Patent Publication Number: US-8530799-B2

Title: Fluid-heating apparatus and methods of operating the same

Description:
RELATED APPLICATIONS 
     This application claims priority to Chinese Patent Application Serial No. 200510094932.8 filed Oct. 21, 2005, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     The invention relates to fluid-heating apparatus, such as a storage-type water heater, and methods of operating the apparatus, such as to reduce energy consumption by the storage-type water heater while providing sufficient hot water to users. 
     Storage-type water heaters are commonly used to provide hot water to residential users. As the cost of energy has continued to rise, attempts have been made to reduce the amount of energy used by these water heaters. Insulation has been employed to reduce the radiant loss of heat from the storage tank, and therefore, reduce the need to reheat the water and to use additional energy. Controllers have been provided which monitor usage patterns and heat water only during periods when demand for hot water is expected or energy costs are low. These methods, while reducing energy usage, can still use energy beyond what is necessary to provide adequate hot water to the user. 
     SUMMARY 
     In one embodiment, the invention provides a fluid-heating apparatus, for heating a fluid. The fluid-heating apparatus includes a vessel, an inlet to introduce fluid into the vessel, an outlet to remove fluid from the vessel, a heating device, a temperature sensor, and a control circuit. The control circuit is configured to monitor the temperature sensor and activate the heating device when a temperature sensed is less than a set point. The control circuit is further configured to determine that a high-quantity usage event has occurred and to adjust the set point following the end of the high-quantity usage event based on a sensed temperature. 
     In another embodiment, the invention provides a method of heating a fluid in a fluid-heating apparatus by sensing a temperature having a relation to the fluid, determining a high-quantity usage event has occurred, increasing a temperature set point if the sensed temperature is less than a low-temperature threshold, or decreasing a temperature set point if the sensed temperature is greater than a high-temperature threshold. A high-quantity usage event is determined to have occurred if a rate of change of the sensed temperature exceeds a first-rate threshold. The high-quantity usage event is determined to have ended if the rate of change of the sensed temperature is less than a second-rate threshold following the rate of change of the sensed temperature exceeding the first-rate threshold. 
     In another embodiment, the invention provides a method of determining a high-quantity usage event in a fluid-heating apparatus by sensing a temperature in the fluid-heating device, calculating a rate of change of the sensed temperature, comparing the rate of change of the sensed temperature to a first threshold, and determining the high-quantity usage event when the rate of change of the sensed temperature traverses the first threshold. 
     In another embodiment, the invention provides a method of determining completion of a high-quantity usage event in a fluid-heating apparatus by determining a high-quantity usage event has occurred, sensing a temperature in the fluid-heating device, calculating a rate of change of the sensed temperature, comparing the rate of change of the sensed temperature to a threshold, and determining the high-quantity usage event has completed when the rate of change of the sensed temperature is less than the threshold. 
     In another embodiment, the invention provides a method of heating a fluid in a fluid-heating apparatus including a temperature sensor for monitoring a temperature of the fluid. The method includes sensing a first temperature with the temperature sensor, controlling a heating device using the first temperature, determining an occurrence of a high-quantity usage event, determining the high-quantity usage event has ended, sensing a second temperature with the temperature sensor following the end of the high-quantity usage event, and increasing the temperature set point if the second temperature is less than a low-temperature threshold or, reducing the temperature set point if the second temperature is greater than a high-temperature threshold. 
     In another embodiment, the invention provides a method of heating a fluid in a fluid-heating apparatus including a first temperature sensor located in an upper portion of the fluid-heating apparatus and a second temperature sensor located in a lower portion of the fluid-heating apparatus. The method includes sensing a first temperature with the first temperature sensor and activating a heating device if the first temperature is less than a temperature set point. Once a high-quantity usage event has ended, the method senses a second temperature with the second temperature sensor, and increases the temperature set point if the second temperature is less than a low-temperature threshold or reduces the temperature set point if the second temperature is greater than a high-temperature threshold. The method further includes determining a rate of change of the first temperature, and reducing the temperature set point by a factor if the second temperature is between the low-temperature threshold and the high-temperature threshold. 
     In another embodiment, the invention provides a method of heating a fluid in a fluid-heating apparatus including a plurality of temperature sensors located at different heights in the fluid-heating apparatus. The method includes sensing a temperature at each of the plurality of temperature sensors, detecting a high-quantity usage event, and determining an end of the high-quantity usage event has occurred. The method further includes raising a temperature set point based on a temperature sensed at the temperature sensor located at the highest position in the fluid-heating apparatus and the temperature sensor at the lowest position in the fluid-heating apparatus if the high-quantity usage event was detected by the temperature sensor in the highest position in the fluid-heating apparatus. The method also includes lowering the temperature set point based on the highest temperature sensor in the fluid-heating apparatus to detect the high-quantity usage event if the high-quantity usage event was not detected by the temperature sensor in the highest position in the fluid-heating apparatus. 
     In another embodiment, the invention provides a method of heating a fluid in a fluid-heating apparatus by repeatedly sensing a temperature in the fluid-heating apparatus, determining an end of a high-quantity usage event using the sensed temperature, and setting a temperature set point based on a relation to the sensed temperature. 
     Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial block diagram, partial sectional view of a first construction of a water heater embodying the invention. 
         FIG. 2  is a flowchart of the operation of the controller of  FIG. 1  for adjusting a temperature set point to heat an accurate quantity of water. 
         FIG. 3  is a partial block diagram, partial sectional view of a second construction of a water heater embodying the invention. 
         FIG. 4  is a flowchart of the operation of the controller of  FIG. 3  for adjusting a temperature set point to heat an accurate quantity of water. 
         FIG. 5  is a partial block diagram, partial sectional view of a third construction of a water heater embodying the invention. 
         FIGS. 6A and 6B  are flowcharts of the operation of the controller of  FIG. 5  for adjusting a temperature set point to heat an accurate quantity of water. 
     
