WO2008104016A1

WO2008104016A1 - A system and method for inhibiting freezing in a solar hot water system

Info

Publication number: WO2008104016A1
Application number: PCT/AU2008/000231
Authority: WO
Inventors: Brendan Vincent Bourke
Original assignee: Rheem Australia Pty Limited
Priority date: 2007-02-26
Filing date: 2008-02-20
Publication date: 2008-09-04
Also published as: AU2008221225B2; AU2008221225A1

Abstract

The system of protecting a solar water heating system from low temperature damage, the solar water heating system including one or more solar collectors (104), a water storage tank (102), a low power heater (120) adapted to deliver sufficient heat to prevent freezing of the water in the solar collector when the ambient temperature is below a minimum temperature. Temperature sensing means are adapted to determine a low temperature threshold and to initiate the heater upon detection of the low temperature threshold and circulation of the water through the solar collector.

Description

A system and method for inhibiting freezing in a solar hot water system

Field of the invention

[001 ] This invention relates to protection of solar water collectors from frost damage.

[002] The invention is applicable to solar water heating systems which have a tank mounted below the solar collectors or above the solar collectors. .

Background of the invention

[003] Direct solar water heaters heat the water in the solar panels, without the use of a heat transfer fluid and intermediate heat exchanger. Direct solar water heater systems operating in frost areas are prone to damage caused by freezing of the water. The frost protection strategy is to circulate water from the tank. There are often frost failures due to the circulated water being too low in temperature to protect the collectors. If the water entering the collector is not warm enough then the buoyancy is minimal and circulation maybe through only part of the collector so frost damage occurs.

[004] Also at some point in time the circulated water itself may freeze. This can even happed when the water heater includes a booster since customers are sometimes reluctant to turn them on. In some heaters, the circulated water exits and returns below the height of the booster element. Booster heaters are designed to heat the water in the tank to within the operating range of the system when there is insufficient solar heating to heat the water to the operating range. Thus the booster heater has high energy consumption. For example, the power rating of a booster may be of the order of 2.5 to 4 kw. Because of the high power rating of the booster, power conscious users may be disinclined to turn the booster on.

[005] In addition, the user may be absent from the building for long periods and may wish to have the booster turned off during those periods. Summary of the invention

[006] According to an embodiment of the invention, there is provided a solar water heating system including a solar collector and a storage tank with a booster heater and control means adapted to operate the booster heater when the temperature of the water falls below a first threshold temperature.

[007] The control means can be adapted to turn the booster heater element off when the temperature is above a second threshold temperature.

[008] According to a further embodiment of the invention, there is provided a method of protecting a solar water heating system from low temperature damage, the solar water heating system including one or more solar collectors, a water storage tank, a low power heater adapted to deliver sufficient heat to prevent freezing of the water in the solar collector when the ambient temperature is above a minimum temperature, the method including the steps of: detecting a first temperature threshold; and initiating a low power heater to heat the water circulating through the solar collector.

[009] The method can include the step of pumping the heated water through the solar collector.

[010] The invention also provides a solar water heating system including a solar collector, a storage tank, a booster heater, and control means adapted to operate the booster heater when the temperature of the water falls below a first threshold temperature, the booster heater means being adapted to deliver sufficient heat energy to prevent freezing of the water in the solar collector.

[011] The booster heater means can include a main booster heater having a first power rating, and a second booster heater having a second power rating less than the first power rating, one or more temperature sensors, and a controller responsive to at least one of the temperature sensors to initiate the second booster heater when the temperature falls below a first temperature threshold.

[012] The solar water heating system can include a controller [013] The solar water heating system can include power regulating means to regulate the power delivered by the heating means, and wherein the controller is programmable to control the power regulating means in response to one or more temperature sensors to operate the heating means in a low power mode when the temperature falls below a first temperature threshold.

[014] The solar water heating system can include a pump adapted to circulate water between the tank and the solar collectors).

[015] The booster heater can be a low powered element, for example a 1 kw heater.

[016] A heater of 300 to 400 watts is required to protect a system to -5°C.

[017] When in frost mode if the water heading to the collectors is < 8°C the booster element will be turned on.

[018] Preferably the element will be turned off when the pump is off or if water temperature is >12°C.

Brief description of the drawings

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

[020] Figure 1 is an illustration of a first solar collector and storage arrangement according to a first embodiment of the invention;

[021 ] Figure 2 shows a variation of the arrangement of Figure 1 ;

[022] Figure 3 is an illustration of an alternative arrangement embodying the invention;

[023] Figure 4 is a variation of the embodiment of Figure 3;

[024] Figure 5 is an illustration of an arrangement according to a further embodiment of the invention.

