GB2155615A - Solar collector and heating system - Google Patents

Abstract

A heating system with a collector 3 for solar radiant energy, the collector 3 being pivotally mounted so as to be rotatable to maintain one side facing the sun, the collector 3 including a heat transfer pipe 5 (Fig. 2) as part of a set configuration of pipes fixed in relation to the collector and completing a circuit through both the collector and a heating coil 14 in a fixed insulated heat exchange vessel 7. Capacity is provided within the heat exchange vessel 7 to accommodate movements of the beating coil 14 as it pivots and rotates along with the collector 3. The pipework circuit is routed twice through the pivot region thereby avoiding the need for flexible or sliding joints. <IMAGE>

Description

SPECIFICATION Solar collector s solar heating system This invention relates to apparatus converting solar energy to a usable form for heating buildings and the transfer of heat to an exchanger vessel.

According to the present invention there is provided a solar heating system comprising a solar collector to be pivotally mounted on a supporting structure in use, for example on the roof of a house, at a most favourable angle to receive solar energy and be able to turn in order to track the apparent motion of the sun. Within said collector is housed a focussing means to concentrate the sun's rays onto at least one pipe for conveying a heat absorbing liquid to and from the interior of the collector.

Further by the invention the pipework or heat absorbing elements within the collector are able to move co-operatively with the concentrating means around a first axis of rotation and are also able to be tilted at variable angles from that axis according to the season of the year.

Whilst solar collectors that focus energy by means of plane or curved reflectors have the advantage of producing higher temperatures than flat plate collectors, it is necessary to constantly adjust position in order to maintain a stationary focus as the sun appears to move.

By this invention, a means is provided for connecting such moving collectors conveniently to a fixed heat exchange vessel.

Essentially, the heat transfer pipework is arranged so that the feed pipe to the collector passes close to, or is co-axial with, the return from the collector at the pivot point on the main axis. Below the pivot point, these two pipes complete a circuit through the heat exchange vessel. By providing sufficient capacity in the heat exchange vessel, enveloping all positions of the pipe from the solar collector, the entire configuration can rotate and pivot with the required motion of the collector without the need for flexible joints.

The collector means may comprise an insulated housing with one large side adapted to admit solar radiation onto an array of reflectors mounted within the housing. Each reflector within the array is set at an angle to the plane of said large side such that solar radiation received normal to that plane is re-directed towards at least one pipe fixed within the housing. Each pipe receives radiation from one or more reflector such that the area or width of radiation is much greater than the projected area or breadth or, in the case of a pipe of circular section, diameter of the pipe or absorbing element.

The focii of the reflectors is maintained constant by moving the collector in its housing or panel by means of an adjustable mounting or support means which is continuously driven so as to hold the collector at the most favourable angle to receive solar energy.

The drive mechanism, by virtue of its continuous non-reversible nature, is economical in it's use of power and since the rate of work is small, energy may be derived from natural sources used to re-charge a battery, compress a spring or lift a weight.

The greatest area of collector surface is presented when the sun's rays are incident normal to that surface, heat being lost according to a cosine law when rays stike the surface of the collector at an oblique angle. A tracking collector thus has a much greater efficiency than a fixed collector, and dual axis tracking is significantly more efficient than single axis tracking.

In order to track the apparent motion of the sun, the supporting framework may be rotatable about a first axis parallel to the axis of the earth's rotation, that is, inclined to the horizontal at an angle equal to the latitude of the position and tilted towards the nearest of the earth's poles, and also be pivotable about a second axis in a predetermined manner so as to compensate for the inclination of the earth's axis to the plane of its orbit, viz. 23+ .

The support framework may conveniently consist of a main spindle or rotating member, within the fixed framework, held parallel to the axis of the earth's rotation and adapted to support the collector housing to pivot at its lower end and be guided to the required tilt angle by a reciprocating mechanism acting from a second point higher on the first axis.

