MULTIPLE EXPANSION VALVES SMART CONTROL FOR REFRIGERANT CIRCUIT SYSTEM

Abstract

A control input represents directed flow rate of refrigerant through a virtual refrigerant metering device. For a plurality of parallel-connected, real, non-virtual, refrigerant metering devices, control input is determined for each, based on refrigerant flow characteristic of each refrigerant metering device, to produce individual flow rates through the refrigerant metering devices that provide an aggregate flow rate equivalent to the directed flow rate. Control signals are sent to the refrigerant metering devices.

Description

TECHNICAL FIELD

The present disclosure relates generally to improved devices, systems, and methods for controlling an expansion valve, for example, by using improved control processes for a circuit that uses multiple electronic expansion valves.

BACKGROUND

Refrigerant systems are in widespread use, for example in buildings, vehicles and appliances, in commercial, industrial, public, private and domestic settings, for cooling thereof, or, when operated as a heat pump, cooling and/or heating. Typically, basics of a refrigerant system include compression of a refrigerant, with heat exchange that removes heat energy from the compressed refrigerant, and expansion of a refrigerant, with heat exchange that moves heat energy into the expanded refrigerant. There are various compressors and expansion valves, of various designs, sizes and refrigerant flow capacities, which can be put to good use with suitable control, for various refrigerant systems of various sizes, capacities and installations. Yet, there is an ongoing need for technological improvements in refrigerant systems, and it is in this environment that present embodiments arise.

SUMMARY

Described herein are various embodiments of a refrigerant circuit system, a controller for same, a related method of operating a refrigerant circuit system, and various aspects and features thereof. The embodiments make use of a virtual refrigerant metering device, and control for various numbers and types of real, non-virtual refrigerant metering devices in accordance with a virtual refrigerant metering device.

Some embodiments include a method of operating a refrigerant circuit system. The method includes receiving a control input that represents a directed flow rate of a refrigerant through a virtual refrigerant metering device. The method includes, for each refrigerant metering device of a plurality of parallel-connected, real, non-virtual, refrigerant metering devices of the refrigerant circuit system, determining individual control input for the refrigerant metering device. Determining individual control input for the refrigerant metering device is based, at least in part, on the control input that represents the directed flow rate, and a refrigerant flow characteristic of the refrigerant metering device, to produce a plurality of individual flow rates through the plurality of refrigerant metering devices that provide an aggregate flow rate that is substantially equivalent to the directed flow rate. The method includes sending a plurality of control inputs to the plurality of refrigerant metering devices based on the determining of the individual control inputs for the plurality of refrigerant metering devices.

Some embodiments include a controller. The controller includes one or more processors. The controller is configured to receive a control input that represents a directed flow rate of a refrigerant through a virtual refrigerant metering device. The controller includes one or more outputs, coupled to the one or more processors and configured to be communicatively coupled to a plurality of parallel-connected, real, non-virtual refrigerant metering devices. The controller includes a computer-readable storage medium coupled to the one or more processors, comprising program instructions, which, when executed by the one or more processors, cause the controller to receive the control input that represents the directed flow rate of the refrigerant through the virtual refrigerant metering device. The program instructions further cause the controller to, for each refrigerant metering device of the plurality of refrigerant metering devices, determine individual control input for the refrigerant metering device, based, at least in part, on the control input that represents the directed flow rate, and a refrigerant flow characteristic of the refrigerant metering device, to produce a plurality of individual flow rates through the plurality of refrigerant metering devices that provides an aggregate flow rate that is substantially equivalent to the directed flow rate. The program instructions further cause the controller to send, via the one or more outputs, one or more control inputs to the plurality of refrigerant metering devices based on the determined individual control inputs for the plurality of refrigerant metering devices.

Other aspects and advantages of the embodiments will become apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the described embodiments. Further embodiments are readily devised in keeping with the teachings herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The described embodiments and the advantages thereof may best be understood by reference to the following description taken in conjunction with the accompanying drawings. These drawings in no way limit any changes in form and detail that may be made to the described embodiments by one skilled in the art without departing from the spirit and scope of the described embodiments.

FIG. 1 illustrates a refrigerant circuit system in accordance with some embodiments.

FIG. 2 illustrates a refrigerant circuit system with a single expansion valve.

FIG. 3 illustrates a refrigerant circuit system with two expansion valves in accordance with some embodiments.

FIG. 4 illustrates modules and parameter passing in some embodiments of a refrigerant circuit system that operates two expansion valves, for example as illustrated in FIGS. 1 and 3, according to a virtual expansion valve.

FIG. 5A illustrates, in graph form, operating values for two expansion valves in phase 1 and phase 2 operating regions of a refrigerant circuit system, for some embodiments.

FIG. 5B illustrates, in graph form, operating values for two expansion valves in phase 1 and phase 2 operating regions of a refrigerant circuit system, for some embodiments as an alternative to FIG. 5A.

FIG. 5C illustrates, in graph form, operating values for two expansion valves in phase 1 and phase 2 operating regions of a refrigerant circuit system, for some embodiments as an alternative to FIGS. 5A and 5B.

FIG. 6 illustrates, in graph form, operating values for two expansion valves in phase 1 and phase 2 operating regions of a refrigerant circuit system, for some embodiments in which hysteresis paths are used.

FIG. 7 illustrates, in table and graph form, operating values for two expansion valves in a refrigerant circuit system, for some embodiments.

FIG. 8A illustrates, in table and graph form, operating values for two expansion valves and an idealized target valve that serves for modeling a virtual expansion valve, for some embodiments.

FIG. 8B illustrates, in table and graph form, operating values for two expansion valves and an idealized target valve that serves for modeling a virtual expansion valve, for some embodiments as an alternative to FIG. 8A.

FIG. 8C illustrates, in table and graph form, operating values for two expansion valves and an idealized target valve that serves for modeling a virtual expansion valve, for some embodiments as an alternative to FIGS. 8A and 8B.

FIG. 9 illustrates a flow diagram for a method of operating a refrigerant circuit system, in accordance with some embodiments.

FIG. 10 illustrates exemplary computing device, in accordance with some embodiments.

DETAILED DESCRIPTION

Various embodiments of a refrigerant circuit system that uses smart control for multiple metering devices are described herein. In some embodiments, the metering devices are expansion valves of various types, including electronic expansion valve, thermal expansion valve, externally-equalized expansion valve, internally-equalized expansion valve. Real-world expansion valves differ from a hypothetical ideal expansion valve in various ways, such as nonlinear, inaccurate and/or non-repeatable behavior of refrigerant flow versus control setting, particularly for low levels of refrigerant flow relative to the maximum flow capacity of a given expansion valve. By using multiple expansion valves in parallel, in some embodiments of same sizes and flow characteristics, in some other embodiments of differing sizes and flow characteristics, each valve can be operated in a suitable range for accurate, repeatable flow control. And, in various embodiments, the system can compensate for non-ideal operation of each real-world expansion valve, and include a control system that operates as if there were a single, wide flow range, ideal (or nearly so) virtual expansion valve, which may be termed a “virtual EXV”, with linear, repeatable, accurate response of flow to control settings over a full range of metered refrigerant flow(s).

FIG. 1 illustrates a refrigerant circuit system in accordance with some embodiments. In various embodiments, a refrigerant circuit system could be considered just the controller 100, including control circuitry and electric expansion valve (EXV) control module, configured to control two (or more) expansion valves, it could be considered the controller coupled to two expansion valves 30, 32 (as depicted, or more), it could be considered that and two heat exchangers 22, 24, it could be considered the entire climate control system 10, or other combinations of components.

As shown in FIG. 1, the climate control system 10 comprises a chiller unit that is configured to cool or heat a conditioned space (e.g., such as the interior of an office building, retail store, convention center, an industrial process, etc.). Thus, the climate control system 10 may be referred to herein as a “chiller unit.”

The climate control system 10 includes a refrigeration assembly 20 that is configured to circulate a refrigerant to exchange heat between the conditioned space and an ambient environment (e.g., such as the outdoor environment that surrounds the conditioned space), so as to cool or heat the conditioned space. The refrigeration assembly may include first heat exchanger 22 and a second heat exchanger 24. The first heat exchanger 22 is configured to exchange heat between the refrigerant and a working fluid 44 of an ambient heat exchange circuit 40, and the second heat exchanger 24 is configured to exchange heat between the refrigerant and a working fluid 54 of a conditioned space heat exchange circuit 50.

In some embodiments, the working fluid 54 of the conditioned space heat exchange circuit 50 may comprise water (or a suitable aqueous mixture). The working fluid 54 may circulate between the second heat exchange 24 of the refrigeration assembly 20 and a conditioned space heat exchange assembly 52 to exchange heat between the refrigerant and the conditioned space during operations. In some embodiments, the conditioned space heat exchange assembly 52 may comprise one or more heat exchangers (e.g., air handler units) that are configured to exchange heat between the working fluid 54 and the conditioned space. In some embodiments, the working fluid 54 may comprise a fluid other than water, such as, for instance air (e.g., air that is directly provided to the conditioned space).

The working fluid 44 of the ambient heat exchange circuit 40 may comprise water or other suitable aqueous mixture such as previously described above for the working fluid 54. Alternatively, the working fluid 44 may comprise air. Still other working fluids may also be used. When the working fluid 44 is water, the chiller unit or climate control system 10 may be referred to as a “water-cooled” chiller unit, and when the working fluid is air, the chiller unit or climate control system 10 may be referred to as an “air-cooled” chiller unit. Regardless, the working fluid 44 may circulate between the first heat exchanger 22 of the refrigeration assembly 20 and an ambient heat exchange assembly 42 to exchange heat between the refrigerant and the ambient environment. In some embodiments, the ambient heat exchange assembly 42 comprises one or more heat exchangers (e.g., water cooling towers, radiators, fin-fan coolers, etc.) that are configured to transfer heat between the ambient environment and the working fluid 44. In some embodiments, such as in the case of air-cooled chiller units, the ambient heat exchange assembly 42 may be integrated and combined with the first heat exchanger 22 so that heat is directly exchanged between the refrigerant and an airflow that is sourced from and provided back to the ambient environment.

