Apparatus and method for reducing overshoot in response to the setpoint change of an air conditioning system

• US 5,415,346 A
• Filed: 01/28/1994
• Issued: 05/16/1995
• Est. Priority Date: 01/28/1994
• Status: Expired due to Term

• Current Assignee: Trane International Inc. (Trane Technologies plc)
• Original Assignee: American Standard Companies Incorporated (Ideal Standard International Topco SCA)
• Inventors: Bishop, Richard A.
• Primary Examiner(s): Wayner, William E.
• Application Number:
  US08/187,968
• Time in Patent Office: 473 Days
• Field of Search: 236/78 D, 236/47, 236/46 R, 165/12
• US Class Current: 236/78.00D
• CPC Class Codes: G05D 23/1917 using digital means

Abstract

A thermostat and method for controlling the overshoot and undershoot of the temperature in a zone that are caused by an air conditioning system responsive to a change in the setpoint of the thermostat is disclosed. The thermostat includes a sensor for detecting the temperature in the zone and being adapted to generate a signal representative of the temperature. A processor for controlling the air conditioning system is communicatively coupled to the sensor and receives the signal representative of the temperature of the zone therefrom. A setpoint input device for changing the setpoint of the thermostat is communicatively coupled to the processor and is adapted to provide a signal representative of the changed setpoint to the processor. The processor controls the air conditioning system in a static condition mode during normal operations and switches the air conditioning system to a full on mode responsive to a setpoint change. The processor is adapted to generate a time based target temperature curve and to compare the target temperature with the temperature in the zone at certain time intervals after the input of the setpoint change. The air conditioning system is switched by the processor from the full on mode of operation to the static condition mode of operation when the sensed temperature in the zone equals the temperature of the target temperature curve.

Claims

1. An improved thermostat for controlling the overshoot and undershoot of the temperature of the air in a zone serviced by an air conditioning system that occurs responsive to a change in the setpoint of the thermostat requiring operation of the air conditioning system, comprising:

sensor means for detecting the temperature in the zone and being adapted to generate a temperature signal representative of the temperature;

processor means operably coupled to the air conditioning system and the sensor means for receiving the temperature signal representative of the temperature of the zone from the sensor means and controlling the operation of the air conditioning system responsive to the temperature signal;

setpoint input means operably coupled to the processor means for setting the setpoint of the thermostat, said setpoint input means including means for providing a setpoint signal representative of the setpoint to the processor means,

the processor means controlling the air conditioning system in a steady state condition mode of operation during normal air conditioning system capacity control operations and switching the air conditioning system to a full on transition mode of operation responsive to a setpoint change requiring operation of the air conditioning system, the processor means being adapted for generating a time based target temperature curve and comparing the target temperature from the target temperature curve to the temperature signal provided by the sensor means at predetermined time intervals after the input of the setpoint change and switching the air conditioning system from the full on transition mode of operation to the steady state condition mode of operation when the sensed temperature in the zone equals the temperature of the target temperature curve.

2. A method for controlling the output of an air conditioning system conditioning the air in a zone, the control of the output being exercised through a thermostat having a temperature setpoint, the improvement controlling overshoot and undershoot of the temperature in a zone that occur responsive to a change in the setpoint of the thermostat, the improved method including the steps of:

detecting the temperature in the zone and generating a temperature signal representative of the temperature;

changing the setpoint of the thermostat and generating a setpoint signal representative of the changed setpoint;

controlling the air conditioning system in a steady state condition mode during normal air conditioning system capacity control operations and switching the air conditioning system to a full on transition mode of operation responsive to a setpoint change requiring operation of the air conditioning system, generating a time based target temperature curve and comparing the target temperature from the target temperature curve to the temperature sensed in the zone by the sensor means at certain time intervals after the input of the setpoint change; and

switching the air conditioning system from the full on transition mode of operation to the steady state condition mode of operation when the sensed temperature in the zone equals the temperature of the target temperature curve.

3. A method for controlling the output of an air conditioning system to minimize the overshoot and undershoot of the temperature in a zone caused by a change in the setpoint of the air conditioning system, the method including the steps of:

generating a signal representative of the temperature in the zone;

generating a signal changing the setpoint of the air conditioning system;

generating a time function responsive to changing the setpoint of the air conditioning system;

developing a time based target temperature curve that is initiated at the time of changing the setpoint of the air conditioning system;

comparing the signal representative of the temperature in the zone to the temperature of the target temperature curve at selected time intervals; and

controlling the output of the air conditioning system as a function of the time at which the signal representative of the temperature in the zone equals the temperature of the target temperature curve.

4. Apparatus for controlling the capacity of an air conditioning system to minimize the overshoot and undershoot of the temperature in a zone caused by a change in the setpoint of the air conditioning system, comprising:

sensor means for generating a signal representative of the temperature in the zone;

setpoint input means for generating a signal changing the setpoint of the air conditioning system;

timing means for generating a time function responsive to changing the setpoint of the air conditioning system;

processor means communicatively coupled to the sensor means and the setpoint input means and receiving said signals therefrom, adapted for developing a time based target temperature curve that is initiated at the time of changing the setpoint of the air conditioning system and being adapted to control the capacity of the air conditioning system as a function of the time at which the signal representative of the temperature in the zone equals the temperature of the target temperature curve.

