This invention relates generally to vapor compression systems, such as chillers, and more specifically to vapor compression systems comprising a refrigerant composition measurement system for determining the composition of a refrigerant blend.

This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.

Refrigeration systems are used in a variety of settings and for many purposes. For example, refrigeration systems may include a free cooling system and a mechanical cooling system. In some cases, the free cooling system may include a liquid-to-air heat exchanger, which is used in some heating, ventilation, and air conditioning applications. Additionally, the mechanical cooling system may be a vapor compression refrigeration cycle, which may include a condenser, an evaporator, a compressor, and/or an expansion device. In the evaporator, liquid or primarily liquid refrigerant is evaporated by drawing thermal energy from an air flow stream and/or a cooling fluid (e.g., water), which may also flow through the liquid-to-air heat exchanger of the free cooling system. In the condenser, the refrigerant is de-superheated, condensed, and/or sub-cooled. As such, the refrigerant flowing within the refrigeration system travels through multiple conduits and components of the refrigeration circuit.

Refrigeration systems typically use a refrigerant, sometimes referred to as a working fluid, that can be a pure fluid having a single refrigerant component or a refrigerant blend that is a mixture with multiple refrigerant components. Certain refrigerant blends can be described as being "non-azeotropic," "zeotropic," or "with glide," meaning that there are composition differences in the refrigerant blend as it transitions between liquid and vapor states as a result of partial distillation of the components at different points in the refrigeration system.

DE 42 30 818 A1 describes a vapor compression system comprising a refrigerant circuit with a condenser, an evaporator, a sample vessel and an expansion valve disposed downstream of the sample vessel and upstream of the evaporator. The expansion valve is controlled based on a liquid level within the sample vessel. A refrigerant composition in the sample vessel is determined based on a measured temperature and a measured pressure within the sample vessel. DE 42 30 818 A1 further describes a method for controlling the capacity of a compression heat pump and/or refrigeration machine operating with a pair of mutually soluble media, in which the working medium circulating in the circuit is condensed, expanded, evaporated, and compressed. The vapor phase and the liquid phase of the working medium are separated at a point in the circuit where there is a large concentration difference between the two phases, and the separated liquid, having a lower concentration, is returned to the circuit at at least one other point and mixed with the separated vapor having a higher concentration. The separated liquid phase is returned to the circuit in a controlled manner by variable storage of the liquid quantity. The heating and/or cooling capacity is controlled by regulating the concentration within the circuit.

The invention is defined in independent claims 1 and 7. Embodiments result from the dependent claims.

• FIG. 1 is a perspective view of a building that may utilize an embodiment of a heating, ventilation, and air conditioning (HVAC) system in a commercial setting, in accordance with an aspect of the present invention;
• FIG. 2 is a perspective view of an embodiment of a vapor compression system, not according to the present invention;
• FIG. 3 is a schematic illustration of an embodiment of a vapor compression system, not according to the present invention;
• FIG. 4 is a schematic illustration of another embodiment of a vapor compression system, not according to the present invention;
• FIG. 5 is a schematic diagram of an embodiment of the vapor compression system having a refrigerant blend measurement system (RBMS), in an accordance with an aspect of the present invention; and
• FIG. 6 is a flow chart representing an embodiment of a process for operating the vapor compressions system having the RBMS illustrated in FIG. 5, in accordance with an aspect of the present invention.

As mentioned, in certain cases, refrigeration systems can use a refrigerant blend as the working fluid. It is presently recognized that a refrigerant blend can have a first composition in a first portion of the refrigerant system, in which the refrigerant comprises a first biphasic mixture (e.g., upstream of an expansion valve) and a second composition in a second portion of the refrigerant system, in which the refrigerant comprises a second biphasic mixture (e.g., downstream of an expansion valve). By further example, this compositional difference in the refrigerant blend can be observed throughout a refrigerant system, including, for example, in differences between the composition of a liquid and a vapor refrigerant blend within a heat exchanger of a refrigeration system, in differences between the composition of a liquid refrigerant blend in a condenser and a liquid refrigerant blend in an evaporator of a refrigeration system, and/or in differences in the composition of a refrigerant blend as a result of stagnation and/or heat transfer between the system and the ambient environment. Furthermore, the composition of a refrigerant blend (e.g., the overall refrigerant charge) in a refrigeration system can vary over its lifetime due to non-homogeneous losses, which will preferentially vent the more volatile component of the refrigerant blend outside the system.

With the foregoing in mind, present embodiments are directed to a vapor compression system with a refrigerant blend measuring system (RBMS) for measuring and determining a current composition of a non-azeotropic (zeotropic) refrigerant blend circulating in the refrigeration system, such as a vapor compression system of a chiller. As discussed in more detail below, the disclosed RBMS includes a sample vessel that is disposed along a liquid line of the refrigeration system to receive a flow of the refrigerant blend for analysis. Control circuitry of the RBMS is communicatively coupled to suitable sensors (e.g., pressure sensors, temperature sensors, liquid level sensors) of the sample vessel and is programmed to measure physical properties (e.g., pressure, temperature, liquid level) of the refrigerant blend within the sample vessel. The control circuitry of the RBMS is further programmed to determine a composition of the refrigerant blend using stored data relating values of the measured physical properties in the sample vessel with different refrigerant blend compositions. The control circuitry of the RBMS may monitor the composition of the refrigerant blend over time and provide an indication (e.g., an alert or alarm) when the composition of the refrigerant blend differs from a target composition by greater than a predetermined threshold. Additionally, in certain embodiments, the control circuitry may modify operation of the refrigeration system based on the determined composition of the refrigerant blend, for example, to improve the efficiency of the refrigeration system, to ensure integrity of the components of the refrigeration system, and/or to ensure regulatory compliance with respect to the composition of the refrigerant blend and/or the refrigeration system.

