U.S. patent application number 09/738112 was filed with the patent office on 2001-06-21 for drainwater heat recovery system.
Invention is credited to MacKelvie, Winston.
Application Number | 20010004009 09/738112 |
Document ID | / |
Family ID | 26930853 |
Filed Date | 2001-06-21 |
United States Patent
Application |
20010004009 |
Kind Code |
A1 |
MacKelvie, Winston |
June 21, 2001 |
Drainwater heat recovery system
Abstract
A fluid-to-fluid heat exchanger for use where two fluid streams
may be of indeterminate composition, temperature, and flow rate,
and, where the two fluid streams may flow at different rates and at
different times. Such conditions are found, for example, in the
flow patterns of a building's hotwater, cold feed water for a water
heater, and drainwater. As defined for heat recovery from
drainwater, the present invention comprises a first, central,
straight-through heat exchanger tube for cooling flowing
drainwater, a second heat exchanger to heat cold water encircling
and spaced from the first, and a non-pressurized reservoir between
first and second heat exchangers permanently filled with water in
thermal contact with first and second heat exchangers. Submerged in
the reservoir water there is at least one insulated convection
chamber, of small volume, enclosing first heat exchanger with a
convection opening uppermost. Opening allows upward convection and
therefore heat transfer when drainwater heats convection chamber
water making it lighter. Convection and heat transfer ceases when
drainwater cools convection chamber water making it heavier,
blanketing drainwater heat exchanger in a small volume of cold
water. This one-way heat transfer prevents heat loss from remaining
reservoir water to cold drainwater. With convection chambers
inverted to have convection opening bottommost, the device serves
to make coldwater, for drinking, as cold as possible by
transferring unwanted heat to colder drainwater. Used in series,
heat recovery and fresh water cooling can both be accomplished.
Units for horizontal and vertical installation are disclosed.
Inventors: |
MacKelvie, Winston;
(Knowlton, CA) |
Correspondence
Address: |
Winston MacKelvie
Box 1156
Knowlton Quebec
CA
|
Family ID: |
26930853 |
Appl. No.: |
09/738112 |
Filed: |
December 15, 2000 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09738112 |
Dec 15, 2000 |
|
|
|
09237611 |
Jan 25, 1999 |
|
|
|
Current U.S.
Class: |
165/47 ;
165/104.14; 165/104.19; 165/154; 165/909 |
Current CPC
Class: |
Y02E 60/142 20130101;
Y02E 60/14 20130101; F28D 20/0034 20130101; F28D 7/0066 20130101;
Y02B 30/18 20130101; F28D 21/0012 20130101; Y02B 30/566 20130101;
F24D 17/0005 20130101; Y02B 30/56 20130101 |
Class at
Publication: |
165/47 ; 165/154;
165/909; 165/104.14; 165/104.19 |
International
Class: |
F28D 015/00 |
Claims
I claim:
1. In a plumbing system for a building, the plumbing system
including a cold water supply and a water disposal conduit, the
improvement comprising an apparatus to transfer heat from waste
water in said water disposal conduit to said cold water, said
apparatus comprising a reservoir; a heat transfer fluid
substantially filling said reservoir; a first heat exchanger for
drainwater in thermal contact with said fluid; a second heat
exchanger having cold water from said cold water supply in thermal
contact with said fluid; convection chamber means partially
surrounding said first heat exchanger, said convection chamber
means having an opening therein allowing convection movement of
said heat transfer fluid into and out of said convection chamber,
said opening being located only at an upper portion of said
convection chamber means, the arrangement being such to heat said
cold feed water by permitting convection of said fluid into and out
of said convection chamber when said drainwater is hotter than said
fluid, and, minimizing flow of said heat transfer fluid out of said
convection chamber when said drainwater is colder than said heat
transfer fluid.
2. The improvement of claim 1 wherein said plumbing system includes
means for heating said cold water, said apparatus being connected
such that cold water passes through said first heat exchange means
prior to entering said means for heating said cold water.
