
provide pre-heated water C to a water heater or other fixture/appliance. Cold
water B enters
via fitting 10 into jacket or conduit 2. Two central flow distribution rings
110' ensure that the
up and down vertical flow through jacket 2 is adjacent inner heat transfer
wall where it then
passes under two additional upper and lower flow distribution rings 110' into
the collection
area (between end seal 34 and ring 110') and out through fittings 213 and 214.
Now cold
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water B (preheated by drainpipe 1, or not) passes through connecting tubes 401
and 402 into
reservoir 400 via fittings 410 and 411 respectively. Tube 402 terminates
higher in reservoir
400 than tube 401. Thus tube 402 terminates in the warmer, lighter layers of
water filling
reservoir 400.
In operation four scenarios are possible:
1. Hot water is being used and used hot drainwater A' is flowing, such as in
showering.
Here the cold water B will be pre-heated in jacket 2 and flow upwards through
tubes 401
and 402 (arrows 403, 404) into reservoir 400 and out outlet 11.
2. Hot water is being used but no drainwater is flowing such as when filling a
wash
machine. Here the cold water B simply passes through jacket 2 and through
tubes 401 and
402 into reservoir 400 and outlet I1 (arrows 403, 404). With fitting 11 on
top, any
previously recovered heated water will be the first to flow out because it is
lighter and
rises.
3. Hot drainwater A' is flowing but no hot water is being used, such as when
an appliance
drains. Then, if the in water B in jacket 2 is being heated by drainwater A'
and is thereby
made lighter, thermosiphoning will automatically take place, whereby any water
in
reservoir 400 which is colder than that in jacket 2, will cause the heavier
cold water to sink
down tube 401 (arrow 403) into jacket 2 via fitting 214, then travel up
through jacket 2
picking up heat and out outlet 213 to return to the upper region of reservoir
400 via tube
402. This continues as long as there is a temperature differential (weight
difference)
between the water in the reservoir and the water in the jacket, that is as
long as heated
drainwater continues to flow. The net result is that the water in the
reservoir is heated ready
to flow into a water heater or other appliance/fixture
4. Cold drainwater is flowing. The water in the jacket 2 is the first to
become cold and
therefore also becomes heavier. Thermosiphoning cannot occur with the
reservoir 400
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since cold water cannot rise into it and therefore whatever heat is present in
the reservoir
will not be lost to the cold drainwater. This automatic cessation of
thermosiphoning
provides protected heat storage for the recovered heat in the reservoir.
Cold water reservoir 400 may be the reservoir may be a rectangular shape or a
square
tube shape or a cylindrical shape and mounted or hung some distance from the
drainpipe
heat exchanger and as high as practical, such as being hung from a ceiling.
This will
increase thermosiphon action (speed the flow) to improve performance provided
tubes
401, 402 are of sufficient diameter. In such cases tubes 401 and 402 should be
well
insulated to maintain the best temperature differential and to prevent heat
loss to the
ambient.
In the event that it is desired to discard heat, as in, for example, a cold
water drinking
fountain, the arrangements may be reversed so that the coldest water remains
in the
reservoir ready to move to the drinking outlet. Then, the reservoir would be
below the
heat exchanger and the tubes 401 and 402 arranged such that hotter water in
the reservoir
rises to be cooled by colder drainwater from the fountain and returns cooler,
thus keeping
the reservoir cool and the drinking water cold as desired.
Fig 29 shows how drainpipe heat exchanger 600 is a half jacket with a
continuous
inner and outer wall 2, 5 that may be used on the bottom portion of a
horizontal drainpipe
1 such as one of copper or steel (cast iron) carrying drainwater A. Cold water
B passes
through exchanger 600 on its way to the water heater. This minimizes material
and so
improves the ROI. In Figs 29 and 30 none of the required external clamps or
reinforcing
sleeves are shown for added clarity.
Fig 30 shows exchanger 700 of composite construction where inner wall 2 is
metal
joined to a thick outer wall 222 made of plastic to further reduce cost and
improve ROI.
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