The control techniques of the present disclosure may be used in a variety of systems. However, to facilitate discussion, examples of systems that may incorporate the control techniques of the present disclosure are depicted in FIGS. 1-4, which are described hereinbelow.

Turning now to the drawings, FIG. 1 is a perspective view of an embodiment of an environment for a heating, ventilation, and air conditioning (HVAC) system 10 in a building 12 for a typical commercial setting. The HVAC system 10 may include a vapor compression system 14 that supplies a chilled liquid, which may be used to cool the building 12. The HVAC system 10 may also include a boiler 16 to supply warm liquid to heat the building 12 and an air distribution system which circulates air through the building 12. The air distribution system can also include an air return duct 18, an air supply duct 20, and/or an air handler 22. In some embodiments, the air handler 22 may include a heat exchanger that is connected to the boiler 16 and the vapor compression system 14 by conduits 24. The heat exchanger in the air handler 22 may receive either heated liquid from the boiler 16 or chilled liquid from the vapor compression system 14, depending on the mode of operation of the HVAC system 10. The HVAC system 10 is shown with a separate air handler on each floor of building 12, but in other embodiments, the HVAC system 10 may include air handlers 22 and/or other components that may be shared between or among floors.

FIGS. 2 and 3 illustrate embodiments of the vapor compression system 14 that can be used in the HVAC system 10. The vapor compression system 14 may circulate a refrigerant through a circuit starting with a compressor 32. The circuit may also include a condenser 34, an expansion valve(s) or device(s) 36, and a liquid chiller or an evaporator 38. The vapor compression system 14 may further include a control panel 40 (e.g., controller) that has an analog to digital (A/D) converter 42, a microprocessor 44, a non-volatile memory 46, and/or an interface board 48.

Some examples of fluids that may be used as refrigerants in the vapor compression system 14 are hydrofluorocarbon (HFC) based refrigerants, for example, R-410A, R-407, R-134a, hydrofluoro-olefin (HFO), "natural" refrigerants like ammonia (NH3), R-717, carbon dioxide (CO2), R-744, or hydrocarbon based refrigerants, water vapor, refrigerants with low global warming potential (GWP), or any other suitable refrigerant. In some embodiments, the vapor compression system 14 may be configured to efficiently utilize refrigerants having a normal boiling point of about 19 degrees Celsius (66 degrees Fahrenheit or less) at one atmosphere of pressure, also referred to as low pressure refrigerants, versus a medium pressure refrigerant, such as R-134a. As used herein, "normal boiling point" may refer to a boiling point temperature measured at one atmosphere of pressure.

In some embodiments, the vapor compression system 14 may use one or more of a variable speed drive (VSDs) 52, a motor 50, the compressor 32, the condenser 34, the expansion valve or device 36, and/or the evaporator 38. The motor 50 may drive the compressor 32 and may be powered by a variable speed drive (VSD) 52. The VSD 52 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 50. In other embodiments, the motor 50 may be powered directly from an AC or direct current (DC) power source. The motor 50 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 32 compresses a refrigerant vapor and delivers the vapor to the condenser 34 through a discharge passage. In some embodiments, the compressor 32 may be a centrifugal compressor. The refrigerant vapor delivered by the compressor 32 to the condenser 34 may transfer heat to a cooling fluid (e.g., water or air) in the condenser 34. The refrigerant vapor may condense to a refrigerant liquid in the condenser 34 as a result of thermal heat transfer with the cooling fluid. The refrigerant liquid from the condenser 34 may flow through the expansion device 36 to the evaporator 38. In the illustrated embodiment of FIG. 3, the condenser 34 is water cooled and includes a tube bundle 54 connected to a cooling tower 56, which supplies the cooling fluid to the condenser.

The refrigerant liquid delivered to the evaporator 38 may absorb heat from another cooling fluid, which may or may not be the same cooling fluid used in the condenser 34. The refrigerant liquid in the evaporator 38 may undergo a phase change from the refrigerant liquid to a refrigerant vapor. As shown in the illustrated embodiment of FIG. 3, the evaporator 38 may include a tube bundle 58 having a supply line 60S and a return line 60R connected to a cooling load 62. The cooling fluid of the evaporator 38 (e.g., water, ethylene glycol, calcium chloride brine, sodium chloride brine, or any other suitable fluid) enters the evaporator 38 via return line 60R and exits the evaporator 38 via supply line 60S. The evaporator 38 may reduce the temperature of the cooling fluid in the tube bundle 58 via thermal heat transfer with the refrigerant. The tube bundle 58 in the evaporator 38 can include a plurality of tubes and/or a plurality of tube bundles. In any case, the refrigerant vapor exits the evaporator 38 and returns to the compressor 32 by a suction line to complete the cycle.

