WO2006039740A2

WO2006039740A2 - Top down water heater

Info

Publication number: WO2006039740A2
Application number: PCT/AU2005/001542
Authority: WO
Inventors: Quentin Arthur Carl Adam; Patrick Michael Conrick
Original assignee: Rheem Australia Pty Limited
Priority date: 2004-10-13
Filing date: 2005-10-06
Publication date: 2006-04-20
Also published as: WO2006039740A3; AU2005294105A1; AU2005294105B2

Abstract

A top down water heater includes a storage tank (10) and a heater enclosed in a housing (14). The housing (14) is arranged to draw cooler water from the bottom of the tank via pipe (12) and to deliver heated water to the top of the tank (10) via pipe (16). The water is circulated by thermosyphoning. The heater can be external to the tank or it can be located internal of the tank. Control means and temperature sensors regulate the heating of the water.

Description

Top down water heater

Field of the invention

[001] This invention relates to water heaters, and is of use in rapid reheating storage water heaters.

[002] B ackground of the invention

[003] On-demand heaters are known which only heat water when it is required. These heaters do not store water but rely on substantial on-demand heat input to heat the water as it passes through a heat exchanger.

[004] Storage hot water systems are known which consist of a tank and a heating element at the bottom of the tank. Storage heaters are capable of heating a large volume of water, but, when the hot water is depleted, they take a long time to reheat because all the water in the tank must be heated. In the known electric storage heaters, the heating element is located at the bottom of the tank to ensure that the water is heated. The heated water rises to the top of the tank by convection and mixes with the cold water as it rises, so that the water at the top of the tank is significantly cooler than the water which had been heated by the element. As a result, the whole of the contents of the tank need to be heated almost to the operating temperature before water at the desired temperature is available for use.

[005] A booster heater element can be added to the top of the tank to reduce this disadvantage.

[006] 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

[007] This invention proposes the use of a heater element in a heated water path adapted to receive water from the bottom of the tank and to deliver heated water to the top of the tank while substantially reducing or eliminating the convection mixing of the heated water with the water in the tank.

[008] In particular, the invention proposes a system in which thermosyphoning is used to circulate heated water.

[009] Thermosyphoning refers to the circulation of water in a circuit driven by the density differential between regions of water at different temperatures. In particular, the phenomenon occurs when a region of cool water is at a higher level than, and connected by a flow path to a warmer region of water at a lower level. Factors which influence the flow rate of thermosyphoning include the temperature differential, the height differential, and the resistance to flow in the thermosyphoning circuit.

[010] hi hot water systems, thermosyphoning can be used in a circuit having a first enclosed path in which warmer water rises from a warm region to a cooler region and a second enclosed path in which the cooler water descends to the warm region. As the warmest water is in the region of the heating region, the heating region optimally should be located near the bottom of, or below the bottom of, the tank. The heating region is connected to the top of the tank by an output water pipe from the heater and to the bottom of the tank by an input water pipe.

[011] A first embodiment of the invention provides a storage hot water system including a storage tank, and a water heating circuit, the water heating circuit including:

[012] a water heating enclosure including heating means;

[013] the heating enclosure having an inlet and an outlet;

[014] the enclosure being located in proximity to a lower portion of the tank;

[015] the inlet being connected at or near the lower portion of the tank;

[016] the outlet being connected by a water delivery pipe to discharge heated water at or near the top of the tank.

[017] The delivery pipe can rise external to the tank and enter the tank at or near a top region of the tank.

[018] Alternatively, the delivery pipe can be internal to the tank. [019] The heating means can be an electric element.

[020] The system can include a controller to control the rate at which heat is delivered by the heating means.

[021] The system can include including at least one temperature sensor located at a predetermined height on or in the tank.

[022] The system can include a controller responsive to at least one temperature sensor to switch the heating means off when the temperature detected by the temperature sensor rises to a first predetermined threshold value, and to switch the heating means on when the temperature detected by the temperature sensor falls to a second predetermined threshold value less than the first predetermined threshold value. [023] The system can include two or more temperature sensors each located at a corresponding height on or in the tank, and the controller can be programmable to permit the selection of a selected one of said temperature sensors, whereby the switching of the heating element can be programmed to occur at a selected height corresponding to the selected one of the temperature sensors.

