The invention relates to a means of controlling the temperature of a solar collector. In particular the invention relates to an apparatus which controls the exposure of sun upon the solar collector

Background Ar

The following discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.

One application of the invention relates to solar water heaters. In the case of solar water heaters the uncontrolled absorption of solar heat by a solar collector generally results in excessive heating of the systems primary heat transfer fluid, typically water. During times of high solar insolation and low or no demand on the stored hot water and, the temperature in the system will continue to rise to its stagnation point which, in the case of solar tubes, cap be in excess of 250°C. The excessive heat and the cycling of the temperature gradients often damages the systems components, and/or creates an unsafe set of conditions for the user e.g. excessively heated water. In addition the likelihood of the water being over heated has required the application of a number of requirements to ensure that the users are not endangered by the excessively heated water. Such requirements can, for example, include the control of the water being delivered to a hot water outlet to ensure that it is delivered at a safe temperature. The excessive heating can also result in the vaporisation of the heat exchange medium passing through the solar collector and/or chemical reactions within the heating medium, resulting in scaling or the precipitation of solids from the liquid.

As a result of these deficiencies it is common practice to accommodate or limit excessive heating by 'under-designing' a solar water heating systems capabilities thus avoiding the excessive temperatures at times when the solar insolation is high. While this addresses the issue of excessively heated water, an under- designed system will underperform on those days of low solar insolation.

The present invention is a development on a current form of a temperature control apparatus which is disclosed in the applicant's international application WO 2009/086603, and which is incorporated herein by reference. The invention disclosed in the International application provides temperature control in the form of a shield which is adapted to shield the solar collector from the sun. This system works well but may encounter inherent difficulties when the solar collector is blocked or covered, as may be the case in areas of snow and ice.

The invention has particular application to solar collectors which utilise a "solar tube". Whilst solar tubes are very effective and efficient in the collection of solar energy they do present a problem resulting from stagnation as outlined above. This can particularly be the case in climates which are subject to a high degree of solar insolation.

Disclosure of the Invention

Throughout the specification and claims, unless the context requires otherwise the term "solar tube" shall be taken as comprising a single walled tube enclosing a closed space, the tube having two ends and a generally circular cross section wherein the closed space has been evacuated and is intended in use to accommodate a medium to be heated. The medium may be contained in a heat exchange device. Such a device may be in the form of a heat exchanger or may be in the form of a liquid, or similar device which enables the heat to be absorbed and used in a useful way.

Accordingly the invention resides in a temperature control apparatus intended for use with a solar collector, the solar collector comprising at least one solar tube, the interior of the solar tube in use accommodating a heat exchange device, the temperature control apparatus comprising a longitudinal member located in a closed space of the at least one solar tube, the longitudinal member being rotatably supported about the heat exchange device so as to be positioned between a first position and a second position, to shield, reflect or expose the heat exchange device to solar insolation, depending upon the required temperature of the heat exchange device.

Accordingly the invention further resides in a temperature control apparatus intended for use with in a solar tube, the interior of the solar tube in use accommodating a heat exchange device, the temperature control apparatus comprising a longitudinal member located in a closed space of the at least one solar tube, the longitudinal member being rotatably supported about the heat exchange device so as to be positioned between a first position and a second position, to shield, reflect or expose the heat exchange device to solar insolation, depending upon the required temperature of the heat exchange device.

As the moving components of the temperature control apparatus are housed within the solar tube, the external condition of the solar tube will have no bearing on the ability to move and adjust the longitudinal member, and therefore regulate the temperature of the heat exchange device.

Preferably the temperature control apparatus also comprises a controller having a sensor adapted to sense the temperature of a base medium. The base medium may be provided by the heat exchange device or a heat storage reservoir which is in communication with the solar tube. The sensor therefore monitors the temperature of the solar tube/solar collector.

Preferably the temperature control apparatus also comprises a drive operatively controlled by the controller to cause rotation of the longitudinal member between the first positions and the second position to shield. The drive may cause rotation of the longitudinal member around the heat exchange device

Preferably the longitudinal member extends for at least a portion of the length of the solar tube. The longitudinal member may'have an angular extent sufficient to extend partially around the heat exchange device,

Preferably, when in the first position the longitudinal member is at its furthest position to the source of radiation.