In addition to the first heat exchanger 22 and the second heat exchanger 24, the refrigeration assembly may include a compressor 26 and a plurality of expansion valves 30, 32. The compressor 26 and expansion valves 30, 32 may be in fluid communication with the first heat exchanger 22 and second heat exchanger 24 along a refrigerant loop or circuit 28. During operations, the refrigeration assembly 20 may be operated to circulate the refrigerant in a first direction shown in FIG. 1 so as to transfer heat from the conditioned space (e.g., via the conditioned space heat exchange circuit 50) to the ambient environment (e.g., via the ambient environment heat exchange circuit 40). Such operation may be referred to herein as a “cooling mode” operation.

Specifically, in the cooling mode operation shown in FIG. 1, the refrigerant (which may be in a vapor or semi-vapor state) may be compressed by the compressor 26 and delivered to the first heat exchanger 22 via the refrigerant loop 28. Within the first heat exchanger 22, heat is transferred from the refrigerant to the working fluid 44, which cools the refrigerant and at least partially condenses the refrigerant to a liquid. Thus, in the cooling mode operation of FIG. 1, the first heat exchanger 22 may be referred to as a “condenser.” Heat is then transferred from the heated working fluid 44 to the ambient environment via the ambient heat exchange assembly 42 of the ambient heat exchange circuit 40 as previously described.

The condensed refrigerant is then expelled from the first heat exchanger 22 and flowed to the second heat exchanger 24 via the expansion valves 30, 32. The expansion valves 30, 32 may be in parallel with one another, between the first heat exchanger 22 and second heat exchanger 24 along the refrigerant loop 28. Thus, the flow of refrigerant out of the first heat exchanger 22 is split and distributed between the expansion valves 30, 32 during operations. The expansion valves 30, 32 may be actuated so as to controllably expand and therefore cool the refrigerant upstream of the second heat exchanger 24.

The expanded and cooled refrigerant is then flowed to the second heat exchanger 24. Within the second heat exchanger 24, heat is transferred from the working fluid 54 to the refrigerant, which vaporizes (or at least partially vaporizes) the refrigerant. Thus, in the cooling mode operation of FIG. 1, the second heat exchanger 24 may be referred to as an “evaporator.” The cooled working fluid 54 is then used to cool the conditioned space via the conditioned space heat exchange assembly 52 of the conditioned space heat exchange circuit 50 as previously described.

While not shown, in some embodiments, the refrigeration assembly 20 may circulate the refrigerant in a second, opposite direction along the refrigerant loop 28 than that shown in FIG. 1 so as to transfer heat from the ambient environment to the conditioned space via the ambient heat exchange circuit 40 and the conditioned space heat exchange circuit 50. Such operation may be referred to herein as a “heating mode” operation, and a refrigeration assembly 20 that is configured to operate in the heating mode may be referred to as a “heat pump.” During a heating mode operation of the refrigeration assembly 20, the first heat exchanger 22 may function as an “evaporator” (which vaporizes the refrigerant) and the second heat exchanger 24 may function as a “condenser” (which condenses the refrigerant).

As previously described, during operation with the chiller unit or climate control system 10 shown in FIG. 1, the refrigerant may be controllably expanded through the expansion valves 30, 32. In some embodiments, each of the expansion valves 30, 32 may be electrically actuated (e.g., by a controller, such as controller 100 described in more detail herein) between a fully closed position, a fully open position, and a plurality of positions between the fully closed position and the fully open position. Thus, the expansion valves 30, 32 may both be referred to herein as “electric expansion valves” (EXV).

In addition, in some embodiments, the compressor 26 may be a variable speed compressor that is configured to operate at a plurality of operating speeds in order to change a cooling (or heating) capacity of the chiller unit or climate control system 10. As a result, the position of the expansion valves 30, 32 may be adjusted based on the operating speed of the compressor 26 (among other factors) in order to accommodate the changing flow rate of refrigerant along the refrigerant loop 28 and ensure efficient operation of the chiller unit or climate control system 10.

Non-ideal behavior and operation of real world expansion valves are compensated for in various embodiments of the system. Below is a control algorithm description for some embodiments, which can be applied to different expansion valve sizes as determined for a specific cooling or heat exchanger installation and system. Generally, the scaling of the system, including selection of expansion valve sizes for two or more expansion valves in the system, involves determining a maximum refrigerant flow and an idealized expansion valve characteristic for the installation and system. In some embodiments, the idealized expansion valve characteristic is represented in the system in the form of a virtual refrigerant metering device, which may be a virtual expansion valve. The selected refrigerant metering devices, which may be expansion valves, are operated in the system in accordance with the virtual expansion valve. Thus, in some embodiments, real, non-virtual refrigerant metering devices or expansion valves are operated as if there is a single, idealized, expansion valve, e.g., the virtual expansion valve. In some embodiments, the control is parameterized as further described below in example system design cases with example control. The developed, parameterized control for the specific, selected, real-world expansion valves, models the real, parallel connected expansion valves as a single, idealized expansion valve, the virtual expansion valve, and is embedded in the controller 100 with control circuitry and EXV control module, in various embodiments. Aspects and features thereof are further described below in examples with reference to FIGS. 2-8C, the flow diagram of FIG. 9 (for a method or algorithm), and FIG. 10 showing an example computing device, which in some examples is the same or similar to the control circuitry discussed herein.

Example System Design and Technological Solution

In one example, a feature development request is for RTWF (helical rotary water-cooled type F chiller), water cooled units which control the EXVs to maintain a condenser refrigerant liquid level over a subcooler section. Also envisioned are products using condenser subcooling, suction superheat or evaporator liquid level control. Considering a RTWF unit that controls an EXV to maintain a desired condenser refrigerant liquid level, it is often possible to select between two different EXV sizes according to customer declared functioning conditions. But, in some cases where the limit between undersized and normal size EXV choice is thin, the normal size one is selected, leading to circuit refrigerant flow control issues when requested circuit capacity is low (e.g., inaccuracy of refrigerant flow modulation when EXV opening is under 10% of wide opening). For example, a normal size EXV opening can remain in the lower part of the control curve during operation where low refrigerant flow is called for, whereupon refrigerant flow regulation inaccuracy can lead to issues. So, for better refrigerant flow controllability, an undersized EXV can be used for conditions where needed refrigerant flow is low, and a normal size EXV can be used to reach higher and highest refrigerant flow.

Thus, in some embodiments, a technological solution to the refrigerant flow regulation issues is to mount a normal size EXV and an undersized EXV in parallel and control them in a way where the undersized EXV is used in the lower part of the control curve while the normal size EXV is used in the upper part of the control curve. In some embodiments, this is done with dual stage control, operating the two EXVs in a low flow regime and a high flow regime, which may be termed herein as phase 1 and phase 2. In some embodiments, the operation is transparent to the circuit EXV control system so that operation of two (or more) EXVs is seen as a single EXV control, according to the virtual EXV.

Control System for Real EXVs and a Virtual EXV

In some embodiments, a control system shows an ideal EXV behavior from closed valve to wide opening valve, e.g., the virtual EXV, but is implemented physically using two real EXVs (mounted, connected or coupled in parallel). In some embodiments, this system compensates as much as possible for the inaccuracy of individual, real EXVs, thereby making circuit refrigerant flow more reliable especially when the refrigerant circuit is running at low flow, e.g. in the low flow regime or phase 1 of a dual stage control.

The virtual EXV models one, two, or more real metering devices, which may be real expansion valves, as an idealized, single, virtual metering device, which may be a virtual expansion valve, in various embodiments. In some embodiments, the control system generates control for the real metering device or devices, e.g., expansion valve or valves, operating each in a defined operating range, that provides overall operation of the system as if operating the idealized, single, virtual metering device or virtual expansion valve.

A goal then, for some embodiments, is to develop a dual EXV system (e.g., two, real EXVs) with dual stage control (e.g., with operation in low flow regime or phase 1, and high flow regime or phase 2) to enhance circuit refrigerant flow controllability especially for the low flow regime. Details of dual stage control of a dual electronic EXV system to enhance circuit refrigerant flow controllability especially for low flow regime are further described after FIG. 3.

Flow Coefficient

One principle of the control system, in some embodiments, is to work with a defined ideal Cv (see below) versus percent opening curve (for an idealized, virtual EXV) and control the physical EXVs to follow as smoothly as possible this ideal curve. According to one EXV Model algorithm specification, valves are sized based on a “flow coefficient”, often designated as Cv. Cv is more properly called a “volumetric flow coefficient” since applying it directly provides volumetric flow rates, not mass flow rates. The flow equation, which uses Cv, allows the estimation of flow rates for pressure drops and fluid densities different from test conditions.

Each qualified EXV has its own Cv versus percent opening curve, which is used by the control to define the EXV opening (or position) according to estimated refrigerant mass flow needed to draw through the actuator, which may be termed the directed refrigerant flow. The Cv versus percent opening curve is a particular example characteristic curve of a refrigerant flow characteristic of a refrigerant metering device. In this context, the characteristic curve governs refrigerant flow rate of the refrigerant through the refrigerant metering device. See, for example, FIG. 7 relating Cv as a variable flow coefficient indicating refrigerant flow, to “position”, or expansion valve opening expressed as a percentage value.

Embodiments may use a single, qualified EXV, two same or equivalent qualified EXVs (e.g., same Cv curve), two differing qualified EXVs (e.g., differing Cv curves), or more EXVs in various combinations of same, equivalent or differing components (and respective Cv curve(s)). Refrigerant circuit systems, controllers thereof, and related methods, may use these various numbers of EXVs with or without dual stage control (e.g., making use of differing parts of Cv curve(s) and weighting thereof), in various embodiments.

Software Integration of Features into Controller

In some embodiments, software integration is used to combine various features or aspects of an embodiment in a system. It should be appreciated that variations can use software executing on a processor, firmware, hardware, and combinations thereof, and particularly that components or features of the system can be embodied in various such modules in various combinations (e.g., software modules, hardware modules, firmware modules, etc.) For example, a specific feature or aspect of the system or operation thereof could be embodied in one or more modules, or such hardware, software, etc.

