Diagnostics of outdoor unit of HVAC system based on sound signatures

The application is a continuation of U.S. patent application Ser. No. 18/299,482, filed Apr. 12, 2023, entitled “DIAGNOSTICS OF OUTDOOR UNIT OF HVAC SYSTEM BASED ON SOUND SIGNATURES,” which is incorporated herein by reference.

The present disclosure relates generally to Heating, Ventilation, and Air Conditioning (HVAC) system control, and more specifically to sound-based diagnostics of an outdoor unit of an HVAC system.

Existing heating, ventilation, and air conditioning (HVAC) systems typically can only provide a general alert when there is an issue with an HVAC system. For example, the HVAC system may report that an error has occurred while trying to operate the HVAC system and that a service is required to repair the HVAC system. Existing HVAC systems cannot typically self-diagnose any issues with the HVAC system. This means that a technician will need to inspect the HVAC system and make repairs to the HVAC system. In many instances, a technician will need to make multiple trips to a location to first diagnose the issue with an HVAC system and then to return with the appropriate parts and tools for servicing the HVAC system. This process results in an extended amount of downtime while the technician diagnoses and makes repairs to the HVAC system.

The system disclosed in the present application provides a technical solution to the technical problems discussed above by providing a visual- and sound-based HVAC diagnostic system that is configured to detect faults and issues within an HVAC system based on sounds made by the components of the HVAC system and detect faults and issues within a filter of an HVAC system based on images of the filter. The disclosed system provides several practical applications and technical advantages which include a process that enables a user of an HVAC system to diagnose faults within the HVAC system and to output information that identifies any faulty components of the HVAC system. These features reduce the amount of downtime that an HVAC system will experience because the HVAC system is able to identify the components that are causing the issues that the HVAC system is experiencing. This process allows the user to provide diagnostic information to a technician, such that the technician is prepared with all of the necessary equipment (i.e., parts and tools) and instructions for servicing the HVAC system without having to first diagnose the HVAC system themselves.

In one embodiment, a system includes a thermostat communicatively coupled to a heating, ventilation, and air conditioning (HVAC) system, and a user device communicatively coupled to the thermostat. The user device includes a first processor configured to determine if a triggering event has occurred. In response to determining that the triggering event has occurred, the first processor enters a filter diagnostics mode. The first processor sends a first instruction to the thermostat to shut down the HVAC system. The first processor instructs a user of the user device to locate a filter of the HVAC system. The first processor instructs the user to remove the filter. The first processor classifies the filter as acceptable or dirty. In response to classifying the filter as acceptable, the first processor instructs the user to the turn on the HVAC system. The first processor determines a desired mode of the HVAC system based on the triggering event. In response to determining that the desired mode is a cooling mode, The first processor determines a first value of a room temperature. The first processor instructs the user to set a temperature setpoint below the first value of the room temperature. The first processor determines a second value of the room temperature. The first processor compares the first value of the room temperature to the second value of the room temperature. In response to determining that the second value of the room temperature is less than the first value of the room temperature, The first processor determines that the HVAC system operates properly.

In another embodiment, a system includes a thermostat communicatively coupled to a heating, ventilation, and air conditioning (HVAC) system, a user device communicatively coupled to the thermostat, and a computing system communicatively coupled to the user device. The user device includes a first processor configured to send a first instruction to the thermostat to shut down the HVAC system. The first processor instructs a user to minimize background noise. The first processor instructs the user to go to an indoor unit of the HVAC system. The first processor instructs the user to capture an image of a nameplate of the indoor unit. The first processor analyzes the image to determine a distance of the user from the indoor unit. The first processor compares the distance to a distance range. In response to determining that the distance is within the distance range, the first processor captures baseline sound data for a first time period. The first processor sends a second instruction to the thermostat to turn on the HVAC system. The first processor determines a value of a room temperature. The first processor sends a third instruction to the thermostat to set a temperature setpoint below or above the value of the room temperature. The first processor captures an indoor unit sound data for a second time period. The first processor sends the indoor unit sound data and the baseline sound data to the computing system. The computing system includes a second processor configured to subtract the baseline sound data from the indoor unit sound data to determine normalized indoor unit sound data. The second processor analyze the normalized indoor unit sound data to determine sound signatures. The second processor identifies expected sound signatures of the indoor unit. The second processor compares the normalized indoor unit sound data to the expected sound signatures. In response to determining that an expected sound signature for a blower is missing from the normalized indoor unit sound data, The second processor determines that the blower has failed. The second processor sends a first notification to the user device that the blower has failed.

