Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SPECIF~CATIONS
Wastewater heat recovery for residential use are not commercially available even in this time of
energy conservation and environmental concern. Hot water for cleaning of bodies, laundry and
kitchenware, consumes approximately one half of the total residential energy consumption (from
s Canadian Electrical Association Project Report number: 913 U 160 Chapter 14, pp. 14). This
energy laden waste water is then fed into a sewer system where it's Yaluable heat is lost into the
earth.
Heat recovery has thus far proven intractable primarily because:
0 (A) the temperature of waste water from human activity in any building, can never be
predicted. It may be very cold or very hot at any given moment, and,
(B) it is necessary to store recovered heat for a time such as over night. The combination of
waste water of indeterminate temperature and the necessity of heat storage, is why a
commercially viable waste water heat recovery apparatus has not yet been invented, in
spite of efforts over long periods of time by many skilled in this field.
The present invention solves this problem with a unique, low cost hea~ exchanger where the
stored heat from previous recovery is not lost to cold waste water flowing at any time therea~ter.
The heat reclaimed from the waste water may be used effectively to preheat the fresh feedwater of a
normal hot-water tank. To prevent contarnination of such fresh water, both the waste water and the
colder fluid to be pre-heated, pass through their own separate heat exchanger elements both of
which are submerged in a non-pressurized heat transfer I storage tank filled with a fluid such as
plain water.
In the present invention, a reservoir is filled wirh a fluid such as water. Natural strati~ication
2s automatically arranges the water into demperature-dependant strata. The waste water heat exchange
element lays at the bottom of the reservoir in the coldest possible strata of the watsr, while the
second heat exchange element passing the coolder fluid to be heated, is submerged in the warmest,
top most strata.
The temperature of the fresh feedwater establishes the base or bottom temperature of the
apparatus since it will cool it's surrounding liquid which then sinks to the bottom. The temperature
of the passing waste water is usually always at least marginally higher than the temperature of the
fresh feedwater because it is somewhat heated by it's passage through the building's plumbing
system. Therefore, virtually all waste water arriving at the apparatus will give up heat energy into
the cold lower strata of liquid which tnen must rise. This reclaimed heat is thereby made available
3s to preheat t'ne always colder feedwater. The apparatus operates entirely under the physical principle
of convection- it does not require any moving parts, controls or valves that add to it's cost.
Moreover no maintenance is normally required. This impor~ant 'simplicity of design' and resultant
short 'pay back' period will ensure widespread acceptance.
Widespread acceptance will have a unexpected cascade effect: a net reduction in the amount of
money required for heating water leads to a significandy lower demand for energy to heat water
and frees up rnonies for other needs; this lower demand also leads to a lower demand for energy
for water heating; that leads to less fuel to be burnt and to conservation of fossil fuels; which leads
to a reduction in smokestack emissions; which leads to a reduction in the amounts of acid rain
falling; which leads to an overall benefit to the environment--our health, our lakes, our forests and
4s our buildings.
The operation of the invention is based on the cornmon physics of fluids wherein heated fluid
becomes less dense and therefore will rise and remain as a upper-most layer in the reservoir, while
cooled fluid becomes more dense and therefore sinks and 'puddles' at the bottomof the reservoir.
This is well known and defined as 'stratificationl. Since tne two heat exchanger coils are displaced
so vertically wherein one is in the upper-most region, and the second in the lower-most, any fluid
passing through either exchanger element will be bathed in the hea~ transfer fluid snost appropriate
~or said exchangers purpose, i.e. the fresh feedwater to which the recovered heat is to be
transferred is bathed in the accumulated warmest fluid while the fluid from which heat is to be
reclaimed, is ba~ed in the coolest fluid.
The four operational conditions of the present invention are:
1. Cold fresh water is passing through the upper element and into the hot water tank when hot
water is being demanded somewhere in the building, but no waste water is flowing, e.g.
filling a bathtub or washing machine. Here the cold ~eedwater will pick up the stored heat
and will thus appear at the entrance to the hot water tank as somewhat warmer than the
ground water temperature.
2. Waste water only, is draining through the apparatus. Here the water temperature at the
bottom of the reservoir is cooler than the waste water in most all occasions and heat will he
transferred to the storage fluid, which rises as this occurs, to the top. Thus any waste heat
will continually be given up until all the storage fluid reaches the waste water temperature.
3. Both warm waste water and cold fresh water are flowing through this apparatus, for
example, a shower is being taken or a sink is being used. Here, a toroidal flow is
established and transfer of heat from the warm draining waste water is transfe~red to the cold
water rais;ng it's temperature considerably, reducing water heating expense.
