AU2009201076B2

AU2009201076B2 - Split non-pressurised solar water heating systems

Info

Publication number: AU2009201076B2
Application number: AU2009201076A
Authority: AU
Inventors: Jie Qin Wu; Jian Hua Zhou
Original assignee: Wu Jie Qin Mr
Current assignee: Wu Jie Qin Mr
Priority date: 2008-04-08
Filing date: 2009-03-18
Publication date: 2010-06-17
Anticipated expiration: 2029-03-18
Also published as: AU2009201076A1

Description

COMPLETE SPECIFICATION STANDARD PATENT SPLIT NON-PRESSURISED SOLAR WATER HEATING SYSTEMS The following statement is a full description of this invention, including the best method of performing it known to me: 1 SOLAR WATER HEATING SYSTEM FIELD OF THE INVENTION This invention relates to solar water heating systems and, in particular, split non-pressurised solar water heating systems. BACKGROUND D There is much interest in solar water heating technology, and many patent specifications have been published, relating to this technology. The following are examples: Japanese Patent No. JP 58210432 entitled "Forced Circulation Type Solar Heat Water Heater" discloses a water heater which is operated economically by a method wherein hot 5 water is introduced into a natural circulation system in which the hot water is circulated by convection between a collector and a tank. An auxiliary tank is provided at a position higher than the collector, and the upper part of the auxiliary tank is connected to the upper part of the collector. A drive-type changeover valve is provided in a pipe which connects the auxiliary tank to a pumped water passage. In addition, a check valve is provided to prevent pumped water Lo from flowing back toward the pump from the collector. A water level sensor in the auxiliary tank closes the changeover valve so that the pump is only operated when the auxiliary tank is sufficiently full of water. Japanese Patent No. JP 9138006 entitled "Solar Heat Water-Heated Facility" discloses a 25 solar water heating system which ensures that the specified hot water temperature is not exceeded, even if the pressure is set to 1kg/cm 2 or more. German Patent No. DE 3814169 entitled "Solar Installation for the Production of Hot Water" discloses a solar installation for the production of hot water, characterised in that, in a collector 50 storage pipe (e.g. a pipe coil), domestic water is heated directly by solar radiation. At the end of the storage pipe there is a temperature sensor which controls an open/close valve. Once the contents of the pipe have reached a set temperature, the valve opens and the heated content of the pipe is conveyed into a non-pressurised storage vessel by the cold domestic water flowing behind it. As soon as the cold water reaches the temperature sensor, the valve closes 35 and the content of the pipe can again be heated by solar radiation.

2 There are many solar water heating systems already on the market, but these have various shortcomings. For example, pressurised systems are generally more expensive to operate than non pressurised systems because water is pumped from a heating unit to a storage tank. Also, in comparison to non-pressurised systems, maintenance problems exist because there are more components which are subject to failure, thereby disrupting hot water supply. However, non-pressurised systems also have disadvantages. In particular, maintaining water temperature within set limits has proven to be difficult. Accordingly, there is a need for an improved non-pressurised solar water heating system, incorporating temperature control means for maintaining water temperature within set limits. SUMMARY OF THE INVENTION In the solar water heating system of the present invention, water may be automatically circulated, by means of differences in temperature (convection), between a heating unit and a storage tank. 0 The solar water heating system of the present invention comprises: (i) a heating unit adapted for heating of water therein by solar radiation, the heating unit having an inlet for receiving water for heating, and an outlet for discharge of heated water; z5 (ii) a storage tank having an inlet for receiving water from the heating unit and an outlet for discharge and/or channelling of water to point of use, or for returning water to the heating unit; (iii) a delivery conduit for delivering water from the heating unit to the storage tank; (iv) a return conduit for returning water from the storage tank to the heating unit; 30 (v) a control conduit for delivering unheated water to the storage tank; (vi) delivery, return and control valves for controlling flow of water through the delivery, return and control conduits respectively; (vii) at least one storage tank water temperature sensor; (vii) at least one heating unit water temperature sensor; and 3 (ix) a controller for controlling the flow of water through the delivery conduit, the return conduit and the control conduit, based on information provided by the storage tank water temperature sensor(s) and/or the heating unit water temperature sensor(s), by controlling operation of the delivery, return and control valves; the controller thereby ensuring that discharge of water from the storage tank conforms to specified temperature constraints. For example, the water will be discharged from the storage tank at a specified temperature, at a temperature selected from a number of specified options, or within a specified temperature range. In a preferred embodiment, if the water temperature in the storage tank exceeds a specified maximum temperature, the controller operates the control valve in the control conduit to allow delivery of unheated water to the storage tank, and the delivery of unheated water to the storage tank continues until the temperature of water in the storage tank drops to a specified lower level. In a further preferred embodiment, discharge of water from the heating unit to the storage tank is similarly controlled by the controller, to ensure that the water being discharged conforms to specified temperature constraints. For example, the water will be discharged from the heating unit at a specified temperature, at a temperature selected from a number of specified options, or within a specified temperature range. Preferably, the water heating system incorporates one or more additional features such as the 5 following: (i) at least one air temperature sensor; (ii) as an alternative safety mechanism, discharge of water from the storage tank being controlled by a pump which ceases operation if the temperature of the water in the storage tank exceeds a specified temperature; 50 (iii) a sensor being provided to ensure that, if the water level in the storage tank drops below a specified level, the pump ceases operation; and/or (iv) the pump ceasing operation after a specified period of time to limit the use/wastage of water.

