Note: Descriptions are shown in the official language in which they were submitted.
CA 02328822 2000-12-28
SPECIFICATIONS
BACKGROUND
s Water heaters are well known to consume vast amounts of energy to heat
cold water to make it hot for human use in washing and cleaning, and for
industrial processes. The resulting hot drainwater (also referred to as
wastewater) flows freely to the sewer taking with it all of that heat energy.
Generation of energy to heat water releases pollutants including those that
o cause global warming.
Although it would seem obvious to use heat in drainwater to heat new cold
water, thereby reducing energy use and saving money, this seemingly simple
heat transfer idea has resisted successful solution in spite of many inventors
having tried over a very long time.
s It is, therefore, the objective of the present invention to provide a heat
exchanger apparatus to remove heat from flowing drainwater, to store that
heat within that apparatus, and to limit heat loss of that stored heat to cold
drainwater that may flow thereafter.
Another objective is to cool drinking water using cold drainwater.
DESCRIPTION
By way of review, the water heater in a building has a continuous cold
water pressure feed to it. When a hot water faucet or valve (hereinafter
2s referred to as 'valve') is opened, the flow of hot water at the valve
reduces
pressure and allows cold water to instantaneously flow into the water heater,
displacing the hot water out of the valve. Thus when hot water is used, cold
water flows at exactly the same time and at exactly the same rate of flow.
Drainwater heat recovery involves removing heat from hotter drainwater
so (cooling it) and transferring the heat to the fresh cold water (warming
it).
This saves energy and money since no new energy is required.
US patent # 4,619,311, to Vasile, describes a drainwater heat recovery
system comprising a copper drainpipe heat exchanger whose exterior is
wrapped with a copper coil heat exchanger through which passes cold water to
35 be pre-heated. This type of tube-on-tube heat exchanger has been long-
available, such as that sold by the Solar Research in Brighton, MI 48116, as
part number 5832. These devices use conductive heat transfer which is
necessarily a two-way process because the two heat exchangers are in direct
physical contact. US patent 4,619,311, to Vasile is a simple, low-cost, easy-
to-
4o install heat exchanger. However, it transfers heat only when both
drainwater
and cold water are flowing simultaneously therethrough. This special flow
condition, referred to as 'continuous use', occurs when showering.
However the other major use of hot water in a building, referred to as
'batch use', occurs when appliances or fixtures, such as a washing machines or
CA 02328822 2000-12-28
sinks, fill with hot water, operate, and then, later, drain. In more detail,
in
batch use, when filling with hot water, cold water is flowing through the heat
exchanger but there is no drainwater flow, so no heat is transferred with tube-
on-tube heat exchanger and the cold water is not warmed before it enters the
water heater. Then, when the wash machine drains, there is hot drainwater
flow but no cold water flow (there being no hot water being used at that time)
and so, again, no heat is transferred and the hot drainwater leaves the
building
uncooled.
The reason tube-on-tube heat exchangers do not work under batch hot
o water use is that their only heat storage is the exterior cold water coil
which
will transfer it's heat back to a cold drainwater flow. Lacking heat storage
means that tube-on-tube heat exchanger can only recover heat from
approximately half of the total drainwater available for heat recovery. This
limits cost effectiveness of this important energy conservation device. A
seemingly obvious solution to this is to enclose the entire heat exchanger in
a
reservoir of water to store heat. However, cold drainwater would again simple
cool the reservoir by conductive heat transfer with no net gain.
Further, US patent 4,619,311, to Vasile is not recommended for horizontal
drainpipe applications, as found in a great many buildings with no basement,
2o because the design requires a generally circular drainpipe upon which to
wind
the outer coil. Further the design cannot have exterior wall finning on the
drainwater heat exchanger also due to the outer coil being wrapped against the
exterior wall. This severely limits heat transfer and so cost effectiveness.
Moreover this design cannot use twisted tube for the drainwater heat
2s exchanger which may add useful heat transfer.
Canadian Patent # 1,329,587 (and US patent #5,736,059) to the present
applicant, does teach of a drainwater heat recovery system with no-loss heat
storage. However, for low volume hot water users, such as in homes, the
system tends to be too large and, with its numerous components, too
so expensive. Further, its installation is essentially limited to vertical
drainpipes
unless mechanical pumping is added.
The object of the present invention is to provide a drainwater heat
exchanger which solves all of the aforementioned problems by providing no-
loss heat storage and low cost construction/installation.
35 A review of the physical principles involved in the present invention
follows.
Firstly, heat is transferred by conduction, convection, and radiation. When
a fluid such as water is adjacent a surface which is heated or cooled, heat is
conducted to or from the water.
4o Secondly, when a fluid such as a body of water is heated or cooled, its
density changes. When heat is added or removed at a particular region in a
body of water the water adjacent the hotter or colder surface becomes more
more less heavy, dense, or buoyant, compared to adjacent water. This added
buoyancy causes the heated mass of water to move vertically by convection
2
CA 02328822 2000-12-28
(mass transfer) whereupon the temperature affected water will convect to a
vertical position within the body of water where it becomes a horizontal layer
or stratum parallel to all other strata and parallel to the earth's surface.
