Refrigerant circuit expansion valve control

Abstract

A method for operating an expansion valve in a refrigerant circuit including a compressor, a condenser, the expansion valve, an evaporator and a working fluid. The method includes determining a modified subcooling value based on a condenser working fluid discharge temperature, a condenser discharge subcooling setpoint, and one or more compressor discharge temperatures and evaporator proximity temperatures. The method further includes adjusting the expansion valve according to the modified supercooling value. A refrigerant circuit for a heating, ventilation, air conditioning, and refrigeration system includes a controller configured to operate an expansion valve according to a modified supercooling value.

Description

Technical Field

[0001] The present invention relates to refrigerant circuits for heating, ventilation, air conditioning and refrigeration ("HVACR") systems. More particularly, the present invention relates to the control of expansion valves in such refrigerant circuits. Background Art

[0002] Heating, ventilation, air conditioning, and refrigeration (HVACR) systems are typically used to heat, cool, and / or ventilate an enclosed space (e.g., the interior of a commercial or residential building, the interior of a refrigerated transport unit, etc.). An HVACR system may include a refrigerant circuit for providing cooled or heated air to the area. The refrigerant circuit cools or heats the air directly or indirectly using a working fluid. Typically, the refrigerant circuit includes a compressor for compressing the working fluid and an expansion valve for expanding the compressed working fluid. Summary of the invention

[0003] In one embodiment, a method for operating an expansion valve in a refrigerant circuit. The refrigerant circuit includes a compressor, a condenser, an expansion valve, and an evaporator in fluid connection, and the refrigerant circuit contains a working fluid. The method includes determining a corrected subcooling value based on a condenser working fluid discharge temperature, a condenser discharge subcooling set point, and one or more compressor discharge temperatures and an evaporator approach temperature. The method also includes adjusting the expansion valve according to the corrected subcooling value.

[0004] In one embodiment, determining the corrected subcooling value includes modifying the subcooling value to incorporate an offset based on one or more of the compressor discharge temperature and the evaporator approach temperature.

[0005] In one embodiment, modifying the subcooling value to incorporate the offset includes applying the offset to at least one of a degree of subcooling of the working fluid discharged from the condenser, a condenser discharge subcooling set point, a condenser discharge working fluid saturation temperature, a pressure of the working fluid discharged from the condenser, and a condenser working fluid discharge temperature.

[0006] In one embodiment, the offset is configured to decrease the working fluid level in the evaporator and increase the working fluid level in the condenser.

[0007] In one embodiment, the modified subcooling value is based on the condenser working fluid discharge temperature, the condenser discharge subcooling set point, the compressor discharge temperature, and the compressor discharge superheat set point.

[0008] In one embodiment, the modified subcooling value is based on a condenser discharge subcooling set point, a compressor discharge superheat set point, a subcooling of the working fluid discharged from the condenser, and a superheat of the working fluid discharged from the compressor.

[0009] In one embodiment, determining the corrected subcooling value includes determining the subcooling value based on the condenser working fluid discharge temperature and a condenser discharge subcooling set point.

[0010] In one embodiment, determining the subcooling value includes determining a degree of subcooling of the working fluid discharged from the condenser. The degree of subcooling is the difference between the condenser working fluid discharge temperature and the saturation temperature of the working fluid discharged from the condenser.

[0011] In one embodiment, the expansion valve is adjusted according to the corrected subcooling value, such that the position of the expansion valve changes in proportion to the corrected subcooling value.

[0012] In one embodiment, the corrected subcooling value is determined based on the condenser working fluid discharge temperature, the condenser discharge subcooling set point, and the evaporator approach temperature.

[0013] In one embodiment, the corrected subcooling value is determined based on changes in the condenser working fluid discharge temperature, the condenser discharge subcooling set point, and the evaporator approach temperature.

[0014] In one embodiment, the method includes sensing a condenser working fluid discharge temperature with a first temperature sensor and sensing a compressor discharge temperature or an evaporator working fluid discharge temperature with a second temperature sensor.

