Field of the invention

[001] This invention relates to solar water heating systems and addresses the problem of overheating of the water and/or the heat transfer fluid. The invention will be described in the context of a thermosyphoning system.

Background of the invention

[002] One type of solar hot water system includes a heat transfer fluid circuit and a water circuit. The heat transfer fluid circuit includes the solar collector through which the heat transfer fluid passes and a heat transfer means where the heat is transferred from the heat transfer fluid to the water.

[003] Solar hot water systems operate in a range of climates, and in warmer areas there is a possibility that the transfer fluid will absorb excessive heat from the collector, so that the temperature of the water exceeds a given threshold value, or, in the extreme, the temperature of the water may exceed the boiling point.

[004] Any reference herein to known prior art does not, unless the contrary indication appears, constitute an admission that such prior art is commonly known by those skilled in the art to which the invention relates, at the priority date of this application.

Summary of the invention

[005] The invention provides a solar water heating system including a heat transfer fluid circuit and heat exchanger for transferring heat from the heat transfer fluid to water, wherein the heat transfer fluid circuit includes a bypass path via which the heat transfer fluid is diverted around the heat exchanger in response to an overheating condition indication.

[006] The bypass path can include a cooling arrangement to remove heat from the heat transfer fluid.

[007] The cooling arrangement can include an air cooled radiator.

[008] The radiator can be cooled by forced air.

[009] The radiator can be provided with a solar shield to block solar radiation from the radiator at least during peak sunlight periods.

[010] The radiator can be enclosed in a housing which constrains the air flow to flow across the radiator.

[Oil] By locating the elements of the system to take advantage of thermal gradients, the heat transfer fluid circuit and/or the water circuit can be driven by thermosyphoning.

[012] The present invention also provides a solar water heating system including a heat transfer fluid circuit, a water tank, and heat transfer means in which heat is transferred between the heat transfer fluid and water to be heated, the system including a bypass valve and bypass path via which the heat transfer fluid or water is circulated around the bypass path in response to an overheating condition indication indicating that the temperature of the heat transfer fluid or the water has exceeded a predetermined value .

[013] The system can include overtemperature sensing means to detect the overheating condition and to operate the bypass valve in response thereto.

[014] The bypass valve can operate over a range of temperatures to progressively open the bypass path and close the flow of heated fluid to the heat transfer means as the temperature increases within the said range of temperatures.

[015] The bypass valve can operate in a step fashion to abruptly open the bypass path and shut off the flow of heated fluid to the heat transfer means when the temperature reaches a threshold value.

[016] The system can include a water circuit which includes the water tank, and wherein heated water from the heat transfer means is fed into a top portion of the water tank.

[017] Water can be fed from the tank to the heat transfer means from a bottom portion of the tank.

[018] Water drawn from the tank for external use can be drawn from the top portion of the tank.

[019] External water to be heated can be fed to the bottom portion of the tank.

[020] The bypass path can include a cooling arrangement to remove heat from the heat transfer fluid.

[021 ] The radiator can be air cooled.

[022] The system can include a fan, wherein the radiator is cooled by forced air from the fan.

[023] The radiator can be provided with a solar shield to block solar radiation from the radiator at least during peak sunlight periods.

[024] The radiator can be enclosed in a housing which constrains the air flow to flow across the radiator.

[025] The heat transfer fluid circuit can be driven by thermosyphoning.

[026] The water can be circulated by thermosyphoning.

[027] The present invention further provides a method of preventing overheating in a solar water heating system having a heat transfer fluid circuit including a solar collector and a heat transfer fluid path of a heat transfer means, the system including a water circuit including a water tank, the heat transfer means transferring heat from the heat transfer fluid to the water, the method including diverting the heat transfer fluid or the water from the heat transfer means to a bypass path in response to an overtemperature condition indication indicating that the temperature of the heat transfer fluid or the water has exceeded a predetermined value.

[028] The heat transfer fluid circuit can be driven by thermosyphoning.

[029] The bypass path can include a radiator, and the method can include cooling the radiator with a forced air draft.

[030] The present invention also provides a diverter valve having an inlet and two outlets, a changeover valve adapted to control the flow from the inlet to the first and second outlets, a temperature sensor sensing the temperature of the fluid entering the inlet and adapted to control the diverter valve to divert at least part of the flow from the first outlet to the second outlet when the temperature exceeds a predetermined value.

[031] The changeover valve can be adapted to change abruptly to divert the fluid to the second outlet when the temperature exceeds the predetermined value.

[032] The changeover valve can be adapted to change continuously to divert progressively more fluid from the first outlet to the second outlet when the temperature exceeds a predetermined value.

[033] The present invention also provides a solar water heating system as described above in paragraphs [12] to [26] including a diverter valve as described in paragraphs [30] to [32] to divert the heat transfer fluid from the heat transfer means to the bypass path.

