Patent Publication Number: US-2019170600-A1

Title: Systems and methods for detecting refrigerant leaks in heating, ventilating, and air conditioning (hvac) systems

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a Non-Provisional application claiming priority to U.S. Provisional Application No. 62/593,597, entitled “SYSTEMS AND METHODS FOR DETERMINING REFRIGERANT LEAKS IN HEATING, VENTILATING, AND AIR CONDITIONING (HVAC) SYSTEMS,” filed Dec. 1, 2017, which is hereby incorporated by reference in its entirety for all purposes. 
    
    
     BACKGROUND 
     The present disclosure relates generally to heating, ventilating, and air conditioning (HVAC) systems, and more particularly to refrigerant leak detection for HVAC systems. 
     A wide range of applications exist for HVAC systems. For example, residential, light commercial, commercial, and industrial HVAC systems are used to control temperatures and air quality in residences and other structures. Certain HVAC units can be dedicated to either heating or cooling, although many HVAC units are capable of performing both functions. In general, HVAC systems operate by implementing a thermal cycle in which a refrigerant undergoes alternating phase changes within a refrigeration circuit to remove heat from or deliver heat to a conditioned interior space of a structure. Similar systems are used for vehicle heating and cooling, and as well as for other types of general refrigeration, such as refrigerators, freezers, and chillers. 
     The refrigerant of a HVAC system may be operated at pressures greater than atmospheric pressure. As such, when a portion of the refrigeration circuit of a HVAC system is damaged, this refrigerant may leak from the refrigeration circuit. Inasmuch as refrigerant leaks compromise system performance or result in increased operating and/or maintenance costs, it is accordingly desirable to provide detection and response systems and methods for the HVAC system to reliably detect and respond to any refrigerant leaks of the HVAC system. 
     SUMMARY 
     The present disclosure relates to a refrigerant leak detection and mitigation system of a heating, ventilating, and air conditioning (HVAC) unit. The refrigerant leak detection and mitigation system includes a controller configured to determine a plurality of parameters correlated to refrigerant leak conditions based on data from a plurality of sensors. The controller is also configured to determine a probability of a refrigerant leak in the HVAC unit based on the plurality of parameters. Additionally, the controller is configured to provide a control signal to modify operation of the HVAC unit in response to comparison of the probability with a threshold value. 
     The present disclosure also relates to a heating, ventilating, and air conditioning (HVAC) system having a condenser, an expansion device, an evaporator, and a compressor fluidly coupled to form a vapor compression system. The HVAC system includes a refrigerant leak detection and mitigation system that includes icing sensors, subcooling sensors, and superheat sensors communicatively coupled to a controller. The controller is configured to determine an amount of icing, an amount of subcooling, and an amount of superheat based on measurements from the icing, subcooling, and superheat sensors, respectively. The controller is also configured to determine a probability of a refrigerant leak in the vapor compression system based on at least two of the determined amount of icing, subcooling, and superheat. Furthermore, the controller is configured to provide a control signal to modify operation of the HVAC system in response to results of comparing the probability to a threshold value. 
     The present disclosure further relates to a heating, ventilating, and air conditioning (HVAC) system having a condenser, an expansion device, an evaporator, and a compressor fluidly coupled to form a vapor compression system. The HVAC system includes a refrigerant leak detection and mitigation system that includes icing sensors, subcooling sensors, and superheat sensors communicatively coupled to a controller. The controller is configured to determine an amount of icing, an amount of subcooling, and an amount of superheat based on measurements from the icing, subcooling, and superheat sensors, respectively. The controller is also configured to determine a probability of a refrigerant leak in the vapor compression system based on the determined amount of icing, subcooling, and superheat. Furthermore, the controller is configured to provide a control signal to modify operation of the HVAC system in response to results of comparing the probability to a threshold value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view a commercial heating, ventilating, and air conditioning (HVAC) system for building environmental management, in accordance with embodiments described herein; 
         FIG. 2  is a perspective view of a single package HVAC unit of the HVAC system illustrated in  FIG. 1 , in accordance with embodiments described herein; 
         FIG. 3  is a perspective view of a residential HVAC system, in accordance with embodiments described herein; 
         FIG. 4  is a schematic diagram of a vapor compression system that may be used in the commercial HVAC system of  FIG. 1  and the residential HVAC system of  FIG. 3 , in accordance with embodiments described herein; 
         FIG. 5  is a schematic diagram of the single package HVAC unit of  FIG. 2 , in accordance with embodiments described herein; 
         FIG. 6  is a flow diagram of a process for determining whether a refrigerant leak exists in the HVAC system and controlling the HVAC system based on such a determination, in accordance with embodiments described herein; and 
         FIG. 7  is a flow diagram of a process for monitoring signals from sensors of the HVAC system over time to determine whether a refrigerant leak exists or predict whether a refrigerant leak will exist at a future time, in accordance with embodiments described herein. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure is generally directed to a refrigerant leak detection and management system that is capable of detecting and addressing refrigerant leaks in a vapor compression system, such as a vapor compression system of an HVAC system. As set forth below, the disclosed system includes a number of sensors that monitor particular conditions or parameters of the vapor compression system that are presently recognized to be correlated to indirect indications of a refrigerant leak. As discussed, these conditions or parameters include: whether icing is occurring on an evaporator of the vapor compression system, whether subcooling is insufficient or not occurring in the vapor compression system, and whether an undesirable amount of superheat is present in the vapor compression system. The disclosed system includes a controller capable of determining the probability that a refrigerant leak exists, or will exist at a future time, based on each of the monitored conditions of the vapor compression system. When the probability of a refrigerant leak exceeds one or more predetermined threshold values, the controller may modify operation of the HVAC system to mitigate the refrigerant leak. For instance, the controller may send signals to open a damper or activate a fan of the HVAC system to dissipate leaked refrigerant from the HVAC system. Accordingly, the presently disclosed system effectively determines or predicts whether a refrigerant leak exists, or will exist at a future time, without directly detecting the leaked refrigerant itself. In this manner, the disclosed techniques enable indirect detection of refrigerant leaks within the HVAC system, and further enables response via any combination of suitable control actions that address the leaked refrigerant. 
