WO2008009289A1

WO2008009289A1 - A heat exchange module, in particular for a ground source heat pump

Info

Publication number: WO2008009289A1
Application number: PCT/DK2007/000356
Authority: WO
Inventors: Poul Svendsen
Original assignee: Poul Svendsen
Priority date: 2006-07-20
Filing date: 2007-07-13
Publication date: 2008-01-24

Abstract

A heat exchanger, in particular for a ground source heat pump is disclosed comprising a leak detection system for detecting leaks in the outer wall of a return pipe as well as a heat exchange module therefore. Thereby, leaks between the heat transfer fluid and the leak detection cavities (7) in the outer wall as well as leaks between the outer surface of the return pipe (3) and the leak detection cavities may be found by the leak detection system, thus providing a high degree of environmental safety.

Description

A HEAT EXCHANGE MODULE, IN PARTICULAR FOR A GROUND SOURCE HEAT PUMP

Background of the invention

The present invention relates to a heat exchange module and a heat exchanger having such module, in particular as a part of a ground source heat pump

Description of the Related Art

Ground source heat pumps (GSHPs) are systems that utilize the stored energy in the ground. These systems use the relatively constant temperature of the ground to provide heating and cooling for e.g. buildings.

A GSHP has an underground heat exchanger, a second heat exchanger, a circulation pump and a conduit system. The conduit system connects the underground heat exchanger with the second heat exchanger; thereby creating a closed loop wherein a heat transfer fluid flows. The underground heat exchanger has long pipes, either drilled vertically into the ground or buried in horizontal trenches. In the underground heat exchanger the heat transfer fluid exchanges heat with the ground. In the second heat exchanger which normally is located in a building the heat transfer fluid exchanges heat with a second heat transfer fluid that flows in conventional ductwork (e.g. connected to heaters) in the building. A GSHP can use the tempering effect of the ground as a heating source in winter and as a heat drain in summer.

Typically the heat transfer fluid is for efficiency of the system a brine, a mixture of water and an anti-freeze agent, such as ethylene glycol, propylene glycol, ethanol or methanol.

The most common GSHP systems comprises a heat exchanger having a length of tubing extending horizontally in the ground at about 80 cm to 1 meter below the surface. Such systems are relatively inexpensive to construct and have the advantage that a possible leak of the heat transfer fluid into the environment will not have severe environmental damaging effects on ground water, before the leak is detected from the loss of heat transfer fluid in the system.

An alternative arrangement of the ground heat exchanger is shown in e.g. US 5,339,890 (Rawlings), in US 6,073,448 (Lozada) and in JP 57187557 (Asai Masaru), where a vertical pipe extends into the ground. This type of arrangement has advantages over the horizontal tubing in the it takes up only little area and may therefore be used where the available area is limited. Furthermore, the vertical pipe extends much deeper into the ground where the temperature is more constant and the GSHP may be operated efficiently also at the end of the winter. The drawback is the environmental concerns linked to the dept to which the heat exchanger extends, in particular the risk of pollution of ground water used for drinking water or irrigation with the brine used as heat transfer fluid, and very few of such GSHP have therefore obtained the necessary permit to be realised as operating GSHP.

Thus, it is an object of the present invention to provide a heat exchanger that may be used to solve the above-mentioned drawbacks for GSHP systems with vertical or substantially vertical heat exchangers.

Brief description of the invention

With the present invention is provided a heat exchange module comprising a longitudinally extending supply pipe made from a plastic material, preferably polyethylene, and surrounded by a return pipe made from a material of high thermal conductivity, preferably an aluminium alloy, wherein a plurality of cavities are provided in the wall of the return pipe, the cavities being suitable for containing a pressurised leak detection fluid.

