WO1996009500A1

WO1996009500A1 - A temperature control system for fluids

Info

Publication number: WO1996009500A1
Application number: PCT/AU1995/000631
Authority: WO
Inventors: Peter Lawrence Murphy; Terry Howard Solomon; Mario Stiffler
Original assignee: Thermal Energy Accumulator Products Pty Ltd; Stiffler Fiorentina
Current assignee: Thermal Energy Accumulator Products Pty Ltd; Stiffler Fiorentina
Priority date: 1994-09-22
Filing date: 1995-09-22
Publication date: 1996-03-28
Anticipated expiration: 1997-03-22
Also published as: AUPM835894A0

Abstract

The present invention relates generally to a temperature control system for fluids and relates particularly, though not exclusively to a temperature control system (10) for a swimming pool (12) using solar heated water. The temperature control system comprises a solar collector (14) and an accumulator (16). The pool is coupled to and in fluid communication with the solar collector (14). The accumulator (16) comprises a plurality of cells (32) each containing a phase change substance having a high latent heat of fusion. The collector (14) is in heat conductive communication with the accumulator (16). The pool water is recirculated from the swimming pool through the solar collector (14), and accumulator (16) back to the swimming pool (12). In operation, sunlight absorbed by the collector (14) transfers heat to the accumulator (16) via recirculated pool water thus melting a portion of the phase change substance. The recirculated pool water then cools and solidifies the phase change substance thereby releasing latent heat and heating the recirculated pool water.

Description

A TEMPERATURE CONTROL SYSTEM FOR FLUIDS

FIELD OF THE INVENTION

The present invention relates generally to a temperature control system for fluids and relates particularly, though not exclusively, to a temperature control system for a swimming pool using solar heated water.

BACKGROUND TO THE INVENTION

There are numerous applications where water is to be heated, generally above atmospheric temperature. Heated swimming pools are an example of this, where water is heated and recirculated through the pool. The water can be heated by a variety of means, such as electric, solar or waste energy. Solar or waste energy is generally preferred since electricity is mostly generated by fossil fuels which are a limited resource. Furthermore, the burning of fossil fuels in producing electricity is harmful to the environment.

Solar water heating systems are known and commonly used for domestic purposes. A known solar water heating system comprises a solar collector located on a roof, the collector plumbed to an insulated tank containing hot water. Because the amount of available sunlight is generally dictated by the number of daylight hours and the seasons, the tank must be insulated to maintain consistently hot water at all times. During winter months and in particularly cold climates a solar collector may not provide sufficient energy to heat water. Most solar hot water systems are, therefore, electrically boosted so that electrical heating is provided when the water temperature falls below a predetermined temperature. Furthermore, storing large volumes of hot water during winter months may not be possible without heating the tank and/or providing the tank with substantial heat insulation. All of the above solutions to maintaining hot water at a consistent temperature are relatively expensive. In remote areas it may not be possible to electrically boost a solar heating system. If other forms of waste heat are not available the collector must rely solely on sunlight for heat.

SUMMARY OF THE INVENTION

An intention of the present invention is to provide a temperature control system for fluids which can efficiently control the temperature of fluids using sunlight or other waste heat.

According to a first aspect of the present invention there is provided a temperature control system for a fluid in a reservoir, the system comprising: a collector adapted for absorbing heat from a waste heat source; and an accumulator containing a phase change substance having a relatively high latent heat of fusion, the accumulator being in heat conductive communication with the collector and in fluid communication with the reservoir, via a portion of said fluid so that, in use, heat absorbed by the collector can be transferred to the accumulator fusing at least a portion of the phase change substance and thereafter the portion of said fluid can cool and effect solidification of at least a fraction of said portion of the phase change substance thereby releasing latent heat and heating said fluid portion.

Typically, the temperature control system further comprises a heat transfer conduit connected between the collector and the accumulator, the heat transfer conduit adapted to carry a heat transfer fluid whereby, in use, heat can be transferred from che collector to the accumulator via the heat transfer fluid. Typically, the heat transfer fluid comprises the portion of said fluid, the collector also being in fluid communication with the reservoir so that, in use, said fluid portion from the reservoir is heated via the collector and thereafter transfers heat to the phase change substance in the accumulator.