    
    
     DETAILED DESCRIPTION 
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. 
     The invention relates to automatically setting a temperature set point in a fluid-heating apparatus, such as a storage-type water heater. The temperature set point is set such that a sufficient quantity of hot water is available for a user but little or no excess hot water remains after an event in which a relatively large quantity of hot water is used. The lack of excess hot water following this usage indicates that energy was not wasted in heating water beyond what was necessary. 
       FIG. 1  illustrates a first construction of a storage-type water heater  100  according to the invention. The water heater  100  includes an enclosed water tank  105  (also referred to herein as an enclosed vessel), a shell  110  surrounding the water tank  105 , and foam insulation  115  filling the annular space between the water tank  105  and the shell  110 . A typical storage tank  105  is made of ferrous metal and lined internally with a glass-like porcelain enamel to protect the metal from corrosion. However, the storage tank  105  can be made of other materials, such as plastic. A water inlet line or dip tube  120  and a water outlet line  125  enter the top of the water tank  105 . The water inlet line  120  has an inlet opening  130  for adding cold water to the water tank  105 , and the water outlet line  125  has an outlet opening  135  for withdrawing hot water from the water tank  105 . The tank may also include a grounding element (or contact) that is in contact with the water stored in the tank. 
     The water heater  100  also includes an electric-resistance heating element  140  that is attached to the tank  105  and extends into the tank  105  to heat the water. While a storage-type water heater  100  having the electric-resistance heating element  140  is shown, the invention can be used with other fluid-heating devices (such as other types of water heaters, oil or gas heaters, etc.), or other heating elements (such as a gas-heating element or gas burner, a combination electric-resistance heating element and gas burner, etc.), element designs, and arrangements. 
       FIG. 1  also shows a controller  150  coupled to the heating element  140  and a temperature sensor  155 . The temperature sensor is positioned between an outside wall of the tank  105  and the insulation  115  in an upper portion of the tank  105 . The temperature sensor  155  detects a temperature indicative of the temperature of the water inside the tank  105 . In some constructions, the temperature sensor  155  can be positioned inside the tank  105 , or coupled to or in the inlet  120  or the outlet  125 . 
     Hot water is drawn from the water heater  100  through the outlet opening  135  and is replaced by relatively colder water entering the water heater  100  through the inlet opening  130 . The entering cold water mixes with the hot water in the tank  105 . Over time or once a large enough volume of hot water has been replaced with the relatively cold water, the temperature of the water surrounding the temperature sensor  155  drops. Once the water surrounding the temperature sensor  155  reaches a threshold, the controller  150  activates the heating element  140  to heat the water in the tank  105 . The controller  150  can include an integrated circuit, discrete circuit elements, a micro device (e.g., a microcontroller, a microprocessor and memory, etc.) and similar components to control the water heater  100 . The controller  150  furthers include a switching element, such as a relay, thyristor, or triac, to selectively control the power applied to the heating element  140 . 
     In one specific construction, the controller  150  includes a microcontroller that receives signals or inputs from a plurality of sensors, analyzes the inputs, and generates outputs to control the heating element  140 . In addition, the microcontroller can receive other inputs (e.g., inputs from a user, an ambient temperature sensor, etc.) and can generate outputs to control other elements of the water heater. The microcontroller can include a processor and memory. The memory includes one or more modules having instructions. The processor obtains, interprets, and executes the instructions to control the water heater  100 , including the heating element  140 . 
     The temperature of the water in the water heater  100  is generally maintained at a level in excess of the temperature a user desires. The user therefore mixes a quantity of cold water with the hot water to achieve the desired temperature. The hotter the water in the water heater  100  (and the warmer the cold water) the greater the quantity of cold water and the lesser the quantity of hot water the user will use in the mix. Therefore, the temperature of the hot water impacts the quantity of hot water used relative to a quantity of total water used. In discussing a quantity of hot water from the hot water heater  100 , the quantity of hot water is greater, for the same amount of water, for a higher temperature of water in the hot water heater  100  than for a lower temperature of water in the hot water heater  100 . 
     A typical water heater provides water for numerous functions. These functions require quantities of hot water that are significantly different from one another. Table 1 summarizes some typical functions and an estimated quantity of hot water required for each. 
     Referring to table 1, hot water usage can be divided into large quantity use (e.g., bathing) and low quantity use (e.g., shaving). Adjusting a temperature set point of a water heater to provide just enough hot water for a low quantity use results in not enough hot water being available for high quantity uses. Therefore, it is a goal of the invention to provide adequate quantities of hot water for high quantity uses while minimizing the quantity of remaining hot water following a high quantity use. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Hot Water Requirements 
               
