WO2007098561A1

WO2007098561A1 - Methods and apparatuses for operating hot water systems

Info

Publication number: WO2007098561A1
Application number: PCT/AU2007/000262
Authority: WO
Inventors: Patrick Pussell
Original assignee: Dux Manufacturing Limited
Priority date: 2006-03-02
Filing date: 2007-03-02
Publication date: 2007-09-07
Also published as: AU2007219645B2; AU2007219645A1

Abstract

The present invention relates to methods and apparatuses for operating hot water systems. In one particular embodiment, a hot water system (100) comprises a water tank (110) for storing water, a heating element (116) disposed in said water tank and a solar heating sub-system (140 and 150) for heating water stored in the water tank (110) and an electronic controller (120) adapted to control operation of the heating element (116) and solar heating sub-system (140 and 150) so as to: ensure that water in the water tank reaches a first predefined temperature at least once in a predefined time duration on a continuous basis, ensure that the temperature of water delivered from the hot water system is greater than or equal to a second predefined temperature and operate the heating element only when energy delivered by the solar heating sub-system is insufficient to heat the water in the hot water system.

Description

METHODS AND APPARATUSES FOR OPERATING HOT WATER

SYSTEMS

Related Applications

This application claims priority from Australian Provisional Patent Application No. 2006901060, filed on 2 March 2006, the entire contents of which are incorporated herein by way of reference.

Field of the Invention The present invention relates to hot water systems and more particularly to methods and apparatuses for economically operating hot water systems in accordance with recommended or mandated requirements.

Background Energy sources such as electricity and gas are limited and costly resources and reduced consumption of such resources thus features strongly in environmental sustainability studies, initiatives and policies. Additionally, a reduction in energy consumption results in reduced pollution and consequential environmental destruction. Domestic and industrial hot water systems are significant energy consumers. As a consequence, methods and systems for controlling operation and energy consumption of hot water systems are highly desirable.

Furthermore, authorities from time-to-time recommend or mandate certain operating requirements for hot water systems. For example: • for health reasons, a hot water system should ensure that the water therein is heated to a specified minimum temperature in a specified period to sanitise the water tank and thus prevent or arrest harmful bacteria and diseases such as legionnaires disease;

• for safety reasons, a hot water system should not discharge boiling water or water above a specified temperature to avoid scalding consumers; • for environmental reasons, a hot water system should derive a specified minimum contribution of its operational heating capability from solar energy; and

• for consumer reasons, a hot water system should not deliver water having a temperature less than a specified minimum temperature.

Not all of the above requirements are necessarily recommended or mandated together by a particular authority. Other requirements may alternatively or additionally be recommended or mandated. Furthermore, for reasons of economy, a hot water system should be capable of using the most economical of a number of heating sources available. Traditional electric hot water systems in Australia generally operate using ON/OFF control based on a dumb thermostat. The thermostat is typically set at about 75 degrees to prevent consumers running out of hot water. This results in significant energy losses when the system is in stand-by mode (i.e., no hot water usage). Certain existing hot water systems utilize a supplementary heating arrangement located externally to a main water tank (also known as "post boost") for heating the water by way of a gas or electrically powered heating element prior to delivery to a consumer. This results in unnecessarily increased system costs.

Certain existing hot water systems delay sanitisation for as long as possible, for example, up to every 30 days.

A need exists to provide methods and apparatuses that facilitate operation of hot water systems so as to overcome or at least ameliorate one or more disadvantages associated with existing arrangements.

Summary

According to one aspect of the present invention, there is provided a hot water system comprising a water tank for storing water, a solar heating sub-system and a heating element disposed in the water tank for heating water stored in the water tank and an electronic controller adapted to control operation of the heating element and solar heating sub-system so as to: ensure that water in the water tank reaches a first predefined temperature at least once in a predefined time duration on a continuous basis, ensure that the temperature of water delivered from the hot water system is greater than or equal to a second predefined temperature and operate the heating element only when energy delivered by the solar heating sub-system is insufficient to heat the water in the hot water system. The electronic controller may further be adapted to ensure that the temperature of water in the water tank is less than or equal to a third predefined temperature.

Another aspect of the present invention provides a method for operating a hot water system. The method comprises the steps of: ensuring that water in the water tank reaches a first predefined temperature at least once in a predefined time duration on a continuous basis, ensuring that temperature of water delivered from the hot water system is greater than or equal to a second predefined temperature and operating the heating element only when energy delivered by the solar heating sub-system is insufficient to heat the water in the hot water system. The method may comprise the further step of ensuring that the temperature of water in the water tank is less than or equal to a third predefined temperature.

Another aspect of the present invention provides an apparatus for operating a hot water system comprising a water tank, a solar heating sub-system and a heating element disposed in the water tank. The apparatus comprises a memory for storing data and instructions to be performed by a processor and a processor coupled to the memory. The processor is programmed to: ensure that water in the water tank reaches a first predefined temperature at least once in a predefined time duration on a continuous basis, ensure that temperature of water delivered from the hot water system is greater than or equal to a second predefined temperature and operate the heating element only when energy delivered by the solar heating sub-system is insufficient to heat the water in the hot water system. The processor may further be programmed to ensure that the temperature of water in the water tank is less than or equal to a third predefined temperature.

In certain embodiments, the first predefined temperature is about 6O⁰C, the second predefined temperature is about 4O⁰C, and the predefined time duration is about 24 hours.

Another aspect of the present invention provides a hot water system comprising a water tank for storing water, a plurality of heating sources for heating water in the water tank and an electronic controller adapted to control operation of the plurality of heating sources. Each of the heating sources is associated with a respective running cost. The electronic controller selectively operates the plurality of heating sources such that predetermined temperature requirements applicable to water in the water tank are met and an overall running cost of the hot water system is minimized.

Another aspect of the present invention provides a method for operating a hot water system comprising a water tank and a plurality of heating sources for heating water in the water tank. Each of the heating sources is associated with a respective running cost. The method comprises the steps of heating water in the water tank and selectively operating the plurality of heating sources such that predetermined temperature requirements applicable to water in the water tank are met and an overall running cost of the hot water system is minimized.

