NZ560282A - A valve that is activated to reduce flow through a solar collector when the temperature of the fluid is too high - Google Patents

Abstract

A method to protect a solar water heating system (10) from an over temperature event. The solar water heating system (10) has a collector (12) to heat water and a storage tank (14) for holding the heated water. In normal operation water is circulated around the system using thermo-siphoning until a desired temperature is reached, at which time circulation is stopped by a temperature controlled valve (30) closing. In some circumstances though, this can lead to a damaging heat build-up in the water in the collector (12). To help prevent this heat build-up a small fluid bypass is built into the valve (30). This reduced flow is able to use the losses associated with the collector (12) to reduce the maximum temperature of the water in the collector. In particular, the system is suitable for collector panels with a 1st order panel loss at or greater than 3-5 watt/m2/°C. To avoid noise problems associated with boiling of the heat exchange fluid, it is desirable to have a 1st order panel loss greater than 3.5 watt/m2/°C and ensure that the system pressure is higher than 1.7 bar gauge.

Description

Thermo-siphon Restrictor Valve Field of the invention

[001] The present invention relates generally to solar heating systems. More particularly, the present invention relates to solar water heating systems. The invention can have broader use in other fields (eg, thermo-valves, thermo-control systems, etc) Background of the invention

[002] .Solar heating systems are well known in the art. Such systems are typically used to capture solar radiation and heat water for domestic and other uses. Over the years, a variety of solar water heating systems have been developed to meet specific consumer needs and environmental conditions.

[003] Although the design of solar water heating systems can significantly differ, certain components are common to all systems. Thus one of the main components of a solar water heating system is a collector adapted to be erected on the roof of a dwelling or other building so that solar energy is absorbed by a circulating fluid flowing within the collector.

[004] All solar water heating systems can b e classified as either direct or indirect, depending on whether household water is heated directly in the collector or a heat exchanger is used for transferring energy from the circulating fluid to a water storage facility containing household water.

[005] In direct systems, the circulating fluid is household water, and solar heated water is stored in a storage tank directly connected to the collector through a hot and cold water pipe. In indirect systems, alternative circulating fluids such as propylene glycol, methyl alcohol, oil or the like are used.

[006] One of the main disadvantages of prior art solar heating systems is heat build-up and the overloading of energy in the storage container occurring when the water temperature in the storage container rises to more 90-96° C. Such overloading triggers pressure and temperature relief which results in discharge of heated water until a 20° C drop in the water temperature has occurred.

[007] Likewise, some high performance solar systems are provided with an arrestor valve, the main function of which is to shut off the flow of the circulating fluid completely when the water temperature reaches a pre-set level.

WO 2007/012108 PCT/AU2006/000918 2

[008] In some high performance solar heating systems, the closing off of the arrestor valve increases the temperature of the collector to dangerous stagnation conditions, causing the fluid within the collector to boil and form gaseous pockets. This often results in increased system pressure, vibration, noise, mineral deposition and accelerated localized corrosion.

[009] The present invention aims to ameliorate the above-mentioned deficiencies of the prior art solar heating systems.

[010] 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

[011] The present invention provides a method of controlling an over-temperature event in a solar heating system, said system including a solar collector, said method including the step of reducing the flow of liquid to the solar collector so as to enable the collector losses to increase through the collector.

[012] The step of reducing the flow can be performed by a valve which will not fully close off said flow or if fully closed shall have a fixed bypass.

[013] The valve can ensure that flow is not fully closed off by providing a by-pass which will allow a minimum flow.

[014] The method is applicable to collectors having first order losses greater than 3.5watt/m2/°C.

