GB1573701A

GB1573701A - Solar heating arrangements

Info

Publication number: GB1573701A
Application number: GB39217/75A
Authority: GB
Original assignee: Mckee J D
Current assignee: Mckee J D
Priority date: 1976-12-29
Filing date: 1976-12-29
Publication date: 1980-08-28

Description

(54) IMPROVEMENTS IN OR RELATING TO SOLAR HEATING ARRANGE MENTS (71) We, FREDERICK BRIAN McKEE and JOY DOROTHY McKEE, of 'Orcades', Mill Road, Burnham-on-Crouch, Essex, both British Subjects, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to solar heating arrangements in which a heat exchange liquid, usually water, flows and is concerned, more particularly, with solar heating arrangements of such type which are protected against damage in the event of excessive solar heat absorption.

One very important failing of solar heating arrangements is that, in the event of pump failure or any form of failure affecting the circulation of heat exchange liquid therein, the temperature of the solar heat absorber which, because of the most usual form thereof is generally termed hereinafter a "solar absorbing panel", can attain such values that boiling of liquid in the arrangement can result with consequent drying out and risk of damage to the arrangement.

According to the present invention, there is provided a solar heating system which comprises a solar heat absorber including duct means therethrough through which a heat exchange liquid circulates, in use, to be heated by solar radiation incident on the absorber and means at which heat produced in said liquid at the absorber is removed therefrom, said duct means including means disposed externally of the heat absorber and of the heat removal means adapted for automatic throughflow of heat exchange liquid from the heat absorber along a path different to that travelled by the heat exchange liquid during normal operation of thc solar energy heating system in the event of prevention of flow of the heat exchange liquid along its normal path through said duct means, thereby to prevent overheating of heat exchange liquid in the solar heat absorber and consequent damage to the heat absorber.

In one preferred form of arrangement embodying this invention, such excess thermal energy may be dissipated by travel of heat exchange liquid through a thermostatically controlled so-called "lossy" by-pass, that is, a by-pass through which heat exchange liquid can be caused to flow, for example by natural thermosyphoning and whose heat dissipative properties have been maximised to achieve heat exchange to the atmosphere.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, wherein: Figure 1 shows schematically a solar heating system embodying the invention; Figures 2 to 5 show a variety of combinations of solar heat absorbers and associated heat dissipators for use in a solar heating system embodying the invention; and Figure 6 shows schematically a further type of solar heating system embodying the invention.

Referring to the drawings, Figure 1 shows a solar heating system embodying this invention and based on a conventional solar domestic water heating circuit. The circuit comprises a solar heat exchanger 1 which will generally be matt black to enable maximum solar heat absorption to be achieved and through which passes a pipe 2 wound in a helix and through which in use passes heat exchange liquid, usually water, supplied by pump 3 and pipe 4. The heated water leaves the heat exchanger through pipes 5 and 6 leading to a cylinder 7 where the pipe 6 adopts the form of a helical pipe 8 before returning to the pump 3. The cylinder 7 has inlet and outlet ducts 9 and 10 respectively for water of a domestic supply which becomes heated in the cylinder 7 by virtue of indirect heat exchange with water from the solar heat exchanger 1 in the helical pipe 8.

This combination of working parts is largely conventional. However, in addition, the illustrated system comprises a pipe 11 branched off from pipe 5 simultaneously with pipe 6 and leading to an expansion or header tank 12. An outflow pipe 13 from the tank 12 leads to a point in pipe 4 upstream of pump 3. Fitted in outlets in the expansion tank 12 is a heat dissipating arrangement comprising outflow and return pipes 14 and 15 respectively and a pair of heat dissipators 16 and 17 parallel to the expansion tank 12.

In normal use of the arrangement shown in Figure 1, water is drawn from pipe 8 through pump 3 and fed through pipe 4 to the section 2 thereof within the heat exchanger 1 and heated liquid then passes through pipes 5 and 6 back to the helical section of pipe 8 within the cylinder 7. However, in the event of failure of the pump 3, there is a strong risk of difficulties being caused at heat exchanger 1 owing to continuanace of heat absorption.

Under such conditions liquid in pipe section 2 will boil and will discharge through pipe 11 to enter the tank 12. The heat exchange liquid then passes through pipe 14 and as it passes through parallel heat dissipators 16 and 17, heat loss occurs before the liquid is returned to the tank 12. The overall effect of this is that water present in the tank 12 undergoes a temperature reduction. When the pump 3 is brought back into use, it will enable liquid to be drawn from tank 12 through the pipe 13 and back into the normal pipe system to circulate through pipes 4,2,5, 6 and 8. Because of this alternative circulation route for heat exchange liquid the heat exchange liquid will not boil away. The dissipators 16 and 17 may simply be finned copper tubes.