            
           
           
               
               
               
            
               
                   
                 Hot Water Use 
                 Average Gallons Per Use 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                   
                 Showering 
                 15 
               
               
                   
                 Bathing 
                 20 
               
               
                   
                 Shaving 
                 2 
               
               
                   
                 Washing hands and face 
                 2 
               
               
                   
                 Shampooing hair 
                 4 
               
               
                   
                 Hand dishwashing 
                 2 
               
               
                   
                 Automatic dishwashing 
                 14 
               
               
                   
                 Food preparation 
                 5 
               
               
                   
                 Clothes washing 
                 32 
               
               
                   
                   
               
            
           
         
       
     
     It is necessary to determine when a high quantity of hot water has been used (also referred to herein as a high-quantity usage event) such that adjustments to the temperature set point can be made only following a high quantity of hot water usage and not following a low quantity of hot water usage. In an embodiment of the invention, a high quantity of hot water is determined to have been used when the temperature sensed at the temperature sensor  155  has fallen at least a predetermined amount (e.g., 2° F. or 1° C.) each time period (e.g., one minute) for a predetermined number of time periods (e.g., three). Alternatively, other methods for determining a high-quantity usage event can be used. For example, a high-quantity usage event can be determined by a flow meter in the path of the water flow measuring an actual quantity of water used. 
       FIG. 2  is an embodiment of a process for automatically adjusting a temperature set point of the water heater  100  in the construction shown in  FIG. 1 . The controller  150  monitors the temperature sensor  155  to determine if a high-quantity usage event is in progress (block  200 ). If the sensed temperature has not dropped sufficiently over the predetermined time periods, a high-quantity usage event has not occurred and the controller  150  continues to monitor the temperature sensor  155  (block  200 ). 
     If the controller determines that a high-quantity usage event is in progress, the controller  150  waits until the high-quantity usage event has ended (block  205 ). The controller  150  determines, in one construction, that a high-quantity usage event has ended when the sensed temperature remains constant for, or rises for, a number (e.g., 2) of time periods (e.g., one minute). If the high-quantity usage event has not ended, the controller  150  continues to monitor the temperature sensor  155  until the high-quantity usage event does end. 
     Before proceeding further, it should be understood that the figures, including  FIG. 2 , show select methods of operating the water heater. However, other methods are possible. For example, the order of steps disclosed in the figures may vary. Furthermore, additional steps can be added to the sequence and not all of the steps may be required. It should also be noted; other processes can run continuously in parallel with the processes described herein. In one parallel process, for example, the controller  150  monitors the temperature sensor  155  and if the sensed temperature is below a temperature set point, the controller activates the heating element  140  to heat the water in the tank  105 . When the sensed temperature is above the temperature set point, the water is at a desired temperature and, the controller  150  deactivates the heating element  140 . In some embodiments, a dead band control scheme activates the heating element  140  at a temperature less than the temperature set point and deactivates the heating element  140  at a temperature above the temperature set point. 
     Referring again to the process of  FIG. 2 , following the end of the high-quantity usage event, the controller compares (block  210 ) the temperature received from the temperature sensor  155  to a high-temperature threshold (e.g., 115° F. or 45° C.). If the sensed temperature is above the high-temperature threshold, the controller determines that excess hot water remains in the water heater  100 . The determination, that excess hot water remains in the water heater  100 , indicates that the water was heated to a higher temperature than was necessary to provide hot water for the high-quantity usage event just ended. Therefore, the controller reduces (block  215 ) the temperature set point by a preset amount (e.g., 10° F. or 5° C.) in an attempt to anticipate the quantity of hot water necessary for the next high-quantity usage event. The controller  150  then waits for the next high-quantity usage event (block  200 ). 