Preferably, when in the second position the longitudinal member is at its closest position to the source of radiation. Preferably the longitudinal member is rotatable about the central axis of the solar tube to a range of positions.

Preferably the longitudinal member has a parabolic cross section.

Preferably the longitudinal member is a combination of a shield and a reflector.

The shield may be provided by the convex face of the longitudinal member and is adapted to shield the heat, exchange device from solar radiation. The shield may be reflective of solar radiation.

The shield may be located in close proximity to the inner face of the tube wall. ,

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The reflector may be provided by the concave face of the longitudinal member and is adapted to reflect solar radiation onto the heat exchange device. This will allow a greater proportion of solar radiation entering the solar tube to be used to provide energy to the heat exchange device. Without the reflector a large portion of the solar energy would pass through the solar tube without impinging upon the heat exchange device.

The curvature of the concave face may differ to the curvature of the convex face.

The reflector may also be adapted to reflect solar radiation onto the surrounding environment. By being able to reflect the solar radiation on the surrounding environment it enables the reflector to reflect energy on any snow or ice covering the solar collector. This will enable the solar collector to reach optimum operational conditions quickly.

Preferably the reflector focus's a vast proportion of the solar radiation impinging thereupon on a focus axis extending along the longitudinal extent of the reflector. Preferably the reflector is orientated with respect to the heat exchange device such that in at least one position of the longitudinal member the focus axis is coaxial with the axis of the heat exchange device. The at least one position may vary according to the relative position of the heat source.

The control apparatus may track the sun. Due to the presence of the reflector and its ability to be positioned in a manner whereby it tracks the sun, solar radiation which would otherwise not impact directly upon the heat exchange device can be captured by the reflector and reflected upon the heat exchange device. As a result the efficiency of the solar collector increases, or to consider it from a different point, the output of each solar tube is greater than a solar collector having solar tubes without a longitudinal member incorporating a reflector. Preferably the longitudinal member extends for substantially the full length of the solar tube.

Preferably the longitudinal member is supported so as to be angularly displaceable relative to the heat exchange device. The longitudinal member may be supported in the closed space by at least one support. Preferably there are two supports, one at either end of the solar tube. Preferably the longitudinal member and the at least one support are slidingly received in the tube.

The at least one support may be in the form of a disc having a diameter smaller than the glass tube and having a hole cut therein for receiving a portion of the heat exchange device.

The at least one support may have a slot in a face thereof for receiving and supporting an edge of the longitudinal member.

The at least one support may support a first set of magnets. The solar tube may have an at least one annular ring secured to an outside surface of the tube wall, whereby once assembled, the at least one annular ring aligns with the at least one support.

The annular ring may support a second set of magnets.

The first set of magnets may be in operative communication with the second set of magnets to enable the control of the angular position of the longitudinal member with respect to the heat exchange device by causing the at least one support to rotate which in turn moves the longitudinal member. In this regard the first set of magnets and second set of magnets form part of the drive. Preferably the outer annular ring and the inner support are magnetically coupled when the electro-magnets are energized.

Preferably one set of magnets are permanent type magnets whilst the other set of magnets are electro-magnets. Preferably one set of magnets are angular spaced such that the angles between magnets in that set are not evenly spaced. In such an arrangement the drive operates in a similar manner as a step motor in order to vary the angular position of the longitudinal member.

In an alternative embodiment of the invention the longitudinal member may be integral with the solar tube of the solar collector whereby an outer face provides the shield and an inner face provides a reflector the drive being operatively _. connected to the solar tube so as to be rotatable between the first position and the second position.

The outer face on the solar tube may be treated to be opaque to solar radiation. The shield may comprise a coating applied to the solar tube. According to an alternative preferred feature of the invention the coating comprises a tape which is adhered to the solar tube. According to an alternative preferred feature of the invention the coating comprises a film applied to the solar tube. .

