EP2435773A2

EP2435773A2 - Heat exchanger for recuperation of residual heat from waste water

Info

Publication number: EP2435773A2
Application number: EP10721298A
Authority: EP
Inventors: Bo Asbjørn CHRISTENSEN
Original assignee: Arkitektfirmaet Bo Christensen ApS
Current assignee: Arkitektfirmaet Bo Christensen ApS
Priority date: 2009-05-30
Filing date: 2010-05-31
Publication date: 2012-04-04
Also published as: WO2010139334A2; DK178002B1; DK200900681A; WO2010139334A3

Abstract

A heat exchanger for recuperation of residual heat from waste water, for instance from a shower, is disclosed, comprising a conduit arranged to pass through a container, wherein the conduit is a drain pipe and the container has an inlet for cold water and an outlet for preheated water.

Description

HEAT EXCHANGER FOR RECUPERATION OF RESIDUAL HEAT FROM WASTE WATER

Field of the invention

The present invention relates to the field of heat exchangers, specifically to the field of heat exchangers for exchanging heat energy between two liquids.

Background of the invention

In many countries with a temperate climate, such as for instance Denmark, around half of the energy consumption is used for the heating and operation of residence housings. In accordance with clear and prevailing political signals, several laws have already been passed with the purpose of decreasing the energy consumption related to the housing stock.

In connection with the United Nations' Climate Change Conference 2009 (also known as the COP 15) newly held in Copenhagen and with constantly more tightened up requirements and restrictions with regard to energy consumption, new arrangements and techniques, which can decrease the energy consumption of the housing stock, are more relevant than ever before.

Already with the rules presently in force, and especially in relation to so-called low energy houses, the energy consumption used for production of hot domestic water constitutes a substantial part of the total energy consumption of the housings. Newly performed calculations show that, for a typical low energy class 2 house, the energy used for hot water production equals the energy used for heating the house. Therefore, it is highly relevant to investigate how the amount of energy used for this purpose can be reduced, optimized or provided from new sources.

More than 60 % of the hot water in a normal household in a country like Denmark is used for bathing and showering. Furthermore, an average of 850 kWh of energy per person per year is used for heating up the hot domestic water. This means that, for each person, about 500 kWh of energy is lost in the drain every year just in connection with bathing and showering. If a way can be found to recuperate just some of the heat energy that disappears into the drain with the waste water from bathing and showering, a lot of the energy used for heating up the domestic water in a household can be saved.

Danish Utility Model No. DK 1999 00285 U3 discloses a heat exchanger for recuperation of heat energy from waste water. Inside a container, a helical heat exchanger is arranged, which is provided with an upper and a lower pipe connection in the container. The helical heat exchanger is connected to a supply of cold domestic water, the water entering the helical heat exchanger through the upper pipe connection and leaving it through the lower pipe connection. The hot waste water is led through the container outside the helical heat exchanger.

A disadvantage of this heat exchanger system is that hair and other impurities from the waste water tend to accumulate in the container.

It is an object of the present invention to provide a heat exchanger without the above - mentioned disadvantage.

Brief description of the invention

The present invention relates to a heat exchanger for recuperation of residual heat from waste water, for instance from a shower, comprising a conduit arranged to pass through a container, wherein the conduit is a drain pipe and the container has an inlet for cold water and an outlet for preheated water.

Letting the waste water pass through the conduit reduces the risk of hair and other impurities to accumulate in the system. In an embodiment of the invention, the conduit has a helical shape.

The helical shape is very useful for obtaining a smooth conduit with a constant slope and without any sharp corners, in which impurities are likely to accumulate.

In an embodiment of the invention, the inlet for cold water is placed near the bottom of the container and the outlet for preheated water is placed near the top of the container.

The best efficiency of a liquid- liquid heat exchanger is obtained if the two liquids, between which heat energy is to be exchanged, flow in opposite directions.

In an embodiment of the invention, the conduit is made from a material with a high thermal conductivity, such as copper.

Using copper for making the conduit is advantageous in that copper has a very high thermal conductivity. In fact, with at sufficiently large surface of the conduit, a heat exchange efficiency of more than 50 % can be expected. Furthermore, the copper material opposes the formation of any biological film on the inner surface of the conduit from the waste water running through the conduit. Such a biological film, if formed on the inner surface of the conduit, is likely to reduce the efficiency of the heat exchanger. The cooling of the waste water in the heat exchanger also prevents the formation of a biological film, because the formation is increasing with increasing temperature.

In an embodiment of the invention, the conduit is arranged to slope with a grade of between 10 % and 15 %, preferably about 12 %.