[025] Figure 6 illustrates a further system embodying the invention. Detailed description of the embodiment or embodiments

[026] The invention will be described with reference to the drawings

[027] The arrangements of the drawings show only a single solar collector, but two or more solar collectors may be used.

[028] In normal solar heating mode of the arrangement shown in Figure 1 , a storage tank 102 is located below the solar collector 104. The tank 102 receives heated water from solar panel 104 via pipe 114 connected to header 108 of the solar collector 104, and returns water to be heated to the lower header 106 of collector 104 via pipe 112. The circulation can be driven by thermosiphon action or, as shown in Figure 1, by pump 124.

[029] Hot water can be drawn from tank 102 via pipe 118, and mains pressure water can be added to the system via pipe 116.

[030] The inlet pipe 114 for the solar heated water is located below a booster heater element 120. This arrangement is desirable as it permits an efficient mode of operation which helps to optimize the use of the solar energy. However, because the booster is above the inlet point of pipe 114, turning on the booster heater 102 will first heat the water in the top of the tank 102 causing thermal stratification, this can result in "top-down" heating, so that the water in the bottom of the tank will not be completely heated. Thus cold water will still be drawn off to the solar collector via pipe 112. It is usual in such an arrangement to use the pump 124 as there may be insufficient buoyancy differential to initiate thermosiphon action.

[031 ] This embodiment of the invention proposes the use of a supplementary booster heater element 122 located below the return pipe 114 inlet. Thus the water heated by heater 122 is in the solar collector circulation path. Preferably, the supplementary booster heater 122 is located near the bottom of the tank.

[032] Optionally an inclined baffle plate 126 can be located above the element 122 and the inlet of pipe 114 to collect the heated water from element 122 as indicated by arrow 128. Alternatively, the element 122 can be located below outlet to pipe 112, and the baffle plate 126 can be located above the outlet to pipe 112 so that most of the water drawn into the outlet is the heated water from heater 122. Figure IA shows detail of the baffle plate 126 which is arcuate in shape to fit against the inner wall of the tank 102.

[033] A controller 130 receives temperature information from one or more temperature sensors located at specific points in the system. Only temperature sensor 132 located to measure the water temperature in the solar collector 104 and temperature sensor 134 located to measure the temperature of the water proximate the solar ports of the tank are shown to reduce the complexity of the drawing. Other sensors can measure the temperature of the water at strategic points in the system, and a sensor can also measure the ambient air temperature.

[034] The controller 130 can operate the pump and/or the supplementary booster heater 122 in response to the water temperature sensor 132 reaching predetermined readings. The dotted arrow 129 indicates the general direction of the solar collector circulation path within the tank 102.

[035] In one embodiment, the pump and heater are turned on when the temperature measured by sensor 132 falls to a first threshold, for example, 8°C. The supplementary booster heater 122 can remain on until the temperature rises to a second threshold value, for example, 12°C. The pump can either remain operating until a third threshold temperature value greater than the second threshold is reached, or the pump can be turned off at the second threshold.

[036] In an alternative arrangement, the temperature sensor 134 can also be used to measure the water temperature between the solar ports of the tank 102. When the temperature measured by sensor 132 falls to 8°C and the temperature measured by sensor 134 is above 12⁰C, the pump can be turned on while the supplementary booster heater is not turned on until the reading from the sensor 134 falls to 12°C or some other suitable temperature threshold, the supplementary booster heater can remain on until the water reading from sensor 132 rises to a fourth threshold value.

[037] While the controller can be adapted to initiate the full power boost when the water temperature in the tank falls below a desired operating temperature range, the controller 130 can be programmable to permit the user to inhibit full power boosting for periods selected by the user. Thus the controller is adapted to initiate the anti- freezing mode of operation when the full power boost has been inhibited by the user.

[038] The low power booster may be designed to prevent freezing down to a first low temperature, such as 5°C. In a further modification, where the temperature falls to a level where the low power booster is incapable of preventing freezing, the full power booster can be initiated by the controller 130 independently of whether or not the user has inhibited the full power operation.

[039] The temperatures specified above are examples only and a person skilled in the art, having read the patent specification will understand that the invention can be implemented over a range of temperatures.

[040] The controller 130 may include a keypad and display to enable the user to select operational preferences. The operation of the frost protection booster heater should be independent of the actions of the user of the system. In other words, the user may be enabled to stop the operation of the full power booster heater, but the low power anti- freeze booster operation should still be implementable by the controller and this should not be able to be overridden by the user. However, the system can also have a master control to permit safe maintenance etc.

