Patent Publication Number: US-2019170413-A1

Title: Electrical monitoring of refrigerant circuit

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and the benefit of U.S. Provisional Patent Application No. 62/593,565, entitled “Electrical Monitoring of Refrigerant Circuit,” filed Dec. 1, 2017, which is herein incorporated by reference in its entirety for all purposes. 
    
    
     BACKGROUND 
     The present disclosure relates generally to environmental control systems, and more particularly, to a refrigerant circuit for an HVAC system. 
     Environmental control systems are utilized in residential, commercial, and industrial environments to control environmental properties, such as temperature and humidity, for occupants of the respective environments. The environmental control system may control the environmental properties through control of an airflow delivered to the environment. For example, a heating, ventilating, and air conditioning (HVAC) system routes refrigerant through a circuit to exchange heat with the airflow and ultimately increases or decreases a temperature of the airflow. The circuit may include a compressor, a condenser, a refrigerant, and tubing that connects the components together. In some cases, changes in physical geometry to the tubing may affect the functioning of the refrigerant circuit. 
     SUMMARY 
     In one embodiment, a leak detection system for heating, ventilating, and air conditioning (HVAC) equipment includes a refrigerant circuit, where the refrigerant circuit includes tubing configured to couple components in the refrigerant circuit and where the tubing is configured to enclose a refrigerant flowing throughout the refrigerant circuit. The leak detection system further includes a processor coupled to the tubing of the refrigerant circuit, where the processor is configured to detect a variation in physical geometry of the tubing by comparing the measured electrical property to a baseline measurement. 
     In one embodiment, a system of leak detection for heating, ventilating, and air conditioning (HVAC) equipment includes a broadcaster configured to transmit current across tubing of the HVAC equipment, a receiver configured to receive electric signals indicative of a measured electrical property of the tubing, and a processor configured to analyze the measured electrical property of the tubing by comparing the measured electrical property to a baseline measurement of the electrical property. 
     In one embodiment, a method for detecting a variation in geometry for tubing in a heating, ventilation, and air conditioning (HVAC) system includes transmitting current across tubing, detecting a measured electrical property of the tubing, and comparing the measured electrical property with a threshold value of the electrical property to identify a variation of physical geometry of the tubing. The tubing is configured to transmit a refrigerant therethrough. 
    
    
     
       DRAWINGS 
         FIG. 1  is a schematic of an environmental control for building environmental management that may employ one or more HVAC units, in accordance with an aspect of the present disclosure; 
         FIG. 2  is a perspective view of an embodiment of the environmental control system of  FIG. 1 , in accordance with an aspect of the present disclosure; 
         FIG. 3  is a schematic of a residential heating and cooling system, in accordance with an aspect of the present disclosure; 
         FIG. 4  is a schematic of an embodiment of a vapor compression system that can be used in any of the systems of  FIGS. 1-3 , in accordance with an aspect the present disclosure; 
         FIG. 5  is a schematic of an embodiment of a sensor system coupled to a tubing segment located in a refrigerant circuit in an HVAC unit, in accordance with an aspect of the present disclosure; 
         FIG. 6  is a schematic of the embodiment of a sensor system, in accordance with an aspect of the present disclosure; 
         FIG. 7  is a schematic of the embodiment of a sensor system coupled to a tubing segment containing a deformation or irregularity, in accordance with an aspect of the present disclosure; 
         FIG. 8  is an embodiment of a graph of electrical properties measured by a sensor system, in accordance with an aspect of the present disclosure; 
         FIG. 9  is a perspective view of an embodiment of an electrically isolated component in a refrigerant circuit in an HVAC unit, in accordance with an aspect of the present disclosure; 
         FIG. 10  is a block diagram of an embodiment of a process to calibrate a sensor system to measure electrical properties of a tubing segment, in accordance with an aspect of the present disclosure; and 
         FIG. 11  is a block diagram of an embodiment of a process to measure electrical properties of a tubing segment, in accordance with an aspect of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure is directed to a sensor system for heating, ventilating, and air conditioning (HVAC) systems that direct a refrigerant through a refrigerant circuit. The refrigerant may flow through tubing within the circuit to facilitate heat transfer between an airflow and the refrigerant. The sensor systems disclosed herein are configured to detect deformation or other physical or geometric irregularity of the tubing or other components of the HVAC system. As described in greater detail below, the sensor system is configured to measure electrical properties of a component, such as a heat exchanger coil, in the HVAC system by transmitting a low current at a high frequency across the coil. Electrical properties of the coil may change based on the coil&#39;s configuration, such as a variation in the coil&#39;s physical geometry. Accordingly, the sensor system may detect the change in electrical properties to warn of potential geometric or physical irregularities in the coil. 