[0015] In one embodiment, a refrigerant circuit for a heating, ventilation, air conditioning and refrigeration system is provided. The refrigerant circuit includes a compressor for compressing a working fluid, a condenser for condensing the working fluid compressed by the compressor, an expansion valve for expanding the working fluid condensed by the condenser, an evaporator for evaporating the working fluid expanded by the expansion valve, and a controller for the refrigerant circuit. The controller is configured to determine a corrected subcooling value based on a condenser working fluid discharge temperature, a condenser discharge subcooling set point, and one or more compressor discharge temperatures and an evaporator approach temperature. The controller is also configured to adjust the expansion valve according to the corrected subcooling value.

[0016] In one embodiment, the controller is configured to incorporate an offset into the subcooling value, the offset being based on one or more of the compressor discharge temperature and the evaporator approach temperature, in order to determine a corrected subcooling value.

[0017] In one embodiment, the offset is configured to decrease the working fluid level in the evaporator and increase the working fluid level in the condenser.

[0018] In one embodiment, the corrected subcooling value is determined based on the condenser working fluid discharge temperature, the condenser discharge subcooling set point, the compressor discharge temperature, and the compressor discharge superheat set point.

[0019] In one embodiment, the modified subcooling value is determined based on a condenser discharge subcooling set point, a compressor discharge superheat set point, a subcooling of the working fluid discharged from the condenser, and a superheat of the working fluid discharged from the compressor.

[0020] In one embodiment, the controller is configured to determine a corrected subcooling value, including the controller determining the subcooling value based on a condenser working fluid discharge temperature and a condenser discharge subcooling set point.

[0021] In one embodiment, the corrected subcooling value is determined based on the condenser working fluid discharge temperature, the condenser discharge subcooling set point, and the evaporator approach temperature.

[0022] In one embodiment, the refrigerant circuit includes a first temperature sensor and a second temperature sensor. The controller is configured to detect a condenser working fluid discharge temperature using the first temperature sensor. The controller is configured to detect a compressor working fluid discharge temperature or an evaporator working fluid discharge temperature using the second temperature sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a schematic diagram of an embodiment of a refrigerant circuit for a heating, ventilation, air conditioning, and refrigeration system.

[0024] Figure 2 According to an embodiment Figure 1 Schematic diagram of a refrigerant circuit in FIG. 1 , including the liquid levels in the condenser and evaporator of the refrigerant circuit.

[0025] Figure 3 According to an embodiment Figure 1 Schematic diagram of a refrigerant circuit in FIG. 1 , including different liquid levels in the condenser and evaporator of the refrigerant circuit.

[0026] Figure 4 is a flow chart of an embodiment of a method for controlling an expansion valve in a refrigerant circuit.

[0027] Figure 5 is a flow chart of an embodiment of a method for controlling an expansion valve in a refrigerant circuit.

[0028] Similar numbers represent similar features. DETAILED DESCRIPTION

[0029] Heating, ventilation, air conditioning, and refrigeration ("HVACR") systems are generally configured to heat and / or cool an enclosed space (e.g., the interior of a commercial or residential building, the interior of a refrigerated transport unit, etc.) The HVACR system includes a refrigerant circuit that includes a working fluid (e.g., a refrigerant, a refrigerant mixture, etc.) that circulates through the refrigerant circuit.

[0030] The refrigerant circuit includes a compressor, a condenser, an expansion valve and an evaporator. The gaseous working fluid is condensed by the condenser using a first process fluid (e.g., air, water and / or ethylene glycol, an intermediate liquid, etc.). The liquid working fluid evaporates in the evaporator to cool a second process fluid (e.g., air, water and / or ethylene glycol and an intermediate liquid, etc.). The subcooling of the working fluid can be used to control the expansion valve in the refrigerant circuit to effectively operate the condenser. During the operation of the refrigerant circuit using subcooling control, the level of the liquid working fluid in the evaporator may increase. For example, the operation of the expansion valve using subcooling control (e.g., with a relatively low subcooling set point) can change the refrigerant distribution in the refrigerant circuit, which can increase the level of the liquid working fluid in the evaporator. For example, an increase in the flow rate of the process fluid through the condenser (e.g., an increase in the condenser fan speed, the condenser pump speed, etc.) can reduce the level of the liquid working fluid in the condenser, which may increase the level of the liquid working fluid in the evaporator. Liquid working fluid in the evaporator may reach a point where liquid carryover may enter the compressor, which may damage and / or destroy the compressor.