Brief description of the drawings

[034] An embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[035] Figure 1 schematically illustrates a solar hot water system embodying the invention;

[036] Figure 2 schematically illustrates modifications to the embodiment of Figure 1;

[037] Figure 3 A & 3B show schematically a first embodiment of a three way valve;

[038] Figure 3 C & 3D show schematically a second embodiment of a three way valve;

[039] Figure 4 shows an alternative three way valve;

[040] Figure 5 shows an alternative system embodying the invention;

[041] Figures 6 A and 6B are a schematic illustration of the use of a phase change wax temperature sensor; and

[042] Figure 7 shows an alternative three way valve to that illustrated in Figure 4

Detailed description of the embodiment or embodiments

[043] The invention prevents overheating of the water by diverting the heat transfer fluid through a bypass path when the temperature of the water reaches a threshold value.

[044] Additionally, a radiator can be included in the bypass path to dissipate the heat collected by the solar collector.

[045] Referring to Figure 1, the solar water heating system 10 includes a heat transfer fluid circuit, including solar collectors 28, and heat transfer jacket 16 and interconnecting plumbing. The heat transfer jacket 16 surrounds the water tank 12. The heat transfer fluid enters the solar collector via inlet 27 and exits via outlet 25. The tank 12 with the heat transfer jacket 16 can be positioned above the solar collectors 28 to facilitate thermosyphoning in the heat transfer fluid circuit. While the tank 12 is shown in a horizontal orientation, thermosyphoning can employ a vertical tank.

[046] Where it is intended to have a fluid circuit driven by thermosyphoning, it is necessary to have at least a portion of the circuit in which there is a reverse temperature/height gradient, i.e., there must be a position in the circuit where cooler fluid is located at a greater height than hotter fluid. Thermosyphoning at a given flow rate will occur when the thermal differential is sufficient to overcome resistance to fluid flow in the circuit at the given flow rate.

[047] The system 10 also includes a diverter valve 26, and a bypass path including a thermal energy dissipation unit, such as a radiator 35 connected in parallel with the heat transfer jacket 16. In the case where the flow of heat transfer fluid through the bypass path is to be

driven by thermosyphoning, it is necessary to have the thermal dissipation unit located above the solar collector 28.

[048] In this embodiment, the water tank 12 is located above the solar collector 28, and this permits the heat transfer fluid to circulate due to thermosyphoning.

[049] Water enters the water tank 12 via inlet 20 and is drawn off via outlet 18.

[050] In operation, the valve 26 is switched to direct the heat transfer fluid into the heat transfer jacket 16 and blocks the heat transfer fluid from entering the radiator 35. However, if the water gets too hot, for example by exceeding a threshold temperature or pressure, a sensor and control arrangement causes valve 26 to switch to divert the heat transfer fluid through radiator 35 and to prevent the heat transfer fluid from entering the jacket 16. Alternatively, the valve 26 is operated by a sensor comparing a characteristic of the heat transfer fluid, such as temperature or pressure, with a threshold value.

[051] The sensor and control arrangement can be a thermostatically actuated valve. A sensor probe such as that used in relief valves in storage water heaters can be used to detect the threshold value at which the valve 26 is switched.

[052] Alternatively a phase-change wax thermostatic actuator such as that used in tempering valves can be used to trip the valve 26.

[053] The temperature sensitive element can be integrated into the valve 26, as discussed in more detail with reference to Figure 4 or Figure 7.

[054] The valve can be operated to gradually switch over from the tank 16 to the bypass path over a predetermined range of temperatures, or the valve 26 can alternatively be operated to switch more rapidly at or near a predetermined threshold temperature.

[055] As an alternative to having a temperature sensor incorporated into the valve 26, one or more sensors 39 (see, e.g., sensor 39 in Figure 2) can be provided to detect an overheating condition. The sensor(s) 39 can measure one or more of several parameters, such as temperature of the water, temperature of the heat transfer fluid, pressure of heat transfer fluid, pressure of water, hi the embodiment of Figure 2, the temperature of the water near the top of tank 12 can be measured by a temperature sensor.

[056] The embodiment shown in Figure 2 contains a number of features in common with those of the embodiment of Figure 1, and the same numbers are used to indicate like features. The embodiment shown in Figure 2 differs from that shown in Figure 1 in that it includes an external heat exchanger 36 in place of the heat exchange jacket 16. The heat transfer

fluid circuit includes a solar collector 28, a heat transfer fluid portion of heat exchanger 36 including inlet 46 and outlet 47, the three-way diverter valve 26 and the radiator 35, together with interconnecting pipes.

[057] The water circuit includes a hot water tank 12, the water path through heat exchanger 36 via the water inlet 38 and hot water outlet 37, cold water inlet 20, hot water outlet 18.