According to an alternative preferred feature of the invention the one end of the solar tube is the open end, whereby upon receiving the longitudinal member and at least one support therein the at least one support seals the solar tube.

In other embodiments of the invention the drive comprises a toothed formation provided in association with the longitudinal member, the toothed formation being engaged with a threaded pinion which is caused to rotate to cause the rotation of the longitudinal member. Preferably the drive, comprises a toothed sprocket provided on a drive shaft and the toothed formation is provided by a further toothed sprocket, the drive further comprising an endless chain which drivingly interconnects with the sprockets.

Preferably the drive includes an element which is subjected to the temperature conditions which are representative of the temperature: conditions of the heat exchange device accommodated within the interior of the solar tube and wherein the element will undergo longitudinal expansion and contraction resulting from temperature change, the element providing the sensor of the controller.

Preferably in one embodiment the drive includes an electric motor. Preferably the electrical power to the electrical motor is derived from a photoelectric device. Preferably the photoelectric device is connected to an electrical storage battery. The motor is driven from the battery and/or the photoelectric device.

The invention may cover those solar tubes comprising a dual walled tube having two ends and a generally circular cross section wherein the dual walls define between themselves a closed space which has been evacuated and the interior of the tube is intended in use to accommodate a medium to be heated which can comprise a fluid and/or a heat exchanger or a like means which is to be heated whereby the longitudinal member is located internally either in the closed space of the inner tube, or in the space between the two walls. Accordingly the invention further provides a temperature control apparatus intended for use with a solar collector, the solar collector comprising one or more of the solar tubes as herein before described.

Accordingly the invention further provides a temperature control apparatus intended for use with a solar collector, the solar collector comprising at least one solar tube, the interior of the solar tube in use accommodating a heat exchange device, the temperature control apparatus comprising: a longitudinal member located in a closed space of the solar tube and extending for at least a portion of the length of the solar tube, the longitudinal member having an angular extent sufficient to extend partially around the heat exchange device, the longitudinal member being rotatably supported about the heat exchange device between a first position and a second position, and a controller comprising a sensor adapted to sense the temperature of the heat exchange device, a drive operatively controlled by the controller to cause rotation of the . longitudinal member around the heat exchange device between a first position and a second position to shield, reflect or expose the heat exchange device to solar insolation, depending upon the required temperature of the heat exchange device. The invention will be more fully understood in light of the following description of several specific embodiments.

Brief Description of the Drawings

The invention will be better understood by reference to the following description of a specific embodiment thereof as shown in the accompanying drawings in which: Figure 1 is the general isometric view of a solar collector incorporating a temperature control apparatus according to a first embodiment;

Figure 2 is a cross sectional isometric view of an end of a solar tube according to the first embodiment; Figure 3 is a cross sectional isometric view of another end of a solar tube showing a longitudinal member acting as a reflector with respect to a heat exchange device according to the first embodiment;

Figure 4 is a cross sectional isometric view similar to figure 3 but with the longitudinal member shielding ^' the heat exchange device;

Figure 5 sectional isometric view of a longitudinal member and drive of the first embodiment;

Figure 6 is an exploded isometric view of the longitudinal member and a support according to the first embodiment Detailed Description of Specific Embodiments

According to a first embodiment, the present invention is in the form of a temperature control apparatus incorporated in a solar tube 11. Figure 1 illustrates an application of the first embodiment whereby a set of solar tubes 11 provides a solar collector 12. The set of solar tubes 11 are supported from a support base 3 in a substantially parallel relationship with respect to each other.

The support base 13 provides a first housing 15 from which an end of each solar tube is supported, and a set of upstanding supports 17 which receive and support the other end of each solar tube 11. The support for the solar tubes is such that the solar tubes are fixed in place. Referring to figures 2 to 5 each solar tube comprises a single walled tube 23 which, once assembled, is closed at both ends to define a closed space 25. The closed space is evacuated. Each solar tube 11 has a heat exchange device 27 supported therein along the central axis of the solar tube 11. The temperature control apparatus 19 comprises a longitudinal member 21 supported by two supports 29 located adjacent each end of the single walled tube 23, all of which are slidingly received in the solar tube before it is closed.