[0031] Embodiments described herein include HVACR systems, refrigerant circuits, and methods for subcooling control of an expansion valve that helps prevent / minimize liquid carryover. The HVACR systems, refrigerant circuits, and methods can provide effective subcooling-based control of an expansion valve while also preventing / minimizing liquid carryover into the compressor.

[0032] Figure 1 is a schematic diagram of a refrigerant circuit 101 of an HVACR system 100 according to one embodiment. The refrigerant circuit 101 includes a compressor 110, a condenser 120, an expansion valve 130, and an evaporator 140. In one embodiment, the refrigerant circuit 101 can be modified to include additional components. For example, the refrigerant circuit 101 in one embodiment can include a lubricant separator, an economizer heat exchanger, one or more flow control devices, a storage tank, a dryer, a suction liquid heat exchanger, etc.

[0033] To make it clear, Figure 1 Dashed lines are provided to illustrate fluid flow through certain components (e.g., condenser 120, evaporator 140), and it should be understood that no specific route within each component is specified. The components of the refrigerant circuit 101 are fluidly connected. Figure 1As shown, the compressor 110, the condenser 120, the expansion valve 130, and the evaporator 140 are fluidly connected (e.g., in series). The refrigerant circuit 101 can be configured as a cooling system (e.g., a fluid cooler of an HVACR system, an air conditioning system, etc.) capable of operating in a cooling mode, and / or the refrigerant circuit 101 can be configured to operate as a heat pump system capable of operating in cooling and heating modes.

[0034] The refrigerant circuit 101 applies known gas compression, gas expansion and heat transfer principles. The refrigerant circuit 101 can be configured to cool a process fluid (e.g., water, air, etc.). In one embodiment, the refrigerant circuit 101 is a cooling process fluid (i.e., the second process fluid PF 2 ), the process fluid is a cooling liquid such as water, a water mixture, etc. In one embodiment, the refrigerant circuit 101 can represent an air conditioner and / or a heat pump that cools and / or heats a process fluid (e.g., air, water, etc.).

[0035] The refrigerant circuit 101 includes a working fluid flowing through the refrigerant circuit 101. The working fluid includes a refrigerant, a refrigerant mixture, etc. It should also be understood that the working fluid may also include other working fluid / refrigerant additives (e.g., lubricant(s), defoamer(s), inhibitor(s), etc.).

[0036] During the operation of the refrigerant circuit 101, the working fluid flows from the evaporator 140 into the compressor 110 in a gaseous state at a relatively low pressure. The compressor 110 compresses the gas to a high pressure state and also heats the gas. The type of compressor is not particularly limited. In one embodiment, the compressor 110 can be a type with a minimum discharge superheat for operation as required. In one example, the compressor 110 can be a scroll compressor.

[0037] After being compressed, the relatively high pressure and high temperature (gaseous) working fluid flows from the compressor 110 to and through the condenser 120. In addition to the working fluid flowing through the condenser 120, the first process fluid PF 1 (eg, external air, external water, cold water, etc.) also flows separately through the condenser 120. The condenser 120 is a heat exchanger configured to allow the working fluid and the first process fluid PF to be 1 When the first process fluid PF 1The first process fluid absorbs heat from the working fluid as it flows through the condenser 120, and the condenser 120 cools the working fluid as it flows through the condenser. In one embodiment, the condenser 120 has a working fluid volume that is equal to the working fluid volume of the evaporator 140. In one example, the working fluid volume of the condenser 120 is greater than the working fluid volume of the evaporator 140. The working fluid volume refers to the total internal volume of the heat exchanger used to accommodate the working fluid / refrigerant flowing through the heat exchanger.