Preferably, the temperature control system further comprises a collector conduit connected between the reservoir and the collector so that, in use, said fluid portion from the reservoir can flow to the collector via the collector conduit.

In another example, the temperature control system further comprises a collector valve, located on the collector conduit, for regulating flow of the portion of said fluid to the collector whereby, in use, when the temperature of the collector is less than a first predetermined temperature the collector valve is closed wherein flow of said fluid to the collector is substantially cut off.

Typically, the temperature control system further comprises a bypass conduit connected between the collector conduit and the heat transfer conduit, or the collector conduit and the accumulator, the bypass conduit adapted to carry a controlled fraction of said fluid portion so that when the temperature of the collector is greater than a second predetermined temperature, flow of the controlled fraction of said fluid portion to the accumulator bypassing the collector is regulated.

Preferably, the flow control system further comprises a bypass valve, located on the bypass conduit, for regulating fluid flow to the accumulator to bypass the collector.

According to a second aspect of the present invention there is provided a method for controlling the temperature of a fluid in a reservoir, said method comprising the steps of: absorbing heat from a waste heat source onto a collector; heating and thus fusing at least a portion of a phase change substance, having a relatively high latent heat of fusion, contained in an accumulator using the heat absorbed by the collector; passing a portion of the fluid from the reservoir into heat conductive communication with the accumulator thus cooling and solidifying at least a fraction of said portion of the phase change substance; and transferring latent heat released from said fraction of the phase change substance to the portion of said fluid thereby heating said fluid portion.

Typically, the step of heating said portion of the phase change substance involves transferring heat to the phase change substance from the collector via a heat transfer fluid.

Preferably, the step of transferring heat to the phase change substance from the collector involves passing the portion of said fluid from the reservoir through the collector prior to passing said fluid portion into heat conductive communication with the accumulator. In this example, the heat transfer fluid comprises the portion of said fluid from the reservoir.

Preferably, the method further comprises the step of monitoring the temperature in the collector and regulating flow of the portion of said fluid to the collector at a first predetermined temperature such that, when the temperature in the collector is less than the first predetermined temperature, flow of said fluid portion to the collector is substantially cut off.

Preferably, the method further comprises the step of regulating a controlled fraction of said fluid portion flowing to the accumulator which bypasses the collector such that, when the temperature in the collector is greater than a second predetermined temperature, flow of said fluid portion to the accumulator that bypasses the collector is regulated.

Typically, the method further comprises the step of recirculating the portion of said fluid from the reservoir via the accumulator so that said fluid portion is returned to the reservoir once it has been heated by the phase change substance.

Typically, the waste heat source is sunlight.

Typically, the phase change substance has a melting-point of between 0°C to 100°C.

Typically, the phase change substance has a latent heat of fusion of greater than approximately 50 kilocalories/litre.

Typically, the phase change substance is a hydrate salt.

In one embodiment the hydrate salt comprises decahydrate sodium sulphate or a derivative thereof.

In another embodiment the accumulator contains a plurality of phase change substances each having a different predetermined melting-point wherein latent heat can be accumulated at a range of temperatures.

The temperature control system can be adapted to be used with an auxiliary application wherein latent heat from the phase change substance of the accumulator can be transferred to the auxiliary application which may involve boiling of a low boiling point fluid to then be used for producing electricity. BRIEF DESCRIPTION OF DRAWING

In order to achieve a better understanding of the nature of the present invention, preferred embodiments of the temperature control system for fluids will now be described in some detail, by way of example only, with reference to the accompanying drawing in which:

Figure 1 is a schematic diagram of a solar water temperature control system for a swimming pool.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS As shown in Figure 1, a solar water temperature control system 10 comprises a fluid reservoir, in this example a swimming pool 12 containing water, a solar collector 14, and an accumulator 16.

The pool 12 is coupled to and in fluid communication with the solar collector 14 via a collector conduit or an upstream flow line 18. The upstream flow line 18 has a filter 20 plumbed therein for removing solids from the water. Downstream of the filter 20 there is connected a bypass conduit or flow line 22. A collector valve, in this embodiment a solenoid collector valve 24, is located in the upstream flow line 18 downstream of the connection of the bypass flow line 22 thereto. A solenoid bypass valve 26, is located in the bypass flow line 22.