[024] The system can include a peak temperature sensor located in or on the tank and at a height at or near the top of the heater enclosure, the peak temperature sensor being connected to a controller, the controller being responsive to the peak temperature sensor to reduce the average power to the heating means when the temperature indication from the peak temperature sensor exceeds a third threshold value.

[025] Preferably, the controller continues to reduce the power to the heating element as the temperature rises above the third threshold value.

[026] In a further embodiment, the controller switches the heating element off when the peak temperature sensor indicates a temperature above a fourth threshold value greater then the third threshold value.

[027] The system can include a thermosyphoning cutoff temperature sensor located in or near the tank at or above the height of the heating means to indicate that the thermosyphoning height and temperature differentials have fallen below a predetermined thermosyphoning value, a controller being responsive to the thermosyphoning cutoff temperature sensor to cut off power to the heating means when the thermosyphoning height and temperature differentials have fallen below the predetermined thermosyphoning value.

[028] The system can include an additional heating means located at or near the bottom of the tank and controlled to heat the water in the lower portion of the tank.

[029] The system can include a programmable or self-learning controller adapted to adjust to operating temperature thresholds according to a programmed or learned load pattern.

[030] The invention also provides a water heating system including a controller and a communication receiver adapted to receive remotely transmitted control signals, wherein the controller is responsive to control signals received by the communications receiver to control the operation of the water heating system. [031] The invention also provides a method of providing on-demand hot water in a storage water heating system including providing a heated water circuit which conducts heated water to or near to the top of the storage tank without convection mixing.

[032] The method can include heating water to be heated in a restricted heating region and transferring the heated water to an upper region of the tank by thermosyphoning.

[033] The method can include restricting the volume of water which is heated by detecting when the depth of heated water stored in the tank reaches a predetermined level, and discontinuing heating the water.

Brief description of the drawings

[034] 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:

[035] Figure 1 shows a schematic illustration of a first embodiment of the invention;

[036] Figure 2 shows detail of an embodiment of the heating element housing of Figure 1 ;

[037] Figure 3 shows an exploded view of the heating element housing of Figure 2;

[038] Figure 4 illustrates temperature stratification in a top down system;

[039] Figure 5 shows an alternative embodiment of the invention; and

[040] Figure 6 represents a daily load cycle.

Detailed description of the embodiment or embodiments

[041] In Figure 1, a storage hot water tank 10 has a cold water inlet 20 and a hot water outlet 18.

[042] A heating element housing 14 is mounted externally of the tank 10.

[043] The housing 14 is connected to the storage tank 10 by an inlet line 12 and an outlet 16. The housing contains a heating element, see, e.g., element 22 in Figure 3.

[044] The element 22 is an electrical heating element.

[045] Alternative embodiments of the heater are within the scope of the invention. For example, the heater can be a gas heater. The gas heater can be of similar operation to an "on- demand" heater, but controlled by the storage temperature tank sensor arrangement to maintain the hot water delivered to outlet 18 at or near the desired operating temperature. [046] The water inlet 12 to the heating element housing 14 draws water off from near the bottom of the tank 10. In operation, this water will be cooler than the water at the top of the tank.

[047] The outlet pipe 16 from the heating element housing 14 connects to the top of tank 10, and the hot water outlet 18 from the tank 10 draws water from the top of the tank 10. Thus the hot water outlet draws water from the zone of the tank 12 where the hot water from the heater 14 enters the tank.

[048] As best seen in Figure 4, the arrangement of the present invention results in a thermal discontinuity during reheating with heated water being above a thermal interface line 46 and cooler water below the thermal interface line. Figure 4 illustrates this schematically with the hot water 42 above line 46 and cooler water 44 below the line 46. While the temperature discontinuity is shown as a step function in the temperature profile graph, in practice there may be a more gradual transition zone, but effectively the water can be considered as being divided into two zones.