     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 package 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 (for example, R-410A, steam, or water) through the heat exchangers  28  and  30 . 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 being 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, not shown) 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 (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 (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 (that is, 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 . Each of the illustrated components, such as the microprocessor or processor  86 , may be representative of multiple such components. 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 above, the HVAC unit  12  includes refrigerant that is used to condition air before the conditioned air is sent to a conditioned space, such as a conditioned interior space of building  10 . In certain embodiments, the refrigerant may include R-32, R-452B, R-134A, R-447A, R-455A, R-32, R-1234ze, R-1234yf, R-454A, R-454C, or R-454B, or any other suitable refrigerant. Under certain circumstances, the refrigerant may inadvertently leak from a component or a flow path of the vapor compression system  72 , also referred to herein as the refrigeration circuit, due to wear or damage to components, or faulty joints or connections within the circuit. The present techniques enable the HVAC system to reliably detect and manage the leak of refrigerant from the vapor compression circuit. The present techniques also enable the HVAC system to reliably predict the occurrence of a refrigerant leak. 
     As discussed below with respect to  FIG. 5 , a processor of a controller, such as processor  86  control panel  78 , may utilize a profile stored in memory  88 , or stored in an accessible remote electronic device, to determine whether a refrigerant leak exists or predict whether a future refrigerant leak will exist. In response, the processor  86  may perform various control actions to mitigate the refrigerant leak. In certain embodiments, a probability or likelihood of a refrigerant leak existing may be determined, and various control actions may be performed based on the probability of the refrigerant leak existing. While the discussion herein relates to the HVAC unit  12 , it should be noted that different types of HVAC units or systems may be used instead. That is, the discussion above it not limited to single package HVAC units and/or commercial or industrial HVAC systems, such as those illustrated in  FIGS. 1 and 2 . For example, the techniques discussed herein may be implemented in the residential heating and cooling system  50  of  FIG. 3 . 
     With the foregoing discussion in mind,  FIG. 5  is a schematic diagram of an embodiment of the HVAC unit  12  that includes a refrigerant leak detection and mitigation system  99 , in accordance with the present technique. As illustrated and discussed above, the HVAC unit  12  includes the vapor compression system  72 , as well as the control panel  82  that controls operation of the HVAC unit  12 . More specifically, processor  86  of the control panel  82  may execute instructions stored on the memory  88  to control the HVAC unit  12 . In certain embodiments, the memory  88  stores a profile  100  that includes information, such as instructions or data, for determining a probability of a refrigerant leak existing, as well as information relating to control actions to be performed based on the determined probability of a refrigerant leak existing. 
     The embodiment of the refrigerant leak detection and mitigation system  99  illustrated in  FIG. 5  includes one or more sensors  102  positioned on or about various components of the vapor compression system  72 . The sensors  102  are communicatively coupled to the processor  86  of the control panel  82 , and the processor  86  may execute instructions to receive one or more signals from the sensors  102 . The signals may include data signals and measurement signals. The sensors  102  may collect data regarding various characteristics of the vapor compression system  72 , including data regarding particular components of the vapor compression system  72  and/or the data regarding refrigerant at particular points in the vapor compression system  72 . 
     Certain sensors  102  of the embodiment of the refrigerant leak detection and mitigation system  99  illustrated in  FIG. 5  may be used to determine whether ice, such as water ice from moisture in the air, is forming at the surface of the evaporator  80 . That is, as mentioned, it is presently recognized that evaporator icing is a vapor compression system condition that may occur as the result of a refrigeration leak. As such, one or more sensors  102  of the refrigerant leak detection and mitigation system  99  may be used to indirectly or directly measure indications of evaporator icing. 