[015] The present invention also provides a heating system including heating means for supplying thermal energy to a fluid to be heated; a delivery line and a discharge line respectively connected to said heating means for feeding thereto the fluid to be heated and for withdrawing the heated fluid therefrom; a valve in said delivery line, said valve including an inlet port, an outlet port, means for defining a fluid flow path from said inlet port to said outlet port, control valve means disposed in said flow path and moveable between open and quasi-closed positions respectively corresponding to flow and quasi no flow conditions in said main flow path for controlling flow of the fluid to said heating means, said quasi-closed position being dependent on a pre-determined temperature of the fluid in said heating means, and whereby a displacement of the control valve means as a result of a temperature change in the fluid temperature influences the flow through said fluid flow path.

WO 2007/012108 PCT/AU2006/000918 3

[016] The present invention also provides a heating system including heating means for supplying thermal energy to a fluid to be heated; a delivery line and a discharge line respectively connected to said heating means for feeding thereto the fluid to be heated and for withdrawing the heated fluid therefrom; a valve in said delivery line, said valve including an inlet port, an outlet port, means for defining a main fluid flow path from said inlet port to said outlet port, control valve means disposed in said main flow path and moveable between open and closed positions respectively corresponding to flow and no flow conditions in said main flow path for controlling flow of the fluid to said heating means; and by-pass means for defining a fluid flow by-pass from said delivery line to said heating means.

[017] Said by-pass means can be located within said valve. Preferably said by-pass means is disposed within said valve control means.

[018] Preferably said by-pass means is at all times in fluid communication with said inlet port and with said outlet port of said valve.

[019] Alternatively said by-pass means can be disposed in by-passing relation to the control valve means.

[020] Preferably said valve includes a valve housing having an inlet chamber and an outlet chamber, a piston guide means located within said housing, a piston slidable within said piston guide means between a valve-closed position wherein said piston closes a main flow path between the inlet and outlet chambers of the valve and a valve-open position wherein said outlet chamber communicates with said inlet chamber via said main flow path, and at least one by-pass duct communicating with said inlet chamber and with said outlet chamber, said communication occurring at least when said valve is in said valve-closed position.

[021] More preferably said by-pass duct is at all times in fluid communication with said inlet chamber and with said outlet chamber of said valve.

[022] Preferably said by-pass duct is located within said piston.

[023] More preferably said by-pass duct is a coaxial bore running through said piston in a direction parallel to the longitudinal axis of said valve.

[024] Preferably said piston includes a cylindrical portion and a collar extending from said cylindrical portion, said collar being provided with one or more main flow ducts running through said collar in a direction perpendicular to the longitudinal axis of said valve.

[025] Preferably said piston is mounted to a thermostatic valve element; said valve includes a retainer to which an end of said thermostatic valve element is secured; said retainer, said WO 2007/012108 PCT/AU2006/000918 4 thermostatic valve element and said piston being arranged such that, at a pre-set temperature, the piston sealingly engages the piston guide means to thereby shut off the flow of the fluid through said one or more main flow dupts.

[026] Preferably said valve further includes bias means.

[027] The present invention also provides a solar water heating system operating under a thermo-siphon principle, said system including a water storage container, a collector, said collector being connected to said water storage container through a delivery line, a valve located in said delivery line, said valve including a valve body having an inlet port and an outlet port defined therein for passage therethrough of a circulating fluid, and a valve member displaceable in said valve body for opening and closing a first communication passage, said valve member including by-pass means defining a second communication passage, said by-pass means at all times connecting said inlet and outlet ports.

[028] The present invention also provides a solar water heating system operating under a thermo-siphon principle, said system including a water storage container; a collector, a heat exchanger, said collector being connected to said heat exchanger through a delivery line; a valve located in said delivery line, said valve including a valve body having an inlet port and an outlet port defined therein for passage therethrough of a circulating fluid, and a valve member displaceable in said valve body for opening and closing a first communication passage, said valve member including by-pass means defining a second communication passage

[029] The present invention further provides a method of preventing boiling noises in a solar water heating system, said system including a heat exchanger, said method including the step of increasing the viscosity of a fluid circulating in said heat exchanger.

[030] The method can include the step of increasing the percentage of a heat transfer fluid circulating in said heat exchanger. [03 1] Said heat exchanger can include an expansion space.

