Estimation of temperature states for an electric water heater from inferred resistance measurement

Patent metadata

Field	Value
Publication number	US-11085667-B2
Application number	US-201916422352-A
Country	US
Kind code	B2
Filing date	May 24, 2019
Priority date	Dec 22, 2014
Publication date	Aug 10, 2021
Grant date	Aug 10, 2021

Abstract

A water heater that includes a cylindrical storage tank and at least one heating element, is modeled using a one-dimensional model that includes: a vertical stack of disks representing the water volume in the cylindrical storage tank, and a stack of annular segments surrounding the vertical stack of disks. Various temperature measurements are determined via resistance calculations of the at least one heating element. The stack of annular segments represents the cylindrical wall of the cylindrical storage tank. The one-dimensional model may be used by a condition-based maintenance system comprising an electronic data processing device configured to detect a failure mode present in the water heater based on an output of the water heating model component. Some illustrative failure modes include insulation disturbance, heating element failure, excessive sediment buildup, or a drip tube rupture.

First claim

The invention claimed is:

1. A water heater control system for controlling a water heater including a vertically oriented cylindrical water storage tank having a cylindrical wall, and at least one heating element arranged to heat water in the water storage tank, the electric water heater control system comprising:
a load controller comprising,
an electronic data processing device configured to operate the water heater including operating the at least one heating element based on temperature readings determined from a resistance of the at least one heating element to control water temperature of water in the water storage tank,
a low energy pulse circuit operative to send a voltage pulse to the at least one heating element, and
a voltage and current measurement circuit operative to measure the current drawn by the at least one heating element responsive to the voltage pulse; and
a water heater modeling component comprising an electronic data processing device configured to model the water heater using a one-dimensional model that includes:
a vertical stack of disks representing the water volume in the cylindrical water storage tank, and
a stack of annular segments surrounding the vertical stack of disks wherein the stack of annular segments represents the cylindrical wall of the cylindrical water storage tank.

2. The water heater control system of claim 1 , wherein the load controller is configured to calculate the resistance of the at least one heating element in accordance with the measured current draw and the voltage pulse.

3. The water heater control system of claim 2 , wherein the load controller is configured to generate the temperature readings in accordance with the calculated resistance.

4. The water heater control system of claim 2 , wherein the load controller is configured to identify the at least one heating element operating responsive to the calculated resistance.

5. The water heater control system of claim 3 further comprising:
a condition-based maintenance system comprising an electronic data processing device configured to detect a failure mode present in the water heater based on an output of the water heating model component.

6. The water heater control system of claim 5 , wherein the condition-based maintenance system is configured to detect a failure mode comprising insulation disturbance present in the water heater based on R-values or thermal conductivity values computed for the annular segments representing the cylindrical wall of the cylindrical water storage tank.

7. The water heater control system of claim 5 , wherein the condition-based maintenance system is configured to detect a failure mode comprising a heating element failure present in the water heater based on an increase over time of the thermal or volumetric capacity of the water in the water storage tank determined using the water heater modeling component.

8. The water heater control system of claim 5 , wherein the water heater is an electric water heater, the at least one heating element is a resistive heating element, and the condition-based maintenance system is configured to detect a failure mode comprising a heating element failure present in the water heater based on an increase in electrical resistance measured for the heating element over time.

9. The water heater control system of claim 5 , wherein the condition-based maintenance system is configured to detect a failure mode comprising sediment buildup present in the water storage tank of the water heater based on a decrease over time of the thermal or volumetric capacity of the water in the water storage tank determined using the water heater modeling component.

10. The water heater control system of claim 5 , wherein the condition-based maintenance system is configured to detect a failure mode comprising a tube rupture present in the water heater based on more rapid cooling of the upper elevation disks of the vertical stacked disks as compared with the lower elevation disks during a hot water draw event.

11. The water heater control system of claim 5 , wherein the load controller is further configured to (i) communicate with an aggregation demand response dispatch engine comprising an electronic data processing device that is configured to send demand response commands to an aggregation of loads including the water heater and (ii) operate the water heater in accord with demand response commands received from the aggregation demand response dispatch engine.

12. The water heater control system of claim 1 wherein the load controller is further configured to (i) communicate with an aggregation demand response dispatch engine comprising an electronic data processing device that is configured to send demand response commands to an aggregation of loads including the water heater and (ii) operate the water heater in accord with demand response commands received from the aggregation demand response dispatch engine,
wherein a demand response operation performed by the cooperating load controller and aggregation demand response dispatch engine is based at least in part on energy stored in the vertically oriented cylindrical water storage tank as determined using the water heater modeling component.

13. The water heater control system of claim 1 wherein the one-dimensional model comprises coupled differential equations including:
for each disk of the vertical stack of disks representing the water volume in the cylindrical water storage tank, a differential equation expressing the time derivative of the temperature of the disk estimated by the one-dimensional model; and
for each annular segment of the stack of annular segments representing the cylindrical wall of the cylindrical water storage tank, a differential equation expressing the time derivative of the temperature of the annular segment estimated by the one-dimensional model.

14. A system comprising:
a water heater including a water storage tank, and at least one heating element arranged to heat water in the water storage tank;
a load controller comprising:
an electronic data processing device,
a low energy pulse circuit operative to send a voltage pulse to the at least one heating element, and
a voltage and current measurement circuit operative to measure the current drawn by the at least one heating element responsive to the voltage pulse,
wherein the electronic data processing device is configured to operate the water heater including operating the at least one heating element based on temperature readings determined from a resistance of the at least one heating element to control water temperature of water in the water storage tank;
an aggregation demand response dispatch engine comprising an electronic data processing device configured to send demand response commands to load controllers of an aggregation of loads including the load controller configured to operate the water heater wherein the load controller is further configured to operate the water heater in accord with demand response commands received from the aggregation demand response dispatch engine; and
a condition-based maintenance system comprising an electronic data processing device configured to detect a failure mode present in the water heater based on information including the temperature readings determined from the resistance of the at least one heating element and power input to the water heater.

15. The system of claim 14 ,
wherein the load controller is configured to calculate the resistance of the at least one heating element in accordance with the measured current draw and the voltage pulse, and to generate the temperature readi

Assignees

• Battelle Memorial Institute

Inventors

• Mccullough Jason J
• Jones Michael A
• Rehberg Eric L

Classifications

• F24H2250/02

  Resistances · CPC title

• G05B17/02

  electric · CPC title

• F24H9/2021 Primary

  Storage heaters · CPC title

• F24H15/176

  Improving or maintaining comfort of users · CPC title

• F24H15/281

  Input from user · CPC title