The
hotter water will occupy the highest stratum and the coldest water will occupy
s the lowest stratum with all other strata in between being determined by
relative temperature. This stratification is a natural phenomena and cannot be
avoided save by agitating, mixing, or stirring the body of stratified water
(or
fluid). Thus heat is first transferred by conduction which thereafter causes
convection.
o Thirdly, fluid flow in a pipe tube or duct (all referred to as conduit) has
components of flow that are called boundary layer, laminar layer, and central
or main flow. The boundary layer is that thin, immobile layer of fluid that
clings to the wall of the conduit and through which conductive heat transfer
occurs first. The laminar layer is a slow moving thin layer between the
, s boundary and central flow and is where conduction also takes place and
where
convective flow begins.
Fourthly, in a vertical conduit, liquid flow is principally adjacent the
conduit wall with no flow down the hollow center. Capillary action and air
motion diverts the liquid to the wall where it clings, spreads, and flows
2o downwards as a relatively thin falling film.
Fifthly, by adding protrusions to a conduit wall, heat transfer can be
further improved due to the turbulent mixing of the three flow regions. Such
turbulence inducing protrusions may take the form of dimples or ridges on the
conduit wall.
25 The present invention prevents unwanted conductive heat transfer of
recovered heat to a cold drainwater flow by adding an intermediate convection
section between the drainwater and freshwater heat exchangers.The convection
section is a tubular reservoir which encloses the drainwater heat exchanger,
is
filled once with water, and is encircled by the freshwater heat exchanger.
so Within the water-filled reservoir there is also at least one convection
chamber
made of an insulative material that fills with reservoir water. It/they holds
a
small but sufficient volume of reservoir water to completely submerge the
drainwater heat exchanger. The convection chamber's opening is in its upper
portion while its lower portion is leak-proof. The small volume of water
35 contained in the convection chamber exchanges heat with the drainwater heat
exchanger by direct thermal conduction. However since the convection
chamber is open at the top and insulated all around, it can only exchange heat
with the reservoir water by convection. Since the convection chamber is leak
proof and has only an upper opening, heat from warmer drainwater drives an
4o upward convection into the reservoir, thereby effecting the desired
drainwater
heat recovery. Cooled convection chamber water, from a cold drainwater
flow, is made heavier and so remains immobile within the convection chamber
isolating the drainwater heat exchanger and thereby preventing the
surrounding warmer reservoir water (and freshwater coil) from losing its heat
3
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to the cold drainwater. Thus the objective of no-loss heat storage is achieved
at
low cost in both horizontal and vertical units.
The drainwater heat exchanger of the present invention generally
comprises at least one straight section of drainpipe that uses thin film heat
transfer and has a central heat transfer portion located within the water-
filled
reservoir. End portions extend out of the reservoir for connecting inline to a
building's drainpipe. The diameter of the drainpipe heat exchanger depends on
drainwater composition and flow. For use with toilet flows, the drainpipe is
generally a minimum of 3 inches in diameter and in this application the
o drainwater heat exchanger would be that diameter, or larger, and generally a
straight through tube. For applications where there is contained in the
drainwater smaller solids than the toilet, the diameter may be reduced, there
being no lower limit. In an application, for example, where the present
invention is to be installed within the cabinet of a dishwasher, the drainpipe
1 5 heat exchanger may be 1 or 2 inches in diameter or even less. It is also
within
the scope of the present invention to have other than a straight through
drainwater heat exchanger where fouling is not a problem such as in a laundry
washing application. Here the drainwater heat exchanger may be coiled or
have several parallel straight tubes or be made of a twisted tube. As well,
oval
20 or rounded rectangle shapes provide larger surface area for horizontally
flowing drainwater. Any shape may be used consistent with fabricating a
suitable convection chamber to work with that shape. For lowest cost, the may
be made from a thin plastic film extruded tube or tube welded from sheet
film, and backed by a thin seamed-metal tube on its exterior. A double
25 drainwater heat exchanger tube of thin plastic film could also be used for
added security.
The convection chambers) used in the present invention is made of an
insulative material and may be one or more in number. The convection
chamber is/are located within the reservoir (described later) and is/are
so submerged in the fluid filling the reservoir. The convection chamber has at
least one convective opening which is arranged such that a horizontal plane
through the lowest point of the opening, lies at least marginally above the
highest point of the that portion of the exposed drainwater heat exchanger
wall
served by the respective convection chamber. In this way, the entire
35 drainwater heat exchanger is fully submerged in the water contained in the
convection chamber(s), and, the convection chamber cannot overfill with cold
water. A convection chamber may be made entirely of plastic or if made of
metal (to act as a heat transfer fin) it must have an insulated exterior
surface,
i.e., it must be thermally insulative. A convection chamber should hold as
4o small a volume of reservoir water as possible, much smaller than the
combined volumes of the reservoir water plus that water filling the cold water
heat exchanger tubing. This volume, however, must not be so small as to
restrict convection speed. Fins attached to the drainwater heat exchanger
outer
wall may advantageously take up volume in the convection chamber, reducing
4
CA 02328822 2000-12-28
water volume, and add heat transfer performance.
