Abstract:
This patent specification relates to methods and systems that can detect over cycling conditions that exist in an HVAC system. The over cycling condition can be caused by overheating of a forced air heating system or furnace of the HVAC system control. When the furnace overheats, a thermally actuated limit switch within the furnace may cut off power to a heat generation apparatus. The limit switch can reconnect the power to the heat generation apparatus after it has cooled down, at which point the thermostat control system may issue another heating call to continue heating the enclosure so that it reaches the desired temperature. If the overheat condition persist, then the thermally actuated switch will cut power, resulting in repeated power cycling. The detection system and methods can monitor these power loss events and use them as data points for determining whether an alert condition exists within the HVAC system.

Description:
TECHNICAL FIELD 
       [0001]    This patent specification relates to systems and methods for the monitoring and control of energy-consuming systems or other resource-consuming systems. More particularly, this patent specification relates to control units that govern the operation of energy-consuming systems, household devices, or other resource-consuming systems, including systems and methods for determining whether abnormal operating conditions exists within heating, ventilation, and air conditioning (HVAC) systems. 
       BACKGROUND 
       [0002]    Substantial effort has been put forth on the development of new and more sustainable energy supplies, as well as efforts to increase energy efficiency of existing energy consumption systems. An example of an energy consumption system is the heating and cooling system of an enclosure such as a home or building. Heating and cooling can account for a large percentage of the energy use in a typical home, making it a significant energy expense. Heating and cooling systems can realize greater efficiency by improving physical aspects of the system (e.g., higher efficiency furnace) and enclosure (e.g., more or better insulation). Substantial increases in energy efficiency can also be achieved through enhanced thermostat control of the heating and cooling system. 
         [0003]    Despite advances in thermostat control of heating and cooling systems, some systems suffer from various conditions that affect a heating and cooling system&#39;s ability to operative efficiently and provide adequate comfort to occupants. Accordingly, what are needed are systems and methods that can detect such conditions and take steps for corrective action. 
       SUMMARY 
       [0004]    This patent specification relates to systems and methods for determining whether abnormal operating conditions exists within heating, ventilation, and air conditioning (HVAC) systems. More particularly, this patent specification relates to methods and systems that can detect over cycling conditions that exist in an HVAC system. The over cycling condition can be caused by overheating of a forced air heating system or furnace of the HVAC system control. When the furnace overheats, a thermally actuated limit switch within the furnace may cut off power to a heat generation apparatus. The limit switch can reconnect the power to the heat generation apparatus after it has cooled down, at which point the thermostat control system may issue another heating call to continue heating the enclosure so that it reaches the desired set point temperature. If the overheat condition persist, then the thermally actuated switch will cut power. Thus, the furnace may power cycle ON and OFF several times before a desired set point temperature is obtained. The detection system and methods can monitor these power loss events and use them as data points for determining whether an alert condition exists within the HVAC system. 
         [0005]    In one embodiment, a method for controlling a HVAC (heating, ventilation, and air conditioning) system that uses forced air heating is provided. The method can be implemented in a thermostat. The method may obtain power loss data points during a moving window of heat cycles, wherein each heat cycle is called by the thermostat to instruct the HVAC system to generate forced air heating from a start time to an end time. The method can calculate a mean duration of a fixed number of provoking heat cycles, wherein a provoking heat cycle is characterized by a premature end time caused by a HVAC system induced power loss. The method can determining whether an alert condition exists by comparing a ratio of the number of provoking heat cycles that exceed the mean duration and the number of heat cycles that exceed the mean duration to an alert threshold, and confirm that the alert condition exists if the ratio exceeds the alert threshold. 
         [0006]    In another embodiment, a thermostat is provided that includes several HVAC (heating, ventilation, and air conditioning) wire connectors operative to receive a plurality of HVAC wires corresponding to an HVAC system including a forced air furnace. The thermostat can include control circuitry operative to execute a heating call that causes the HVAC system to run the forced air furnace through a heat cycle, monitor whether the heat cycle results in a provoking heat cycle, wherein the provoking heat cycle is characterized by a premature ending of the heat cycle caused by a furnace system induced power loss, and determine whether an alert condition exists when at least one provoking heat cycle is monitored. 