3. The improvement of claim 1 wherein said second heat exchange
means is connected to a water disposal conduit from a heat
generating appliance.
4. The improvement of claim 1 wherein said first heat exchange
means is connected to a toilet.
5. The improvement of claim 1 wherein said first heat exchange
means is connected to a washing machine.
6. The improvement of claim 1 wherein said building is a
residential house.
7. The improvement of claim 1 wherein said heat transfer fluid is
water.
8. The improvement of claim 1 further including means to disturb
the boundary layer of liquid about at least one of said first and
second heat exchange means.
9. The improvement of claim 1 wherein at least one of said first
and second heat exchange means comprise at least one tube having a
plurality of inwardly directed dimples to thereby create turbulence
in liquid flowing therethrough, said dimples being spaced
sufficiently close together to provide continuous turbulence in
said liquid passing therethrough.
10. The improvement of claim 1 further including a plurality of
said apparatuses connected in a plumbing system, said apparatuses
being connected in series or in parallel or in series-parallel.
11. A heat transfer system suitable for recovering heat from waste
water comprising: a reservoir having a heat transfer fluid therein;
a first heat exchanger for receiving said waste water within said
reservoir; said first heat exchanger having a first heat exchanger
inlet and a first heat exchanger outlet; a second heat exchanger
within said reservoir in thermal contact with said heat transfer
fluid, said second heat exchanger having a first heat exchanger
inlet and a second heat exchanger outlet; convection chamber means
at least partially surrounding said first heat exchanger, said
convection chamber means permitting convective movement of said
heat transfer fluid from adjacent said first heat exchanger when
said waste water flowing therethrough is warmer than said heat
transfer fluid, said convection chamber means being arranged such
that convective movement of said heat transfer fluid from adjacent
said first heat exchanger is impeded when said waste water flowing
therethrough is colder than said heat transfer fluid.
12. The heat transfer system of claim 11 wherein said first heat
exchanger includes a first heat exchanger conduit extending in a
generally horizontal direction, said second heat exchanger
including a second heat exchanger conduit also extending in a
generally horizontal direction, said first heat exchanger conduit
being located below said second heat exchanger conduit in said
reservoir.
13. The heat transfer system of claim 12 wherein said convection
chamber means comprises a horizontally extending convection chamber
encircling at least an upper portion of said horizontally extending
first heat exchanger conduit.
14. The heat transfer system of claim 13 further including spacers
spacing said convection chamber from said first heat exchanger
conduit.
15. The heat transfer system of claim 13 wherein said convection
chamber has a plurality of longitudinally extending slots formed
therein.
16. The heat transfer system of claim 11 wherein said first heat
exchanger comprises a vertically extending conduit within said
reservoir, said second heat exchanger comprising a coiled conduit
coiled about said first heat exchanger conduit and spaced
therefrom.
17. The heat transfer system of claim 16 wherein said convection
chamber means comprises a plurality of upwardly and outwardly
extending flanges secured to said first heat exchanger conduit.
18. In a plumbing system for a building, the plumbing system
including a cold water supply and a water disposal conduit, the
improvement comprising an apparatus to transfer heat from said cold
water to said waste water in said water disposal conduit, said
apparatus comprising a reservoir; a heat transfer fluid
substantially filling said reservoir; a first heat exchanger for
drainwater in thermal contact with said fluid; a second heat
exchanger having cold water from said cold water supply in thermal
contact with said fluid; convection chamber means partially
surrounding said first heat exchanger, said convection chamber
means having an opening therein allowing convection movement of
said heat transfer fluid into and out of said convection chamber,
said opening being located only at a lower portion of said
convection chamber means, the arrangement being such to cool said
cold feed water by permitting convection of said fluid into and out
of said convection chamber when said drainwater is colder than said
fluid, and, minimizing flow of said heat transfer fluid out of said
convection chamber when said drainwater is hotter than said heat
transfer fluid.