Simpler arrangements to that shown in Figure 1 which are particularly suitable for use with solar heat exchangers of the panel type are shown in Figures 2 to 6 of the drawings. In these drawings, like reference numerals denote like parts. Heat exchange liquid is normally supplied, in each case, through a pipe 21 to a heat exchanger panel 23 which it leaves through pipe 24. However, in each case a conduit is provided for enabling parallel flow of liquid to take place through one or more dissipators constituted by finned tubing. Fluid flow through the heat dissipators which bear the reference numerals 25 and 26 is by thermosyphoning achieved when a thermostatic valve 22 in association therewith is opened in response to the temperature being achieved by heat exchange liquid within the solar heat exchange panel 23.

In Figure 2, a pair of heat dissipators 25 and 26 are branched off in parallel to each other and to the short transverse dimension of the heat exchanger panel 23 with a thermostatic valve 22 of the type, for example, used in association with mass produced automobile radiators being provided in a pipe 27 leading from the downstream end of the heat dissipators 25 and 26 to the solar heat exchange panel 23. In Figure 3 a single heat dissipator 25 having its own associated thermostatic valve 22 is branched off from pipe 21 to a solar heat exchange panel 23 and a second heat dissipator 26 parallel to heat dissipator 25 communicates the downflow side of the solar heat exchange panel 23 through a thermostatic valve 29 with a position on outflow pipe 24 leading from the solar heat exchanger panel.In Figure 4, only a single heat dissipator is provided, this being positioned in and operating in the same manner as the dissipator 26 in Figure 3. The arrangement shown in Figure 5 is similar to that shown in Figure 2 except that only a single heat dissipator is provided on the upstream side of the solar heat exchange panel 23 and moreover the single heat dissipator 25 is of greater length than that shown in Figure 2 by virtue of its being disposed parallel to the longer transverse direction of the solar heat exchanger 23.

The arrangement shown in Figure 6 differs from that shown in each of Figures 2 to 5 in that a single heat dissipator 25 branched off from pipe 21 and having its own thermostatic valve 22 completely by-passes the solar heat exchange panel 23, feeding heat exchange liquid from pipe 21 directly into pipe 24 after subjecting it to cooling as a result of the provision of the heat dissipation means.

The arrangement shown in Figures 2 to 6 all work on the simple principle that when the temperature of water in the solar panel 23 exceeds a predetermined temperature, the thermostatic valve or valves isi are opened and water is drawn through finned pipes acting as heat dissipators and through the valve(s) 22 thereby achieving cooling of the cooling liquid before and/or after passage through the heat exchanger panel 23 or otherwise as the case may be.

Turning finally to Figure 7 of the drawings, there is shown a solar heating system which differs fundamentally from those shown in the preceding Figures. Here. a pump 30 is used to circulate heat exchange liquid through a pipe 31 to a solar heat exchange panel 32 and from there through a pipe 33 which passes through an indirect cylinder 34 having inlet 35 and outlet 36 for water to be heated up by indirect heat exchange. The system so far described is conventional.

However, the system differs from a conventional one in that an outflow pipe 37 for heat exchange liquid empties into a holding tank 38 which is in communication with the pump 30 through a limited flow return valve 39. In addition, an air relief valve 40 is provided in the pipe 33 and communicates with the holding tank 38 through a descending pipe 41.

Normal operation of the system is similar to that described for the system of Figure 1, with the small difference that heat exchange liquid flows out of the pipe 37 into the holding tank 38 before being drawn therefrom by the pump 30 for recycling. In the event of malfunctioning of the pump, however, whether due to power failure or otherwise, the limited flow return valve 39 allows heat exchanger liquid to drain back into the holding tank over a preset time. The drain back time may be set in accordance with adjustment of the limited flow return valve 39 so that with normal control action, the system does not have to drain and accordingly be re-filled particularly often.In this way, in the event of such malfunctioning, liquid will not remain in the solar heat exchanger panel and be subject to heating up excessively due to solar radiation with the consequent risk of its boiling away and damaging the system.

The solar heat exchange panel 32 has its surface on which solar radiation is incident in use thereof made of transparent or translucent material with the opposite surface of the panel being opaque and carrying within the solar heat exchanger panel itself, a radiation reflecting layer (not shown). Pipes through which heat exchange liquid travels in the heat exchange panel 32 are likewise transparent or translucent. The heat exchange liquid then used is a dark liquid for example as a result of its having suspended therein a black pigment, for example carbon black of suitable pigment size for it to remain in suspension.