         [0007]    A further understanding of the nature and advantages of the embodiments discussed herein may be realized by reference to the remaining portions of the specification and the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a diagram of an enclosure with an HVAC system, according to some embodiments; 
           [0009]      FIG. 2  is a diagram of an HVAC system, according to some embodiments; 
           [0010]      FIG. 3  is a schematic block diagram that provides an overview of some components inside a thermostat, according to some embodiments; 
           [0011]      FIG. 4  illustrates a self-descriptive overview of the functional software, firmware, and/or programming architecture of the head unit microprocessor, according to an embodiment; 
           [0012]      FIG. 5  illustrates a self-descriptive overview of the functional software, firmware, and/or programming architecture of the backplate microcontroller, according to an embodiment; 
           [0013]      FIG. 6  shows illustrative timing diagram of heat cycles that may occur throughout a day, according to an embodiment; 
           [0014]      FIG. 7  shows illustrative timing diagram of provoking heat cycles that may occur when an HVAC heating system is experiencing premature shutdown due to one or more issues, according to an embodiment; 
           [0015]      FIG. 8  shows illustrative timing diagram showing provoking heat cycles and heat cycles over several days, according to an embodiment; and 
           [0016]      FIG. 9  shows illustrative over cycling detection process, according to an embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    In the following detailed description, for purposes of explanation, numerous specific details are set forth to provide a thorough understanding of the various embodiments of the present invention. Those of ordinary skill in the art will realize that these various embodiments of the present invention are illustrative only and are not intended to be limiting in any way. Other embodiments of the present invention will readily suggest themselves to such skilled persons having the benefit of this disclosure. 
         [0018]    In addition, for clarity purposes, not all of the routine features of the embodiments described herein are shown or described. One of ordinary skill in the art would readily appreciate that in the development of any such actual embodiment, numerous embodiment-specific decisions may be required to achieve specific design objectives. These design objectives will vary from one embodiment to another and from one developer to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming but would nevertheless be a routine engineering undertaking for those of ordinary skill in the art having the benefit of this disclosure. 
         [0019]    It is to be appreciated that while one or more embodiments are described further herein in the context of typical HVAC systems used in a residential home, such as single-family residential home, the scope of the present teachings is not so limited. More generally, thermostats according to one or more of the preferred embodiments are applicable for a wide variety of enclosures having one or more HVAC systems including, without limitation, duplexes, townhomes, multi-unit apartment buildings, hotels, retail stores, office buildings and industrial buildings. Further, it is to be appreciated that while the terms user, customer, installer, homeowner, occupant, guest, tenant, landlord, repair person, and the like may be used to refer to the person or persons who are interacting with the thermostat or other device or user interface in the context of one or more scenarios described herein, these references are by no means to be considered as limiting the scope of the present teachings with respect to the person or persons who are performing such actions. 
         [0020]    Provided according to one or more embodiments are systems, methods, computer program products, and related business methods for controlling one or more HVAC systems based on one or more versatile sensing and control units (VSCU units), each VSCU unit being configured and adapted to provide sophisticated, customized, energy-saving HVAC control functionality while at the same time being visually appealing, non-intimidating, elegant to behold, and delightfully easy to use. The term “thermostat” is used hereinbelow to represent a particular type of VSCU unit (Versatile Sensing and Control) that is particularly applicable for HVAC control in an enclosure. Although “thermostat” and “VSCU unit” may be seen as generally interchangeable for the contexts of HVAC control of an enclosure, it is within the scope of the present teachings for each of the embodiments hereinabove and hereinbelow to be applied to VSCU units having control functionality over measurable characteristics other than temperature (e.g., pressure, flow rate, height, position, velocity, acceleration, capacity, power, loudness, brightness) for any of a variety of different control systems involving the governance of one or more measurable characteristics of one or more physical systems, and/or the governance of other energy or resource consuming systems such as water usage systems, air usage systems, systems involving the usage of other natural resources, and systems involving the usage of various other forms of energy. 