The convection chamber takes on two distinct shapes depending on whether
the heat exchanger is to be used horizontally or vertically.
For the horizontal embodiment, the convection chamber may be a long,
s one-piece channel-shaped trough (more than one may also be used) which may
advantageously be made of insulating material, i.e., thermally non-conductive.
A metal, such as copper, may be made into a channel form to which the
insulative convection chamber is attached. The metal may first be attached
directly (i.e., soldered) to the bottom of a copper drainwater heat exchanger
to
o also act as a fin to greatly enhance heat transfer. Several such metal
channels
may be nested to further enhance heat transfer, however, the outside of the
outermost one must be insulative, the insulation defining the convection
chamber. The convection chamber is closed and sealed at the ends to ensure
that when cooled (heavier) water is contained therein it does not leak into
the
15 surrounding and warmer reservoir water, cooling same. Because drainpipes
are necessarily sloped downwards for flow, the entire drainwater heat
recovery device may also be sloped. However cold water is created up to the
level of the highest point of thermal conduction from the drainwater heat
exchanger. This level, the cold water line, must be entirely within the
2o convection chamber. If designed for dead horizontal use but then sloped to
match the building's drainpipe, the cold water would flow down to the low end
of the convection chamber and continually overflow the walls of the
convection chamber defeating the no heat-loss objective. Therefore the sloped
drainwater heat exchanger may have spaced fins along its horizontal length
25 that act as bulkheads or sealing partitions, dividing the convection
chamber
into short separate sections where the cold water level in each segment will
remain within a minimum overall convection chamber volume. For this
arrangement, the outer insulation layer will need to wrap around the top of
the
convection chamber and down the inside wall so that no conductive heat
so transfer can take place anywhere above the cold water line. Alternatively
the
convection chamber walls may merely be made higher (taller) to enclose
horizontal pooling of any cold water in the convection chamber(s). This
alternative however, adds unwanted volume to the convection chamber. Also
for this arrangement, the outer insulation layer will need to wrap around the
35 top of the convection chamber and down the inside wall, at least at the
high
end, so that conductive heat transfer cannot take place anywhere above the
cold water line.
The drainwater heat exchanger may be of any shape suited to the task
including round, oval, twisted tube, multiple parallel, and labyrinth, as long
as
4o a suitable convection chamber can be constructed to enclose same and not
hold
too much volume. The opening in the convection chamber may be designed to
enhance fluid flow having, for example, it may have a nozzle-shaped slit with
a gentle upward and outward flare to ensure rising convection currents are not
slowed by edges.
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For the vertical embodiment the convection chambers are generally several
in number (although one is sufficient) which take the form of tapered cups
with holes in their bottoms for them to slip and seal to the drainpipe heat
exchanger. These cups, being open (a convective opening) at their tops, are
arranged to slightly nest one into the next such that, no horizontal strata of
reservoir water can contact any exposed wall of the drainwater heat
exchanger. Sufficient numbers of nested cups are used such that they extend
the length of the drainwater heat exchanger and are submerged in the
reservoir water. A short, bottommost portion of the drainpipe heat exchanger
o may be left plain (no convection chamber) as the coldest water will
naturally
collect there and so heat transfer to a cold drainpipe will be minimal. This
would be done mainly in the interests of ease of assembly. If a metal
convection chamber is used to enhance heat transfer, then the outside of the
convection chamber must be covered with an insulating skin to prevent
15 conductive heat transfer through it's wall.
The reservoir of the present invention is a water-filled, generally tubular
container of any cross-sectional shape suitable for enclosing the drainwater
heat exchanger and having a volume for the required heat capacity, where,
size and weight aside, the larger the volume the better. The reservoir need
not
2o be pressurized. Depending on whether the cold water heat exchanger is
installed inside or outside of this reservoir, the reservoir may be made from
a
several different materials. If the cold water heat exchanger is wrapped about
the exterior of the reservoir and high heat transfer rates are desirable with
cost being a secondary consideration, then the reservoir may be made from a
2s highly thermally conductive metal, such as copper. For similar performance
at
a lower cost, the reservoir may be made of thin plastic membrane such as
vinyl or polyethylene film welded into a 'bag' shape. This bag would be
supported against the weight of contained water by the exterior cold water
heat exchanger coil. The reservoir is sealed by clamp means to the tube ends
30 of the drainwater heat exchanger. If the cold water heat exchanger is to be
installed within the reservoir then a thick walled plastic tube may be used
for
the reservoir. Various combinations of these materials may be used for the
reservoir. For example a membrane bag with an exterior thin metal foil for
enhanced heat transfer at moderate cost increase. A metal insert (i.e., a
sheet
35 of metal) within the reservoir will allow temperature to even out within
the
reservoir.