For condenser liquid level control, the application software (loaded into the controller) controls the EXV by sending a flow coefficient value (related to EXV wide opening Cv) to an expansion software module. The expansion software module converts this flow coefficient value into an EXV opening (or position in percent) and applies the converted flow coefficient value to the real EXV(s), in various embodiments. For some embodiments of the dual EXV case, in which two, real EXVs are used, the same opening value, based on doubled wide opening Cv, is applied to both EXVs. For some other embodiments of the dual EXV case, differing opening values are applied to the two EXVs. For yet some other embodiments of the dual EXV case, differing opening values are applied to the two EXVs in one operation realm (e.g., low flow), and further differing opening values are applied to the two EXVs in another operation realm (e.g., higher flow), for dual stage control. For still some other embodiments of the dual EXV case, differing opening values are applied to the two EXVs in one operation realm (e.g., low refrigerant flow), and same opening values are applied to the two EXVs in one operation realm (e.g., higher refrigerant flow), for dual stage control.

Further, it is understood that the directed flow rate discussed herein may be sent and/or received from various sources. For example, the climate control system discussed above in connection with FIG. 1 may set a directed flow rate for the one or more EXV based on various conditions associated with the refrigeration system, e.g., requested demand, ambient conditions, superheat, etc. Based on those conditions the directed flow rate may be set by a given controller. Further, the process for controller the EXV(s) discussed herein to achieve, or attempt to achieve, that directed flow rate may be utilized by that same controller, or in some examples, an additional controller, software module, etc., may interface with the controller providing the directed flow rate.

To walk through an example, a first controller in the climate control system may determine the directed flow rate through one or more EXV valves. That directed flow rate may be for refrigerant within the refrigeration system, and it may be based on a cooling load requested by the conditioned space. The first controller may encode the directed flow rate into a control input. In some examples, this control input provided by the first controller may be directed to controlling a system with a single EXV to the directed flow rate. Other control inputs may also be utilized/determined by the controller. Further, in some examples, a second controller may be communicatively coupled to the first controller and receive the control input. The second controller may utilize one or more of the processes described herein to control the position of one or more EXV valves, potentially to obtain a flow rate approximately the same as the directed flow rate. In these examples, separating the controller for determining the directed flow rate, e.g., the desired refrigerant flow, from the controls used to implement the EXV controls to achieve that flow rate may have various advantages. For example, this may allow these more advanced EXV controls to be implemented into an existing system that utilizes only a single EXV valve and/or has different controls, improving the overall performance of that system without the need for significant changes. These and other advantages may also be realized.

Single Expansion Valve

FIG. 2 illustrates a refrigerant circuit system with a single expansion valve 62. Referring to FIG. 2, the expansion software module 60 processes a received flow coefficient and determines a valve position, which is communicated to the EXV 62. In some embodiments, this control is performing according to an algorithm described in more detail below.

In some embodiments, in order to be transparent for the main EXV control software (e.g., condenser liquid level control) with dual stage EXV control, the expansion software module shows a virtual EXV and converts its flow coefficient to individualized inputs for two EXV openings, which will be applied to the physical EXVs (see FIG. 3) with smooth transition between low stage valve (LSV) and high stage valve (HSV).

Dual Expansion Valves and Virtual EXV

FIG. 3 illustrates a refrigerant circuit system with two expansion valves 66, 68 in accordance with some embodiments. The expansion software module 64 includes a virtual EXV, which it uses in processing a received flow coefficient in order to determine the LSV position and the HSV position. The expansion software module 64 communicates the LSV position to the low stage valve, EXV 66 and the HSV position to the high stage valve, EXV 68.

Below are described some embodiments of a virtual EXV. In some embodiments, the virtual EXV is based on the wide-open (or 100% opened) Cv (Max Cv) parameter to be defined according to the circuit maximum capacity and as it will follow an ideal curve, the below equations show linear, proportional behavior of the virtual EXV.

$\mathrm{CV}=\mathrm{RampCoef}*\mathrm{Opening}\left(\%\right)\mathrm{with}\mathrm{RampCoef}=\mathrm{MaxCV}/100$ $\mathrm{Or}\mathrm{Opening}\left(\%\right)=\left(\mathrm{CV}*100\right)/\mathrm{MaxC}$

In one example for an “ideal SEHI-400”, e.g., modeling a specific, real flow control valve by Micro Control Systems, with MaxCv=14.5:

$\mathrm{Opening}\left(\%\right)=\left(\mathrm{Cv}/14.5\right)*100=6.897*Cv$

As modeled above, the percentage of expansion valve opening is linearly proportional to the refrigerant flow, as modified by the ramp coefficient, for the idealized, virtual EXV, reaching 100% expansion valve opening for the targeted maximum refrigerant flow.

Dual Stage Control

Dual stage control is described below, for some embodiments as suitable for FIG. 4. Here, two real expansion valves are used, one expansion valve operated as a low stage valve (LSV) and another expansion valve operated as a high stage valve (HSV), with the combination of expansion valves operated as a virtual expansion valve using dual stage control. FIG. 4 illustrates modules and parameter passing in some embodiments of a refrigerant circuit system that operates two expansion valves, for example as illustrated in FIGS. 1 and 3, according to a virtual expansion valve. In various embodiments, these modules are embedded in the controller 100 (see FIG. 1), distributed into two or more physical controllers, or in the EXV control module, etc.

At a high level, the system determines a directed flow rate for refrigerant, based on control input, then encodes the directed flow rate in individual control inputs for refrigerant metering devices, one operated as LSV, the other as HSV. More specifically, at the module level, the virtual MaxCv/100 module 70 receives a flow coefficient, and determines and passes the EXV Cv parameter value to the LSV versus HSV weighting logic module 72. The LSV versus HSV weighting logic module 72 also receives a virtual EXV opening parameter value, to which it applies the aforementioned weighting, to determine LSV Cv and HSV Cv, for the two expansion valves. LSV Cv is communicated to the 100/LSV MaxCv module 74, which determines % FC LSV and communicates this to the LSV UniEXVDriver module 76, to control the low stage expansion valve. HSV Cv is communicated to the 100/HSV MaxCv module 74, which determines % FC HSV and communicates this to the HSV UniEXVDriver module 76, to control the low stage expansion valve.

Continuing with FIG. 4, for dual stage, dual EXV control, the % FlowCoef should be converted back to virtual EXV Cv (VEXVCv) which will be divided into two Cv (one for LSV and the other for HSV considering that two Cv in parallel can be added to give one total Cv), then converted to % FlowCoefLSV and % FlowCoefHSV and applied to related physical EXV. Thus, the modules and parameter passing in FIG. 4 show a controller of some embodiments of a refrigerant circuit receiving a virtual EXV opening as an input representing a directed flow rate of a refrigerant through a virtual refrigerant metering device, applying weighting for operating one EXV as a low stage valve, operating another EXV as a high stage valve, and generating individual control inputs for the two real, non-virtual EXVs or refrigerant metering devices.

Alternatively, for an embodiment using single EXV control, the % FlowCoef coming from main EXV control (e.g. condenser liquid level control) is converted to % opening and applied to the single, physical EXV (see, e.g., FIG. 2). This control may be single stage, or dual stage, for the single EXV, in various embodiments.

LSV Vs HSV Weighting Logic

The weighting logic links between a virtual perfect or ideal actuator, e.g., the virtual refrigerant metering device or virtual EXV, and two real (imperfect) actuators, e.g., real, non-virtual, refrigerant metering devices or EXVs. In addition, the developed, parameterized implementation of such an algorithm in a specific system embodiment (see, e.g., FIGS. 4-8C and FIG. 9 flow diagram) controls the real EXVs in a way to ensure that there will be the lowest delay as possible as well as no or low discontinuity to respect the virtual EXV curve as circuit EXV control is based on an incremental PID in some embodiments. In some embodiments, it is desirable, as much as possible, to avoid a perturbation effect that can lead to unintended refrigerant flow behavior.

In some embodiments, there are two or more different control phases (see, e.g., Phase 1 and Phase 2 in FIGS. 5A-6, and see also alternatives in FIGS. 8A-8C). Examples of weights for the control phases, e.g., for the LSV versus HSV weighting logic module 72 of FIG. 4, are discussed below with reference to FIG. 5A-8C. For these examples, at any point on the horizontal axis, the two weights (for the two expansion valves) add up to a value of “1”. In parametric terms, what this means is the sum of the weighting at any given operating point in any control phase is normalized to “1” or, equivalently, 100%. More specifically, for a dual EXV embodiment, the weighting on the LSV plus the weighting on the HSV add up to “1”, at any operating point. The weighting applied to the respective Cv curves, or characteristic curves of the refrigerant metering devices, maps to the ideal characteristic curve of the virtual refrigerant metering device and vice versa.

Dual Stage, Dual EXV Operation and Parameters

Three versions of dual stage operation of two real, non-virtual, expansion valves or refrigerant metering devices are described below with reference to FIG. 5A-5C, for various embodiments of a refrigerant circuit system or controller thereof, and related method. These embodiments feature operation of one EXV as a low stage expansion valve or LSV, and operation of another EXV as a high stage expansion valve or HSV, as dual EXV operation. The embodiments have similar operation and parameters in phase 1, and differ in phase 2 operation and parameters, as dual stage operation.

FIG. 5A illustrates, in graph form, operating values for two expansion valves in phase 1 and phase 2 operating regions of a refrigerant circuit system, for some embodiments. LSV 82, the weight for the low stage expansion valve, is a steady “1” value throughout Phase 1, and then drops linearly from there to “0” across Phase 2. HSV 84, the weight for the high-stage expansion valve, is a steady “0” value throughout phase 1, and then rises linearly from there to “1” across Phase 2. The system thus performs dual stage operation of two EXVs, operating one as the low stage expansion valve, and operating the other as the high stage expansion valve, using these weighting functions.

FIG. 5B illustrates, in graph form, operating values for two expansion valves in phase 1 and phase 2 operating regions of a refrigerant circuit system, for some embodiments as an alternative to FIG. 5A. Phase 1 operation is comparable to FIG. 5A weighting functions. In Phase 2, LSV 86 drops and HSV 88 climbs, until the weighting functions both meet at “0.5” value, where they remain for the remainder of Phase 2. It is noted in this example, 50% is the minimum weight for LSV 86 and the maximum weight for HSV 88.

