Controller for two-stage heat source usable with single and two stage thermostats

• US 20070095520A1
• Filed: 11/02/2005
• Published: 05/03/2007
• Est. Priority Date: 11/02/2005
• Status: Active Grant

• Current Assignee: Copeland Comfort Control LP (Emerson Electric Company)
• Original Assignee: Emerson Electric Company
• Inventors: Perry, David, Lorenz, Thomas
• Granted Patent: US 7,731,096 B2
• Time in Patent Office: Days
• US Class Current: 165/267
• CPC Class Codes: F23N 2223/04 Memory
• CPC Class Codes: F23N 2223/08 Microprocessor; Microcomputer
• CPC Class Codes: F23N 5/203 using electronic means

Abstract

A controller for a two-stage heat source is provide, which may be connected to either a single stage or a two-stage thermostat to provide low stage heating for a variable time period before switching to high stage heating. The controller includes at least a first terminal for receiving a signal requesting heating from a single-stage thermostat or a two-stage thermostat connected to the first terminal. A microcontroller in communication with the first terminal determines a duty cycle value for a heating cycle based on the duration in which a signal at the first terminal is present relative to the duration of the heating cycle. The microcontroller determines a low stage time limit from the duty cycle, and provides low stage heating when a signal is present at the first terminal for a time period not more than the time limit, and switches to high stage heating after the time limit.

Claims

1. A controller for a two-stage heat source, adapted to be connected to either a single stage or two-stage thermostat, the controller comprising:

a first terminal for receiving a signal for first-stage heat from a single-stage or two-stage thermostat connected to the first terminal;

a microcontroller in communication with the first terminal, the microcontroller being configured to calculate a duty cycle value based on the duration of time in which a heat signal is present at the first terminal relative to the duration of a heating cycle, and to determine a first stage time limit from the duty cycle, wherein the microcontroller controls the operation of the two stage heat source to provide first stage heating while a first stage heat signal is present up to the first stage time limit, and to provide second stage heating when a first stage signal is present beyond the first stage time limit period.

2. The controller of claim 1, further comprising a second terminal for receiving a signal for second stage heat from a two-stage thermostat connected to the second terminal, wherein the microcontroller is in communication with the second terminal and initiates second stage heating upon receiving a signal for second stage heat from a two-stage thermostat.

3. The controller of claim 1, wherein the microcontroller selects a time limit value from a look-up table in a memory of the microcontroller that corresponds to said calculated duty cycle value.

4. The controller of claim 1, wherein first stage heat operation provides a lower level of heating than second stage heat operation.

5. The controller of claim 4, wherein the duty cycle value is proportionate to the heating load demand of the two stage heating system.

6. The controller of claim 5, wherein the first stage time limit value diminishes as the duty cycle value indicative of the heating load demand increases, such that first stage heat operates for a minimum first stage time limit period prior to activation of second stage heat operation when heating demand is high, and first stage heat operates for a maximum first stage time limit period prior to activation of second stage heat operation when heating demand is low.

7. The controller of claim 1, wherein the microcontroller calculates one or more duty cycle values during one or more heating cycles.

8. The controller of claim 1, wherein the microcontroller stores at least one calculated duty cycle value in a memory.

9. The controller of claim 8, wherein the microcontroller averages the calculated duty cycle value and at least one previously stored duty cycle value, and determines a first stage time limit period from the averaged duty cycle value.

10. A controller for a two-stage heat source, adapted to be connected to either a single stage or two-stage thermostat, the controller comprising:

a first terminal for receiving a signal requesting heating from a single-stage thermostat connected to the first terminal, or for receiving a signal requesting low-stage heating from a two-stage thermostat connected to the first terminal;

a second terminal for receiving a signal requesting high-stage heat operation from a two-stage thermostat connected to the second terminal;

a microcontroller in communication with the first and second terminals, the microcontroller being configured to determine a duty cycle value for one or more heating cycles based on the duration of time in which a heat signal at the first terminal is present relative to the duration of the heating cycle, and to select one of a number of low stage time limits from a look-up table in a memory of the microcontroller which corresponds to said calculated duty cycle value, wherein the microcontroller controls the operation of the two stage heat source to provide low stage heating operation when a signal is present at the first terminal for a time period not more than the low stage time limit, and to provide high stage heating operation while a signal is present at the first terminal beyond the low stage time limit; and

wherein the microcontroller controls the operation of the two stage heat source to provide second stage heating whenever a signal requesting second stage heat operation is present at the second terminal.

