Abstract:
A method for self-determining a root cause of a system fault in a heating, ventilation, and cooling (HVAC) system includes receiving a fault message indicative of a fault condition in an operating characteristic of the HVAC system; determining a causal relationship between the fault condition and a predetermined list of root causes associated with the fault condition; receiving information indicative of operating conditions of the HVAC system; and eliminating at least one root cause that is unrelated to the fault condition in response to the receiving of the information.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. provisional patent application Ser. No. 61/590,934 filed Jan. 26, 2012, the contents of which are incorporated by referenced herein in their entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    This invention relates generally to heating, ventilation, and cooling (HVAC) systems for residential or light commercial air conditioning applications and, more particularly, to a method and system for a root cause self-determination of fault conditions in an HVAC system. 
       DESCRIPTION OF RELATED ART 
       [0003]    HVAC systems often do not function as well as expected due to faults developed during routine operation. While these faults are indicative of a failure mode, many faults do not result in immediate system shut down or costly damages. However, most faults, if unnoticed for a long period of time, could adversely affect system performance, life, and lifecycle cost. 
         [0004]    Fault diagnostics refer to detection of faults and identification of solutions to the fault. A fault mode in one system component may cause issues in another component. Approaches to diagnostics may deal with direct measurement of monitored quantities as well as dedicated sensors for measurement of crucial system parameters in order to isolate the problem and provide a solution. Misdiagnosis of a root cause for the fault may result in good operating components to be replaced, resulting in repeated callbacks for a service technician and increased warranty costs. Additionally, dedicated sensors for diagnosis are typically costly to implement. Therefore, it is desirable to provide a method and system for self-determining a root cause in an HVAC system utilizing algorithms and sensors that provide a prompt and economical resolution of faults in an HVAC system. 
       BRIEF SUMMARY 
       [0005]    According to one aspect of the invention, a method for self-determining a root cause of a system fault in a heating, ventilation, and cooling (HVAC) system includes receiving a fault message indicative of a fault condition in an operating characteristic of the HVAC system; determining a causal relationship between the fault condition and a predetermined list of root causes associated with the fault condition; receiving information indicative of operating conditions of the HVAC system; and eliminating at least one root cause that is unrelated to the fault condition in response to the receiving of the information. 
         [0006]    According to another aspect of the invention, a method for self-determining a root cause of a system fault in a heating, ventilation, and cooling (HVAC) system includes receiving a first list associated with a plurality of fault conditions in the HVAC system; identifying a second list of root causes associated with a particular fault condition of the plurality of fault conditions; receiving information indicative of operating conditions of the HVAC system; and eliminating at least one root cause from the second list of root causes that is unrelated to the particular fault condition in response to the receiving of the information. 
         [0007]    According to yet another aspect of the invention, a programmable control unit for self-determining a root cause in an HVAC system includes a controller configured for receiving a fault message indicative of a fault condition in an operating characteristic of the HVAC system and for determining a causal relationship between the fault condition and a predetermined list of root causes associated with the fault condition; where the controller receives information indicative of operating conditions of the HVAC system and eliminates at least one root cause in response to the receiving of the sensed information. 
         [0008]    According to yet another aspect of the invention, an environmental control system for an HVAC system includes a programmable control unit configured for establishing user desired environmental control parameters for one or more control zones; and at least one unit controller configured for storing information indicative of at least one system parameter for a control system, the at least one unit controller operatively coupled to the programmable control unit; where the programmable control unit or the unit controller is configured for receiving a fault message indicative of a fault condition in an operating characteristic of the HVAC system, for determining a causal relationship between the fault condition and a predetermined list of root causes associated with the fault condition, for receiving information indicative of operating conditions of the HVAC system, and for eliminating at least one root cause in response to the receiving of the sensed information. 
         [0009]    Other aspects, features, and techniques of the invention will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0010]    Referring now to the drawings wherein like elements are numbered alike in the FIGURES: 
           [0011]      FIG. 1  is a schematic view of an environmental control system including a programmable controller for root cause determination in accordance with an embodiment of the invention; and 
           [0012]      FIG. 2  is a flow diagram illustrating a method for determining a root cause of a fault condition in accordance with an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Embodiments of a system for root cause self-determination of a fault condition in an HVAC system include a control unit assembly including software for utilizing fault tree analysis techniques, predetermined system knowledge, and current sensed information that is received from one or more sensors during the time of the fault condition. In an embodiment, the control unit assembly includes an integrated controller for operating the system in a diagnostic mode in order to gather additional data needed to narrow the fault condition down to a single root cause. In other embodiments, where the root causes may not be narrowed to a single root cause, the control unit assembly utilizes historical probabilities of the system as well as cost information regarding the components in the system to present the root causes in an optimal order to a user, for example, a technician to fix. 