The rotary motion about the first axis is required to be a constant controlled angular speed of 360 per solar day. This is sufficient only at the equinoxes. A cyclic pivotal motion, approximating to simple harmonic, with a period of one solar year and an angular amplitude of 47 (that is twice 23+ ). Approximation is an essential quality in the economics of the practical application of this apparatus; circular motions are acceptable although variations are known and the reflectors may arranged to accommodate several degrees of error by focussing on the middle part of the absorber pipes.

The absorber pipework may be coated black or a colour to improve the ability to absorb heat, a surface texture or specific cross-section may also be employed, and may be made from a material of high thermal conductivity in order to transmit heat effectively to the fluid therein. Re-radiation of energy from that part of the surface of the pipework not absorbing heat may be reduced by providing a polished surface to that part or parts.

A fluid is able to circulate within a pipework circuit comprising the aforementioned at least one pipe within the collector, at least two pipes connecting the collector with the heat exchanger, and that pipework within the heat exchange vessel. The fluid flow which may be induced thermally or by external means, is to cause transfer of heat from the collector to the heat exchanger whilst energy is being received in sufficient quantity to maintain the temperature of the collector above the temperature in the heat exchanger by a margin adequate for heat transfer to take place in the required direction.

A thermostatically controlled valve may be provided to cut off or divert or short circuit communication between the at least one pipe in the collector and the pipework within the heat exchanger when received energy levels are lower than required, for instance during cloudy weather or at night.

Usually, the axis of the absober pipe within the collector will not coincide with the axis of rotation, but in one embodiment of the invention it may be possible using one large reflector or concentrating means with a single point or axis of focus so as to avoid the need for the pipework to rotate but nevertheless it may still require to be pivotable in one sense with the collector.

The solar heating system may employ a plurality of pivotable collector units; a preferred embodimet may utilise two collectors mounted either side of the main spindle or axis of rotation such that a balance is achieved against wind or other forces. The elements within each collector are nevertheless routed through the common pivot point on the main axis.

Still further according to the present invention, there is provided a solar heating system comprising a solar heat collector pivotally mounted on an adjustable support so as to track the apparent motion of the sun with at least one pipe for conveying heat absorbing fluid to and from the interior of the collector but not necessarily employing a means for focussing the sun's rays.

In a practical application, the collector may be mounted on a roof so that the heat exchanger is located closely adjacent within the roof space. The pivot point is thereby in the plane of the roof surface and minimal disturbance to the roof is required for installation.

The upper end of the main spindle would then be supported on a framework extended to the ground or founded on an adequately strong member of the roof structure.

Advantageously, only the collector is enclosed in a housing, but since it will be subjected to wind loads in use, the supporting structure and gearing must have adequate strength to hold the collector in its required position. An extensive housing over the entire structure is, however, avoided.

As an improvement to the external appearance, it may be possible to provide the necessary support from within the roof space by cantilevering the main spindle and eliminating the need for the external framework to support its upper end.

The concentrator assembly may be a plurality of reflective troughs of approximately parabolic cross-section made up of a number of contiguous flat strips of such a width as to focus onto the middle third of the diameter of the absorber element. The reflectors may conveniently be made by folding a flat sheet of adequate rigidity, for example anodised aluminium or polished stainless steel, to the required angles of the parabolic form.

The collector elements may be connected at their lower ends to a fluid inlet pipe and at their upper ends to a fluid outlet pipe so as to take advantage of any natural tendency for thermally induced flow. In the illustrations, the pipework configuration is shown, for example only, as a plurality of parallel collector elements linked at their heads by a manifold from which fluid passes to a coil within the heat exchanger. From the coil a pipe completes the circuit to a second manifold which distributes fluid to the bases of the collector elements.

The concentrator assembly, collector elements and upper and lower manifolds may be enclosed in an insulated housing one side of which is constructed of transparent cellular material, for instance, polycarbonate, or a laminated material combining the ability to transmit radiant heat and light with insulation against heat loss.