[0038] The working fluid condenses into a liquid and then flows into the expansion valve 130. The expansion valve 130 allows the working fluid to expand, which converts the working fluid into a mixed vapor and liquid state. The expansion valve 130 is an electronic flow control valve that is adjustable to control the flow of the working fluid through the expansion valve 130 (e.g., having an opening that is adjustable to change the volume of the working fluid flowing through the valve). For example, an "electronic" flow control valve is driven by an electronic motor to adjust the degree of opening of the valve (e.g., to change the flow of the working fluid through the expansion valve 130). The "position" of the expansion valve 130 refers to the degree to which the valve is open or closed. The position of the expansion valve 130 includes a first position (e.g., a 100% open position), a second position (e.g., a 100% closed position or a 0% open position), and a plurality of intermediate positions (i.e., stages) between the first position and the second position (e.g., 90% open, 80% open, 70% open, 60% open, etc.). The number of intermediate positions can be selected based on the desired sensitivity of the valve. For example, based on the desired flow control of the valve, the valve may have, but is not limited to, a 10th step position, a 100th step position, a 1000th step position, etc. Control of the expansion valve 130 will be discussed in more detail below.

[0039] The relatively low temperature vapor / liquid working fluid then flows from expansion valve 130 into evaporator 140. The second process fluid PF 2 (eg, air, water, etc.) also flows through the evaporator 140. The evaporator 140 is a heat exchanger configured to allow the working fluid and the second process fluid PF 2 The evaporator 140 may be a heat exchanger used with a subcooling control expansion valve. For example, the evaporator 140 may be, but is not limited to, a flooded heat exchanger, a brazed plate heat exchanger, etc. In one embodiment, the evaporator 140 is a flooded evaporator. The working fluid is transferred from the second process fluid PF to the working fluid while flowing through the evaporator 140. 2 The second process fluid PF is cooled as it flows through the evaporator 140. 2 As the working fluid absorbs heat, the working fluid evaporates into vapor. The working fluid then returns from the evaporator 140 to the compressor 110. The above process continues while the refrigerant circuit 101 is operating, for example, in a cooling mode.

[0040] The refrigerant circuit 101 includes a controller 190. The controller 190 controls the operation of the refrigerant circuit 101 (e.g., components of the refrigerant circuit 101). In particular, the controller 190 is configured to control the operation of the expansion valve 130. The operation of the expansion valve 130 will be discussed in more detail below. The controller 190 described in the figures and below is described / illustrated as a single component. However, it should be understood that the "controller" as shown in the figures and described herein may include multiple discrete or interconnected components, which in one embodiment include a memory (not shown) and a processor (not shown). In one embodiment, the controller 190 can be a controller of the HVACR system 100.

[0041] like Figure 3 As shown, the refrigerant circuit 101 may include a device for detecting the working fluid and / or the second process fluid PF 2 For example, the temperature sensor 192A is used to detect the temperature T of the working fluid flowing from the condenser 120 to the expansion valve 130. 1 Temperature T 1 is the discharge temperature of the working fluid from the condenser 130, which may also be referred to as the condenser working fluid discharge temperature. For example, the temperature sensor 192B is used to detect the temperature T of the working fluid flowing from the compressor 110 to the condenser 120. 2 Temperature T 2 is the discharge temperature of the working fluid from compressor 110, which may also be referred to as the compressor working fluid discharge temperature or the compressor discharge temperature. For example, temperature sensor 192C is used to detect the (second) process fluid PF discharged from evaporator 140. 2 Temperature T 3 Temperature T 3 is the process fluid PF flowing out of the evaporator 140 2 The discharge temperature of the evaporator process fluid may also be referred to as the evaporator process fluid discharge temperature.

[0042] For example, the pressure sensor 194A is used to detect the pressure P of the working fluid discharged from the condenser 120. l The saturation temperature T of the working fluid discharged from the condenser 120 Sat-CD The pressure P detected by the pressure sensor 194A can be l For example, the pressure sensor 194B is used to detect the pressure P of the working fluid discharged from the compressor 110 (eg, flowing from the compressor 110 to the condenser 120). 2 The saturation temperature T of the working fluid discharged from the compressor 110 Sat-CP The pressure P detected by the pressure sensor 194B can be 2For example, the pressure sensor 194C is used to detect the pressure P of the working fluid discharged from the evaporator 140 (eg, flowing from the evaporator 140 to the compressor 110). 3 The saturation temperature T of the working fluid discharged from the evaporator 140 Sat-E The pressure P detected by the pressure sensor 194C can be 3 to detect (e.g., indirectly).