         [0014]    Referring to  FIG. 1 , there is shown an example of an environmental control system  100  including a control unit assembly  105  for self-determining a root-cause of a fault condition or error associated with one or more environmental control zones in an HVAC system according to an embodiment of the invention. Particularly, environmental control system  100  includes a programmable control unit assembly  105  including a housing  110  and a user input/output device shown in the form of a touch screen display  115  that allows a user of the HVAC system to establish and view various environmental control parameters or conditions for one or more environmental control zones  120 ,  125  such as, for example, environmental parameters related to temperature, humidity and/or airflow in a first and second environmental control zone  120 ,  125 . Also, as well as to provide fault conditions detected in any of the first and second control zones  120 ,  125  and root-causes of the fault conditions for a service technician to fix, which is shown and described below in  FIG. 2 . In other embodiments, programmable control unit assembly  105  may be used to control a single environmental zone, for example environmental control zone  120  or more than two environmental control zones. Further, programmable control unit assembly  105  includes an integrated controller  130  that is operatively connected to, in embodiments, a temperature control system  150  such as, for example, a gas furnace, air conditioner, and/or heat pump, a humidity control system  155  such as, for example, an air conditioner or a humidifier, and an airflow control system  160 . The integrated controller  130  establishes user desired environmental control parameters such as, for example, temperature, indoor air quality, humidity and/or airflow for first and second environmental control zones  120  and  125  as well as self-determination of root causes in systems  150 ,  155 , and  160  associated with a deviation in the desired environmental control parameters in zones  140 ,  145 , as is shown and described below in  FIG. 2 . 
         [0015]    In an embodiment, systems  150 ,  155 ,  160  include respective unit controllers  165 ,  170 ,  175 , each having a processor and a memory (not shown) that stores local sensed information as well as information regarding predetermined system parameters for the respective temperature control system  150 , humidity control system  155 , and airflow control system  160  in order to eliminate root causes for fault detected within systems  150 ,  155 ,  160 . It is to be appreciated that integrated controller  130  may be utilized to establish other user desired environmental control parameters in addition to indoor air quality control, and the like for first and second environmental control zones  120  and  125  as well as self-determination of root causes in these control zones  120 ,  125 . 
         [0016]    The touch screen display  115  causes fault conditions from, in one embodiment, desired environmental parameters, for example, temperature, humidity and/or airflow for the environmental control zones  120 ,  125  or fault conditions in temperature control system  150 , humidity control system  155  and/or airflow control system  160 , to be displayed to a technician including a reporting of one or more root causes the displayed fault condition. Additionally, the touch screen display  115  may provide information on one or more possible components to be replaced for components associated with the fault conditions in the environmental control zones  120 ,  125  and systems  150 ,  155 , and  160 . Also, controller  130  includes a processor and a memory  135  that stores various programs for execution including algorithms utilizing, in one embodiment, a fault tree analysis technique that is executed by the processor for self-identifying a list of root causes of the fault conditions (i.e., predetermining a list of root causes) detected in the environmental control system  100 . The processor of controller  130  can be any type of processor (CPU), including a general purpose processor, a digital signal processor, a microcontroller, an application specific integrated circuit, a field programmable gate array, or the like. Additionally, controller  130  receives information regarding parameters of system  100  as well as predetermined historical information regarding system  100  that are stored in memory  135 , and utilizes these for narrowing down the list of root causes. In one embodiment, memory  135  stores information about the current sensed conditions at the time of the fault condition, which is received from the one or more devices  150 ,  155 ,  160  and one or more sensors  140 ,  145 . In other embodiments, the memory  135  may store sensed information preceding the fault condition or sensed information generated during a root causes determination one or more programs stored in memory  135 . It is to be appreciated that while controller  130  is shown integrated within programmable control unit assembly  105 , controller  130  may, in an embodiment, be remotely located from housing  110 . 
         [0017]    In an embodiment, a process of narrowing the list of root causes of a particular fault condition can occur in several places in a coordinated manner. For example, one or more of the unit controllers  165 ,  170 ,  175 , can begin the process of diagnosing a fault in its respective unit by starting from a predetermined list of possible root causes for the fault and, based on information available to, for example, unit controller  165 , eliminate one or more of the root causes. In one non-limiting example, the unit controller  165  passes the narrower list of root causes to the integrated controller,  130 , which then further narrows the list based on information available to it as well as information received from other units in the system. Furthermore, the integrated controller,  130 , may transmit its narrowed list of root causes over a communication channel, such as a WiFi network or the internet, to a remote device such as, for example, a personal computer or a server. These remote devices may have additional databases with historical and other information related to the fault, which may be used to narrow the root cause list even further. The final narrowed list may be displayed to the technician or user on the touch screen display  115 , as well as on any remote display such as on the personal computer or a smart phone. It is to be appreciated that any of the other unit controllers  170 ,  175  may also perform the process of narrowing the possible list of root causes as described above with respect to unit controller  165 . 
