GREYWATER HEAT RECOVERY DEVICE USING A COMBINED THERMOSYPHON/HEAT PIPE PRINCIPLE

DISPOSITIF DE RECUPERATION DE LA CHALEUR DES EAUX USEES METTANT EN APPLICATION LES PRINCIPES COMBINES DU THERMOSIPHON ET DU CALODUC

English Abstract

A heat recovery device recovers heat from a waste water pipe or the like. The device includes an evaporator chamber surrounding a length of the pipe. The chamber contains a refrigerant in both liquid and vapour states. A wick surrounding the pipe within the evaporator chamber extends into the liquid state refrigerant. A vapour outlet from the evaporator chamber above the liquid refrigerant leads to a condenser chamber around a container for liquid to be heated. The condenser chamber has an outlet connected to the evaporator chamber for delivering liquid refrigerant from the condenser chamber to the evaporator chamber. Heat in the pipe evaporates refrigerant from the wick. The evaporated refrigerant then travels into the condenser chamber where the cold surface of the water chamber extracts heat from the refrigerant and condenses it to be discharged back to the evaporator chamber. The water container in the condenser chamber is connected into the hot water system.

French Abstract

Un dispositif de récupération de chaleur récupère de la chaleur à partir d'un tuyau d'eaux usées ou analogues. Le dispositif comprend une chambre d'évaporateur entourant une longueur du tuyau. La chambre contient un liquide frigorigène à la fois dans des états liquide et gazeux. Une mèche entourant le tuyau à l'intérieur de la chambre d'évaporateur s'étend dans le fluide frigorigène à l'état liquide. Un orifice de sortie de vapeur à partir de la chambre d'évaporateur au-dessus du fluide frigorigène liquide conduit à une chambre de condenseur autour d'un contenant pour qu'un liquide soit chauffé. La chambre de condenseur a un orifice de sortie relié à la chambre d'évaporateur pour distribuer le fluide frigorigène liquide de la chambre de condenseur à la chambre d'évaporateur. La chaleur dans le tuyau fait évaporer le fluide frigorigène à partir de la mèche. Le fluide frigorigène évaporé se déplace ensuite dans la chambre de condenseur dans laquelle la surface froide de la chambre d'eau extrait de la chaleur à partir du fluide frigorigène et la condense pour que celle-ci soit de nouveau évacuée vers la chambre d'évaporateur. Le contenant d'eau dans la chambre de condenseur est relié dans le système d'eau chaude.

Claims

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CLAIMS
1. A heat recovery device for recovering heat from an elongate object
such as a pipe, said heat recovery device comprising:
an evaporator chamber extending along a length of the object;
a refrigerant in liquid and vapour states in the evaporator chamber;
a wick engaging the object within the evaporator chamber and
extending into the liquid state refrigerant;
a vapour outlet from the evaporator chamber above the liquid
refrigerant;
a condenser chamber receiving vapour from the vapour outlet and
delivering liquid refrigerant from the condenser chamber to the evaporator
chamber; and
a container for liquid to be heated in heat exchange relationship with
the condenser chamber.
2. A heat recovery device according to Claim 1 wherein the evaporator
chamber surrounds a portion of the object.
3. A heat recovery device according to Claim 1 or 2 wherein the
container for liquid to be heated is within the condenser chamber.
4. A heat recovery device according to Claim 1, 2 or 3 including a
vapour pipe leading from the evaporator chamber to the condenser chamber.
5. A heat recovery device according to Claim 1, 2, 3 or 4 including a
condensate pipe leading from the condenser chamber to the evaporator chamber.
6. A heat recovery device according to any preceding claim wherein
the object is a waste water pipe.

Description

CA 02217972 1998-10-02
GREYWATER HEAT RECOVERY DEVICE USING A
COMBINED THERMOSYPHON/HEAT PIPE PRINCIPLE
FIELD OF THE INVENTION
The present invention relates to the recovery of energy which would
otherwise be wasted. It has particular application to the recovery of heat
from
greywater when it is sent down the drain. "Greywater" is water which has been
used
and may contain contaminants such as soap, grease, etc..
BACKGROUND
Various types of greywater heat recovery systems have been developed
over the years. Most have been relatively simple devices consisting of a
combined
storage tank/preheater into which the house's greywater is plumbed. Some form
of
piping coil (copper or plastic) is then inserted in or around the tank through
which the
incoming water is plumbed. Fresh water to the house is directed to this coil
where it
picks up heat from the greywater and is then directed to the hot water heater.
A
complication to these designs is that greywater plumbing has to be modified so
that
wastewater from toilets and cold sinks is not directed into the storage tank.
A relatively recent development has been a system developed by
Carmine Vasile of Water Film Energy Inc. and being marketed by Vaughn
Manufacturing Corp. of Salisbury MA as the "GFX" system This system is
described
in U.S. Patent number 4,619,311. It consists of a copper coil which is wrapped
around a vertical section of the normal drain, waste, vent line (DWV) of a
house.
Greywater flowing down the DWV line preheats incoming fresh water in the
copper
coil. The main advantage of this system is that a very high heat transfer
coefficient is
achieved because water (or greywater) falling vertically through a pipe tends
to cling
to the walls of the pipe (this is described as "falling-film" technology).
Segregated
plumbing is not required. The main disadvantage of the system is that there is
very
little inherent thermal storage which means it only works effectively when the