         [0021]      FIG. 1  is a diagram illustrating an exemplary enclosure using a thermostat  110  implemented in accordance with the present invention for controlling one or more environmental conditions. For example, enclosure  100  illustrates a single-family dwelling type of enclosure using a learning thermostat  110  (also referred to for convenience as “thermostat  110 ”) for the control of heating and cooling provided by an HVAC system  120 . Alternate embodiments of the present invention may be used with other types of enclosures including a duplex, an apartment within an apartment building, a light commercial structure such as an office or retail store, or a structure or enclosure that is a combination of these and other types of enclosures. 
         [0022]    Some embodiments of thermostat  110  in  FIG. 1  incorporate one or more sensors to gather data from the environment associated with enclosure  100 . Sensors incorporated in thermostat  110  may detect occupancy, temperature, light and other environmental conditions and influence the control and operation of HVAC system  120 . Sensors incorporated within thermostat  110  do not protrude from the surface of the thermostat  110  thereby providing a sleek and elegant design that does not draw attention from the occupants in a house or other enclosure. As a result, thermostat  110  and readily fits with almost any décor while adding to the overall appeal of the interior design. 
         [0023]    As used herein, a “learning” thermostat refers to a thermostat, or one of plural communicating thermostats in a multi-thermostat network, having an ability to automatically establish and/or modify at least one future setpoint in a heating and/or cooling schedule based on at least one automatically sensed event and/or at least one past or current user input. 
         [0024]    As used herein, a “primary” thermostat refers to a thermostat that is electrically connected to actuate all or part of an HVAC system, such as by virtue of electrical connection to HVAC control wires (e.g. W, G, Y, etc.) leading to the HVAC system. 
         [0025]    As used herein, an “auxiliary” thermostat refers to a thermostat that is not electrically connected to actuate an HVAC system, but that otherwise contains at least one sensor and influences or facilitates primary thermostat control of an HVAC system by virtue of data communications with the primary thermostat. 
         [0026]    In one particularly useful scenario, the thermostat  110  is a primary learning thermostat and is wall-mounted and connected to all of the HVAC control wires, while the remote thermostat  112  is an auxiliary learning thermostat positioned on a nightstand or dresser, the auxiliary learning thermostat being similar in appearance and user-interface features as the primary learning thermostat, the auxiliary learning thermostat further having similar sensing capabilities (e.g., temperature, humidity, motion, ambient light, proximity) as the primary learning thermostat, but the auxiliary learning thermostat not being connected to any of the HVAC wires. Although it is not connected to any HVAC wires, the auxiliary learning thermostat wirelessly communicates with and cooperates with the primary learning thermostat for improved control of the HVAC system, such as by providing additional temperature data at its respective location in the enclosure, providing additional occupancy information, providing an additional user interface for the user, and so forth. 
         [0027]    It is to be appreciated that while certain embodiments are particularly advantageous where the thermostat  110  is a primary learning thermostat and the remote thermostat  112  is an auxiliary learning thermostat, the scope of the present teachings is not so limited. Thus, for example, while certain initial provisioning methods that automatically pair associate a network-connected thermostat with an online user account are particularly advantageous where the thermostat is a primary learning thermostat, the methods are more generally applicable to scenarios involving primary non-learning thermostats, auxiliary learning thermostats, auxiliary non-learning thermostats, or other types of network-connected thermostats and/or network-connected sensors. By way of further example, while certain graphical user interfaces for remote control of a thermostat may be particularly advantageous where the thermostat is a primary learning thermostat, the methods are more generally applicable to scenarios involving primary non-learning thermostats, auxiliary learning thermostats, auxiliary non-learning thermostats, or other types of network-connected thermostats and/or network-connected sensors. By way of even further example, while certain methods for cooperative, battery-conserving information polling of a thermostat by a remote cloud-based management server may be particularly advantageous where the thermostat is a primary learning thermostat, the methods are more generally applicable to scenarios involving primary non-learning thermostats, auxiliary learning thermostats, auxiliary non-learning thermostats, or other types of network-connected thermostats and/or network-connected sensors. 