     For example, in the embodiment illustrated in  FIG. 5 , a temperature sensor  102 A and a pressure sensor  102 B are positioned at a refrigerant outlet  103  of the evaporator  80 , which may be used by the processor  86  to indirectly determine a probability the evaporator icing is occurring or will occur in the near future. The temperature sensor  102 A sends signals to the processor  86  indicating a temperature of refrigerant exiting the evaporator  80 . Similarly, the pressure sensor  102 B sends signals to the processor  86  indicating a pressure of the refrigerant leaving the evaporator  80 . Using the respective signals from sensor  102 A and  102 B, the processor  86  determines a temperature and pressure of refrigerant exiting the evaporator  80 . In some embodiments, a single sensor may be used to collect data regarding the temperature and pressure of refrigerant exiting evaporator  80 . For instance, the sensor may be a combination pressure and temperature sensor. 
     As such, in certain embodiments, based on the determined temperature and pressure of refrigerant exiting the evaporator  80 , the processor  86  may determine a probability that evaporator icing has occurred, is occurring, or will occur in the near future. For example, the processor  86  may determine the probability of evaporator icing by utilizing a look-up table stored in the memory  88  that defines a relationship between the probability of icing and the temperature and/or pressure of the refrigerant at the outlet  103  of the evaporator  80 . The look-up table may be based on physical properties of the refrigerant, such as a saturation point or quantity of the refrigerant. Additionally, the data contained in the look-up table may be experimentally determined by simulating refrigerant leaks in the vapor compression system  72  while monitoring the temperature and/or pressure of the refrigerant at the outlet  103  of the evaporator  80  and visually inspecting for evaporator icing. 
     Additionally or alternatively, other types of sensors  102  may be used to directly detect or measure evaporator icing, in certain embodiments. For example, the embodiment of the refrigerant leak detection and mitigation system  99  illustrated in  FIG. 5  includes an ice sensor  102 C that directly detects and/or measures a level of evaporator icing. The ice sensor  102 C is communicatively coupled to the processor  86  of the control panel  82  and sends signals to the processor  86  regarding icing of the evaporator  80 . For example, the sensor  102 C may be disposed on the outer surface of the evaporator  80  or on a coil of the evaporator  80  provide signals indicating that ice is present and/or a relative amount of ice that is present. Based on signals from the sensor  102 C, the processor  86  may determine the degree of icing occurring on the evaporator  80 . That is, the sensor  102 C may not only detect the presence of ice, but also detect an amount of ice formed at the surface of the evaporator. In some embodiments, the sensor  102 C may not be included. In such embodiments, the processor  86  may determine a probability of ice being present on the evaporator based on pressure sensed via the pressure sensor  102 B and/or temperature measurements obtained via the temperature sensor  102 A. 
     Certain sensors  102  of the embodiment of the refrigerant leak detection and mitigation system  99  illustrated in  FIG. 5  may be used to determine whether subcooling within the vapor compression system  72  has diminished or disappeared. Subcooling refers to a degree or an amount that a liquid refrigerant temperature is below the boiling point of the refrigerant. It is presently recognized that a loss of subcooling is a vapor compression system condition that may occur as the result of a refrigeration leak. As such, one or more sensors  102  of the refrigerant leak detection and mitigation system  99  may be used to indirectly or directly measure indications of subcooling loss. 
     For example, the embodiment of the refrigerant leak detection and mitigation system  99  illustrated in  FIG. 5  includes a temperature sensor  102 D disposed downstream from the condenser  76  in the vapor compression system  72 . More specifically, for the illustrated embodiment, the temperature sensor  102 D is located at an outlet  104  of the condenser  76  to measure the temperature of refrigerant exiting the condenser  76 . The sensor  102 D is communicatively coupled to the processor  86  and sends signals to the processor  86  indicative of the temperature of the refrigerant. In some embodiments, the sensor  102 D may also detect a pressure of the refrigerant exiting the condenser  76 . Also, the sensor  102 D may be disposed in any suitable location between the condenser  76  and the expansion valve  78 . 
     Based on the signals received from the sensor  102 D, the processor  86  calculates subcooling of the refrigerant in the vapor compression system  72 . The processor  86  may determine whether subcooling is occurring and/or a degree of subcooling by utilizing a look-up table stored in the memory  88  that defines a relationship between a degree or amount of subcooling and the temperature and/or pressure of the refrigerant at the outlet  104  of the condenser  76 . The look-up table may be based on physical properties of the refrigerant, such as a boiling point of the refrigerant. As another example, the processor  86  may determine subcooling exists when a temperature of the refrigerant is below the boiling point of the refrigerant, and the processor  86  may determine an amount of subcooling by determining the extent to which the temperature of the refrigerant is below the boiling point of the refrigerant. Similar to icing of the evaporator  80 , the processor  86  may also be able to determine a probability of subcooling occurring or not occurring, or predict whether the subcooling will decrease in the near future. Such a determination may be made based on subcooling trends over time. 
     Certain sensors  102  of the embodiment of the refrigerant leak detection and mitigation system  99  illustrated in  FIG. 5  may be used to determine whether superheat within the vapor compression system  72  has increased. Superheat generally refers to a degree or amount that the temperature of refrigerant vapor is above a saturation temperature of the refrigerant at a particular pressure. Moreover, superheat may include discharge superheat and/or suction superheat. Discharge superheat generally refers to superheat that is determined based on measurements of the refrigerant downstream of the compressor  74 , while suction superheat generally refers to superheat that is determined based on measurements of the refrigerant upstream of the compressor  74 . As mentioned, it is presently recognized that an increase in superheat is a vapor compression system condition that may occur as the result of a refrigeration leak. As such, one or more sensors  102  of the refrigerant leak detection and mitigation system  99  may be used to indirectly or directly measure indications of increasing superheat. 