11. The controller of claim 10, further comprising a timer means that is initiated upon activation of low stage heating operation and is set to the low stage time limit, whereupon expiration of the timer the microprocessor provides for high stage heating operation as long as a signal is still present at the first terminal.

12. The controller of claim 10, wherein the low stage time limit value diminishes as the duty cycle value indicative of the heating load demand increases, such that low stage heat operates for a minimum low stage time limit period prior to activation of high stage heat operation when heating demand is high, and low stage heat operates for a maximum low stage time limit period prior to activation of high stage heat operation when heating demand is low.

13. The controller of claim 12, further comprising a timer means that is initiated upon activation of low stage heating operation and is set to the low stage time limit, whereupon expiration of the timer the microprocessor provides for high stage heating operation as long as a signal is still present at the first terminal.

14. The controller of claim 12, wherein the microcontroller calculates one or more duty cycle values during one or more heating cycles.

15. The controller of claim 12, further comprising a memory in which the microcontroller stores the calculated duty cycle, wherein the microcontroller averages a subsequently calculated duty cycle value with at least one previously stored duty cycle value for determining a first stage time limit period based on the average of calculated duty cycle value with at least one previously stored duty cycle value.

16. A method for controlling the operation of a two stage furnace comprising:

determining whether a request signal for heat operation is present at a first terminal;

calculating at least one duty cycle value based on the duration of time in which a request signal was present at the first terminal in a previous heating cycle relative to the total duration of the previous heating cycle;

determining a low stage time limit value from the at least one calculated duty cycle value;

providing for low stage heating operation as long as a signal is present at the first terminal until either a low stage time limit or a default time limit is reached;

providing for high stage heating operation after the low stage time limit or default time limit has been reached, as long as the signal at the first terminal remains present; and

discontinuing all heating operation when the signal at the first terminal is no longer present.

17. The method of claim 16 further comprising the step of activating high stage heating operation upon detecting a request signal for high stage heating operation at a second terminal.

18. The method of claim 17 wherein the low stage time limit value diminishes as the duty cycle value indicative of the heating load demand increases, such that low stage heat operates for a minimum low stage time limit period prior to activation of high stage heat operation when heating demand is high, and low stage heat operates for a maximum low stage time limit period prior to activation of high stage heat operation when heating demand is low.

19. A method for controlling the operation of a two-stage heating system, the method comprising the steps of:

actuating low stage heating operation upon detecting a request signal for heat operation at a first terminal;

calculating at least one duty cycle value based on the duration of time in which a request signal was present at the first terminal in a previous heating cycle relative to the total duration of the previous heating cycle;

determining a low stage time limit value from the at least one calculated duty cycle value;

initiating a low stage timer means that is set to the low stage time limit or a default value absent such a limit;

continuing low stage heating operation as long as a signal is present at the first terminal until either the low stage time limit or the default time limit of the timer expires, or until detecting a request signal for high stage heating operation at a second terminal;

activating high stage heating operation after the timer has expired or upon detecting a request signal for high stage heating operation at a second terminal;

continuing high stage heating operation as long as a signal is present at the first terminal after the expiration of the timer, or as long as a signal requesting high stage heating is present at the second terminal; and

discontinuing all heating operation when the signal at the first terminal is no longer present.

20. The method of claim 19 wherein the low stage time limit value diminishes as the duty cycle value indicative of the heating load demand increases, such that low stage heat operates for a minimum low stage time limit period prior to activation of high stage heat operation when heating demand is high, and low stage heat operates for a maximum low stage time limit period prior to activation of high stage heat operation when heating demand is low.