FIG. 5C illustrates, in graph form, operating values for two expansion valves in phase 1 and phase 2 operating regions of a refrigerant circuit system, for some embodiments as an alternative to FIGS. 5A and 5B. Phase 1 operation is comparable to FIGS. 5A and 5B weighting functions. In Phase 2, LSV 90 drops to “0.3” value, HSV 92 rises to “0.7” value, where the weighting functions remain for the remainder of Phase 2. It is noted the two weighting functions cross over one another, and the minimum weight for LSV 90 is 30%.

In the low part of virtual EXV curve (e.g., phase 1), only the LSV 90 is used:

LSVCv=VEXVCv and HSVCv=0

Over HighLSVCv (related to LSV MaxCv) while VEXVCv is increasing, LSVCv will linearly decrease to be 0 (LSV closed) when VEXVCv=VEXV MaxCv. Here, in this embodiment, the control system should not let LSVCv be lower than LowLSVCv (related to current VEXVCv). And, in this case, the control system should compensate for virtual EXV Cv with HSVCv:

$\mathrm{LSVC}=\mathrm{HighLSVCv}*\left(\mathrm{MaxVEXVCv}-\mathrm{VEXVCv}\right)$ $\left(\mathrm{MaxVEXVCv}-\mathrm{HighLSVCv}\right)$

In some embodiments, the control system does not allow LSV 90 going lower than LowLSVCv (related to current VEXVCv, and here shown as value “0.3” or 30%), as follows.

$\mathrm{LowLSVCv}=\mathrm{VEXVCv}*\mathrm{LSVMinWeight}$ $\mathrm{if}\mathrm{LSVCv}<\mathrm{LowLSVCv}\mathrm{then}\mathrm{LSVCV}=\mathrm{LowLSVCv}$

In some embodiments, the control system should not allow HSV 92 going higher than HighLSVCv (related to LSV MaxCv, and here shown as value “0.7” or 70%)

if LSVCv > HighLSVCv then
LSVCV = HighLSVCv
Compensate for LSVCv with HSVCv
HSVCV = VEXVCv − LSVCv

By experience, in some embodiments for a real EXV actuator the expansion valve may not move under a 5% opening and the Cv can be erratic under a 10% opening. In order to avoid refrigerant circuit erratic refrigerant flow when the HSV starts to open, the system uses a HSV minimum opening parameter (default 5%) and uses a method to smooth as much as possible the transition from phase 1 to phase 2. A parametric example is given below.

While in phase 2:

if HSVCv < HSVCv(Min opening) then
{
Force HSV to its min opening HSVCV = HSVCv(Min opening)
Compensate for HSVCv with LSVCv LSVCV = VEXVCv − HSVCv
}

Dual Stage, Dual EXV Operation and Parameters with Hysteresis

In some embodiments, the system has a hysteresis when EXV control moves from phase 2 to phase 1 region in order to not get an “oscillating” HSV control (from 0% to Min opening) if EXV control is sticking around Phase 1 and phase 2 boundary (Phase 1 sometimes referred to as P1, and Phase 2 sometimes referred to as P2). Operating the HSV according to a hysteresis path, in some embodiments, operating the LSV according to a hysteresis path, in some embodiments, or operating the HSV according to one hysteresis path and operating the LSV according to another hysteresis path in some embodiments (see FIG. 6), mitigates such oscillating behavior.

FIG. 6 illustrates, in graph form, operating values for two expansion valves in phase 1 and phase 2 operating regions of a refrigerant circuit system, for some embodiments in which hysteresis paths are used. LSV 94 follows an upper path when transitioning from left to right in the graph, and follows a lower path when transitioning from right to left in the graph, in the hysteresis region. HSV 96 follows a lower path when transitioning from left to right in the graph, and follows an upper path when transitioning from right to left in the graph, in the hysteresis region. The hysteresis, more specifically the hysteresis paths, are provided by applying weighting functions to the characteristics curves, in refrigerant metering device operation by the refrigerant circuit system, or more specifically a controller, in various embodiments. For example, this can be done through software integration. Parametric and algorithmic description follows (and see also, FIG. 9 flow diagram).

While in the phase 2 to phase 1 transition, the HSV is kept at Min opening and phase 1 normal functioning is restored when VEXVCv is less than 90% of HighLSVCv:

if Phase2toPhase1Mode then
{
HSVCV = HSVCv(Min opening)
LSVCV = VEXVCv − HSVCv
if VEXVCv < 0.9 * HighLSVCv then
{
LSVCV = VEXVCv HSVCV = 0
Leave Phase2toPhase1Mode
}
}

LSV with HSV Combination Selection

According to real EXVs available and the virtual EXV Max Cv parameter, it is possible to create numerous new virtual actuators with different LSV and HSV behavior according to HighLSVCv and LSVMinWeight parameters definition.

Parametric Examples of Virtual EXV and Real EXVs

Following are some examples of virtual EXV creation with different and similar or same real EXVs cases. The examples illustrate system and controller embodiments, and embodiments of a development method used to develop system embodiments and controller embodiments.

In some embodiments, a development method is used to confirm control system operation with a simulator first, then on a real unit for dynamic confirmation. In some embodiments, various rules are used for Virtual EXV Maximum Cv, Low Stage Valve High Cv, Low Stage Valve Min Weighting and High Stage Valve Min Opening parameters definition. Below, in table form, are operating parameters for various example real-world expansion valves, from which examples of virtual and real EXV models are developed in accordance with some embodiments. In addition, one of the tables below also shows an example of a user interface/service tool that may include various settings, commands, etc. This example table shows the information for two example user interfaces, TD7 and TU.

	Low Stage	High Stage	Low Stage	Low Stage	Behavior
Virtual EXV	Valve	Valve	Valve	Valve	(High Stage Valve
Max Cv	(Max Cv)	(MaxCv)	High Cv	Min Weighting	Min Opening = 5%)
14.5	SEHI-175	SEHI-400	100%	0%	P1: VEXVCv ↑ 10; LSV ↑ 100%; HSV = 0% P1   P2:
	(~10)	(14.5)	(~10)		VEXVCv = 10+; HSV = 5% (0.5); LSV = 95% (9.5)
					P2: VEXVCv ↑ P; HSV = 5% (0.5); LSV ↑ (Cv-0.5) P2:
					VEXVCv ↑ 14.5; LSV ↓ 0%; HSV ↑ 100% P2:
					VEXVCv ↓ P; HSV ↓ 5%; LSV ↑
					P2   P1: VEXVCv ↓ 0.9*HighLSVCv; HSV = 5% (0.5);
					LSV ↓ (Cv-0.5)
					P1: VEXVCv ↓ 0; LSV ↓ 0%; HSV = 0%
14.5	SEHI-175	SEHI-175	82%	50%	P1: VEXVCv ↑ 7.26; LSV ↑ 82%; HSV = 0%
	(~10)	(~10)	(7.26)		P1   P2: VEXVCv = 7.26+; HSV = 5% (0.02); LSV = 81%
					(7.24)
					P2: VEXVCv ↑ P; HSV = 5% (0.02); LSV ↑ (Cv- 0.02)
					P2: VEXVCv ↑; LSV ↓ 0.5*Cv; HSV ↑ 0.5*Cv P2:
					VEXVCv ↑ 14.5; LSV ↑ 82%; HSV ↑ 82% P2: VEXVCv
					↓ P; HSV ↓ 5%; LSV ↑
					P2   P1: VEXVCv ↓ 0.9*HighLSVCv; HSV = 5% (0.02);
					LSV ↓ (Cv-0.02)
					P1: VEXVCv ↓ 0; LSV ↓ 0%; HSV = 0%
20	SEHI-175	SEHI-175	100%	50%	P1: VEXVCv ↑ 10; LSV ↑ 100%; HSV = 0% P1   P2:
	(~10)	(~10)	(~10)		VEXVCv = 10+; HSV = 5% (0.02); LSV = 99% (9.98)
					P2: VEXVCv ↑ P; HSV = 5% (0.02); LSV ↑ (Cv- 0.02)
					P2: VEXVCv ↑; LSV ↓ 0.5*Cv; HSV ↑ 0.5*Cv P2:
					VEXVCv ↑ 20; LSV ↑ 100%; HSV ↑ 100% P2: VEXVCv
					↓ P; HSV ↓ 5%; LSV ↑
					P2   P1: VEXVCv ↓ 0.9*HighLSVCv; HSV = 5% (0.02);
					LSV ↓ (Cv-0.02)
					P1: VEXVCv ↓ 0; LSV ↓ 0%; HSV = 0%
58	SEHI-T	SEHI-T	100%	50%	P1: VEXVCv ↑ 29; LSV ↑ 100%; HSV = 0% P1   P2:
	(~29)	(~29)	(~29)		VEXVCv = 29+; HSV = 5% (0.5); LSV = 97% (28.5)
					P2: VEXVCv ↑ P; HSV = 5% (0.5); LSV ↑ (Cv-0.5) P2:
					VEXVCv ↑; LSV ↓ 0.5*Cv; HSV ↑ 0.5*Cv
					P2: VEXVCv ↑ 58; LSV ↑ 100%; HSV ↑ 100% P2:
					VEXVCv ↓ P; HSV ↓ 5%; LSV ↑
					P2   P1: VEXVCv ↓ 0.9*HighLSVCv; HSV = 5% (0.5);
					LSV ↓ (Cv-0.5)
					P1: VEXVCv ↓ 0; LSV ↓ 0%; HSV = 0%
13.9	SERI-LS	SEHI-175	100%	30%	P1: VEXVCv ↑ 3.9; LSV ↑ 100%; HSV = 0% P1   P2:
(~SEHI-400)	(~3.9)	(~10)	(~3.9)		VEXVCv = 3.9+; HSV = 5% (0.02); LSV = 99% (3.88)
					P2: VEXVCv ↑ P; HSV = 5% (0.02); LSV ↑ (Cv- 0.02)
					P2: VEXVCv ↑ 13.9; LSV ↓↑ 100%; HSV ↑ 100% P2:
					VEXVCv ↓ P; HSV ↓ 5%; LSV ↑
					P2   P1: VEXVCv ↓ 0.9*HighLSVCv; HSV = 5% (0.02);
					LSV ↓ (Cv-0.02)
					P1: VEXVCv ↓ 0; LSV ↓ 0%; HSV = 0%