Another aspect of the present invention provides an apparatus for operating a hot water system comprising a water tank and a plurality of heating sources for heating water in said water tank. Each heating source is associated with a respective running cost. The apparatus comprises a memory for storing data and instructions to be performed by a processor and a processor coupled to the memory. The processor is programmed to selectively operate the plurality of heating sources such that predetermined temperature requirements applicable to water in the water tank are met and an overall running cost of the hot water system is minimized.

Li certain embodiments of the present invention, the heating element is only activated when the solar heating sub-system is incapable of meeting the predetermined temperature requirements applicable to water in the water tank. hi certain embodiments of the present invention, a determination is made whether water in the water tank has reached a predefined sanitisation temperature during an immediately past predefined time period and the heating element is activated if water in the water tank has not reached the predefined sanitisation temperature during the immediately past predefined time period. Another aspect of the present invention provides a method for operating a hot water system comprising a water tank, at least one heating source and consumption detecting means for detecting water consumption from the hot water system. The method comprises the steps of predisposing the temperature of water in the hot water system to be within a predefined temperature range by selectively operating the at least one heating source, periodically heating water in the water tank to a predefined sanitisation temperature, and selectively operating the at least one heating source in response to detection of water consumption from the hot water system.

Another aspect of the present invention provides a hot water system comprising a water tank for storing water, at least one heating source for heating water in the hot water system, consumption detecting means for detecting water consumption from the hot water system, and an electronic controller coupled to the at least one heating source and the consumption detecting means. The electronic controller is adapted to predispose the temperature of water in the hot water system to be within a predefined temperature range by selectively operating the at least one heating source, periodically heat water in the water tank to a predefined sanitisation temperature, and selectively operate the at least one heating source in response to detection of water consumption from the hot water system.

Another aspect of the present invention provides an apparatus for operating a hot water system comprising a water tank, at least one heating source and consumption detecting means for detecting water consumption from the hot water system. The apparatus comprises a memory for storing data and instructions to be performed by a processor and a processor coupled to the memory. The processor is programmed to predispose the temperature of water in the hot water system to be within a predefined temperature range by selectively operating the at least one heating source, periodically heat water in the water tank to a predefined sanitisation temperature, and selectively operate the at least one heating source in response to detection of water consumption from the hot water system. The hot water system may comprise primary and secondary heating sources and the primary heating source may only be operated when energy delivered by the secondary heating source is insufficient to heat the water in the hot water system. The secondary heating source may comprise a solar heating sub-system. The water in the water tank may be heated to the predefined sanitisation temperature once every 24 hours. A time for heating water in the water tank may be determined based on operation of a pump in the solar heating sub-system. Detection of water consumption may be performed by comparing water temperature at the middle of the water tank with water temperature at the bottom of the water tank.

Brief Description of the Drawings

Embodiments are described hereinafter, by way of example only, with reference to the accompanying drawings in which:

Fig. 1 is a system block diagram of a hot water system according to an embodiment of the present invention;

Fig. 2 is a block diagram of an electronic controller for the hot water system of Fig.

1;

Fig. 3 is a flow diagram of a method for operating a hot water system such as the hot water system of Fig. 1; Fig. 4 is a flow diagram of another method for operating a hot water system such as the hot water system of Fig. 1;

Fig. 5 is a system block diagram of a hot water system according to another embodiment of the present invention;

Fig. 6 is a flow diagram of another method for operating a hot water system such as the hot water system of Fig. 5;

Fig. 7 is a flow diagram of another method for operating a hot water system such as the hot water system of Fig. 5; and

Fig. 8 is a graph showing water temperature as a function of time for a hot water system and/or method in accordance with an embodiment of the present invention. Detailed Description

Embodiments of methods and apparatuses are described herein for operating hot water systems in accordance with one or more operational requirements. Although the embodiments described hereinafter are described with reference to gas and electrically heated hot water systems, the embodiments described hereinafter have application to other types of hot water systems, including heat pump driven hot water systems.

Use of the term "consumer" in the context of this specification includes, but is not limited to, households and commercial premises within the scope intended.

Fig. 1 is a system block diagram of a hot water system 100 that comprises a hot water tank 110, a heating element 116 disposed in the water tank 110, an electronic controller 120, a flow measuring device 130, a solar collector 140 and a circulation pump 150. Cold water is introduced into the hot water tank 110 via the inlet path 114, typically from a water supply main. Hot water is drawn from the hot water tank 110 for consumption via the outlet path 112. The amount of water consumed from the hot water tank 110 may be measured by the flow measuring device 130 or by another alternative arrangement such as detection of a temperature differential in or across the water tank, which is caused by cold water replenishment when hot water is consumed. The flow measuring device 130 may alternatively be disposed in the outlet path 112. Furthermore, certain embodiments of the present invention may not require determination of hot water consumption and a consumption determining device (e.g., the flow measuring device 130) is thus not essential for all embodiments.

Water in the hot water tank 110 is heated by a solar heating sub-system that comprises the solar collector 140 and the pump 150, and/or a heating element 116. Colder water is pumped from the bottom of the hot water tank 110 by the pump 150 to the solar collector 140 via paths 144 and 146. The water in the solar collector 140 is heated by solar panels and re-enters the hot water tank 110 via path 142.

The electronic controller 120 is processor-based (i.e., microprocessor or microcontroller) for controlling operation of the hot water system 100. Specifically, the controller 120 may be used to activate and de-activate the heating element 116 and/or the pump 150. The hot water system 100 may further comprise temperature sensors (not shown) for determining the temperature of: water in the solar collector (T₀), water at the top of the water tank 110 (T_t) and water at the bottom of the water tank 110 (T_b). The temperature sensors are interfaced to the controller 120 for providing temperature readings. The hot water system 100 described with reference to Fig. 1 may be operated in accordance with the methods described hereinafter with reference to Figs. 3 and 4.