     If, at block  210 , the sensed temperature was not greater than the high-temperature threshold, the controller  150  compares (block  220 ) the sensed temperature to a low-temperature threshold (e.g., 90° F. or 30° C.). If the sensed temperature is above the low-temperature threshold, the controller  150  determines that the correct amount of hot water was available for the high-quantity usage event. The controller  150 , therefore, leaves the temperature set point unchanged as the controller  150  had correctly anticipated the quantity of hot water necessary for the just ended high-quantity usage event. The controller  150  then continues by waiting for the next high-quantity usage event (block  200 ). 
     If, at block  220 , the sensed temperature is below the low-temperature threshold, the controller  150  determines that there was not enough hot water available for the high-quantity usage event and, therefore, the temperature set point was too low. The controller  150  then increases (block  225 ) the set point by a predetermined amount (e.g., 10° F. or 5° C.) in an attempt to anticipate the quantity of hot water necessary for the next high-quantity usage event. The controller  150  then waits for the next high-quantity usage event (block  200 ). 
       FIG. 3  shows a second construction of a water heater  300  of the invention including a first temperature sensor  355  and a second temperature sensor  360 . The first temperature sensor  355  is positioned on the outside of the tank  305  at a point higher than the second temperature sensor  360  which is also positioned on the outside of the tank  305 . A controller  350  receives the sensed temperature readings from the first and second temperature sensors  355  and  360  and controls a heating element  340 . 
     In some constructions, the controller  350  activates and deactivates the heating element  340  based on a temperature set point and at least one of a temperature sensed by the first temperature sensor  355 , a temperature sensed by the second temperature sensor  360 , and an average of a temperature sensed by the first temperature sensor  355  and a temperature sensed by the second temperature sensor  360 . 
       FIG. 4  shows an embodiment of a process for automatically adjusting a temperature set point of a water heater for the construction shown in  FIG. 3 . The controller  350  determines if a high-quantity usage event has occurred (block  400 ) by monitoring the second temperature sensor  360  in the same manner as described above for block  200  of  FIG. 2 . The controller  350  also determines when a high-quantity usage event has ended (block  405 ) by monitoring the second temperature sensor  360  in the same manner as described above for block  205  of  FIG. 2 . 
     Following the end of a high-quantity usage event, the controller  350  compares (block  410 ) the temperature detected by the first temperature sensor  355  to a low-temperature threshold (e.g., 90° F. or 30° C.). If the temperature sensed by the first temperature sensor is equal or below the low-temperature threshold, the water heater  300  did not have enough hot water for the high-quantity usage event. The controller  350 , therefore, increases the temperature set point (block  415 ) by a predetermined amount (e.g., 10° F. or 5° C.) in an attempt to ensure enough hot water is available for the next high-quantity usage event. The controller  350  then waits for the next high-quantity usage event (block  400 ). 
     If the temperature sensed by the first temperature sensor  355  was above the low-temperature threshold, the controller  350  checks (block  420 ) the temperature set point to determine if the temperature set point is equal or below a low set point threshold (e.g., 115° F. or 45° C.). If the temperature set point is equal or below the set point threshold, the controller  350  determines that the temperature set point should not be lowered any further and continues with waiting for the next high-quantity usage event (block  400 ). 
     If, at block  420 , the temperature set point was above the low set point threshold, the controller  350  compares (block  425 ) the temperature sensed by the second temperature sensor  360  to a high-temperature threshold (e.g., 115° F. or 45° C.). If the sensed temperature is not below the high-temperature threshold an excess of hot water remained in the water heater following the high-quantity usage event. The controller  350 , therefore, reduces (block  430 ) the temperature set point by multiplying the temperature set point by a first ratio or percentage (e.g., 75%) in an attempt to anticipate the quantity of hot water necessary for the next high-quantity usage event. The controller  350  then continues processing at block  400  waiting for the next high-quantity usage event. 
