Abstract:
A water heater performance monitoring device for monitoring whether a water heater is functioning optimally or whether it requires service. The device uses maximum heating rates taken from a plurality of measured heating rates to determine if the performance of the water heater has degraded from a threshold performance level. A water heater performance monitoring device can reduce the number of false alarms that occur regarding the need for water heater service by filtering out temporary factors, lasting less than a time cycle, which affect heating rate of water in the water heater. This can save users time and money by reducing unnecessary water heater inspections.

Description:
BACKGROUND 
   1. Field of the Invention 
   The present invention relates in general to water heater performance monitoring and, more particularly, to a system and method for using water heating rates to determine whether a water heater is functioning optimally. 
   2. Description of Related Art 
   Gas water heaters are typically constructed with a burner to heat water stored in a water tank. The burner is typically located directly below the water tank, and transfers heat to the water in the water tank via conduction through the water tank bottom. Problems with a water heater can impede this transfer of heat to the water in various ways (e.g., sediment buildup inside the water tank, defects in the manufacture of the water heater, misassembly of the water heater, damage to the water heater), thus slowing down the rate at which the water is heated. Such a reduction in the rate of heat transfer can undesirably affect the efficiency of the water heater, resulting in higher fuel usage and decreased water heating capability. 
   To address the problem of reduced heat transfer rates between the burner and the water in the water tank of a water heater, detection and warning systems have been used. For instance, in U.S. Pat. No. 6,265,699 B1 (the &#39;699 patent), an electronic control for an electric water heater measures heating rates of water near electric heating elements of the water heater and, when the heating rate falls below a threshold level, sends an error indication to a user. Such an approach, however, can falsely identify or fail to identify problems with the operation of the water heater. By way of example, the control described in the &#39;699 patent would send an error indication to a user after a single heating cycle having a heating rate below a threshold level. The fact that the device in the &#39;699 patent relies on a single heating cycle to determine whether the water heater is functioning properly would likely result in a substantial number of false alarms due to normal fluctuations in heating rate from one heating cycle to the next. 
   Additionally, the &#39;699 patent uses a preprogrammed threshold heating rate to determine whether the water heater is functioning properly. Such a preprogrammed threshold heating rate does not account for variations in heating rates between different water heaters, nor does it account for variations in the different environments in which water heaters may be installed. Consequently, it would be desirable to have a gas water heater performance monitoring system and method that filters out the effects of at least some external and/or short-term factors in determining when to alert a user that the water heater requires service. 
   SUMMARY 
   An exemplary embodiment provides a performance monitoring device for a water heater. The performance monitoring device is comprised of a processing unit; a temperature sensing apparatus; at least one output device; data storage; a threshold heating rate stored in the data storage; maximum heating rate data stored in the data storage, the maximum heating rate data defining (from a plurality of calculated heating rates for the water heater) a maximum heating rate for a predefined operation period; and monitoring logic stored in the data storage and executable by the processing unit (i) to monitor the heating rate of water in the water heater, (ii) to determine when the performance of the water heater has degraded, and (iii) in response to a determination of degradation in performance, to notify a user of the water heater of the degradation. The performance monitoring device makes the determination when the performance of the water has been degraded, in part, by comparing the maximum heating rate to the threshold heating rate. 
   These as well as other aspects and advantages of the present invention will become apparent to those of ordinary skill in the art by reading the following detailed description, with appropriate reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An exemplary embodiment of the present invention is described herein with reference to the following drawings, wherein: 
       FIG. 1  is a simplified cross-sectional diagram illustrating components of a typical gas water heater that may be used in accordance with the exemplary embodiment; 
       FIG. 2  is a block diagram illustrating components of an exemplary performance monitoring device in accordance with the exemplary embodiment; 
       FIG. 3  is a simplified cross-sectional diagram illustrating components of an exemplary performance monitoring system in accordance with the exemplary embodiment; and 
       FIGS. 4A and 4B  are flowcharts illustrating a functional process flow in accordance with the exemplary embodiment. 
   

   DETAILED DESCRIPTION 
   In view of the wide variety of embodiments to which the principles of the present invention can be applied, it should be understood that the illustrated embodiments are exemplary only, and should not be taken as limiting the scope of the present invention. 