     For example, the embodiment of the refrigerant leak detection and mitigation system  99  illustrated in  FIG. 5  includes a combined pressure and temperature sensor  102 E disposed downstream from the compressor  74  in the vapor compression system  72 . More specifically, for the illustrated embodiment, the sensor  102 E is located at the outlet  105  of the compressor  74  to measure the temperature and pressure of refrigerant as the refrigerant exits the compressor  74 . In other embodiments, the sensor  102 E may be disposed in any suitable location between the compressor  74  and the condenser  76 , at the outlet  105  of the compressor  74 , or at the inlet  106  of the condenser  76 . 
     The sensor  102 E is communicatively coupled to the processor  86  and sends signals to the processor  86  regarding a temperature and pressure of the refrigerant exiting the compressor  74 . Based on the signals from the sensor  102 E, the processor  86  determines a discharge superheat of refrigerant exiting the compressor  74 . For instance, the processor  86  may determine the discharge superheat by utilizing a look-up table stored in the memory  88  that defines a relationship between an amount or degree of discharge superheat and the temperature and pressure of the refrigerant at the outlet  105  of the compressor  74 . The look-up table may be based on physical properties of the refrigerant, such as a saturation point and/or quantity of the refrigerant. 
     In other embodiments, the refrigerant leak detection and mitigation system  99  may include a sensor  102 F disposed upstream of the compressor  74  in alternative to, or in addition to, the sensor  102 E. The sensor  102 F may measure the temperature and pressure of refrigerant as the refrigerant enters an inlet of the compressor  74  and send corresponding signals to the processor  86 . Based on these signals, the processor  86  may determine the suction superheat, for example, using a look-up table that defines a relationship between an amount or degree of suction superheat and the temperature and pressure of the refrigerant as the refrigerant enters the compressor  74 . 
     Additionally, certain embodiments of the refrigerant leak detection and mitigation system  99  may include additional sensors  102  that measure other properties and conditions of the HVAC unit  12  or the surrounding environment. For example, the embodiment of the refrigerant leak detection and mitigation system  99  illustrated in  FIG. 5  includes temperature sensors  102 G and  102 H that are suitably positioned to measure different air temperatures that may be used in one or more of the determinations of one or more of the conditions of the vapor compression system  72  set forth above. The sensors  102 G and  102 H are communicatively coupled to the processor  86  of the control panel  82  and send signals to the processor  86  to indicate air temperatures at different locations. More specifically, the sensor  102 G sends signals indicative of a temperature of environmental air  96 , while the sensor  102 H sends signals indicative of an air temperature within the HVAC unit  12 , proximate to the vapor compression system  72 . While the sensors  102 A,  102 B,  102 C,  102 D,  102 E,  102 F,  102 G, and  102 H are described in detail, any suitable sensors that detect operating conditions of the vapor compression system  72  relevant to refrigerant leakage may be used, in accordance with the present disclosure. 
     As described above, the processor  86  may determine or predict the presence of various conditions of the vapor compression system  72  based on data received from the sensors  102 . As discussed, these vapor compression system conditions include icing of the evaporator  80 , decreasing subcooling, and increasing superheat. The processor  86  may determine a probability that a refrigerant leak exists based on these conditions. More specifically, the processor  86  may weight each of these conditions based on the profile  100 , which may be stored in the memory  88  of the control panel  82 , or stored on another electronic device communicatively coupled to the control panel  82 . Additionally, each of these conditions may be assigned a factor of severity. For example, Equation 1 below presents one possible manner of determining a probability of a leak existing in accordance with embodiments of the present disclosure. 
         P   leak   =aF   icing   +bF   subcooling   +cF   superheat    Equation 1
 
     where: P leak  is the probability of a leak existing; a, b, and c are weighting coefficients that sum to one and are each greater than zero; F icing  is an icing factor that corresponds to the probability of icing being present on the evaporator  80  and has a value ranging from zero to one; F subcooling  is a subcooling factor indicative of a degree of subcooling and has a value ranging from zero to one, wherein the lower the value of F subcooling , the more subcooling present; and F superheat  is a superheat factor that has a value ranging from zero to one, where the higher the value of F superheat , the greater the amount of superheat. 
     The processor  86  may determine the icing factor (F icing ) by determining a probability of icing on the evaporator  80 , as described above. For instance, the processor  86  may determine the probability of the icing based on signals from the sensors  102 A,  102 B, and  102 C. A formula for determining the probability of icing may be stored on the memory  88  and implemented by the processor  86 . 