     Turning now to the drawings,  FIG. 1  illustrates a heating, ventilating, and air conditioning (HVAC) system for building environmental management that may employ one or more HVAC units. In the illustrated embodiment, a building  10  is air conditioned by a system that includes an HVAC unit  12 . The building  10  may be a commercial structure or a residential structure. As shown, the HVAC unit  12  is disposed on the roof of the building  10 ; however, the HVAC unit  12  may be located in other equipment rooms or areas adjacent the building  10 . The HVAC unit  12  may be a single package unit containing other equipment, such as a blower, integrated air handler, and/or auxiliary heating unit. In other embodiments, the HVAC unit  12  may be part of a split HVAC system, such as the system shown in  FIG. 3 , which includes an outdoor HVAC unit  58  and an indoor HVAC unit  56 . 
     The HVAC unit  12  is an air cooled device that implements a refrigeration cycle to provide conditioned air to the building  10 . Specifically, the HVAC unit  12  may include one or more heat exchangers across which an air flow is passed to condition the air flow before the air flow is supplied to the building. In the illustrated embodiment, the HVAC unit  12  is a rooftop unit (RTU) that conditions a supply air stream, such as environmental air and/or a return air flow from the building  10 . After the HVAC unit  12  conditions the air, the air is supplied to the building  10  via ductwork  14  extending throughout the building  10  from the HVAC unit  12 . For example, the ductwork  14  may extend to various individual floors or other sections of the building  10 . In certain embodiments, the HVAC unit  12  may be a heat pump that provides both heating and cooling to the building with one refrigeration circuit configured to operate in different modes. In other embodiments, the HVAC unit  12  may include one or more refrigeration circuits for cooling an air stream and a furnace for heating the air stream. 
     A control device  16 , one type of which may be a thermostat, may be used to designate the temperature of the conditioned air. The control device  16  also may be used to control the flow of air through the ductwork  14 . For example, the control device  16  may be used to regulate operation of one or more components of the HVAC unit  12  or other components, such as dampers and fans, within the building  10  that may control flow of air through and/or from the ductwork  14 . In some embodiments, other devices may be included in the system, such as pressure and/or temperature transducers or switches that sense the temperatures and pressures of the supply air, return air, and so forth. Moreover, the control device  16  may include computer systems that are integrated with or separate from other building control or monitoring systems, and even systems that are remote from the building  10 . 
       FIG. 2  is a perspective view of an embodiment of the HVAC unit  12 . In the illustrated embodiment, the HVAC unit  12  is a single packaged unit that may include one or more independent refrigeration circuits and components that are tested, charged, wired, piped, and ready for installation. The HVAC unit  12  may provide a variety of heating and/or cooling functions, such as cooling only, heating only, cooling with electric heat, cooling with dehumidification, cooling with gas heat, or cooling with a heat pump. As described above, the HVAC unit  12  may directly cool and/or heat an air stream provided to the building  10  to condition a space in the building  10 . 
     As shown in the illustrated embodiment of  FIG. 2 , a cabinet  24  encloses the HVAC unit  12  and provides structural support and protection to the internal components from environmental and other contaminants. In some embodiments, the cabinet  24  may be constructed of galvanized steel and insulated with aluminum foil faced insulation. Rails  26  may be joined to the bottom perimeter of the cabinet  24  and provide a foundation for the HVAC unit  12 . In certain embodiments, the rails  26  may provide access for a forklift and/or overhead rigging to facilitate installation and/or removal of the HVAC unit  12 . In some embodiments, the rails  26  may fit into “curbs” on the roof to enable the HVAC unit  12  to provide air to the ductwork  14  from the bottom of the HVAC unit  12  while blocking elements such as rain from leaking into the building  10 . 