         [0028]    Enclosure  100  further includes a private network accessible both wirelessly and through wired connections and may also be referred to as a Local Area Network or LAN. Network devices on the private network include a computer  124 , thermostat  110  and remote thermostat  112  in accordance with some embodiments of the present invention. In one embodiment, the private network is implemented using an integrated router  122  that provides routing, wireless access point functionality, firewall and multiple wired connection ports for connecting to various wired network devices, such as computer  124 . Each device is assigned a private network address from the integrated router  122  either dynamically through a service like Dynamic Host Configuration Protocol (DHCP) or statically through actions of a network administrator. These private network addresses may be used to allow the devices to communicate with each directly over the LAN. Other embodiments may instead use multiple discrete switches, routers and other devices (not shown) to perform more other networking functions in addition to functions as provided by integrated router  122 . 
         [0029]    Integrated router  122  further provides network devices access to a public network, such as the Internet, provided enclosure  100  has a connection to the public network generally through a cable-modem, DSL modern and an Internet service provider or provider of other public network service. Public networks like the Internet are sometimes referred to as a Wide-Area Network or WAN. In the case of the Internet, a public address is assigned to a specific device allowing the device to be addressed directly by other devices on the Internet. Because these public addresses on the Internet are in limited supply, devices and computers on the private network often use a router device, like integrated router  122 , to share a single public address through entries in Network Address Translation (NAT) table. The router makes an entry in the NAT table for each communication channel opened between a device on the private network and a device, server, or service on the Internet. A packet sent from a device on the private network initially has a “source” address containing the private network address of the sending device and a “destination” address corresponding to the public network address of the server or service on the Internet. As packets pass from within the private network through the router, the router replaces the “source” address with the public network address of the router and a “source port” that references the entry in the NAT table. The server on the Internet receiving the packet uses the “source” address and “source port” to send packets back to the router on the private network which in turn forwards the packets to the proper device on the private network doing a corresponding lookup on an entry in the NAT table. 
         [0030]    Entries in the NAT table allow both the computer device  124  and the thermostat  110  to establish individual communication channels with a thermostat management system (not shown) located on a public network such as the Internet. In accordance with some embodiments, a thermostat management account on the thermostat management system enables a computer device  124  in enclosure  100  to remotely access thermostat  110 . The thermostat management system passes information from the computer device  124  over the Internet and back to thermostat  110  provided the thermostat management account is associated with or paired with thermostat  110 . Accordingly, data collected by thermostat  110  also passes from the private network associated with enclosure  100  through integrated router  122  and to the thermostat management system over the public network. Other computer devices not in enclosure  100  such as Smartphones, laptops and tablet computers (not shown in  FIG. 1 ) may also control thermostat  110  provided they have access to the public network where the thermostat management system and thermostat management account may be accessed. Further details on accessing the public network, such as the Internet, and remotely accessing a thermostat like thermostat  110  in accordance with embodiments of the present invention is described in further detail later herein. 
         [0031]    In some embodiments, thermostat  110  may wirelessly communicate with remote thermostat  112  over the private network or through an ad hoc network formed directly with remote thermostat  112 . During communication with remote thermostat  112 , thermostat  110  may gather information remotely from the user and from the environment detectable by the remote thermostat  112 . For example, remote thermostat  112  may wirelessly communicate with the thermostat  110  providing user input from the remote location of remote thermostat  112  or may be used to display information to a user, or both. Like thermostat  110 , embodiments of remote thermostat  112  may also include sensors to gather data related to occupancy, temperature, light and other environmental conditions. In an alternate embodiment, remote thermostat  112  may also be located outside of the enclosure  100 . 