An inlet of the solar collector 14 is connected to the upstream flow line 18 at a downstream end thereof. An outlet of the solar collector 14 is connected to a heat transfer conduit or an accumulator flow line 28 at an upstream end thereof. The accumulator flow line 28 is connected at a downstream end to an inlet of the accumulator 16. The bypass flow line 22 at a downstream end thereof connects to the accumulator flow line 28. An outlet of the accumulator 16 is coupled to and in fluid communication with the pool 12 via a downstream flow line 30. The temperature of water in the solar collector 14 is monitored by an appropriate sensor (not illustrated) , such as a thermocouple sensor, electrically connected to a controller 31. The controller 31 has two electrical outputs connected to the solenoid collector valve 24 and solenoid bypass 26 valve, respectively. The controller 31 can be programmed to control the valves responsive to the temperature sensor wherein each valve 24, 26 is actuated or regulated at a predetermined temperature set point.

The solar collector 14 of this embodiment of the invention may take various configurations. One type of solar collector 14 which can be used comprises a collector tube laid, in a serpentine-type configuration, on a heat insulated base. The tube carries an appropriate heat exchange fluid, in this example recirculated pool water. The collector tube is then set in concrete. An upper surface of the concrete is coated with a heat absorbent layer having a low reflectivity and radiation. In this example the heat absorbent layer is a coating consisting of a bitumen/latex product sold under the trade mark IMPERSPRAY.

The accumulator 16, of this embodiment, comprises a plurality of cells 32 mixed within and evenly dispersed through a concrete structure 34. Each of the cells 32, in this example, is extruded from a polyethylene material and filled under vacuum with a phase change substance having a high latent heat of fusion. It is preferable that each cell has an internal volume of not greater than 1 litre (1) . In this example the phase change substance is the hydrate salt decahydrate sodium sulphate, having a melting-point of approximately 32 degrees Celsius (°C) and a latent heat of fusion of 85 kilocalories/litre (kcal/1) .

Various phase change substances, each having a high latent heat of fusion, can be used in the accumulator 16 depending on the particular application. For example, where hot water is required for sanitary purposes, heptahydrate bisodium phosphate may be used having a melting-point of approximately 48°C.

The accumulator 16, in this embodiment, further comprises a serpentine-type arrangement of at least one heat transfer tube set in the concrete structure 34. Where there is more than one tube they are each, at an inlet and outlet end, connected to the accumulator 16 at the inlet and outlet thereof, respectively.

Alternatively the accumulator 16 may comprise a sealed reservoir containing a heat transfer fluid in which a plurality of cells, containing a phase change substance, are suspended. The heat transfer fluid may be recirculated through the solar collector 14. The pool water, for example, will then circulate through a heat exchange tube contained in the accumulator 16 and heat may be transferred to or from the pool water via the heat transfer fluid.

In particularly hot climates where the temperature of the pool water is greater than the melting-point of the phase change substance, the phase change substances contained in the accumulator 16 may for extended periods be in a liquid state. Another process stream containing water or a low boiling-point fluid may then be used to cool the phase change substance. The latent heat of the phase change substance will then heat the water or low boiling point fluid which can be used in, for example, a greenhouse, or possibly for generating electricity. Advantageously the phase change substance when it subsequently fuses or melts then absorbs heat from the pool water thus lowering its temperature. The accumulator 16 may be cooled by other means wherein the phase change substance solidifies.

The accumulator 16 may contain banks of phase change substances each of a different predetermined melting-point. For example, the acctimulator 16 may contain a first bank of a decahydrate sodium sulphate salt, having a melting-point of approximately 32°C, adjacent a second bank of a dodecahydrate bisodium phosphate salt, having a melting-point of approximately 36°C. When the temperature of the solar collector 14 is consistently greater than 32°C the latent heat of the dodecahydrate bisodium phosphate salt of the second bank can be used by another process stream.