     The HVAC unit  12  includes heat exchangers  28  and  30  in fluid communication with one or more refrigeration circuits. Tubes within the heat exchangers  28  and  30  may circulate refrigerant through the heat exchangers  28  and  30 . For example, the refrigerant may be R- 410 A. The tubes may be of various types, such as multichannel tubes, conventional copper or aluminum tubing, and so forth. Together, the heat exchangers  28  and  30  may implement a thermal cycle in which the refrigerant undergoes phase changes and/or temperature changes as it flows through the heat exchangers  28  and  30  to produce heated and/or cooled air. For example, the heat exchanger  28  may function as a condenser where heat is released from the refrigerant to ambient air, and the heat exchanger  30  may function as an evaporator where the refrigerant absorbs heat to cool an air stream. In other embodiments, the HVAC unit  12  may operate in a heat pump mode where the roles of the heat exchangers  28  and  30  may be reversed. That is, the heat exchanger  28  may function as an evaporator and the heat exchanger  30  may function as a condenser. In further embodiments, the HVAC unit  12  may include a furnace for heating the air stream that is supplied to the building  10 . While the illustrated embodiment of  FIG. 2  shows the HVAC unit  12  having two of the heat exchangers  28  and  30 , in other embodiments, the HVAC unit  12  may include one heat exchanger or more than two heat exchangers. 
     The heat exchanger  30  is located within a compartment  31  that separates the heat exchanger  30  from the heat exchanger  28 . Fans  32  draw air from the environment through the heat exchanger  28 . Air may be heated and/or cooled as the air flows through the heat exchanger  28  before being released back to the environment surrounding the rooftop unit  12 . A blower assembly  34 , powered by a motor  36 , draws air through the heat exchanger  30  to heat or cool the air. The heated or cooled air may be directed to the building  10  by the ductwork  14 , which may be connected to the HVAC unit  12 . Before flowing through the heat exchanger  30 , the conditioned air flows through one or more filters  38  that may remove particulates and contaminants from the air. In certain embodiments, the filters  38  may be disposed on the air intake side of the heat exchanger  30  to prevent contaminants from contacting the heat exchanger  30 . 
     The HVAC unit  12  also may include other equipment for implementing the thermal cycle. Compressors  42  increase the pressure and temperature of the refrigerant before the refrigerant enters the heat exchanger  28 . The compressors  42  may be any suitable type of compressors, such as scroll compressors, rotary compressors, screw compressors, or reciprocating compressors. In some embodiments, the compressors  42  may include a pair of hermetic direct drive compressors arranged in a dual stage configuration  44 . However, in other embodiments, any number of the compressors  42  may be provided to achieve various stages of heating and/or cooling. As may be appreciated, additional equipment and devices may be included in the HVAC unit  12 , such as a solid-core filter drier, a drain pan, a disconnect switch, an economizer, pressure switches, phase monitors, and humidity sensors, among other things. 
     The HVAC unit  12  may receive power through a terminal block  46 . For example, a high voltage power source may be connected to the terminal block  46  to power the equipment. The operation of the HVAC unit  12  may be governed or regulated by a control board  48 . The control board  48  may include control circuitry connected to a thermostat, sensors, and alarms. One or more of these components may be referred to herein separately or collectively as the control device  16 . The control circuitry may be configured to control operation of the equipment, provide alarms, and monitor safety switches. Wiring  49  may connect the control board  48  and the terminal block  46  to the equipment of the HVAC unit  12 . 
       FIG. 3  illustrates a residential heating and cooling system  50 , also in accordance with present techniques. The residential heating and cooling system  50  may provide heated and cooled air to a residential structure, as well as provide outside air for ventilation and provide improved indoor air quality (IAQ) through devices such as ultraviolet lights and air filters. In the illustrated embodiment, the residential heating and cooling system  50  is a split HVAC system. In general, a residence  52  conditioned by a split HVAC system may include refrigerant conduits  54  that operatively couple the indoor unit  56  to the outdoor unit  58 . The indoor unit  56  may be positioned in a utility room, an attic, a basement, and so forth. The outdoor unit  58  is typically situated adjacent to a side of residence  52  and is covered by a shroud to protect the system components and to prevent leaves and other debris or contaminants from entering the unit. The refrigerant conduits  54  transfer refrigerant between the indoor unit  56  and the outdoor unit  58 , typically transferring primarily liquid refrigerant in one direction and primarily vaporized refrigerant in an opposite direction. 