4 BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagram of a first embodiment of a solar water heating system according to the present invention; and Figure 2 is a diagram of a second embodiment of a solar water heating system according to the present invention. DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION The solar water heating system will now be described in terms of preferred embodiments, which are illustrative, but not restrictive, of the present invention. The operation of a solar water heating system 10 according to the present invention is illustrated by Figures 1 and 2. Figure 1 illustrates a basic version of the solar water heating system, and Figure 2 illustrates a further version of the solar water heating system, which incorporates additional features. The water to be heated travels via pipeline A, B to a heating unit 11. Water may be supplied by connecting to the municipal water supply (mains water) or, for example, a rainwater tank, using o associated piping. The water may be supplied at mains pressure and/or using a pump. The heating unit 11 is conveniently located on the roof 12 of the building to be supplied with hot water, or at any other location sited so as to take advantage of incident solar radiation. The flow of water into the heating unit may be controlled by a valve 13 (which may, for example, be 5 a mechanical valve), and a non-return valve 14 may be provided to prevent back-flow. Junction 15 in the pipeline allows water from storage tank 16 to be re-circulated (via pipeline C, D) to heating unit 11 for reheating. Water in the heating unit 11 is heated by solar energy, utilising any appropriate means (e.g. 50 heat-collecting vacuum tubes 17, which may be manufactured from glass or other suitable materials). The heated water is then delivered via pipeline E to the storage tank 16. It is preferred that at least one release vent 11 a is provided in the heating unit 11 to allow release of steam because steam can create pressure which will affect the efficiency of the 5 system.