Fig. 2 is a block diagram of an embodiment of the electronic controller 120 in Fig. 1. Control of the hot water system 100 is performed by a software control program resident in the memory of the microcontroller 210. In one particular embodiment, the microcontroller 210 comprises a Microchip PIC16F676 CMOS 8-bit microcontroller. The PIC16F676 has 1,792 bytes of flash-based program memory, 64 bytes of RAM and 128 bytes of EEPROM and also includes an on-board 10-bit analog-to-digital (AfD) converter. However, as would readily be appreciated by those skilled in the art, other microcontrollers or microprocessors may alternatively be practiced in the controller 210. Various memory and peripheral configurations may also be practiced, such as a combination of on-board and off-board memory.

The microcontroller 210 controls devices in the hot water system 100 via output ports that are interfaced to the devices by means of input/output interface circuitry 220. In one embodiment, the heating element 116 and the pump 150 are controlled via relays, which form part of the input/output interface circuitry 220. However, alternative control elements may also be practiced, including solid state switches such as thyristors and triacs.

The microcontroller 210 obtains data from devices in the hot water system 100 via input ports that are interfaced to the devices by means of input/output interface circuitry 220. This enables the volume of hot water consumed (i.e., drawn from the hot water system 100) to be communicated to the microcontroller 210. Thus, the microcontroller 210 is able to control operation of the heating element 116 in accordance with usage of hot water from the hot water system 100. The microcontroller 210 may also obtain data relating to the temperature of the water at the top and bottom of the hot water tank 110 (T_t and Tb, respectively) and at the solar collector 140 (T_c) from temperature sensors (not shown in Fig. 1) coupled via the input/output interface circuitry to input ports of the microcontroller 210. Thus, the microcontroller 210 is able to control the pump 150 to circulate the water in the solar heating sub-system in accordance with the differential in temperature between the water in the hot water tank 110 and the solar collector 140.

The microcontroller 210 may also be coupled to an RF transceiver 250 via an RF communications interface 240 for receiving information from and/or transmitting information to a remote entity. Such information may, for example, be used to perform intelligent metering of consumption by the remote entity. The RF transceiver 250 may comprise a communications module for cellular telephone type communication (e.g., GSM, GPRS or CDMA). Other types of communications transceivers may alternatively be practiced, which may use communications channels such as the ultra-high frequency (UHF), very-high frequency (VHF) or microwave bands. Still further, a receiver only may be practiced in place of the RF transceiver 250. The RF transceiver may be used to communicate with fixed or mobile, hand-held RF communication devices.

The microcontroller 210 may also be coupled to an RS-232 communications interface 230 to provide a communication link to a computer apparatus (not shown). Various other types of communications interfaces may be practiced in place of the RS- 232 interface, such as a RS-485 interface, a parallel interface, an infra-red interface, a Universal Serial Bus (USB) interface, or any other commonly available or proprietary communications interfaces. The computer apparatus may comprise a Personal Computer (PC), a Personal Digital Assistant (PDA), a mobile telephone, or any other off-the-shelf or proprietary computer apparatus. Parameters for operation of the controller 210 may be adjusted by, and/or downloaded to, the controller 210 from such a computer apparatus via the RS-232 communications interface 230. In certain embodiments, bootstrap loader software installed in the program memory of the microcontroller 210 enables downloading of new and/or revised control software to the controller 210 via the RS-232 communications interface 230.

The microcontroller 210, RF communications interface 240, the RF transceiver 250 and the RS-232 communications interface are powered by a power supply 260, which receives input power from the mains supply. Fig. 3 is a flow diagram of a method for operating a hot water system comprising a water tank, a solar heating sub-system and a heating element, such as the hot water system shown in Fig. 1.

Referring to Fig. 3, step 310 ensures that water in the water tank reaches a first predefined temperature at least once in a predefined time duration on a continuous basis.

In a particular embodiment, it is ensured that water in the water tank reaches 6O⁰C at least once in every 24 hour cycle for purposes of sanitising the water tank (e.g., for the prevention of legionnaires disease). It should be noted, however, that alternative predefined temperatures and/or time durations may be practiced, for example, in accordance with specific requirements for a particular authority or region.

Step 320 ensures that the temperature of water delivered from the hot water system is greater than or equal to a second predefined temperature. This is a consumer issue, which may also be mandated by an authority, that water delivered by the hot water system is sufficiently hot. In a particular embodiment, it is ensured that the temperature of the water delivered by the hot water system does not drop below 4O⁰C despite a sustained lack of solar power. Once again, alternative predefined temperatures may be practiced.

For reasons of energy conservation, it is desirable that the temperature of the water in the water tank be maintained at a temperature only slightly above the second predefined temperature. In a particular embodiment, the tank water temperature is generally maintained between 4O⁰C and 45⁰C, except when the water is deliberately heated to a first predefined temperature for sanitisation purposes.

Step 330 ensures that the heating element is only operated when energy delivered by the solar heating sub-system is insufficient to heat the water in the hot water system to a predefined temperature (e.g., 4O⁰C). An optional further step may ensure that the temperature of water in the water tank is less than or equal to a predefined maximum temperature to avoid water of too high a temperature being delivered to a consumer, which may cause burns or scalding.

The method of Fig. 3 may be practiced as a computer program executed by the electronic controller 120 shown in Fig. 1 or Fig. 2. Those skilled in the art will appreciate that the temperature values and ranges referred to in the description hereinbefore relating to Fig. 3 are for purposes of explaining a particular embodiment of the present invention only and that other values and ranges may alternatively be practiced. For example, the tank water temperature may alternatively be maintained generally between 4O⁰C and 55⁰C.

Fig. 4 is a flow diagram of a method for operating a solar-boosted, gas-heated hot water system. The method of Fig. 4 is described when operational to control the hot water system 100 of Fig. 1 and may be practiced as a computer program executed by the controller 120.

The method begins at step 401. At step 401, two counters or timers (Cntr_t and Cntr_p) are initialized to zero and turned on and a variable representative of the maximum temperature of water in the water tank (T_stored) is initialized to zero. Cntr_t is a 24-hour incrementing timer used to ensure that the water tank is sanitised at least once every 24 hours. Cntrp is an incrementing timer for determining the length of time the solar pump has been turned off. The main program loop comprising steps 402 to 437 is executed approximately every 5 minutes and may, for example, be triggered by a timer interrupt. Other timer interrupt intervals may alternatively be practiced.