Brief description of the drawings

[032] An embodiment or embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: WO 2007/012108 PCT/AU2006/000918

[033] Figure 1 is a schematic view of a direct solar water heating system according to the present invention;

[034] Figure la is a schematic view of an indirect solar water heating system according to the present invention ;

[035] Figure 2 is an exploded perspective view of a valve adapted to be installed in a solar flow line of the solar water heating system of Fig. 1;

[036] and

[037] Figure 3 is a schematic cross-sectional view of the valve of Fig. 2 in a closed position;

[038] Figure 4 illustrates atop view of the valve of Fig. 2;

[039] Figure 5 shows the valve of Fig. 2 in an open position;

[040] Figure 6 illustrates a linear test data correlation between the efficiency of a collector of a solar water heating system and the mean temperature in the collector; and

[041] Figure 7 is a schematic, cross-sectional view of a water storage container of the system of Fig. la.

Detailed description of the embodiment or embodiments

[042] Illustrated in Fig. 1 is a direct solar water heating system 10 operating under a thermo-siphon principle. The system 10 includes a collector 12 in the form of a flat panel adapted to be erected on a roof of a building (not shown), and a water storage container 14 connected to the collector 12 by two pipes - a delivery pipe 16 supplying "cold water" to the collector 12 (also known as 'solar flow line5) and a discharge pipe 18 carrying "hot water" to the storage container 14 (also known as 'solar return line).

[043] The storage container 14 is held at a height slightly above that of the collector 12 to thereby enable the thermo-siphon flow of water between the collector 12 and the container 14. The storage container 14 is provided with a "cold water" inlet port 20 and with a pressure and temperature relief valve 22, the functions of which has been described earlier in this specification.

[044] Illustrated in Fig. Ia is an indirect solar water heating system. Similarly to the direct system 10, the system 11 includes a collector 12 and a water storage container 14. The WO 2007/012108 PCT/AU2006/000918 6 storage container 14 is provided with a "cold water" inlet port 20 and with a pressure and temperature relief valve 22.

[045] The system 11 further includes a heat exchange jacket 13 connected to the collector 12 by two pipes - a delivery pipe 16 supplying "cold water" to the collector 12 ('the solar flow line) and a discharge pipe 18 carrying "hot water" to the heat exchange jacket 13 ('the solar return line).

[046] The heat exchange jacket 13 is provided with a pressure relief valve 23 operable at the pressure of 200kPa.

[047] As shown in Fig. 7, the heat exchange jacket 13 includes a heat exchange jacket • filling point 90. The jacket 13 includes a heat exchange fluid 92 and an expansion space 94 defined by a heat exchange fluid level 96.

[048] The water storage container 14 containing potable water 98 is disposed in a casing 100. The space between the casing 100 and the water storage container 14 includes an insulating material 102.

[049] Located in the solar flow line 16 is a valve 30 designed to control the flow of water through the solar flow line 16 when the water temperature in the storage container 14 reaches a pre-set temperature T. In a preferred embodiment of the present invention, the pre-set temperature is 65° C. It will be appreciated by those skilled in the art that a different pre-set temperature can be chosen.

[050] As best illustrated in Figs. 2 and 3, the valve assembly 30 includes a valve housing 32, a retainer 34, a thermostatic valve element 36, a piston 38 mounted to said valve element, and a spring 40.

[051] The valve housing 32 is designed to be installed "in-line" in the solar flow line 16 and includes two external threaded portions 42.1 and 42.2 adapted to engage complementary internal threaded portions (not shown) of the delivery pipe 16. As shown in Figs. 3 and 4, the valve housing 32 is provided with a middle portion 42.3 adapted to engage a driving portion of a complementary instrument. It will be appreciated by those skilled in the art that the middle portion 42.3 can be in the form of a hexagonal nut or any other suitable form known in the prior art.