     When the system shown in  FIG. 3  is operating as an air conditioner, a heat exchanger  60  in the outdoor unit  58  serves as a condenser for re-condensing vaporized refrigerant flowing from the indoor unit  56  to the outdoor unit  58  via one of the refrigerant conduits  54 . In these applications, a heat exchanger  62  of the indoor unit functions as an evaporator. Specifically, the heat exchanger  62  receives liquid refrigerant, which may be expanded by an expansion device, and evaporates the refrigerant before returning it to the outdoor unit  58 . 
     The outdoor unit  58  draws environmental air through the heat exchanger  60  using a fan  64  and expels the air above the outdoor unit  58 . When operating as an air conditioner, the air is heated by the heat exchanger  60  within the outdoor unit  58  and exits the unit at a temperature higher than it entered. The indoor unit  56  includes a blower or fan  66  that directs air through or across the indoor heat exchanger  62 , where the air is cooled when the system is operating in air conditioning mode. Thereafter, the air is passed through ductwork  68  that directs the air to the residence  52 . The overall system operates to maintain a desired temperature as set by a system controller. When the temperature sensed inside the residence  52  is higher than the set point on the thermostat, or the set point plus a small amount, the residential heating and cooling system  50  may become operative to refrigerate additional air for circulation through the residence  52 . When the temperature reaches the set point, or the set point minus a small amount, the residential heating and cooling system  50  may stop the refrigeration cycle temporarily. 
     The residential heating and cooling system  50  may also operate as a heat pump. When operating as a heat pump, the roles of heat exchangers  60  and  62  are reversed. That is, the heat exchanger  60  of the outdoor unit  58  will serve as an evaporator to evaporate refrigerant and thereby cool air entering the outdoor unit  58  as the air passes over outdoor the heat exchanger  60 . The indoor heat exchanger  62  will receive a stream of air blown over it and will heat the air by condensing the refrigerant. 
     In some embodiments, the indoor unit  56  may include a furnace system  70 . For example, the indoor unit  56  may include the furnace system  70  when the residential heating and cooling system  50  is not configured to operate as a heat pump. The furnace system  70  may include a burner assembly and heat exchanger, among other components, inside the indoor unit  56 . Fuel is provided to the burner assembly of the furnace  70  where it is mixed with air and combusted to form combustion products. The combustion products may pass through tubes or piping in a heat exchanger separate from heat exchanger  62 , such that air directed by the blower  66  passes over the tubes or pipes and extracts heat from the combustion products. The heated air may then be routed from the furnace system  70  to the ductwork  68  for heating the residence  52 . 
       FIG. 4  is an embodiment of a vapor compression system  72  that can be used in any of the systems described above. The vapor compression system  72  may circulate a refrigerant through a circuit starting with a compressor  74 . The circuit may also include a condenser  76 , an expansion valve(s) or device(s)  78 , and an evaporator  80 . The vapor compression system  72  may further include a control panel  82  that has an analog to digital (A/D) converter  84 , a microprocessor  86 , a non-volatile memory  88 , and/or an interface board  90 . The control panel  82  and its components may function to regulate operation of the vapor compression system  72  based on feedback from an operator, from sensors of the vapor compression system  72  that detect operating conditions, and so forth. 
     In some embodiments, the vapor compression system  72  may use one or more of a variable speed drive (VSDs)  92 , a motor  94 , the compressor  74 , the condenser  76 , the expansion valve or device  78 , and/or the evaporator  80 . The motor  94  may drive the compressor  74  and may be powered by the variable speed drive (VSD)  92 . The VSD  92  receives alternating current (AC) power having a particular fixed line voltage and fixed line frequency from an AC power source, and provides power having a variable voltage and frequency to the motor  94 . In other embodiments, the motor  94  may be powered directly from an AC or direct current (DC) power source. The motor  94  may include any type of electric motor that can be powered by a VSD or directly from an AC or DC power source, such as a switched reluctance motor, an induction motor, an electronically commutated permanent magnet motor, or another suitable motor. 