FIG. 4 is a schematic of the vapor compression system 14 with an intermediate circuit 64 incorporated between condenser 34 and the expansion device 36. The intermediate circuit 64 may have an inlet line 68 that is directly fluidly connected to the condenser 34. In other embodiments, the inlet line 68 may be indirectly fluidly coupled to the condenser 34. As shown in the illustrated embodiment of FIG. 4, the inlet line 68 includes a first expansion device 66 positioned upstream of an intermediate vessel 70. In some embodiments, the intermediate vessel 70 may be a flash tank (e.g., a flash intercooler). In other embodiments, the intermediate vessel 70 may be configured as a heat exchanger or a "surface economizer." In the illustrated embodiment of FIG. 4, the intermediate vessel 70 is used as a flash tank, and the first expansion device 66 is configured to lower the pressure of (e.g., expand) the refrigerant liquid received from the condenser 34. During the expansion process, a portion of the liquid may vaporize, and thus, the intermediate vessel 70 may be used to separate the vapor from the liquid received from the first expansion device 66. Additionally, the intermediate vessel 70 may provide for further expansion of the refrigerant liquid because of a pressure drop experienced by the refrigerant liquid when entering the intermediate vessel 70 (e.g., due to a rapid increase in volume experienced when entering the intermediate vessel 70). The vapor in the intermediate vessel 70 may be drawn by the compressor 32 through a suction line 74 of the compressor 32. In other embodiments, the vapor in the intermediate vessel may be drawn to an intermediate stage of the compressor 32 (e.g., not the suction stage). The liquid that collects in the intermediate vessel 70 may be at a lower enthalpy than the refrigerant liquid exiting the condenser 34 because of the expansion in the expansion device 66 and/or the intermediate vessel 70. The liquid from intermediate vessel 70 may then flow in line 72 through a second expansion device 36 to the evaporator 38.

It is presently recognized that, in certain embodiments, it may be advantageous for the intermediate vessel 70 to be a sample vessel including suitable sensors for measuring properties of a refrigerant blend flowing within the vapor compression system 14. In certain embodiments, the intermediate vessel 70 may serve more than one function (e.g., sample vessel, flash intercooler, heat exchanger, surface economizer, or a combination thereof) in the vapor compression system 14. As discussed above, the relative composition of a refrigerant blend (e.g., a refrigerant mixture comprising two or more refrigerants) circulating through the vapor compression system 14 may change during operation due to the different properties (e.g., vapor pressure, saturation temperature) of the components of the refrigerant blends. For example, the refrigerant blend may be a mixture of refrigerant components A and B, where component A is more volatile (e.g., has a higher vapor pressure) than component B under the operating conditions of the vapor compression system 14. As such, in the event of refrigerant loss within the vapor compression system 14, it is presently recognized that component A, the more volatile refrigerant, will evaporate more readily than component B. This can leave the refrigerant blend deficient with respect to component A, which changes the properties (e.g., vapor pressure, saturation temperature) of the refrigerant blend within the vapor compression system 14.

With the foregoing in mind, FIG. 5 is a schematic diagram illustrating an embodiment of a refrigerant circuit 76 of the vapor compression system 14 that includes a refrigerant blend measurement system (RBMS) 77, in accordance with the present invention. In particular, for the embodiment illustrated in FIG. 5, the intermediate vessel 70 discussed above with respect to FIG. 4 is, more specifically, a sample vessel 78. According to the invention, the sample vessel 78 is disposed downstream of the condenser 34, upstream of the evaporator 38, and along a liquid line 79 (also referred to herein as an expansion line) of the refrigerant circuit 76. The illustrated sample vessel 78 includes suitable sensors 80, such as a pressure sensor 80A, a liquid temperature sensor 80B, and a liquid level sensor 80C, configured to measuring properties of a refrigerant blend 82 within the sample vessel 78.

It should be appreciated that, in other embodiments, the sensors (80A, 80B) may be positioned in other locations in the refrigerant circuit 76, in addition or in alternative to being positioned within the sample vessel 78. That is, it is recognized that temperature and pressure measurements may be performed in one or more locations along the liquid (expansion) line 79 in various embodiments. For embodiments that include the sample vessel 78 (or another suitable intermediate vessel 70) sensors (80A, 80B) may be disposed upstream of the sample vessel 78, within the sample vessel 78, and/or downstream of the sample vessel 78. The refrigerant circuit 76 includes a first set of pressure and temperature sensors (80A, 80B) disposed downstream of the EEV 66 and upstream of the EEV 36. The refrigerant circuit may also include a second set of pressure and temperature sensors (80A, 80B) disposed downstream of the EEV 36 and upstream of the evaporator 38.

In addition to the sample vessel 78, the embodiment of the RBMS 77 illustrated in FIG. 5 also includes a control unit 84 that is communicatively coupled to the sensors 80 (e.g., sensors 80A, 80B, 80C) to receive measurement data. The control unit 84 includes memory circuitry 86 configured to store instructions and processing circuity 88 configured to execute the instructions to determine the composition of the refrigerant blend 82 within sample vessel 78, as discussed below. The control unit 84 is communicatively coupled to other components of the vapor compression system 14, such as the compressor 32, to modify or alter operation of the vapor compression system 14 in response to the determined refrigerant blend composition. Furthermore, in certain embodiments, the control unit 84 may be the control panel 40, may be included as part of the control panel 40, or may be communicatively coupled to the control panel 40, such that the control panel 40 can control operation of the vapor compression system 14 based on the determined refrigerant blend composition. As such, one or more of the control panel 40 and the control unit 84 may perform any or all of the monitoring, determining, and/or controlling aspects discussed herein, in different embodiments.