At step 402, the temperature at the top of the water tank (T_t) is read and compared to the stored temperature (T_stored)- If the temperature at the top of the water tank (T_t) is greater than the stored temperature (T_stOr_ed)_> then the temperature at the top of the water tank (Tt) is saved in the variable T_stOred- Thus, T_stored maintains the maximum water temperature in the water tank.

At step 403, a determination is made whether Cntr_t is less than or equal to 24 hours. If not (NO), a determination is made whether the water in the water tank has reached 6O⁰C in the last 24 hours, at step 411. If T_stored < 6O⁰C (YES), the water has not reached 6O⁰C in the last 24 hours and the solar pump is turned off and the gas heating is turned on, at step 421. At step 423, a determination is made whether T_t. is greater than or equal to 6O⁰C. If not (NO), processing returns to step 421 until the water reaches 6O⁰C. When the water reaches 6O⁰C (YES), Cntr_t and T_stOre_d are both reset to zero at step 425 and processing continues at step 427. At step 427, a determination is made whether the gas heating and the solar pump are off. If so (YES), processing continues at step 431. If not (NO), the gas heating and the solar pump are turned off at step 429 before processing continues at step 431.

Returning to step 411, if T_stored is greater than or equal to 6O⁰C (NO), the water in the water tank has reached 6O⁰C in the last 24 hours and Cntr_t and T_stOred are both reset to zero at step 413 and processing continues at step 415.

Steps 415 and 417 maintain the temperature that water is typically delivered at within a range of 4O⁰C to 45⁰C. At step 415, a determination is made whether T_t is less than or equal to 45⁰C. If not (NO), no heating is required and processing continues at step 427. If so (YES), a determination is made at step 417 whether T_t is less than or equal to 4O⁰C. If not (NO), no heating is required and processing continues at step 427. If so (YES), a determination is made at step 418 whether the gas heating is on. If so (YES), processing continues at step 431. If not (NO), the gas heating is turned on and the solar pump is turned off at step 419 before processing continues at step 431.

Returning to step 403, if Cntr_t is less than or equal to 24 hours (YES), a determination is made at step 404 whether the temperature of the water in the solar panels (T₀) is more than 2⁰C higher than the temperature of the water at the bottom of the hot water tank (T_b). If not (N), processing continues at step 415. If so (YES), a determination is made at step 405 whether the temperature of the water at the top of the water tank (T_t) is less than or equal to 45⁰C. If so (YES), processing continues at step 417. If not (NO), a determination is made at step 406 whether the temperature of the water in the solar panels (T_c) is more than 1O⁰C higher than the temperature of the water at the bottom of the hot water tank Tb. If not (N), processing continues at step 402. If so (YES), a determination is made at step 407 whether the solar pump is on. If the solar pump is on, processing continues at step 435. If not (NO), the solar pump is turned on and the gas heating is turned off at step 408, Cntr_p is turned off and reset to zero at step 409 and processing continues at step 435.

At step 435, a determination is made whether the temperature of the water in the solar collector (T_c) is higher than 9⁰C and less than or equal to 115⁰C. If so (YES), processing continues at step 402. If not (NO), a determination is made at step 436 whether the temperature of the water in the solar collector (T₀) is less than or equal to 5⁰C. If so (YES), processing returns to step 407. If not (NO), a determination is made at step 437 whether the temperature of the water in the solar collector (T₀) is higher than or equal to 12O⁰C. If so (YES), processing returns to step 407. If not (NO), processing returns to step 402.

Returning now to step 431, a determination is made whether Cntr_p is on. If so (YES), processing continues at step 433. If not (NO), Cntr_p is reset to zero and turned on at step 432 and processing continues at step 433. At step 433, a determination is made whether Cntr_p is greater than or equal to 10 hours. If not (NO), processing continues at step 435. If so (YES), Cntr_t is preset to 16 hours and Cntr_p is turned off and reset to zero at step 434, before processing continues at step 435.

Thus, when Cntr_p has run for 10 hours (i.e., the solar pump has been off overnight), Cntr_t is preset to 16 hours so that 8 hours will elapse before Cntr_t is next detected to reach 24 hours at step 403. This enables the temperature of the water in the water tank to be heated to 6O⁰C (using gas heating) in the late afternoon for sanitation purposes, provided it has not already reached 6O⁰C in the past 24 hours. Gas heating of the water to 6O⁰C in the late afternoon is advantageous in that more hot water becomes available to the consumer before commencement of a peak demand period. The late afternoon activation of the sanitisation cycle is automatically adjusted for seasonal changes by virtue of the overnight detection performed using Cntr_p. Use of Cntr_p and Cntr_t to measure time durations relative to overnight detection advantageously avoids the need for a real-time clock. This, in turn, enables use of a more economical electronic controller.

The method of Fig. 4 may be practiced as a computer program executed by the controller 120 shown in Fig. 1 or Fig. 2. Those skilled in the art will appreciate that the temperature values and ranges referred to in the description hereinbefore relating to Fig. 4 are for purposes of explaining a particular embodiment of the present invention only and that other values and ranges may alternatively be practiced.

hi other embodiments of the present invention, water in the water tank is heated by selectively operating a plurality of heating sources such that predetermined temperature requirements applicable to water in the water tank are met and an overall running cost of the hot water system is minimized. hi one particular embodiment, the plurality of heating sources comprises a solar heating sub-system and a heating element disposed in the water tank. The heating element is only activated when the solar heating sub-system is incapable of meeting the predetermined temperature requirements applicable to water in the water tank, as solar heating is more economical than gas or electrical heating. A determination is made whether water in the water tank has reached a predefined sanitisation temperature during an immediately past predefined time period. The predefined time period is preferably about 24 hours, as per the embodiment of Fig. 4, but other predefined time periods may alternatively be practiced. The heating element is activated if water in the water tank has not reached the predefined sanitisation temperature during the immediately past predefined time period. The predefined sanitisation temperature is preferably about 6O⁰C but other predefined sanitisation temperature may alternatively be practiced.