Alternatively a secondary accumulator may contain the second bank of the dodecahydrate bisodium phosphate salt which is used to transfer latent heat via a heat transfer fluid to the first bank of decahydrate sodium sulphate salts. This can occur during cold periods when the solar collector 14 cannot provide sufficient heat to fuse or melt the first bank of hydrate salts contained in the accumulator 16.

Operation of the solar temperature control system 10 described above will now be explained in some detail. Pool water is recirculated through the pool 12, solar collector 14, and accumulator 16 via the adjoining flow lines. When the temperature in the solar collector 14 is greater than a predetermined set-point, for example 20°C, the collector valve 24 is opened and the bypass valve 26 closed by the controller 31. When the temperature in the solar collector 14 is less than the set-point, for example during winter, on cool or overcast days, and at night, the collector valve 24 is closed and the bypass valve 26 opened.

As the solar collector 14 absorbs sunlight and heats up, heat is transferred to the phase change substance contained in the accumulator 16 via the recirculated pool water, or in another embodiment via the heat transfer fluid, thereby fusing or melting the phase change substance. The recirculated pool water then cools and solidifies a fraction of the phase change substance and the latent heat thereof transfers heat to the pool water which flows to the pool 12. As the atmospheric temperature falls the pool water temperature may also fall. When the temperature in the solar collector 14 falls below the predetermined set-point the pool water bypasses the solar collector 14 and recirculates through the accumulator 16. Latent heat from the phase change substance is then transferred to the recirculated pool water.

Now that preferred embodiments of the present invention have been described in some detail, it will be apparent to persons skilled in the relevant art that the temperature control system for fluids according to the present invention has at least the following advantages:

1) A fluid can be maintained at a predetermined temperature without the use of an electric booster;

2) An acctimulator containing a phase change substance having a relatively high latent heat of fusion or melting can be used for heating or cooling fluids substantially all year- round;

3) The fluid temperature control system can be adapted to be used with other applications such as in a greenhouse or in aquacultural applications, where temperature control may be required; and

4) Various phase change substances can be used for applications where fluid of different temperatures is required.

It will be apparent to persons skilled in the relevant art that numerous variations and modifications can be made to the temperature control system for fluids in addition to those already mentioned above without departing from the basic inventive concepts of the present invention. For example, the system may be used to heat or cool a fluid for any application and is not restricted to a swimming pool as herein described. The system may be used to heat a fluid, either a liquid or a gas, in industrial applications such as in a mineral processing or beneficiation plant where heated water may be required. In these applications, unlike the system described, the water is not recirculated through the reservoir via the accumulator. Furthermore, various phase change substances having a relatively high latent heat of fusion or melting can be used and the invention is not restricted to those hydrate salts disclosed herein. The solar collector described may be substituted by any form of collector for heat such as that obtained from a waste heat or process stream. Different heat transfer fluids may be used to exchange heat between the collector and accumulator and this may not in fact be the fluid which is to be heated as described in the possible embodiment above. The collector valve and bypass valve may be regulated, using the controller, at different predetermined temperatures rather than the same temperature set point as described above. Furthermore, the flow of recirculated fluid may be regulated rather than shut-off as described. All such variations and modifications are considered to be within the scope of the present invention, the nature of which is to be determined from the foregoing description.

Claims

CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A temperature control system for a fluid in a reservoir, the system comprising: a collector adapted for absorbing heat from a waste heat source; and an accumulator containing a phase change substance having a relatively high latent heat of fusion, the accumulator being in heat conductive communication with the collector and in fluid communication with the reservoir, via a portion of said fluid so that, in use, heat absorbed by the collector can be transferred to the accumulator fusing at least a portion of the phase change substance and thereafter the portion of said fluid can cool and effect solidification of at least a fraction of said portion of the phase change substance thereby releasing latent heat and heating said fluid portion.

2. A temperature control system as defined in claim 1 further comprising a heat transfer conduit connected between the collector and the accumulator, the heat transfer conduit adapted to carry a heat transfer fluid whereby, in use, heat can be transferred from the collector to the accumulator via the heat transfer fluid.

3. A temperature control system as defined in claim 2 wherein the heat transfer fluid comprises the portion of said fluid, the collector also being in fluid communication with the reservoir so that, in use, said fluid portion from the reservoir is heated via the collector and thereafter transfers heat to the phase change substance in the accumulator.