For the illustrated embodiment, the first expansion device 36 and the second expansion device 66 are electronic expansion valves (EEV) that are controlled by the control unit 84. For example, in some embodiments, the EEVs 36 and 66 may be controlled by a proportional-integral-derivative (PID) controller 90 that is part of the control unit 84, or a separate PID controller. As such, in certain embodiments, the EEVs 36 and 66 may operate based on measured conditions of the refrigerant circuit 76. For example, EEV 36 may operate to maintain a predefined target liquid level 92 within the condenser 34, as measured by a liquid level sensor 94 disposed within the condenser 34. Additionally, EEV 66 may operate to maintain a predefined liquid level 96 within the sample vessel 78, as measured by the liquid level sensor 80C disposed in the sample vessel 78. As such, based on signals from the control unit 84, the EEVs 36 and 66 operate to regulate the flow of the refrigerant blend 82 into and out of the sample vessel 78.

In certain embodiments, in addition to the flow path illustrated in FIG. 5, the refrigerant circuit 76 may include a secondary flow path, such as a bypass line 98, fluidly coupling the condenser 34 and the evaporator 30, which where the bypass line 90 includes the expansion device 36 but not the sample vessel 78 or the expansion device 66. For such embodiments, the control unit 84 may provide suitable signals to three-way control valves 100A and 100B associated with the bypass line 98 to divert the refrigerant blend 82 to flow through the bypass line 98 instead of the sample vessel 78. For example, the control unit 84 may provide such signals to improve the efficiency of the operation of the refrigerant circuit 76 and the vapor compression system 14 at times when the composition of the refrigerant blend 82 is not being measured and determined. In other embodiments, the bypass line 98 may not be present in the vapor compression system 14.

The illustrated sample vessel 78 of the disclosed RBMS 77 generally receives a flow of the refrigerant blend 82 for compositional analysis that has traversed the EEV 66. Accordingly, the flow of the refrigerant blend 82 delivered to the sample vessel 78 exists in both a vapor phase 82A and a liquid phase 82B during operation of the vapor compression system 14. The sensors 80 of the sample vessel 78 interact with the received portion of the refrigerant blend to measure properties thereof. More specifically, the pressure sensor 80A is designed and suitably positioned to measure a static pressure of the received refrigerant blend 82 (e.g., within either of the vapor phase 82A or the liquid phase 82B), while the liquid temperature sensor 80B is designed and suitably positioned to measure a temperature of the liquid phase 82B of the received refrigerant blend 82.

It may be appreciated that, since the refrigerant blend 82 is a non-azeotropic refrigerant blend, vapor phase 82A and the liquid phase 82B can each have a different composition due to the different physical properties (e.g., vapor pressure, saturation temperature) of the refrigerant components that make up the refrigerant blend 82. For example, a composition of the vapor phase 82A of the refrigerant blend 82 may include a relatively greater amount of a more volatile refrigerant component of the refrigerant blend 82, whereas the liquid phase 82B of the refrigerant blend 82 may include a relatively greater amount of a less volatile refrigerant component. As discussed below, the control unit 84 is configured to receive pressure measurements from the pressure sensor 80A and temperature measurements from the liquid temperature sensor 80B and is configured to use these measurements, along with physical property data stored in the memory 86 for different refrigerant blend compositions, to determine the composition of the current refrigerant blend 82 in the sample vessel 78. In certain embodiments, the control unit 84 may determine the composition of the refrigerant blend 82 continuously, periodically (e.g., at the beginning a cycle), or based on input received from an operator.

In certain embodiments, the determined composition of the refrigerant blend 82 may be provided (e.g., via the control panel 40, a thermostat panel, or a portable electronic device) to an operator or technician to monitor for potential maintenance issues. For example, in the illustrated embodiment, the control unit 84 may provide the current composition of the refrigerant blend 82 to the control panel 40 to be presented via a display device 102. Additionally, based on one or more predetermined limits stored in the memory 86 of the control unit 84, the memory 46 of the control panel 40, or stored in other suitable memory of the vapor compression system 14, the control unit 84 and/or the control panel 40 may determine and present, on the display device 102, an amount of one or more refrigerant components of the refrigerant blend 82 that should be added to the refrigeration system to modify the composition of the refrigerant blend (e.g., back to the originally charged refrigerant blend composition or to a completely different refrigerant blend). As a specific example, in situations where local regulations restrict use of refrigerants and/or refrigerant blends with certain global warming potential (GWP) properties or values, the composition of a refrigerant blend 82 can be modified, in accordance with the present method, to create a dedicated refrigerant blend that meets or adapts to these restrictions. Additionally, the disclosed RBMS 77 can monitor (e.g., periodically or on-demand) the composition of the refrigerant blend 82 within the vapor compression system 14 over time to ensure that the composition of the refrigerant blend 82 remains in compliance with operator defined thresholds, which may be based on GWP regulations.