[049] As hot water from heater 14 enters via pipe 16, the hot water in the hot zone 42 is forced down the tank, so the dividing line 46 moves down the tank, and cooler water from the cooler zone 44 is forced into heating pipe 12 and thence to the heater 14. This action can be effected by the use of thermosyphoning because the hottest water is at top of the heater housing 14 and rises up pipe 16 to displace water in tank 10, forcing cooler water into the heater via pipe 12.

[050] The external element should be located as close to the bottom as possible and should be compact so as not to extend upwards to a large extent as the top of the housing 14 defines a limit of the thermosyphoning action. The restriction to the thermosyphoning flow can.be fixed and the power to the element varied to achieve a constant hot water set temperature. As the tank fills with heated water the distance between the thermal interface and the external element decreases. This means that the power to the element can be 'backed off to maintain the set temperature to avoid overheating of the water. Electrical power to the element can be regulated by an electronic controller, for example by 'pulse width modulation', i.e., varying the active part of the duty cycle, and the thermal interface can be located by thermo couples attached to the side of the tank.

[051] One or more temperature sensors can be placed on the side of the tank to measure the temperature.

[052] The temperature sensors can be thermistors whose resistance varies according to the temperature. [053] In one embodiment, two or more temperature sensors are arranged at different heights.

This permits a temperature profile of the water in the tank to be measured. The temperature readings can be fed to a controller, such as a microcomputer or a controller circuit. Where two or more temperature sensors are used, this can be used to control the position of the dividing line 46 to keep it between the lines by switching off the heater 14 when the sensor at the lower height equals or is slightly less than the temperature of the sensor which is placed higher on the tank 10. A number of such zones can be defined by a series of temperature sensors, and used to control the volume of the tank 10 which contains hot water. Thus if the load is less than the design load of the tank, it can be set to an effective volume which is less than the total volume of the tank. This provides an energy saving feature. This feature can be useful where, for example, the number of people in the household changes.

[054] Figures 2 & 3 show details of an embodiment of the heater arrangement 14. The housing 14 is attached to the tank via inlet pipe 12 and outlet pipe 16. Inlet pipe 12 delivers water from near the bottom of the tank 10 to heater arrangement 14. Outlet pipe 16 delivers heated water to near the top of tank 10.

[055] The housing includes a cap 26 to which a heater element 22 (Figure 3) is connected. A pair of electrical terminals 28 for supplying power to the element 22 protrude through the cap 26. The cap is threaded and fitted with a seal to prevent leakage.

[056] An electrical cut-out switch can be incorporated into the cap. This is particularly useful in the case of an open circuit fault in the heating element which could result in electrification of the water heating system. Thus the cut-out switch. is designed to detect an open circuit fault in the heating element. In addition, the cut-out switch can be designed to operate in the case of a short circuit or an earth fault, where the active side is connected through a fault to the housing.

[057] Temperature sensors 24 are located to respond to the incoming and outgoing water temperatures. Thermocouples can be used for this purpose. The temperature sensors 24 are connected to a controller (not shown) which can control the operation of the heater element 22.

[058] In this embodiment, the housing 14 is shown installed at an angle to the vertical with the hot water outlet 16 from the heater 14 rising up the outside of the tank. Pipe 16 connects slightly below the top of the housing 14. This arrangement is designed so that that heated water is not trapped in the top of the housing 14 and recirculated. This avoids the possibility of overheated water being trapped in the top of the housing of heater arrangement 14 which could lead to boiling of the trapped water. [059] The housing 14 and pipe 16 can be insulated to reduce heat loss.

[060] In an alternative arrangement, the pipe 16 can re enter the tank immediately at the top of the heater, and conduct the water to the top of the tank on the inside of the tank.