         [0032]      FIG. 2  is a schematic diagram of an HVAC system controlled using a thermostat designed in accordance with embodiments of the present invention. HVAC system  120  provides heating, cooling, ventilation, and/or air handling for an enclosure  100 , such as a single-family home depicted in  FIG. 1 . System  120  depicts a forced air type heating and cooling system, although according to other embodiments, other types of HVAC systems could be used such as radiant heat based systems, heat-pump based systems, and others. 
         [0033]    In heating, heating coils or elements  242  within air handler  240  provide a source of heat using electricity or gas via line  236 . Cool air is drawn from the enclosure via return air duct  246  through filter  270 , using fan  238  and is heated through heating coils or elements  242 . The heated air flows back into the enclosure at one or more locations via supply air duct system  252  and supply air registers such as register  250 . The forced air system (e.g., furnace) may have a built in safety mechanism to prevent overheat conditions. For example, the furnace may have a sensor that detects an internal temperature, and if that internal temperature exceeds a threshold, the sensor can shut the furnace off. The sensor may turn the furnace off by cutting power to one or more components (e.g., air handler  240 ). Overheat situations may be caused by any number of different factors, one of them being restricted inlet air flow caused by dirty air filters. 
         [0034]    In situations where the sensor is being repeatedly tripped, thereby turning the furnace off, this can affect the system&#39;s ability to efficiently heat the enclosure. Inefficiency in heating the enclosure may be realized because the thermostat is not able to complete a heat cycle because the furnace if forced to be turned off prior to the end of the heat cycle. As result, the thermostat may continue to run additional heat cycles in an attempt to reach the desired temperature. This can cause an inordinate number of heat cycles to achieve the desired setpoint temperature. Embodiments discussed herein are able determine if these prematurely ending heat cycles are occurring and can alert occupants or owner of the enclosure of a potential problem. 
         [0035]    In cooling, an outside compressor  230  passes a gas such as Freon through a set of heat exchanger coils  244  to cool the gas. The gas then goes through line  232  to the cooling coils  234  in the air handler  240  where it expands, cools and cools the air being circulated via fan  238 . A humidifier  254  may optionally be included in various embodiments that returns moisture to the air before it passes through duct system  252 . Although not shown in  FIG. 2 , alternate embodiments of HVAC system  120  may have other functionality such as venting air to and from the outside, one or more dampers to control airflow within the duct system  252  and an emergency heating unit. Overall operation of HVAC system  120  is selectively actuated by control electronics  212  communicating with thermostat  110  over control wires  248 . 
         [0036]    Referring to  FIG. 3 , a schematic block diagram provides an overview of some components inside a thermostat in accordance with embodiments of the present invention. Thermostat  308  is similar to thermostat  112  in  FIG. 1  except that thermostat  308  also illustrates and highlights selected internal components including a Wi-Fi module  312  and antenna, a head unit processor  314  with associated memory  315 , a backplate processor  316  with associated memory, and sensors  322  (e.g., temperature, humidity, motion, ambient light, proximity). In one embodiment, head unit processor  314  can be a Texas Instruments AM3703 Sitara ARM microprocessor while backplate processor  316 , which may be more specifically referenced to as a “microcontroller”, can be a Texas Instruments MSP430F microcontroller. 
         [0037]    For some embodiments, the backplate processor  316  is a very low-power device that, while having some computational capabilities, is substantially less powerful than the head unit processor  314 . The backplate processor  316  is coupled to, and responsible for polling on a regular basis, most or all of the sensors  322  including the temperature and humidity sensors, motion sensors, ambient light sensors, and proximity sensors. For sensors  322  that may not be located on the backplate hardware itself but rather are located in the head unit, ribbon cables or other electrical connections between the head unit and backplate are provided for this purpose. Notably, there may be other sensors (not shown) for which the head unit processor  314  is responsible, with one example being a ring rotation sensor that senses the user rotation of an outer ring of the thermostat. Each of the head unit processor  314  and backplate processor  316  is capable of entering into a “sleep” state, and then “waking up” to perform various tasks. 