The longitudinal member is supported at each end in a slot 31 incorporated in a face of the support 29. Each support 29 is circular and receives a portion of the heat exchange device 27 through the centre thereof.

A square section 26 of the support 29 locks into a beam section 28 on the longitudinal member 21 to provide torsional strength so that the longitudinal member can be driven from one end. The longitudinal member 21 has a parabolic cross section whereby a concave face of the longitudinal member 21 provides a reflector 33 whilst a convex face of the longitudinal member 21 provides a shield 35,

The longitudinal member 21 is rotatably moveable about the heat exchange device 27 whereby the longitudinal member 21 may be angularly displaced between a first position and a second position relative to the heat exchange device 27. The position of the longitudinal member 21 relative to the heat exchange device 27 is largely governed by the temperature requirement of the system. In order to determine the position of the longitudinal member 21 to optimise performance and maintain the required energy absorbing area, the temperature control apparatus considers the relative position of the sun, the temperature of the heat energy being absorbed, and the surrounding conditions. In this regard the temperature control apparatus incorporates a sensor which feeds data in to the system. When certain conditions are meet (e.g. water is becoming over heated), the drive is activated to operably position the longitudinal member 21 at the required angular position.

In this embodiment the longitudinal member 21 is rotated using a drive which operates in a similar manner as a step motor. In this regard each support 29 has a first set of permanent magnets 37 angularly spaced around the outside of the support 29, in a non-uniform manner. A second set of magnets 39 are located in an annular ring 41 secured to an outer wall of the solar tube 11. The annular ring 41 is positioned such that when the solar tube 11 is assembled an annular ring 41 aligns with each support 29. The second set of magnets 39 is electromagnetic, allowing the drive to energise the appropriate magnet/s in order to rotatably move the magnets and therefore accurately position the longitudinal member 21 relative to the heat exchange device 27

In an alternative embodiment the longitudinal member 21 may be rotated using a mechanical system whereby the longitudinal member 21 is connected to a shaft extending from the solar tube 1 , the shaft being connected to the mechanical system such as a geared arrangement, for indirectly positioning the longitudinal member 21.

In operation and under a solar collecting mode the longitudinal member is located such that it is in a position most remote from the source of solar radiation whereby the heat exchanger device and reflector are fully exposed to the solar radiation. In this position the reflector 33 focus' the solar radiation which passes the heat exchange device 27 and reflects it back thereon. This increases the efficiency of the solar tube 11. The reflector 33 serves to maximise the collection of solar radiation which is incident on the solar tube 11 when the longitudinal member 21 is in its remote position. In prior art solar tubes which do not have a longitudinal member 21 the solar radiation which is incident on the space between the walls of the solar tube will not be collected. The presence of the reflector 33 in the present invention serves to reflect and focus such solar radiation on to the heat exchanger 27.

In the event that the heat exchange device 27 or a heat reservoir in communication with the solar collector is heated to an undesirable temperature the control causes activation of the drive system which will in turn cause rotation of the longitudinal member 21 to a position at which the longitudinal member 21 overlies at least a portion of the solar tube 11 to reduce the amount of solar radiation which is incident upon the inner wall of the solar tube. In practice a misalignment of the reflector of 20 degree or so will almost totally stop the heating process.

The degree of rotation of the longitudinal member 21 will depend upon the degree of overheating of the medium contained within the solar tube. Under the most extreme conditions the longitudinal member 21 will occupy a position fully overlying the solar tube to prevent the incidence of any solar radiation on the solar tube. The reflective nature of the shield of the longitudinal member 21 will ensure that when the longitudinal member 21 is overlying the solar tube any solar radiation incident thereon will be reflected and the degree of heating of the solar tube will be minimised.

The present invention is not to be limited in scope by any of the specific embodiments described herein. These embodiments are intended for the purpose of exemplification only. Functionally equivalent products, structures and methods are clearly within the scope of the invention as described herein.

Throughout the specification and claims, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.