User Interface/Service Tool

	Status or	Allowed Values,	Volatile or
Data Item	Setting	Setting Default	Non-Volatile	TD7	TU
Virtual EXV (circuit EXV					X
seen by the control)
EXV Command (%) CktX	Status	%			X
EXV Flow Coefficient CktX	Status	%			X
EXV Flow Coefficient Command CktX	Status
EXV Override Time Remaining CktX	Status	Min:Sec		X	X
EXV Percent Open CktX	Status	%		X	X
EXV Manual Control Override CktX	Setting	[Auto; Manual] Auto	Volatile	X	X
EXV Recalibration Time	Setting	[0; 1000]	Non-Volatile
		24 Hr
Manual EXV Position Command CktX	Setting	[0; 100]	Volatile	X	X
		0%
EXV Command (steps) CktX	Status	No more used
EXV Position Steps CktX	Status	No more used
EXV Maximum Steps CktX	Status	No more used
Virtual EXV Maximum Cv CktX	Setting	[0; 200]	Non-Volatile		X
		14.5			Lvl4
Low Stage EXV
Low Stage EXV Flow Coefficient CktX	Status	%			X
Low Stage EXV Percent Open CktX	Status	%		X	X
Low Stage EXV Command Steps CktX	Status				X
Low Stage EXV Position Steps CktX	Status				X
Low Stage EXV Maximum Steps CktX	Status				X
Low Stage EXV High Cv CktX	Setting	[50; 100]	Non-Volatile		X
(relative to low stage EXV max Cv)		100%			Lvl4
Low Stage EXV Min Weighting CktX	Setting	[0; 50]	Non-Volatile		X
(relative to virtual EXV current Cv)		0%			Lvl4
High Stage EXV
High Stage EXV Flow Coefficient CktX	Status	%			X
High Stage EXV Percent Open CktX	Status	%		X	X
High Stage EXV Command Steps CktX	Status				X
High Stage EXV Position Steps CktX	Status				X
High Stage EXV Maximum Steps CktX	Status				X
High Stage EXV Min Opening CktX	Setting	[0; 20]	Non-Volatile		X
		5%			Lvl4

Examples are given below of EXV models developed based on the above example real-world EXVs, for refrigerant circuit systems that have a single, virtual LXV and multiple real EXVs, and control operation thereof, in various embodiments. A virtual LXV model is developed based on a real LXV (see FIGS. 8A-8C), real LXV models are developed (see FIG. 7), a weighting model is developed (see FIGS. 5A-5C, 6, 8A-8C), and weighting is combined with real LXV models to map to the virtual LXV model (and vice versa). The developed system or controller embodiment (see FIGS. 1, 3, 4) then controls the real EXVs according to the virtual EXV model as mapped through the weighting to the real LXV models (see FIG. 9 flow diagram).

Example Expansion Valves for Dual Stage, Dual EXV

FIG. 7 illustrates, in table and graph form, operating values for two expansion valves in a refrigerant circuit system, for some embodiments. Specifically, the SEHI-400 Cv curve 102 and the SEHI-175 Cv curve 104 (e.g., characteristics curves for the real refrigerant metering devices) are shown, in 0-100% refrigerant flow and valve opening position range on the left, with dashed line at 10%, and 0-50% low refrigerant flow range 106 or operating region (magnified) on the right. Although developed for specific EXVs in this embodiment, further embodiments with other, specific EXVs or refrigerant metering devices are readily developed in keeping with the teachings herein.

For this example, the refrigerant flow controllability performance explanation is as follows. Consider a RTWF case where a SEHI-400 has been selected while selection possibility is at the limit between SEHI-175 and SEHI-400. Here are the Cv curves 102, 104 in FIG. 7, which can be found in or based on EXV model specification(s):

	SEHI-175		SY1214 (SEHI-400)
	Cv	Position	Cv	Position
	0.000	0%	0.000	0%
	0.010	2%	0.100	2%
	0.020	5%	0.500	5%
	0.050	8%	0.900	8%
	0.200	10%	1.152	10%
	0.267	12%	1.408	12%
	0.453	16%	1.799	15%
	0.646	21%	2.469	20%
	0.865	24%	3.156	25%
	1.142	28%	3.857	30%
	1.710	36%	4.569	35%
	2.261	41%	5.292	40%
	3.636	52%	6.764	50%
	5.458	67%	8.267	60%
	7.261	82%	9.794	70%
	9.979	100%	11.344	80%
			12.913	90%
			14.500	100%

By inspection of the Cv curves 102, 104 of the two expansion valves, and particularly of the low refrigerant flow range 106 in FIG. 7 (full view on the left, magnified view on the right), it is observed that refrigerant flow control under a 10% EXV opening of the larger EXV can be inaccurate and can lead to issue(s). Specifically, the Cv curve 102, for SEHI-400 (the larger LXV) shows high gain and immediate refrigerant flow for small valve opening values, which may make controllability and repeatability problematic in a real-world system in this low refrigerant flow operation realm. With reference to FIGS. 8A and 8B, and reference back to FIG. 7, these specific example real EXVs and issues relating thereto are considered, for an embodiment using dual stage control of these specific example dual expansion valves or dual refrigerant metering devices.

To develop some embodiments (e.g., make and use a specific control system or refrigerant circuit system embodiment), consider a SEHI-400 opening from 2 to 10% (8 points dynamic) which from the curve 102 in FIG. 7 gives a Cv from 0.1 to 1.15, which could indicate issues with refrigerant flow controllability such as linearity, reliability, repeatability, etc. Whereas, with a SEHI-175 there is approximately 9 to 28% opening (19 points dynamic) for the same Cv range, which could indicate relatively more linear, reliable and repeatable refrigerant flow controllability for that range. So, for better refrigerant flow controllability, some embodiments use the SEHI-175 for conditions where the needed Cv is low, while the SEHI-400 is used to reach the highest Cv. Some embodiments use two SEHI-175. Some embodiments use two SEHI-T. Further embodiments with other refrigerant metering devices or expansion valves, in various combinations, are readily developed, for example based on below description and illustration.

Example Dual Stage, Dual EXV Development with SEHI-175 and SEHI-400

FIG. 8A illustrates, in table and graph form, operating values for two expansion valves and an idealized target valve that serves for modeling a virtual expansion valve, for some embodiments. Specifically, the SEHI-175 Cv curve 107 for operating the “low stage valve” (LSV), the SEHI-400 Cv curve 110 for operating the “high stage valve” (HSV), and the idealized Cv curve 108 for operating the virtual or target expansion valve are shown. The idealized Cv curve 108 (or variation thereof) may be termed a target characteristic curve of the virtual refrigerant metering device.

In some embodiments with reference to FIG. 8A, the principle is applied to a RTWF with a SEHI-175 and a SEHI-400. These two real EXVs are controlled by the control system in accordance with a virtual EXV, in some embodiments, as follows. The SEHI-175 is considered smaller, e.g. a low-volume expansion valve with maximum flow rate lower than a maximum flow rate of the larger, high-volume expansion valve, the SEHI-400.

In some embodiments, the control system uses a virtual EXV (Target) defined with ideal Cv curve 108 (Cv=A×opening) from 0 to 100% opening (e.g., with a choice of 5% interval, but other intervals could be used) based on SEHI-400 max Cv (e.g., 14.5). Then, considering a dual real EXV mounting with SEHI-175 as the low stage valve (LSV) and SEHI-400 as the high stage valve (HSV), define weighting for LSV from 100% to 0% by taking care of the virtual position where it is judicious to ramp down the LSV weight (here chosen at 50%) while HSV weight (=100−LSV weight) ramps up. With the weights defined, compute LSV and HSV requested Cv (=weight×virtual EXV Cv) which is then converted to LSV and HSV positions according to respective weighted, real EXV Cv curves 107, 110.

Thus, FIG. 8A illustrates development of a dual stage, dual EXV refrigerant circuit system, or controller for same, in which the two EXVs or refrigerant metering devices differ. The smaller EXV is operated as a low stage valve with one weighting function applied to the characteristic curve for the smaller EXV (e.g., Cv curve 106). The larger EXV is operated as a high stage valve with another weighting function applied to the characteristic curve for the larger EXV (e.g., Cv curve 110). The two EXVs are operated with dual stage control according to the target characteristic curve of the virtual refrigerant metering device (e.g., ideal Cv curve 108).

Example Dual Stage, Dual EXV Development with Two SEHI-175

FIG. 8B illustrates, in table and graph form, operating values for two expansion valves and an idealized target valve that serves for modeling a virtual expansion valve, for some embodiments as an alternative to FIG. 8A. Specifically, the SEHI-175 Cv curve 112 for operating the “low stage valve”, the SEHI-175 Cv curve 116 for operating the “high stage valve”, and the idealized Cv curve 114 for operating the virtual or target expansion valve are shown. Note that the two real-world EXVs are the same physical units (e.g., identical components, physically), but one is operated as the low stage valve with one weighting function applied for the Cv curve 112 and the other is operated as the high stage valve with another weighting function applied for the Cv curve 116, thus control of the units differs in the system embodiment, from the embodiment illustrated in FIG. 8A.

FIG. 8B thus illustrates development of a dual stage, dual EXV refrigerant circuit system, or controller for same, in which the two EXVs or refrigerant metering devices are the same (e.g., identical or substantially so, examples of the same specific expansion valve). One of the two identical EXVs is operated as a low stage valve (see left side of FIG. 8B), the two identical EXVs are operated together as a high stage valve (see right side of FIG. 8B), and there is a transition region in which the EXV operated as the low stage valve is ramped down and the other EXV is ramped up (see middle of FIG. 8B).

Continuing with the example with reference to FIG. 8B, if the above principle is applied to a RTWF with double SEHI-175 expansion valves, the double SEHI-175 expansion valves can cover the SEHI-400 max Cv. That is, the system with the two, smaller expansion valves and control can achieve the intended maximum refrigerant flow that would be available with the single, larger expansion valve.

In some embodiments based on the above, the system defines a virtual EXV based on SEHI-400 max Cv. The intent here is that the maximum refrigerant flow for the dual EXV system should match maximum refrigerant flow that would be available if the larger EXV were used in a single EXV-based system. Then, considering a dual real EXV mounting, with one SEHI-175 as low stage valve and another as high stage valve, define the weighting for the LSV from 100% to 50% by taking care of the virtual position where it is judicious to ramp down the LSV weight (here arbitrary chosen at 50%) while the HSV weight ramps up. By stopping ramp down of LSV weight and ramp up of HSV weight at 50% there is a point where both EXVs follow the same opening until the virtual EXV 100% opening (see right side of FIG. 8B).