         [0038]    The backplate processor  316 , which in some embodiments will have a low-power sleep state that corresponds simply to a lower clock speed, generally enters into and out of its sleep mode substantially more often than does the more powerful head unit processor  314 . The backplate processor  316  is capable of waking up the head unit processor  314  from its sleep state. For one preferred embodiment directed to optimal battery conservation, the head unit processor  314  is allowed to sleep when its operations are not being called for, while the backplate processor  316  performs polling of the sensors  322  on an ongoing basis, maintaining the sensor results in memory  317 . The backplate processor  316  will wake up the head unit processor  314  in the event that (i) the sensor data indicates that an HVAC operation may be called for, such as if the current temperature goes below a currently active heating setpoint, or GO the memory  317  gets full and the sensor data needs to be transferred up to the head unit processor  314  for storage in the memory  315 . The sensor data can then be pushed up to the cloud server (thermostat management server) during a subsequent active communication session between the cloud server and the head unit processor  314 . 
         [0039]    In the case of Wi-Fi module  312 , one embodiment may be implemented using Murata Wireless Solutions LBWA19XSLZ module, which is based on the Texas Instruments WL1270 chipset supporting the 802.11 b/g/n WLAN standard. Embodiments of the present invention configure and program Wi-Fi module  312  to allow thermostat  308  to enter into a low power or “sleep” mode to conserve energy until one or several events occurs. For example, in some embodiments the Wi-Fi module  312  may leave this low power mode when a user physically operates thermostat  308 , which in turn may also cause activation of both head-unit processor  314  and backplate processor  316  for controlling functions in head-unit and backplate portions of thermostat  110 . 
         [0040]    It is also possible for Wi-Fi module  312  to wake from a low power mode at regular intervals in response to a beacon from wireless access point  372 . To conserve energy, Wi-Fi module  312  may briefly leave the low power mode to acknowledge the beacon as dictated by the appropriate wireless standard and then return to a low power mode without activating the processors or other components of thermostat  308  in  FIG. 3A . In an alternative embodiment, Wi-Fi module  312  may also respond to the beacon by awaking briefly and then activating backplate processor  316 , head unit processor  314 , or other portions of thermostat  308  to gather data through sensors  322  and store the results in a data log  326  with a time stamp, event type and corresponding data listed for future reference. In accordance with one embodiment, backplate processor  316  may collect data in data log  326  and store in memory  320  for a period of time or until the log reaches a maximum predetermined size. At that point, the backplate processor  316  may wake head unit processor  314  to coordinate an upload of the data log  326  stored in memory  320  over a public network, such as the Internet, to cloud-based management server  516 . Uploading data log  326  less frequently saves time and energy associated with more frequent transmission of individual records or log entries. 
         [0041]    In yet another embodiment, Wi-Fi module  312  may selectively filter an incoming data packet to determine if the header is merely an acknowledgement packet (i.e., a keep-alive packet) or contains a payload that needs further processing. If the packet contains only a header and no payload, the Wi-Fi module  312  may be configured to either ignore the packet or send a return acknowledgement to the thermostat management system or other source of the packet received. 
         [0042]    In further embodiments, Wi-Fi module  312  may be used to establish multiple communication channels between thermostat  112  and a cloud-based management server as will be described and illustrated later in this disclosure. As previously described, thermostat  112  uses multiple communication channels to receive different types of data classified with different levels of priority. In one embodiment, Wi-Fi module  312  may be programmed to use one or more filters and a wake-on-LAN feature to then selectively ignore or discard data arriving over one or more of these communication channels. For example, low-priority data arriving over a port on Wi-Fi module  312  may be discarded by disabling the corresponding wake-on-LAN feature associated with the port. This allows the communication channel to continue to operate yet conserves battery power by discarding or ignoring the low-priority packets. 
         [0043]    Operation of the microprocessors  314 ,  316 , Wi-Fi module  312 , and other electronics may be powered by a rechargeable battery (not shown) located within the thermostat  110 . In some embodiments, the battery is recharged directly using 24 VAC power off a “C” wire drawn from the HVAC system or an AC-DC transformer coupled directly into the thermostat  110 . Alternatively, one or more different types of energy harvesting may also be used to recharge the internal battery if these direct methods are not available. 
         [0044]      FIG. 4  illustrates a self-descriptive overview of the functional software, firmware, and/or programming architecture of the head unit microprocessor for achieving its described functionalities.  FIG. 5  illustrates a self-descriptive overview of the functional software, firmware, and/or programming architecture of the backplate microcontroller for achieving its described functionalities. 