     The compressor  74  compresses a refrigerant vapor and delivers the vapor to the condenser  76  through a discharge passage. In some embodiments, the compressor  74  may be a centrifugal compressor. The refrigerant vapor delivered by the compressor  74  to the condenser  76  may transfer heat to a fluid passing across the condenser  76 , such as ambient or environmental air  96 . The refrigerant vapor may condense to a refrigerant liquid in the condenser  76  as a result of thermal heat transfer with the environmental air  96 . The liquid refrigerant from the condenser  76  may flow through the expansion device  78  to the evaporator  80 . 
     The liquid refrigerant delivered to the evaporator  80  may absorb heat from another air stream, such as a supply air stream  98  provided to the building  10  or the residence  52 . For example, the supply air stream  98  may include ambient or environmental air, return air from a building, or a combination of the two. The liquid refrigerant in the evaporator  80  may undergo a phase change from the liquid refrigerant to a refrigerant vapor. In this manner, the evaporator  80  may reduce the temperature of the supply air stream  98  via thermal heat transfer with the refrigerant. Thereafter, the vapor refrigerant exits the evaporator  80  and returns to the compressor  74  by a suction line to complete the cycle. 
     In some embodiments, the vapor compression system  72  may further include a reheat coil in addition to the evaporator  80 . For example, the reheat coil may be positioned downstream of the evaporator relative to the supply air stream  98  and may reheat the supply air stream  98  when the supply air stream  98  is overcooled to remove humidity from the supply air stream  98  before the supply air stream  98  is directed to the building  10  or the residence  52 . 
     It should be appreciated that any of the features described herein may be incorporated with the HVAC unit  12 , the residential heating and cooling system  50 , or other HVAC systems. Additionally, while the features disclosed herein are described in the context of embodiments that directly heat and cool a supply air stream provided to a building or other load, embodiments of the present disclosure may be applicable to other HVAC systems as well. For example, the features described herein may be applied to mechanical cooling systems, free cooling systems, chiller systems, or other heat pump or refrigeration applications. 
     As discussed, embodiments of the present disclosure are directed to the HVAC unit  12  having a system for measuring electrical properties of tubing in a refrigerant circuit of the HVAC unit  12 . For example, a tubing segment in the refrigerant circuit, such as a heat exchanger coil, may be coupled to a system that measures capacitance and resistance of the tubing segment. The system may contain a control board electrically coupled to the tubing segment that sends a high frequency, low current over the surface of the tubing segment. To this end, the tubing segment may be made out of metal or another electrically conductive material to enable the current to travel a length or portion of the tubing segment. In some embodiments, when the current encounters a variation in physical geometry of the tubing, the system may detect a variation in the electronic signals, such an electrical signal deflection, that are sent back to the system. In other embodiments, the system may use the current to measure the values of resistance and/or capacitance of the tubing segment, and these values may vary or change when the current encounters a variation in physical geometry of the tubing segment. The system may output a signal for further actions if the system detects signal deflection beyond a threshold or if the detected capacitance and/or resistance values of the tubing segment are outside of an acceptable or predetermined range of values. The system may detect deformation and/or irregularity in the tubing, such as bending, and, in some embodiments, may detect the location of the deformation and/or irregularity immediately or shortly after the deformation and/or irregularity occurs. Such deformation or irregularity in the tubing segment may decrease the performance of the HVAC unit  12  and/or may lead to further deformation and/or irregularity in other components of the HVAC unit  12 . As a result, the disclosed system for measuring electrical properties may save costs of inspection and maintenance of the refrigerant circuit. 
     For example,  FIG. 5  is a schematic view of an embodiment of a sensor system  100  that may be used with the HVAC unit  12 . In the figure, the sensor system  100  is in electrical communication with tubing segment  102  and measures electrical properties of the tubing segment  102 . The tubing segment  102  is a section in the refrigerant circuit of the HVAC unit  12 , and refrigerant may flow through the tubing segment  102 . For example, the refrigerant in the tubing segment  102  may be in thermal communication with air flowing through the HVAC unit  12 . For purposes of discussion, the tubing segment  102  will be referred as a segment of coil in a heat exchanger, such as an evaporator, but it should be appreciated that the tubing segment  102  may also be located in another component of the refrigerant circuit in the HVAC unit  12 , such as a compressor or condenser. Over time, the tubing segment  102  may experience deformation and/or irregularity due to usage and operation. For example, the coil may undergo thermal stress from fluctuation of temperature of the refrigerant during heat exchange with the air flow. This may cause the tubing segment  102  to expand and contract in diameter, which may eventually result in a variation, such as a permanent variation, in physical geometry of the tubing segment  102 . The variation in physical geometry may result in a change of electrical properties of the tubing segment  102 . The sensor system  100  may detect the change of electrical properties and may be able to output a signal indicating the detection. 