5 The circulation of water through the system, via pipelines C, D, E, F and G, is controlled by (for example) a microcomputer controller 18. A pump 22 is located in the pipeline G for delivery of water from storage tank 16 to the point of use of the hot water. The microcomputer controller 18 controls water flow by means of electromagnetic valves 19, 20, 21 and water pump 22, based (for example) on data provided by air temperature sensor 23, water temperature sensor 24 in the heating unit 11, water temperature sensor 25b in the storage tank 16, and water level and water temperature sensors located at levels 25a and 25 and 25b (close to the maximum and minimum water levels respectively) of the storage tank 16. Pipeline E delivers heated water from heating unit 11 to a discharge tube 26, which preferably has a substantial portion of its length located within storage tank 16, and which discharges the hot water at or proximal to the base 27 of the tank 16. The water flow from the heating unit 11 to the storage tank 16 is controlled by electromagnetic valve 19, operated by the microcomputer controller 18. A vent pipe 28 at the top of storage tank 16 allows air to escape, as it is displaced by rising water levels (or, conversely, allows air to enter the tank 16 to replace water, as the water level falls). An overflow pipe 29 is also provided, in case of over-filling of storage tank 16. The water level sensor located at 25a (being close to the recommended maximum water level for storage tank 16) will send a signal to microcomputer controller 18 if this maximum level is being approached. The microcomputer controller 18 will then close valves 19 (if not already closed), to prevent further water from entering the storage tank. These valves 19 will remain 5 closed at least until the water level in the storage tank has dropped to an appropriate level. Junction 30 in pipeline A, B allows unheated water to be added to storage tank 16, via pipeline F controlled by electromagnetic valve 20, if the temperature of the water in tank 16 is too high. The unheated water is preferably delivered at or proximal to the top of the storage tank 16. 0 Delivery of heated (hot) water (via discharge tube 26) in the vicinity of the base of storage tank 16, and delivery of unheated (cold) water (via pipeline F) in the vicinity of the top of the tank, takes advantage of automatic, convection-powered mixing of the water in the tank to provide an even temperature distribution throughout the tank. This enhances the accuracy of readings 5 provided by water temperature sensor 25b, and minimises the risk that water outside the desired temperature range will be delivered from the storage tank to point of use.

6 Hot water is pumped from the storage tank 16 by pump 22, the operation of which is controlled by the microcomputer controller 18, based on readings provided by instruments such as the water level and/or water temperature sensors 25, 25a and 25b in the storage tank 16. Operation of the pump 22 may also be controlled by a timer, to ensure that it ceases operation after a specified period of time. This has the effect of limiting the use/wastage of water, and also is an added precaution to prevent the water level in the storage tank 16 from dropping too low. The outlet for water being discharged from storage tank 16 may conveniently be located at or proximal to the base 27 of the tank. The discharge of water from storage tank 16 may be further controlled by cock 31, which will normally be in the "on" position, but can be turned off if required (e.g. to allow maintenance or repairs to the system). Pipeline G allows hot water from storage tank 16 to be delivered to where it is needed, for example for domestic or industrial use. ) A junction 32 in the pipeline G allows the water from storage tank 16 to be diverted back to heating unit 11, via pipeline C, D (controlled by electromagnetic valve 21, operated by the microcomputer controller 18), if the temperature of the water drops below acceptable levels for use. 5 Features of the System The solar water heating system of the present invention employs a controller (e.g. microcomputer controller 18) to automatically control water temperature and maintain the temperature in storage tank 16 within an appropriate range (e.g. between 45 0 C and 60 0 C), regardless of season. Storage tank 16 is preferably encased in heat-insulating material to assist in maintaining the stored water at a reasonably constant temperature. The system of the present invention can provide a number of advantageous features, as described below: 7 Feature 1: Non-pressurised system. The system is non-pressurised, and does not require pumping of water from the heating unit to the storage tank. This feature contributes to the safety, low running cost and longer service life of the system. Feature 2: Temperature adjustment and water discharge from heating unit to storage tank at controlled temperature. Option 1 - Fully Automatic: Air temperature is measured by sensor 23 and, based on data provided by sensor 23 to the controller (e.g. microcomputer controller 18), the temperature at which water is discharged from the heating unit 11 to the storage tank 16 is selected. Lower air temperatures will require higher temperatures for the water discharged from the heating unit. For example, the controller may be set to provide 3 levels of temperature selection: Level X: When the air temperature is below 200C, the temperature of water discharged from heating unit 11 is 690C. Level Y: When the air temperature is 200C - 300C, the temperature of the discharged water is 670C. Level Z: When the air temperature is above 300C, the temperature of the discharged water is 65 0 C. Option 2 - Fully Automatic: Water temperature in the storage tank 16 is measured by sensor 5 25b. Based on data provided by sensor 25b to the controller (e.g. microcomputer controller 18), the temperature at which water is discharged from the heating unit 11 to the storage tank 16 is selected. Lower water temperatures in the storage tank 16 will require higher temperatures for the water discharged from the heating unit. ) For example, the controller may be set to provide 3 levels of temperature selection: Level X: When the water temperature in storage tank 16 is below 500C, the temperature of water discharged from heating unit 11 is 690C. Level Y: When the water temperature in storage tank 16 is 500C - 550C, the temperature of water discharged from heating unit 11 is 670C. 5 Level Z: When the water temperature in storage tank 16 is 560C - 60*C, the temperature of water discharged from heating unit 11 is 650C.