[061] Figure 4 exemplifies the thermal profile of the water in the tank. The thermosyphoning distance (TSD) is the distance between the thermal interface 46 and the heater 14. Where thermosyphoning is relied on to circulate the water through the heater housing 14, the rate of circulation due to thermosyphoning decreases as the thermal interface 46 moves lower in the tank. If the power supplied to the heater remains constant, the temperature of the water from the heater will increase due to the decreased flow rate. This can lead to overheating. Thus the power to the heater is reduced as the thermal interface descends. The reduction in power can be achieved by reducing the duty cycle of the heater, for example, by using pulse width modulation of the power to the heater.

[062] In addition, as the thermal interface approaches the lower portion of the tank, the thermosyphoning effect reduces to the extent that, where the thermal interface 46 is at or near the same height as the top of the heater, thermosyphoning effectively stops. While this does not prevent the system from performing satisfactorily in many circumstances, where it is desirable to heat all the water in the tank, a secondary heating element can be provided at the bottom of the tank to heat the portion which remains unheated by thermosyphoning.

[063] Temperature sensors can be used to detect various conditions, such as the lowering of the thermal interface to a point where the power needs to be reduced, and the point where the thermosyphoning has effectively ceased.

[064] When the thermal interface 46 reaches a point where thermosyphoning has slowed to a low rate, the external thermosyphoning heater element 22 is switched off to prevent overheating, and the secondary internal heater can be switched on to heat the remaining unheated water.

[065] Figure 5 illustrates an alternative embodiment of the invention in which the heating element, heater enclosure and heated water delivery pipe 16 are inside the tank 10. This arrangement can also support thermosyphoning because the internal pipe 16 delivers the heated water to the top of the tank and avoids the convection mixing which would occur if the housing 14 and pipe 16 were not included.

[066] Figure 6 illustrates an example of a daily load cycle for a hot water system exhibiting three heavy load periods interleaved with low load periods. The controller can be set to recognize these patterns and to adjust the heating cycles accordingly. For example, during the heavy load cycles the controller can be set to maintain the temperature between temperatures Tl and T2, while in the low load periods, the controller can maintain the temperatures between T3 and T4. Alternatively the controller can permit the temperature to fall to the lower threshold T4 before reheating while maintaining the upper threshold at Tl. The temperatures Tl to T4 can correspond to the temperature at the top of the tank, or Tl and T3 can correspond to temperatures at the top of the tank, and T2 and T4 can correspond to the temperature at a selected depth in the tank. The lower temperature thresholds T3 and T4 can reduce the power consumption during low load periods. Various other temperature thresholds can be set and temperature sensors can be located at various levels to sense the temperature of the water at different levels. This can be used to control a number of heating patterns. The load pattern can also be programmed to take account of varying usage patterns on different days of the week.

[067] In an alternative embodiment, the heater controller can be programmed to cooperate with the electricity supply utility to spread the peak load by heating to a first upper cutoff threshold temperature during a pre-peak period, and heating to a second, upper cutoff threshold temperature during peak electricity demand periods, where the second cutoff is lower than the first cutoff. The temperature could also be permitted to fall to a first reheat threshold temperature during off-peak electrical loading, and to a second, lower reheat threshold temperature during peak electrical load. This could be done on a time program or in response to a peak load indication, transmitted by the electricity utility either over the power lines or other suitable communication means.

[068] Thus a communication receiver, 54 in Figure 5, can be associated with the heater system to receive such signals. In particular, the communications receiver 54 could provide input signals for controller 52, which, in addition to the signals from the temperature transducers 56 from the tank, can also be responsive to external signals from the communication receiver 54 to control the operation of the heater. The temperature transducers 56 can be internal to the tank or external to the tank and in close contact therewith.

[069] The association of a communications receiver with a water heater also provides the ability to remotely control the operation of the heater, for example by switching off in advance of a prolonged absence, and switching on in advance of return after a prolonged absence. The controller/communication means can be adapted to provide restricted access to remotely adjust the operation of the heater system. An authorized user can communicate with communication means by the appropriate communication means and can have a PIN or other security code to provide authorized access to set the control functions of the controller. U2005/001542

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[070] While the embodiment has been describe with reference to electrical heating, other heating modes are possible. For example, gas heating can be used. It will be understood that the invention disclose and defined herein extends to all practicable alternative combinations of two or more of the individual features mentioned or evident from the text. All these different combinations constitute various aspects of the invention.