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greywater and fresh water flows occur continuously and simultaneously, such as
occurs with a shower but which does not occur with a bath or dishwasher.
Unfortunately, in most houses the majority of the hot water flows do not occur
simultaneously with the resulting greywater flows. Another limitation of the
Vaughn
system is that whenever cold water goes down the DWV stack it will cool down
(rather
than heat up) the fresh water in the copper coil. Hence, the potential savings
achievable by the Vaughn system are somewhat limited.
The present invention is concerned with solutions to these problems.
SUMMARY
According to the present invention there is provided a heat recovery
device for recovering heat from an elongate object such as a pipe, said heat
recovery device comprising:
an evaporator chamber surrounding a length of the object;
a refrigerant in liquid and vapour states in the evaporator chamber;
a wick surrounding the object within the evaporator chamber and
extending into the liquid state refrigerant;
a vapour outlet from the evaporator chamber above the liquid
refrigerant;
a condenser chamber receiving vapour from the vapour outlet and
having an outlet connected to the evaporator chamber for delivering liquid
refrigerant from the condenser chamber to the evaporator chamber; and
a container for liquid to be heated within the condenser chamber.
Heat in the pipe, normally a waste water pipe in the application
discussed above, evaporates the refrigerant from the wick. The evaporated
refrigerant then travels into the condenser chamber where the cold surface of
a
water chamber extracts heat from the refrigerant and condenses it to be

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discharged back to the evaporator chamber. The water container in the
condenser chamber is, in the greywater application, connected into a hot water
line.
Because the heat is being transferred as the result of phase
changes, large amounts of heat can be transferred with little or no change in
temperature. The water supply in the condenser chamber provides significant
thermal storage to take advantage of non-coincident greywater/freshwater
flows.
The vapour flow between the evaporator and condenser sections of
the apparatus operates the thermosyphon principle so that the apparatus
operates as a thermal diode, transferring heat in one direction only.
Devices according to the invention are primarily intended for residential
applications but could also be used in commercial and industrial environments.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings, which illustrate an exemplary
embodiments of the present invention:
Figure 1 is a schematic view showing an embodiment of the present
invention; and
Figure 2 is a schematic view of another embodiment of the present
invention.
DETAILED DESCRIPTION
A heat recovery device 10 is shown in Figures 1 and 2. It includes
an evaporator section 11 having an evaporator chamber 12 which surrounds the
DWV stack 14. A condenser section 15 has a condenser chamber 16 extending
over the sides and bottom of a preheat tank 18. A connecting pipe 20 leads
from adjacent the top of the evaporator chamber to adjacent the top of the
condenser chamber. A pipe 22 leads from the bottom of condenser chamber to

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the evaporator chamber near its bottom. The bottom of the condenser chamber
is above the bottom of the evaporator chamber so that liquid will flow from
the
condenser to the evaporator. A water supply line 24 delivers fresh water to
the
preheat tank 18, while water is discharged from the preheat tank through a
discharge line 26.
Inside the evaporator chamber 12 is a wick 28 which is wrapped
around the DWV stack 14. A small amount of refrigerant 30 is located in the
bottom of the evaporator 12 such that it is free to climb up through the wick
28
by capillary action. A very low pressure (below atmospheric) is maintained in
the
evaporator 12 and condenser 16 to facilitate evaporation of the refrigerant.
The principle of operation is as follows. When greywater flows
down the DWV stack 14 heat is transferred from the greywater, through the
walls of the stack 14 to the refrigerant in the wick 28. Because of the very
low
pressure in the evaporator 12, this slight increase in temperature causes
evaporation of the liquid refrigerant in the wick. The refrigerant gas flows
through pipe 20 to the condenser 16 where the cold surface of the preheat tank
18 causes the refrigerant 30 to condense back into a liquid state which then
drains back to the condenser through return pipe 22. Heat is thus very
efficiently
transferred from the greywater to water in the preheat tank. The key to this
process is that heat is being transferred as the result of phase changes
(evaporatiow in the evaporator and condensation in the condenser), a process
in
which huge amounts of heat can be transferred with little or no change in
temperature. The device takes advantage of the high heat transfer coefficients
recognized in Vaughn's falling-film technology but overcomes the limitations
of
the Vaughn system by incorporating thermal storage using a combined "heat
pipe/thermosyphon" process.

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An alternate arrangement is shown in Figure 2 in which the
condensate is delivered to a cup 32 around the upper portion of the wick 28 so
that it can flow up the wick by capillary action and down the wick due to
gravity
action. The purpose of this arrangement is to improve refrigerant wetting of
the
entire wick.
The preheat tank is shown in Figures 1 and 2 as a tank-within-a-
tank. An alternate arrangement could also be used in which the outer tank was
replaced with a coil, thermally attached to the preheat tank, through which
the
refrigerant could flow. While Figure 1 shows the evaporator and condenser as
separate units, they could be combined into a single device to facilitate easy
installation.
The advantages of the device are that it not only has high heat
recovery and does not require separate greywater plumbing, but also provides
significant thermal storage to accommodate non-coincident greywater/fresh
water flows, providing an overall energy recovery greater than that of the
prior
art. In addition, the thermosyphon principle allows the device to operate as a
thermal diode, transferring heat in only one direction. Because of the thermal
diode effect, segregated plumbing is not needed. This combined
thermosyphon/heat pipe process may also be applied to other heat transfer
processes.
While two particular embodiments of the present invention have
been described in the foregoing, it is to be understood that other embodiments
are possible within the scope of the invention. The invention is to be
considered
limited solely by the scope of the appended claims.

Representative Drawing