By providing the cavities in the wall of the outer return pipe, a leak detection system is prepared for where a pressurised leak detection fluid may be provided in the cavities, so that a leak between the heat transfer fluid inside the return pipe and the cavities or between the cavities and the external side of the return pipe will be detected by the leak detection system, thus ensuring that a leak will be detected before an actual environmental endangering leakage of the heat transfer fluid happens. Thus, GSHP systems having the heat exchange module of the present invention have received the necessary environmental certifications and permission to install and operate.

The cavities of the return pipe naturally lower the thermal conductivity of the return pipe form the external surface and to the internal surface where the heat transfer fluid is present, and in order to enhance the heat transfer, the return pipe is in a preferred embodiment equipped with a plurality of longitudinal fins extending inwardly in the axial direction of said return pipe

The length of the module is preferably within the range of 2 to 20 meter, preferably 3 to 10 meter and most preferred within 4 to 8 meter, and the heat exchanger constructed by means of the module may comprise a plurality of the modules, either arranged in direct extension of one another as one heat exchanger or in parallel.

The present invention also relates to a heat exchanger comprising a substantially closed heat transferring system including a heat exchange module of the present invention and means for circulating a heat transfer fluid into the supply pipe and out from the return pipe, and a leak detection system for detecting leaks in said heat transfer system, comprising a pressurized leak detection fluid, means for providing said fluid to the plurality of cavities in the return pipe and means for monitoring the pressure of said leak detection fluid.

The leak detection system is preferably arranged to detect an unwanted passage between said plurality of cavities and said heat transfer fluid or a part of the surroundings of said heat exchanger. By having the leak detection fluid surrounding at least a part of the heat exchanger, preferably at least the part of the heat exchanger positioned in the ground in a ground source heat pump, the leak detection fluid will act as a buffer that any leak will have to pass before a direct and damaging passage is established between the heat transfer fluid and the surroundings. This is advantageous in that by detecting a change in the pressure of the leak detection fluid it is indicated that a damaging passage is in the process of being formed and measures can be taken before this happens.

The pressure of said pressurized leak detection fluid is in a preferred embodiment higher that the pressure of the surroundings of said heat exchanger and less that the pressure of said heat transfer fluid.

By detecting a leak between the leak detection fluid and the heat transfer fluid or the surroundings of the part of the heat exchanger which exchange heat with the surroundings it is possible to detect a deterioration, damage or other of the heat exchanger before a possibly damaging passage between the heat transfer fluid and the surroundings is established.

The pressurized leak detection fluid is preferably a pressurized gas such as pressurized air.

The heat exchanger module of the present invention may be employed for a variety of heat exchanging tasks between an internal heat transfer fluid and the external surface of the return pipe, such as cooling or heating of e.g. manure. However, the preferred utilisation is for heat pumps, in particular for ground source heat pumps. Thus, the present invention furthermore relates to a heat pump comprising a heat exchanger according to the present invention, wherein an outer surface of the return pipe of the heat exchange module is in heat exchanging contact with the surroundings, so as to exchange heat between the heat transfer fluid and the surroundings. The heat exchanger extends preferably in the range of 10 to 300 meter, preferably 20 to 200 meter and most preferred 30 to 150 meter into the ground, and the heat exchanger extends in a preferred embodiment substantially vertically.

The drawings

In the following, the invention is explained in more detail with reference to the drawings, where

fig. 1. illustrates an embodiment of a heat exchanger in form of a ground source heat pump, as seen from the front,

% 2 illustrates an embodiment of an array of heat exchangers in form of a ground source heat pump, as seen from the front,

% 3 illustrates a cross-section of an embodiment of a heat exchanger, as seen from the front,

fig. 4 illustrates a cross-section of another embodiment of a heat exchanger, as seen from the front, and

fig. 5 illustrates a cross-section of an embodiment of a heat exchanging part of a heat exchanger, as seen from the top.