19. An apparatus for exchanging heat between drainwater and
freshwater comprising, a first heat exchanger comprising, tube
means having central portion for heat transfer and having end
portions for connection to a supply of drainwater, a second heat
exchanger comprising tube means having central portion for heat
transfer and having end portions for connection to a supply of
freshwater, reservoir means separating said first and second heat
exchangers, said reservoir means substantially filled with a fluid
in thermal contact with said first and second heat exchangers, at
least one convection chamber submerged in said fluid comprising,
wall means, said wall means being thermally insulative, said wall
means enclosing at least a portion said central portion said first
heat exchanger, said wall means including at least one convection
opening, the whole arranged to control the direction of heat
transfer between drainwater and freshwater by orienting said
convection opening upwardly or downwardly.
Description
[0001] The present application is a continuation-in-part of
application Ser. No. 09/237,611, filed Jan. 25, 1999.
BACKGROUND
[0002] 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 cause global
warming.
[0003] 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.
[0004] 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.
[0005] Another objective is to cool drinking water using cold
drainwater.
DESCRIPTION
[0006] 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 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.
[0007] Drainwater heat recovery involves removing heat from hotter
drainwater (cooling it) and transferring the heat to the fresh cold
water (warming it). This saves energy and money since no new energy
is required.
[0008] U.S. Pat. No. 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 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, Mich. 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. U.S. Pat. No. 4,619,311, to Vasile is a simple, low-cost,
easy-to-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.
[0009] 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 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.
[0010] The reason tube-on-tube heat exchangers do not work under
batch hot 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.
[0011] Further, U.S. Pat. No. 4,619,311, to Vasile is not
recommended for horizontal drainpipe applications, as found in a
great many buildings with no basement, 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 exchanger which may add useful heat
transfer.
[0012] U.S. Pat. No. 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
expensive. Further, its installation is essentially limited to
vertical drainpipes unless mechanical pumping is added.
[0013] 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.
[0014] A review of the physical principles involved in the present
invention follows.
[0015] 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.
[0016] 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 water to
move vertically by convection 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
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.
[0017] 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 boundary
and central flow and is where conduction also takes place and where
convective flow begins.
[0018] 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 downwards as a relatively thin
falling film.
[0019] 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.
[0020] 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.
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
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 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 to the cold
drainwater. Thus the objective of no-loss heat storage is achieved
at low cost in both horizontal and vertical units.
[0021] 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 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 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
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 drainwater heat
exchanger tube of thin plastic film could also be used for added
security.
[0022] In the present invention the convection chamber is/are
located within the reservoir and may be one or more in number. The
convective opening 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 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. A
convection chamber should hold as 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 water volume, and add heat transfer
performance.
[0023] The convection chamber takes on two distinct shapes
depending on whether the heat exchanger is to be used horizontally
or vertically.
[0024] For the horizontal embodiment, the convection chamber may be
a long, channel-shaped trough which may advantageously be made of
metal such as copper and attached directly (i.e., soldered) to the
bottom of a copper drainwater heat exchanger to enhance heat
transfer. Several such metal channels may be nested to further
enhance heat transfer. The outside of the outermost convection
chamber channel is covered with an insulating skin. It is closed
and sealed at the ends to ensure that when cooled (heavier) water
is contained therein it does not leak into the warmer reservoir
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 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 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 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 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.
[0025] 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 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.
[0026] For the vertical embodiment the convection chambers are
generally several in number and 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 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 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 conductive heat transfer through it's
wall.
[0027] 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 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 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 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 of metal) within the reservoir will
allow temperature to even out within the reservoir.
[0028] 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 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 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 the copper coil would heat first and fastest and conduct heat to
the plastic.
[0029] 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 chamber(s) by
conductive heat transfer. This makes that water more buoyant which
causes it to naturally convect upwards out of the 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 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 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.
[0030] 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.