The heating element may be de-activated when water in the water tank has reached the predefined sanitisation temperature. Alternatively, the heating element may be deactivated when water in the water tank has reached or exceeded the predefined sanitisation temperature for a predefined time duration.

Fig. 5 is a system block diagram of a hot water system 500 that is substantially similar to the hot water system 100 shown in Fig. 1. Elements of the hot water system 500 of Fig. 5 having the same reference numerals as those of the hot water system 100 of Fig. 1 are the same as, or substantially similar to, those described hereinbefore in relation to Fig. 1. For example, the hot water system 500 of Fig. 5 comprises a hot water tank 110, a heating element 116 disposed in the water tank 110, an electronic controller 120, a solar collector 140 and a circulation pump 150, as described in relation to the hot water system 100 of Fig. 1. However, the hot water system 500 of Fig. 5 does not comprise a flow measuring device 130 as shown in Fig. 1. The hot water system 500 of Fig. 5 comprises 4 temperature sensors 510, 520, 530 and 540, which are interfaced to the controller 120 for providing temperature readings. The temperature sensor 510 provides the temperature of water at the bottom of the tank (T_b), the temperature sensor 520 provides the temperature of water at the middle of the tank (T_m), the temperature sensor 530 provides the temperature of water at the top of the tank (Tt), and the temperature sensor 540 provides the temperature of water in the solar panels/collector (T_c). In an alternative embodiment, the temperature sensor 520 for providing the temperature of water at the middle of the tank (T_n,) may be omitted. CoId water is introduced into the hot water tank 110 via the inlet path 114, typically from a water supply main. Hot water is drawn from the hot water tank 110 for consumption via the outlet path 112. The amount of water consumed from the hot water tank 110 may be measured by the detection of a temperature differential in or across the hot water tank 110, which is caused by cold water replenishment when hot water is consumed. Such a temperature differential may be detected using any combination of the temperature sensors 510, 520 and/or 530

Water in the hot water tank 110 is heated by a solar heating sub-system that comprises the solar collector 140 and the solar pump 150, and/or a heating element 116. Colder water is pumped from the bottom of the hot water tank 110 by the pump 150 to the solar collector 140 via paths 144 and 146. The water in the solar collector 140 is heated by solar panels and re-enters the hot water tank 110 via path 142.

The electronic controller 120 is processor-based (i.e., microprocessor or microcontroller) for controlling operation of the hot water system 100. Specifically, the controller 120 may activate and de-activate the heating element 116 and the pump 150.

The hot water system 500 described with reference to Fig. 5 may be operated in accordance with the methods described hereinafter with reference to Figs. 6 and 7.

Fig. 6, comprising Figs. 6a and 6b, is a flow diagram of a method for operating a solar-boosted, electrically-heated, hot water system. The method of Fig. 6 is described when operational to control the hot water system 500 of Fig. 5 and may be practiced as a computer program executed by the controller 120.

The method begins at step 602. At step 602, a counter or timer (Cntr) is initialized to zero and turned on, a variable representative of the maximum temperature of water in the water tank (T_stOred) is initialized to zero, and a solenoid valve (S) in the solar subsystem is closed. The solenoid valve enables the water in the solar sub-system to be drained or filled. Cntr is a 24-hour incrementing timer.

The main program loop comprising steps 604 to 658 is executed approximately every 1 minute and may, for example, be triggered by a timer interrupt. Other timer interrupt intervals may alternatively be practiced.

At step 604, the temperature at the top of the water tank T_t is read and compared to the stored temperature T_st_ored. The current value of Cntr is also read. If the temperature at the top of the water tank T_t is greater than the stored temperature T_stored and more than 4 hours have elapsed since Cntr was last reset (i.e., Cntr > 4 hours), then the temperature at the top of the water tank (T_t) is saved in the variable T_stOred- Thus, T_stOre_d maintains the maximum water temperature in the water tank. Use of the counter/timer (Cntr) as a qualification provides a delay of at least 4 hours before the stored temperature T_stored is updated after a sterilisation event occurs.

Steps 606, 608 and 610 provide over-temperature protection for the hot water system.

At step 606, a determination is made whether T_t is less than 85 ⁰C. If T_t is greater than or equal to 85⁰C (NO), a determination is made at step 608 whether the solar pump is on. If the solar pump is off (NO), processing continues at step 626. Otherwise, if the solar pump is on (YES), the solar pump is turned off at step 610 and processing continues at step 626. The solar pump is turned off at step 610 to stop further heating of the water in the hot water tank to prevent damage to, or extend the life of, the hot water tank. Steps 612 to 624 comprise a control loop for controlling the solar sub-system.

Returning to step 606, if T_t is less than 85⁰C (YES), a determination is made whether the solar pump is on, at step 612. If the solar pump is on (YES), a determination is made at step 614 whether the temperature of the water in the solar panels T₀ is greater than 2⁰C higher than the temperature of the water at the bottom of the hot water tank T_b. If so (Y), processing continues at step 626. If not (NO), the solar pump is turned off at step 616 as the solar heating is inefficient at a temperature differential of less than 2⁰C. A determination is made at step 618 whether more than 4 hours have elapsed since Cntr was last reset (i.e., Cntr >= 4 hours). If not (NO), processing continues at step 626. If more than 4 hours have elapsed since Cntr was last reset, then Cntr is reset at step 620 and processing continues at step 626.

Returning to step 612, if the solar pump is off (N), a determination is made whether the temperature of the water in the solar panels (T₀) is more than 1O⁰C higher than the temperature of the water at the bottom of the hot water tank (T_b). If T₀ - T_b > 10⁰C (Y), the solar pump is turned on at step 624, Cntr is reset at step 620, and processing continues at step 626. If not (NO), processing continues at step 626.