Detailed description

The present invention relates to an improvement in heat exchangers 1, which improvement offers a better protection of the environment, e.g. the drinking water, against heat transfer fluid 2 contaminations from heat exchangers 1. The heat exchanger 1 in the present invention comprises at least one heat exchange unit which is at least partly located underground, where each heat exchange unit comprises a supply header 14, a return header 15 and at least one heat exchange module 16, a return pipe 3 in each heat exchange unit, and a supply pipe 4 in each heat exchange unit where each heat exchange unit comprises at least one closed space which is located between the heat transfer fluid 2 and the surrounding ground and contains pressurized leak detection fluid and at least one pressure sensor 6 that measures the pressure in the at least one cavity 7.

By the term "pressurized ... fluid" 5 is meant a fluid that has any pressure which is different from both the pressure of the heat transfer fluid 2 and from the pressure of the surroundings.

The present invention can predict leaks in a leak detection system 8 e.g. from gradual breakdown of the part of the heat exchanger 1 that is located underground. Gradual breakdown can either occur from without or from within. If one of these kinds of breakdowns occur then the pressure measured/monitored by the at least one pressure sensor 6 will change.

In a preferred embodiment the pressurized fluid 5 is a gas, e.g. normal air.

In a preferred embodiment of the invention the at least one pressure sensor 6 supplies an input signal to a safety control device which is located externally to the heat exchanger 1. If the input signal indicates a change in the pressure of the pressurized fluid 5 then appropriate measures for protection of the environment can be taken.

The function of the second heat exchanger 9 is transfer of heat between the heat transfer fluid 2 and a fluid inside the building (e.g. running in radiators).

Figure 1 shows a heat exchanger 1 according to a preferred embodiment of the invention, where the heat exchanger 1 is connected with a second heat exchanger 9, a circulation pump 10 and a conduit system 11 which together form a ground source heat pump (GSHP) 12. The GSHP comprises a closed loop containing a heat transfer fluid 2 which normally is circulated by the circulation pump 10.

Figure 2 shows another preferred embodiment of the invention, where three heat exchangers 1 are connected to the second heat exchanger 9 in parallel. It is noted that the number of heat exchangers 1 is not limited to one or three.

The heat exchanger 1 can e.g. be installed substantially vertical or substantially horizontal. The available land areas and the soil and rock type at the installation site can be used to select an appropriate type of installation. Heat exchangers 1 can be installed under lawns, driveways, the house itself or similar places. These and other factors will help determine the most appropriate choice for installation of the heat exchanger 1.

Figure 3 shows a vertical cross section of a heat exchanger 1 according to a preferred embodiment of the invention, where the heat exchanger 1 is vertically installed in a well, the supply pipe 4 is surrounded by the return pipe 3, and a leak detection fluid 5 is located inside the outer wall of the return pipe 3. In a typical installation most of the heat exchanger 1 is surrounded by soil. The upper part of the heat exchanger 1 that is not surrounded by soil has an outer wall, which is thicker than the wall of the heat exchanging part 13 of the heat exchanger 1 which is surrounded by soil. In the lower part or the heat exchanging part 13 of the heat exchanger 1 the leak detection fluid 5 is contained in one or more cavities 7 inside the outer wall of the return pipe 3.

The invention is not limited to the configuration of the supply pipe 4 and return pipe 3 as shown i figure 3 as long as the closed space 7 containing the leak detection fluid 5 is located between the heat transfer fluid 2 and the surround soil. In a preferred embodiment of the invention the leak detection system 8 comprises a pressure sensor 6 that measures/monitors the pressure of the leak detection fluid 5 either continuously or with appropriate time intervals.

If a leak occurs in the heat exchanging part 13 of the heat exchanger 1 from within - with the effect that a passage between the heat transfer fluid 2 and the pressurized leak detection fluid 5 is established - then the pressure of the leak detection fluid 5 changes. If a leak occurs in the lower part 13 of the heat exchanger 1 from without - with the effect that a passage between the pressurized leak detection fluid 5 and at least a part of the surrounding ground is established - then the pressure of the leak detection fluid 5 also changes. This means that in both situations the pressure of the leak detection fluid 5 changes before the heat transfer fluid 2 can interact with the surroundings and result in a contamination of the environment. When a change in the pressure of the leak detection fluid 5 occurs then appropriate measures for protection of the environment can be taken. Appropriate measures could e.g. be a manual procedure whereby the heat transfer fluid 2 is removed from the heat exchanger 1 and replaced with another fluid e.g. ordinary water which is not harmful to the environment.