Example Dual Stage, Dual EXV Development with Two SEHI-T

FIG. 8C illustrates, in table and graph form, operating values for two expansion valves and an idealized target valve that serves for modeling a virtual expansion valve, for some embodiments as an alternative to FIGS. 8A and 8B. In one example, the above principle(s) are applied to an RTHF product with double SEHI-T mounting, which may be referred to as a large tonnage unit. But, prior to applying the above principle(s), the two SEHI-T expansion valves would be controlled with the same opening request so that valve opening position range varies from 0 to 100% at the same time for both expansion valves. This could (or can, and does) lead to refrigerant flow control issue(s) when low refrigerant flow is requested, as discussed above. By using the dual stage feature with control as further described below, it is possible to overcome this risk, in an embodiment. Specifically, the SEHI-T Cv curve 118 with one weighting function for operating the “low stage valve”, the SEHI-T Cv curve 122 with another weighting function for operating the “high stage valve”, and the idealized Cv curve 120 for operating the virtual or target expansion valve are shown in FIG. 8C. Note that the two real-world EXVs are the same physical units (e.g., identical components, physically), but one is operated as the low stage valve and the other is operated as the high stage valve, using different weighting functions, and thus control of the units differs in the system.

A virtual EXV is defined, based on doubled SEHI-T max Cv (see x2 at lower left of FIG. 8C). In the low refrigerant flow realm of operation (see left side of FIG. 8C), a weighting is defined to operate only one SEHI-T as the low stage valve (see left part of SEHI-T Cv curve 118), while the other SEHI-T is “off” or valve closed (left part of SEHI-T Cv curve 122 omitted but implicitly at “0” along horizontal axis). A weighting for LSV from 100% to 50% is defined by taking care of the virtual position where it is judicious to ramp down the LSV weight (here chosen at 45% to not request LSV to go to 100% in the middle of the virtual curve) while the HSV weight ramps up (see middle of FIG. 8C). By stopping ramp down of LSV weighting in the SEHI-T Cv curve 118, and ramp up of HSV weighting in the SEHI-T Cv curve 122, at 50% there is a point (in this example at virtual EXV 70% opening on idealized Cv curve 120) where both EXVs and respective Cv curves 118, 122 follow the same expansion valve opening until the virtual EXV 100% opening (see right side of FIG. 8C).

FIG. 9 illustrates a flow diagram for a method of operating a refrigerant circuit system, in accordance with some embodiments. The method may be practiced by embodiments of a refrigerant circuit system, a controller thereof, or more generally, a processor. The method may be embodied in tangible, non-transient computer-readable media through instructions for execution by a processor. A virtual refrigerant metering device may be a virtual expansion valve or virtual EXV. A refrigerant metering device may be an expansion valve or EXV. Various specific real, non-virtual refrigerant metering devices described herein, and variations thereof, are applicable to embodiments. The method may include an algorithm and parameters as described herein in various examples and embodiments, or variation thereof.

In an action 902, the system or a controller thereof receives a control input that represents a directed flow rate of a refrigerant through a virtual refrigerant metering device. Examples are described herein for various control inputs and parameters relating thereto, and for various versions of a virtual refrigerant metering device and parameters relating thereto. In various embodiments, the refrigerant circuit system has multiple, parallel-connected, real, non-virtual, refrigerant metering devices, which are operated, by the system, according to the control input, as follows in actions 904, 906.

In an action 904, the system or controller thereof, for each refrigerant metering device of a plurality of refrigerant metering devices, determines individual control input. Individual control input, for each refrigerant metering device, is based on the control input that represents the directed flow rate, and a refrigerant flow characteristic of the refrigerant metering device. In aggregate, with each of the plurality of refrigerant metering devices controlled as to individual control input, the refrigerant metering devices provide an aggregate flow rate that is substantially equivalent to the directed flow rate. In various embodiments, the system or controller accomplishes this by modeling the virtual refrigerant metering device and the refrigerant flow characteristics of the refrigerant metering devices, as described herein with weighting, Cv curves, dual stage operation, with or without hysteresis, and further features and aspects, in various combinations or variations. “Substantially” herein means within the system and/or components manufacturing, operating, tuning, wear and/or measurement tolerances.

In an action 906, the system or controller thereof sends control inputs to the refrigerant metering devices. The control inputs, and the sending thereof, is based on determining the individual control inputs for the refrigerant metering devices, in the action 904. This action 906 may be accomplished, for example, with appropriate parameter(s) and value(s) thereof, and may be through a device driver for example, and/or further electrical, electronic, electromechanical, interface or components, etc.

It should be appreciated that the methods described herein may be performed with a digital processing system, such as a conventional, general-purpose computer system. Special purpose computers, which are designed or programmed to perform only one function may be used in the alternative. FIG. 10 is an illustration showing an exemplary computing device which may implement the embodiments described herein. The computing device of FIG. 10 may be used to perform embodiments of the functionality for the PROCESSES in accordance with some embodiments. The computing device includes a central processing unit (CPU) 1001, which may include one or more processors and which is coupled through a bus 1005 to a memory 1003, and mass storage device 1007. Mass storage device 1007 represents a persistent data storage device such as a floppy disc drive or a fixed disc drive, which may be local or remote in some embodiments. Memory 1003 may include read only memory, random access memory, etc. Applications resident on the computing device may be stored on or accessed via a computer readable medium such as memory 1003 or mass storage device 1007 in some embodiments. Applications may also be in the form of modulated electronic signals modulated accessed via a network modem or other network interface of the computing device. It should be appreciated that CPU 1001 may be embodied in a general-purpose processor, a special purpose processor, or a specially programmed logic device in some embodiments.

Display 1011 is in communication with CPU 1001, memory 1003, and mass storage device 1007, through bus 1005. Display 1011 is configured to display any visualization tools or reports associated with the system described herein. Input/output device 1009 is coupled to bus 1005 in order to communicate information in command selections to CPU 1001. It should be appreciated that data to and from external devices may be communicated through the input/output device 1009. CPU 1001 can be defined to execute the functionality described herein to enable the functionality described with reference to FIGS. 1-9. The code embodying this functionality may be stored within memory 1003 or mass storage device 1007 for execution by a processor such as CPU 1001 in some embodiments. The operating system on the computing device may be MS DOS™, MS-WINDOWS™, OS/2™, UNIX™, LINUX™, or other known operating systems. It should be appreciated that the embodiments described herein may also be integrated with a virtualized computing system implemented with physical computing resources.

It is herein shown how to develop a virtual “ideal” EXV control feature, using a virtual EXV, based on the use of two real EXVs. In some embodiments, the two real EXVs are physically identical to each other and have same refrigerant flow capacities and operating characteristics, and in some embodiments the two real EXVs are of differing refrigerant flow capacities, sizes and/or operating characteristics. This is extensible to further EXV development as it is possible to create multiple new virtual EXVs from further dual EXV combinations, with matched EXVs and differing EXVs or differing sizes, and multiple EXV combinations with matched and differing EXVs and/or sizes, refrigerant flow capacities and operating characteristics.

Clause 1. A method of operating a refrigerant circuit system, comprising: receiving a control input that represents a directed flow rate of a refrigerant through a virtual refrigerant metering device; for each refrigerant metering device of a plurality of parallel-connected, real, non-virtual, refrigerant metering devices of the refrigerant circuit system, determining individual control input for the refrigerant metering device, based, at least in part, on the control input that represents the directed flow rate, and a refrigerant flow characteristic of the refrigerant metering device, to produce a plurality of individual flow rates through the plurality of refrigerant metering devices that provide an aggregate flow rate that is substantially equivalent to the directed flow rate; and sending a plurality of control inputs to the plurality of refrigerant metering devices based on the determining of the individual control inputs for the plurality of refrigerant metering devices.

Clause 2. A method of any of the clauses listed herein, wherein the sending comprises: sending a first control input of the plurality of control inputs to a first refrigerant metering device of the plurality of refrigerant metering devices; and sending a second control input of the plurality of control inputs to a second refrigerant metering device of the plurality of refrigerant metering devices, wherein the refrigerant flow characteristic of the refrigerant metering device comprises a characteristic curve that governs a refrigerant flow rate of the refrigerant through the refrigerant metering device, the refrigerant flow characteristic of the first refrigerant metering device comprises a first characteristic curve that governs a first refrigerant flow rate of the refrigerant through the first refrigerant metering device, the refrigerant flow characteristic of the second metering device comprises a second characteristic curve that governs a second refrigerant flow rate of the refrigerant through the second refrigerant metering device, and the determining the individual control input for the first refrigerant metering device and the individual control input for the second refrigerant metering device is performed such that the aggregate flow rate comprises a combination of the first refrigerant flow rate and the second refrigerant flow rate.

Clause 3. A method of any of the clauses listed herein, wherein the individual control input for the first refrigerant metering device according to the first characteristic curve and the individual control input for the second refrigerant metering device according to the second characteristic curve are determined to follow a target characteristic curve of the virtual refrigerant metering device.

Clause 4. A method of any of the clauses listed herein, wherein the first characteristic curve is a first flow coefficient versus refrigerant metering device setting curve, the second characteristic curve is a second flow coefficient versus refrigerant metering device setting curve, the individual control input for the first refrigerant metering device is determined, at least in part, by determining a first refrigerant metering device setting, based, at least in part, on a first weighting function, the first characteristic curve, and the target characteristic curve of the virtual refrigerant metering device, and the individual control input for the second refrigerant metering device is determined, at least in part, by determining a second refrigerant metering device setting, based, at least in part, on a second weighting function, the second characteristic curve, and the target characteristic curve of the virtual refrigerant metering device.

Clause 5. A method of any of the clauses listed herein, wherein the first refrigerant metering device is a first electronic expansion valve, the second refrigerant metering device is a second electronic expansion valve, the first refrigerant metering device setting is a first valve opening percentage, and the second refrigerant metering device setting is a second valve opening percentage.