     FIG. 1  is a simplified cross-sectional diagram of a typical gas water heater  100  for use in accordance with an exemplary embodiment of the present invention. As illustrated, the gas water heater  100  includes a water tank  102 , a burner  104  below the water tank  102 , insulation  106 , a water inlet pipe  108 , and a water outlet pipe  110 . Other types of gas water heaters are also possible. 
     FIG. 2  is a block diagram of a performance monitoring device  200  in accordance with an exemplary embodiment of the present invention. As shown in  FIG. 2 , the performance monitoring device  200  includes a processing unit  202 ; a sensing device  204 , including a first temperature sensor  206  and a second temperature sensor  208 ; output components  210 ; and data storage  212 , all coupled to at least one bus, illustrated as bus  214 . In the exemplary embodiment, the data storage  212  stores data, including overfire data  216 , learning mode data  218 , operation mode data  220 , and history data  222 , as well as computer instructions, including monitoring logic  224 , executable by the processing unit  202 . 
   The processing unit  202  may be one or more processors, such as a general-purpose processor and/or a digital signal processor. Other types of processors are also possible. 
   The first and second temperature sensors  206  and  208  may be surface mount temperature sensors, such as thermistors, thermocouples, and/or resistance temperature sensors. Other types and/or combinations of surface mount and non-surface mount temperature sensors are also possible. Additionally, more or fewer temperature sensors are possible. 
   The output components  210  allow the performance monitoring device to communicate with a user of a water heater by, for instance, warning the user when the water heater is not functioning properly. As such, the output device  210  may include a speaker  226 , as illustrated in  FIG. 2 . The performance monitoring device  200  may also comprise alternative and/or additional output components (e.g., a liquid crystal display (LCD) or a light emitting diode (LED)) not shown in  FIG. 2 . 
   Data storage  212  may be any medium or media readable by the processing unit  202 , such as solid-state memory, magnetic discs, optical discs, and/or any other volatile and/or non-volatile data storage system. The data storage  212  may be used to store data and/or machine-readable instructions to be read and/or executed by the processing unit  202 . 
   The stored overfire data  216  shown in  FIG. 2  can define the maximum overfire threshold heating rate for the water heater. 
   The learning mode data  218  can store one or more copies of the maximum calculated heating rates (discussed in detail below) for the water heater during learning mode. The reason to keep the maximum heating rate is that, during the heating time, the heating rate may not be at or close to the expected heating rate if hot water is being taken out from the tank. However, during a relatively long period of time, such as two weeks, unless the hot water is drawn continuously, the heating rate will at times be detected at or close to the maximum. Redundant copies of the maximum rate can be stored for a data integrity check. 
   The operation mode data  220  can be a running maximum of heating rates for the water heater  100 , calculated during an operation mode (discussed in detail below) during a relatively long operation time period, such as two weeks. 
   The history data  222 , shown in  FIG. 2 , can define the maximum calculated heating rates for each operating mode time cycle. The history data  222  may be a table having one row and a plurality of columns resulting in a number of cells equal to the typical number of time cycles in a calendar year. For example, for a two-week operating mode time cycle, the history data  222  table would generally have twenty-six cells. 
   The stored monitoring logic  224  shown in  FIG. 2  may contain instructions for operation of the performance monitoring device  200 . The monitoring logic  224  can include instructions for, among other things, measuring the water temperature at a first time using the first and/or second temperature sensors  206  and  208 , and a second time using the first and/or second temperature sensors  206  and  208 ; calculating a water heating rate using the measured water temperatures; comparing a calculated heating rate to an overfire heating rate; determining if the performance monitoring device  200  is in learning mode or operation mode; storing the calculated heating rate in the data storage  212 ; calculating an average heating rate using the stored heating rates; determining whether a data table is full; determining the highest heating rate from a plurality of stored heating rates; and comparing a calculated heating rate to a threshold heating rate. The monitoring logic  224  may additionally contain instructions for determining whether to apply ambient temperature compensation (discussed in detail below), and if so, to what extent it should be applied. Other instructions are also possible. 
   Although the performance monitoring device  200  is shown as a single physical device in  FIG. 2 , the various components of the apparatus  200  could also be separate, discrete devices in direct or indirect (i.e. via one or more intermediate devices) communication, either wirelessly or otherwise. Additional or fewer performance monitoring device components are possible as well. 
