Abstract:
A method of determining an operating water temperature for a boiling water heater includes the following steps: (a) adding water to a tank to a predetermined level; (b) heating the water in the tank to approximately 95 degrees Celsius; (c) applying sufficient heat to the water in the tanks so as to cause boiling of the water in the tank within a predetermined first period of time; (d) measuring the boiling water temperature of the water in the tank; and (e) subtracting a predetermined temperature from the boiling water temperature measured in step (d) to arrive at the operating water temperature.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a water heater and a method of operating same. 
         [0002]    The invention has been primarily developed in relation to a boiling water heater and will be described hereinafter with reference to this application. However, it will be appreciated that the invention is not limited to this particular field of use and is also, for example, suitable for use in combined water heater and water chiller units. 
       BACKGROUND OF THE INVENTION 
       [0003]    In order to achieve maximum performance, water heaters should operate at a temperature very close to water&#39;s boiling point. However, water boils at different temperatures at different atmospheric pressures. This change is relatively minor for different atmospheric conditions at a given altitude, but becomes more significant when comparing operation at sea level versus operation at a high altitude above sea level. 
         [0004]    As an example, a boiling water heater designed to operate at 1 or 2° C. below boiling point at sea level may operate in an over boil condition when taken to an elevated altitude. This situation is further complicated due to the inaccuracies of temperature measuring devices, particularly when attempting to control water temperature to within 1 or 2° C. of the boiling point. Hitherto, there have been a number of attempts to solve this problem. 
         [0005]    One simple method has been to set the heater operating temperature below that at which water would boil at the highest expected altitude. However, this compromises the performance of the heater at lower altitudes, where the majority of sales occur. 
         [0006]    Another more complex and costly approach is to provide the heater with a manual temperature adjustment that can be altered depending on location. However, in most cases, this will require adjustment by a skilled service technician and would not be able to be adjusted by the user. Further, whilst the adjustment may, in some instances, be carried out at the time of initial installation, the normal practice would be a follow up service call to adjust the settings for a user unhappy with performance. Disadvantages of this approach include the cost to the user for the service call and that, even after the adjustment, performance may still be compromised. The latter is due to the fact that any adjustment made by the service technician will be to an operating temperature closer to the correct boiling point, but still leaving sufficient temperature differential between the actual preferred operating temperature and boiling point to prevent any nuisance over boil occurring. Over boil can result in excess steam generation and/or nuisance tripping of the water heater power cut-out. In either case, a further service call is required to rectify the fault, which would result in most service technicians adjusting the heater to an operating temperature sufficiently low to prevent this condition arising. This again leads to compromised performance. 
         [0007]    Boiling water heaters require less energy and operating time when compared to traditional kettles and urns. However, maintaining water at boiling temperature requires a constant energy input. In most instances, boiling water units are installed in commercial applications where the need for instant boiling water is limited to typical office hours. Notwithstanding that outside of those hours instant boiling water is not often required, boiling water units are either left on at full operating temperature or timers are installed to switch the heater off at pre-programmed times. 
         [0008]    Whilst it is beneficial to switch off the heater during periods of prolonged non use, there are some disadvantages to this approach. Firstly, the resultant power saving is often less expensive than the cost of a programmable timer. Accordingly, whilst it may not be cost efficient to install a timer it is energy efficient from an environmental standpoint. Secondly, if boiling water in the tank is allowed to cool below about 45° C. then various forms of bacteria, including legionella, may grow. Bringing the water back to the boil will kill any bacteria, as long as the water is boiling before being drawn off by a user. Disadvantages of programmable timers include that someone needs to be taught to do the programming and, if for some reason boiling water is required outside of the pre-programmed hours, it may be difficult or complicated to bypass the timer. 
         [0009]    Another disadvantage associated with known water heaters is that when the temperature control system recognises that a desired water temperature has been reached, it will shut off power to the heating element. However, hysteresis normally causes the residual heat in the element to provide some additional heating, which can result in over boiling and therefore energy wastage. 