         [0045]      FIG. 6  shows illustrative timing diagram  600  of heat cycles  610  that may occur throughout a day. As defined herein, a heat cycle may represent a heating function call executed by a thermostat to run a forced air heating system such as a furnace to raise the temperature of an enclosure from a start time to an end time. The start and end times of each heat cycle may vary depending, for example, on various monitored conditions within an enclosure and the desired set point temperature. Each of the heat cycles in diagram  600  are shown to run their full term without being prematurely cutoff prior to its scheduled end time. As such, diagram  600  represents an example of fully functional HVAC system that is not experiencing any issues. 
         [0046]      FIG. 7  shows illustrative timing diagram  700  of provoking heat cycles  720  that may occur when an HVAC heating system is experiencing premature shutdown due to one or more issues. As defined herein, a provoking heat cycle may represent a heat cycle that ends prematurely, due to power loss. That is, the provoking heat cycle may be initiated as a thermostat controlled function call to run a forced air heating system, but is not able to run to the scheduled end time because the forced air heating system shuts itself down by cutting power to one or more components controlling the operation of the system. In simplistic terms, a provoking heat cycle is a heat cycle ended by a power loss. 
         [0047]    Timing diagram  700  shows that the thermostat may have to cycle the heating system several times in order to raise the temperature to a desired set point when it is constantly implementing provoking heat cycles. This is contrast to normal heat cycles that run, and are followed by a period of rest before running another normal heat cycle. Provoking heat cycles, as shown, can run continuously without any break in between function calls so that the desired set point temperature can be obtained within the enclosure. This can cause excessive system cycling. Embodiments discussed herein can detect when such excessive system cycling is occurring and can alert occupants, owners, and/or service repair technicians of a potential issue. 
         [0048]      FIG. 8  shows illustrative timing diagram  800  showing provoking heat cycles and heat cycles over several days. Timing diagram  800  shows that days 1-4 and part of day 5 have several instances of provoking heat cycles  820 . An over cycling detection algorithm according to embodiments discussed herein may detect the occurrence of provoking heat cycles  820  and prompted corrective action. In one embodiment, the corrective action may be the replacement of a cold air return air filter. Such corrective action is shown to have taken place during day 5. After the corrective action has been taken, timing diagram  800  shows the heating system ceases repetitive occurrences of provoking heat cycles and returns to normal heat cycles  810  for the latter part of day 5 and all of day 6. 
         [0049]    A method for detecting over cycling in a HVAC system, and in particular, a forced air heating system is now discussed. The over cycling detecting method can be executed by the thermostat without requiring any additional wire or wireless connections to the HVAC system. That is, the existing wired HVAC connections are all that are needed in order the control system of the thermostat to receive data needed to perform the over cycling detection method. In addition, the over cycling detection method can maintain a moving window during which only data acquired within that window is used for assessing whether to alert to corrective action. In some embodiments, the moving window can include data acquired during time spanning from the present to a fixed period of time in the past or can be a given number of samples (e.g., heat cycles). 
         [0050]      FIG. 9  shows illustrative over cycling detection process  900  according to an embodiment. Process  900  may be executed in a thermostat and include data acquired during a moving window of heat cycles, wherein each heat cycle is called by the thermostat to instruct a HVAC system to generate forced air heating from a start time to an end time. In one embodiment, the moving window of heat cycles can include a fixed number of the previously monitored heat cycles. It should be understood that the heat cycles can include normal heat cycles and provoking heat cycles. Starting at step  910 , a mean duration of a fixed number of provoking heat cycles can be calculated. As mentioned above, a provoking heat cycle can be characterized by a premature end time caused by a HVAC system induced power loss. The fixed number of provoking heat cycles may be less than the fixed number of monitored heat cycles. 
         [0051]    At step  920 , a determination of whether an alert condition exists can be performed by comparing a ratio of the number of provoking heat cycles that exceed the mean duration and the number of heat cycles that exceed the mean duration to an alert threshold. The ratio can be calculated in the equation below. 
         [0000]    
       
