OVERTEMPERATURE PROTECTION SYSTEM FOR A SOLAR WATER HEATING SYSTEM
The invention provides a solar hot water heating system including one or more solar energy absorbers (102) having at least a first fluid circulation path wherein, an over temperature path (119) is provided, the over temperature path including a pressure vessel (120) which is normally closed to atmosphere, the over temperature path being connected to the first fluid circulation path (108) so that, in the event that fluid in the solar energy absorber vaporizes, the fluid is forced out of the solar energy absorber and into the pressure vessel. The present invention also provides a temperature sensitive valve leaving a flow path and a valve member operated by a thermal element having thermal expansion characteristic the valve including a support member against which the thermal element expands to force the valve element to close the flow path.
This invention relates to an arrangement for dealing with the effects of overheating in solar water heating systems.
BACKGROUND OF THE INVENTIONSolar water heating systems include a solar collector which acts to convert solar radiation to heat energy to heat water. Usually this involves a solar panel having a heat transfer fluid which absorbs the solar energy, the heat from the heat transfer fluid being transferred to the water via a heat exchanger. The heat transfer fluid may be water with additives. Solar energy is an unregulated source of input heat energy. Thus, there is a possibility that the heat transfer fluid will boil if the rate of energy input from the solar energy exceeds the rate of heat removal from the heat transfer fluid. Boiling of the heat transfer fluid may damage the solar water heating system due to excessive pressure.
Any reference herein to known prior art does not, unless the contrary indication appears, constitute an admission that such prior art is commonly known by those skilled in the art to which the invention relates, at the priority date of this application.
SUMMARY OF THE INVENTIONThe present invention provides a solar hot water heating system including one or more solar energy absorbers having at least a first fluid circulation path wherein, an overtemperature path is provided, the overtemperature path including a pressure vessel which is normally closed to atmosphere, the overtemperature path being connected to the first fluid circulation path so that, in the event that fluid in the solar energy absorber vaporizes, the fluid is forced out of the solar energy absorber and into the pressure vessel.
The present invention also provides a solar hot water heating system including one or more solar energy absorbers having a heat transfer fluid circulation path, therethrough, the heat transfer fluid circulation path including a heat exchanger, wherein, an overtemperature path is provided, the overtemperature path including a pressure vessel which is normally closed to atmosphere, the overtemperature path being connected to the heat transfer fluid circulation path so that, when heat transfer fluid in the solar energy absorber vaporizes, the, heat transfer fluid is forced out of the solar energy absorber and into the pressure vessel.
The heat transfer fluid circulation path can include a valve arranged to facilitate the evacuation of heat transfer fluid from the solar energy absorber under the pressure from evaporated heat transfer fluid in the solar collector.
The valve can be a one way valve.
The valve can be a pressure actuated valve.
The valve can be a temperature actuated valve.
The valve can be a controllable valve.
The heat transfer fluid entering the pressure vessel can increase the pressure in the pressure vessel, so that, when the temperature of the heat transfer fluid vapour in the solar collector falls below the vaporization temperature, the pressure in the pressure vessel forces the heat transfer fluid back into the heat transfer fluid circulation path and the solar energy collector is replenished with heat transfer fluid.
The overtemperature path can include a pressure relief valve.
The pressure vessel can have a substantially tubular shape.
The pressure vessel can be inclined at an angle to the horizontal.
The pressure vessel can include a riser.
The pressure vessel tube can be formed from a pipe suitable for use as a flue in a centrally flued hot water tank.
The present invention also provides a temperature sensitive valve having a flow path and a valve member operated by a thermal element having thermal expansion characteristic, the valve including a support member against which the thermal element expands to force the valve element to close the flow path.
The valve can include a hollow body containing wax and a piston.
The piston is spring biased to tend to compress the wax.
An embodiment or embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
The invention is applicable to systems in which potable water is heated directly in the solar panels, and to systems in which a heat transfer fluid is heated in the solar panels and then passed through a heat exchanger where the heat is transferred to the potable water. Embodiments of the invention will be described with reference to a heat transfer fluid system.
Heat exchanger 116 may consist of a water tank surrounded by a heat transfer fluid jacket. However, other heat exchanger arrangements can be used. Heat exchanger 116 has cool water inlet 114 and hot water outlet 112.
In a thermosyphoning system where the height (gravitational) differential and the thermal differential are sufficient to overcome flow resistance and produce a required flow rate, the heat transfer fluid is heated in the solar panel channels 132 and rises under convection to the header 128, passes through pipe 110 to heat exchanger 116 and returns to lower header 130 via pipe 108. A flow control device 122 controls the direction of flow between the heat exchanger 116 and the solar panel 102. The flow control device can be, for example a one-way valve or a controllable valve.
The expansion vessel 120 can be connected to the heat transfer circuit at any convenient point. It can be connected to the outlet side of the solar panels 102 as shown in
Where the gravitational and thermal differentials are not sufficient to meet the heating performance requirements by thermosyphoning, the heat transfer fluid circuit can be pump driven.