       OBJECT OF THE INVENTION 
       [0010]    It is the object of the present invention to overcome or at least ameliorate one or more of the prior art disadvantages noted above. 
       SUMMARY OF THE INVENTION 
       [0011]    Accordingly, in a first aspect, the present invention provides a method of determining an operating water temperature for a boiling water heater, the method including the following steps: 
         [0012]    (a) adding water to a tank to a predetermined level; 
         [0013]    (b) heating the water in the tank to approximately 95 degrees Celsius; 
         [0014]    (c) applying sufficient heat to the water in the tank so as to cause boiling of the water in the tank within a predetermined first period of time; 
         [0015]    (d) measuring the boiling water temperature of the water in the tank; and 
         [0016]    (e) subtracting a predetermined temperature from the boiling water temperature measured in step (d) to arrive at the operating water temperature. 
         [0017]    The method preferably also includes the step of maintaining the water in the tank at approximately 95 degrees Celsius for a predetermined second period of time between steps (b) and (c). 
         [0018]    The first and second predetermined periods of time are preferably approximately 90 and 120 seconds respectively. 
         [0019]    The predetermined temperature subtracted in step (e) is preferably 1.5 degrees Celsius. 
         [0020]    In a second aspect, the present invention provides a water heater adapted to determine an operating water temperature, the heater including: 
         [0021]    a water tank; 
         [0022]    means to measure the water temperature of the water in the tank; 
         [0023]    a timer; and 
         [0024]    heating means adapted to heat the water in the tank to approximately 95 degrees Celsius, the heating means also being adapted to apply sufficient heat to the water in the tank so as to cause boiling of the water in the tank within a predetermined first period of time, 
         [0025]    wherein the operating water temperature of the water is the measured boiling water temperature minus a predetermined temperature. 
         [0026]    The heating means is preferably also adapted to maintain the water in the tank at approximately 95 degrees Celsius for a predetermined second period of time, prior to the heating means applying sufficient heat to the water in the tank so as to cause boiling of the water in the tank within a predetermined first period of time. 
         [0027]    The first and second predetermined periods of time are preferably approximately 90 and 120 seconds respectively. 
         [0028]    The predetermined temperature subtracted is preferably 1.5 degrees Celsius. 
         [0029]    The heater preferably also includes a controller adapted to control the heating means in response to input from the timer and/or the temperature measuring means. 
         [0030]    In a third aspect, the present invention provides a method of operating a water heater, the method including the following steps: 
         [0031]    (a) adding water to a tank to a predetermined level; 
         [0032]    (b) monitoring the time period since water was last dispensed from the water tank; and 
         [0033]    (c) if the monitored time period reaches a predetermined time, then removing water heating energy from the tank until the water in the tank cools to a predetermined temperature, above a temperature where bacterial growth can occur, and applying sufficient heat to the water in the tank so as to maintain the temperature of the water in the tank approximately at the predetermined temperature. 
         [0034]    The predetermined temperature is preferably about 64 degrees Celsius. 
         [0035]    The predetermined time period is preferably about 2 or 4 hours, most preferably at the user&#39;s option. 
         [0036]    The method preferably also includes the step of returning the heater to full power operation upon sensing that water has been dispensed. 
         [0037]    In a fourth aspect, the present invention a water heater including: 
         [0038]    a water tank; 
         [0039]    means to sense when water is dispensed from the tank; 
         [0040]    a timer to monitor the time period since water was last dispensed from the water tank; 
         [0041]    means to measure the temperature of the water in the tank; and 
         [0042]    heating means to heat the water in the tank, 
         [0043]    wherein, if the monitored time period reaches a predetermined time, energy is removed from the heating means until the water in the tank cools to a predetermined temperature which is above a temperature where bacterial growth can occur, and thereafter the heating means applies sufficient heat to the water in the tank so as to maintain the temperature of the water in the tank approximately at the predetermined temperature. 