8 When the water temperature in the heating unit 11 reaches the selected temperature or above, the discharging valve 19 opens automatically, allowing the heated water to fill the storage tank 16. Preferably, the system is computer controlled (e.g. by microcomputer controller 18) so as to provide timed discharges of hot water from heating unit 11. The discharging procedure is repeated until the storage tank is filled to capacity with heated water - at this point, the heating unit 11 stops discharging. As the heated water is emptied from the heating unit, it is replaced with cold water through automatic valve 13, which is preferably a mechanical valve. In a preferred embodiment, each hot water discharge lasts for 60 seconds, with intervals of at least 7 minutes between discharges. This discharge time has been selected according to the dimensions of the currently manufactured heating unit 11 and discharge tube 26 (heating unit: 15 litres, discharge tube: 16mm diameter). If these measurements are varied, the discharge time should be modified accordingly, because it is directly related to the resulting water temperature in the storage tank 16, and hence needs to be carefully selected to provide an accurately controlled temperature. Option 3 - Semi-Automatic: In this version of the system, the temperature at which water is discharged from heating unit 11 is selected from a number of specified options. There may, for example, be three different temperature levels: Level X - 690C, Level Y - 670C and Level Z 650C. The temperature can be selected according to air temperature and personal preference. The controller (e.g. microcomputer controller 18) automatically selects one of the specified temperatures (for example, Level Z) for water discharge. The discharging valve 19 opens automatically when the water temperature in the heating unit 11 reaches the specified temperature (Level Z, in this case) or above. Alternatively, the system can be adjusted manually to allow discharge when the water temperature reaches one of the other specified levels (Level X or Y). The timing of discharges of heated water, and the other operations, are the same as for the Fully Automatic versions described above. 5 Option 4 - Automatic Fixed Temperature: In this version, water is discharged from the heating unit 11 at a specified temperature. The discharging valve 19 is computer controlled (e.g. by microcomputer controller 18) so as to 5 have one fixed temperature (e.g. 670C) for discharge. This fixed temperature can be selected during manufacture according to ambient temperatures in the target location for sale. Using sensor 24, the computer measures the water temperature in the heating unit 11. When the 9 water temperature reaches the specified, fixed temperature (e.g. 67*C) or above, the discharging valve 19 opens automatically to allow the heated water to enter the storage tank 16. The timing of discharges of heated water, and the other operations, are the same as for the Fully Automatic versions described above. NOTE: If a country has certain specifications regarding water temperature, the system may be set to comply with those specifications. For example, in Australia, the requirements are that water in the storage tank must be maintained over 600C (so as to prevent, or at least minimise, the risk of microbial growth), but that water supplied to the outlets (taps/faucets) where it is to be used must be 500C or below. A further embodiment with additional components, as illustrated in Figure 2, is preferred where there is a need or desire to meet the above (or similar) requirements. The water in the heating unit 11 must reach a temperature of over 600C before it is allowed to enter the storage tank 16, and the operation of electromagnetic valve 19 is controlled accordingly by the control unit 18. As shown in Figure 2, a valve 33 is installed downstream of the pump 22 (which