Temperature control system for a water heater

• US 7,798,107 B2
• Filed: 11/14/2007
• Issued: 09/21/2010
• Est. Priority Date: 11/14/2007
• Status: Active Grant

• Current Assignee: Ademco Inc. (Resideo Technologies, Inc.)
• Original Assignee: Honeywell International Inc.
• Inventors: Chian, Brent, Nordberg, Timothy J.
• Primary Examiner(s): Wilson; Gregory A
• Application Number:
  US11/939,764
• Publication Number:
  US 20090120380A1
• Time in Patent Office: 1,042 Days
• Field of Search: 122/14.1, 122/14.2, 122/14.22, 236/20.R, 236/78.B, 219/483, 219/492, 700/299, 700/300, 700/304
• US Class Current: 122/14.22
• CPC Class Codes: F24H 1/206 with submerged combustion chamber
• CPC Class Codes: F24H 15/174 Supplying heated water with desired temperature or desired range of temperature
• CPC Class Codes: F24H 15/223 in the water storage tank
• CPC Class Codes: F24H 15/269 Time, e.g. hour or date
• CPC Class Codes: F24H 15/281 Input from user
• CPC Class Codes: F24H 15/31 of valves having only one inlet port and one outlet port, e.g. flow rate regulating valves
• CPC Class Codes: F24H 15/33 Control of dampers
• CPC Class Codes: F24H 15/37 of electric heaters
• CPC Class Codes: F24H 15/414 using electronic processing, e.g. computer-based
• CPC Class Codes: F24H 15/486 using timers
• CPC Class Codes: F24H 9/2007 for water heaters
• CPC Class Codes: G05D 23/1904 variable in time

Abstract

A system for detecting stacking and controlling temperature in a water heater. A controller with a connection to a temperature sensor and heating element in a water tank of the heater may be designed to limit stacking and its effects. The controller may use a sensing and calculation technique to detect the stacking. If stacking is detected, then the setpoint for the heater may be lowered so that the outlet water temperature is within a safe limit. If stacking is not detected, then the setpoint may be gradually restored to optimize water heater capacity.

Claims

1. A water heater control system comprising:

a water temperature sensor for providing a sense signal indicative of a temperature of water proximate to the sensor;

a heating element for heating water proximate to the element according to a control signal; and

a controller having a water temperature set point mechanism for receiving the sense signal and for sending the control signal; and

wherein;

the controller determines a water temperature change rate from the sense signal;

the controller provides the control signal according to the water temperature set point mechanism and the sense signal; and

the controller detects stacking and compensates the set point mechanism according to the sense signal to keep temperature stacking of the water within a safe limit.

2. The system of claim 1, wherein:

upon a control signal that initially turns on the heating element when temperature of the water is nearly uniform, a water temperature change rate is determined and saved as a base heat rate; and

upon subsequent heating of the water by the heating element, if the water temperature change rate is greater than N times the base heat rate where, N is greater than one, then set point is reduced M degrees.

3. The system of claim 2, wherein if a water temperature change rate is less than P times the base heat rate and the sensed temperature is within Q degrees of the set point, then reduce the set point by Q degrees.

4. The system of claim 3, wherein if the water temperature change rate is within (1±

R) times the base heat rate, then the set point is reset to an original value.

5. The system of claim 4, wherein after the heating element is turned off at least about L hour, and if the set point is lower than the original value, then increase the set point by V degrees about each L hour.

6. The system of claim 5, wherein if the water temperature becomes less than the set point minus S, and the water temperature rate change is greater than N times the base heat rate for T minutes before the heating rate slows to within (1±

R) times the base heat rate and stays at the latter rate for U minutes, then the base heat rate is updated a small increment towards the present water temperature rate change.

7. The system of claim 6, wherein L is in range from 0.25 to 2.5, M is in a range from 5 to 30, N is in a range from 1 to 2.5, P is in a range from 0.1 to 0.4, Q is in a range from 5 to 30, R is in a range from 0.1 to 0.3, S is in a range from 20 to 50, T is in a range from 1 to 8, U is in a range from 1 to 8, and/or V is in a range from 0.5 to 2.5.

8. The system of claim 1, wherein upon a control signal to the heating element to heat water, the water temperature change rate is monitored to note whether there is an increase or no change of the water temperature change rate.

9. The system of claim 8, wherein if the water temperature change rate has an increase or no change, then a set point of the water set point mechanism is set to a maximum of a present water temperature from the sensor plus a constant, or of a present set point minus a maximum set point offset.

10. The system of claim 9, wherein:

the constant is in a range from one degree to five degrees F.; and

the maximum set point offset is in a range from ten degrees to thirty degrees F.

11. The system of claim 9, wherein:

the constant is approximately two degrees F.; and

the maximum set point offset is approximately ten degrees F.

12. A method for operating a water heater, comprising:

sensing water temperature in a water heater;

measuring the water temperature change rate; and

detecting whether stacking is occurring; and

wherein;

if stacking is occurring, then a set point is lowered to prevent an excessive top temperature;

if stacking is not occurring or reduced to an acceptable level, then the set point is gradually or immediately restored as needed to optimize water heater capacity.

13. The method of claim 12, further comprising:

upon a start of heating water in the water heater, monitoring the water temperature change rate; and

wherein if the water temperature change rate is equal to or greater than zero, then set the set point to a maximum of the present water temperature plus a constant or of the set point minus a maximum set point offset permitted.

14. The method of claim 13, wherein:

if the temperature change rate is small during a long burn time, then the set point is not returned to an initial setting; and

if the heating rate is sufficiently high, and there is a long burn time, then the set point offset is reduced.

15. The method of claim 12, further comprising detecting a basic heating rate (B) upon a start of heating water in the water heater.

16. The method of claim 15, further comprising if a heating rate after the start of heating water is greater than N times B, then reduce the set point by M, wherein N is greater than one and M is less than 30 degrees F.

17. The method of claim 16, further comprising if a heating rate is less than P times B and the water temperature is within Q of the set point, then reduce the set point by Q, wherein P is less than 0.4 and Q is less than 30 degrees.

18. The method of claim 17, further comprising after heating water is stopped for about L hour and if the set point is lower than the initial value, then increase the set point by V about every L hour as needed, and wherein L is less than 2.5 and V is less than 2.5 degrees.

19. The method of claim 18, further comprising if the water temperature is less than a set point minus S, the heating rate is greater than N times B for T minutes before slowing down to within (1±

R) times B for U minutes, then update B a small step towards a present heating rate, wherein S is less than 50 degrees, R is less than 0.3, T is less than 8 and U is less than 8.

20. A water temperature control system comprising:

a sensor that detects water temperature in a container;

a heater that heats water in the container; and

a mechanism, having a water temperature set point, connected to the sensor and heater, wherein the mechanism detects a water temperature change rate according to the sensor at initial start-up of the heater and afterwards, the mechanism detects stacking, and the mechanism adjusts the water temperature set point via a set point offset to turn on or off the heater to limit top water temperature within a safe range when the stacking occurs in the container.

21. The system of claim 20, wherein:

if the water temperature change is small during a long heater on time, then the water temperature set point is not returned to an original setting because the stacking of water is still present due to a low water draw from the container; and

if the heating rate is sufficiently high heating rate and there is a long heater “

on”

time, then the set point offset is reduced.