     In order to measure the electrical properties of the tubing segment  102 , the sensor system  100  may transmit a low current across the tubing segment  102 , such as across an outer surface  103  of the tubing segment  102 . In some embodiments, the tubing segment  102  may be a coil, and the sensor system  100  may transmit the current across an entire length of the coil. If there is a variation in physical geometry, a variation in electronic signals may reflect back to the sensor system  100 . In other embodiments, the tubing segment  102  is a section of the coil, and the sensor system  100  may measure electrical property values of that section of coil. The sensor system  100  may transmit the current across the tubing segment  102  and may receive the transmitted current after the current travels across a length of the tubing segment  102 . From the received current, the sensor system  100  may be able to measure electrical properties of the tubing segment  102 . To send and receive the current, the sensor system  100  may be electrically coupled to the tubing segment  102  via electrical connections  104 . The electrical connections  104  may be wires or any other components that allow current to flow between the sensor system  100  and the tubing segment  102 . Furthermore, the tubing segment  102  may be electrically isolated from ground so that the traveling of the current is not interfered. To facilitate conductivity, the tubing segment  102  may be made of material such as a metal, such as copper, a semimetal, another material that may conduct electricity, or any combination of materials thereof. There may also be multiple sensor systems  100  used with the HVAC unit  12 , and each sensor system  100  may be placed at any section of the refrigerant circuit to measure the electrical properties of the respective sections of the refrigerant circuit. For example, in some embodiments, the tubing segment  102  may contain multiple sensor systems  100 , where each sensor system  100  measures a different section of the tubing segment  102 . 
       FIG. 6  is a schematic view of the sensor system  100 , illustrating components of the sensor system  100 . For example, the sensor system  100  may contain a broadcaster  120  and a receiver  122 . The broadcaster  120  may transmit the low current at a high frequency to the tubing segment  102 . The receiver  122  may receive the low current after the current has traveled across the tubing segment  102 . The sensor system  100  may also contain a power source  124  that provides power to the sensor system  100  to function. Further, the sensor system  100  may contain a microprocessor  126  that can execute instructions to measure electrical properties of the tubing segment  102 . In some embodiments, such as if the sensor system  100  measures an entire length of a heat exchanger coil, the microprocessor  126  may be electrically coupled to the tubing and may measure the electrical properties from reflected electronic signals. In other embodiments, such as if the sensor system  100  measures a segment or portion of the coil, the microprocessor  126  may use the current received by the receiver  122  to measure the resistance and/or capacitance values of the segment of the coil and compare to a baseline value. In either case, the microprocessor  126  may detect a variation in physical geometry of the tubing via the measurements. The microprocessor  126  may also adjust the current transmitted by the broadcaster  120  based on the measured electrical properties obtained by the receiver  122 . For example, the microprocessor  126  may adjust the current&#39;s ampere value or the frequency at which the broadcaster  120  transmits the current. The microprocessor&#39;s executable instructions may be stored in a memory  128 . The memory  128  may also store a set of threshold values associated with electrical properties of an unaltered segment of tubing. 
     After measuring the electrical properties, the microprocessor  126  may transmit a signal to an output unit  130 . The output unit  130  may be coupled with a display  132  for displaying the measured electrical properties. For example, the display  132  may show a graph of the measured resistance and/or capacitance of the tubing segment  102  over time. When the measured electrical properties exceed threshold values, thereby indicating a possible variation of physical geometry of the tubing segment  102 , the output unit  130  may create a warning or alarm associated with the change in geometry. For example, the output unit  130  may show an error on the display  132  or the output unit  130  may output an auditory alarm. To determine the threshold values for the electrical properties, the sensor system  100  may first undergo a calibration process. The calibration process obtains measurements of the electrical properties of the tubing segment  102  under normal operations, such as without modified or deformed components. The calibration process may then use the initial measurements to determine a baseline value for normal operation and/or threshold values indicating changes in physical geometry that should be identified by the sensor system  100 . 