     The processor  86  may determine the subcooling factor (F subcooling ) based on signals from the sensor  102 D. For instance, an amount or degree of subcooling may be determined based on pressure and temperature data collected via the sensor  102 D, as discussed above. The processor  86  may determine the subcooling factor by referencing the amount of subcooling to a look-up table included in the profile  100  or otherwise stored on the memory  88 . Because the subcooling factor is ultimately tied into the probability of a refrigerant leak being present, higher amounts of subcooling correspond to lower values of the subcooling factor. That is, the greater the amount of subcooling present, the lower the probability of a refrigerant leak being present. 
     Additionally, the subcooling factor (F subcooling ) may be determined partially based on an air temperature sensed by sensor  102 G or  102 H. For example, at higher air temperatures, the degree of subcooling in the vapor compression system  72  may decrease without a refrigerant leak being present. Additionally, the HVAC unit  12  continues to supply conditioned air to a conditioned space, such as building  10 , even though the amount of subcooling is relatively lower at the higher outdoor temperature. A look-up table, such as the look-up table described above, may be accessed by the processor  86  to determine the subcooling factor based on an air temperature in conjunction with a temperature and/or pressure of the refrigerant between the condenser  76  and the expansion valve  78 . 
     The processor  86  may also determine the superheat factor (F superheat ) based on signals from the sensor  102 E. As described above, the processor  86  may determine an amount or degree of superheat value based on temperature and pressure data received via the sensor  102 E. The processor  86  may determine the superheat factor by comparing the amount of superheat with a look-up table included within the profile  100  or stored on the memory  88 . A relatively high superheat compared to typical operation of the HVAC unit  12  would result in a higher value for the superheat factor. That is, the greater the amount of superheat present, the greater the probability of a refrigerant leak being present. 
     As described above, in certain embodiments, the sensor  102 F that measures refrigerant flowing into the compressor  74  may collect data that the processor  86  can use to determine suction superheat. For instance, the processor  86  may determine the superheat factor by comparing the amount of suction superheat, as determined based on data from the sensor  102 F, with a look-up table included within the profile  100  or stored on the memory  88 . In other words, the superheat factor (F superheat ) may be determined by the processor  86  based on an amount of discharge superheat, an amount of suction superheat, or a combination thereof. 
     The subcooling factor and superheat factor may be determined in some cases by comparing the determined amounts of subcooling and superheat to respective predetermined threshold values. For example, due to the inverse relationship between subcooling and refrigerant leaks, when the amount of subcooling is above a predetermined threshold value, the subcooling factor (F subcooling ) may be assigned a zero or a near-zero value. That is, when the refrigerant is cooled to a temperature lower than the boiling point of the refrigerant and below the predetermined threshold value, the subcooling factor may be assigned a zero or a near-zero value. Similarly, when the amount of superheat is below a predetermined threshold value, the superheat factor (F superheat ) may be assigned a zero or a near-zero value. 
     The processor  86  may determine a refrigerant leak exists when the probability of a refrigerant leak is greater than a predetermined threshold value. For example, the predetermined threshold value may be a value stored on the memory  88 . When the processor  86  determines that the predetermined threshold value has been exceeded, the processor  86  may send one or more signals to change one or more operations of the HVAC unit  12 . For example, the processor  86  may send a signal to adjust a damper  107  to change an amount of environmental air  96  that enters the HVAC unit  12 . As another example, the processor  86  may send a signal to a motor  108  that drives a supply fan  109  to operate at a different speed, such as a faster speed. That is, the processor  86  may send a signal to alter an amount of supply air  98  that is delivered to the building  10 . For example, in certain embodiments, the supply fan  109  may be a variable speed fan that is operated at a speed proportional to the determined probability of a refrigerant leak existing. That is, the higher the probability of a refrigerant leak being present, the faster the supply fan  109  is operated, and thus, the more supply air  98  delivered to the building  10 . As yet another example, the refrigerant may be pumped by the compressor  74  into a particular portion of the vapor compression system  72  to reduce a potential for continued refrigerant leakage within a certain portion of the HVAC system or building  10 . For instance, the refrigerant may be pumped into a portion of the vapor compression system  72  that is located within the outdoor HVAC unit  58  of  FIG. 3  to reduce a risk of refrigerant leakage within the indoor unit  56  of  FIG. 3 . 
     In addition to the actions described above, the processor  86  may send a signal to activate an alarm system in the building  10  and/or otherwise indicate that a refrigerant leak is present. For instance, the processor  86  may be send signals to a transceiver  110  that can transmit data to, and receive data from, a network  112 . Via the network  112 , the processor  86  may send signals to cause notifications and/or alarms on other electronic devices  114 , which may include computers, tablets, phones, or other electronic devices. For example, the electronic devices  114  may receive emails, phone calls, text messages, or other forms of notifications based on signals sent from the processor  86 . 
     With the foregoing in mind, it should be noted that Equation 1 is provided as an example of an equation that may be used to determine a probability of a refrigerant leak. However, whether a refrigerant leak exists may be determined by the processor  86  by utilizing an algorithm that includes other equations and/or limitations other than Equation 1. For example, when certain conditions are met, the processor  86  may determine that a refrigerant leak exists even though the probability of a leak existing may not surpass a predetermined threshold value. For instance, predetermined threshold values may be associated with the icing factor, the subcooling factor, and the superheat factor. When one or more of those predetermined threshold values are surpassed, the processor  86  may send one or more signals to change one or more operations of the HVAC unit  12  and/or activate an alarm, as described above. 