     FIG. 3  is a simplified cross-sectional diagram of a water heater performance monitoring system  300  in accordance with an exemplary embodiment of the present invention. As shown in  FIG. 3 , the water heater performance monitoring system  300  includes the water heater  100  of  FIG. 1  and the performance monitoring device  200  of  FIG. 2 . As shown in  FIG. 3 , the first temperature sensor  206  of the performance monitoring device  200  is mounted on the outer side surface of the water heater tank, inside the insulator layer, near the water tank top  302 , and the second temperature sensor  208  of the performance monitoring device is mounted on the outer side surface of the water heater tank, inside the insulator layer, near the water tank bottom  304 . In the exemplary embodiment shown in  FIG. 3 , the first and second temperature sensors  206  and  208  are communicatively coupled to the remaining components of the performance monitoring device  200  via insulated wires  306 . Other types of communicative coupling such as fiber optics or radio frequency (RF) wireless communication, for instance, are also possible. 
     FIGS. 4A and 4B  are flow charts that illustrate exemplary functions performed by the performance monitoring device  200  in accordance with an exemplary embodiment of the present invention. At step  400 , the first and second temperature sensors  206  and  208  measure the temperature of the water in the water tank  102  at a first time. Next, at step  402 , the temperature sensors  206  and  208  measure the water temperature at a second time, after a predefined delay from the first time. In an exemplary embodiment, the predefined delay period is preferably one minute; however, the delay period could be any period of time shorter than a typical heating cycle for the water heater  100 . In alternative embodiments, more or fewer temperature sensors may be used. 
   At step  404 , after the temperature sensors  206  and  208  have measured the second water temperature in step  402 , the processing unit  202  calculates the heating rate for that moment of the water heater  100 . The processing unit  202  can do this by subtracting the first measured water temperature from the second measured water temperature, and then dividing the result by the predefined time (e.g., one minute). If multiple temperature sensors were used to measure water temperature, the value for water temperature used to calculate the heating rate may be the average of the water temperatures measured at the first and second temperature sensors  206  and  208  at that time. Alternatively, only one of the measured temperatures may be used to calculate the heating rate. Next, at step  406 , the processing unit determines whether the calculated heating rate is greater than an overfire preprogrammed threshold. The processing unit  202  can do this by comparing the measured heating rate to the overfire threshold heating rate stored in the overfire data  216 . If the calculated heating rate is greater than the threshold heating rate stored in the overfire data  216 , the performance monitoring device  200  warns the user of the water heater performance monitoring system  300  of a possible overfire condition, at step  408 . The monitoring device  200  can do this by using at least one of its output components  210 , such as the speaker  226 . An overfire condition may be caused by, among other things, an empty or partly empty water tank, high gas pressure, installation of incorrect burner components, or other part defects and/or assembly errors. 
   If the measured heating rate is not greater than the overfire preset limit, the processing unit  202  determines, at step  410 , whether the performance monitoring device  200  is in a learning mode. The performance monitoring device&#39;s  200  learning mode operates for a period after the water heater  100  begins to operate. The learning mode allows the performance monitoring device  200  to obtain an accurate maximum heating rate for that particular water heater  100  installed in its particular environment. Additionally, the learning mode permits exclusion of transitory factors that might alter the maximum heating rate of the water heater  100  as long as the transitory factors last for a shorter time than the learning period. The processing unit  202  can determine if the performance monitoring device  200  is in learning mode by reviewing the learning mode data  218 . Specifically, if the learning mode data  218  has any empty cells, the performance monitoring device  200  is in the learning mode, if the learning mode data  218  does not have empty cells, the performance monitoring device  200  is not in the learning mode. If the processing unit  202  determines that the performance monitoring device  200  is in the learning mode, the processing unit  202 , at step  412 , causes the measured heating rate to be stored in the learning mode data  218 . The process then starts over at step  400 . 
   If, at step  410 , the processing unit  202  determines that the performance monitoring device  200  is not in learning mode, the processing unit  202  causes the determined heating rate to be stored in the operation mode data  220 , at step  414 . Next, at step  416  of  FIG. 4B , the processor determines whether all of the cells of the operation mode data  220  are full. If they are not, the process returns to step  400  of  FIG. 4A . However, if all of the cells of the operation mode data  220  are full, the processor, at step  418 , compares the highest heating rate stored in operation mode data  220 , the “maximum operation mode heating rate,” to the highest heating rate stored in the learning mode data  218 , the “maximum learning mode heating rate.” In making that comparison in step  418 , if the processor  202  determines in step  420  that the maximum operation mode heating rate is substantially less than the maximum learning mode heating rate, or if the historical data shows a significant declining trend in water heater performance, the processor  202  causes the performance monitoring device  200  to transmit a warning to a user of the water heater  100  in step  422 . The warning of step  422  informs the user of the degradation of water heater  100  performance. The monitoring device  200  can provide the warning using at least one of its output components  210 , such as the speaker  226 . The warning can include, for example, a recommendation that the user contact a water heater professional repair service to determine whether the water heater  100  requires maintenance or repair. In an exemplary embodiment, the maximum operation mode heating rate is substantially less than the maximum learning mode heating rate when it is lower than 50% of the maximum learning mode heating rate. Other definitions of the maximum operation mode heating rate being substantially less than the maximum learning mode heating rate are also possible. 