In certain embodiments, the operation of the vapor compression system 14 is controlled, at least in part, based on the determined composition of the refrigerant blend 82. According to the invention, the memory 86 stores one or more predefined thresholds, and the control unit 84 may repeatedly compare the current composition of the refrigerant blend 82 to the stored thresholds to determine whether they have been exceeded. When one or more of the predefined thresholds are exceeded, the control unit 84 modifies operation of the vapor compression system 14. For example, the control unit 84 (e.g., alone or in cooperation with the control panel 40) may suspend operation of the vapor compression system 14 by deactivating the motor 50 of the compressor 32.

Additionally, in certain embodiments, the control unit 84 may store a collection of previously determined compositions of the refrigerant blend 82 in the memory 86 and may identify and track changes to the composition of the refrigerant blend 82 over time. For such embodiments, the control unit 84 may store predefined thresholds for a rate of change of the composition of the refrigerant blend 82 that, when exceeded, may result in the control unit 84 modifying operation of the vapor compression system 14. It may be appreciated that this approach can enable the control unit 84 to differentiate between a large, gradual shift in composition of the refrigerant blend 82 (e.g., due to slow refrigerant loss or long-term degradation of a refrigerant component) and a large, sudden shift in composition of the refrigerant blend 82 (e.g., due to a substantial loss of refrigerant in the refrigerant circuit 76).

Additionally, in terms of modifying operation of the vapor compression system 14, in certain embodiments, the composition of a refrigerant blend 82 can be adjusted to accommodate differences in the performance of certain refrigeration system components between implementations and/or to accommodate potentially varying performance of certain refrigeration system components over the life of the system 14. For example, if a volumetric flow associated with the compressor 32 of the refrigerant circuit 76 is or becomes too high to reach peak efficiency, a dedicated refrigerant blend having a lower saturated pressure can be introduced or created to increase the performance of the vapor compression system 14 despite this high volumetric flow. Conversely, if the volumetric flow associated with the compressor 32 is or becomes too small to reach peak efficiency, a dedicated refrigerant blend having a higher saturated pressure can be introduced or created to increase the performance of the system 14 despite this low volumetric flow.

For example, in some embodiments, it may be desirable to add more of one or more refrigerant components of the refrigerant blend 82 when the control unit 84 determines that the composition of the refrigerant blend 82 has changed significantly (e.g., is outside of a desired operation threshold or range). For the embodiment illustrated in FIG. 5, the refrigerant circuit 76 includes two refrigerant reservoirs 104A and 104B that are both selectively fluidly coupled to the refrigerant circuit 76 via respective two-way valves 106A and 106B (e.g., two-way solenoid valves). The valves 106 A and 106B are each communicatively coupled to the control unit 84. In general, the control unit 84 may send suitable control signals to actuate (e.g., open and/or close) one or more of the valves 106A and 106B to provide a refrigerant component or refrigerant blend to the refrigerant circuit 76 to compensate for a loss of refrigerant of the refrigerant blend 82 (e.g., based on the composition of the refrigerant blend 82 determined by the control unit 84). In some embodiments, the refrigerant circuit 76 may include one reservoir (e.g., reservoir 104A). It is presently recognized that it may be advantageous to store a single refrigerant component, such as the more volatile component of the refrigerant blend 82, as this component is more likely to volatilize and escape the refrigerant circuit 76 over time in the event of refrigerant loss.

FIG. 6 is a flow chart illustrating an embodiment of a process 110 for operating the refrigerant circuit 76 using the RBMS 77, in accordance with the present invention. The process 110 is discussed with reference to elements illustrated in FIG. 5. It is to be understood that the steps discussed herein are merely provided as an example, and certain steps may be omitted or performed in a different order than the order described below in other embodiments. While the process 110 is discussed below with respect to the control unit 84, it may be appreciated that, in different embodiments, the process 110 may be stored in the memory 86 and executed by the processor 88 of the control unit 84, stored in the memory 46 and executed by the processor 44 of the control panel 40, or stored in other suitable memory circuitry and executed by other suitable processing circuitry of the vapor compression system 14.

The illustrated embodiment of the process 110 begins with the processor 88 directing (block 1 12) the flow of the refrigerant blend 82 into the sample vessel 78 downstream of the condenser 34 and the EEV 66. For example, for embodiments of the vapor compression system 14 that include the bypass line 98, the processor 88 may provide suitable signals to the three-way control valves 100A and 100B associated with the bypass line 98 to discontinue the flow of the refrigerant blend 82 through the bypass line 98 and to instead direct the flow to through the sample vessel 78 for analysis. As discussed above, the processor 88 may provide suitable control signals to actuate the EEVs 36 and 66 to maintain the predetermined liquid level 92 of refrigerant blend 82 in the condenser 34 based on measurements received from the liquid level sensor 94 and to maintain the predetermined liquid level 96 in the sample vessel 78 based on measurements received from the liquid level sensor 80C of the sample vessel 78.

Continuing through the process 110, the processor 88 then receives (block 1 14) measurements of properties of the refrigerant blend 82 from the sensors 80 of the sample vessel 78. As discussed above, the refrigerant blend 82 within the sample vessel 78 includes a vapor phase 82A and a liquid phase 82B. As such, the processor 88 may receive a pressure measurement that corresponds to the static pressure of the refrigerant blend 82 and receive a temperature measurement that corresponds to the temperature of the liquid phase 82B from the liquid temperature sensor 80B.