[041 ] The water heater can be heated to above a sterilizing temperature to kill bacteria. For Legionella, the water can be heated to above 60°C for ten minutes. Using the main booster heater and the supplementary booster located in the lower portion of the tank, the heating can be carried out more efficiently than using the main booster heater located in the upper portion of the tank on its own.

[042] The controller 130 can thus be programmed to operate in a number of modes depending on the control inputs and user commands. It can operate in a first anti-freeze mode where the water in the tank has sufficient heat to prevent freezing, so that the supplementary heater is not used.

[043] The controller 130 can use the supplementary heater when the temperature of the tank water falls below a threshold value when the collector temperature sensor indicates the tank temperature is insufficient to reliably inhibit freezing in the collector. [044] Various other operational modes will present themselves to the person skilled in the art in the light of the use of the reduced power booster heater without departing from the inventive concept.

[045] Figure 2 illustrates a variation of the embodiment of Figure 1 in which the supplementary booster heater 222 is located in the circulation path of the solar collector on the inlet side of the collector. An enlarged housing 240 can be provided to house the supplementary heater 222. The housing 240 can form an inclined duct so that theπnosiphon action can be used to circulate the water when the element 222 is on. However, a pump such as 124 in Figure 1 can be used in this arrangement if desired. Details of temperature sensors and controller have been omitted from Figure 2.

[046] Figure 3 illustrates a solar water heater system in which the tank 302 is located above the solar collector 304. For example the solar collector and tank could be roof-mounted. Another difference from the arrangement of Figure 1 is that the tank 302 is oriented horizontally.

[047] Preferably, the supplementary booster heater 322 is located proximate the solar circulation outlet port 313 of tank 302.

[048] Figure 4 shows an alternative location for the supplementary booster heater 422 in the lower header 406.

[049] Figure 5 illustrates a further embodiment of the invention. In this arrangement, the configuration of the tank connexions differs from those of the arrangement of Figure 1. The tank has a single booster heating element 520 located in the lower portion of the tank. The heater element 520 is supplied via a power regulator 550 controlled by the controller 530 to regulate the power delivered to the element 520 from the power mains 560. Thus, when the anti-frost initiating conditions are detected by the temperature sensors such as 532, the controller 530 can initiate the anti- freezing mode of operation which involves the use of the element 520 in reduced power mode, so that sufficient heat energy is delivered to the water circulating through the solar collectors by pump 524 to prevent freezing. Preferably the element 520 is located in the lower portion of the tank so as to heat the water in the solar circulation path.

[050] In the embodiment of the invention illustrated in Figure 6, the tank is inside a building, as indicated by line 662, and the solar collector is outside the building. A branch pipe 660 includes the auxiliary heater 620 and a controllable valve 664. The valve 620 can be closed when the heater 620 is not energized. When the temperature falls to the chosen threshold value, the controller (not shown) opens valve 664 and starts the heater 620.

[051] 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.

[052] 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.

[053] 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 are therefore intended to be embraced therein.

Claims

1. A method of protecting a solar water heating system from low temperature damage, the solar water heating system including one or more solar collectors, a water storage tank, a low power heater adapted to deliver sufficient heat to prevent freezing of the water in the solar collector when the ambient temperature is above a minimum temperature, the method including the steps of: detecting a first temperature threshold; and initiating a low power heater to heat the water circulating through the solar collector.

2. A method as claimed in claim 1 , including the step of pumping the heated water through the solar collector.

3. A solar water heating system including a solar collector, a storage tank, a booster heater, and control means adapted to operate the booster heater when the temperature of the water falls below a first threshold temperature, the booster heater means being adapted to deliver sufficient heat energy to prevent freezing of the water in the solar collector.

4. A solar water heating system as claimed in claim 3, wherein the booster heater means includes a main booster heater having a first power rating, and a second booster heater having a second power rating less than the first power rating, one or more temperature sensors, and a controller responsive to at least one of the temperature sensors to initiate the second booster heater when the temperature falls below a first temperature threshold.

5. A solar water heater as claimed in claim 3, including a controller and power regulating means to regulate the power delivered by the heating means, and wherein the controller is programmable to control the power regulating means in response to one or more temperature sensors to operate the heating means in a low power mode when the temperature falls below a first temperature threshold.

6. A solar water heating system as claimed in any one of claims 3 to 5, including a pump adapted to circulate water between the tank and the solar collector(s).

7. A method of protecting a solar water heating system from low temperature damage substantially as herein described with reference to the accompanying drawings.

8. A solar water heating system substantially as herein described with reference to the accompanying drawings.