The heat exchange liquid may also be rendered dark by the presence of colloidal material such as graphite suspended therein.

This system is to be distinguished from conventional systems in which, as with the heat exchanger of Figure 1, the surface of the heat exchanger on which radiation is incident is matt black and is responsible for all radiation uptake, heat being transferred to heat exchange liquid by means of suitable heat conductive surfaces. Such modification of the heat exchange panel has the particular advantage that solar radiation is absorbed directly by the heat exchange liquid.Because the radiation does not encounter a solid matt black surface initially thereby allowing heat transfer from the matt black surface to only a surface portion of heat exchanger liquid, radiation is now able to pass right through the heat exchange liquid with only a portion of it being absorbed by suspended or dissolved dark matter. with the remainder reaching the reflecting surface at the back of the panel to be reflected back through the heat exchanger liquid to undergo absorption. The result achieved is that a much greater proportion of solar radiation incident on a solar heat exchange panel is, in effect, absorbed and the absorption is a more efficient process.

Insofar as the arrangement of Figure 7 is concerned, in the event of failure of the pump 30, if the heat exchanger panel is constructed as aforesaid and a dark heat exchanger liquid is employed which is allowed to drain back to the holding tank 38, then the empty heat exchange panel itself will be secure from undergoing overheating because solar radiation will be reflected back out of the panel by means of the reflective layer comprised thereby. In contrast, if the absorber has a matt black surface on which solar radiation is incident, it will undergo a gradual increase in temperature when drained with consequent risk of damage to the heat absorber and parts associated therewith. Even if circulation stops and the limited flow return valve fails, damage to the system will be reduced overall even if the panel boils dry.As the level of heat exchange fluid falls during boiling, the absorber will again come into operation and the only attention needed once the system is restored to a full working condition will be the replenishment of lost liquid.

Our copending application Number 7920423, Serial No. 1573702 describes and claims a solar heating system in which a dark coloured leaf exchange liquid flows through a duct which is transparent or translucent with respect to solar radiation within an areal structure having a new reflective wall surface.

WHAT WE CLAIM IS: 1. A solar heating system which comprises a solar heat absorber including duct means therethrough through which a heat exchange liquid circulates, in use, to be heated by solar radiation incident on the absorber and means at which heat produced in said liquid at the absorber is removed therefrom, said duct means including means disposed externally of the heat absorber and of the heat removal means adapted for automatic throughflow of heat exchange liquid from the heat absorber along a path different to that travelled by the heat exchange liquid during normal operation of the solar energy heating system in the event of prevention of flow of the heat exchange liquid along its normal path through said duct means, thereby to prevent overheating of heat exchange liquid in the solar heat absorber and consequent damage to the heat absorber.

2. A system as claimed in claim 1, which comprises a by-pass pipe for said liquid bypassing a section of inlet pipe for heat exchange liquid to said absorber or a section of outlet pipe for heat exchange liquid from said absorber, which by-pass pipe comprises a thermostatically controlled valve responsive to said temperature build-up and has

