Patent Publication Number: US-10330344-B2

Title: Temperature algorithm for water heater

Description:
FIELD OF APPLICATION 
     Embodiments relate to water heaters. 
     SUMMARY 
     Water heating systems may include a hot water storage tank, an external heater, a circulation pump, and a tank thermostat. Some external heaters include tank thermostats that are set below the setpoint of the external heater by a set number (for example, 10° F.). This method may not provide optimal tank temperature regulation. For example, when there is a hot water draw, depending on the location of the tank thermostat, the circulation pump may be activated quickly even if the majority of the storage tank is full of hot water. When the amount of hot water discharge is small, the external heater would rapidly turn off. This may result in short cycling both the pump and the external heater. In addition, depending on the setpoint of the external heater, hot water may enter the inlet of the external water heater, reducing energy efficiency. 
     Therefore, in one embodiment, the application provides a water heater including a storage tank including a water inlet and a water outlet, a pump, an upper temperature sensor configured to sense an upper temperature related to an upper area of the tank and output an upper temperature signal corresponding to the upper temperature, a lower temperature sensor configured to sense a lower temperature related to a lower area of the tank and output a lower temperature signal corresponding to the lower temperature, and an electronic processor. The electronic processor is configured to receive an upper temperature signal and a lower temperature signal, compare the upper temperature signal to a sum of a setpoint temperature threshold minus a temperature differential, and compare the lower temperature signal to a high limit temperature threshold. The electronic processor is further configured to activate the pump in response to the first upper temperature signal being less than the sum of the setpoint temperature threshold minus the temperature differential and the first lower temperature signal being less than the predetermined high limit temperature threshold. 
     In another embodiment, the application provides a method of operating a water heater including a storage tank including a water inlet and a water outlet, a pump, an upper temperature sensor configured to sense an upper temperature related to an upper area of the tank and output an upper temperature signal corresponding to the upper temperature, and a lower temperature sensor configured to sense a lower temperature related to a lower area of the tank and output a lower temperature signal corresponding to the lower temperature. The method includes receiving a first upper temperature signal and a first lower temperature signal, comparing the first upper temperature signal to a sum of a setpoint temperature threshold minus a temperature differential, comparing the first lower temperature signal to a high limit temperature threshold, and activating the pump in response to the first upper temperature signal being less than the sum of the setpoint temperature threshold minus the temperature differential and the first lower temperature signal being less than the predetermined high limit temperature threshold. 
     Other aspects of the application will become apparent by consideration of the detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial exposed view of a water heater according to some embodiments of the application. 
         FIG. 2  is a schematic diagram of a control system of the water heater of  FIG. 1  according to some embodiments of the application. 
         FIG. 3  is a flowchart illustrating a method of operating the water heater of  FIG. 1  according to some embodiments of the application. 
         FIG. 4  is a partial exposed view of a water heater with a recirculation loop according to some embodiments of the application. 
         FIG. 5  is a flowchart illustrating a method of operating the water heater of  FIG. 4  according to some embodiments of the application. 
     
    
    
     DETAILED DESCRIPTION 
     Before any embodiments of the application are explained in detail, it is to be understood that the application 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 drawing. The application 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. 
       FIG. 1  is a partial exposed view of a storage-type water heater system  100  according to some embodiments of the application. In some embodiments, the water heater system  100  is a hybrid tank and tankless water heater system. The water heater system  100  includes an enclosed water tank  105 , a shell  110  surrounding the water tank  105 , and foam insulation  115  filling an annular space between the water tank  105  and the shell  110 . The water tank  105  may be made of ferrous metal and lined internally with a glass-like porcelain enamel or other materials to protect the metal from corrosion. In other embodiments, the water tank  105  may be made of other materials, such as plastic or stainless steel. 
     The water heater system  100  may further include a cold water inlet opening  120 , a hot water inlet opening  125 , a water t-valve  126 , a hot water outlet  127 , an upper temperature sensor  130 , a lower temperature sensor  135 , an external heater  140 , a circulation pump (or valve)  145 , and a controller  150 . A cold water source  155  provides cold water to the water tank  105  through the cold water inlet opening  120 . The cold water source  155  also delivers cold water to the external heater  140  through the circulation pump  145 . The circulation pump  145  may be controlled by the controller  150 . When the circulation pump  145  is active, the external heater  140  receives the cold water and heats the cold water to a predetermined temperature. From the external heater  140 , the water is then delivered to the water t-valve  126 , which directs the water to the water tank  105 , via hot water inlet opening  125 , or to a user, via hot water outlet  127 . 