Steps 626 and 640 to 646 comprise a control loop for effecting sterilization of the hot water tank when necessary (e.g., once every 24 hours). At step 626, a determination is made whether Cntr is greater than 24 hours. If Cntr > 24hrs (YES), a determination is made whether the water in the water tank has exceeded 6O⁰C in the last 24 hours (i.e., a sterilization event has occurred in the last 24 hours), at step 642. If T_sto_red ^> 6O⁰C (YES), sterilization is unnecessary. Accordingly, Cntr and T_stored are reset at step 646 and processing continues at step 648. However, if the water in the water tank has not exceeded 6O⁰C in the last 24 hours (NO at step 642), sterilization is required. A determination is made at step 644 whether the heating element is on. If the heating element is on (YES)₅ processing continues at step 648. If not (NO), the heating element is turned on at step 640 and processing continues at step 648. Steps 626 to 640 comprise a control loop for generally maintaining the temperature in the hot water tank within a temperature range of 45⁰C to 5O⁰C. The water temperature is generally maintained with reference to the middle of the hot water tank (i.e., T₀). However, if the water temperature at the bottom of the hot water tank T_b is substantially colder than the water temperature at the middle of the hot water tank T_m, the water is heated. This ameliorates the problem of "segmentation" (i.e., bands of water at different temperatures forming in the tank) caused by cold water replenishment at the bottom of the tank as hot water is drawn off (i.e., consumed) from the top of the tank.

Returning to step 626, if Cntr is less than or equal to 24 hours (NO), a determination is made at step 628 whether the heating element is on. If so (YES), a determination is made at step 630 whether the temperature of the water at the middle of the tank T_m is greater than 5O⁰C. If not (NO), processing continues at step 648. However, if T_m > 5O⁰C (YES), a determination is made at step 632 whether the temperature of the water at the middle of the tank T_m exceeds the temperature of the water at the bottom of the tank T_b by more than 25⁰C. If not (NO), the heating element is turned off at step 634 and processing continues at step 648. IfT_n,- Tb > 25⁰C (YES), processing continues at step 648.

Returning to step 628, if the heating element is off (NO), a determination is made at step 636 whether the temperature of water at the middle of the tank T_m is less than 45⁰C. If T_n, < 45⁰C (YES), the heating element is turned on at step 640 and processing continues at step 648. If not (NO), a determination is made at step 638 whether the temperature of the water at the middle of the tank exceeds the temperature of the water at the bottom of the tank by more than 25⁰C. If T_m - T_b > 25⁰C (YES), the heating element is turned off at step 634 and processing continues at step 648. If not (NO)₅ processing continues at step 648.

Steps 648 to 656 comprise a control loop for protecting the solar sub-system against frost. This control loop may be unnecessary in certain deployment areas and is thus an inessential feature of the system. A solenoid (S) controls a valve that enables the water in the solar sub-system to be drained or filled.

At step 648, a determination is made whether the solenoid valve is open. If the solenoid valve is closed (NO), a determination is made at step 650 whether the water temperature in the solar collector T_c is greater than 5⁰C. If T₀ > 5⁰C (YES), processing reverts to step 604. If not (NO), the solenoid valve is opened at step 652 and processing reverts to step 604.

Returning to step 648, if the solenoid is open (YES), a determination is made at step 654 whether the water temperature in the solar collector T_c is greater than 9⁰C. IfT₀ > 9⁰C (YES), the solenoid valve is closed at step 656 and processing reverts to step 604. If not (NO), processing reverts to step 604 without closing the solenoid valve.

Fig. 7 is a flow diagram of a method for operating a hot water system comprising a water tank, at least one heating source and consumption detecting means for detecting water consumption from the hot water system. Referring to Fig. 7, at step 710, the temperature of water in the hot water system is predisposed to be within a predefined temperature range by selectively operating the at least one heating source. Predisposition implies that, although the water temperature may at times be outside the predefined temperature range (e.g., due to sanitisation or consumption), the method continuously seeks to drive the water temperature to within the predefined temperature range.

The hot water system may comprise primary and secondary heating sources. The primary heating source may comprise a gas, electrically, or heat pump driven source. The secondary heating source may comprise a solar heating sub-system. The primary heating source may only be operated when energy delivered by the secondary heating source is insufficient to heat the water in the hot water system. At step 720, the water in the water tank is periodically heated to a predefined sanitisation temperature. Sanitisation is preferably performed about once every 24 hours. The sanitisation temperature is typically about 6O⁰C.

At step 730, the at least one heating source is selectively operated in response to detection of water consumption from the hot water system. A time for heating the water in the water tank may be determined based on operation of a pump in the solar heating sub-system. Detection of water consumption may be performed by comparing water temperature at the middle of the water tank with water temperature at the bottom of the water tank.

The methods of Figs. 6 and 7 may be practiced as a computer program executed by the controller 120 shown in Fig. 5 or Fig. 2. Those skilled in the art will appreciate that the temperature values and ranges referred to in the description hereinbefore relating to

Figs. 6 and 7 are for purposes of explaining a particular embodiment of the present invention only and that other values and ranges may alternatively be practiced.

Fig. 8 is a graph showing water temperature as a function of time for a hot water system and/or method in accordance with an embodiment of the present invention.

Referring to Fig. 8, the waveform 810 is representative of water temperature in the hot water system that is predisposed to remain within the predefined range of 45⁰C to 5O⁰C. The peaks 820 and 830 are representative of two sanitisation spikes that reach 6O⁰C and that are spaced apart in time by 24 hours.

As described hereinbefore with reference to Fig. 4, one or more counter/timer/s synchronized to operation of the solar pump may be used to determine day or night for optimizing heating cycles and/or sanitisation events. This feature, which avoids the need for a real-time clock in the controller, may generally be used in conjunction with any hot water system that includes a solar sub-system. A light sensor may alternatively be used for this purpose, particularly for hot water systems not having a solar sub-system. For example, the method described hereinbefore with reference to Fig. 6 may perform day/night detection based on one or more counter/timer/s synchronized to operation of the solar pump, as described hereinbefore with reference to Fig. 4. Day/night detection is particularly useful for optimizing operation of the hot water system as this information enables identification of periods of peak and low hot water consumption. Sanitisation may thus be performed when the water temperature is already relatively high, thus reducing the amount of heating required to do so.

Embodiments of the present invention advantageously provide intelligent methods and systems for operating hot water systems that reduce mean tank temperatures, whilst also performing a once-a-day sanitisation event. Certain of the embodiments described are also particularly responsive to unpredictable usage or consumption patterns (e.g., measurement of the temperature differential bptween water at the bottom and middle of the tank). The methods and systems described herein can save up to 40% of energy losses resulting in conventional hot water systems.