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. addition, an air relief valve 40 is provided in the pipe 33 and communicates with the holding tank 38 through a descending pipe 41. Normal operation of the system is similar to that described for the system of Figure 1, with the small difference that heat exchange liquid flows out of the pipe 37 into the holding tank 38 before being drawn therefrom by the pump 30 for recycling. In the event of malfunctioning of the pump, however, whether due to power failure or otherwise, the limited flow return valve 39 allows heat exchanger liquid to drain back into the holding tank over a preset time. The drain back time may be set in accordance with adjustment of the limited flow return valve 39 so that with normal control action, the system does not have to drain and accordingly be re-filled particularly often.In this way, in the event of such malfunctioning, liquid will not remain in the solar heat exchanger panel and be subject to heating up excessively due to solar radiation with the consequent risk of its boiling away and damaging the system. The solar heat exchange panel 32 has its surface on which solar radiation is incident in use thereof made of transparent or translucent material with the opposite surface of the panel being opaque and carrying within the solar heat exchanger panel itself, a radiation reflecting layer (not shown). Pipes through which heat exchange liquid travels in the heat exchange panel 32 are likewise transparent or translucent. The heat exchange liquid then used is a dark liquid for example as a result of its having suspended therein a black pigment, for example carbon black of suitable pigment size for it to remain in suspension. The heat exchange liquid may also be rendered dark by the presence of colloidal material such as graphite suspended therein. This system is to be distinguished from conventional systems in which, as with the heat exchanger of Figure 1, the surface of the heat exchanger on which radiation is incident is matt black and is responsible for all radiation uptake, heat being transferred to heat exchange liquid by means of suitable heat conductive surfaces. Such modification of the heat exchange panel has the particular advantage that solar radiation is absorbed directly by the heat exchange liquid.Because the radiation does not encounter a solid matt black surface initially thereby allowing heat transfer from the matt black surface to only a surface portion of heat exchanger liquid, radiation is now able to pass right through the heat exchange liquid with only a portion of it being absorbed by suspended or dissolved dark matter. with the remainder reaching the reflecting surface at the back of the panel to be reflected back through the heat exchanger liquid to undergo absorption. The result achieved is that a much greater proportion of solar radiation incident on a solar heat exchange panel is, in effect, absorbed and the absorption is a more efficient process. Insofar as the arrangement of Figure 7 is concerned, in the event of failure of the pump 30, if the heat exchanger panel is constructed as aforesaid and a dark heat exchanger liquid is employed which is allowed to drain back to the holding tank 38, then the empty heat exchange panel itself will be secure from undergoing overheating because solar radiation will be reflected back out of the panel by means of the reflective layer comprised thereby. In contrast, if the absorber has a matt black surface on which solar radiation is incident, it will undergo a gradual increase in temperature when drained with consequent risk of damage to the heat absorber and parts associated therewith. Even if circulation stops and the limited flow return valve fails, damage to the system will be reduced overall even if the panel boils dry.As the level of heat exchange fluid falls during boiling, the absorber will again come into operation and the only attention needed once the system is restored to a full working condition will be the replenishment of lost liquid. Our copending application Number 7920423, Serial No. 1573702 describes and claims a solar heating system in which a dark coloured leaf exchange liquid flows through a duct which is transparent or translucent with respect to solar radiation within an areal structure having a new reflective wall surface. WHAT WE CLAIM IS:

1. A solar heating system which comprises a solar heat absorber including duct means therethrough through which a heat exchange liquid circulates, in use, to be heated by solar radiation incident on the absorber and means at which heat produced in said liquid at the absorber is removed therefrom, said duct means including means disposed externally of the heat absorber and of the heat removal means adapted for automatic throughflow of heat exchange liquid from the heat absorber along a path different to that travelled by the heat exchange liquid during normal operation of the solar energy heating system in the event of prevention of flow of the heat exchange liquid along its normal path through said duct means, thereby to prevent overheating of heat exchange liquid in the solar heat absorber and consequent damage to the heat absorber.

associated means for cooling liquid flowing therethrough.

3. A system as claimed in claim 2, wherein said by-pass pipe by-passes the solar heat absorber.

4. A system as claimed in claim 1, which additionally comprises an expansion tank in a circuit for heat exchange liquid at a position downstream of the heat absorber, said system being adapted to discharge heat exchange liquid into said tank when the heat exchange liquid boils.

5. A system as claimed in claim 4, which comprises a pipe feeding off an upper region of said tank and having a return portion to a lower region of said tank, which pipe has associated means for cooling liquid flowing therethrough.

6. A system as claimed in claim 2, 3 or 5, wherein said liquid cooling means is constituted by fins disposed at intervals along said pipe.

7. A system as claimed in any one of the preceding claims, wherein the solar heat absorber is a panel which comprises a window on which solar radiation is incident, in use, and which is transparent or translucent and a rear wall member parallel to said window whose surface which is nearer to said window is capable of reflecting solar radiation, the panel having duct means for passage of heat exchange liquid therethrough which is transparent or translucent with respect to solar radiation.

8. A system as claimed in claim 7, incorporating therein a dark coloured heat exchange liquid.

9. A system as claimed in claim 8, wherein the heat exchange liquid is rendered dark by means of a black pigment suspended therein.

10. A system as claimed in claim 8, wherein the heat exchange liquid is rendered dark by the presence therein of colloidal graphite.

11. A system as claimed in any one of claims 7 to 10, which additionally comprises a circulation pump for said heat exchange liquid and a holding tank positioned in relation to the solar heat absorber for heat exchange liquid to drain thereinto in the event of failure of the pump.

12. A system as claimed in claim 11, which additionally comprises a limited flow return valve for enabling said liquid to drain from the solar heat absorber to the holding tank.

13. A solar heating system, substantially as described herein with reference to any one of Figures 1 to 6 of the accompanying drawings.

14. A solar heating system, substantially as described herein with reference to Figure 7 of the accompanying drawings.