In yet another embodiment, a system includes a thermostat communicatively coupled to a heating, ventilation, and air conditioning (HVAC) system, a user device communicatively coupled to the thermostat, and a computing system communicatively coupled to the user device. The user device includes a first processor configured to send a first instruction to the thermostat to shut down the HVAC system. The first processor instructs a user to minimize background noise. The first processor instructs the user to go to an outdoor unit of the HVAC system. The first processor instructs the user to capture an image of a nameplate of the outdoor unit. The first processor analyzes the image to determine a distance of the user from the outdoor unit. The first processor compares the distance to a distance range. In response to determining that the distance is within the distance range, the first processor captures baseline sound data for a first time period. The first processor sends a second instruction to the thermostat to turn on the HVAC system. The first processor determines a value of a room temperature. The first processor sends a third instruction to the thermostat to set a temperature setpoint below or above the value of the room temperature. The first processor captures first outdoor unit sound data for a second time period. The first processor sends the first outdoor unit sound data and the baseline sound data to the computing system. The computing system includes a second processor configured to subtract the baseline sound data from the first outdoor unit sound data to determine first normalized outdoor unit sound data. The second processor analyzes the first normalized outdoor unit sound data to determine first sound signatures. The second processor identifies expected first sound signatures of the outdoor unit. The second processor compares the first normalized outdoor unit sound data to the expected first sound signatures. In response to determining that an expected sound signature for a compressor is missing from the first normalized outdoor unit sound data, the second processor determines that the compressor has failed. The second processor sends a first notification to the user device that the compressor has failed.

Certain embodiments of the present disclosure may include some, all, or none of these advantages. These advantages and other features will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings and claims.

is a schematic diagram of an embodiment of a diagnostic systemfor a heating, ventilation, and air conditioning (HVAC) system. In one embodiment, the diagnostic systemcomprises a user device, a thermostat, a computing system, and the HVAC systemthat are in signal communication with each other over a network. Networkenables the communication between the components of the diagnostic system. In other embodiments, the diagnostic systemmay not have all the components listed and/or may have other elements instead of, or in addition to, those listed above. For example, functionalities of the computing systemmay be fully or partially integrated into the user device. For another example, functionalities of the computing systemmay be fully or partially integrated into the thermostat.

In general, the diagnostic systemis configured to use visual and sound data for detecting and diagnosing faults within the HVAC system. More specifically, the analysis systemis configured to diagnose various faults within the HVAC systemand to notify a userthat one or more components of the HVAC system have failed or are malfunctioning. The usermay provide this information to a technician. These features reduce the amount of downtime that the HVAC systemwill experience because the diagnostic system is able to output information about the components that are causing the issues that the HVAC systemis experiencing. This process allows the technician to be prepared with all of the necessary equipment (i.e., parts and tools) and instructions for servicing the HVAC systemwithout having to first diagnose the HVAC systemthemselves.

The networkmay be any suitable type of wireless and/or wired network including, but not limited to, all or a portion of the Internet, an Intranet, a private network, a public network, a peer-to-peer network, the public switched telephone network, a cellular network, a local area network (LAN), a metropolitan area network (MAN), a personal area network (PAN), a wide area network (WAN), and a satellite network. The networkmay be configured to support any suitable type of communication protocol as would be appreciated by one of ordinary skill in the art.

The user deviceis generally any device that is configured to process data and interact with the user. Examples of the user deviceinclude, but are not limited to, a personal computer, a desktop computer, a workstation, a server, a laptop, a tablet computer, a mobile phone (such as a smartphone), etc. The user devicemay include a user interface, such as a display, one or more cameras, one or more microphones, keypad, or other appropriate terminal equipment usable by the user.

The user devicemay comprise a processorin signal communication with a memoryand a network interface. The processorcomprises one or more processors operably coupled to the memory. The processoris any electronic circuitry including, but not limited to, state machines, one or more central processing unit (CPU) chips, logic units, cores (e.g., a multi-core processor), field-programmable gate array (FPGAs), application-specific integrated circuits (ASICs), or digital signal processors (DSPs). The processormay be a programmable logic device, a microcontroller, a microprocessor, or any suitable combination of the preceding. The processoris communicatively coupled to and in signal communication with the memory, a display, one or more cameras, one or more microphones, and the network interface. The one or more processors are configured to process data and may be implemented in hardware or software. For example, the processormay be 8-bit, 16-bit, 32-bit, 64-bit, or of any other suitable architecture. The processormay include an arithmetic logic unit (ALU) for performing arithmetic and logic operations, processor registers that supply operands to the ALU and store the results of ALU operations, and a control unit that fetches instructions from memory and executes them by directing the coordinated operations of the ALU, registers and other components.