         
           
             Ratio 
             = 
             
               
                 
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                   provoking 
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                    
                   cycles 
                 
                 &gt; 
                 
                   mean 
                    
                   
                       
                   
                    
                   duration 
                 
               
               
                 
                   # 
                    
                   
                       
                   
                    
                   heat 
                    
                   
                       
                   
                    
                   cycles 
                 
                 &gt; 
                 
                   mean 
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                    
                   duration 
                 
               
             
           
         
       
     
         [0000]    The alert threshold can be a number that determines whether an alert condition exists. That is, at step  930 , a determination is made whether the ratio exceeds the alert threshold. If the determination is YES, process  900  proceeds to step  940 , otherwise process  900  returns to step  910 . Step  940  and steps  942 , and  944  represent various non-alert conditions. The non-alert conditions may represent conditions that, if satisfied, prevent process  900  from confirming that an alert condition does exist. 
         [0052]    At step  940 , a determination is made whether the number of provoking heat cycles is less than a non-alert threshold. If the determination is YES, process  900  returns to step  910 . If the determination is NO, process  900  can proceed to step  942 . At step  942 , a determination is made whether any heat cycle exceeded a non-alert duration. For example, if any one of the heat cycles within the moving window exceeded the non-alert duration, the determination is YES, and process  900  returns to step  910 . If the determination is NO, process  900  can proceed to step  944 . 
         [0053]    At step  944 , a determination is made whether non-heating related power loss are responsible for causing the provoking heat cycles. This determination can be made by counting a number of normal power loss events that occur after a fixed period of time following the end of a heat cycle and comparing the count to a power loss threshold. The count can be tallied over a fixed time duration (e.g., last few days). If the count exceeds the power loss threshold, then process  900  returns to step  910 . If the count is equal to or less than the power loss threshold, then process  900  can proceed to step  950 . 
         [0054]    At step  950 , the alert condition is confirmed and notice can be provided. Notice can be provided in a number of different ways. Notice may be provided on the thermostat in the form a graphic, light, or audio message. Notice may be provided to a user by way of his or her mobile device in the form of a text message, email, or other notices. Notice may be provided a service technician who is registered to service the enclosure. The notice can instruct the owner to replace an air filter, for example. 
         [0055]    It should be appreciated that the steps of  FIG. 9  can be omitted or re-ordered, and additional steps can be added. For example, after the user confirms that he has replaced the air filter, the over cycling condition process can continue running. If no alert conditions are detected, the user may be notified as such. However, if an alert condition is detected, the user may be notified that a problem persist and can suggest that he make a service call on his HVAC system. 
         [0056]    Whereas many alterations and modifications of the present invention will no doubt become apparent to a person of ordinary skill in the art after having read the foregoing description, it is to be understood that the particular embodiments shown and described by way of illustration are in no way intended to be considered limiting.