The cold water heat exchanger of the present invention may be submerged
inside the reservoir or wrapped in conductive contact around the exterior of
the reservoir. The tubing used can advantageously be as large a diameter as
4o practical in order to hold more volume of water for more heat storage. Heat
is
better stored in the cold water coil as it is then instantly available for
delivery
to the water heater. Cold water tubing may also be of a plastic material {for
lower cost) since there are often long periods of time (i.e., overnight) that
pass
between a drainwater heat recovery event and a hot water use event. Such
s
CA 02328822 2000-12-28
plastic tubing may be readily extruded to have a square cross section to
increase heat transfer surface area in contact with the reservoir wall. Long
time periods overcome the poor heat transfer coefficient of plastic. In
addition, in a preferred embodiment, both a metal and a plastic coil may be
co-jointly used being plumbed together in series or parallel and wrapped about
the exterior of the reservoir wall. This dual material cold water heat
exchanger arrangement will allow both fast and slow heat transfer to be
utilized at the best possible cost-performance ratio. The plastic tube (low
cost)
would be wrapped outside of the copper coil (expensive) so that the water in
o the copper coil would heat first and fastest and conduct heat to the
plastic.
Moving now to a description of operation. Any hotter drainwater flowing
at any time (from either continuous and batch hot water use) heats the water
in
the convection chambers) by conductive heat transfer. This makes that water
more buoyant which causes it to naturally convect upwards out of the
s convection chamber and become heated reservoir water. The main reservoir
water being less buoyant (heavier), naturally convects downwards into the
convection chamber for heating. This convection continues for as long as there
is a temperature differential between the drainpipe heat exchanger and the
reservoir water. The main reservoir water therefore becomes warmer as it
2o stores more and more recovered drainwater heat energy. The cold, water heat
exchanger and the water it contains, are, of course, heated at this same time
by
conductive heat transfer from the warm reservoir water. If and when colder
drainwater flows, convection chamber water is cooled first, becoming less
buoyant (heavier) than the surrounding warmer reservoir water. The cooled
25 convection chamber water therefore remains within the convection chamber
and convective heat transfer with the reservoir water ceases. This prevents
stored heat in the reservoir from being transferred to cold drainwater thereby
achieving the objective of one-way-only heat transfer. The entire drainwater
heat recovery device may be enclosed in insulation and protective jacket.
so The present invention finally solves the problem of drainwater heat
recovery from a building's entire drainwater supply by providing no-loss heat
storage in a simple, low cost design, and with widespread installation
potential.
The present invention in another embodiment may also be used for water
cooling (i.e., cooling drinking water) by inverting the device such that
35 convection chambers) have downwards facing opening. In such an
orientation, the hot drainwater would just fill the insulated convection
chambers) with more buoyant heated water preventing convection and
thereby prevent heating the reservoir water. When drainwater is colder,
convection would be downwards cooling the reservoir water, as intended. This
40 of course, would cool water flowing through the fresh water heat exchanger.
Small pin-holes in the uppermost portion of the convection chambers) may be
used to allow air pockets (i.e., from initial filling of reservoir with water)
to
leak out.
With one of each embodiment of the present invention installed in-series,
CA 02328822 2000-12-28
drainwater heat recovery and drainwater fresh water cooling may both be
accomplished.
In the present invention three walls of separation exist between drainwater
and fresh water which ensures absolute safety from contanunation of fresh
s water, (drainwater heat exchanger wall, reservoir wall, fresh water heat
exchanger wall). In addition the no-pressurized reservoir adds even more
safety.
Additional details. To reduce fouling of the drainwater heat exchanger and
to increase rate of heat transfer, dimpling of the exterior of the drainpipe
heat
o exchanger may be used as disclosed in this applicant's US patent #5,736,059,
mentioned above, where high velocity punches or projectiles (such as fired
shot) are applied to at least a portion of the drainpipe heat exchanger. Masks
prevent dimpling in the portions where the convection chamber seals to the
drainpipe. Other enhancements can be devised to create turbulence, including:
s rolled ridges, twists, fins, bubbled air, and vibration, and ultra-sonics.
The present invention may be used in various combinations such as: more
than one unit plumbed in series, or in parallel, in series-parallel, and where
vertical and horizontal embodiments are combined. In addition, one or more
miniature systems may be integrated into the cabinetry of sinks or dish- and
20 laundry washing machines and used with tankless or instantaneous water
heaters.
Further, it should be remembered that all indoor plumbing fixtures are
heated by ambient air and so even cold water used at the fixture is warmed as
it flows over warm fixture and drainpipe surfaces. When the drainwater heat
25 is recycled by the present heat exchanger invention, this warm drainwater
can
provide fresh warm water with no need for a traditional hot water supply. The
pre-heated fresh water provided may be plumbed directly to the fixture's
faucet, providing warm water at no energy cost, the heat being repeatedly
recycled from the drainwater to the fresh water.
so Moreover the reservoir of the present invention could be pressurized with
fresh water, thus avoiding the cost for the second cold water heat exchanger.
This heated water could then be used as feed water to a fixture, or, used for
toilet flush where the heated water would reduce condensation on the exterior
of the tank and resultant dripping onto the floor. This dripping is known to
35 cause structural damage, and to support fungus/mould growth which results
in
dangerous airborne spores in the building.