supplies hot water to the taps/faucets where it is to be used). That valve 33 can be a thermostatic valve, it can control water output temperature to be 500C or below. In case of failure of valve 33, there is an additional temperature sensor 34 downstream of the valve 33. Sensor 34 is connected to the temperature control unit 18. In a situation where failure of the valve 33 causes water to pass through that valve at a 5 temperature above 500C, the sensor 34 will signal the control unit 18 of the problem, and the control unit 18 will cut power to the water pump 22. This will prevent water above 500C from exiting the system. Pipeline H allows cold water (e.g. from the mains system or from a rainwater tank) to be D supplied to thermostatic valve 33, so as to reduce the temperature of the hot water to an appropriate level of 500C or below. Water supplied from the mains or a rainwater tank would be drinkable and therefore usable without first entering the heating unit 11. Once the temperature is 50*C or below, sensor 34 will then signal the water pump 22 to re-commence working, so that hot water can exit the system. S Option 5 - Semi-Circulation: When the water level in storage tank 16 is at its minimum, or anywhere less than half of its recommended maximum level, the valve 20 will automatically 10 open to add unheated water to the storage tank 16 until it has reached substantially its halfway point (i.e. half of its recommended maximum level). The following procedure (which is similarly applicable if storage tank 16 is already half-full) will then occur: If the water temperature in the storage tank 16 is, at that stage, lower than (for example) 400C, the circulation system will automatically begin working to increase the temperature of the water in the storage tank 16 by delivery of heated water (via pipeline E and discharge tube 26) from heating unit 11, and re-circulation of water from the storage tank 16 to heating unit 11 via pipeline C, D. This circulation will stop when the water temperature in the storage tank 16 reaches a pre-determined level (e.g. 580C), at which point water may be discharged as required from storage tank 16 to point of use, with storage tank 16 being re-filled by discharge of water from the heating tank 11. If the water temperature in the storage tank 16 is above 400C, re-circulation of water back to heating unit 11 will not occur. Instead, heating of the water will occur via discharge of water from the heating tank 11 to storage tank 16. The temperature at which water in the storage tank 16 is to be maintained may depend on mandatory limits or requirements set by municipal or government authorities in the country or region in which the water heating system is to be used, or may be a matter of customer preference. The working principles for Semi-Circulation are the same as for Feature 3 below; i.e. Automatic circulation powered by differences in temperature (convection). Once the circulation stops, 5 discharge can be controlled by microcomputer controller 18 according to Option 1: Fully Automatic, Option 2: Fully Automatic, Option 3: Semi-Automatic or Option 4: Automatic Fixed Temperature (as described above). The other operations are the same as for the Fully Automatic versions described above. O Option 6 - Full Circulation: When the water level in storage tank 16 is at its minimum level, the valve 20 will automatically open and add unheated water to storage tank 16 until it is full (i.e. at its recommended maximum level). Once the storage tank 16 is full, circulation between storage tank 16 and heating unit 11 will begin in order to heat the water in the tank 16. The working principles for Full Circulation are the same as for Feature 3 below; i.e. Automatic i5 circulation powered by differences in temperature (convection). The other operations are the same as for the second Fully Automatic version described above (Option 2).