This insulated housing is fixed to the main rotating member, or spindle, at the pivot bearing and caused to rotate 360' per solar day by means of a worm or helical gear. A second worm, mounted on the spindle turns a crank by means of further gearing through one revolution in 365 solar days. Provision may be made for manual re-setting after several years. The crank drives a mechanism which tilts and holds the housing at the predetermined angle appropriate to the season of the year. The almost non-reversible quality of the worm gearing together with the large gear ratios is sufficient to prevent the collector housing being turned by wind or snow loads.

A preferred embodiment of the system may consist of two or more collector panels mounted either side of the main spindle such that a balance is achieved. The elements within each collector panel would then be routed through the common pivot point on the main spindle.

According to a further aspect of the invention, if required, the circulating pump can be driven from the daily rotation of the main spindle and advantageously, if situated at the pivot, again no flexible joints are necessary.

Whilst the volume of the heat absorbing fluid is kept to a minimum to reduce heat loss from re radiation during discontinuity of heat input, it may be necessary to make provision for thermal expansion within the pipework circuit. A chamber containing compressible gas or fluid is connected, the volume being proportional to the amount of fluid in the circuit.

The invention is not limited solely to use as a heater and could equally be used in an air conditioning or cooling system.

An embodiment of solar connector and solar heating system in according with the invention will now be described, by way of example only, with reference to the following drawings, in which: Figure 1 shows diagrammatically a sectional view of a solar heating system mounted on the roof of a house.

Figure 2 shows the front view of a preferred solar collector in its insulated housing (support means omitted for clarity).

Figure 3 shows a section through the colector in Fig. 2 looking in the direction of arrow A.

Figure 4 shows a perspective view of a system in use with sections cut away to indicate working parts.

Figure 5 shows details of the lower spindle bearing and pivot housing Figure 6 shows diagrammatically the operation of the crank and linkage.

Figure 7 shows a typical pipework configuration.

Figure 8 shows the cross-section through a preferred reflector.

Figure 9 shows an alternative profile for a collector housing.

Referring to the diagrammatic sectional view (Fig. 1) the collector housing (3) is shown with its large face in the plane of the paper, mounted on a roof (2) of a building.

Daily rotation about the axis (X) is indicated by the arrow X1. Mid-day positions at the summer and winter solstices are indicated by (S) and (W) respctively. As shown, the apparatus is assumed to be in the northern hemisphere, since the direction 'north' is indicated.

For use in the southern hemisphere the direction note would read 'south'.

The main axis (X) is inclined to the horizontal at the angle a" where a is the latitude of the location of the apparatus. The collector will rotate parallel to this axis at the equinoxes.

The collector housing (3) in Fig. 1, is able to both rotate about the axis (X) and also pivot about the point (Y) in a north-south direction.

Moving in co-operation with the collector is the heating coil (14) which is provided with enough space in the exchange vessel (7), to move in a conical fashion and remain below the water level.

Below the line (1) is in shadow in winter, so the base of the panel is not extended below it.

The area of the roof marked (4) may be required as support for an external framework, provided that suitable bearing points can be found.

Preferred details of the collector means are shown in Figs. 2 and 3. Within the collector housing (3) are provided a plurality of pipes (5) for absorbing heat, and two pipes (10 eft 11) for conveying heat absorbing fluid to and from the interior of the collector, together with the array of reflectors (6) which focus onto the pipes (5). Insulation (9) is provided on all sides except one large side which is enclosed by a double layer of transparent material (8), for example, perspex, polycarbonate, or glass, or a clear cellular sheet may be used. The pipes (10 s & 11) are preferably enclosed inside the hollow spindle (12) used to support the collector housing.

An alternative housing profile is indicated in Fig. 9 wherein variable width reflectors are employed (6') necessitating variable diameter pipes (5') to avoid uncontrolled thermosyphonic effects due to unequal heating. The tapered and rounded profile has the advantage of being more aerodynamic and presenting less resistance to the wind.