In yet another embodiment, a thermostatically controlled low wattage
heater may be provided within the reservoir to maintain a minimum
temperature for use at the site.
BRIEF EXPLANATION OF THE DRAWINGS
Figure 1 shows a cross section of one horizontal embodiment where the
s
CA 02328822 2000-12-28
coldwater heat exchanger is a series of straight tubes, the convection chamber
is tubular, and lower water inlet ports are flap controlled;
Figure 2 is a perspective detail view of one end of the same embodiment;
Figure 3, 4, 5, 6 are end views of the horizontal embodiment showing
s different shapes and positions of components, so to best use minimal
vertical
space in the installation;
Figure 7 is a partial section view of a vertical embodiment;
Figure 8 is a cross section top view taken at line 8-8 of same embodiment
and including heat conducting element next to reservoir interior wall;
o Figure 9 is a transparent view of one embodiment of a convection chamber
for the vertical embodiment showing the hole in the convection chamber
bottom which allows it to slide on and seal to the heat exchanger and, a
single
fin for heat transfer therein;
Figure 9b shows a fin ring on drainwater heat exchanger within a
15 convection chamber;
Figure 10 shows a double drainwater heat exchanger vertical embodiment;
Figure 11 shows a double vertical embodiment in series arrangement where
the top unit shows the volume of convection chamber water only for clarity
and with internal coldwater heat exchanger while the bottom unit shows the
2o full reservoir with coldwater heat exchanger removed for clarity;
Figure 12 shows an end cross section of a horizontal embodiment with slit
tune convection chamber spread and sealed to drainwater heat exchange which
leaves the lower portion exposed to the reservoir fluid for heat transfer;
Figure 12a shows the same embodiment with end caps, reservoir body and
2s coiled cold water heat exchanger therein, but with drainwater heat
exchanger
and convection chamber removed for clarity;
Figure 13 shows a perspective of the embodiment of Figure 12 with
convection chamber horizontal on a sloped drainwater heat exchanger;
Figure 14 shows a horizontal embodiment where the drainwater heat
so exchanger comprises several smaller drainwater heat exchanger tubes for use
where no large solids are present in the drainwater;
Figure 15 shows a partial phantom view of a vertical embodiment with
internal coldwater heat exchanger;
Figure 16 shows a partial phantom view of a vertical embodiment where
35 the coldwater heat exchanger is coiled around the exterior of the reservoir
wall and deflectors against the reservoir wall direct cooled reservoir water
to
the convection chambers;
Figure 17 shows a partial phantom view of an embodiment where the
reservoir wall is grove-threaded to improve heat transfer with the exterior
4o coldwater heat exchanger;
Figure 18 shows a conical element that deflects cooler, convecting
reservoir interior wall water, as it descends, into convection chamber
elements;the embodiment of Figure 16;
Figure 20 shows a cross section view of a preferred horizontal embodiment
s
CA 02328822 2000-12-28
with the square tube coldwater heat exchanger coiled around the exterior of
the metal reservoir wall, and showing a drainwater heat exchanger having
partitioning fin-separator within a metal convection chamber trough and with
exterior insulating sleeve, having upper convection openings, enclosing the
s entire assembly, convection chamber water and reservoir water are not shown
for clarity;
Figure 20a shows the same embodiment (less insulation) with rectangular
drainwater heat exchanger and associated fin-divider to segment the
convection chamber;
o Figure 21 shows a partial phantom perspective of a horizontal embodiment
where the convection chamber is an open trough insulated on its exterior wall;
Figure 22 shows a sloped drainwater heat exchanger and convection
chamber only, and, a horizontal reference to show how the walls of the
convection chamber need to taller to fully contain all water when cooled by
15 cold drainwater;
Figure 22b shows the effect of using multiple fin-dividers that keep the
total volume of the convection chamber at the desired minimum in a sloped
installation;
Figure 23 shows a cross section end view of a preferred horizontal
2o embodiment with nested convection chambers, the outer one of which has
exterior insulation and and where the external coldwater heat exchanger is a
large diameter tube and where the entire apparatus is enclosed in an
insulating
j acket;
Figure 24 is a cross section of a preferred horizontal embodiment with
25 doubled cold water heat exchanger;
Figure 25 is a cross section of a water cooling embodiment for use with
horizontal drainpipes.
so DESCRIPTION OF DRAWINGS
There are two principal embodiments of the present drainwater heat
recovery invention, a generally horizontal embodiment 45 (Figs 1 0 6, 12 to
14, 20-25) and generally vertical embodiment 50 (all other Figs). Each
35 principle embodiment has reservoir 1 filled with a water 3 (or other
suitable
fluid) to serve as both a heat transfer medium and a heat storage medium.
Drainwater heat exchanger 4 is located within reservoir 1 and has end portions
extending therefrom for connection in-line to a drainpipe from which an
appropriate section has been removed. Drainwater heat exchanger 4 may be
4o made from seamless copper tube as is typically available from plumbing
supply shops. It may be dimpled or grooved to enhance internal turbulent
flow. Arranged on this drainwater heat exchanger 4 is a convection
chambers) 5 made of an insulative material such as plastic to greatly minimize
conductive heat transfer therethrough. A cold water heat exchanger 2 transfers
CA 02328822 2000-12-28
recovered heat to cold water. The entire device is preferably enclosed in an
insulating jacket 55 to maintain heat as long as possible.