     If the sensed temperature, at block  425 , is less than the high-temperature threshold, the controller  350  compares (block  435 ) a rate at which the sensed temperature of the water was dropping at the first temperature sensor. The rate the temperature was dropping is determined by dividing a drop in temperature detected by the first temperature sensor  355  over a period of time (e.g., two minutes) by the time. If the rate at which the temperature sensed by the first temperature sensor  355  was dropping is equal to or greater than a rate threshold (e.g., 0.6° F./minute or 0.3° C./minute), the controller  350  reduces (block  440 ) the temperature set point by multiplying the temperature set point by a second ratio or percentage (e.g., 83.3%) and continues processing at block  400  waiting for the next high-quantity usage event. If the rate at which the temperature sensed by the first temperature sensor  355  was dropping is less than the rate threshold, the controller  350  reduces (block  445 ) the temperature set point by multiplying the temperature set point by a third ratio or percentage (e.g., 91.7%) and continues processing at block  400  waiting for the next high-quantity usage event. 
       FIG. 5  shows another construction of the invention including a first temperature sensor  555 , a second temperature sensor  560 , a third temperature sensor  565 , a fourth temperature sensor  570 , and a fifth temperature sensor  575 . The first temperature sensor  555  is positioned near the top of a tank  505 . The second temperature sensor  560 , third temperature sensor  565 , fourth temperature sensor  570 , and fifth temperature sensor  575  are positioned at successively lower positions on the tank  505 . The temperature sensors  555  to  575  provide signals to a controller  550  that are indicative of the temperature of the water near the respective sensors  555  to  575 . The controller  550  activates a heating element  540  when a temperature detected by one or more of the temperature sensors  555  to  575  is below a temperature set point. 
     In the construction shown, the controller  550  determines if a high-quantity usage event has occurred as described in the previous constructions and embodiments. Following the end of the high-quantity usage event, the controller  550  determines the highest positioned temperature sensor to detect the high-quantity usage event. Since relatively cold water enters the water heater  500  through an inlet  530  which is located in the lower portion of the tank  505 , the fifth temperature sensor  575  may be the first sensor to detect a high-quantity usage event. As how water continues to be removed from the water heater  500 , the second temperature sensor may detect the high-quantity usage event next. This process continues until the high-quantity usage event ends or all of the temperature sensors have detected the event. The controller  550  can estimate the quantity of hot water remaining in the water heater  500 , after the high-quantity usage event, based on the highest temperature sensor to detect the event. The controller  550  can then adjust the temperature set point to provide an accurate quantity of hot water for the next high-quantity usage event. 
       FIGS. 6A and 6B  are flow charts of an embodiment of the operation of the construction shown in  FIG. 5  for providing a correct quantity of hot water to a high-quantity usage event. The controller  550  begins operation by resetting a plurality of flags in the system (block  600 ). Next the controller  550  checks if a first temperature sensor event detection flag has been set (block  605 ) If the first temperature sensor event detection flag has been set, the first temperature sensor  555  has previously detected a high-quantity usage event and the controller  550  checks if the high-quantity usage event has ended (block  610 ). 
     Determination of the end of a high-quantity usage event, in the construction shown, can be accomplished as shown in previous embodiments using one or more temperature sensors alone or in combination with one another. The determination of the end of a high quantity usage event can be made using the same or different rates for each sensor. In some embodiments, the end of a high-quantity usage event is determined, as discussed previously, using the highest temperature sensor to detect the high-quantity usage event. 
     If, at block  610 , the controller  550  determines that the high-quantity usage event has ended, the controller  550  adds the temperature sensed by the first temperature sensor  555  to the temperature sensed by the fifth temperature sensor  575  (block  615 ) producing a sum of the temperatures. The controller  550  then compares (block  620 ) the sum of the temperatures to a first summed threshold (e.g., 130° F. or 55° C.). If the sum of the temperatures is less than the first summed threshold, the quantity of hot water was substantially less than required for the high-quantity usage event. The controller then increases (block  625 ) the temperature set point by a first incremental amount (e.g., 40° F. or 20° C.) in an attempt to anticipate the quantity of hot water necessary for the next high-quantity usage event. The controller  550  then resets the flags (block  600 ) and waits for the next high-quantity usage event. 