Choosing a slope within this range assures that the waste water flows through the conduit at a suitable rate. The relatively steep slope results in a high flow rate, which together with the centrifugal force distributes the waste water on a large portion of the inner surface of the conduit, resulting in turn in a high level of heat exchange with the colder water on the outside of the conduit.

In an embodiment of the invention, the cold water is tap water.

I most cases, the preheated water will be used for bathing or washing and, therefore, tap water can advantageously be used.

In an embodiment of the invention, the container is thermally insulated from the surroundings.

Insulating the container reduces the amount of heat energy being lost from the preheated water to the surroundings.

In an embodiment of the invention, the cold and preheated water is forced to pass through the container in relatively close contact with the outer surface of the conduit, for instance by a first filler element being arranged centrally the container, around which first filler element the conduit is arranged and/or by a second filler element being arranged along the periphery of the container, within which second filler element the conduit is arranged.

Keeping the cold and preheated water in relatively close contact with the outer surface of the conduit increases the efficiency of the heat exchanger. The use of filler elements to reduce the volume of the container, in which the cold and preheated water passes, further increases the rise of the cold water along the helical conduit with a raising temperature as the top of the container is approached.

In an embodiment of the invention, an outer surface of the conduit is provided with a number of ribs for increasing the heat exchange between hot waste water inside the conduit and cold water outside the conduit. Using ribs on the outer surface of the conduit increases the surface area and, thus, the exchange of heat energy to the cold and preheated water passing along the surface.

In an embodiment of the invention, the conduit is provided with an activatable, gradual constriction near the place, where the conduit exits the container.

Being able to constrict the conduit near its exit from the container enables for reducing the flow rate of the waste water inside the conduit, thus keeping the waste water in contact with the cold and preheated water for a longer time for obtaining a larger exchange of heat energy between the waste water inside and the cold and preheated water outside the conduit. Such a constriction must at all times allow a flow rate corresponding to the maximum output from the water source being drained through the conduit in order to avoid flooding anywhere in the drain system.

In a further embodiment of the invention, the constriction can be activated by a decrease in the pressure of the cold water so that, when no preheated water is being drawn from the container, no constriction of the conduit takes place.

Letting the amount of constriction of the conduit be related to the pressure of the cold water in this way is advantageous in that it assures that the flow of waste water through the heat exchanger, i.e. through the drain pipe constituted by the conduit, is only restricted when preheated water is actually used and more cold water to be preheated flows into the container.

In an embodiment of the invention, the constriction can be activated by heating from the waste water so that, when the temperature of the waste water inside the conduit exceeds a predetermined value, a constriction of the conduit takes place, thus reducing the flow rate of waste water through the conduit.

Letting the amount of constriction of the conduit be related to the temperature of the waste water in this way is advantageous in that it assures that the flow through the heat exchanger, i.e. through the drain pipe constituted by the conduit, is only restricted when the temperature of the waste water is actually high enough to enable heat energy to be exchanged from the waste water to the cold water outside the conduit.

In an embodiment of the invention, the heat exchanger is arranged within a floor drain.

In another embodiment of the invention, the heat exchanger is arranged after a floor drain, such as close to and in direct connection with the floor drain or close to and in direct connection with a hot-water tank which may, for instance, be placed in a technical room.

The heat exchanger can be arranged at different places within a hot-water system. If arranged within a floor drain or in immediate connection with a floor drain, it can be used both in new building constructions and in connection with renovations of bathrooms, primarily in residence buildings. The heat exchanger can be constructed with a relatively modest built-in height making it applicable also for bathrooms and the like in the upper floors of multi-storey buildings.

Heat exchangers to be placed centrally in a building, such as in a technical room, are well-suited for new constructions, wherein careful planning can assure that the bathrooms are placed so that the drain pipes therefrom can easily be led to a central heat exchanger. Other obvious applications are in connection with showers in locker rooms and in hotels and multi-storey buildings, where the heat exchanger can be arranged to preheat the water before it reaches the hot- water tank.

The figures

In the following, a few exemplary embodiments of the invention are described and explained in more detail with reference to the drawings, wherein Fig. Ia is a schematic view of a heat exchanger according to the invention,

Fig. Ib is a cross-sectional view of the heat exchanger shown in Fig. Ia,

Fig. 2a is a schematic view of a heat exchanger according to the invention, which is arranged directly beneath a floor drain,

Fig. 2b is a cross-sectional view of the heat exchanger and the floor drain, which are shown in Fig. 2a,

Fig. 3a is a schematic view of a heat exchanger according to the invention, which is arranged within a floor drain,

Fig. 3b is a cross-sectional view of the main parts of the heat exchanger and the floor drain, which are shown in Fig. 3a,

Fig. 3c is a cross-sectional view of the heat exchanger and the floor drain, which are shown in Fig. 3a, and

Fig. 4 is a schematic diagram illustrating the effects obtained by using a heat exchanger according to the invention.