In vertical embodiment 50 there are typically multiple convection chambers
each an open-topped tapered cup with a hole in the bottom, arranged in a
slightly nested relationship such that the bottom of one sits just within the
top
opening of the next lower. For example for a 3 inch drainwater heat
exchanger 4, they may be made from common polyethylene plastic tubs such
as are commonly used for food stuffs such as yogurt. A hole 25 (Fig 9) is
punched through the bottom to be a tight fit onto the drainwater heat
o exchanger 4. They may be trimmed to a height such that the larger end will
fit
within the reservoir 1. A preferred material is a foamed polyethylene
convection chamber cup to provide the best insulation. Fins 30 and 30b may be
added to the drainwater heat exchanger 4 as a strip or band of copper folded
alternately to create a 'vee' corrugated band (Fig 9b) that fits tightly to
the
drainwater heat exchanger 4 for heat transfer. Fin bands and convection
chambers may then be alternately slid onto the drainwater heat exchanger 4
leaving plain ends for extension out of reservoir at each end.
For the horizontal embodiment 45 the convection chamber 5 is trough-
shaped and may be made from a copper strip rolled to an open cylinder. Its
2o side walls must be at lease marginally higher than the highest exposed
point of
the drainwater heat exchanger 4 (as represented by horizontal dotted line 6c
in
Fig 22-23) so as to prevent conductive heat transfer with reservoir water 3.
Troughs may be nested for added heat transfer as shown in Figure 23 where
two are shown. They may be sweat soldered to the bottom of drainwater heat
2s exchanger 4 to add maximum fin effect for heat transfer. Alternatively the
two may be forced into thermal contact using spacers 26b as shown in Figs 5,
6 and 12. One design is shown in Fig 23 where insulative convection chamber
5 has a metal heat conducting core Sb. The convection chamber 5 may be
bound to conductive fin Sb by wrapping with a string-like material, or, it may
so be adhesively attached or clipped in place. The volume of convection
chamber
water 24 should be as small as possible to minimize heat loss to cold
drainwater yet allow unimpeded convection. The ends of convection chamber
5 may be butted against reservoir ends 74 (Figure 21 ) with a gasket washer
therebetween (not shown) to prevent leaking.
35 For the reservoir 1 it may be a simple tube of circular cross section or a
more optimized shape depending on application such as a preferred shape
shown in Fig 20a. Where installation clearances are tight in the building,
oval
and flattened shapes may be more appropriate (see Figures 3 to 6): Doubled,
side-by-side units may also suit certain conditions as shown in Figure 3. The
4o reservoir may be made of metal or plastic tube, or plastic film, depending
on
price and payback requirements. If the cold water heat exchanger is contained
within the reservoir, the reservoir will best be of plastic with sufficient
wall
thickness (say 1 /8 to 1 /4 inch thick) to withstand the weight and static
pressure
of the water contained therein. If the cold water heat exchanger is to be
11
CA 02328822 2000-12-28
external then it can support a much thinner reservoir including a plastic film
pieces made from, say, 0.005 - 0.010 inch thick PVC or polyethylene which
are heat or high frequency welded into a suitable tubular reservoir shape. The
assembled film reservoir is clamped or otherwise sealed to the drainwater heat
s exchanger 4, at each end for the horizontal embodiment 45 and at least to
the
bottom for the vertical embodiment 50.
A reservoir for a 3 inch drainwater heat exchanger may be metal such as a
4-5 inch copper tube. The sum of the masses of the materials of the reservoir
and coldwater heat exchanger, and the waters contained therein, represents the
o heat storage capacity of the reservoir. The higher temperature they become
the greater the amount of energy that has been recovered from the drainwater
and the greater the energy savings for hot water.
The coldwater heat exchanger 2, 2d may be a coil of tubing of large
diameter to hold a maximum amount of water. It may be installed within
15 reservoir 1 as shown in Figures l, 3-8, 12, 12a or exterior of reservoir 1
as
shown in Figures 16, 17-25. Installed on the exterior adds a large measure of
safety from contamination by the additional reservoir wall of separation. Cold
water heat exchanger 2a, 2d (Figure 24, 25) may also be a double coil where
the outer cold water heat exchanger 2a may be made of plastic tube while
2o inner cold water heat exchanger 2d may be made of copper tube where their
respective ends are show as 2b and 2c in Figure 24-25. This dual arrangement
will allow fast heat transfer through the more expensive copper and a slower
heat transfer into the lower cost plastic, this where long time periods for
such
slow heat transfer are the norm as is the case in many homes. Coldwater heat
2s exchanger may also be of straight lengths of tubing as shown in Figures 3-6
with u-connectors at their ends to effect a single path or manifolded for
parallel flow. More than one coldwater heat exchanger 2 may be manifolded
together in parallel for higher water flow rates.