The one or more processors are configured to implement various instructions. For example, the one or more processors are configured to execute instructionsto implement various functions of the user device. The one or more processors are configured to execute an applicationto implement a diagnostic process described in this disclosure. In this way, processormay be a special-purpose computer designed to implement the functions disclosed herein. The processor, when executing the application, is configured to operate as described in. For example, the processor, when executing the application, may be configured to perform operations of processes-as described in, respectively.

The network interfaceis configured to enable wired and/or wireless communications. The network interfaceis configured to communicate data between the user deviceand other components of the diagnostic system. For example, the network interfacemay comprise an NFC interface, a Bluetooth interface, a Zigbee interface, a Z-wave interface, an RFID interface, a WIFI interface, a LAN interface, a WAN interface, a PAN interface, a modem, a switch, or a router. The processoris configured to send and receive data using the network interface. The network interfacemay be configured to use any suitable type of communication protocol as would be appreciated by one of ordinary skill in the art.

The memorycomprises one or more disks, tape drives, or solid-state drives, and may be used as an over-flow data storage device, to store programs when such programs are selected for execution, and to store instructions and data that are read during program execution. The memorymay be volatile or non-volatile and may comprise a read-only memory (ROM), random-access memory (RAM), ternary content-addressable memory (TCAM), dynamic random-access memory (DRAM), and static random-access memory (SRAM).

The memoryis operable to store any of the information described herein with respect toalong with any other data, instructions, logic, rules, or code operable to implement the function(s) described herein when executed by the processor. The memoryis operable to store the instructions, the application, and/or any other data or instructions that is used by the processorto perform the function(s) of the user devicedescribed herein. The instructionsmay comprise any suitable set of instructions, logic, rules, or code operable to implement the function(s) of the user devicewhen executed by the processor. The applicationmay comprise any suitable set of instructions, logic, rules, or code operable to implement a diagnostic process when executed by the processor.

The user devicemay comprise one or more microphones. The microphonesare generally configured to record the sounds that are made by electrical and mechanical components of the HVAC system. For example, a microphonemay be positioned proximate or adjacent to a blower, an integrated furnace control board, a relay, a compressor, a gas valve, a furnace, a fan, or any other component of the HVAC system. Each microphone is configured to capture sound data of one or more components of the HVAC system. The microphonesmay be configured to capture sound data continuously, at predetermined intervals, or on-demand. Each microphoneis operably coupled to the processorand provides captured sound data to the processorfor processing.

The user devicemay comprise a display. The displayis a graphical user interface that is configured to present visual information to the userusing graphical objects. Examples of the displayinclude, but are not limited to, a liquid crystal display (LCD), a liquid crystal on silicon (LCOS) display, a light-emitting diode (LED) display, an active-matrix OLED (AMOLED), an organic LED (OLED) display, a projector display, or any other suitable type of display as would be appreciated by one of ordinary skill in the art.

The user devicemay comprise one or more cameras. The cameras may be configured to captures images of various components of the HVAC system, such as a filter, a nameplate, or any other component of the HVAC system. The camerasare operably coupled to the processorand provide captured images to the processorfor processing.

In operation, the user deviceis configured to capture sound data (e.g., indoor unit sound data) of one or more indoor units (e.g., indoor unitof) of the HVAC systemin various modes, such as cooling mode and heating mode (including a heat pump heating mode and a supplemental heating mode). The user deviceis further configured to capture sound data (e.g., outdoor unit sound data) of an outdoor unit (e.g., outdoor unitof) of the HVAC systemis various modes, such as a cooling mode and heating mode (including a heat pump heating mode and a supplemental heating mode). The user deviceis further configured to send the captured sound data to the computing systemfor further analysis.

The user deviceis configured capture images (e.g., imagesand) of a front side and a back side of a filter (e.g., filterof). The captured images are then analyzed to classify the filter as acceptable or dirty.