       FIG. 7  is a schematic of an embodiment of the sensor system  100  and the tubing segment  102 , illustrating a physical deformation  150  in the tubing segment  102 . As discussed, the tubing segment  102  may undergo thermal stress due to fluctuation in temperature, which may eventually result in a variation of physical geometry of the tubing segment  102 . The variation of physical geometry may lead to a change in an electrical property that is measured by the sensor system  100 . In some embodiments, the variation of physical geometry may increase the deflection of the capacitance and/or resistance of the current. In other embodiments, the variation of physical geometry may change the measured capacitance and/or resistance of the tubing segment  102 . For example, the formation of the physical deformation  150  may increase the measured resistance value of the tubing segment  102 . As will be appreciated, the change in physical geometry, such as the physical deformation  150 , may include an expansion of the diameter, a bend, a twist, any other physical variation, or any combination thereof of the tubing segment  102 . 
       FIG. 8  is a graph  160  of a measurement  170  of an electrical property of the tubing segment  102  over time. The measurement  170  may be associated with a deflection of electrical properties or a measurement of electrical properties after a current has traveled a length of the tubing segment  102 . As discussed above, the electrical property may be resistance or current. A threshold value  172  may depict a maximum acceptable or baseline value of the electrical property to indicate normal operations and normal physical geometry of the tubing segment  102 , as determined by calibration. At t 0 , the measurement  170  may be at a value, such as a baseline value, below the threshold value  172  to indicate normal operations and physical geometry. At t 1 , a physical deformation or irregularity may be forming in the tubing segment  102  and the measurement  170  may begin to increase. Eventually, the measurement  170  may exceed the threshold value  172 , as shown at t 2 , which may indicate a physical geometry deformation that may inhibit the functioning of the HVAC unit  12 . When the measurement  170  exceeds the threshold value  172 , it may lead to a warning, such as a display or an alarm, indicating the variation of physical geometry and prompting attention to the tubing segment  102 , such as maintenance or repair. In some embodiments, the amount that the measurement  170  exceeds the threshold value  172  may result in a different output. For example, the amount exceeded may be utilized to determine the type of variation of physical geometry in the tubing segment  102 , such as a bend or an expansion of diameter, and the output may cause the sensor system  100  to display the suggested type of variation of physical geometry on the display  132 . As such, a more suitable form of maintenance, repair, or other attention to the tubing segment  102  may be prompted. 
       FIG. 9  is a schematic perspective view of a refrigerant circuit component  200  in the HVAC unit  12 . The refrigerant circuit component  200  may be enclosed by a frame  202  that surrounds an entirety of the component  200 . The refrigerant circuit component  200  may be coupled to the sensor system  100  to measure electrical properties of the refrigerant circuit component  200 . In some embodiments, the refrigerant circuit component  200  may be a heat exchanger, and the sensor system  100  may be coupled to a coil of the heat exchanger. In other embodiments, the component  200  may be any other portion of the HVAC unit  12 , such as a compressor, evaporator, condenser, expansion valve, and so forth. 
     In order for the sensor system  100  to transmit and receive current properly and to measure the electrical properties of the refrigerant circuit component  200  accurately, the refrigerant circuit component  200  may be isolated from ground. That is, the refrigerant circuit component  200  may use isolating elements  204  that separate the component  200  from the frame  202 . The isolating elements  204  may be bushings, rubber bumpers, insulations, other components that may electrically isolate the refrigerant circuit component  200  from the frame  202 , or any combination thereof. In this manner, there may not be elements interfering with the electrical circuit that is generated by the sensor system  100  and/or the section of the refrigerant circuit component  200  that is charged with the current supplied by the sensor system  100 . 
