Water heater stacking detection and control

• US 8,875,664 B2
• Filed: 11/30/2012
• Issued: 11/04/2014
• Est. Priority Date: 06/19/2007
• Status: Active Grant

• Current Assignee: Ademco Inc. (Resideo Technologies, Inc.)
• Original Assignee: Honeywell International Inc.
• Inventors: Strand, Rolf L.
• Primary Examiner(s): Wilson, Gregory A
• Application Number:
  US13/691,573
• Publication Number:
  US 20130092103A1
• Time in Patent Office: 704 Days
• Field of Search: 122/14.2, 122/14.22, 392/498, 700/299, 700/300
• US Class Current: 122/14.22
• CPC Class Codes: F24H 1/206 with submerged combustion chamber
• CPC Class Codes: F24H 9/2007 for water heaters
• CPC Class Codes: F24H 9/2035 using fluid fuel
• CPC Class Codes: F28D 20/0034 using liquid heat storage material
• CPC Class Codes: G05D 23/1919 characterised by the type of controller

Abstract

Methods and systems for operating a water heater to limit the effects of stacking in a water heater tank are disclosed. In some cases, the water heater controller may determine a rate of change of the water temperature in the water heater tank. If the rate of change exceeds a threshold value, the controller may adjust the water heater temperature set point downward to help reduce stacking in the water heater. In some cases, the water heater temperature set point may be returned to the original water heater temperature set point when stacking is no longer likely to be of a concern. In one illustrative embodiment, the controller may track the time that the heater of the water heater is in the “on” state, or the time that the heater is in the “off” state, during subsequent heating cycles. The controller may then compare the “on” time or the “off” time to respective recovery threshold times. If the “on” time or the “off” time exceeds its respective recovery threshold time, then the controller may adjust the set point toward the original water heater temperature set point, sometimes in an incremental manner.

Claims

1. A water heater comprising:

a tank;

a heater for heating water in the tank;

a sensor provided a signal corresponding to the temperature of water in the tank;

a controller coupled to the sensor for receiving the signal corresponding to the temperature of the water in the tank, the controller storing a normal user-defined temperature set point for the water in the tank;

the controller is configured to control the temperature of the water in the tank based on the normal user-defined temperature set point by selectively operating the heater in a sequence of heating cycles, wherein the controller determines a measure related to a length of time of at least some of the heating cycles, and if the measure falls below a threshold value, the controller determines that stacking is likely occurring in the tank;

if the controller determines that stacking is likely occurring in the tank, the controller is configured to control the temperature of the water in the tank based on a second temperature set point, wherein the second temperature set point is lower than the normal user-defined temperature set point; and

wherein if the measure falls below the threshold value for one or more heating cycles, and then during a subsequent heating cycle the measure rises above the threshold value, the controller is configured to increase the second temperature set point toward the normal user-defined temperature set point.

2. The water heater of claim 1 wherein the measure related to the length of time of a heating cycle corresponds to the time that the heater is on during the heating cycle.

3. The water heater of claim 1 wherein the measure related to the length of time of a heating cycle corresponds to the time that the heater is off during the heating cycle.

4. The water heater of claim 1 wherein the measure related to the length of time of a heating cycle corresponds to the time that the heater is on and off during the heating cycle.

5. The water heater of claim 1, wherein the second temperature set point is defined by an offset from the normal user-defined temperature set point.

6. The water heater of claim 1, wherein the controller is configured to increase the second temperature set point toward the normal user-defined temperature set point by a recovery offset amount.

7. The water heater of claim 6, wherein the recovery offset amount is less than a difference between normal user-defined temperature set point and the second temperature set point.

8. The water heater of claim 1, wherein the controller is configured to increase the second temperature set point toward the normal user-defined temperature set point during each of two or more heating cycles where the measure remains above the threshold value.

9. A method of operating a water heater having a water tank to limit the effects of stacking in the water tank, the method comprising:

sensing the temperature of the water in the water tank;

controlling the temperature of the water in the water tank based on the sensed water temperature and a first temperature set point;

determining if stacking is likely occurring in the water tank using the sensed water temperature; and

if it is determined that stacking is likely occurring in the water tank, controlling the temperature of the water in the water tank based on the sensed water temperature and a second temperature set point, wherein the second temperature set point is lower than the first temperature set point.

10. The method of claim 9, wherein the step of determining if stacking is likely occurring in the water tank comprises:

determining a measure related to a length of time of at least some heating cycles of the water heater;

comparing the measure to a threshold value; and

if the measure falls below the threshold value, determines that stacking is likely occurring in the water tank.

11. The method of claim 10, wherein if the measure falls below the threshold value for one or more heating cycles, and then during a subsequent heating cycle of the water heater the measure rises above the threshold value, increasing the second temperature set point toward the first temperature set point.

12. The method of claim 11 wherein the second temperature set point is increased toward the first temperature set point in incremental steps.

13. The method of claim 9, further comprises increasing the second temperature set point toward the first temperature set point during each of two or more heating cycles where the measure remains above the threshold value.

14. The method of claim 9 wherein the step of determining if stacking is likely occurring in the water tank comprises:

determining a rate of change of the water temperature in the water tank; and

comparing the rate of change of the water temperature to a threshold rate of change; and

determining that stacking is likely occurring in the water tank if the rate of change of the water temperature in the water tank is greater than the threshold rate of change.