The thermal overflow vessel 120 is connected to the heat transfer fluid circuit. The overflow vessel 120 is normally sealed to atmosphere, but can be provided with a pressure relief valve to relieve pressure above a predetermined value.
The overflow vessel can be connected to the heat transfer fluid circuit in a manner which facilitates the evacuation of heat transfer fluid from the solar collector 102 when the heat transfer fluid reaches its boiling point. This can be achieved by preventing “reverse” flow of heat transfer fluid into the top of the heat exchanger 128 via pipe 110, for example by a valve 122, which may be a one way valve, a pressure operated shut-off valve, a temperature operated shut-off valve, or a controllable valve which prevents the flow of heat transfer fluid into the top of the solar panel 102 via pipe 110 when the heat transfer fluid boils.
As a consequence, when the heat transfer fluid begins to boil, the vapour will rise to the top of the solar panel 102 and also generate a significant increase in pressure. That part of the heat transfer fluid which is still in liquid form is forced out of the solar collector 102 through pipe 108 by the increased pressure. Because the overflow vessel 120 contains compressible gas, and is connected to the heat transfer fluid circuit, the heat transfer fluid forced out of the solar panel is forced into the overflow vessel 120 via pipe 108, and, in this embodiment, through heat exchanger 116. As heat transfer fluid is forced into the overflow vessel, the gas in overflow vessel 120 is compressed and this increases the pressure in the overflow vessel until it is sufficient to prevent further heat transfer fluid being forced into the overflow vessel 120. The volume of the overflow vessel 120 is selected to permit the overflow vessel to contain substantially all the heat transfer fluid in the solar collector channels with sufficient volume for the gas in the overflow vessel to be compressed to a pressure to balance the vaporization pressure. Preferably, the overflow tank can also accommodate a volume of heat transfer fluid corresponding to the volume of the upper header tank 128.
The valve 122 blocks the heat transfer fluid from being forced through pipe 110 to the top header 128 of solar panel 102.
Only a small amount of heat transfer fluid needs to vaporize to cause substantially all the heat transfer fluid to be forced out of the solar panel. When all the liquid heat transfer fluid is forced out of the solar panel, the heat absorption by the heat transfer fluid in the solar panel is substantially reduced because only vapour is contained in the solar panel.
When the overtemperature conditions are removed, the compressed gas in the overflow tank forces the heat transfer fluid back into the solar panel.
In cases where the solar panel is located above the other components of the system, the valve 122 may be dispensed with as the heat transfer fluid vapour will rise to the top and fill the solar collector, forcing the heat transfer fluid from the solar collector and preventing its return until the vaporization condition dissipates.
The heat exchanger can be located above the solar collector panels and the overflow tank can be designed with sufficient capacity to contain the volume of heat transfer fluid in the heat exchanger and in the solar panels.
The overflow tank 120 is preferably arranged to ensure that the heat transfer fluid can be returned to the heat transfer fluid circuit to recharge the solar panel. This can be done by the use of a riser pipe (c.f. 406 in
A pair of solar panels 102, 104 have their upper headers connected and feeding to the heat transfer fluid input of the heat exchanger 116 via pipe 110. The lower headers are also connected and linked to the heat transfer fluid outlet of the heat exchanger 116 via pipe 108. The solar panels 102, 104 are installed at an angle to the horizontal so that the upper headers are above the lower headers.
A heat exchanger (116 in
An overflow tank 120 is connected to the heat transfer fluid path in the heat exchanger 116 by pipe 118. This tank is effectively sealed to atmosphere, but may include a pressure relief valve to relieve pressure above a predetermined value. The overflow tank 120 is oriented with its axis at an angle to the horizontal so that the pipe connects near the lowest point of the tank and the gas will be compressed to the upper region of the tank as described above.
As seen in
Other configurations of expansion tank are possible. For example, as shown in
In a further embodiment, the tank may be spherical, with the heat transfer fluid pipe connected to the lowest point of the sphere.
In
The valve 700 includes a housing 720 which has a through bore 724 which is enlarged to form a chamber 726. The valve actuator is a thermal element 702, which is an elongate cylinder containing wax. The wax can be chosen to have a phase change at a selected temperature, such as, for example, 95° C. The wax expands rapidly at this transition temperature.
The cylinder 702 is closed at one end, and includes a piston at the other end, the shaft 714 of the piston projecting from the other end of the cylinder. The piston can be spring biased to tend to compress the wax. The cylinder 702 is attached to a valve disc 706 via a truncated conic section 707.
The piston shaft 704 projects into a blind bore 714 in a support member 710. This support member is provided with flow holes such as 712 to permit the heat transfer fluid to pass through the support member.
A closure member 722 closes the chamber 726 of the housing 720.