[071] 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.

[072] 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. AU of these different combinations constitute various alternative aspects of the invention.

[073] While particular embodiments of this invention have, been described, it will be evident to those skilled in the art that the present invention can 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 storage hot water system including a storage tank, and a water heating circuit, the water heating circuit including: a water heating enclosure including heating means; the heating enclosure having an inlet and an outlet; the enclosure being located in proximity to a lower portion of the tank; the inlet being connected at or near the lower portion of the tank; the outlet being connected to by a heated water delivery pipe to discharge heated water at or near the top of the tank.

2. A system as claimed in claim 1, wherein the delivery pipe rises external to the tank and enters the tank at or near a top region of the tank.

3. A system as claimed in claim 1, wherein the delivery pipe is internal to the tank.

4. A system as claimed in any one of claims 1 to 3, wherein the heating means is an electric element.

5. A system as claimed in any one of claims 1 to 4, including a controller to control the rate at which heat is delivered by the heating means.

6. A system as claimed in any one of claims 1 to 5, including at least one temperature sensor located at a predetermined height on or in the tank.

7. A system as claimed in claim 6, including a controller responsive to said at least one temperature sensor to switch the heating means off when the temperature detected by the temperature sensor rises to a first predetermined threshold value, and to switch the heating means on when the temperature detected by the temperature sensor falls to a second predetermined threshold value less than the first predetermined threshold value.

8. A system as claimed in any one of claims 6 or 7, including two or more temperature sensors each located at a different height on or in the tank, and wherein the controller is programmable to permit the selection of a selected one of said temperature sensors, whereby the switching of the heating element can be programmed to occur at a selected height/temperature combination corresponding to the selected one of the temperature sensors.

9. A system as claimed in any one of claims 1 to 8, including a peak temperature sensor located at or near the top of the heater enclosure, the peak temperature sensor being connected to a controller, the controller being responsive to the peak temperature sensor to reduce the average power to the heating means when the temperature indication from the peak temperature sensor exceeds a third threshold value.

10. A system as claimed in claim 9, wherein the controller continues to reduce the power to the heating element as the temperature rises above the third threshold value.

11. A system as claimed in claim 9 or claim 10, wherein the controller switches the heating element off when the peak temperature sensor indicates a temperature above a fourth threshold value greater then the third threshold value.

12. A system as claimed in any one of the preceding claims, including a thermosyphoning cutoff temperature sensor located in or near the tank at or above the height of the heating means to indicate that the thermosyphoning height and temperature differentials have fallen below a predetermined thermosyphoning value, a controller being responsive to the thermosyphoning cutoff temperature sensor to cut off power to the heating means when the thermosyphoning height and temperature differentials have fallen below the predetermined thermosyphoning value.

13. A system as claimed in any one of the preceding claims, including an additional heating means located at or near the bottom of the tank and controlled to heat the water in the lower portion of the tank.

14. A system as claimed in any one of the preceding claims, including a programmable or self- learning controller adapted to adjust to operating temperature thresholds according to a programmed or learned load pattern.

15. A water heating system including a controller and a communication receiver adapted to receive remotely transmitted control signals, wherein the controller is responsive to control signals received by the communications receiver to control the operation of the water heating system.

16. A method of providing on-demand hot water in a storage water heating system including providing a heated water circuit which conducts heated water to or near to the top of the storage tank without convection mixing.

17. A method of providing on-demand hot water in a storage water heating system as claimed in claim 16, including heating water to be heated in a restricted heating region and transferring the heated water to an upper region of the tank by thermosyphoning.

18. A method as claimed in claim 16 or 17, including restricting the volume of water which is heated by detecting when the depth of heated water stored in the tank reaches a predetermined level, and discontinuing heating the water.

19. A storage hot water system being substantially as hereinbefore described with reference to the figures of the accompanying drawings.