Detailed description

Fig. Ia is a schematic view of a heat exchanger 1 according to the invention, showing a cylindrical container 3, at the top of which container 3 is an axial entry 6 into the container 3 of a conduit 2, and at the bottom of which container 3 is a sideways exit 7 from the container 3 of the same conduit 2. Furthermore, the figure shows an inlet 4 for cold water near the bottom of the container 3 and an outlet 5 for preheated water near the top of the container 3. In Fig. Ib, which is a cross-sectional view of the heat exchanger 1 shown in Fig. Ia, it is illustrated how the conduit 2 is formed to have a helical shape extending with a substantially constant slope from the top to the bottom of the container 3. The helical conduit 2 is arranged around a first, central filler element 8 arranged centrally in the circular container 3 and within a second, peripheral filler element 14 arranged along the periphery of the container 3. In the illustrated embodiment, both filler elements

8, 14 are filled with air and, thus, also have a certain insulating function. In other embodiments, one or both of the filler elements 8, 14 may be filled with other insulating materials than air.

A configuration like this assures that the cold water entering the container 3 through the inlet 4 for cold water (not shown in this figure) near the bottom of the container 3 is forced to pass upwards through the container 3 in relatively close contact with the outer surface of the conduit 2 before leaving the container as preheated water through the outlet 5 for preheated water, resulting in a very high efficiency of the heat exchanger 1.

Figs. 2a and 2b are a schematic view and a cross-sectional view of another heat exchanger 1 according to the invention, respectively, which heat exchanger 1 is arranged directly beneath a floor drain 9. Apart from technical details similar to the ones shown in Figs. Ia and Ib, these figures also illustrate a floor drain 9 arranged on top of the heat exchanger 1 , the conduit 2 being a direct continuation of the drain pipe of the floor drain 9.

Fig. 3a is a schematic view of yet another heat exchanger 1 according to the invention, which heat exchanger 1 is arranged within a floor drain 9. The figure shows a container 3 with an inlet 4 for cold water and an outlet 5 for preheated water, on top of which container is seen the upper part of a floor drain 9 and a grating 10 for the floor drain 9. Fig. 3b is a cross-sectional view of the main parts of the heat exchanger 1 and the floor drain 9, which are shown in Fig. 3a. These parts comprise a grating 10 for the floor drain 9 and the floor drain 9 itself, having a conical shape leading the waste water into the top opening of a filler element 8 and having a horizontal part forming a lid for the container 3. The filler element 8 forms an essential part of the drain system in the illustrated embodiment. The helical conduit 2 leaves the filler element 8 at a point 6 near its top and enters the filler element 8 again at a point 7 near its bottom. A removable lid 11 can be placed into the filler element 8 resting on a protrusion 15. When the waste water from the floor drain 9 enters the filler element 8, the upper surface of this lid 11 will force the waste water to continue its flow through the helical conduit 2. The waste water leaves the container 3 and, thus, the heat exchanger 1 through an axially arranged drain pipe 13 at the bottom of the container 3.

Furthermore, a standpipe 12 to be placed at the bottom of the container 3 is illustrated. This standpipe 12 has several functions. First of all, it assures that the level of the water surface inside the filler element 8, i.e. in the drain, is always above the point 7, where the waste water enters the filler element 8 from the helical conduit 2, thus forming a drain trap for preventing obnoxious smells from the drain. Secondly, the removable lid 11 and the removable standpipe 12 allows for emptying and cleaning the drain. Finally, the standpipe 12 delays the emptying of the drain, which increases the degree of recuperation of the heat energy from the waste water in the heat exchanger 1.

Fig. 3c is a cross-sectional view of the heat exchanger 1 and the floor drain 9, which are shown in Fig. 3a, with all the parts shown in Fig. 3b assembled together. The holes 22 in the standpipe 12 are arranged just above the desired water surface level, which is needed to assure the function of the drain trap, so that the drain is emptied down to this level when not in use. This assures that no more than the necessary amount of cooled waste water is left behind in the drain. Fig. 4 is a schematic diagram illustrating the effect obtained by using a heat exchanger 1 according to the invention.

The normal situation without a heat exchanger 1 is shown to the left in the figure: Hot water at a temperature of about 60° C is supplied by a hot water supply pipe 16, and cold water at a temperature of about 8° C is supplied by a cold water supply pipe 17. In a mixer tap 18, the hot and the cold water is mixed together to supply water at a temperature of about 38° C for a shower 19. The waste water 20 leaves the floor under the shower 19 through a floor drain 9, still at a temperature of about 38° C.