         [0044]    The predetermined temperature is preferably about 64 degrees Celsius. 
         [0045]    The predetermined time period is preferably about 2 or 4 hours, most preferably at the user&#39;s option. 
         [0046]    The heater is preferably adapted to return to full power operation upon sensing that water has been dispensed. 
         [0047]    The heater preferably also includes a controller adapted to control the heating means in response to input from the timer and/or the sensing means and/or the temperature measuring means. 
         [0048]    In a fifth aspect, the present invention provides a method of operating a water heater, the method including the following steps: 
         [0049]    (a) adding water to a tank to a predetermined level; 
         [0050]    (b) adding heat to the water at a first energy level until a first predetermined water temperature is reached; 
         [0051]    (c) adding heat to the water at a second energy level, lower than the first energy level, until a second predetermined water temperature, higher than the first predetermined water temperature, is reached. 
         [0052]    The method preferably also includes the step of adding heat to the water at a third energy level, lower than the second energy level, until a third predetermined water temperature, higher than the second predetermined water temperature, is reached. 
         [0053]    The method preferably also includes the step of adding heat to the water at a fourth energy level, lower than the third energy level, until a fourth predetermined water temperature, higher than the third predetermined water temperature, is reached. 
         [0054]    The first energy level is preferably the full power capacity of the water heater. 
         [0055]    The first predetermined water temperature is preferably about 2 degrees Celsius below the water heater&#39;s desired operating temperature. 
         [0056]    The second energy level is preferably about 50% of the full power capacity of the water heater. 
         [0057]    The second predetermined water temperature is preferably about 1 degree Celsius below the water heater&#39;s desired operating temperature. 
         [0058]    The third energy level is preferably about 25% of the full power capacity of the water heater. 
         [0059]    The third predetermined water temperature is preferably about 0.5 degrees Celsius below the water heater&#39;s desired operating temperature. 
         [0060]    The fourth energy level is preferably about 10% of the full power capacity of the water heater, and is preferably provided in pulses. 
         [0061]    In a sixth aspect, the present invention provides a water heater including: 
         [0062]    a water tank; 
         [0063]    means to measure the temperature of the water in the tank; and 
         [0064]    adjustable heating means adapted to add selectively variable heat to the water in the tank, 
         [0065]    wherein the heating means operates at a first energy level until a first predetermined water temperature is reached whereafter the heating means operates at a second energy level, lower than the first energy level, until a second predetermined water temperature, higher than the first predetermined water temperature, is reached. 
         [0066]    The heating means is preferably also adapted to operate at a third energy level, lower than the second energy level, until a third predetermined water temperature, higher than the second predetermined water temperature, is reached. 
         [0067]    The heating means is preferably also adapted to operate at a fourth energy level, lower than the third energy level, until a fourth predetermined water temperature, higher than the third predetermined water temperature, is reached. 
         [0068]    The first energy level is preferably the full power capacity of the water heater. 
         [0069]    The first predetermined water temperature is preferably about 2 degrees Celsius below the water heater&#39;s desired operating temperature. 
         [0070]    The second energy level is preferably about 50% of the full power capacity of the water heater. 
         [0071]    The second predetermined water temperature is preferably about 1 degree Celsius below the water heater&#39;s desired operating temperature. 
         [0072]    The third energy level is preferably about 25% of the full power capacity of the water heater. 
         [0073]    The third predetermined water temperature is preferably about 0.5 degrees Celsius below the water heater&#39;s desired operating temperature. 
         [0074]    The fourth energy level is preferably about 10% of the full power capacity of the water heater, and is preferably provided in pulses. 