     The upper temperature sensor  130  may be positioned in the upper portion of the water tank  105  to determine a temperature of the water stored in the upper portion of the water tank  105 . Analogously, the lower temperature sensor  135  may be positioned in the lower portion of the water tank  105  to determine a temperature of the water in the lower portion of the water tank  105 . The upper temperature sensor  130  and the lower temperature sensor  135  may be attached to the water tank  105 , and may include, for example, thermistor type sensors. The upper temperature sensor  130  and the lower temperature sensor  135  may be electrically and/or communicatively coupled to the controller  150  to periodically provide the sensed temperatures to the controller  150 . In some embodiments, the water tank  105  may include more temperature sensors to provide a more accurate indication of the temperature of water inside the water tank  105 . For example, the water tank  105  may be divided into three or more portions and a temperature sensor may be positioned in each portion. The distance between the upper temperature sensor  130  and the lower temperature sensor  135  may be determined based on the geometry of the tank, a desired tank recovery, and the water stratification pattern inside the water tank  105 . In some embodiments, the shorter the distance between sensors  130  and  135 , the sooner the external heater  140  and circulation pump  145  may activate (when implementing a control method  300  described in  FIG. 3  or a control method  500  described in  FIG. 5 ). 
     The controller  150  is electrically and/or communicatively coupled to the upper temperature sensor  130 , the lower temperature sensor  135 , and the circulation pump  145 . In some embodiments, the controller  150  is also electrically and/or communicatively coupled to the external heater  140 . The controller  150  receives the temperature signals from the upper temperature sensor  130  and the lower temperature sensor  135 . Based on the received temperature signals, the controller  150  may control the operation of the external heater  140  and/or the circulation pump  145  as described in detail below. 
       FIG. 2  is schematic diagram of a control system  200  of the water heater of  FIG. 1  according to some embodiments of the application. The control system  200  includes the controller  150 , the upper temperature sensor  130 , the lower temperature sensor  135 , the external heater  140 , and the circulation pump  145 . In some embodiments, the control system  200 , or at least part of the control system  200  may be located remotely from the water heater system  100 . The control system  200  includes combinations of hardware and software that are operable to, among other things, control the operation of the water heater system  100 . As shown in  FIG. 2 , the controller  150  includes an electronic processor  205 , a memory  210 , and input/output devices  215 . In some embodiments, the controller  150  also includes a communication module to transmit and receive information via wired or wireless communication with one or more external devices. In further embodiments, the controller  150  also includes a display  225  and a user interface  230 . 
     The electronic processor  205  is communicatively coupled to the memory  210  and to the input/output device  215 . The electronic processor  205  receives information regarding the operation of the water heater system  100  through the input/output devices  215 . The electronic processor  205  may receive command signals received from the user interface  230  or a network and determine control signals based on the command signals received. The electronic processor  205  may then output the control signals to the input/output devices  215 . 
     The memory  210  is configured to store algorithms and/or programs used to control the circulation pump  145 , the external heater  140 , and other components of the water heater system  100 . The memory  210  may also store historical data, usage patterns, and the like to help control the water heater system  100 . The memory  210  also stores the control method  300  described in  FIG. 3  and the control method  500  described in  FIG. 5  executed by the electronic processor  205  to operate the circulation pump  145  based on the measurements 
     The input/output devices  215  output information to the user regarding the operation of the water heater system  100  and may also receive inputs. The controller  150  communicates (via wireless or wired connection) with the upper temperature sensor  130 , the lower temperature sensor  135 , the external heater  140 , and the circulation pump  145  via the input/output devices  215 . In some embodiments, the input/output devices  215  may include the user interface  230  for the water heater system  100 . The input/output devices  215  may include a combination of digital and analog input or output devices required to achieve level of control and monitoring for the water heater system  100 . For example, the input/output devices  215  may include a touch screen, a speaker, buttons, and the like to receive user input regarding the operation of the water heater system  100  (for example, a temperature set point at which water is to be delivered from the water tank  105 ). The electronic processor  205  also outputs information to the user in the form of, for example, graphics, alarm sounds, and/or other known output devices. The input/output devices  215  may be used to control and/or monitor the water heater system  100 . For example, the input/output devices  215  may be operably coupled to the controller  150  to control temperature settings of the water heater system  100 . For example, using the input/output devices  215 , a user may set one or more temperature set points for the water heater system  100 . 