     As another example, the probability of a refrigerant leak existing may be determined based on two of icing, subcooling, and superheat. For example, an equation similar to Equation 1 that only includes two of the icing factor, subcooling factor, and superheat factor and the two respective weighting coefficients—that is, two of a, b, and c—may be used to determine the probability of a leak. In such a case, the processor  86  may compare the probability to a threshold value, as described above, to determine whether a leak exists. 
     Additionally, the processor  86  may monitor data from the sensors  102  over time and send signals to alter operation of the HVAC unit  12  and/or cause notification actions to be taken based on the changes in the conditions of the vapor compression system  72  over time. For example, at one time, the processor  86  may determine, based on data from the sensors  102 , that the probability of a refrigerant leak has a first value, and send signals to open the damper  107  and/or adjust the speed of the motor  108 . At a second time, the processor  86  may receive signals from the sensors  102  and determine that the probability of a refrigerant leak then has a second, higher value, indicating an increase in the probability of a refrigerant leak. In response to the higher or increasing probability, the processor  86  may send signals to further adjust the operation of the HVAC unit, enabling a variable response to the refrigeration leak according to leak severity. Other escalating response actions may include further opening the damper  107  and/or operating the motor  108  at an even faster speed to drive more supply air  98  into the building  10 . Furthermore, an alarm may grow in intensity in response to higher refrigerant leak probabilities. For instance, an alarm may increase in volume or brightness. Additionally, notifications may be sent at a higher rate or the type of notification may change. For example, for one probability, an email may be sent, whereas for another probability, a text message may be sent or an automated phone call may be placed in addition, or in the alternative, to the email. In other words, the processor  86  may cause changes in operation that correspond to a particular probability value. However, it in some cases, no action may be taken by the processor  86  until the probability of a refrigerant leak exceeds a predetermined threshold value. 
     The processor  86  receives data from the sensors  102  over time and sends signals to perform various actions when the probability of a refrigerant leak existing increases towards a predetermined threshold value. In other words, the processor  86  may monitor changes in the probability of a refrigerant leak existing and determine whether the changes are indicative of the predetermined threshold value being exceeded at a future time. The closer the probability becomes to the predetermined threshold value, such as a predetermined tolerance of the threshold value, the greater the amount or degree of response of the processor  86  may become. For instance, as described above, the supply fan  109  may be operated at faster speeds and/or the damper  107  may be opened to further extents. However, in certain embodiments, when the predetermined threshold value is exceeded, the processor  86  sends a signal to stop operation of the HVAC unit  12  and/or pump the refrigerant into a specific portion of the vapor compression system  72 . Additionally, upon recognizing that a predetermined threshold value is being approached or likely to be exceeded, the processor  86  may send signals to notify a person of such a determination. For instance, as described above, a notification may be sent in the form of an email or text message, among other suitable methods. 
     Alternatively, a series of predetermined threshold values may be used. For example, several predetermined threshold values relating to a probability of a refrigerant leak may be stored in the profile  100  or memory  88 , and each predetermined threshold value may be associated with an action to be performed in response to the probability exceeding a respective predetermined threshold value. For instance, a first predetermined threshold value may correspond to a first probability value. When the first predetermined threshold value is exceeded, the processor  86  may send a signal to open the damper  107  to a partially opened position and/or modify a speed of the supply fan  109 . A second predetermined threshold value corresponds to a higher probability than the first predetermined threshold value. When the second predetermined threshold value is exceeded, the processor  86  may send signal to open the damper  107  to a position that is more open than the position associated with the first predetermined threshold value. Additionally, the processor  86  may send a signal for the supply fan  109  to operate at a speed that is faster than the speed associated with the first predetermined threshold value. In other words, as predetermined threshold values associated with higher probabilities of a refrigerant leak being present are surpassed, the processor  86  may send signals to alter operation of the HVAC unit to a greater degree. 
     Furthermore, each of the predetermined threshold values and look-up tables discussed above may be determined experimentally via a test HVAC unit substantially similar to the HVAC unit  12 . Using this test HVAC unit, experiments are performed in which leaks are intentionally generated, and resulting conditions of the vapor compression system are monitored via sensors similar to the sensors  102  to determine values stored in the look-up tables, as well as particular threshold values. More specifically, predetermined threshold values may be based on experimental simulations of the HVAC unit  12  that determine vapor compression system conditions and expected HVAC parameters, such as particular pressures, temperatures, and ice levels in the vapor compression system  72 , when refrigerant leaks occur in different portions of the vapor compression system  72 . Moreover, the coefficients a, b, and c of Equation 1 may be determined based on similar experimentation. 
