SYSTEMS AND METHODS FOR FAULT DETECTION OF AIR HANDLING UNITS

• US 20100324741A1
• Filed: 06/18/2009
• Published: 12/23/2010
• Est. Priority Date: 06/18/2009
• Status: Active Grant

• Current Assignee: Tyco Fire & Security GmbH (Johnson Controls International plc)
• Original Assignee: Johnson Controls Technology Company (Johnson Controls International plc)
• Inventors: House, John M., Seem, John E.
• Granted Patent: US 8,239,168 B2
• Time in Patent Office: Days
• US Class Current: 700/278
• CPC Class Codes: F24D 19/1084 for air heating systems
• CPC Class Codes: F24D 5/02 operating with discharge of hot air into the space or area to be heated
• CPC Class Codes: F24D 5/04 with return of the air or the air-heater
• CPC Class Codes: F24F 11/30 for purposes related to the operation of the system, e.g. for safety or monitoring
• CPC Class Codes: F24F 11/32 Responding to malfunctions or emergencies
• CPC Class Codes: F24F 11/38 Failure diagnosis
• CPC Class Codes: F24F 11/64 using pre-stored data
• CPC Class Codes: G05B 23/0254 based on a quantitative model, e.g. mathematical relationships between inputs and outputs; functions: observer, Kalman filter, residual calculation, Neural Networks

Abstract

A system is disclosed for detecting faults in an environmental control system for a building zone. The environmental control system is controlled by a finite state machine that causes states of the environmental control system to change based on a varying climate condition. A circuit is configured to receive a current value for the climate condition when the environmental control system is in a heating state and to calculate an estimate of the climate condition at which a transition from the heating state to a state of no heating by the environmental control system is expected to be caused by the finite state machine. The circuit is configured to determine that a fault exists based on a comparison of the current value for the climate condition in the heating state and the estimate of the climate condition at which a transition from the heating state to the no heating state is expected to be caused by the finite state machine.

Claims

1. A system for detecting faults in an environmental control system for a building zone, the environmental control system controlled by a finite state machine that causes states of the environmental control system to change based on a varying climate condition, the system comprising:

a circuit configured to receive a current value for the climate condition when the environmental control system is in a heating state and to calculate an estimate of the climate condition at which a transition from the heating state to a state of no heating by the environmental control system is expected to be caused by the finite state machine;

wherein the circuit is configured to determine that a fault exists based on a comparison of;

(a) the current value for the climate condition in the heating state, and

(b) the estimate of the climate condition at which a transition from the heating state to the no heating state is expected to be caused by the finite state machine.

2. The system of claim 1, wherein the comparison of (a) and (b) comprises subtracting (b) from (a).

3. The system of claim 2, wherein the circuit is configured to determine that the fault exists when the result of the subtraction is positive.

4. The system of claim 2, wherein the comparison comprises calculating a residual r using the equation r=max(0,T_o,1−

T_o,bnd12), where T_o,1 represents the outdoor air temperature in the heating state and T_o,bnd12 is the estimate of the outdoor air temperature at which the transition from the heating state to the no heating state is expected to be caused by the finite state machine.

5. The system of claim 4, wherein T_o,bnd12 is estimated using the return air temperature in the heating state.

6. The system of claim 5, wherein the environmental control system is an air handling unit (AHU), and wherein normal operation of the AHU in the heating state will result in negative values of T_o,1−

T_o,bnd12, causing r to be zero, and wherein positive values of r indicate that the AHU is operating in the heating state even though the system and environmental conditions should not require heating to achieve a target supply air temperature setpoint.

7. The system of claim 1, wherein the environmental control system is an air handling unit (AHU), and wherein the circuit is configured to receive an outdoor air temperature provided by a sensor and to use the outdoor air temperature as the current value for the climate condition.

8. The system of claim 7, wherein the circuit is configured to estimate the climate condition at which the transition will occur while in the heating state.

9. The system of claim 8, wherein the circuit is configured to estimate the climate condition at which the transition from the heating state to the no heating state is expected based on a design minimum fraction of the mass flow rate of outdoor air in the AHU over the mass flow rate of the supply air in the AHU at the transition from the heating state to the no heating state;

and wherein the estimate is also based on a supply air temperature setpoint.

10. The system of claim 9, wherein the circuit is configured to estimate the climate condition at which the transition from the heating state to the no heating state is expected to occur by calculating

11. A system for detecting faults in an environmental control system for a building zone, the environmental control system controlled by a finite state machine that causes states of the environmental control system to change based on a varying climate condition, the system comprising:

a circuit configured to receive a current value for the climate condition when the environmental control system is in a no heating state and to calculate an estimate of the climate condition at which a transition from the no heating state to a heating state is expected to be caused by the finite state machine;

wherein the circuit is configured to determine that a fault exists based on a comparison of;

(a) the current value for the climate condition in the no heating state, and

(b) the estimate of the climate condition at which a transition from the no heating state to the heating state is expected to be caused by the finite state machine.

12. The system of claim 11, wherein the comparison of (a) and (b) comprises subtracting (b) from (a).

13. The system of claim 12, wherein the circuit is configured to determine that the fault exists when the result of the subtraction is negative.

14. The system of claim 13, wherein the comparison comprises calculating a residual r using the equation r=min(0,T_o,2−

T_o,bnd12), where T_o,2 represents the outdoor air temperature in the no heating state and T_o,bnd12 is the estimate of the climate condition at which the transition from the no heating state to the heating state is expected to be caused by the finite state machine.

15. The system of claim 11, wherein the environmental control system is an air handling unit (AHU), and wherein normal operation of the AHU in the no heating state will result in positive values of T_o,2−

T_o,bnd12, causing r to be zero, and wherein negative values of r indicate that the AHU is operating in the no heating state even though the system and environmental conditions should require heating to achieve the supply air temperature setpoint.

16. The system of claim 15, wherein the processing circuit further includes a diagnostics module configured to aggregate historical values of r in memory.

17. The system of claim 16, wherein the diagnostics module is further configured to calculate and store in memory at least one of:

(a) a trend for rover time,

(b) a percentage of operating time that r indicates a fault, and

(c) a highest value for rover a period of time.

18. The system of claim 17, wherein the long term diagnostics module is further configured to record a plurality of system values when a new highest value for r is detected.

19. A method for detecting faults in an environmental control system affecting a building zone, the method comprising:

controlling the environmental control system using a controller implementing the control via finite state machine logic, the controller causing the environmental control system to change states based on a varying climate condition;

receiving, at a circuit, a current value for the climate condition when the environmental control system is in a no heating state;

calculating, using the circuit, an estimate of the climate condition at which a transition from the no heating state to a heating state is expected to be caused by the controller'"'"'s finite state machine logic;

comparing the current value for the climate condition when the environmental control system is in a no heating state to the estimate of the climate condition at which the transition from the no heating state to the heating state is expected to be caused; and

determining that a fault exists based on the comparison.

20. A method for detecting faults in an environmental control system affecting a building zone, the method comprising:

controlling the environmental control system using a controller implementing the control via finite state machine logic, the controller causing the environmental control system to change states based on a varying climate condition;

receiving, at a circuit, a current value for the climate condition when the environmental control system is in a heating state;

calculating, using the circuit, an estimate of the climate condition at which a transition from the heating state to a no heating state is expected to be caused by the controller'"'"'s finite state machine logic;

comparing the current value for the climate condition when the environmental control system is in a heating state to the estimate of the climate condition at which the transition from the heating state to the no heating state is expected to be caused; and

determining that a fault exists based on the comparison.