The foregoing detailed description provides exemplary embodiments only, and is not intended to limit the scope, applicability or configurations of the invention. Rather, the description of the exemplary embodiments provides those skilled in the art with enabling descriptions for implementing an embodiment of the invention. Various changes may be made in the function and arrangement of elements without departing from the spirit and scope of the invention as set forth in the claims hereinafter. Where specific features, elements and steps referred to herein have known equivalents in the art to which the invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth. Furthermore, features, elements and steps referred to in respect of particular embodiments may optionally form part of any of the other embodiments unless specifically stated to the contrary.

In the context of this specification, the word "comprising" means "including principally but not necessarily solely" or "having" or "including", and not "consisting only of. Variations of the word "comprising", such as "comprise" and "comprises" have correspondingly varied meanings.

Claims

The claims defining the invention are as follows:

1. A hot water system, comprising: a water tank for storing water;

5 a solar heating sub-system for heating water in said hot water system; a heating element disposed in said water tank for heating water in said water tank; and an electronic controller adapted to control operation of said solar heating subsystem and said heating element so as to: Q ensure that water in said water tank reaches a first predefined temperature at least once in a predefined time duration on a continuous basis; ensure that the temperature of water delivered from said hot water system is greater than or equal to a second predefined temperature; and operate said heating element only when energy delivered by said solar heating sub- s system is insufficient to heat the water in said hot water system.

2. A hot water system according to claim 1, wherein said first predefined temperature is about 6O⁰C.

0 3. A hot water system according to claim 1 or claim 2, wherein said predefined time duration is about 24 hours.

4. A hot water system according to any one of claims 1 to 3, wherein said second predefined temperature is about 4O⁰C. S

5. A hot water system according to claim 1, wherein said electronic controller is further adapted to ensure that the temperature of water in said water tank is less than or equal to a third predefined temperature.

0 6. A hot water system according to any one of claims 1 to 5, wherein said heating element is selected from the group of heating elements consisting of: a gas-powered heating element; and an electrically-powered heating element.

7. A method for operating a hot water system comprising a water tank, a solar heating sub-system and a heating element disposed in said water tank, said method comprising the steps of: ensuring that water in said water tank reaches a first predefined temperature at least once in a predefined time duration on a continuous basis; ensuring that temperature of water delivered from said hot water system is greater than or equal to a second predefined temperature; and operating said heating element only when energy delivered by said solar heating sub-system is insufficient to heat the water in said hot water system.

8. A method according to claim 7, wherein said first predefined temperature is about 6O⁰C.

9. A method according to claim 7 or claim 8, wherein said predefined time duration is about 24 hours.

10. A method according to any one of claims 7 to 9, wherein said second predefined temperature is about 4O⁰C.

11. A method according to claim 7, comprising the further step of ensuring that the temperature of water in said water tank is less than or equal to a third predefined temperature.

12. An apparatus for operating a hot water system comprising a water tank, a solar heating sub-system and a heating element disposed in said water tank, said apparatus comprising: a memory for storing data and instructions to be performed by a processor; and a processor coupled to said memory, said processor programmed to: control operation of said solar heating sub-system and said heating element so as to; ensure that water in said water tank reaches a first predefined temperature at least once in a predefined time duration on a continuous basis; ensure that temperature of water delivered from said hot water system is greater than or equal to a second predefined temperature; and operate said heating element only when energy delivered by said solar heating subsystem is insufficient to heat the water in said hot water system.

13. An apparatus according to claim 12, wherein said first predefined temperature is about 6O⁰C.

14. An apparatus according to claim 12 or claim 13, wherein said predefined time duration is 24 hours.

15. An apparatus according to any one of claims 12 to 14, wherein said second predefined temperature is about 4O⁰C.

16. An apparatus according to claim 12, wherein said processor is further programmed to ensure that the temperature of water in said water tank is less than or equal to a third predefined temperature.

17. An apparatus according to any one of claims 12 to 16, wherein said heating element is selected from the group of heating elements consisting of: a gas-powered heating element; and an electrically-powered heating element.

18. A hot water system, comprising: a water tank for storing water; a plurality of heating sources for heating water in said water tank, each of said heating sources associated with a respective running cost; and an electronic controller adapted to control operation of said plurality of heating sources; wherein said electronic controller selectively operates said plurality of heating sources such that predetermined temperature requirements applicable to water in said water tank are met and an overall running cost of said hot water system is minimized.

19. A hot water system according to claim 18, wherein said plurality of heating sources comprise a solar heating sub-system and a heating element disposed in said water tank.

20. A hot water system according to claim 19, wherein said heating element comprises a heating element selected from the group of heating elements consisting of: a gas-powered heating element; and an electrically-powered heating element.

21. A hot water system according to claim 18, wherein said electronic controller is adapted to activate said heating element only when said solar heating sub-system is incapable of meeting said predetermined temperature requirements applicable to water in said water tank.

22. A hot water system according to claim 21, wherein said electronic controller is adapted to: determine whether water in said water tank has reached a predefined sanitisation temperature during an immediately past predefined time period; and activate said heating element if water in said water tank has not reached said predefined sanitisation temperature during said immediately past predefined time period.

23. A hot water system according to claim 22, wherein said electronic controller is further adapted to deactivate said heating element when water in said water tank has reached said predefined sanitisation temperature.

24. A hot water system according to claim 22, wherein said electronic controller is further adapted to deactivate said heating element when water in said water tank has reached or exceeded said predefined sanitisation temperature for a predefined time duration.

25. A hot water system according to claim 22, wherein said immediately past time period is about 24 hours.

26. A method for operating a hot water system comprising a water tank and a plurality of heating sources for heating water in said water tank, each of said heating sources associated with a respective running cost, said method comprising the steps of: heating water in said water tank; and selectively operating said plurality of heating sources such that predetermined temperature requirements applicable to water in said water tank are met and an overall running cost of said hot water system is minimized.