         [0075]    The heater preferably also includes a controller adapted to control the heating means in response to input from the temperature measuring means. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0076]    A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: 
           [0077]      FIG. 1  is a partial perspective view of an embodiment of a water heater according to the invention, during initial filling; 
           [0078]      FIG. 2  is a partial perspective view of the heater shown in  FIG. 1  during intermediate filling; 
           [0079]      FIG. 3  is a partial perspective view of the heater shown in  FIG. 1 , when full; 
           [0080]      FIG. 4  is a logic diagram associated with the operating temperature calibration of the heater shown in  FIG. 1 ; and 
           [0081]      FIG. 5  is a logic diagram associated with the sleep mode of the heater shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0082]    Referring to  FIGS. 1 to 3  there is shown an embodiment of a boiling water heater  10  according to the present invention. The water heater  10  has a water tank  12 , an outer casing  14  and insulation  16  therebetween. Inside the water tank  12 , there is an electric heating element  18 , which has a lower coiled end  18   a , and first, second and third level sensors  20 ,  22  and  24  respectively. The water heater  10  also includes a mounting block  26  for the three level sensors  20 ,  22  and  24 . 
         [0083]    The heater  10  also has PCB controller (not shown) which is connected to the three level sensors  20 ,  22  and  24 , a temperature sensor (not shown) within the tank  12 , a timer and a number of other components. The controller can control the energy supply to the heating coil  18  in response to signals received from the three level sensors  20 ,  22  and  24  and the temperature sensor. 
         [0084]    The water heater  10  also includes a water inlet pipe  28  with an inlet elbow  30 . The elbow  30 , and thus the pipe  28 , is supplied with mains water through a solenoid operated inlet valve (not shown), which is also controlled by the controller. The water heater  10  also includes a solenoid operated outlet valve, which is also controlled by the controller, and outlet pipe, which are not shown in  FIGS. 1 to 3  for clarity purposes. 
         [0085]    A method of determining an operating water temperature (i.e. calibrating) for the water heater  10  will now be described in conjunction with  FIG. 4  which represents the basic steps  40 ,  42 ,  44  and  46  of the method. 
         [0086]    The first step  40  of the method occurs after the heater  10  has been installed and comprises the tank  12  being filled with water  32  until the level reaches that of the first level sensor  20 . This amount of the water  32  is sufficient to immerse the coiled end  18   a  of the heating element  18 . 
         [0087]    As indicated in step  42 , the controller then energises the heating element  18  to heat the water to 95° C. and then, as indicated in step  44 , maintain the water  32  at this temperature for a period of 120 seconds in order to saturate the tank  12  with heat. 
         [0088]    As indicated in step  46 , at the end of this saturation period the water  32  is then heated to boiling point in a 90 second time period and the controller  26  records the maximum water temperature reached. It is important to note that the heating element  18  can boil the water  32  prior to the completion of the 90 second period and that but the temperature of boiling water remains constant until all the water has boiled away. 
         [0089]    At the end of the 90 second period the controller recalls the maximum temperature reached, which will be the boiling point for the atmospheric conditions where the heater  10  has been installed. The controller will then set the operating temperature or set point of the water heater  10  at 1.5 below the measured boiling point. 
         [0090]    When this calibration process has taken place the water heater  10  will then continue to fill and heat up. More particularly, the controller will open the valve  32  and fill the tank  12  with water until it reaches the second water level sensor  24  (see  FIG. 2 ) and at a controlled rate which will not allow the water  32  in the tank  12  to drop 2° C. below the set point temperature. When the water  30  reaches the set point temperature the inlet valve  32  opens and allows water to enter the tank  12  until such time as the temperature of the water drops 3° C. below the set point. If the water at any time drops to more than 3° C. below the set point the inlet valve  30  is closed and the heater  10  allowed to heat up to the set point temperature. During this filling period the controller energises the heating element to operate at 100% power. 