Continuing through the process 110, the processor 88 determines (block 1 16) a composition of the refrigerant blend 82 based at least in part on the measurements received from the sensors 80 and data (e.g., lookup tables stored in the memory 86) that relates these measurements for different refrigerant blend compositions. For example, in certain embodiments, an enthalpy value may be calculated using the upstream temperature and/or pressure measurements (e.g., using suitable sensors 80 disposed upstream of EEV 36) and an assumed refrigerant blend composition. For this method, the enthalpy may be assumed to be constant throughout the expansion line 79. Then, using this calculated enthalpy value, in conjunction with the downstream temperature and pressure measurements (e.g., using suitable sensors 80 disposed downstream of EEV 36), and the aforementioned relationships stored in the memory 86, the processor 88 can determine the current composition of the refrigerant blend 82 in the expansion line 79. The processor 88 can continue to iterate this process until convergence is reached between the assumed composition and new composition. An example of an iterative computation process is discussed below. In these embodiments not according to the invention, the sample vessel 78 or intermediate vessel 70 may not be present.

For the illustrated embodiment, the process 110 continues with the processor 88 storing (block 120) the determined composition of the refrigerant blend 82 in the memory 86 of the control unit 84. In certain embodiments, the processor 88 may compare the current determined composition of the refrigerant blend 82 to previously determined and stored compositions to identify trends. For example, the processor 88 may determine a rate of change of the composition of the refrigerant blend 82 based on the stored composition values. In certain embodiments, the steps recited in block 120 may be skipped, and the processor 88 may proceed through the remainder of the process 110 based only the current determined composition of the refrigerant blend 82. Additionally, in certain embodiments, the compositions stored in the memory 86 may be accessible (e.g., by a service technician or a regulatory compliance officer) via the display device 102 of the control panel 40, or another suitable display device 102, to enable presentation of the determined compositions of the refrigerant blend 82, as well as trends of changes in the determined compositions over time.

For the embodiment of the process 110 illustrated in FIG. 6, the processor 88 then determines (block 122) whether the composition of the refrigerant blend 82 determined in block 1 16 is outside or beyond a predetermined threshold value or range stored in the memory 86, and if it is, the processor 88 modifies operation of the vapor compression system 14 and/or takes other corrective action (block 124). For embodiments in which the processor 88 identifies trends in stored refrigerant composition data, the processor 88 may further compare the trends to one or more predetermined threshold values stored in the memory 86. For example, the memory 86 may store at threshold value defining an acceptable rate of change in the composition of the refrigerant blend 82 over time (e.g., < 0.01% per week), and when the processor 88 determines that the determined rate of change of the composition is greater than this threshold value, the processor 88 may proceed to block 124 to take corrective action. When the processor 88 determines that the composition determined in block 116 (and, potentially, the trends identified in block 120) are within the corresponding threshold values stored in the memory 86, then the processor 88 may proceed back to block 1 12, as indicated by the arrow 126. In certain embodiments, the processor 88 may wait a predetermined amount of time before repeating the process 110. Additionally, for embodiments that include the bypass line 98, the processor 88 may provide control signals to direct the refrigerant blend 82 to traverse the bypass line 98 instead of the sample vessel 78 until the processor 88 is ready to repeat execution of the process 110.

As mentioned in block 124, when the processor 88 determines that the composition of the refrigerant blend 82 is outside of a predefined threshold or range, and/or that one or more identified trends are beyond a respective predefined threshold or range, the processor 88 takes corrective action. More specifically, when the processor 88 determines that the composition of the refrigerant blend 82 has changed (e.g., has exceeded an inner or smaller predefined threshold), but is still within an acceptable range to allow operation of the vapor compression system 14 (e.g., has not exceeded an outer or greater predefined threshold), the processor 88 may perform one or more corrective actions. For example, in certain embodiments, the processor 88 may provide suitable signals to present (e.g., to an operator or service technician) that the inner threshold has been exceeded, and that the outer threshold has not yet been exceed. Additionally, in certain embodiments, the processor 88 may use the determined composition (e.g., as one or more inputs to one or more control algorithms executed by the processor 88) to determine how to modify the operation of one or more electrical and/or mechanical components of the vapor compression system 14 to improve efficiency and/or to ensure proper operation of the system 14.

For example, when the processor 88 determines that the current composition of the refrigerant blend 82 is different from design conditions (e.g., the originally charged composition of the refrigerant blend 82), the processor 88 may provide control signals to one or more components or devices of the vapor compression system 14 to adapt to these actual conditions (e.g., a different vapor pressure, saturation pressure, saturation temperature of the determined composition of the refrigerant blend 82). As a specific example, in certain embodiments, the processor 88 may directly provide control signals to adjust a component depending on the determined composition of the refrigerant blend 82 or indirectly provide control signals by providing communication signals to the control panel 40, such that the processor 44 provides suitable control signals to adjust operation of the component. In certain embodiments, the processor 44 or 88 may, for example, provide suitable control signals to adjust a speed of a compressor 32, adjust a position of EEVs 36 and/or 66, or make any other suitable adjustments based on the determined composition of the refrigerant blend 82.