       FIG. 10  illustrates an embodiment of a method  210  used by the sensor system  100  to calibrate the measurements of electrical properties of the tubing segment  102  prior to full operation of the sensor system  100 . At block  220 , the sensor system  100  may transmit current at a high frequency across the tubing segment  102 . The tubing segment  102  may be free of deformities or other physical changes that may deviate its electrical properties from values during normal operations. At block  222 , the sensor system  100  may measure the resistance and/or capacitance associated with the tubing segment  102 . In some embodiments, the sensor system  100  may measure based off the deflected signal. In other embodiments, the sensor system  100  may measure based off the current after the current has traveled across a length of the tubing segment  102 . At block  224 , the sensor system  100  may determine a suitable range of resistance and capacitance values based on the measurements taken when the tubing segment  102  remains physically unaltered. 
     At block  226 , the sensor system  100  may set threshold values associated with resistance and/or capacitance values that may indicate a variation of physical geometry of tubing segment  102 . The threshold value may also be selected to prevent or reduce false positives. For example, debris, such as leaves or dirt, contacting the tubing segment  102  may alter the electrical properties of the tubing segment  102  measured by the sensor system  100 . To avoid such a detection being interpreted as a variation in physical geometry of the tubing segment  102 , which could be considered a false positive, the threshold value may be of sufficient magnitude to indicate changes in physical geometry of the tubing segment  102 . For example, the threshold value may be empirically determined and/or associated with a type of physical geometry deformation or irregularity sought to be detected. In some embodiments, the sensor system  100  may perform additional processing to prevent or reduce false positives. In additional embodiments, the sensor system  100  may adjust properties of the transmitted current based at least on the measured electrical properties, such as to modify the current to be able to receive suitable measurements of electrical properties reflecting the configuration of the tubing segment  102 . 
       FIG. 11  illustrates an embodiment of a method  240  used by the sensor system  100  to measure the electrical properties of the tubing segment  102  during normal operation. At block  250 , the sensor system  100  may transmit a high frequency current across the tubing segment  102 . At block  252 , the sensor system  100  may measure the resistance and/or capacitance of the tubing segment  102 . As discussed, the sensor system  100  may detect physical geometry irregularities of the tubing segment  102  based off a deflected signal or the current after it has traveled across a length of tubing segment  102 . In any case, at block  254 , the sensor system  100  may compare the values of the measured resistance and/or capacitance with the threshold values determined by the method  210  described in  FIG. 10 . If the measured values do not exceed the threshold values, the sensor system  100  repeats blocks  250  to  254  to continue to measure the electrical properties of the tubing segment  102 . However, if the measured resistance and capacitance values exceed the threshold values, the sensor system  100  may output a signal as shown at block  256 . The signal may be used to alert that a variation of physical geometry of the tubing segment  102  has occurred. For example, the signal may display a notification or may sound an alarm. Furthermore, in some embodiments, method  210  and  240  may be performed by a processor, such as the microprocessor  126 , which may be attached to or may be a component of the sensor system  100 . 
     As set forth above, embodiments of the sensor system of the present disclosure may provide one or more technical effects useful in the detection of variation of physical geometry of refrigerant or refrigerant circuit components HVAC systems. For example, the sensor system may measure electric properties of the component and detect when the electric properties deviate from values during normal operation. The sensor system may transmit a low current at a high frequency across a tubing segment, such as a heat exchanger coil. In some embodiments, the sensor system monitors an entire length of tubing and detects electric signals reflected back due to a variation in physical geometry of the monitored tubing segment. In other embodiments, the sensor system measures a segment of tubing and detects electric signals after the current has traveled a length of the tubing segment. In any case, the sensor system uses the electric signals to compare measured electric properties with that during normal operations. If the measured electric properties exceed a threshold, the sensor system may perform further action to indicate the detection. Thus, undesired or unintended variations in physical geometry of refrigerant circuit components may be detected. The technical effects and technical problems in the specification are examples and are not limiting. It should be noted that the embodiments described in the specification may have other technical effects and can solve other technical problems. 
     While only certain features and embodiments of the present disclosure have been illustrated and described, many modifications and changes may occur to those skilled in the art, such as variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc., without materially departing from the novel teachings and advantages of the subject matter recited in the claims. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the disclosure. Furthermore, in an effort to provide a concise description of the exemplary embodiments, all features of an actual implementation may not have been described, such as those unrelated to the presently contemplated best mode of carrying out the disclosure, or those unrelated to enabling the claimed subject matter. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation specific decisions may be made. Such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure, without undue experimentation.