         [0018]    Referring now to  FIG. 2 , there is shown a flow diagram illustrating a root cause self-determination process  200  according to an embodiment of the invention. The process  200  includes self-determining a root cause of one or more system fault conditions in the environmental control system  100  or root cause in any of the systems  150 ,  155 , or  160  (shown in  FIG. 1 ) including self-determining the root cause to a system fault event in one system component that may cause issues in another component. In an exemplary embodiment, the root cause process  200  may identify a fault condition such as, for example, a low pressure on an outdoor unit (not shown) of a temperature control system  150  ( FIG. 1 ), for example, an air conditioner or a heat pump unit, and accurately narrows the root cause to low indoor airflow from several other root causes such as, in some non-limiting examples, low refrigerant charge, faulty outdoor pressure switches, faulty outdoor expansion valve, faulty outdoor reversing valve, or faulty outdoor compressor. While a single fault condition is described below, it is to be appreciated that a root cause of additional fault conditions may be determined by the environmental control system  100  utilizing a similar process  200  described herein. It is to be appreciated that a root cause elimination may occur within the controller  130  or any of the unit controllers  165 ,  170 ,  175  through a similar process as shown and described below. 
         [0019]    The process  200  is initiated at  202 , and, in  204 , a fault condition such as, for example, low-pressure lockout in the cooling mode may be stored in the memory  135  ( FIG. 1 ) for determining a root cause. The controller  130  may receive local sensed data or any other information from, in one embodiment, systems  150 ,  155 ,  160  and one or more sensors  140 ,  145 , in order to determine fault conditions that cause the system  100  to deviate from user or system defined environmental parameters, e.g., temperature, humidity and/or airflow for the environmental control zones  120 ,  125  ( FIG. 1 ). Further, controller  130  determines whether the received information indicates a deviation from the desired environmental parameters and presents these as a fault condition on display  115  ( FIG. 1 ). This fault condition is stored in memory  135  ( FIG. 1 ), in embodiments, as either error codes, for example fault code  83  and/or as a text message, for example “Fault  83 : Low Pressure Lockout for 4 Hours”. 
         [0020]    In  206 , controller  130  ( FIG. 1 ) determines a causal relationship between the fault condition and one or more root causes of the fault condition. In one embodiment, the controller  130  ( FIG. 1 ) utilizes algorithms stored in memory  135  ( FIG. 1 ) to implement a fault tree model such as, for example, a cause-and-effect diagram in order to identify a predetermined list of root causes associated with the particular fault condition. In an embodiment, the predetermined list of root causes associated with the fault condition are causally linked by the fault tree model within the controller  130  and may be accessed for each fault condition that is particularly detected by controller  130 . In  208 , the controller  130  analyzes the information on the current sensed conditions received from controllers  165 ,  170 ,  175  in the respective systems  150 ,  155 ,  160  using locally sensed information from systems  150 ,  155 ,  160  as well as predetermined information that are received about systems  150 ,  155 ,  160  substantially contemporaneous at the time of the fault condition or preceding the fault condition in order to eliminate unrelated root causes from the predetermined list of root causes and limit it to a single root cause for the fault condition. Particularly, the controller  130  ( FIG. 1 ) analyzes the current sensed conditions obtained from, in embodiments, sensors  140 ,  145 , temperature control system  150 , humidity control system  155  and/or airflow control system  160  ( FIG. 1 ) at the time of the fault condition or preceding the fault condition in order to eliminate one or more root causes not related to the fault condition 
         [0021]    In  210 , if the sensed information indicates that there is a single root cause, then in  212 , the single root cause is provided to the technician on touch screen display  115  including the solutions for fixing the particular fault condition. However, if the controller  130  determines that there may be several root causes associated with the fault condition, then, in  214 , the controller  130  will run the system  100  in a particular diagnostic mode in order to generated additional specific data and further limit the possible root causes and eliminate unrelated root causes. In the diagnostic mode, the controller  130  is programmed for presetting the system  100  to predefined parameters associated with an operating characteristic of the HVAC system that generated the fault condition such as, for example controlling the speed of the compressor or the speed of the indoor fan, in order to obtain additional data needed for eliminating one or more root causes of a particular fault condition. This additional information obtained is stored in memory  135  for additional fault diagnosis by the controller  130 . In  216 , if a single root cause remains after the diagnostic mode is implemented, then the root cause is provided to the technician on touch screen display  115  in  212 . However, in  216 , if more than one root cause remains then, in  218 , the controller  103  utilizes the predetermined historical information regarding the probability or likelihood of a defect in one of the various components in system  100  that is associated with the fault condition to display a list of possible root causes in the order of priority for the technician to fix or address. In one embodiment, the root causes may be prioritized base on historical probabilities of the system  100  as well as the cost associated with replacing one or more components associated with the root cause. The process end at  220 . 
         [0022]    The technical effects and benefits of embodiments relate to an HVAC a system programmed for determining a root cause of a fault condition including software utilizing a fault tree analysis methodology, historical information of the HVAC system, and current sensed information for eliminating one or more erroneous root causes of the fault condition. 
         [0023]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. While the description of the present invention has been presented for purposes of illustration and description, it is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications, variations, alterations, substitutions, or equivalent arrangement not hereto described will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. Additionally, while various embodiment of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.