     Keeping the discussion of  FIG. 5  in mind,  FIG. 6  is a flow diagram of an embodiment of a process  150  whereby the refrigerant leak detection and mitigation system  99  of the HVAC unit  12  determines whether a refrigerant leak is present in the vapor compression system  72  and controls operation of the HVAC unit  12  based on such a determination. The process  150  may be performed by the processor  86  by executing instructions stored on the memory  88 , or other suitable processing circuitry, in accordance with the present disclosure. 
     At block  152 , the processor  86  receives signals from sensors  102  of the refrigerant leak detection and mitigation system  99  of the HVAC unit  12 . As described above, the sensors  102  may include sensors  102  that send signals regarding pressures and temperatures of refrigerant at various portions of the vapor compression system  72 . Additionally, the sensors  102  may include sensor  102 C that can detect the presence or amount of ice on the evaporator  80 . The sensors  102  may also include sensors  102 G,  102 H that can measure different air temperatures, as discussed above. 
     At block  154 , the processor  86  determines the icing factor, subcooling factor, and superheat factor based on the signals received from the sensors  102 . For example, as described above, the icing factor may be based on signals received from sensors  102 A,  102 B, and  102 C. The subcooling factor may be determined based signals from the sensor  102 D, alone or in combination with signals from one or both of the sensors  102 G and  102 H. Additionally, the superheat factor may be determined based on a signal received from the sensor  102 E and/or the sensor  102 F. Each of these factors corresponds to a probability of a refrigerant leak being present. In other words, the higher the value of a given factor, the higher the probability or likelihood that a refrigerant leak is present. 
     At block  156 , the processor  86  determines a refrigerant leak probability. That is, the processor  86  may determine how likely it is that a refrigerant leak exists. As explained above in relation to Equation 1, in certain embodiments, the probability of a refrigerant leak existing may be determined based on the value of the icing factor, subcooling factor, and superheat factor. 
     Each of the icing factor, subcooling factor, and superheat factor may be associated with respective predetermined threshold values. The predetermined threshold values may be stored as part of the profile  100  or elsewhere on the memory  88 . At block  158 , the processor  86  may determine whether the icing factor exceeds an icing factor threshold value. When icing factor exceeds the icing factor threshold value, the processor  86  sends a signal to change operation of the HVAC system, as indicated in block  160 . For example, as described above, the processor  86  may send a signal to cause damper  107  to open or close to a certain position. The processor  86  may also send a signal to change a speed at which the supply fan  109  sends air to the building  10 . 
     However, if the processor  86  determines that the icing factor does not exceed the icing factor threshold value, the processor  86  determines whether the subcooling factor exceeds a subcooling factor threshold value, as indicated in block  162 . If the processor  86  determines that the subcooling factor exceeds the subcooling factor threshold value, the processor  86  may send a signal to alter operation of the HVAC system, as indicated in block  160 . However, when the processor  86  determines that the subcooling factor does not exceed the subcooling factor threshold value, the processor  86  may determine whether the superheat factor exceeds a superheat threshold value, as indicated in block  164 . When the superheat threshold value is exceeded, the processor  86  sends a signal to change operation of the HVAC system, as described above with relation to block  160 . 
     When the processor  86  determines that the superheat does not exceed the superheat threshold value, the processor  86  determines whether the refrigerant leak probability exceeds a threshold associated with the refrigerant leak probability, as indicated in block  166 . Such a threshold value may also be stored as part of the profile  100  or included within the memory  88 . When the refrigerant leak probability exceeds the threshold value, the processor  86  sends a signal to alter operation of the HVAC system, as indicated in block  160 . However, when the processor  86  determines that the refrigerant leak probability does not exceed the threshold value, the processor  86  may proceed back to block  152 , as illustrated, to continue to receive signals from the sensors  102 . 
     In other embodiments of the process  150  may include other steps. For example, in addition to determining whether the icing factor, subcooling factor, and superheat factor each exceed predetermined threshold values, the processor  86  may determine whether a combination of any two of the icing factor, subcooling factor, and superheat factor exceeds a predetermined threshold value associated with such a combination. As with the other predetermined threshold values, threshold values associated with a combination of two of the icing factor, subcooling factor, and superheat factor may be stored on the memory  88  or included in the profile  100 . 
     The processor  86  of the refrigerant leak detection and mitigation system  99  may also monitor signals from the sensors  102  over time and make determinations based on those signals.  FIG. 7  is a flow diagram of an embodiment of a process  200  whereby the refrigerant leak detection and mitigation system  99  may monitor signals from sensors  102  over time to determine whether a refrigerant leak exists or may exist at a future time. The process  200  may be performed by the processor  86  by executing instructions stored in the memory  88 , or other suitable memory circuitry, in accordance with the present disclosure. 
     For the illustrated embodiment of the process  200 , the processor  86  receives a first set of signals from sensors  102  at a first time, as indicated in block  202 . As discussed above, the sensors  102  may collect data regarding conditions of the vapor compression system  72 , such as temperatures and pressures of a refrigerant at various portions of the vapor compression system  72 . The sensors  102  may also collect data regarding icing of the evaporator  80  and/or air temperatures. Subsequently, the processor  86  may determine a probability of a refrigerant leak existing based on the first set of signals, as indicated in block  204 . In certain embodiments, the probability may be determined as described above. 