By means of the two axes of movement (X,Y) the collector may be turned to any angle, but more particularly, it is possible to track the sun mechanically by rotating 360 per solar day about the axis (X) and pivoting 23+ alternately to north or south about the axis (Y) in a cyclical manner lasting 365 solar days before repeating.

Rotation about the axis (X) may be achieved by any convenient drive means; the electric motor (24) shown in Fig. 4 operates intermittently to compress a spring within the casing (25). Final drive to the worm (18) and wormgear (19) is time controlled so that the main spindle through the pivot housing (12) is turned continuously at the correct angular rate.

The annual cycle of pivotting about the axis (Y) is caused by means of a double crank (13) fixed at its fulcrum to the spindle (12).

The crank (13) in Fig. 6 is geared from the rotating spindle to turn 360 in 365 days and operate by means of a second worm and gear (16) and a chain drive. The outer ends of the crank arms run in two slides (17) connected through a parallel motion linkage to the collector housing (3). Operation of this mechanism is diagrammatically shown in Fig. 6 and also illustrated in Fig. 4.

When the crank arms (13) are parallel to the axis X the main beam (20) of the parallel linkage and the collector housing are also parallel. This is the position required at the equinoxes. The fixed arm (21) and the trailing links (22) are parallel to each other throughout and the connection points (23) on the sliding frame (1 7) to the linkage beam (20) and the collector also form parallelograms.

Division of the main beam (20) is calculated to cause the collector to be 23+ to the axis X when the crank is square to main spindle.

This is the position required at the summer and winter solstices.

Whilst the pivot point Y is arranged for convenience at the base of the collector and has many advantages, it is not possible to locate all the bearings, gears, drives means and also route moving pipework through one point. A housing (28) as shown in Fig. 5 may be formed as part of the spindle (12) to provide the necessary accommodation.

In a similar way, increasing the dimension h on the trunnion frame (32) affects the size of housing (28) in the direction perpendicular to the plane of the drawing (Fig. 5). It will also be seen that the bearings (33) permitting movement of the trunnion (32) about axis Y do themselves rotate with the housing about axis X and hence must clear the fixed drive chain (26) and the sprocket and worm (18) as well as the roof surface (2). Rather than increase dimension h to provide clearance beneath the base of the collectors a spacer frame (34) may be fixed to the trunnion frame (32).

The extension (31) to the roof of the fixed vessel, shown in Fig. 5, supports the lower spindle bearing (30) and accommodates the conical motion of pipes (10, 11). As the angle of the trunnion (32) increases up to the maximum 23it, the cone of revolution of these two pipes becomes wider accordingly.

Within the housing (28), the space (27) may conveniently be used to locate a circulating pump which may then be driven by gearing from the same drive means as is provided to cause rotation of the main spindle (12).

Fig. 7 shows one example of a pipework configuration embodying the invention for use with multiple heat absorbing elements (5) conveniently arranged parallel if used with parabolic trough reflectors (6) of a type previously described and illustrated in Figs. 2 and 3 in use in a collector housing and shown in detail in Fig. 8. The pipework arrangement may vary considerably according to the shape of reflector means used, but if connecting pipes to the coil (14) are kept close to the pivot axis Y then no rotating or flexible joints are necessary to permit movement of the set configuration co-operatively with the collector housing.

Claims (24)

1. Apparatus for converting solar energy by means of a movable concentrating means aligned with received radiant energy from the sun by a drive means in order to re-direct said energy onto a set configuration of pipework which moves co-operatively with and consequent upon movements of said concentrating means such that part of said set configuration of pipework remains immersed in fluid contained in a fixed vessel.

2. Apparatus as claimed in claim 1 wherein the set configuration of pipes comprises a circuit with rigid non-flexible joints throughout for the purpose of containing a circulating heat absorbing fluid.