     If, at block  620 , the sum of the temperatures was not less than the first summed threshold, the controller  550  compares (block  630 ) the sum of the temperatures to a second summed threshold (e.g., 135° F. or 58° C.). If the sum of the temperatures is less than the second summed threshold, the quantity of hot water was substantially less (but was closer to the accurate quantity than at block  625 ) than required for the high-quantity usage event. The controller then increases (block  635 ) the temperature set point by a second incremental amount (e.g., 30° F. or 15° C.) in an attempt to anticipate the quantity of hot water necessary for the next high-quantity usage event. The controller  550  then resets the flags (block  600 ) and waits for the next high-quantity usage event. 
     If, at block  630 , the sum of the temperatures was not less than the second summed threshold, the controller  550  compares (block  640 ) the sum of the temperatures to a third summed threshold (e.g., 140° F. or 61° C.). If the sum of the temperatures is less than the third summed threshold, the quantity of hot water was substantially less (but, again, was closer to the accurate quantity than at block  635 ) than required for the high-quantity usage event. The controller then increases (block  645 ) the temperature set point by a third incremental amount (e.g., 20° F. or 10° C.) in an attempt to anticipate the quantity of hot water necessary for the next high-quantity usage event. The controller  550  then resets the flags (block  600 ) and waits for the next high-quantity usage event. 
     If, at block  640 , the sum of the temperatures was not less than the third summed threshold, the controller  550  compares (block  650 ) the sum of the temperatures to a fourth summed threshold (e.g., 145° F. or 63° C.). If the sum of the temperatures is less than the fourth summed threshold, the quantity of hot water was less than required for the high-quantity usage event. The controller then increases (block  655 ) the temperature set point by a fourth incremental amount (e.g., 10° F. or 5° C.) in an attempt to anticipate the quantity of hot water necessary for the next high-quantity usage event. The controller  550  then resets the flags (block  600 ) and waits for the next high-quantity usage event. 
     If, at block  650 , the sum of the temperatures was not less than the fourth summed threshold, the controller  550  determines that an appropriate quantity of hot water was available for the high-quantity usage event and the controller does not adjust the temperature set point. The controller  550  then resets the flags (block  600 ) and waits for the next high-quantity usage event. 
     If, at block  605 , the first temperature sensor event detection flag is not set, the controller  550  determines if the first temperature sensor  555  has detected a high-quantity usage event (block  660 ). If the first temperature sensor  555  has detected a high-quantity usage event, the controller  550  sets the first temperature sensor event detection flag (block  665 ) and continues processing at block  605 . 
     If, at block  660 , the first temperature sensor  555  has not detected a high-quantity usage event, the controller  550  determines if a second temperature sensor event detection flag is set (block  670 ). If the second temperature sensor event detection flag is set, the second temperature sensor  560  has previously detected a high-quantity usage event and the controller  550  checks if the high-quantity usage event has ended (block  675 ). If the high-quantity usage event has ended, the controller  550  decreases (block  680 ) the temperature set point by a first decremental amount (e.g., 10° F. or 5° C.) in an attempt to anticipate the quantity of hot water necessary for the next high-quantity usage event. The controller  550  then continues with resetting the flags at block  600 . 
     If, at block  670 , the second temperature sensor event detection flag is not set, the controller  550  determines if the second temperature sensor  560  has detected a high-quantity usage event (block  685 ). If the second temperature sensor  560  has detected a high-quantity usage event, the controller  550  sets the second temperature sensor event detection flag (block  690 ) and continues processing at block  605 . 
     If, at block  685 , the second temperature sensor  560  has not detected a high-quantity usage event, the controller  550  determines if a third temperature sensor event detection flag is set (block  695 ). If the third temperature sensor event detection flag is set, the third temperature sensor  565  has previously detected a high-quantity usage event and the controller  550  checks if the high-quantity usage event has ended (block  700 ). If the high-quantity usage event has ended, the controller  550  decreases (block  705 ) the temperature set point by a second decremental amount (e.g., 20° F. or 10° C.) in an attempt to anticipate the quantity of hot water necessary for the next high-quantity usage event. The controller  550  then continues with resetting the flags at block  600 . 