The following paragraphs describe some aspects of the present invention in
so greater detail.
Another design of convection chamber 5 shown in Figures 1-7, 12-14 for
horizontal embodiment 45 may have outlet convection openings) 7a in a split
tube exposing bottommost portion of drainwater heat exchanger 4 to reservoir
fluid 3. The outlet convection openings 7a in convection chamber 5 are located
35 only at the top of convection chamber 5. Convection chamber 5 also seals at
edge 41 to exchanger 4.
Fig 12a shows cold water heat exchanger 2 as a tubular coil that fits next to
the interior wall of reservoir. This arrangement maintains an even
temperature throughout the reservoir for horizontal embodiment 45 since the
4o coil material will conduct heat readily from warmer fluid 3 on top to any
colder fluid 3 on bottom until temperature equilibrium is reached. Coil ends
31 and 32 extend out of reservoir for connection to water supply. Fitting 75
serves to fill and drain the reservoir. End caps 72 and 74 seal to reservoir 1
and extension 73 serves to seal to end of exchanger 4.
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CA 02328822 2000-12-28
Refernng to Figs 3-6 of horizontal embodiment 45, Fig 3 shows how
exchangers and volume of fluid 3 may be doubled-up to add volume for heat
storage fluid 3 while maintaining a low profile for installation. Fig. 4 shows
an off centered embodiment to add volume for heat storage fluid 3. Fig 5
shows the use of an ovalized drainwater heat exchanger 4 and fin 51 which
offer greater surface area for heat transfer from drainwater flowing
therethrough and greater surface area for heat transfer into fluid 24,
respectively. Fig 6 shows an embodiment with large volume cold water heat
exchangers 2. Although Figs. 3-6 shown the horizontal embodiment, it is
o understood that this side-by-side arrangement can be used for the vertical
embodiments also. In some applications where long periods lapse between hot
water use, these large volume cold water exchangers 2 may be made of plastic
to reduce overall system cost. The low thermal conductivity of the plastic is
overcome by the longer time available for heat transfer and the larger volume
1 5 of cold water thereby heated.
Reservoir 1 may be roll-threaded as shown in Fig 17 such that the external
coil fits into the thread to increase surface-to-surface contact. The entire
unit
may be dipped in zinc, solder, or tin, to further increase the rate of heat
transfer. In the embodiments where exchanger 2 is outside reservoir 1 an
2o advantage is gained from eliminating the liquid contact with exchanger 2.
This
embodiment more readily meets plumbing code and health code safety
requirements that generally demand having potable water separated, from
reservoir water which will become stagnant water, by at least two barrier
walls. In this embodiment, the two heat exchanger tubing walls plus the
2s reservoir wall, total three such safety barners.
In Figs. 1 and 2 the convection chamber 5 is shown as having separate inlet
openings 6a and outlet openings 7a to allow convective flow 6 and 7
respectively. Inlet convective openings 6a and outlet convective opening 7a
may be of any suitable shape, but their lowermost extremity must be at least
so marginally above the upper most surface of heat exchanger 4 represented by
line 6c in Fig 1, 14, 22, 22b, 23, 24, so that heavy, cold convection chamber
fluid 24 will not flow out of any of these openings and cool reservoir fluid
3.
Also in Figs. 1 and 2 is shown a more sophisticated convection inlet opening 9
where a flexible flap valve 10 is attached with hinge 14 such that heavier
cold
35 convection chamber fluid 3 will force flap valve 10 against inlet opening
9,
preventing leakage. However if reservoir fluid 3 is colder and heavier, then
fluid 3 will force flap valve 10 inwardly from lower opening 9, and thereby
flow 6 into convection chamber 5. In Fig. 1 closed flap valve 10 is shown in
open position 11, as a dotted line. In Fig 1 is shown dimple 26a used to
create
4o a flow space between convection chamber 5 and drainwater heat exchanger 4.
Alternatively a rod 26 may be used for that same spacing purpose.
In all embodiments of horizontal embodiment 45 the tube walls of heat
exchangers 2 and 4 may be processed by dimpling or grooving the exterior to
create interior 'bumps' that induce turbulent flow which reduces fouling and
13
CA 02328822 2000-12-28
increases heat transfer.
In Fig. 10 of vertical embodiment 50, upper convection chambers 5 may be
shorter to benefit overall heat transfer and may be flared Sa at their tops so
as
to collect cold fluid 3 descending from cold water heat exchanger 2 (not
shown}. Funnel deflectors 60 shown in Figs 16 and 18 likewise serve to direct
the cold fluid 3, descending by convection, towards the center such that fluid
24 in convection chambers 5 is as cold as possible to improve heat transfer.
Although not shown, heat exchanger 4 may be positioned off center in
reservoir 1 so as to allow vertical installation closer to a wall where
existing
o drainpipe plumbing is close to the wall. Fig 19 shows the components of
vertical embodiment 50 with fresh water heat exchanger 2a coiled around
outside of reservoir 1.