The user devicemay be further configured exchange various instructions (e.g., instructions) and responses (e.g., responses) with the thermostatand receive various notifications (e.g., notifications) from the computing system. In one embodiment, the user devicemay receive a notification that the indoor unitof the HVAC systemoperates properly. In another embodiment, the user devicemay receive a notification that the outdoor unitof the HVAC systemoperates properly. In yet another embodiment, the user devicemay receive a notification that a component of HVAC systemhas failed or is malfunctioning.

The thermostatis generally configured to control various operations of the HVAC system. In one embodiment, the thermostatcomprises a processorin signal communication with a memoryand a network interface. The thermostatmay further comprise a graphical user interface, a display, a touch screen, buttons, knobs, or any other suitable combination of components.

The processormay be similar to the processorand the description is not repeated herein. The processoris configured to implement various instructions. For example, the processoris configured to execute instructionsto implement various functions of the thermostat.

The network interfacemay be similar to the network interfaceand the description is not repeated herein. The network interfaceis configured to enable wired and/or wireless communications. The network interfaceis configured to communicate data between the thermostatand other components of the diagnostic system.

The memorymay be similar to the memoryand the description is not repeated herein. The memoryis operable to store any of the information described herein with respect toalong with any other data, instructions, logic, rules, or code operable to implement the function(s) described herein when executed by the processor. The memoryis operable to store the instructions, and/or any other data or instructions that is used by the processorto perform the function(s) of the thermostatdescribed herein. The instructionsmay comprise any suitable set of instructions, logic, rules, or code operable to implement the function(s) of the thermostatwhen executed by the processor.

In operation, the thermostatis configured to exchange various instructions (e.g., instructions) and responses (e.g., responses) with the user device. The thermostatis configured to send various instructions (e.g., instructions) to the HVAC systemto control various operations of the HVAC system.

The computing systemmay be a remote computing system or a cloud computing system. In one embodiment, the computing systemcomprises a processorin signal communication with a memoryand a network interface. The processormay be similar to the processorand the description is not repeated herein. The processoris configured to implement various instructions. For example, the processoris configured to execute instructionsto implement various functions of the computing systemdescribed herein.

The network interfacemay be similar to the network interfaceand the description is not repeated herein. The network interfaceis configured to enable wired and/or wireless communications. The network interfaceis configured to communicate data between the computing systemand other components of the analysis system.

The memorymay be similar to the memoryand the description is not repeated herein. The memoryis operable to store any of the information described herein with respect toalong with any other data, instructions, logic, rules, or code operable to implement the function(s) described herein when executed by the processor. The memoryis operable to store the instructions, a filter image library, a sound signature library, and/or any other data or instructions that is used by the processorto perform the function(s) of the computing systemdescribed herein. The instructionsmay comprise any suitable set of instructions, logic, rules, or code operable to implement the function(s) of the computing systemwhen executed by the processor. The filter image librarymay comprise used filter imagesfor various filter types. The sound signature librarycomprises expected sound signaturesfor various components of the HVAC systemlinked to respective component identifiers. The component identifiermay be a part name, a part number, a serial number, a model number, a barcode, or any other suitable type of alphanumeric identifier that uniquely identifies a component of the HVAC system.

In operation, the computing systemis configured to receive various sound data (e.g., sound data-) from the user device. The computing systemanalyzes the received sound data and determines if a component of the HVAC systemis malfunctioning or has failed. In an embodiment, the computing systemidentifies sound signatures (e.g., expected sound signatures) that are expected to be present in the received sound data and compares them to the received sound data. If an expected sound signature of a component of the HVAC systemis not present in the received sound data, the computing systemdetermines that the component has failed. If a sound signature of a component of the HVAC systemis different from the expected sound signature of the component, the computing systemdetermines that the component is malfunctioning.

An HVAC systemis generally configured to control the temperature of a space. Examples of the space include, but are not limited to, a room, a home, an apartment, a mall, an office, a warehouse, or a building. Althoughillustrates a single HVAC system, a location or space may comprise a plurality of HVAC systemsthat are configured to work together. For example, a large building may comprise multiple HVAC systemsthat work cooperatively to control the temperature within the building.

is a schematic diagram of an embodiment of an HVAC systemconfigured to integrate with a diagnostic system. The HVAC systemconditions air for delivery to an interior space of a building or home. In some embodiments, a portion of the HVAC systemmay be located within the building and may be referred to as an indoor unit, and a portion of the HVAC systemmay be located outside the building and may be referred to as an outdoor unit. In other embodiments, the HVAC systemis a rooftop unit (RTU) that is positioned on the roof of a building and the conditioned air is delivered to the interior of the building. The HVAC systemmay be configured as shown inor in any other suitable configuration. For example, the HVAC systemmay include additional components or may omit one or more components shown in.