In a preferred embodiment of the invention the leak detection system 8 comprises a pressure sensor 6 that measures/monitors the pressure of the leak detection fluid 5.

In a preferred embodiment of the invention the pressure of the heat transfer fluid 2 is approximately 3.5 Bar and the pressure of the leak detection fluid 5 is approximately 1.5 Bar. The pressure of the heat transfer fluid 2 and the pressure of the leak detection fluid 5 could of course be any other value, as long as the pressure of the heat transfer fluid 2 is different from the pressure of the leak detection fluid 5 and as long as the pressure of the leak detection fluid 5 is different that then pressure of the surroundings of the heat exchanger 1. In a preferred embodiment of the invention the heat transfer fluid 2 is some kind of anti-freeze and water solution, such as brine or isopropyl alcohol. The heat transfer fluid 2 could also be any anti-freeze solution, such as e.g. methanol, propylene glycol or potassium acetate.

In a preferred embodiment of the invention the leak detection fluid 5 is normal air. The leak detection fluid 5 could also be other kinds of fluid as long as it is not harmful to the environment.

In a preferred embodiment of the invention the return pipe 3 is made of an aluminium alloy, but is could also be other kinds of material that has god thermal conductivity. Leakages in the return pipe 3, or other part of the heat exchanger 1, can occur because of e.g. mechanical impacts or corrosion.

In a preferred embodiment of the invention the heat exchanger 1 is installed in a well where an upper part of the heat exchanger 1 is not in directly contact with the surrounding ground.

Figure 4 shows a vertical cross section of the heat exchanger 1 according to an embodiment of the invention, where the heat exchanger 1 comprises a supply header 14 and a return header 15 and there between at least one heat exchange module 16. The supply header 14, the return header 15 and the at least one heat exchange module 16 is connected with connection means.

When the heat exchanger 1 is installed vertically in the ground as shown in figure 4, then supply header 14 is located above the at least one heat exchange module 16 and the return header 15 is located beneath the at least one heat exchange module 16. The at least one heat exchange module 16 is typically a cylinder, but could have other shapes. The wall of the at least one heat exchange module comprises cavities 7 in the axial direction of the modules 16. The supply header 14 comprises a recess/depression with an opening in the surface of the supply header 14 that faces the uppermost of the at least one heat exchange module 16. The return header 15 also comprises a recess/depression with an opening in the surface of the return header 15 that faces the lowermost of the at least one heat exchange module 16. When the supply header 14, the at least one heat exchange module 16 and the return header 15 are aligned with the supply header 14 at one end and the return header 15 at the other end, they are aligned so that all the cavities 7 and the recesses/depressions are in contact with each other and thereby forming a single closed space 7 which can contain the leak detection fluid 5.

In a preferred embodiment a supply pipe 4 is disposed within the aligned supply header 14 and the at least one heat exchange module 16, so that one end of the supply pipe 4 extends through an opening in the supply header 14 and the length of the supply pipe 4 is about the same as the length of the aligned supply header 14 and the at least one heat exchange module 16. This means that the supply pipe 4 is located substantially concentric to the return pipe 3.

In a preferred embodiment the supply pipe 4 is a normal plastic pipe made from a plastic material such as polyethylene.

Fig. 5 illustrates a cross-section of an embodiment of the heat exchanging part 13 of a heat exchanger 1, as seen from the top.