5. Apparatus for controlling the output of an air conditioning system that conditions the air in a zone in response to a setpoint change, the apparatus having a temperature sensor that senses the temperature in the zone, a setpoint input device for selectively setting the setpoint and a processor that receives a signal input from the sensor representative of the temperature in the zone and receives a temperature setpoint signal representative of the temperature desired to be maintained in the zone from the setpoint input device and that compares the zone temperature and the setpoint temperature to generate an output signal comprising an operating command to the air conditioning system to effect the desired temperature in the zone, the apparatus including:

the processor being adapted for generating a time-based target temperature curve at the time of the setpoint change and comparing the received zone temperature signal from the sensor to the target temperature at selected time intervals after the setpoint change, and controlling the output of the air conditioning system as a function of the occurrence of the received zone temperature signal equalling the temperature of the target temperature curve.

6. Apparatus adapted to control an air conditioning system in transition from a first temperature setpoint to a second temperature setpoint requiring operation of the air conditioning system, the air conditioning system having a steady state mode of control to control air temperature in a zone serviced by the air conditioning system at a setpoint and a transition mode of control to control air temperature in the zone responsive to a change of setpoint from the first setpoint to the second setpoint, including sensor means for providing a sensed air temperature representative of the air temperature in said zone and actuation means operably coupled to said sensor means for switching the air conditioning system from the transition mode of control to the steady state mode of control as a function of said sensed temperature and a predetermined rate of temperature increase over time, wherein the control apparatus switches the air conditioning system from the transition mode of control to the steady state mode of control at a point in the transition prior to the sensed temperature in the zone equaling the temperature of the second setpoint.

7. Apparatus as claimed in claim 6 including a processor adapted to receive a signal representative of the sensed temperature in the zone, generating a target temperature curve, comparing the sensed temperature signal to the target temperature curve and switching the air conditioning system from the transition mode of control to the steady state mode of control as a function of the sensed temperature in relation to the target temperature curve.

8. Apparatus as claimed in claim 7 wherein the target temperature curve is an exponentially derived function that is responsive to that rate of change of the temperature in the zone which the air conditioning system is capable of producing when the air conditioning system is in the transition mode of operation and to the temperature difference between the first temperature setpoint and the second temperature setpoint.

9. A method for controlling the output of an air conditioning system to minimize the overshoot and undershoot of the temperature in a zone resulting from a transition from a first temperature setpoint to a second temperature setpoint, the method including the steps of:

sensing the temperature in the zone;

generating a target temperature curve as a function of (1) the rate of temperature change that the air conditioning system is able to effect in the zone during the transition from the first temperature setpoint to the second temperature setpoint and (2) the temperature differential between the first temperature setpoint and the second temperature setpoint;

periodically comparing the sensed temperature in the zone to the target temperature curve; and

altering the output of the air conditioning system responsive to the occurrence of the sensed temperature being at a selected temperature relative to the target temperature curve.

10. The method for controlling the output of an air conditioning system as claimed in claim 9 wherein the target temperature curve is an exponentially derived function.

11. The method for controlling the output of an air conditioning system as claimed in claim 9 wherein the target temperature curve has a relatively steep slope after departure from the first temperature setpoint, gradually decreasing in slope with time to asymptotically approach the second temperature setpoint.

12. The method for controlling the output of an air conditioning system as claimed in claim 9 wherein the output of the air conditioning system is altered at the time that the sensed temperature in the zone equals the temperature of the target temperature curve.

13. A method for controlling the output of an air conditioning system to minimize the overshoot and undershoot of the temperature in a zone during the transition from a first temperature setpoint to a second temperature setpoint, the air conditioning system being adapted to function in a steady state mode of control about a temperature setpoint and in a transition mode of control when in transition from a first temperature setpoint to a second temperature setpoint, the method comprising the steps of:

sensing the temperature in the zone during the transition from the first temperature setpoint to the second temperature setpoint;

generating a target temperature curve;

switching the air conditioning system from the transition mode of operation to the steady state mode of operation utilizing the relation of the sensed temperature in the zone to the target temperature curve to predict when the actual temperature in the zone was proximate the second temperature setpoint.

14. The method for controlling the output of an air conditioning system as claimed in claim 13 wherein the target temperature curve is an exponentially derived function.

15. The method for controlling the output of an air conditioning system as claimed in claim 13 wherein the target temperature curve has a relatively steep slope after departure from the first temperature setpoint, gradually decreasing in slope with time to asymptotically approach the second temperature setpoint.

16. The method for controlling the output of an air conditioning system as claimed in claim 13 wherein the mode of control of the air conditioning system is a switched at the time that the sensed temperature in the zone equals the temperature of the target temperature curve.

17. A method of minimizing overshoot or undershoot while changing a setpoint in an HVAC system having a steady state mode of operation and a transitional mode of operation, comprising the steps of:

operating the HVAC system in the steady state control mode of operation responsive to an old setpoint so as to maintain a condition in a zone;

monitoring the condition in the zone;

accepting a new setpoint;

generating a target condition curve as a function of the old setpoint and the new setpoint;

operating the HVAC system in the transitional mode of operation;

periodically comparing the monitored condition to the target condition curve;

continuing to operate in the transitional mode of operation if the monitored condition is farther from the new setpoint than the target condition curve; and

returning to the steady state mode of operation if the target condition curve is the same as the monitored condition or farther from the new setpoint than the monitored condition.

18. The method of claim 17 wherein the monitored condition is temperature and the target condition curve is an exponential function.