The HVAC systemcomprises a working-fluid conduit subsystemfor moving a working fluid, or refrigerant. The working fluid may be any acceptable working fluid, or refrigerant, including, but not limited to, fluorocarbons (e.g., chlorofluorocarbons), ammonia, non-halogenated hydrocarbons (e.g., propane), hydrofluorocarbons (e.g., R-A), or any other suitable type of refrigerant.

The HVAC systemcomprises one or more outdoor units. The outdoor unitsmay be also referred to as condensing units. In one embodiment, the outdoor unitcomprises a compressor, an outdoor heat exchanger, and a fan. The compressoris coupled to the working-fluid conduit subsystemthat compresses the working fluid. The outdoor unitmay be configured with a single-stage or multi-stage compressor. A single-stage compressoris configured to operate at a constant speed to increase the pressure of the working fluid to keep the working fluid moving along the working-fluid conduit subsystem. A multi-stage compressormay comprise multiple compressors or a single compressor with multiple internal stages and may be configured to operate at a constant speed to increase the pressure of the working fluid to keep the working fluid moving along the working-fluid conduit subsystem. In this configuration, one or more compressors can be turned on or off to adjust the cooling/heating capacity of the HVAC system. In some embodiments, the compressormay be configured to operate at multiple speeds or as a variable speed compressor. For example, the compressormay be configured to operate at multiple predetermined speeds.

In one embodiment, the outdoor unit(e.g., the compressor) is in signal communication with a controller or thermostatusing a wired or wireless connection. The thermostatis configured to provide commands, instructions, or signals to control the operation of the compressor. For example, the thermostatis configured to send signals to turn on or off one or more compressorswhen the outdoor unitcomprises a multi-stage compressor. In this configuration, the thermostatmay operate the multi-stage compressorsin a first mode where all the compressorsare on and a second mode where at least one of the compressorsis off. In some examples, the thermostatmay be configured to control the speed of the compressor.

The outdoor heat exchangeris configured to assist with moving the working fluid through the working-fluid conduit subsystem. The outdoor heat exchangeris located downstream of the compressorfor exchanging heat. The fanis configured to move airacross the outdoor heat exchanger. For example, the fanmay be configured to blow outside air through the heat exchanger to help cool the working fluid. The compressed, cooled working fluid flows downstream from the outdoor heat exchangerto one or more expansion devices, or metering devices, and subsequently to the indoor unit.

The outdoor unitmay also comprises one or more relaysand one or more contactorsthat are configured to provide power to the compressorand the fanbased on instructions received from the thermostat.

In certain embodiments, the HVAC systemmay be configured to operate in a heat pump heating mode. In such embodiments, the outdoor unitmay further comprise a reversing valvethat is configured to reverse a flow of the working fluid through the working-fluid conduit subsystem. In the heat pump heating mode, the heated working fluid flows downstream from the indoor unitto the one or more expansion devices, and subsequently to the outdoor heat exchanger.

The expansion deviceis configured to remove pressure from the working fluid. The expansion deviceis coupled to the working-fluid conduit subsystemdownstream of the outdoor heat exchanger. The expansion deviceis closely associated with an indoor heat exchanger. The expansion deviceis coupled to the working-fluid conduit subsystemdownstream of the outdoor heat exchangerfor removing pressure from the working fluid. In this way, the working fluid is delivered to the indoor heat exchangerand receives heat from airflowto produce a treated airflowthat is delivered by a duct sub-systemto the desired space, for example, a room in the building.

The indoor unitof the HVAC systemis configured to move air across the indoor heat exchangerand/or a heating unitand out of the duct sub-system. The heating unitmay be also referred to as a supplemental heating unit or an emergency heating unit. The heating unitmay comprise one or more relaysthat are configured to provide power to the heating unitbased on instructions received from the thermostat. The heating unitmay also include one or more heating elements. The heating elementsmay be also referred to as supplemental heating elements.

Return air, which may be air returning from the building, fresh air from outside, or some combination, is pulled into a return ductthrough a filter. A suction side of a variable-speed blowerpulls the return air. The variable-speed blowerdischarges airflowinto a ductfrom where the airflowcrosses the indoor heat exchangeror heating unitto produce the treated airflow.