     The input/output devices  215  are configured to display conditions, or data, associated with the water heater system  100  in real-time or substantially real-time. For example, but not limited to, the input/output devices  215  may be configured to display the temperature sensed by temperature sensors  130 ,  135 . The input/output devices  215  may be mounted on the shell  110  of the water heater system  100 , remotely from the water heater system  100  in the same room (e.g., on a wall), in another room in the building, or even outside of the building. In some embodiments, the input/output devices  215  may also generate alarms regarding the operation of the water heater system  100 . The input/output devices  215  allow the controller  150  to communicate with the upper temperature sensor  130 , the lower temperature sensor  135 , the circulation pump  145  and the external heater  140 . 
       FIG. 3  is a flowchart illustrating a method  300  of operating the water heater system  100  according to some embodiments of the application. At block  302 , the controller  150  receives an upper temperature signal (T__upper) from the upper temperature sensor  130  and a lower temperature signal (T_lower) from the lower temperature sensor  135 . At block  304 , T_upper is compared to the sum of a setpoint temperature threshold (T_setpoint) minus a temperature differential (T_diff). When T_upper exceeds (is greater than) or equal to T_setpoint-T_diff, block  302  is repeated. When T_upper is less than T_setpoint-T_diff, T_lower is compared to a high limit threshold (T_HL) at block  306 . When T_lower is less than T_HL, the circulation pump  145  (and the external heater  140 ) are activated at block  308 . When T_lower is greater than or equal to T_HL and the circulation pump  145  is not activated (block  310 ), the method  300  starts again at block  302 . 
     In some embodiments, T_setpoint is a measured temperature from a sensor, for example the upper sensor  130 , received by the controller  150 . In some embodiments, where the controller  150  is communicatively coupled to the external heater  140 , T_setpoint may be a set desired temperature of water at the outlet of the external heater  140  selected by an operator of the water heater system  100  (for example, via the user interface  230 ). 
     After the circulation pump  145  is activated at block  308 , hot water is supplied to the water tank  105  and the method  300  returns to block  302 . When the system starts from a cold tank, T_upper is less than T_setpoint-T_diff. As the external heater  140  continues to run and the circulation pump  145  supplies hot water to the water tank  105 , the hot water within the water tank  105  rises to the upper portion of the tank. The water within the lower portion of the water tank  105  will remain at a constant, lower temperature as a result of the hot water entering the water tank  105  stratifying to the top of the water tank. The hot water stratification continues until the temperature of water in the upper portion of the water tank  105  reaches an approximately constant temperature. At this point, the water in the lower portion of the water tank  105  will increase in temperature, causing T_lower to increase. 
     Once it is determined that T_lower is greater than or equal to T_HL (block  306 ), and it is determined that the pump is active (block  310 ), a determination is made whether a rate of temperature of T_lower is increasing and a difference between T_upper and T_lower ( T_delta) is decreasing (block  311 ). At block  311 , the controller  150  may determine if T_lower is increasing and if T_delta is decreasing by collecting multiple readings of T_upper and T_lower for a predetermined time from the upper temperature sensor  130  and the lower temperature sensor  135  respectively. When the controller  150  determines T_lower is increasing and T_delta is decreasing, the circulation pump  145  and external heater  140  are deactivated and the water heater  100  is placed into a standby mode (block  312 ). When the controller  150  determines T_lower is not increasing and/or T_delta is not decreasing, the controller  150  returns to block  302 . When the controller  150  determines that the circulation pump  145  is not active (block  310 ), the controller  150  returns to block  302 . At block  312 , when the water heater  100  is placed into the standby mode, the controller  150  returns to block  302 . 
     In some embodiments, the controller  150  is not communicatively coupled to the external heater  140 . In such embodiments, when the desired outlet temperature is set at the external heater  140 , the desired outlet temperature of the external heater  140  may be adjusted to a temperature greater than the current T_setpoint, stored by the controller  150 , minus T_diff (block  304 ). A hot water draw may reduce T_lower to be less than T_HL while T_upper remains the same, which may lead to short cycling of the water heater. To prevent short cycling, the controller  150  determines if T_lower is less than T_HL (block  314 ). When the controller  150  determines that T_lower is less than T_HL, the controller further determines if the circulation pump  145  is activated (block  316 ). When the controller  150  determines the circulation pump  145  is activated, it returns to block  302 ; when the controller  150  determines that the circulation pump  145  is not activated, the controller  150  continues to keep the circulation pump  145  deactivated and the water heater  100  remains in the standby mode (block  312 ). When the controller  150  determines that T_lower is greater than or equal to T_HL (block  314 ), the controller  150  returns to block  312  and then block  302 . 