Clause 6. A method of any of the clauses listed herein, wherein for a point on the target characteristic curve of the virtual refrigerant metering device, the first weighting function and the second weighting function transition between a first phase and a second phase relative to the first characteristic curve and the second characteristic curve.

Clause 7. A method of any of the clauses listed herein, wherein the first weighting function and the second weighting function provide hysteresis in refrigerant metering device operation relative to the first characteristic curve and the second characteristic curve.

Clause 8. A method of any of the clauses listed herein, wherein the individual control input for the refrigerant metering device differs between ones of the plurality of refrigerant metering devices as a result of the characteristic curve of the refrigerant metering device differing between the ones of the plurality of refrigerant metering devices.

Clause 9. A method of any of the clauses listed herein, wherein each refrigerant metering device is of a respective refrigerant metering device type such that the characteristic curve of each one of the plurality of refrigerant metering devices is different from at least one other refrigerant metering device of the plurality of refrigerant metering devices.

Clause 10. A method of any of the clauses listed herein, wherein the respective refrigerant metering device type is selected from a set consisting of a low-volume expansion valve, and a high-volume expansion valve; and wherein a maximum flow rate of the low-volume expansion valve is lower than a maximum flow rate of the high-volume expansion valve.

Clause 11. A method of any of the clauses listed herein, further comprising determining the directed flow rate, based on the control input; and encoding the directed flow rate in the individual control input for the refrigerant metering device, for each of the plurality of refrigerant metering devices.

Clause 12. A method of any of the clauses listed herein, wherein the refrigerant is a metered refrigerant, the plurality of control inputs are of a single signal type, and the single signal type is one of an electrical signal or a mechanical signal.

Clause 13. A method of any of the clauses listed herein, wherein the plurality of refrigerant metering devices is of a single metering device type, and the single metering device type comprises one of an electronic expansion valve, a thermal expansion valve, an externally-equalized expansion valve, or an internally-equalized expansion valve.

Clause 14. A controller comprising one or more processors, wherein the controller is configured to receive a control input that represents a directed flow rate of a refrigerant through a virtual refrigerant metering device; one or more outputs, coupled to the one or more processors and configured to be communicatively coupled to a plurality of parallel-connected, real, non-virtual refrigerant metering devices; and a computer-readable storage medium coupled to the one or more processors, comprising program instructions, which, when executed by the one or more processors, cause the controller to: receive the control input that represents the directed flow rate of the refrigerant through the virtual refrigerant metering device; for each refrigerant metering device of the plurality of refrigerant metering devices, determine individual control input for the refrigerant metering device, based, at least in part, on the control input that represents the directed flow rate, and a refrigerant flow characteristic of the refrigerant metering device, to produce a plurality of individual flow rates through the plurality of refrigerant metering devices that provides an aggregate flow rate that is substantially equivalent to the directed flow rate, and send, via the one or more outputs, one or more control inputs to the plurality of refrigerant metering devices based on the determined individual control inputs for the plurality of refrigerant metering devices.

Clause 15. The controller of any of the clauses listed herein, wherein the program instructions that send the one or more control signals comprise further program instructions that cause the controller to send a first control input of the one or more control inputs to a first refrigerant metering device of the plurality of refrigerant metering devices; and send a second control input of the one or more control inputs to a second refrigerant metering device of the plurality of refrigerant metering devices, wherein that refrigerant flow characteristic of the refrigerant metering device comprises a characteristic curve that governs a refrigerant flow rate of the refrigerant through the refrigerant metering device, the characteristic of the first refrigerant metering device comprises a first characteristic curve that governs a first refrigerant flow rate of the refrigerant through the first refrigerant metering device, the characteristic of the second refrigerant metering device is described by a second characteristic curve that governs a second refrigerant flow rate of the refrigerant through the second refrigerant metering device, and the individual control input for the first refrigerant metering device and the individual control input for the second refrigerant metering device are determined such that the aggregate refrigerant flow rate comprises a combination of the first refrigerant flow rate and the second refrigerant flow rate.

Clause 16. The controller of any of the clauses listed herein, wherein the individual control input for the first refrigerant metering device according to the first characteristic curve and the individual control input for the second refrigerant metering device according to the second characteristic curve are determined to follow a target characteristic curve of the virtual refrigerant metering device, the first characteristic curve is a first flow coefficient versus refrigerant metering device setting curve, the second characteristic curve is a second flow coefficient versus refrigerant metering device setting curve, the individual control input for the first refrigerant metering device is determined, at least in part, by determining a first refrigerant metering device setting, based, at least in part, on a first weighting function, the first characteristic curve, and the target characteristic curve of the virtual refrigerant metering device, and the individual control input for the second refrigerant metering device is determined, at least in part, by determining a second refrigerant metering device setting, based, at least in part, on a second weighting function, the second characteristic curve, and the target characteristic curve of the virtual refrigerant metering device.

Clause 17. The controller of any of the clauses listed herein, wherein the first refrigerant metering device is a first electronic expansion valve, the second refrigerant metering device is a second electronic expansion valve, the first refrigerant metering device setting is a first valve opening percentage, and the second refrigerant metering device setting is a second valve opening percentage.

Clause 18. The controller of any of the clauses listed herein, wherein for a point on the target characteristic curve of the virtual refrigerant metering device, the first weighting function and the second weighting function transition between a first phase and a second phase relative to the first characteristic curve and the second characteristic curve, and the first weighting function and the second weighting function provide hysteresis in refrigerant metering device operation relative to the first characteristic curve and the second characteristic curve.

Clause 19. The controller of any of the clauses listed herein, wherein the individual control input for the refrigerant metering device differs between ones of the plurality of refrigerant metering devices as a result of the characteristic curve of the refrigerant metering device differing between the ones of the plurality of refrigerant metering devices, and the characteristic of the refrigerant metering device comprises a maximum flow rate of the refrigerant metering device.

Clause 20. The controller of any of the clauses listed herein, wherein each refrigerant metering device is of a respective refrigerant metering device type such that the characteristic curve of each one of the plurality of refrigerant metering devices is different from at least one other refrigerant metering device of the plurality of refrigerant metering devices, the respective refrigerant metering device type is selected from a set consisting of a low-volume expansion valve, and a high-volume expansion valve; and wherein a maximum flow rate of the low-volume expansion valve is lower than a maximum flow rate of the high-volume expansion valve.

Clause 21. The controller of any of the clauses listed herein, wherein the controller is in a system that comprises another controller, the controller is communicatively coupled to receive the control input from the another controller, and the another controller is configured to determine the directed flow rate, encode the directed flow rate in the control input, and send the control input to the controller.

Detailed illustrative embodiments are disclosed herein. However, specific functional details disclosed herein are merely representative for purposes of describing embodiments. Embodiments may, however, be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein.

It should be understood that although the terms first, second, etc. may be used herein to describe various steps or calculations, these steps or calculations should not be limited by these terms. These terms are only used to distinguish one step or calculation from another. For example, a first calculation could be termed a second calculation, and, similarly, a second step could be termed a first step, without departing from the scope of this disclosure. As used herein, the term “and/or” and the “/” symbol includes any and all combinations of one or more of the associated listed items.

As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “includes”, and/or “including”, when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Therefore, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.

It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed substantially concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.

With the above embodiments in mind, it should be understood that the embodiments might employ various computer-implemented operations involving data stored in computer systems. These operations are those requiring physical manipulation of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. Further, the manipulations performed are often referred to in terms, such as producing, identifying, determining, or comparing. Any of the operations described herein that form part of the embodiments are useful machine operations. The embodiments also relate to a device or an apparatus for performing these operations. The apparatus can be specially constructed for the required purpose, or the apparatus can be a general-purpose computer selectively activated or configured by a computer program stored in the computer. In particular, various general-purpose machines can be used with computer programs written in accordance with the teachings herein, or it may be more convenient to construct a more specialized apparatus to perform the required operations.

A module, an application, a layer, an agent or other method-operable entity could be implemented as hardware, firmware, or a processor executing software, or combinations thereof. It should be appreciated that, where a software-based embodiment is disclosed herein, the software can be embodied in a physical machine such as a controller. For example, a controller could include a first module and a second module. A controller could be configured to perform various actions, e.g., of a method, an application, a layer or an agent.

The embodiments can also be embodied as computer readable code on a tangible non-transitory computer readable medium. The computer readable medium is any data storage device that can store data, which can be thereafter read by a computer system. Examples of the computer readable medium include hard drives, network attached storage (NAS), read-only memory, random-access memory, CD-ROMs, CD-Rs, CD-RWs, magnetic tapes, and other optical and non-optical data storage devices. The computer readable medium can also be distributed over a network coupled computer system so that the computer readable code is stored and executed in a distributed fashion. Embodiments described herein may be practiced with various computer system configurations including hand-held devices, tablets, microprocessor systems, microprocessor-based or programmable consumer electronics, minicomputers, mainframe computers and the like. The embodiments can also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a wire-based or wireless network.

Although the method operations were described in a specific order, it should be understood that other operations may be performed in between described operations, described operations may be adjusted so that they occur at slightly different times or the described operations may be distributed in a system which allows the occurrence of the processing operations at various intervals associated with the processing.

In various embodiments, one or more portions of the methods and mechanisms described herein may form part of a cloud-computing environment. In such embodiments, resources may be provided over the Internet as services according to one or more various models. Such models may include Infrastructure as a Service (IaaS), Platform as a Service (PaaS), and Software as a Service (SaaS). In IaaS, computer infrastructure is delivered as a service. In such a case, the computing equipment is generally owned and operated by the service provider. In the PaaS model, software tools and underlying equipment used by developers to develop software solutions may be provided as a service and hosted by the service provider. SaaS typically includes a service provider licensing software as a service on demand. The service provider may host the software, or may deploy the software to a customer for a given period of time. Numerous combinations of the above models are possible and are contemplated.