In an embodiment of the invention the outside wall of the return pipe 3 has an expanded internal surface by provisions of fins 17 that increases the internal surface area of the return pipe 3. Hereby more efficient heat transfer between the heat transfer fluid 2 and the surrounding is achieved. The return pipe 3 is preferably produced by extrusion of aluminium or an alloy containing aluminium, whereby the whole pipe including cavities and fins may be produced in one operation.

In this embodiment of the invention the heat exchanger extend 70 meters into the ground but in another embodiment of the invention the heat exchanger extend 10-300 meters, more preferably 20-200 meters, and most preferably 30-150 meters into the ground.

The invention has been exemplified above with reference to specific examples of heat exchangers 1 and other. However, it should be understood that the invention is not limited to the particular examples described above but may be designed and altered in a multitude of varieties within the scope of the invention as specified in the claims.

In a preferred embodiment of the invention the length of the heat change unit is 2-20 meter, more preferably 3-10 meter, and most preferably 4-8 meters.

List

1. Heat exchanger

2. Heat transfer fluid 3. Return pipe

4. Supply pipe

5. Leak detection fluid

6. Means for monitoring the pressure of the leak detection fluid

7. Cavity 8. Leak detection system

9. Second heat exchanger

10. Circulation pump

11. Conduit system

12. Ground source heat pump 13. Heat exchanging part

14. Supply header

15. Return header

16. Heat exchange module / heat exchange unit

17. Fins on the inside of the return pipe

Claims

1. A heat exchange module (16) comprising a longitudinally extending supply pipe (4) made from a plastic material and surrounded by a return pipe (3) made from a material of high thermal conductivity, wherein a plurality of cavities (7) are provided in the wall of the return pipe, the cavities being suitable for containing a pressurised leak detection fluid (5).

2. A heat exchange module according to claim 1, wherein said material of high thermal conductivity is an aluminium alloy.

3. A heat exchange module according to claim 1 or 2, wherein said return pipe comprises a plurality of longitudinal fins (17) extending inwardly in the axial direction of said return pipe

4. A heat exchange module according to any of claims 1-3, wherein the supply pipe is made from polyethylene.

5. A heat exchange module according to any of claims 1 -4, wherein the length of the module is within the range of 2 to 20 meter, preferably 3 to 10 meter and most preferred within 4 to 8 meter.

6. A heat exchanger comprising a substantially closed heat transferring system including a heat exchange module according to any of claim 1-5 and means for circulating a heat transfer fluid into the supply pipe and out from the return pipe, and a leak detection system for detecting leaks in said heat transfer system, comprising a pressurized leak detection fluid, means for providing said fluid to the plurality of cavities in the return pipe and means for monitoring the pressure of said leak detection fluid.

7. A heat exchanger according to claim 6 wherein the leak detection system is arranged to detect an unwanted passage between said plurality of cavities and said heat transfer fluid or a part of the surroundings of said heat exchanger.

8. A heat exchanger according to claim 6 or 7, wherein the pressure of said pressurized leak detection fluid is higher that the pressure of the surroundings of said heat exchanger and less that the pressure of said heat transfer fluid.

9. A heat exchanger according to any of claims 6 to 8, wherein said pressurized leak detection fluid is a pressurized gas such as pressurized air.

10. A heat pump comprising a heat exchanger according to any of claims 6 to 9, wherein an outer surface of the return pipe of the heat exchange module is in heat exchanging contact with the surroundings, so as to exchange heat between the heat transfer fluid and the surroundings.

11. A heat pump according to claim 10 being a ground source heat pump, where the heat exchange module is entirely or partly buried in soil.

12. A heat pump according to claim 10 or 11, wherein the heat exchanger extends in the range of 10 to 300 meter, preferably 20 to 200 meter and most preferred 30 to 150 meter into the ground.

13. A heat pump according to any of claims 10 to 12, wherein the heat exchanger extends substantially vertically.

14. Use of a heat exchanger according to any of claims 6 to 9, wherein an outer surface of the return pipe is in heat exchanging contact with the surroundings, so as to exchange heat between the heat transfer fluid and the surroundings.