[052] The valve housing 32 includes an inlet chamber 44 and an outlet chamber 48 terminating to an inlet port 46 and an outlet port 50 respectively thereby defining a flow path for "cold water" flowing through the pipe 16 into the collector 12.

WO 2007/012108 PCT/AU2006/000918 7

[053] The inlet chamber 44 includes a cylindrical guide portion 52 for guiding the axial movement of the piston 38 within the chamber 44. As best illustrated in Fig. 2, the spring 40 is disposed within the inlet chamber 44 between an annular region 54 of the housing 42 and the piston 38.

[054] The outlet chamber 48 includes an internal threaded portion 56 adapted to engage an external threaded portion 58 of the retainer 38.

[055] The retainer 38 includes a sleeve portion 60 to which the stem 62 of the valve element 36 is secured. The body of the retainer 38 is provided with a plurality of coaxial openings 64.1, 64.2, 64.3 forming a portion of the flow passage through the valve 30.

[056] As best illustrated in Fig. 3, the piston 38 is secured to the stem 62 of the valve element 36 by means of a threaded connection 66, the arrangement being such that a thermostatic extension of the valve element 36 causes the piston 38 to move upwards within the cylindrical guide portion 52 of the inlet chamber 44.

[057] The piston 38 is adapted to slidably engage the piston guide 52. The piston 38 includes a cylindrical portion 68 provided with a collar 70 extending therefrom in a direction parallel to the axis of the valve 30. The collar 70 includes one or more main flow ducts 72.1 and 72.2 running through the collar 70 in a direction perpendicular to the axis of the valve 30 and diverting the main flow from the inlet port 46 through the communication passage indicated by airows 74 to the outlet port 50 of the valve 30.

[058] As a result, the main flow ducts 72.1 and 72.2 define the main flow passage 74 between the inlet chamber 44 and the outlet chamber 48 when the valve 30 is an open position, as illustrated in Fig. 5.

[059] As best illustrated in Fig. 3, the piston 38 includes a by-pass duct 80 running through the cylindrical portion 68 of the piston 38 in a direction parallel to the axis of the valve 30 and defining a flow by-pass route between the inlet port 46 and the outlet port 50, regardless of whether the valve 30 is in an open or closed position.

[060] As illustrated in Fig. 3, when the valve 30 is in a closed position the cylindrical surface of the piston guide 52 seals the main flow ducts 72.1 and 72.2 thereby preventing the flow of the fluid through the communication passage 74.

[061] The solar hot water system 10 operates as follows. The valve 30 is installed "inline" in the solar flow line 16 so that the outlet port 50 of the valve is connected to an inlet port WO 2007/012108 PCT/AU2006/000918 8 (not shown) of the collector 12 via the lower portion of the supply line 16 and the inlet port 46 of the valve 30 is connected to the upper portion of the supply line 16.

[062] When the water temperature in the collector 12 reaches a pre-set level T, the thermostatic material of the stem 66 undergoes expansion causing the stem 66 of the valve element 36 to move upwards overcoming the stiffness of the spring 40 and the force of the pressure acting on the upper surface of the piston 38. As a result, the stem 66 urges the cylindrical sealing portion of the piston 38 to progressively seal the ducts 72.1 and 72.2 against the cylindrical piston guide 52 to thereby prevent communication between ports 46 and 50 through the communication passage 74.

[063] When the valve 30 is in the closed position, the inlet chamber 44 is in communication with the outlet chamber 50 by way of the by-pass route through the duct 80. It will be understood by those skilled in the art that the above statement is made on the assumption that the piston 38 forms a substantially fluid-tight seal against the cylindrical guide 52 when the valve 30 is in a closed position.

[064] When the water temperature drops, the bias of the spring 40 combined with the force of pressure acting on the piston 38 cause disengagement of the sealing portion of the piston 38 and the piston guide 52. As a result, the main ducts 72.1 and 72.2 are being cleared progressively, allowing water to flow through the communication passage 74.