Additionally or alternatively, for embodiments that include at least one refrigerant reservoir (e.g., refrigerant reservoirs 104 A and/or 104B), the processor 88 may provide suitable signals to temporarily open at least one corresponding valve (e.g., valves 106A and/or 106B) to introduce one or more refrigerant components to the refrigerant blend 82 as part of the corrective action of block 124 in order to modify the composition of the refrigerant blend 82. In certain embodiments, the processor 88 opens the valves 106A and/or 106B of the associated reservoirs 104A and/or 104B for a predetermined period of time to introduce the corresponding refrigerant components, and then the processor 88 repeats the process 110 again (as indicated by the arrow 128) to determine the composition of the adjusted refrigerant blend 82. In certain embodiments, the processor 88 may continue repeating these steps until the composition of the refrigerant blend 82 is gradually modified to once again be within one or more predetermined threshold values stored in the memory 86.

In certain embodiments, when the processor 88 determines that the composition is beyond a predefined outer threshold or range, meaning that the vapor compression system 14 can no longer suitably operate using the determined composition of the refrigerant blend 82, then the corrective action may include the processor 88 providing signals to discontinue operation of the refrigerant circuit 76 and/or the vapor compression system 14. For example, the processor 88 may provide signals to deactivate the refrigerant circuit 76 (e.g., deactivate the compressor 32) and to block or prevent the system 14 from returning to an active state. In some embodiments, the corrective action of block 124 may include the processor 88 providing an indication to an operator (e.g., via the display device 102 of the control panel 40) that the refrigerant blend 82 should be adjusted, or the vapor compression system 14 otherwise serviced, to restore operation of the refrigerant circuit 76.

The following is a non-limiting example of determining the composition of a two-component refrigerant blend 82 via an iterative process, in accordance with an embodiment of the present approach. For this example, the temperature of refrigerant blend 82 inside the sample vessel 78 (e.g., measured by the liquid temperature sensor 80B) is determined to have a value T₁, which corresponds to the saturation temperature of the liquid phase 82B of the refrigerant blend 82 in the sample vessel 78. The pressure inside the sample vessel 78 (e.g., measured by pressure sensor 80A) is determined have a value Pi, which corresponds to the saturation pressure of the vapor phase 82A of the refrigerant blend 82 in the sample vessel 78. Additionally, a composition of the refrigerant blend 82, expressed as a mass fraction of a first of the two refrigerant components, is assumed to have an initial value C₁, which may be based on the composition of the refrigerant blend 82 charged in the refrigerant circuit 76.

For the refrigerant blend 82 in the sample vessel 78, saturation temperature (7), the saturation pressure (P), and composition of the refrigerant blend ( ) are related by the following function: $$T=\mathit{TsatLiq}\left(P,C\right)$$

In other words, TsatLiq is a function that returns liquid saturated temperature (7) at a given pressure (P) and a given refrigerant blend composition (C). In certain embodiments, the TsatLiq function accesses a look-up table stored in memory 86 that includes data available from National Institute of Standards and Technology (NIST) Reference Fluid Thermodynamic and Transport Properties Database (REFPROP) (e.g., available from https://www.nist.gov/srd/refprop). For example, the look-up table may include a plurality of rows that each describe a relationship between particular values of T, P, and C, for various combinations of the refrigerant components of the refrigerant blend 82.

With the foregoing in mind, the iterative process involves providing the measured pressure, Pi, and the initial refrigerant blend composition, C₁, as inputs to the TsatLiq function. The value of liquid saturation temperature, T, returned by the function is compared to the measured liquid saturation temperature, T₁. Based on a difference between the two values, a new value for the composition of the refrigerant blend, C₂, is selected. For example, in certain cases, when T > T₁, C₂ may be assigned a new value resulting in lower saturated temperature than C₁, while when T₁ > T, C₂ may be assigned a new value resulting in higher saturated temperature than C₁. In the next step of the iterative process, the measured pressure, P₁, and the new refrigerant blend composition, C₂, are then provided as inputs to the TsatLiq function. This iterative process of adjusting the values of C_x continues until the output of the function, T, substantially matches (e.g., is within a predefined tolerance of 3%, 2%, 1% of) the measured temperature value Ti, at which the final value of the composition, C_z, is determined to be indicative of the composition of the refrigerant blend 82 in the sample vessel 78.

By way of particular example, a particular refrigerant circuit 76 is charged with a refrigerant blend 82 that includes 174 kilograms (kg) of R125 and 225 kg of R134a. As such, the refrigerant blend 82 includes a mass fraction of 0.44 (or 44%) of R125 and a mass fraction of 0.56 (or 56%) R125. During operation of the refrigerant circuit 76 (e.g., once the evaporator outlet temperature and a condenser outlet temperature are stabilized), the refrigerant blend 82 within the sample vessel 78 is measured by the sensors 80 and these measurements are provided to the control unit 84 for analysis. For this example, the temperature of the liquid phase 82 in the sample vessel 78 is measured to be 23.6 °C, and the pressure 82A of the refrigerant blend 82 in the sample vessel is measure to be 9.73 bar. As such, the processor 88 provides the pressure value of 9.73 bar and an initial estimate of the mass fraction of R125 (e.g., 0.44) as inputs to the TsatLiq function, which generally returns a temperature value that is different than (e.g. greater than, less than) the 23.6 °C measured temperature value. Accordingly, the processor 88 continues to adjust (e.g., increase or decrease) the estimated mass fraction of R125 until the returned temperature value is substantially the same as the 23.6 °C measured temperature value. For this example, based on the relative nature of R125 and R134a, the processor 88 increases the mass fraction of R125 incrementally, as discussed above, until the processor 88 determines or estimates that the composition of the refrigerant blend 82 in the sample vessel 78 is approximately 53% R125 and 47% R134a. It may be appreciated that the determined composition of the refrigerant blend 82 in the sample vessel 78, or anywhere along the liquid line 79, should be substantially the same as the composition of the refrigerant blend 82 in certain portions of the refrigerant circuit 76 (e.g., compressor suction lines, discharge lines), and will vary from the composition of the refrigerant blend 82 in other portions of the refrigerant circuit 76 (e.g., in the condenser 34 and the evaporator 38) due to partial distillation of the refrigerant blend 82.