[0031] The present invention in another embodiment may also be used
for water cooling (i.e., cooling drinking water) by inverting the
device such that convection chamber(s) have downwards facing
opening. In such an orientation, the hot drainwater would just fill
the insulated convection chamber(s) 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 of course, would
cool water flowing through the fresh water heat exchanger.
[0032] With one of each embodiment of the present invention
installed in-series, drainwater heat recovery and drainwater fresh
water cooling may both be accomplished.
[0033] In the present invention three walls of separation exist
between drainwater and fresh water which ensures absolute safety
from contamination of fresh water, (drainwater heat exchanger wall,
reservoir wall, fresh water heat exchanger wall). In addition the
no-pressurized reservoir adds even more safety.
[0034] 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 exchanger may be used as disclosed
in this applicant's U.S. Pat. No. 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: rolled ridges, twists, fins, bubbled air,
and vibration, and ultrasonics.
[0035] 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 laundry washing
machines and used with tankless or instantaneous water heaters.
[0036] 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 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.
[0037] 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 cause
structural damage, and to support fungus/mould growth which results
in dangerous airborne spores in the building.
[0038] 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
[0039] FIG. 1 shows a cross section of one horizontal embodiment
where the coldwater heat exchanger is a series of straight tubes,
the convection chamber is tubular, and lower water inlet ports are
flap controlled;
[0040] FIG. 2 is a perspective detail view of one end of the same
embodiment;
[0041] FIG. 3, 4, 5, 6 are end views of the horizontal embodiment
showing different shapes and positions of components, so to best
use minimal vertical space in the installation;
[0042] FIG. 7 is a partial section view of a vertical
embodiment;
[0043] FIG. 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;
[0044] FIG. 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;
[0045] FIG. 9b shows a fin ring on drainwater heat exchanger within
a convection chamber;
[0046] FIG. 10 shows a double drainwater heat exchanger vertical
embodiment;
[0047] FIG. 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 full reservoir with
coldwater heat exchanger removed for clarity;
[0048] FIG. 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;
[0049] FIG. 12a shows the same embodiment with end caps, reservoir
body and coiled cold water heat exchanger therein, but with
drainwater heat exchanger and convection chamber removed for
clarity;
[0050] FIG. 13 shows a perspective of the embodiment of FIG. 12
with convection chamber horizontal on a sloped drainwater heat
exchanger;
[0051] FIG. 14 shows a horizontal embodiment where the drainwater
heat exchanger comprises several smaller drainwater heat exchanger
tubes for use where no large solids are present in the
drainwater;
[0052] FIG. 15 shows a partial phantom view of a vertical
embodiment with internal coldwater heat exchanger;
[0053] FIG. 16 shows a partial phantom view of a vertical
embodiment where 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;
[0054] FIG. 17 shows a partial phantom view of an embodiment where
the reservoir wall is grove-threaded to improve heat transfer with
the exterior coldwater heat exchanger;
[0055] FIG. 18 shows a conical element that deflects cooler,
convecting reservoir interior wall water, as it descends, into
convection chamber elements; the embodiment of FIG. 16;
[0056] FIG. 20 shows a cross section view of a preferred horizontal
embodiment 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 entire
assembly, convection chamber water and reservoir water are not
shown for clarity;
[0057] FIG. 20a shows the same embodiment (less insulation) with
rectangular drainwater heat exchanger and associated fin-divider to
segment the convection chamber;
[0058] FIG. 21 shows a partial phantom perspective of a horizontal
embodiment where the convection chamber is an open trough insulated
on its exterior wall;
[0059] FIG. 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 cold drainwater;
[0060] FIG. 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;
[0061] FIG. 23 shows a cross section end view of a preferred
horizontal 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 jacket;
[0062] FIG. 24 is a cross section of a preferred horizontal
embodiment with doubled cold water heat exchanger;
[0063] FIG. 25 is a cross section of a water cooling embodiment for
use with horizontal drainpipes.