11 Feature 3: Automatic circulation powered by differences in temperature (convection). The solar water heating system of the present invention maintains, as far as possible, water temperatures within the storage tank 16. Generally speaking (with the exception of an extended period of overcast or rainy days), it should be possible to maintain the water temperature in the storage tank within the desired range (e.g. between 450C and 600C). The water temperature in the storage tank 16 will still be maintained, even if the water in the storage tank is not used for a couple of days. Re-circulation of water from the storage tank 16 back to the heating unit 11 is activated if the storage tank 16 is sufficiently full of water, the water temperature in the storage tank drops below a minimum temperature (e.g. 550C), and the temperature of the water in the heating unit 11 is sufficiently greater (for example, 100C higher) than the temperature of the water in storage tank 16. In those circumstances, the circulation pump 22 automatically starts working, and valve 21 in pipeline C, D and valve 19 in pipeline E simultaneously open. Re-circulation stops when the difference in temperature between water in storage tank 16 and water in heating unit 11 becomes less than a specified figure (e.g. 30C). Alternatively, the length of time of re-circulation (e.g. 1 minute) can be controlled by a timer, or re-circulation will stop when the water temperature in the storage tank 16 reaches a specified level (e.g. 60*C). Re-circulation will not take place if the water temperature in the heating unit 11 is lower than the water temperature in the storage tank 16. Feature 3a: Automatic Circulation Powered by Fixed Temperature 5 When the water temperature in the storage tank 16 is less than the set minimum temperature and the tank is full, circulation mode will begin so as to increase the water temperature in the storage tank. Working Principle: When the storage tank 16 is at full capacity and the water temperature is 0 below the minimum set temperature (e.g. below 600C), and the water temperature in the heating unit / heat collector tank 11 is 95 0 C or above, then circulation will begin. Referring to Figure 1: Electromagnetic valves 19 and 21 will open simultaneously, and the water pump 22 will also begin working at the same time, all for an appropriate duration of (for example) one minute, if (for example) the size of the storage tank 16 is 200 litres (The duration will depend 5 on the size of storage tank 16 - if the system has a 300 litre storage tank 16, then the duration will be increased to, for example, 1.5 minutes.) The water pump 22 will pump water from the storage tank 16 back into the heat collector tank 11, and the higher temperature water in the 12 heat collector tank 11 will be discharged into the storage tank 16. Once circulation has ceased, there will be a lull for an appropriate period of time (e.g. 6 minutes) to allow the water to mix. After this period of time has elapsed, and if the temperature of the water in the storage tank 16 is still too low, then the circulation process will repeat until the water reaches the required temperature of 600C or above. Feature 4: Automatic temperature lowering if the water temperature becomes too high. In a preferred embodiment, a temperature-lowering mechanism is automatically activated when the water temperature in the storage tank 16 reaches a specified maximum (e.g. 600C), in order to maintain the water temperature within safe or desired limits. The maximum temperature may be a mandatory limit or requirement set by municipal or government authorities in the country or region in which the water heating system is to be used, or may be a matter of customer preference. If the water temperature in the storage tank 16 surpasses the specified maximum temperature, the automatic cold water supply valve 20 in pipeline F opens. Unheated (cold) water is then delivered directly to the storage tank, bypassing the heating unit 11. Discharges of cold water into storage tank 16 are timed. For example, each discharge may last for 30 seconds, and the discharges of cold water may be separated by suitable (e.g. 10 minute) intervals, so as to ensure full mixing of the hot and cold water. Preferably, the cold water enters from the top of storage tank 16, and the amount discharged at any one time is preferably less than 3 litres. If the water temperature still remains above the specified maximum (e.g. 600C) at the end of the interval (of, for example, 10 minutes) after the last discharge of cold water, the procedure is 5~ repeated until the temperature reaches the desired lower temperature (e.g. 580C). This function is not affected by the volume of water in the storage tank. Feature 5: Secondary mechanism for preventing over-heating of the water discharged from the storage tank. 0 This system preferably comprises a secondary safety protection mechanism in case the water temperature in the storage tank 16 exceeds a specified maximum of, for example, 600C. The pump 22 used to pump hot water from storage tank 16 to where it is needed (for example, 5 for domestic or industrial use) will not operate if the water temperature in the storage tank surpasses the specified maximum temperature (e.g. 600C), and only re-activates if the water temperature drops to an acceptable level (e.g. 580C).