[058] Hot water from heat exchanger 36 is piped to the top of tank 12 via outlet 37, driven by the thermal water density gradient. This provides top down heating so that the hot water is delivered to the top of the tank 12. The hot water is drawn off from the system via hot water outlet 18. Due to the top down heating, hot water is made available at the top of the tank 12 more quickly than would be the case if the hot water were delivered to the bottom of the tank 12 from the heat exchanger 36 and the water in the tank heated more uniformly by convection within tank 12.

[059] To drive the thermosyphoning of the water circuit, the top portion of the tank 12 to which the hot water is delivered should be located above the top of the water path through the heat exchanger 36. Preferably the heat exchanger 36 is located below the bottom of the tank 12.

[060] In addition, the embodiment of Figure 2 includes a cowling41 around radiator 35.

Cowling 41 can serve one or more of a number of functions. It can act as a solar shade to prevent solar radiation impinging on the radiator 35, in which case the cowling 41 only needs to cover the top of the radiator. Direct sunlight would otherwise reduce the effectiveness of the radiator.

[061] In a further modification, a fan 42 is provided to blow air across the radiator 35.

Fan 42 can be used alone or. in conjunction with cowling 41 to constrain the air flow to a path across the radiator 35 and increase the rate of heat removal from the radiator.

[062] The fan can be powered by a number of alternative means including mains power and solar power. The embodiment of Figure 2 shows a solar-electric array 43 which can be used to power the fan 42. An optional storage battery 44 can also be provided. Voltage and current regulation and switching means (not shown) can also be provided.

[063] Figure 2 also schematically illustrates a controller 45 which can serve to control the operation of the fan 42 in response to one or more sensors 39. In addition, controller 45 can control the operation of the diverter valve 26. The controller is not essential to operate the valve

26, which can be self-actuating, as in the examples discussed with reference to Figure 1.

Similarly, the fan 42 can be operated by an autonomous control such as a thermal switch.

[064] In normal operation, the three-way valve directs the heat transfer fluid from the solar collector into the heat exchanger 36. The controller 45 determines if the water temperature or other measured parameter has exceeded a first predetermined threshold value, and causes three-way valve 26 to operate to divert the heat transfer fluid away from the exchanger 36 and into the radiator 35. This stops the transfer of heat from the heat transfer fluid to the water and diverts the heated heat transfer fluid to the radiator 35 which dissipates the heat to the atmosphere.

[065] The controller 45 can respond to a second sensor, not shown, which determines the temperature of the heat transfer fluid, and switches the fan 42 on when the temperature of the heat transfer fluid exceeds a second predetermined threshold value. Alternatively, the fan 42 can be switched on at the same time as the three-way valve 26 is switched to divert the heat. transfer fluid to the radiator 35. In a further alternative, the fan can have an autonomous control means such as a thermal switch.

[066] Figure 5 shows a further embodiment, in which the water is diverted to the bypass radiator. This figure is similar to Figure 1, except that valve 26 now connects the water circuit to the bypass radiator 35. The water can circulate through the bypass radiator 35 by thermosyphoning or it can be pumped by a pump (not shown).

[067] Figure 3 A & 3B show details of an embodiment of the diverter valve 26.

[068] Figure 3 A shows a first cylindrical valve element 131 having a closed end 132 and an open end 133. The cylinder also has first and second side openings 134A and 134B on opposite sides of the cylinder.

[069] In Figure 3B, the valve element 131 is shown in ghost inside a valve housing 136.

The valve housing has an axial opening 137 at one end and two branch openings 138 and 139 which are axially displaced from one another by a distance sufficient to ensure that when hole 134A aligns with _. opening 138, opening 139 is occluded by the cylinder wall of element 131 so that hole 134B does not align with opening 139, and vice versa.

[070] The element 131 is able to move axially in the housing 136 to align either hole

134A and opening 138 or hole 134B and opening 139.

[071] This drawing is intended to illustrate the operating principle of the valve. The drive mechanism is not shown, nor are the seals and key arrangements which would be used in the complete device.

[072] Figures 3 C & 3D show an alternative arrangement in which the valve element 301 is rotatable. The element 301 includes a closed end 302, an inlet aperture 303 and only one hole 304.

[073] The corresponding housing 306 has two openings at the same axial position, and the flow is controlled by rotating the element 301 to align hole 304 with either opening 308 or 309.

[074] The valve 140 of Figure 4 is a three-way valve with an inlet 145, a first outlet 146 and a second outlet 147. A piston 144 is designed to control the flow between the inlet 145 and the first and second outlets 146 and 147. In the present application, the piston is set to open the path between the inlet 145 and the first outlet 146, and to occlude the path between the inlet 145 and the second outlet 147. The valve includes a temperature sensor/valve trip 149, which is designed to trigger the piston to close off the path between the inlet 145 and the first outlet 146, and to open the path between the inlet and the second outlet 147 when the temperature of the water around the sensor 149 exceeds a threshold value.