The housing 802 defines the chamber 826. The thermal element 802 is connected to the valve disc 806. A skirt 807 is attached to the disc 806 and provides flow apertures 808 so that heat transfer fluid can flow around the valve disc via these flow apertures. The chamber 726, 826 includes a portion of a larger diameter in than the valve disc 706, 806 in the region of the valve disc 706, 806 to permit the heat transfer fluid to flow around the edge of the valve disc 706, 806. A seal ring 818 can be provided around the periphery of valve disc 806. As seen in
In
The operation of the valve will be described with reference to
The reduced section 930 of the chamber permits over-travel of the disk 906 and skirt 907 to allow for the continued expansion of the wax after closure.
Where ever it is used, the word “comprising” is to be understood in its “open” sense, that is, in the sense of “including”, and thus not limited to its “closed” sense, that is the sense of “consisting only of”. A corresponding meaning is to be attributed to the corresponding words “comprise”, “comprised” and “comprises” where they appear.
It will be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text. All of these different combinations constitute various alternative aspects of the invention.
While particular embodiments of this invention have been described, it will be evident to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiments and examples are therefore to be considered in all respects as illustrative and not restrictive, and all modifications which would be obvious to those skilled in the art are therefore intended to be embraced therein.
Claims
1. A solar water heating system including one or more solar energy absorbers having at least a first fluid circulation path, wherein an overtemperature path is provided, the overtemperature path including a pressure vessel which is normally closed to atmosphere, the overtemperature path being connected to the first fluid circulation path so that, in the event that fluid in the solar energy absorber vaporizes, the fluid is forced out of the solar energy absorber and into the pressure vessel.
2. A solar water heating system including one or more solar energy absorbers and a heat exchanger connected in a fluid circulation path, wherein:
- an overtemperature path is provided;
- the overtemperature path including a pressure vessel which is normally closed to atmosphere;
- the overtemperature path being connected to the fluid circulation path so that, when heat transfer fluid in the solar energy absorber vaporizes, the heat transfer fluid is forced out of the solar energy absorber and into the pressure vessel.
3. A solar water heating system as claimed in claim 2, wherein the fluid circulation path includes a valve arranged to facilitate the evacuation of heat transfer fluid from the solar energy absorber under the pressure from evaporated heat transfer fluid in the solar collector.
4. A solar water heating system as claimed in claim 3, wherein the valve can be one of:
- a one way valve;
- a pressure actuated valve;
- a temperature actuated valve;
- a controllable valve; or
- a combination thereof.
5. A solar water heating system as claimed in claim 1, wherein the fluid entering the pressure vessel increases the pressure in the pressure vessel, so that, when the temperature of the fluid vapour in the solar collector falls below the vaporization temperature, the pressure in the pressure vessel forces the fluid back into the fluid circulation path and the solar energy collector is replenished with fluid.
6. A solar water heating system as claimed in claim 1, wherein the overtemperature path include a pressure relief valve.
7. A solar water heating system as claimed in claim 1, wherein the pressure vessel has a substantially tubular shape.
8. A solar water heating system as claimed in claim 1, wherein the pressure vessel is inclined at an angle to the horizontal.
9. A solar water heating system as claimed in claim 1, wherein the pressure vessel includes a riser.
10. A solar water heating system as claimed in claim 10, wherein the pressure vessel tube is formed from a pipe suitable for use as a flue in a centrally flued hot water tank.
11. A solar water heating system as claimed in claim 1, wherein the overtemperature path is connected at the to of the fluid circulation path.
12. A solar water heating system as claimed in claim 3, wherein the fluid entering the pressure vessel increases the pressure in the pressure vessel, so that, when the temperature of the fluid vapor in the solar collector falls below the vaporization temperature, the pressure in the pressure vessel forces the fluid back into the fluid circulation path and the solar energy collector is replenished with fluid.
13. A solar water heating system as claimed in claim 3, wherein the overtemperature path include a pressure relief valve.
14. A solar water heating system as claimed in claim 3, wherein the pressure vessel has a substantially tubular shape.
15. A solar water heating system as claimed in claim 3, wherein the pressure vessel is inclined at an angle to the horizontal.
16. A solar water heating system as claimed in claim 3, wherein the pressure vessel includes a riser.
17. A solar water heating system as claimed in claim 16, wherein the pressure vessel tube is formed from a pipe suitable for use as a flue in a centrally flued hot water tank.
18. A solar water heating system as claimed in claim 3, wherein the overtemperature path is connected at the top of the fluid circulation path.
19. A temperature sensitive valve having a flow path and a valve member operated by a thermal element having thermal expansion characteristic, the valve including a support member against which the thermal element expands to force the valve element to close the flow path.
20. A temperature sensitive valve as claimed in claim 19, wherein the valve includes a hollow body containing wax and a piston.
21. A temperature sensitive valve as claimed in claim 20, wherein the piston is spring biased to tend to compress the wax.
Type: Application
Filed: Jan 31, 2006
Publication Date: Mar 11, 2010
Inventors: Brendan Bourke (New South Wales), Raymond Hill (West Australia)
Application Number: 11/815,279