   The cooling effects seen at one or both sensors can also be used to further verify the correct performance of water heater. For example, by using the maximum cooling rate of the upper tank sensor versus the lower sensor, the controller can determine an improperly installed or broken dip-tube in the heater. If the cooling rate of the upper sensor far exceeds that of the lower sensor (before the tank has used most of its capacity), then the condition can be detected. The thresholds for this measurement can be learned in a similar fashion as the heating rate data, or can be preprogrammed into controller memory. 
   In an alternative embodiment, the cooling effects of ambient temperatures lower than those of the heated water on the heated water in the water tank  102  can be used in determining what difference between the maximum operation mode heating rate and the maximum learning mode heating would render the maximum operation mode heating rate substantially less than the maximum learning mode heating rate. Use of ambient temperature in such a way can be referred to as applying ambient temperature compensation. Ambient temperature compensation may be necessary if the insulation of the water heater is poor, or the heating capability is very low. Ambient temperature compensation may be accomplished in a number of ways. In one embodiment, a processing unit  202  with an internal, on chip temperature sensor (such as Texas Instruments MSP430F1132 microcontroller) can determine the temperature of the ambient air outside the water heater  100  and, using that ambient temperature, determine whether ambient temperature compensation should be applied to the calculation of whether the maximum operation mode heating rate is substantially less than the maximum learning mode heating rate. 
   In another alternative embodiment, the cooling rate of the water in the water tank  102  could be used to determine whether ambient temperature compensation should be applied. The cooling rate could be determined using the temperature sensors  206  and  208  in much the same way that the heating rate is calculated, as described above, when the main valve of the water heater  100  is off and there is no water draw (i.e., water flowing from the water heater). The cooling rate is preferably determined at about the same water temperature at which the heating rate is calculated. By way of example, if the ambient temperature were determined to be especially cold, and the water in the water tank  102  therefore cooled more quickly (or failed to heat as quickly), the maximum operation mode heating rate for that time cycle could be determined to not be substantially less than the maximum learning mode heating rate, even though it would have been considered to be substantially lower in warmer ambient temperature conditions. 
   In addition to ambient temperature compensation, maximum heating rate history compensation could be applied in determining whether the maximum operation mode heating rate is substantially less than the maximum learning mode heating rate. Maximum heating rate history compensation could be applied using a stored history of maximum operation mode heating rates in the history data  222 . This data could be accessed by the processor and considered to determine whether any seasonal compensation should be applied in determining whether the maximum operation mode heating rate for any one time cycle is substantially less than the maximum learning mode heating rate. 
   Alternatively, if the processing unit  202  determines that the maximum operation mode heating rate is not substantially less than the maximum learning mode heating rate, the processing unit  202 , at step  424 , can delete the heating rates stored in the operation mode data  220  and the process can return to step  400  of  FIG. 4A . 
   Conclusion 
   Prior attempts to monitor the performance of a water heater have typically involved detection and warning systems that use only single heat rate reading to determine whether the water heater is functioning optimally. The water heater performance monitoring system of the present invention, however, provides for a detection and warning system that uses the maximum heating rate from a plurality of heating rate measurements taken over a time cycle, such as two weeks, to determine whether the water heater is functioning properly. This approach allows temporary factors that affect the heating rate of water in a water heater to be filtered out, thereby decreasing the possibility of false alarms that could result in unnecessary service expenses. Further, this water heater monitoring device allows ambient temperature and seasonal compensation to further improve the accuracy of the device. 
   An exemplary embodiment of the present invention has been described above. Those skilled in the art will understand, however, that changes and modifications may be made to this embodiment without departing from the true scope and spirit of the present invention, which is defined by the claims.