[075] In the arrangement of Figure 4, the return spring 148 will push the piston 144 back to its upper location, once the fluid entering the inlet 145 has cooled down, thereby closing off outlet 147 from inlet 145. In the arrangement of Figure 4, the piston 144 can be locked in an initial position by an adjustment lock 152. The knob 141 can be used to load up a pre-load spring 151, which will also control the initial position of the piston 144 depending upon what ratio of opening between the outlets 146 and 147 is required. Thus if outlet 147 is to be initially shut off from inlet 145, no or little loading of preload spring 151 is required and the piston 144 position adjusted to maintain outlet 147 closed..

[076] In one embodiment, the sensor/valve trip 149 can be set to cause the piston to gradually change over between the normal operating position and the over temperature position by gradually moving the piston as the temperature of the water enters a range of temperatures, finally cutting off the normal path when a maximum temperature threshold is reached.

[077] In another embodiment, the sensor 149 can cause an abrupt switching over between the normal operating path and the over temperature path when the water temperature exceeds a specific threshold value.

[078] The sensor 149 can include a temperature sensitive material which expands and contracts with variation in temperature. Wax can be used for this application. A wax element can be contained in a cylinder with a latch-operating piston arrangement, so that thermal expansion of the wax causes the sensor piston to move and trip a latch arrangement which causes the path between inlet 145 and outlet 146 to be closed by the piston 144.

[079] The piston 144 can be spring loaded to facilitate abrupt tripping of the piston 144.

[080] Cooling of the wax causes the sensor piston to be restored to the normal operating position.

[081] The operation of a phase change wax temperature sensor is illustrated schematically in Figure 6. Figure 6A illustrates the case where the temperature has exceeded the phase change temperature of the wax. In Figure 6 A, a cylinder 61 is filled with wax 62 in its expanded phase. A piston, 63 is driven inside the cylinder to an extended position. The piston is shown as driving a pivoted armature 67 via a first member 65. The armature 67 is spring loaded by spring 64 to bias it towards a contracted position so that the spring force tends to resist the expansion of the wax. The spring stores some of the expansion energy of the wax.

[082] Figure 6B shows the phase change wax temperature sensor in its contracted position when the temperature is below the wax phase change temperature. The wax has contracted and the piston has been driven to the left by the return force of the spring 64 which assists the "suction" of the piston by the contracting wax to move the piston to the left.

[083] The wax phase change takes place over a limited temperature range so the change from the extended position of Figure 6 A to the contracted position of Figure 6B is fairly abrupt.

[084] Figures 6A & 6B are intended to illustrate the operation of the phase change wax temperature sensor. This operation can be adapted to controlling the operation of the change¬ over valve 44 in Figure 4 by the person skilled in the art without the need to exercise any inventive faculty.

[085] Illustrated in Figure 7 is a valve 140A, which is similar to the valve 140 of Figure

4, with like parts being like numbered. The valve 140A is operated by a probe 149 A which is made from a polymeric, metal or other material which will extend/expand by means of an increase in temperature. As the material of the probe 149 A expands, the portion of the probe above the piston 144 expands downwardly relative to, or away from the preload spring 151, thereby pushing the piston 144 in a downward direction to close off the outlet 146 and thereby opening the outlet 147. This compresses return spring 148, so that as the temperature of the fluid

cools the return spring 148 will push or return the piston 144, by means of an intermediate guide or push rod 151, to an upwardmost location, being the location of its initial position, thereby closing off outlet 147 and re-opening outlet 146.

[086] The invention has been described in the context of a solar water heater, but the person skilled in the art will readily recognise that the invention can readily be adapted to analogous applications without departing from the inventive concept.

[087] While the foregoing description and referenced figures show solar collection tubes with a single orientation, the solar collectors can employ panels which have the collection tubes oriented in a combination of one or more of: vertically oriented, horizontally oriented, or oriented at an angle to either the horizontal or vertical.

[088] Where ever it is used, the word "comprising" is to be understood in its "open" sense, that is, in the sense of "including", and thus not limited to its "closed" sense, that is the sense of "consisting only of. A corresponding meaning is to be attributed to the corresponding words "comprise", "comprised" and "comprises" where they appear.

[089] It will be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text. All of these different combinations constitute various alternative aspects of the invention.

[090] While particular embodiments of this invention have been described, it will be evident to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiments and examples are therefore to be considered in all respects as illustrative and not restrictive, and all modifications which would be obvious to those skilled in the art on reading the specification are therefore intended to be embraced therein.