13 In a particularly preferred embodiment, this feature is combined with the automatic temperature lowering Feature 4 described above. If water temperature sensor 25b record a temperature or temperature range of water in the tank 16 exceeding a pre-determined maximum temperature or temperature range, the controller 18 de-activates pump 22 and opens control valve 20 to allow unheated water to flow through control conduit F and into tank 16. Once the controller 18 determines (through sensor 25b) that a pre-determined acceptably lower temperature or temperature range has been reached in the tank, control valve 20 is closed and the pump 22 is re-activated for use. Feature 6: Protection of the water pump from damage. A water level sensor is located at the bottom level of 25 in storage tank 16. This water level sensor sends a signal to microcomputer controller 18 when the sensor is exposed to air, thereby indicating that the water level has dropped to (or below) a specified minimum level. If this happens, microcomputer controller 18 will cause pump 22 to cease operation. It is only when the water level has risen sufficiently that pump 22 will be re-activated, so that it can begin operating again. This is a precaution to guard against the damage which would occur if the pump continued to operate while empty of water. Feature 7: Alternative mechanism for protecting the water pump from damage. The pump 22 can be set to stop after a specified period of time. This has the effect of limiting the use/wastage of water.

Claims

1. A solar water heating system comprising: (i) a heating unit adapted for heating of water therein by solar radiation, the heating unit having an inlet for receiving water for heating, and an outlet for discharge of heated water; (ii) a storage tank having an inlet for receiving water from the heating unit and an outlet for discharge and/or channelling of water to point of use, or for returning water to the heating unit; (iii) a delivery conduit for delivering water from the heating unit to the storage tank; (iv) a return conduit for returning water from the storage tank to the heating unit; (v) a control conduit for delivering unheated water to the storage tank; (vi) delivery, return and control valves for controlling flow of water through the delivery, return and control conduits respectively; (vii) at least one storage tank water temperature sensor; (viii) at least one heating unit water temperature sensor; and (ix) a controller for controlling the flow of water through the delivery conduit, the return conduit and the control conduit, based on information provided by the storage tank water temperature sensor(s) and/or the heating unit water temperature sensor(s), by controlling operation of the delivery, return and control valves; the controller thereby ensuring that discharge of water from the storage tank conforms to specified temperature constraints.

2. A solar water heating system according to Claim 1, wherein water is discharged from the storage tank at a specified temperature, at a temperature selected from a number of specified options, or within a specified temperature range.

3. A solar water heating system according to Claim 1 or Claim 2 wherein, if the water temperature in the storage tank exceeds a specified maximum temperature, the controller operates the control valve in the control conduit to allow delivery of unheated water to the storage tank, and the delivery of unheated water to the storage tank continues until the temperature of water in the storage tank drops to a specified lower level. 15

4. A solar water heating unit according to any one of Claims 1 to 3, wherein the unheated water is delivered to the storage tank at or proximal to the top thereof.

5. A solar water heating system according to any one of Claims 1 to 4, wherein the inlet of the storage tank, for receiving water from the heating unit, is located at or proximal to the base of the storage tank.

6. A solar water heating system according to any one of Claims 1 to 5, wherein discharge of water from the heating unit to the storage tank is controlled by the controller, to ensure that the water being discharged conforms to specified temperature constraints.

7. A solar water heating system according to Claim 6, wherein water is discharged from the heating unit to the storage tank at a specified temperature, at a temperature selected from a number of specified options, or within a specified temperature range.

8. A solar water heating system according to any one of Claims 1 to 7, wherein discharge of water from the storage tank is controlled by a pump, and the pump ceases operation if the temperature of the water in the storage tank exceeds a specified temperature.

9. A solar water heating system according to any one of Claims 1 to 8, wherein discharge of water from the storage tank is controlled by a pump, and the pump ceases operation if the water level in the storage tank drops below a specified level.

10. A solar water heating system according to any one of Claims 1 to 9, wherein discharge of water from the storage tank is controlled by a pump, and the pump ceases operation after a specified period of time.

11. A solar water heating system according to any one of Claims 1 to 10, wherein the storage tank is encased in heat-insulating material.

12. A solar water heating system according to any one of Claims 1 to 11, further including at least one air temperature sensor.

13. A solar water heating system according to Claim 12, wherein the temperature at which water is discharged from the heating unit is selected based on data provided by the air temperature sensor(s) to the controller. 16

14. A solar water heating system according to any one of Claims 1 to 12, wherein the temperature at which water is discharged from the heating unit is selected based on data provided by the storage tank water temperature sensor(s) to the controller.

15. A solar water heating system according to any one of Claims 1 to 14, wherein the storage tank water temperature sensor within the storage tank.

16. A solar water heating system according to any one of Claims 1 to 15, wherein the temperature at which water is discharged from the heating unit is selected from a number of specified options.

17. A solar water heating system according to any one of Claims 1 to 15, wherein water is discharged from the heating unit at a specified temperature.

18. A solar water heating system according to any one of Claims 1 to 17, substantially as described herein with reference to accompanying Figure 1 or 2. DATED this 18 th of March 2009 Jieqin Wu