Examples of a variable-speed blowerinclude, but are not limited to, belt-drive blowers controlled by inverters, direct-drive blowers with electronically commutated motors (ECM), or any other suitable types of blowers. In some configurations, the variable-speed bloweris configured to operate at multiple predetermined fan speeds. In other configurations, the fan speed of the variable-speed blowercan vary dynamically based on a corresponding temperature value instead of relying on using predetermined fan speeds. In other words, the variable-speed blowermay be configured to dynamically adjust its fan speed over a range of fan speeds rather than using a set of predetermined fan speeds. This feature also allows the thermostatto gradually transition the speed of the variable-speed blowerbetween different operating speeds. This contrasts with conventional configurations where a variable-speed bloweris abruptly switched between different predetermined fan speeds. The variable-speed bloweris in signal communication with the thermostatusing any suitable type of wired or wireless connection. The thermostatis configured to provide commands or signals to the variable-speed blowerto control the operation of the variable-speed blower. For example, the thermostatis configured to send signals to the variable-speed blowerto control the fan speed of the variable-speed blower. In some embodiments, the thermostatmay be configured to send other commands or signals to the variable-speed blowerto control any other functionality of the variable-speed blower.

The HVAC systemcomprises one or more sensorsin signal communication with the thermostat. The sensorsmay comprise any suitable type of sensor for measuring the air temperature, relative humidity, pressure, and/or other variables. The sensorsmay be positioned anywhere within a conditioned space (e.g., a room or building) and/or the HVAC system. For example, the HVAC systemmay comprise a sensorpositioned and configured to measure an outdoor air temperature. As another example, the HVAC systemmay comprise a sensorpositioned and configured to measure a supply or treated air temperature and/or a return air temperature. In other examples, the HVAC systemmay comprise sensorspositioned and configured to measure any other suitable type of air temperature, relative humidity, pressure, and/or other variables.

The HVAC systemcomprises one or more thermostats, for example, located within a conditioned space (e.g., a room or building). A thermostatmay be a single-stage thermostat, a multi-stage thermostat, or any suitable type of thermostat as would be appreciated by one of ordinary skill in the art. The thermostatis configured to allow a user (e.g., userof) to input a desired temperature or temperature set point for a designated space or zone such as the room.

is a cross-sectional view of an embodiment of a filterA. In certain embodiments, the filterA may comprise a plurality of pleats. The pleatsincrease an effective surface of the filterA. Each pleatmay have a depth D. In the illustrated embodiments, the filterA is a new filter and is free of dust(see, for example,). In some embodiments when the user device(see) determines that the filteris dirty, the filter(see) may be replaced by the filterA.

is a cross-sectional view of an embodiment of a used filterB. The used filterB may be the filterA after it has been used by the HVAC system(see) for a certain period. Dustmay accumulate on the filterB and may fill the pleats, such that pleatshave a depth D, which is less the depth Dof the filterA (see). In certain embodiments, the used filterB may be used as a reference used filter. In such embodiments, images of the used filterB may be stored in the filter image libraryof the computing system(see). The depth Dmay be also referred to as a depth threshold (e.g., depth thresholdof).

is a cross-sectional view of an embodiment of a used filterC. The used filterC may be the filterA (see) after it has been used by the HVAC system(see) for a certain period. Dustmay accumulate on the filterC and may fill the pleats. In the illustrated embodiment, the used filterC comprises less dustthan the used filterB (see), such that pleatshave a depth D, which is less than the depth Dof the filterA (see) but is greater than the depth Dof the filterB (see). In certain embodiments, the user devicecaptures an image of the used filterC. In embodiments when the used filterB is used as a reference used filter, the image of the used filterC is compared to the image of the used filterB. In response to determining that the depth Dis greater than the depth D, the user deviceclassifies the used filterC as acceptable for further use.

is a cross-sectional view of an embodiment of a used filterD. The used filterD may be the filterA (see) after it has been used by the HVAC system(see) for a certain period. Dustmay accumulate on the filterD and may fill the pleats. In the illustrated embodiment, the used filterD comprises more dustthan the used filterB (see), such that pleatshave a depth Dwhich is less than the depth Dof the filterA (see) and the depth Dof the filterB (see). In certain embodiments, the user devicecaptures an image of the used filterD. In embodiments when the used filterB is used as a reference used filter, the image of the used filterD is compared to the image of the used filterB. In response to determining that the depth Dis less than the depth D, the user deviceclassifies the used filterD as dirty and determines that the used filterD is unacceptable for further use.