     If, at block  695 , the third temperature sensor event detection flag is not set, the controller  550  determines if the third temperature sensor  565  has detected a high-quantity usage event (block  710 ). If the third temperature sensor  565  has detected a high-quantity usage event, the controller  550  sets the third temperature sensor event detection flag (block  715 ) and continues processing at block  605 . 
     If, at block  710 , the third temperature sensor  565  has not detected a high-quantity usage event, the controller  550  determines if a fourth temperature sensor event detection flag is set (block  720 ). If the fourth temperature sensor event detection flag is set, the fourth temperature sensor  570  has previously detected a high-quantity usage event and the controller  550  checks if the high-quantity usage event has ended (block  725 ). If the high-quantity usage event has ended, the controller  550  decreases (block  730 ) the temperature set point by a third decremental amount (e.g., 30° F. or 15° C.) in an attempt to anticipate the quantity of hot water necessary for the next high-quantity usage event. The controller  550  then continues with resetting the flags at block  600 . 
     If, at block  720 , the fourth temperature sensor event detection flag is not set, the controller  550  determines if the fourth temperature sensor  570  has detected a high-quantity usage event (block  735 ). If the fourth temperature sensor  570  has detected a high-quantity usage event, the controller  550  sets the fourth temperature sensor event detection flag (block  740 ) and continues processing at block  605 . 
     If, at block  735 , the fourth temperature sensor  570  has not detected a high-quantity usage event, the controller  550  determines if a fifth temperature sensor event detection flag is set (block  745 ). If the fifth temperature sensor event detection flag is set, the fifth temperature sensor  575  has previously detected a high-quantity usage event and the controller  550  checks if the high-quantity usage event has ended (block  750 ). If the high-quantity usage event has ended, the controller  550  decreases (block  755 ) the temperature set point by a fourth decremental amount (e.g., 40° F. or 20° C.) in an attempt to anticipate the quantity of hot water necessary for the next high-quantity usage event. The controller  550  then continues with resetting the flags at block  600 . 
     If, at block  745 , the fifth temperature sensor event detection flag is not set, the controller  550  determines if the fifth temperature sensor  575  has detected a high-quantity usage event (block  760 ). If the fifth temperature sensor  575  has detected a high-quantity usage event, the controller  550  sets the fifth temperature sensor event detection flag (block  765 ) and continues processing at block  605 . 
     If, at block  760 , the fifth temperature sensor  575  has not detected a high-quantity usage event, a high-quantity usage event has not occurred and processing continues at block  605 . 
     For each test of whether the high-quantity usage event has ended (blocks  610 ,  675 ,  700 ,  725 , and  750 ) if the high-quantity usage event has not ended, processing continues at block  605 . 
     In some embodiments, a relation between a sensed temperature following completion of a high-quantity usage event and a desired temperature set point can be determined through experimentation. A controller can detect the sensed temperature following the high-quantity usage event and can set a temperature set point based on the relation (e.g., via a look up table). 
     In the above embodiments, a temperature set point is adjusted based on the one or more sensed temperatures or rates of change of sensed temperatures following a high-quantity usage event. In some embodiments, the adjusted temperature set point can be used to control the temperature of the water in a water heater immediately following the high-quantity usage event to anticipate the quantity of hot water necessary for the next high-quantity usage event. In some embodiments, the adjusted temperature set point can be used in combination with other control algorithms which can anticipate when a high-quantity usage event may occur. The adjusted temperature set point can be used in anticipation of these events and other temperature set points can be used during periods when high-quantity usage events are not expected. 
     Thus, the invention provides, among other things, systems and methods for automatically adjusting a temperature set point of a fluid-heating device such that an accurate quantity of fluid is available for high-quantity usage events. Various features and advantages of the invention are set forth in the following claims.