     While the water heater system  100  is in the standby mode, the controller  150  updates T_setpoint and T_HL. In some embodiments, T_setpoint is updated based on a maximum temperature sensed by the upper temperature sensor  130  while in the standby mode. In some embodiments, T_setpoint is set by an operator of the water heater system  100  (for example, via the user interface  230 ) and is associated with the outlet temperature of the external heater  140 . In some embodiments, T_HL is a predetermined default value automatically set based on a set temperature of the external heater  140 . In further embodiments, the operator of the water heater system  100  is able to configure T_HL to be higher (or lower) than the predetermined default value. 
     The method  300  may be applied to other types, configurations, geometries, and sizes of water heaters beyond what is illustrated. Such embodiments may include more than one tank, external heater, sensors, pumps, and the like. Depending on such characteristics of the water heater, additional steps may be added to the method  300 . For example,  FIG. 4  is a partial exposed view of a water heater  400  with a recirculation loop  402  according to some embodiments of the application. The water heater  400  includes similar components and is configured similarly to the water heater system  100  illustrated in FIG. 1  described above. However, the embodiment illustrated in  FIG. 4  includes additional components, such as the recirculation loop  402  and a recirculation pump  404 . The recirculation loop  402  is configured to return hot water to the cold water inlet  120  through the recirculation pump  404 . The recirculation pump  404  may be communicatively coupled to and controlled by the controller  150 . In the embodiment illustrated in  FIG. 4 , the control method  300  may still be implemented. However, due to the draw of the recirculation loop  402 , additional blocks to the control method  300  may be necessary. 
       FIG. 5  illustrates the control method  500  for the water heater  400 . The control method  500  includes the similar components of the method  300  of  FIG. 3  with some additions. In the illustrated embodiment, when the pump is not activated and when T_upper is less than the sum of T_setpoint-T_diff (block  304 ), T_lower may be greater than T_HL. Such a situation may occur when there is no hot water draw other than from the recirculation loop  402 . To compensate for the loss due to the recirculation loop  402 , as described in more detail below, the circulation pump  145  and the external heater  140  are activated (block  505 ) when it is determined that T_lower is greater than or equal to T_HL (at block  306 ) and that the circulation pump  145  is not activated (at block  310 ), and that T_upper is less than T_setpoint and T_lower is less than a second high limit temperature threshold T_HL2 (block  504 ). 
     When it is determined at block  310  that the circulation pump  145  is not activated, T_upper is compared to T_setpoint (block  502 ). When T_upper is greater than or equal to T_setpoint (block  502 ), the circulation pump  145  and the external heater  140  are deactivated and the water heater  400  is placed into the standby mode (block  506 ) and the controller  150  returns to block  302 . When T_upper is less than T_setpoint (block  502 ), T_lower is compared to a second high limit temperature threshold T_HL2 at block  504 . When T_lower is greater than T_HL2 (block  504 ), the circulation pump  145  and external heater  140  are deactivated and the water heater  400  is placed into the standby mode (block  506 ). 
     When T_lower is less than T_HL2 and circulation pump  145  is activated, T_lower is compared to T_HL at block  508 . When T_lower is less than T_HL (block  508 ), the controller  150  returns to block  302 . When T_lower is greater than or equal to T_HL (block  508 ), the controller  150  may determine if T_lower is increasing and if T_delta is decreasing (block  510 ). 
     At block  510 , the controller  150  may determine if T_lower is increasing and if T_delta is decreasing by collecting multiple readings of T_upper and T_lower for a predetermined time from the upper temperature sensor  130  and the lower temperature sensor  135  respectively. When the controller  150  determines T_lower is increasing and T_delta is decreasing (block  510 ), the circulation pump  145  and external heater  140  are deactivated and the water heater  400  is placed into the standby mode (block  506 ). When the controller  150  determines T_lower is not increasing and/or T_delta is not decreasing (block  510 ), the controller  150  receives another T_upper from the upper temperature sensor  130  and another T_lower from the lower temperature sensor  135  (block  512 ) and returns to block  505 . 
     Within the control method  500 , when there is an external hot water draw (a hot water draw not by the recirculation loop  402 ) that causes T_lower to be less than T_HL, the controller  150  may execute only the blocks within the control method  500  that are in control method  300  (blocks  302 ,  304 ,  306 ,  308 ,  310 ,  311 , and  312 ). 
     The controller  150  may include additional features to aid in the efficiency of the water heater system  100 . In some embodiments, the controller  150  is further configured to drive a modulation pump. For example, when the upper temperature sensor  130  senses the temperature in the upper area of the tank approaching T_setpoint, the controller  150  modulates down the pump so to reduce the flow rate running through the external heater  140 . 
     Various features and advantages of the application are set forth in the following claims.