Various units, circuits, or other components may be described or claimed as “configured to” or “configurable to” perform a task or tasks. In such contexts, the phrase “configured to” or “configurable to” is used to connote structure by indicating that the units/circuits/components include structure (e.g., circuitry) that performs the task or tasks during operation. As such, the unit/circuit/component can be said to be configured to perform the task, or configurable to perform the task, even when the specified unit/circuit/component is not currently operational (e.g., is not on). The units/circuits/components used with the “configured to” or “configurable to” language include hardware—for example, circuits, memory storing program instructions executable to implement the operation, etc. Reciting that a unit/circuit/component is “configured to” perform one or more tasks, or is “configurable to” perform one or more tasks, is expressly intended not to invoke 35 U.S.C. 112, sixth paragraph, for that unit/circuit/component. Additionally, “configured to” or “configurable to” can include generic structure (e.g., generic circuitry) that is manipulated by software and/or firmware (e.g., an FPGA or a general-purpose processor executing software) to operate in manner that is capable of performing the task(s) at issue. “Configured to” may also include adapting a manufacturing process (e.g., a semiconductor fabrication facility) to fabricate devices (e.g., integrated circuits) that are adapted to implement or perform one or more tasks. “Configurable to” is expressly intended not to apply to blank media, an unprogrammed processor or unprogrammed generic computer, or an unprogrammed programmable logic device, programmable gate array, or other unprogrammed device, unless accompanied by programmed media that confers the ability to the unprogrammed device to be configured to perform the disclosed function(s).

The foregoing description, for the purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the embodiments and its practical applications, to thereby enable others skilled in the art to best utilize the embodiments and various modifications as may be suited to the particular use contemplated. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.

Claims

1. A method of operating a refrigerant circuit system, comprising: receiving a control input that represents a directed flow rate of a refrigerant through a virtual refrigerant metering device;for each refrigerant metering device of a plurality of parallel-connected, real, non-virtual, refrigerant metering devices of the refrigerant circuit system, determining individual control input for the refrigerant metering device, based, at least in part, on the control input that represents the directed flow rate, and a refrigerant flow characteristic of the refrigerant metering device, to produce a plurality of individual flow rates through the plurality of refrigerant metering devices that provide an aggregate flow rate that is substantially equivalent to the directed flow rate; andsending a plurality of control inputs to the plurality of refrigerant metering devices based on the determining of the individual control inputs for the plurality of refrigerant metering devices.

2. The method of claim 1, wherein the sending comprises: sending a first control input of the plurality of control inputs to a first refrigerant metering device of the plurality of refrigerant metering devices; andsending a second control input of the plurality of control inputs to a second refrigerant metering device of the plurality of refrigerant metering devices, wherein the refrigerant flow characteristic of the refrigerant metering device comprises a characteristic curve that governs a refrigerant flow rate of the refrigerant through the refrigerant metering device,the refrigerant flow characteristic of the first refrigerant metering device comprises a first characteristic curve that governs a first refrigerant flow rate of the refrigerant through the first refrigerant metering device,the refrigerant flow characteristic of the second metering device comprises a second characteristic curve that governs a second refrigerant flow rate of the refrigerant through the second refrigerant metering device, andthe determining the individual control input for the first refrigerant metering device and the individual control input for the second refrigerant metering device is performed such that the aggregate flow rate comprises a combination of the first refrigerant flow rate and the second refrigerant flow rate.

3. The method of claim 2, wherein the individual control input for the first refrigerant metering device according to the first characteristic curve and the individual control input for the second refrigerant metering device according to the second characteristic curve are determined to follow a target characteristic curve of the virtual refrigerant metering device.

4. The method of claim 3, wherein: the first characteristic curve is a first flow coefficient versus refrigerant metering device setting curve,the second characteristic curve is a second flow coefficient versus refrigerant metering device setting curve,the individual control input for the first refrigerant metering device is determined, at least in part, by determining a first refrigerant metering device setting, based, at least in part, on a first weighting function, the first characteristic curve, and the target characteristic curve of the virtual refrigerant metering device, andthe individual control input for the second refrigerant metering device is determined, at least in part, by determining a second refrigerant metering device setting, based, at least in part, on a second weighting function, the second characteristic curve, and the target characteristic curve of the virtual refrigerant metering device.

5. The method of claim 4, wherein the first refrigerant metering device is a first electronic expansion valve,the second refrigerant metering device is a second electronic expansion valve,the first refrigerant metering device setting is a first valve opening percentage, andthe second refrigerant metering device setting is a second valve opening percentage.

6. The method of claim 4, wherein for a point on the target characteristic curve of the virtual refrigerant metering device, the first weighting function and the second weighting function transition between a first phase and a second phase relative to the first characteristic curve and the second characteristic curve.

7. The method of claim 6, wherein the first weighting function and the second weighting function provide hysteresis in refrigerant metering device operation relative to the first characteristic curve and the second characteristic curve.

8. The method of claim 1, wherein the individual control input for the refrigerant metering device differs between ones of the plurality of refrigerant metering devices as a result of the characteristic curve of the refrigerant metering device differing between the ones of the plurality of refrigerant metering devices.

9. The method of claim 1, wherein each refrigerant metering device is of a respective refrigerant metering device type such that the characteristic curve of each one of the plurality of refrigerant metering devices is different from at least one other refrigerant metering device of the plurality of refrigerant metering devices.

10. The method of claim 9, wherein the respective refrigerant metering device type is selected from a set consisting of a low-volume expansion valve, and a high-volume expansion valve; and whereina maximum flow rate of the low-volume expansion valve is lower than a maximum flow rate of the high-volume expansion valve.

11. The method of claim 1, further comprising: determining the directed flow rate, based on the control input; andencoding the directed flow rate in the individual control input for the refrigerant metering device, for each of the plurality of refrigerant metering devices.

12. The method of claim 1, wherein the refrigerant is a metered refrigerant,the plurality of control inputs are of a single signal type, andthe single signal type is one of an electrical signal or a mechanical signal.

13. The method of claim 11, wherein the plurality of refrigerant metering devices is of a single metering device type, andthe single metering device type comprises one of an electronic expansion valve, a thermal expansion valve, an externally-equalized expansion valve, or an internally-equalized expansion valve.

14. A controller comprising: one or more processors, wherein the controller is configured to receive a control input that represents a directed flow rate of a refrigerant through a virtual refrigerant metering device;one or more outputs, coupled to the one or more processors and configured to be communicatively coupled to a plurality of parallel-connected, real, non-virtual refrigerant metering devices; anda computer-readable storage medium coupled to the one or more processors, comprising program instructions, which, when executed by the one or more processors, cause the controller to: receive the control input that represents the directed flow rate of the refrigerant through the virtual refrigerant metering device;for each refrigerant metering device of the plurality of refrigerant metering devices, determine individual control input for the refrigerant metering device, based, at least in part, on the control input that represents the directed flow rate, and a refrigerant flow characteristic of the refrigerant metering device, to produce a plurality of individual flow rates through the plurality of refrigerant metering devices that provides an aggregate flow rate that is substantially equivalent to the directed flow rate, andsend, via the one or more outputs, one or more control inputs to the plurality of refrigerant metering devices based on the determined individual control inputs for the plurality of refrigerant metering devices.

15. The controller of claim 14, wherein the program instructions that send the one or more control signals comprise further program instructions that cause the controller to: send a first control input of the one or more control inputs to a first refrigerant metering device of the plurality of refrigerant metering devices; andsend a second control input of the one or more control inputs to a second refrigerant metering device of the plurality of refrigerant metering devices, wherein that refrigerant flow characteristic of the refrigerant metering device comprises a characteristic curve that governs a refrigerant flow rate of the refrigerant through the refrigerant metering device,the characteristic of the first refrigerant metering device comprises a first characteristic curve that governs a first refrigerant flow rate of the refrigerant through the first refrigerant metering device,the characteristic of the second refrigerant metering device is described by a second characteristic curve that governs a second refrigerant flow rate of the refrigerant through the second refrigerant metering device, andthe individual control input for the first refrigerant metering device and the individual control input for the second refrigerant metering device are determined such that the aggregate refrigerant flow rate comprises a combination of the first refrigerant flow rate and the second refrigerant flow rate.

16. The controller of claim 15, wherein the individual control input for the first refrigerant metering device according to the first characteristic curve and the individual control input for the second refrigerant metering device according to the second characteristic curve are determined to follow a target characteristic curve of the virtual refrigerant metering device,the first characteristic curve is a first flow coefficient versus refrigerant metering device setting curve,the second characteristic curve is a second flow coefficient versus refrigerant metering device setting curve,the individual control input for the first refrigerant metering device is determined, at least in part, by determining a first refrigerant metering device setting, based, at least in part, on a first weighting function, the first characteristic curve, and the target characteristic curve of the virtual refrigerant metering device, andthe individual control input for the second refrigerant metering device is determined, at least in part, by determining a second refrigerant metering device setting, based, at least in part, on a second weighting function, the second characteristic curve, and the target characteristic curve of the virtual refrigerant metering device.

17. The controller of claim 16, wherein the first refrigerant metering device is a first electronic expansion valve,the second refrigerant metering device is a second electronic expansion valve,the first refrigerant metering device setting is a first valve opening percentage, andthe second refrigerant metering device setting is a second valve opening percentage.

18. The controller of claim 16, wherein for a point on the target characteristic curve of the virtual refrigerant metering device, the first weighting function and the second weighting function transition between a first phase and a second phase relative to the first characteristic curve and the second characteristic curve, andthe first weighting function and the second weighting function provide hysteresis in refrigerant metering device operation relative to the first characteristic curve and the second characteristic curve.

19. The controller of claim 14, wherein the individual control input for the refrigerant metering device differs between ones of the plurality of refrigerant metering devices as a result of the characteristic curve of the refrigerant metering device differing between the ones of the plurality of refrigerant metering devices, andthe characteristic of the refrigerant metering device comprises a maximum flow rate of the refrigerant metering device.

20. The controller of claim 14, wherein each refrigerant metering device is of a respective refrigerant metering device type such that the characteristic curve of each one of the plurality of refrigerant metering devices is different from at least one other refrigerant metering device of the plurality of refrigerant metering devices,the respective refrigerant metering device type is selected from a set consisting of a low-volume expansion valve, and a high-volume expansion valve; and whereina maximum flow rate of the low-volume expansion valve is lower than a maximum flow rate of the high-volume expansion valve.

21. The controller of claim 14, wherein the controller is in a system that comprises another controller,the controller is communicatively coupled to receive the control input from the another controller, andthe another controller is configured to determine the directed flow rate,encode the directed flow rate in the control input, andsend the control input to the controller.