4. A temperature control system as defined in claim 3 further comprising a collector conduit connected between the reservoir and the collector so that, in use, said fluid portion from the reservoir can flow to the collector via the collector conduit.

5. A temperature control system as defined in claim 4 further comprising a bypass conduit connected between the collector conduit and the heat transfer conduit, or the collector conduit and the accumulator, the bypass conduit adapted to carry a controlled fraction of said fluid portion so that when the temperature of the collector is greater than a second predetermined temperature, flow of the controlled fraction of said fluid portion to the accumulator bypassing the collector is regulated.

6. A temperature control system as defined in claim 5 further comprising a bypass valve, located on the bypass conduit, for regulating fluid flow to the accumulator to bypass the collector.

7. A method for controlling the temperature of a fluid in a reservoir, said method comprising the steps of: absorbing heat from a waste heat source onto a collector; heating and thus fusing at least a portion of a phase change substance, having a relatively high latent heat of fusion, contained in an accumulator using the heat absorbed by the collector; passing a portion of the fluid from the reservoir into heat conductive communication with the accumulator thus cooling and solidifying at least a fraction of said portion of the phase change substance; and transferring latent heat released from said fraction of the phase change substance to the portion of said fluid thereby heating said fluid portion.

8. A method for controlling the temperature of a fluid in a reservoir as defined in claim 7 wherein the step of heating said portion of the phase change substance involves transferring heat to the phase change substance from the collector via a heat transfer fluid.

9. A method for controlling the temperature of a flui in a reservoir as defined in claim 8 wherein the step o transferring heat to the phase change substance from th collector involves passing the portion of said fluid from th reservoir through the collector prior to passing said flui portion into heat conductive communication with th acctimulator.

10. A method for controlling the temperature of a flui in a reservoir as defined in claim 9 further comprising th step of monitoring the temperature in the collector an regulating flow of the portion of said liquid to th collector at a first predetermined temperature such that, when the temperature in the collector is less than the firs predetermined temperature, flow of said fluid portion to th collector is substantially cut off.

11. A method for controlling the temperature of a flui in a reservoir as defined in either claim 9 or 10 furthe comprising the step of regulating a controlled fraction o said fluid portion flowing to the acctimulator which bypasse the collector such that, when the temperature in th collector is greater than a second predetermined temperature, the flow of said fluid portion to the accumulator tha bypasses the collector is regulated.

12. A method for controlling the temperature of a flui in a reservoir as defined in any one of claims 7 to 1 wherein the method further comprises the step o recirculating the portion of said fluid from the reservoi via the acctimulator so that said fluid portion is returned t the reservoir once it has been heated by the phase chang substance.

13. A temperature control system or method fo controlling the temperature of a fluid in a reservoir a defined in any one of the preceding claims wherein the wast heat source is sunlight.

14. A temperature control system or method for controlling the temperature of a fluid in a reservoir as defined in any one of the preceding claims wherein the phase change substance has a melting-point of between 0°C to 100°C.

15. A temperature control system or method for controlling the temperature of a fluid in a reservoir as defined in any one of the preceding claims wherein the phase change substance has a latent heat of fusion of greater than approximately 50 kilocalories/litre.

16. A temperature control system or method for controlling the temperature of a fluid in a reservoir as defined in any one of the preceding claims wherein the phase change substance is a hydrate salt.

17. A temperature control system or method for controlling the temperature of a fluid in a reservoir as defined in claim 14 wherein the hydrate salt comprises decahydrate sodium sulphate or a derivative thereof.

18. A temperature control system or method for controlling the temperature of a fluid in a reservoir as defined in any one of the preceding claims wherein the accumulator contains a plurality of phase change substances each having a different predetermined melting-point wherein latent heat can be accumulated at a range of temperatures.

19. A temperature control system or method for controlling the temperature of a fluid in a reservoir as defined in any one of the preceding claims wherein latent heat from the phase change substance of the accumulator can be transferred to the auxiliary application which may involve boiling of a low boiling point fluid to then be used for producing electricity.