In another example, the refrigerant circuit 76 is charged with another refrigerant blend (R454B). This refrigerant blend 82 initially has a composition that has a mass fraction that is 0.689 (about 69%) R32 and 0.311 (about 31%) R1234yf. Since R32 is more volatile than R1234yf, the relative amount of R32 may change within the refrigerant blend 82 as a result of refrigerant loss. Additionally, it is presently recognized that, a saturation temperature of the refrigerant blend 82 (e.g., as measured by the liquid temperature sensor 80B) will be reduced by about 0.1 °C each time the mass fraction of R32 in the mixture is reduced by about 1%. As such, it is recognized that, for certain embodiments, the saturation temperature of the refrigerant blend 82 may be monitored and tracked over time by the processor 88, and the processor 88 may subsequently use a determined reduction in saturation temperature to initially estimate an amount of R32 that has been lost from the refrigerant blend 82. For example, in certain embodiments, this may be used to determine an initial value for the composition of the refrigerant blend (Ci) that is provided to the TsatLiq function, along with a measured pressure value (P), and the process may be iterated until the output of the TsatLiq function is substantially the same as a measured temperature value (7).

Table 1 is an example table that includes the mass fractions of R32 and R1234yf in the liquid and vapor phases based on a refrigerant loss and fractional distillation of the refrigerant blend (% loss). The data of Table 1 is based on a modeled refrigerant loss scenario performed for R454B following American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standard 34, assuming a temperature of 23 °C and a charge of 15% of the capacity of the refrigerant circuit 76. As indicated by Table 1, as an amount of the refrigerant blend R454B is lost, the mass fraction of the more volatile refrigerant component, R32, continually drops, while the mass fraction of the less volatile refrigerant component, R1234yf, continually increases, with increasing losses of the refrigerant blend 82. It may be appreciated that Table 1, or other similar tables, may be stored within a suitable memory (e.g., memory 86 or 46) for use as a look-up table. For example, in an embodiment, the after determining the composition of the refrigerant blend 82 using the iterative method described above, the processor 88 may use the determined composition to determine the total loss of refrigerant from the refrigerant circuit 76. % Loss R32 Liquid R1234yf Liquid R32 Vapor R1234yf Vapor 0 64.348 35.652 74.264 25.736 2 64.110 35.890 74.096 25.904 10 63.083 36.916 73.368 26.632 20 61.593 38.407 72.304 27.696 30 59.795 40.205 71.012 28.988 40 57.563 42.437 69.390 30.610 50 54.688 45.312 67.268 32.732 60 50.800 49.200 64.326 35.674

It may be appreciated that, while the above example describes an implementation in the expansion line 79, in other embodiments, the presently disclosed technique may be applied, additionally or alternatively, to other portions of the refrigeration system (e.g., refrigerators, chillers, heat pumps, Organic Rankine Cycle (ORC) units) as well as with different types of refrigerant blends (e.g., ORC fluids). It may also be appreciated that, in certain embodiments, the present approach may be applied to refrigerant blends 82 having more than two components (e.g., three, four, five, or more components). For such embodiments, it may be noted that, for each additional refrigerant blend component, additional information (e.g., equations, values, models) may be stored in the memory and utilized, in conjunction with the aforementioned information and measurements, to determine the actual refrigerant blend from local pressure and temperature measurements. For example, for embodiments in which refrigerant blends 82 include three components, the system can be solved applying the Raoult law or by use of REFPROP, mentioned above.

The technical effects of the present disclosure include a refrigerant blend measuring system (RBMS) configured to measure the current composition of a non-azeotropic (zeotropic) refrigerant blend circulating in a vapor compression system. The control circuitry of the RBMS is further programmed to determine a composition of the refrigerant blend using stored data relating values of the measured physical properties in the sample vessel with different refrigerant blend compositions. The control circuitry of the RBMS can monitor the composition of the refrigerant blend over time and take corrective action when the composition of the refrigerant blend differs from a target composition by greater than a predetermined threshold. For example, the control circuitry may modify operation of the refrigeration system based on the determined composition of the refrigerant blend, for example, to improve the efficiency of the refrigeration system, to ensure the integrity of the components of the refrigeration system, and/or to ensure regulatory compliance with respect to the composition of the refrigerant blend and/or the refrigeration system.

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 (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters (e.g., temperatures, pressures, etc.), mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the invention defined 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 as long as they fall within the scope of the claims. Furthermore, in an effort to provide a concise description of the exemplary embodiments, all features of an actual implementation may not have been described (i.e., those unrelated to the presently contemplated best mode of carrying out the disclosed techniques, or those unrelated to enabling the claimed embodiments).