On the other hand, when a heat exchanger 1 is arranged within the floor drain 9 as indicated to the right in the figure, some of the heat energy from the waste water 20 can be recuperated and reused for heating the shower water. The waste water 20 is led through a helical conduit 2 as seen in the previous figures. Now, the cold water supply pipe 17 is not connected to the mixer tap 18. Instead, it is connected to the heat exchanger 1 , in which the cold water is preheated by being in contact with the helical conduit 2, inside which the warmer waste water 20 is flowing. From the heat exchanger 1, the preheated water is led to the mixer tap 18 through a pipe 21 for preheated water.

In the example shown in the figure, the cold water is preheated from 8° C to 23° C, while the waste water 20 leaving the floor drain 9 is cooled down from 38° C to 23° C. This means that a certain amount of heat energy is taken by the preheated water back to the mixer tap 18 instead of leaving the system with the waste water 20. In the mixer tap 18, the hot water at a temperature of 60° C now has to be mixed with water at a temperature of 23° C instead of with water at a temperature of only 8° C. Therefore, less hot water will be used for obtaining the desired temperature of 38° C of the shower water, and energy for heating up hot water is saved. List of reference numbers

1. Heat exchanger

2. Conduit 3. Container

4. Inlet for cold water

5. Outlet for preheated water

6. Conduit entrance into container

7. Conduit exit from container 8. Central filler element for container

9. Floor drain

10. Grating for floor drain

11. Removable lid for filler element

12. Floor drain standpipe 13. Drain pipe leaving the heat exchanger

14. Peripheral filler element for container

15. Protrusion for removable lid

16. Hot water supply pipe

17. Cold water supply pipe 18. Mixer tap

19. Shower

20. Waste water

21. Pipe for preheated water

22. Hole in standpipe

Claims

1. A heat exchanger (1) for recuperation of residual heat from waste water, for instance from a shower, comprising a conduit (2) arranged to pass through a container (3),

characterised in that

the conduit (2) is a drain pipe and the container (3) has an inlet (4) for cold water and an outlet (5) for preheated water.

2. A heat exchanger (1) according to claim 1, wherein the conduit (2) has a helical shape.

3. A heat exchanger (1) according to claim 1 or 2, wherein the inlet (4) for cold water is placed near the bottom of the container (3) and the outlet (5) for preheated water is placed near the top of the container (3).

4. A heat exchanger (1) according to any of the preceding claims, wherein the conduit (2) is made from a material with a high thermal conductivity, such as copper.

5. A heat exchanger (1) according to any of the preceding claims, wherein the conduit (2) is arranged to slope with a grade of between 10 % and 15 %, preferably about 12 %.

6. A heat exchanger (1) according to any of the preceding claims, wherein the cold water is tap water.

7. A heat exchanger (1) according to any of the preceding claims, wherein the container (3) is thermally insulated from the surroundings.

8. A heat exchanger (1) according to any of claims 2-7, wherein the cold and preheated water is forced to pass through the container (3) in relatively close contact with the outer surface of the conduit (2), for instance by a first filler element (8) being arranged centrally the container (3), around which first filler element (8) the conduit (2) is arranged and/or a second filler element (14) being arranged along the periphery of the container (3), within which second filler element (14) the conduit (2) is arranged.

9. A heat exchanger (1) according to any of the preceding claims, wherein an outer surface of the conduit (2) is provided with a number of ribs for increasing the heat exchange between hot waste water inside the conduit (2) and cold water outside the conduit (2).

10. A heat exchanger (1) according to any of the preceding claims, wherein the conduit (2) is provided with an activatable, gradual constriction near the place (7) , where the conduit (2) exits the container (3).

11. A heat exchanger (1) according to claim 10, wherein the constriction can be activated by a decrease in the pressure of the cold water so that, when no preheated water is being drawn from the container (3), no constriction of the conduit (2) takes place.

12. A heat exchanger (1) according to claim 10, wherein the constriction can be activated by heating from the waste water so that, when the temperature of the waste water inside the conduit (2) exceeds a predetermined value, a constriction of the conduit (2) takes place, thus reducing the flow rate of waste water through the conduit (2).

13. A heat exchanger (1) according to any of the preceding claims, which is arranged within a floor drain (9).

14. A heat exchanger (1) according to any of claims 1-12, which is arranged after a floor drain (9), such as close to and in direct connection with the floor drain (9) or close to and in direct connection with a hot- water tank.