3. Apparatus as claimed in claim 2 wherein the concentrating means has a composite motion comprising continuous rotation about a first axis at an angular rate of 360 per solar day, and pivotal in a reciprocating manner 23+ alternat-ely north and south of the first axis, so as to be always held at the most favourable attitude to receive solar energy.

4. Apparatus as claimed in claim 3 wherein the concentrating means is an array of reflectors arranged to re-direct radiation received by an area onto a smaller area occupied by an absorber element forming part of the set configuration of pipework.

5. Apparatus as claimed in claim 4 wherein the set configuration of pipework is arranged to pass twice close to the pivot point on the main axis of rotation in order to link that part of the circuit fixed within the concentrating means, to that part free to move within a fixed vessel whilst facilitating the movements required.

6. Apparatus as claimed in claim 5 wherein the two pipes adjacent to the pivot point are co-axial thereby saving space.

7. Apparatus as claimed in claim 6 wherein flow of fluid in the pipework circuit is prevented by a thermostatic device when the level of energy received is insufficient to cause further rise in temperature of fluid in the fixed vessel.

8. Apparatus as claimed in claim 7 wherein the concentrator means is enclosed in an insulated housing having one large side transparent to solar radiation arranged such that solar energy can be directed onto the absorber elements within the concentrating means when said transparent side is perpendicular to the sun's rays.

9. Apparatus as claimed in claim 8 wherein at least one absorber element is provided within the concentrating means at focii which remain in fixed relationship by moving the enclosing housing to track the sun.

10. Apparatus as claimed in claim 9 wherein the required motion is derived from a time controlled drive means through non-reversible gearing capable of resisting external forces tending to move the concentrating means from the predetermined course.

11. Apparatus as claimed in claim 10 wherein the pivotal movements are caused by a lever mechanism driven by a second nonreversible gear fixed to rotating support means such that only one source of motive power is required.

1 2. Apparatus as claimed in claim 11 wherein the motive power for the drive means is intermittent, energy being stored for gradual release to provide the continuous motion at the speed required.

13. Apparatus as claimed in claim 12 wherein the means to store energy from the drive is a spring.

1 4. Apparatus as claimed in claim 1 2 wherein the means to store energy from the drive is a suspended mass.

1 5. Apparatus as claimed in claim 1 2 wherein the support means takes the form of a spindle rotating on the said first axis to which is fixed a crank mechanism connected to the collector housing through a parallel motion linkage.

16. Apparatus as claimed in claim 9 wherein at least one absorber element has a prepared surface of suitable colour and texture for receiving energy only where such energy is likely to be incident, the remainder being prepared to minimise re-radiation

1 7. Apparatus as claimed in claim 16 wherein the at least one absorber elements are connected at their head to a pipe within the set configuration for the purpose of conveying fluid from the concentrating means to the fixed vessel and at their bases by a pipe conveying fluid from the fixed vessel to the concentrating means.

1 8. Apparatus as claimed in claim 1 7 wherein the set configuration of pipework is linked to an expansion chamber.

1 9. Apparatus as claimed in claim 5 wherein the flow of heat absorbing fluid is induced by a pump.

20. Apparatus as claimed in claim 4 wherein the concentrating means has a single reflector with one focus eliminating the need for rotation about the first axis but still requiring to be pivotted about the Y axis on a seasonal cycle.

21. Apparatus as claimed in claim 8 wherein the concentrator means is provided with a plurality of housings.

22. Apparatus for converting solar energy by means of a receiver not necessarily employing a concentrating means but movable with a set configuration of pipework which moves co-operatively with and consequent upon movements of said receiver such that part of the said configuration of pipework remains immersed in fluid contained in a fixed vessel.

23. Apparatus as claimed in claim 4 wherein the concentrating means is by a refractive device arranged to re-direct radiation received by an area onto a smaller area occupied by an absorber element forming part of a set configuration of pipework.

24. Apparatus for utilising solar energy as claimed in any one of claims 1-23 to heat a fluid in a set configuration of pipework for the purpose of conveying absorbed heat to evaporate refrigerant in a cooling system.