4. Only cold waste water is passing through the apparatus, as when rins;ng with cold water.
Here upwards convection stops and the net result is a thin layer of cold water up to the level
E f the lower element's upper surface-a small percentage of the reservoir's volume, so
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virtually none of the stored heat is lost under this, the worst of conditions, for thermal
storage heat exchangers and for wsate water heat recovery devices described in the prior art.
In drawings which illustrate embodiments of the invention;
s Figure 1 is a three dimensional view, partially in section, showing a preferred embodiment but
with the cover and the insulation removed for clarity;
Figure 2 is a three dimensional view of the simplest embodiment where the reservoir and
submerging fluid are omitted and the toroidal convection current are shown clearly;
Figure 3 is the same embodiment partially in section with the reservoir and submerging fluid
0 shown;
Figure 4 is the same embodiment partially in section with the duct added for convection
énhancement;
Figure S shows the manner in which the invention can be plumbed into a residential system.
Reservoir 1 is made of a plastic (for low thermal conduction) with a fitted cover ~not shown) to
eliminate evaporation, and wrapped in insulation (not shown) to reduce heat loss, and is mostly
filled with a Fluid 2, such as water, which must naturally and autornatically stratify into
temperature dependent strata, the coldest stratum at the bottom of the reservoir and the warmest
stratum floating at the top. The reservoir is filled to a Level 2a such that Convection Curr~nts 15,
20 20 can easily move about the colder fluid Upper Element 3 which is plumbed to the colder fluid,
such as the feed water for a hot water tank, via Fittings 9 and 10 the cold fluid entry and exit
indicated by Flow Arrows 21. The upper end of Duct 5 is encircled by the upper heat exchanger
element. At the lower end of the duct, and enclosed by it, is the Waste Water Element 4 through
which the waste water liquid, from which heat is to be recovered, passes through via plumbing
25 Fittings 7 and 8 and indicated by Flow Arrows 21. When the bottom most stratum of fluid is
heated by the waste water element, Rising Convection Currents 14 in Fig. l, form and due to their
reduced density, must rise. The duct improves the temperature spread between the top and bottom
of the fluid since the rising convection currents, are kept separate from Downwards Convection
Currents 12 in Fig. 1, so that they both arrive at their respective strata as quickly and with as little
30 ternperature change as possible. Lower Convection CulTents 13, in Fig. 1, is fluid passing under
the duct to meet up with the waste water element to repeat the cycle.
Should the lower stratum of the reservoir fluid be warmer than waste water element, then no
upwards convection takes place, and, no significant amount of previously recovered heat is lost to
the waste water. Should no fluid flow through the upper element but warm liquid pass through the
35 waste water element then warmed fluid moving in the direction of 11 and 14, accumulates as a
heated layer at the top of the reservoir. When the upper element is passing a cooler fluid it will
absorb the accumulated heat and exit at fitting 9 wanner than it entered at fitting 10.
In this way the invention produces net temperature gain ul the colder fluid virtually all the time.
If cooler fluid passes through the upper element while no waste water passes through the waste
40 water element, then a layer of dense cool fluid seffles in the bottom of the reservoir which is then
ready to absorb heat as soon as waste water is flowing. When the upper element is passing cool
liquid and the waste water element is passing warm liquid, then a toroidal convection takes place as
indicated by the path described by 14, 11, 15, 12 and 13, in Fig. 1, and 20 in Figs. 2, 3, and 4,
providing an efficient flow of fluid over and between both upper and lower heat exchanger
45 e~ments.
In Drawing S a typical setup is shown where Hot Water Outlet 30 to the building, is plumbed
as normal from Hot Water Tank 32 which is an electrically heated device connected to the mains
wiring by Wire 43. Of course it could also be a ga~s- or oil- fired water heater.
Feedwater Supply Pipe 31 is intercepted from being connected to the hot water tank and instead
sû connects to the reclaiming element in the Present Invention 33. The water bea~ng the reclaimed
heat is then fed to the hot water tank via Outlet Pipe 40. Stand 34 ensures that the present invention
is at an appropriate height off the Ground Level 39. Basement Ceiling 37 has, emerging from the
va~ous drains above, the Main Drain 38 through which all the waste water flows on the way to
Sewer Connection 42. A Non-Blocking Separator 35 allows solids to pass through while liquids
55 are conducted via Connection Pipe 41 into the reclaiming element in the present invention where
the heat is reclaimed and the the waste water then passes out, back into main drain via Connecting
Pipe 36. Thus feedwater entering the present invention from the feed water swpply pipe is
preheated by waste water from the main drain and then enters the hot water tank at an elevated
temperature.
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