27. A method according to claim 26, wherein said plurality of heating sources comprise a solar heating sub-system and a heating element disposed in said water tank; and wherein said method comprises the step of activating said heating element only when said solar heating sub-system is incapable of meeting said predetermined temperature requirements applicable to water in said water tank.

28. A method according to claim 27, comprising the further steps of: determining whether water in said water tank has reached a predefined sanitisation temperature during an immediately past predefined time period; and activating said heating element if water in said water tank has not reached said predefined sanitisation temperature during said immediately past predefined time period.

29. A method according to claim 28, comprising the further step of: de-activating said heating element when water in said water tank has reached said predefined sanitisation temperature.

30. A method according to claim 28, comprising the further step of: de-activating said heating element when water in said water tank has reached or exceeded said predefined sanitisation temperature for a predefined time duration.

31. A method according to claim 28, wherein said immediately past time period is about 24 hours.

32. An apparatus for operating a hot water system comprising a water tank and a s plurality of heating sources for heating water in said water tank, each said heating source associated with a respective running cost, said apparatus comprising: a memory for storing data and instructions to be performed by a processor; and a processor coupled to said memory, said processor programmed to selectively operate said plurality of heating sources such that predetermined temperature o requirements applicable to water in said water tank are met and an overall running cost of said hot water system is minimized.

33. An apparatus according to claim 32, wherein said plurality of heating sources consist of a solar heating sub-system and a heating element disposed in said water tank; 5 and wherein said processor is programmed to activate said heating element only when said solar heating sub-system is incapable of meeting said predetermined temperature requirements applicable to water in said water tank.

0 34. An apparatus according to claim 33, wherein said processor is programmed to: determine whether water in said water tank has reached a predefined sanitisation temperature during an immediately past predefined time period; and activate said heating element if water in said water tank has not reached said predefined sanitisation temperature during said immediately past predefined time period. 5

35. An apparatus according to claim 34, wherein said processor is further programmed to deactivate said heating element when water in said water tank has reached said predefined sanitisation temperature.

0 36. An apparatus according to claim 34, wherein said processor is further programmed to deactivate said heating element when water in said water tank has reached or exceeded said predefined sanitisation temperature for a predefined time duration.

37. An apparatus according to claim 33, wherein said immediately past time period is about 24 hours.

38. A method for operating a hot water system comprising a water tank, at least one heating source and consumption detecting means for detecting water consumption from said hot water system, said method comprising the steps of: predisposing the temperature of water in said hot water system to be within a predefined temperature range by selectively operating said at least one heating source; periodically heating water in said water tank to a predefined sanitisation temperature; and selectively operating said at least one heating source in response to detection of water consumption from said hot water system.

39. A method according to claim 38, wherein said hot water system comprises primary and secondary heating sources and wherein said primary heating source is only operated when energy delivered by said secondary heating source is insufficient to heat the water in said hot water system.

40. A method according to claim 39, wherein said secondary heating source comprises a solar heating sub-system.

41. A method according to claim 38, wherein said water in said water tank is heated to said predefined sanitisation temperature once every 24 hours.

42. A method according to claim 39, wherein a time for heating said water in said water tank is determined based on operation of a pump in said solar heating sub-system.

43. A method according to claim 38, wherein said detection of water consumption is performed by comparing water temperature at the middle of said water tank with water temperature at the bottom of said water tank.

44. A hot water system, comprising: a water tank for storing water; at least one heating source for heating water in said hot water system; consumption detecting means for detecting water consumption from said hot water 5 system; and an electronic controller coupled to said at least one heating source and said consumption detecting means, said electronic controller adapted to: predispose the temperature of water in said hot water system to be within a predefined temperature range by selectively operating said at least one heating source; I₀ periodically heat water in said water tank to a predefined sanitisation temperature; and selectively operate said at least one heating source in response to detection of water consumption from said hot water system.

is 45. A hot water system according to claim 44, wherein said hot water system comprises primary and secondary heating sources and wherein said primary heating source is only operated when energy delivered by said secondary heating source is insufficient to heat the water in said hot water system.

0 46. A hot water system according to claim 45, wherein said secondary heating source comprises a solar heating sub-system.

47. A hot water system according to claim 44, wherein said electronic controller is adapted to heat water in said water tank to said predefined sanitisation temperature once 5 every 24 hours.

48. A hot water system according to claim 46, wherein said electronic controller is adapted to determine a time for heating said water in said water tank based on operation of a pump in said solar heating sub-system. 0

49. A hot water system according to claim 44, wherein said consumption detecting means comprises at least two temperature sensors coupled to said electronic controller and said electronic controller is adapted to detect consumption based on the temperature differential between said at least two temperature sensors.

50. A hot water system according to claim 49, wherein said consumption detecting means comprises a temperature sensor adapted to measure water temperature at the bottom of said water tank and a temperature sensor adapted to measure water temperature at the middle of said water tank.

51. An apparatus for operating a hot water system comprising a water tank, at least one heating source and consumption detecting means for detecting water consumption from said hot water system, said apparatus comprising: a memory for storing data and instructions to be performed by a processor; and a processor coupled to said memory, said processor programmed to: predispose the temperature of water in said hot water system to be within a predefined temperature range by selectively operating said at least one heating source; periodically heat water in said water tank to a predefined sanitisation temperature; and selectively operate said at least one heating source in response to detection of water consumption from said hot water system.

52. An apparatus according to claim 51, wherein said hot water system comprises primary and secondary heating sources and wherein said primary heating source is only operated when energy delivered by said secondary heating source is insufficient to heat the water in said hot water system.

53. An apparatus according to claim 52, wherein said secondary heating source comprises a solar heating sub-system.

54. An apparatus according to claim 51, wherein said processor is programmed to heat said water in said water tank to said predefined sanitisation temperature once every 24 hours.

55. An apparatus according to claim 53, wherein said processor is programmed to determine a time for heating said water in said water tank based on operation of a pump in said solar heating sub-system.

56. An apparatus according to claim 51, wherein said processor is programmed to detect consumption based on the temperature differential between said at least two temperature sensors.

57. An apparatus according to claim 51, wherein said processor is programmed to detect consumption based on a difference in water temperature at the bottom of the water tank and the middle of the water tank.