         [0091]    There are numerous advantages arising from the above calibration method. Firstly, the performance from one heater to another is always consistent. Secondly, the exact accuracy of the temperature measuring device utilised in the heater is not critical, as long as the device is stable. Thirdly, the performance of the heater relative to actual boiling point is always consistent. Fourthly, the operating water temperature is always maintained extremely close to the actual boiling point as the actual boiling point is firstly determined by the heater. Fifthly, no compromises in performance are required to achieve optimum performance at different sites having different atmospheric conditions. Sixthly, no external adjustment is required to achieve optimum performance and no skilled service technician is required for optimum performance. The above advantages also lead to lower cost to the user, reduced energy consumption as over boil conditions are prevented and overall improved customer satisfaction. 
         [0092]    A method of operating the water heater  10  in an energy saving or sleep mode will now be described in conjunction with  FIG. 5  which represents the basic steps  50 ,  52  and  54  of the method. 
         [0093]    As indicated in step  50 , during normal operation of the water heater  10  the controller monitors the length of time since the hot water outlet valve (not shown) has been activated. More particularly, the controller monitors whether the period of valve inactivity is 2 or 4 hours, depending on the setting selected. 
         [0094]    As indicated in step  52 , if the hot water outlet valve has not operated for the selected time, then energy is removed from the heating element  18  to place the water heater  10 , to place it in an energy saving mode (sleep mode), until the temperature of the water in the tank  12  has fallen to about 64° C. 
         [0095]    As indicated in step  54 , once the water temperature has reached 64° C., power is pulsed to the element  18  at a rate sufficient to maintain the water temperature at about 64° C. However, and as indicated in step  56 , if the hot water outlet valve is activated the sleep mode is cancelled and the element  18  is energised to bring the water  32  back up to its operating set point. Typically, the water  32  will reach the preferred operating temperature within about 2 to 3 minutes. 
         [0096]    The advantages of the sleep mode described above are as follows. Firstly, no pre-programmed timer is required. Secondly, no external influence is required. Thirdly, the system is far more flexible for the user. Fourthly, energy savings are achieved with an impact on both energy cost and environmental greenhouse gases reductions. Lastly, health considerations are not compromised as the water is not allowed to cool to a temperature where bacteria growth may occur. 
         [0097]    The heater  10  also has a general mode of operation which leads to increased energy savings as will be described below. 
         [0098]    As stated earlier, when water is brought to boil, the temperature of the water remains constant whilst the water boils. Also, when the controller recognises that a desired temperature has been reached and shuts off power to the element, hysteresis normally causes the residual heat from the element to cause some over boiling and therefore energy wastage. This can be further complicated by the response time lag of the controller. 
         [0099]    In the heater  10 , the controller recognises when the temperature of the water is approaching the predetermined operating temperature and begins to reduce the energy applied to the element  18 . Put another way, the closer the water  32  is to the boiling temperature the lower the energy input. 
         [0100]    More particularly, when the tank  12  is filled to the second water level sensor  22  (see  FIG. 2 ), the controller supplies full power to the element  18  until the water  32  in the tank  12  is heated to within 2° C. of the set point. At this point the power supplied to the element  18  is reduced to 50% of its maximum capacity. This prevents the heater  10  from venting excessive steam 
         [0101]    Further, when the tank  12  is filled to the third water level sensor  24  (see  FIG. 3 ), the inlet valve is kept open for 20 seconds. This allows a slight overfilling of the tank  12  and prevents nuisance operating of the valve  32  due to evaporation or water turbulence. The element  18  is also set to operate at 25% of its maximum and maintained there until the set point temperature is reached. Finally, when the water temperature is within 0.5° C. of the set point the power supplied to the element  18  is reduced to 10% of its maximum capacity and supplied in pulses to maintain the water temperature at the set point. 
         [0102]    The advantages arising from this are as follows. Firstly, the method provides more accurate temperature control at the operating condition. Secondly, the heater has reduced power consumption. The minimising of over boiling results in less steam generation, minimal resource wastage and a quieter running water heater. 
         [0103]    Although the invention has been described with reference to a preferred embodiment, it would be appreciated by those skilled in the art that the invention may be embodied in many other forms.