     Continuing thought the illustrated process  200 , the processor  86  determines whether the probability exceeds a first threshold value, as indicated in block  206 . The first threshold value, as well as the other threshold values described below in relation to the process  200 , may be stored in the memory  88 . When the processor  86  determines that the probability does not exceed the first threshold value, the processor  86  receives a second set of signals from the sensors  102  at a second time that occurs after the first time, as indicated in block  208 . 
     However, the processor  86  determines that the probability exceeds the first threshold value, the processor  86  determines whether the probability exceeds a second threshold value that corresponds to a value that is greater than the first threshold value, as indicated in block  210 . If the processor  86  determines that the probability does not exceed the second threshold value, then the processor  86  sends a signal to change an operation of the HVAC system in a manner that is associated with the first threshold value being exceeded, as indicated at block  212 . For example, the profile  100  may include instructions regarding how the HVAC system should operate when the first threshold is exceeded, and the processor  86  may send a signal for the HVAC system to operate in that manner. For example, the damper  107  may be adjusted to a first position or the supply fan  109  may be commanded to operate at a first speed. 
     If the processor  86  determines that the probability exceeds the second threshold value, then the processor  86  determines whether the probability exceeds a third threshold value that is greater than the second threshold value, as indicated in block  214 . If the processor  86  determines that the probability does not exceed the third threshold, then the processor  86  sends a signal to change an operation of the HVAC system in a manner that is associated with the second threshold being exceeded, as indicated in block  216 . For instance, the profile  100  may include instructions regarding how the HVAC system should be operated when the second threshold value is exceeded, and the processor  86  may send a signal for the HVAC system to operate accordingly. For instance, the second threshold value may be associated with a second damper position that is further open that the first position. As another example, a second operating speed of the supply fan  109  associated with the second threshold value may be higher than the first speed. 
     However, if the processor  86  determines that the probability exceeds the third threshold value, then the processor  86  sends a signal to change an operation of the HVAC system in a manner that is associated with the third threshold value being exceeded, as indicated in block  218 . For example, the profile  100  may include instructions that cause the vapor compression system  72  or HVAC system to be shut down. The instructions may also include pumping the refrigerant into a specific portion of the vapor compression system  72 . Furthermore, in other embodiments, the instructions may include operating the supply fan  109  at a third speed that is faster than the second speed and/or opening the damper  107  to a third position that is further open than the second position. The processor  86  may send a signal to cause the HVAC unit  12  to operate in such a manner as indicated by the instructions that are included in the profile  100 . 
     When the processor  86  sends signals to change an operation of the HVAC unit in a manner associated with the first or second threshold value, the processor  86  may also receive the second set of signals at the second time, as indicated by block  208 . At block  220 , the processor  86  may determine a second probability of a refrigerant leak existing based on the second set of signals. That is, the processor  86  may determine a new probability associated with data collected by sensors  102  at a time that occurs after the first set of data was collected. 
     The processor  86  may determine whether the second probability exceeds the first threshold value, as indicated by block  222 . When it does, the processor  86 , the processor  86  may determine whether the second probability exceeds the second threshold value, as indicated in block  224 . As with block  212 , in at block  226 , the processor  86  sends a signal to operate the HVAC system in a manner associated with the first threshold value being exceeded when the processor  86  determines that the second probability does not exceed the second threshold value. 
     However, when the processor  86  determines that the second probability exceeds the second threshold value, the processor  86  determines whether the second probability exceeds the third threshold, as indicated in block  228 . If the processor  86  determines that the second probability does not exceed the third threshold, the processor  86  sends a signal to change operation of the HVAC system in a manner that is associated with the second threshold value being exceeded, as indicated in block  230 . Conversely, when the processor  86  determines that the second probability exceeds the third threshold, the processor  86  sends a signal to change operation of the HVAC system in a manner associated with the third threshold being exceeded, as indicated in block  218 . 
     Returning to block  222 , if the processor  86  determines that the second probability does not exceed the first threshold value, then the processor  86  may determine whether the first threshold value will likely be exceeded at a future time, as indicated in at block  232 . The profile  100  may include instructions that may be executed by the processor  86  to make such a determination. For example, a rate of change in the probability of a refrigerant leak may be determined by determining a difference between the second probability and the probability and dividing that difference by the amount of time that passed between the first and second times. Future probabilities may then be extrapolated based on the determined rate of change. 
     If the processor  86  determines that the first threshold value will be exceeded, the processor  86  may send a signal to notify a user of the HVAC system or another person, as indicated in block  234 . For example, as explained above, an email notification or text message, among other forms of notifications, may be generated and sent to various electronic devices. If the processor  86  determines that the first threshold value will not be exceeded, the processor  86  may terminate the process  200 , as indicated in block  236 . 
     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 without materially departing from the novel teachings and advantages of the subject matter recited in the claims. For instance, the modifications and changes may include variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters such as temperatures or pressures, mounting arrangements, use of materials, colors, orientations, and the like. 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 present 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 present disclosure or those unrelated to enabling the claimed embodiments. 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.