In Figs. 7, 8 and 9, and 9b fins 30 are shown with broad thermal contact
onto outer wall of heat exchanger 4. Fining may be a deeply corrugated
15 clamp-on ring 30b in each convection chamber (Fig 9b), fitting tightly on
exchanger 4. Internal cold feed water heat exchanger 2 is shown as an
encircling coil but many other arrangements are possible, such as a vertical
picket fence-like arrangement with u-loops at each end to interconnect the
individual tubes. In vertical embodiments 50, reservoir 1 need only be sealed
2o at the bottom while the top may have a removable cap. Fig. 9 also shows
hole
25 of convection chamber 5 that seals against heat exchanger 4. Fig 8 shows
the inclusion of a thermal conductive liner 1 b that serves to even out fluid
3
temperature in reservoir 1 wherein fluid 3 would normally stratify in
temperature layers. This is particularly useful at the upper end of the
2s reservoir where, above the top convection chamber 5, there is only a small
volume of fluid 3 to store heat from upward convecting fluid 7 (Fig 16).
Thermal conductive liner lb will conduct top-layer heat downward enabling
more overall heat storage.
In Fig 10 a dual vertical embodiment 50 is depicted with the entering 'Y'
so 31 made in plastic and outside of the reservoir l, while the lower 'Y' 32
is
preferably metallic and submerged, adding heat transfer surface area. The
cold water heat exchanger is not shown but may be internal or external. This
dual embodiment can be a triple, quadruple, or any number of exchangers 4.
This embodiment is particularly suitable when vertical length is not
sufficient
35 to accomplish requires rate of heat transfer. Such multiple units provide
large
heat transfer surface in a short overall height. Convection chambers 5 of
different heights are shown to compensate for low volume of reservoir water
3 above uppermost convection chambers.
Fig. 11 shows a vertical embodiment 50 of two identical units installed in
4o tandem. Cold feed water heat exchangers 2 (shown only in upper unit) may be
plumbed in series or parallel. This embodiment enables a single module to be
manufactured and then multiples of them connected into the building's
plumbing system so as to increase overall performance.
Heat exchanger 4 in all embodiments preferably has multiple external
14
CA 02328822 2000-12-28
dimples 40 (or rolled grooves, not shown), save where a seal to convection
chamber 5 is required. This will induce turbulence in the drainwater 8 (Fig. 1
to improve heat transfer and reduce fouling. In Fig. 12 the cold feed water
heat exchanger 2 is shown to have dimples 40 to improve heat transfer. Such
turbulence may also be achieved with grooves rolled into the exterior.
In Fig. 14 there is shown a horizontal embodiment comprised of several
smaller pipes all enclosed in convection chamber 5, and manifolded at the
entrance and exit (not shown) to single pipes. These may be dimpled to
improve heat transfer (not shown). The convection chamber fluid 24
o submerges all the tubes. Convection opening 6a, 7a is shown at the top of
convection chamber 5 fully above the upper surface 6c of the drainwater heat
exchanger. The convection chamber 5 forms a seal 41 which, in Fig. 14 is
shown sealing against one drainwater heat exchanger pipe 4a. This
embodiment is highly suited to washing machines, including commercial
s dishwashers, which use relatively small amounts of very hot water with no
large solids. In Fig. 14 the reservoir and the cold feed water heat exchanger
are not shown.
In another embodiment, where laws permit, reservoir 1 of both vertical
and horizontal embodiments may be pressurized with the fresh cold feed water
2o directly which, therefore, temporarily becomes fluid 3. Such an embodiment
would avoid the expense of a cold water heat exchanger 2. Such an
arrangement may also be used as a cold water pre-heater for non-potable
water such as for toilet flushing. Such a warm water supply to a toilet would
greatly reduce condensation and dripping, and the resultant water damage to
2 s the floor beneath toilets. Such wet areas also contribute significantly to
mold
and fungus growth in a building with attendant health hazards.
Drainwater heat exchanger 4 may be double walled (telescopic tubing) for
potable water safety in such an embodiment.
Since heat transfer is well known to be a direct function of surface area,
so heat exchanger 4 may be made larger in diameter within the reservoir to
increase internal surface. Inlet and outlet plumbing reducer fittings would
funnel drainwater appropriately.
Fig. 15 is a partial phantom view that shows the relative placement of
components in vertical embodiment 50.
35 Figure 25 shows an water cooling horizontal embodiment 60 where the
convection chamber 5 is inverted so that the convection opening is at the
bottom at a position at least marginally above drainwater heat exchanger's
lowermost surface represented by line 6d in Fig 25. This arrangement will
trap drainwater heat as it floats upwards from the drainwater heat exchanger 4
4o preventing the heating of the reservoir water 3 and the cold water heat
exchanger 2j and 2r. Used in this way the reservoir will receive heat from the
cold water coils 2j and 2r (whose ends are shown respectively as 2m and 2p)
cooling same, and give that heat to colder drainwater for the purpose of
supplying cold drinking water in hot climates. An inverted vertical
CA 02328822 2000-12-28
embodiment (not shown) will accomplish this same cooling function.
Both heat recovery (first) and heat rejection (second) can be used together
in tandem to accomplish both objectives.
yo
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