[065] Since the valve 30 does not shut off the flow in the delivery pipe 16 completely, fluid stagnancy can be avoided even if the main flow passage 74 is closed off. Consequently, the present invention ensures temperature protection without the interruption of the flow of the fluid between the collector 12 and the storage container 14. It is expected that a 90% restriction in flow (eg, 4 litres/minute - the valve 30 fully open, 0.4 litres/minute - the valve 30 closed) will be satisfactory to provide temperature protection.

[066] In particular, the valve of the present invention reduces the thermo-siphon flow at a pre-set temperature which in turn increases the mean temperature Tm in the collector 12 up to 130°. This results in reduced efficiency r| of the collector 12, as illustrated in Fig. 6 (where r| 0 Q -power output, A- the aperture area of the collector, G - radiation, Q= mCp(te-ti), m - collector water mass flow rate, Cp- specific heat of water, te - collector water outlet temperature, ti - collector water inlet temperature, Tm - the mean temperature in the collector 12, Ta- ambient temperature). The efficiency graph illustrates that the efficiency r| of the WO 2007/012108 PCT/AU2006/000918 9 collector drops off with higher AT/G, where AT=Tm-Ta. Thus, when Tm=I 30 C, AT/G = 0.1 and the power is less than 10% of peak radiation.

[067] In particular, the present invention is suitable for collector panels with the 1st order panel loss at or greater than 3-5watt/m2/°C. To avoid noise problems associated with boiling of the heat exchange fluid, it is desirable to have the 1st order panel loss greater than 3.5watt/m2/°C and ensure that the system pressure is higher than 1.7 bar gauge. The invention is particularly effective for collector panels with the 1st order panel loss up to 8 watt/m2/°C.Boiling noises can be reduced by increasing the percentage of the heat transfer fluid circulating in the heat exchange jacket 13. Ln particular, the boiling noises can be reduced by increasing the percentage of propylene glycol from 30% to 40%, which results in an increased viscosity of the fluid. Thus, the kinematic viscosity of 30% propylene glycol @20°C is 3 mm2/sec; the kinematic viscosity of 40% propylene glycol @20°c is 4.33 mm2/sec; the kinematic viscosity of 50% propylene glycol @20°c is 6.21 mm2/sec.

[068] A by-pass effect can also be achieved if a separate flow by-pass line is branched from the solar flow line 16 of the hot water system 10. Such a branch can be located within the body of the valve housing 32. Alternatively, a separate by-pass pipe can be connected to the solar flow line 16, the branch points of the by-pass pipe being located upstream and downstream of the valve 30 respectively.

[069] A by-pass effect can also be achieved by a valve which does not fully close off the flow of the fluid through the valve thereby providing a minimum flow sufficient to prevent the stagnation of the fluid. Such minimum flow can be described as a "quasi no flow" condition.

[070] 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.

[071] 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.

[072] 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 WO 2007/012108 PCT/AU2006/000918 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 are therefore intended to be embraced therein.

Received at IPONZ 30 November 11

Claims (28)

1. A method of controlling an over-temperature event in a solar heating system, said system including a solar collector, said method including the steps of detecting an overtemperature condition, and reducing the flow of liquid through the solar collector so as to enable the collector losses to increase through the collector.

2. A method of claim 1 wherein the step of reducing the flow of liquid is performed by a valve which does not fully close off said flow.

3. A method of claim 2 wherein said valve provides a by-pass which allows a minimum flow.

4. A method of claim 1 wherein the first order losses of said collector are greater than 3.5 watt/m2/°C.

5. A method as claimed in claim 1, the method being adapted to reduce boiling noises in a solar water heating system including a heat exchanger, wherein the over-temperature event is the generation of noise from the boiling of the liquid, and wherein the step of reducing the flow of liquid includes the step of increasing the viscosity of a the liquid.

6. A method as claimed in any one of claims 1 to 5, wherein the fluid includes a heat transfer fluid additive which acts as a viscosity modifier, the method including the step of increasing the percentage of a heat transfer fluid additive in the circulating fluid.