DESCRIPTION OF DRAWINGS
[0064] There are two principal embodiments of the present
drainwater heat recovery invention, a generally horizontal
embodiment 45 (FIGS. 1 to 6, 12 to 14, 20-25) and generally
vertical embodiment 50 (all other Figs). Each 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 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 chamber(s) 5 made
of an insulative material such as plastic to greatly minimize
conductive heat transfer therethrough. A cold water heat exchanger
2 transfers recovered heat to cold water. The entire device is
preferably enclosed in an insulating jacket 55 to maintain heat as
long as possible.
[0065] In vertical embodiment 50 there are typically multiple
convection chambers 5 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 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.
[0066] 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 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 FIG. 23 where two
are shown. They may be sweat soldered to the bottom of drainwater
heat 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 5b. The convection chamber 5 may be bound to
conductive fin 5b by wrapping with a string-like material, or, it
may 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 (FIG. 21) with a gasket washer therebetween (not
shown) to prevent leaking.
[0067] 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 FIGS. 3 to 6). Doubled, side-by-side units
may also suit certain conditions as shown in FIG. 3. The 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 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 exchanger 4, at each end
for the horizontal embodiment 45 and at least to the bottom for the
vertical embodiment 50.
[0068] 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 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.
[0069] 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 reservoir 1 as shown in FIGS. 1, 3-8, 12, 12a or
exterior of reservoir 1 as shown in FIGS. 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 (FIG. 24, 25) may also be a double coil where the
outer cold water heat exchanger 2a may be made of plastic tube
while inner cold water heat exchanger 2d may be made of copper tube
where their respective ends are show as 2b and 2c in FIG. 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
exchanger may also be of straight lengths of tubing as shown in
FIGS. 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.
[0070] The following paragraphs describe some aspects of the
present invention in greater detail.
[0071] Another design of convection chamber 5 shown in FIGS. 1-7,
12-14 for horizontal embodiment 45 may have outlet convection
opening(s) 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 only at
the top of convection chamber 5. Convection chamber 5 also seals at
edge 41 to exchanger 4.
[0072] 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 since the
coil material will conduct heat readily from any warmer fluid 3 to
any colder fluid 3 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.
[0073] Referring 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 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 of
cold water thereby heated.
[0074] 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
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 reservoir wall, total
three such safety barriers.
[0075] 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 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
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 a flow
space between convection chamber 5 and drainwater heat exchanger 4.
Alternatively a rod 26 may be used for that same spacing
purpose.
[0076] 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 increases heat
transfer.
[0077] In FIG. 10 of vertical embodiment 50, upper convection
chambers 5 may be shorter to benefit overall heat transfer and may
be flared 5a 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.
[0078] 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 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.
[0079] 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 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
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 1b 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 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 1b will conduct top-layer heat downward
enabling more overall heat storage.
[0080] In FIG. 10 a dual vertical embodiment 50 is depicted with
the entering `Y` 31 made in plastic and outside of the reservoir 1,
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 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
chamber 5.
[0081] FIG. 11 shows a vertical embodiment 50 of two identical
units installed in 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.
[0082] Heat exchanger 4 in all embodiments preferably has external
dimples 40 completely covering the tube wall, 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.
[0083] 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 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 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.
[0084] In another embodiment, where laws permit, reservoir 1 of
both vertical and horizontal embodiments may be pressurized with
the fresh cold feed water 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 the
floor beneath toilets. Such wet areas also contribute significantly
to mold and fungus growth in a building with attendant health
hazards.
[0085] Drainwater heat exchanger 4 may be double walled (telescopic
tubing) for potable water safety in such an embodiment.
[0086] Since heat transfer is well known to be a direct function of
surface area, 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.
[0087] FIG. 15 is a partial phantom view that shows the relative
placement of components in vertical embodiment 50.
[0088] FIG. 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 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 embodiment (not shown) will accomplish this
same cooling function.
[0089] Both heat recovery (first) and heat rejection (second) can
be used together in tandem to accomplish both objectives.
* * * * *