7. A method of claim 6 wherein said heat transfer fluid additive is propylene glycol.

8. A method of claim 6 wherein the percentage of a heat transfer fluid additive is more than 30%.

9. A method of claim 6 wherein the percentage of a heat transfer fluid additive is more than 40%.

10. A method of claim 6 wherein said the viscosity of said circulating fluid is more 3 mm2/sec.

11. A method of claim 6 wherein said the viscosity of said circulating fluid is more 4 mm2/sec.

12. A heating system including: a storage tank to store heated water; a heat source adapted to deliver heat to a fluid to be heated; a fluid path to circulate the fluid between the heat source and either (1) a heat exchanger adapted to deliver heat to the water in the storage tank, or (2) the storage tank; a thermally controlled valve in the fluid path; the valve being operable between a first state and a second state; the first state being an open state; the second state being a quasi-closed state wherein flow of the fluid in the fluid path is reduced to a non-zero flow; Received at IPONZ 30 November 12 valve control means to control the valve; the valve control means controlling the valve to assume the first state when the temperature of the heated fluid is below a first threshold temperature; and the valve control means including a thermostatic element controlling the valve to assume the second state when the temperature of the fluid exceeds first threshold temperature.

13. A heating system as claimed in claim 12 , wherein the tank and the heat source are located to enable the fluid to circulate by thermosiphoning.

14. A heating system as claimed in claim 12 or claim 13, wherein the heat source is a solar collector.

15. A heating system as claimed in claim 14, wherein the non-zero flow is chosen to reduce the efficiency of the solar collector to a level such that the first order collector loss exceeds the heat delivered to the fluid by the collector.

16. A heating system as claimed in any one of claims claim 12 to 15, including a fluid bypass path adapted to permit a reduced non-zero flow of fluid in the fluid path past the valve when the valve is in the second state.

17. A system of claim 16 wherein said by-pass path is located within said valve.

18. A system of claim 16 wherein said by-pass path is disposed within said valve control means.

19. A system of claim 16, wherein said valve includes an inlet port and an outlet port, wherein said by-pass path is at all times in fluid communication with said inlet port and with said outlet port of said valve.

20. A system of claim 16 wherein said valve includes a valve housing having an inlet chamber and an outlet chamber, a piston guide means located within said housing, a piston slidable within said piston guide means between a valve-closed position wherein said piston closes a main flow path between the inlet and outlet chambers of the valve and a valve-open position wherein said outlet chamber communicates with said inlet chamber via said main flow path, and at least one by-pass duct communicating with said inlet chamber and with said outlet chamber, said communication occurring at least when said valve is in said valve-closed position.

21. A system of claim 20 wherein said by-pass duct is at all times in fluid communication with said inlet chamber and with said outlet chamber of said valve.

22. A system of claim 20 or 21 wherein said by-pass duct is located within said piston.

23. A system of claim 22 wherein said by-pass duct is a coaxial bore running through said piston in a direction parallel to the longitudinal axis of said valve. Received at IPONZ 30 November 13

24. A system of claim 20 wherein said piston includes a cylindrical portion and a collar extending from said cylindrical portion, said collar being provided with one or more main flow ducts running through said collar in a direction perpendicular to the longitudinal axis of said valve.

25. A system of claim 20 wherein said piston is mounted to a thermostatic valve element; said valve includes a retainer to which an end of said thermostatic valve element is secured; said retainer, said thermostatic valve element and said piston being arranged such that, at a pre-set temperature, the piston sealingly engages the piston guide means to thereby shut off the flow of the fluid through said one or more main flow ducts.

26. A system as claimed in any one of claims 20 to 25 wherein said valve further includes bias means.

27. A system as claimed in any one of claims 20 to 26 wherein said heat exchanger includes an expansion space.

28. A system as claimed in any one of claims 20 to 29, wherein the valve is a two-port valve.