[0043] In one embodiment, the pressure drop across the condenser 120 may be minimal (eg, pressure P 1 At or about pressure P 2 ), so that the condenser discharge saturation temperature T Sat-CD and compressor discharge saturation temperature T Sat-CP Basically the same (for example, T Sat-CD ≈T Sat-CP ). In another embodiment, the pressure drop across the condenser 120 may be known from previous testing or computational modeling of the refrigerant circuit 101. In such an embodiment, a single pressure sensor 194A, 194B may be used to simultaneously detect the condenser discharge saturation temperature T Sat-CD and compressor discharge saturation temperature T Sat-CP Pressure P 1 , P 2 .

[0044] The refrigerant circuit 101 may include Figure 1 For example, the refrigerant circuit 101 may include temperature sensors for detecting the outlet temperature of the compressor 110, detecting the working fluid inlet temperature of the evaporator 140, detecting the process fluid inlet temperature of the evaporator 140, etc.

[0045] It should be understood that the saturation temperature-pressure relationship of the working fluid (e.g., a lookup table, a formula, etc.) can be determined based on previous testing of the working fluid or similar working fluids, computational modeling, etc. The controller 190 can use the saturation temperature-pressure relationship of the working fluid (e.g., stored in a memory of the controller 190) to convert the detected pressure to a corresponding saturation temperature of the working fluid.

[0046] Dashed lines are provided in the figure to illustrate electrical communication between different features. Figure 1, when the controller 190 receives measurements (e.g., temperature measurements) from each temperature sensor 192A, 192B, 192C, the dashed line extends from the controller 190 to the temperature sensor 192A, 192B, 192C. For example, when the controller 190 controls the expansion valve 130 (e.g., position of the expansion valve, regulation of the expansion valve, closing of the expansion valve), the dashed line extends from the controller 190 to the expansion valve 130. For example, in the illustrated embodiment, when the controller 190 controls the compressor 110 (e.g., controlling the speed of the compressor, controlling unloading of the compressor, etc.), the dashed line extends from the controller 190 to the compressor 110.

[0047] Figure 2 and Figure 3 is a schematic diagram of a refrigerant circuit 101 according to one embodiment. Figure 2 and Figure 3 The liquid levels of the working fluid in the condenser 120 and the evaporator 140 are shown. In the illustrated embodiment, the first process fluid PF 1 (like Figure 1 120 (eg, outside thereof), while the working fluid flows alone through one or more condenser coils 122 of the condenser 120 (eg, inside). In the illustrated embodiment, the second process fluid PF 2 (like Figure 1 As shown in FIG. 1 , the working fluid flows through the condenser tube 142 of the evaporator 140 , while the working fluid flows alone along the outside of the condenser tube 142 of the evaporator 140 .

[0048] exist Figure 2 The working fluid level LL in the condenser 120 C-1 and working fluid level LL E-1 For example, the working fluid level LL in the condenser 120 C-1 is high enough to ensure that there is almost no gas in the working fluid discharged from the condenser 120 to the expansion valve 130. For example, the working fluid level LL in the condenser 120 C-1 Low enough to allow the gaseous working fluid enough space to pass over / through the condenser coil 122 within the condenser 120.

[0049] For example, the working fluid level LL in the evaporator 140 E - 1 is low enough to ensure that there is substantially no liquid working fluid in the working fluid discharged from the evaporator 140 to the compressor 110. For example, the working fluid level LL in the evaporator 140 E-1High enough to ensure that the condenser tubes 142 are immersed (e.g., most to all of the condenser tubes 142 are covered and the liquid working fluid level is at or above the top row of condenser tubes 142). Figure 2 The expansion valve 130 in the embodiment is controlled according to the corrected subcooling value. The control of the expansion valve 130 will be discussed in more detail below.

[0050] exist Figure 3 In the process, the working fluid accumulates in the evaporator 130, resulting in the working fluid level LL in the evaporator 140 E - 2 The relatively high working fluid level may cause liquid working fluid to be carried from the evaporator 140 to the compressor 110. For example, the working fluid flowing from the evaporator 140 to the compressor 110 may be in a mixed liquid and vapor state containing liquid working fluid (e.g., the working fluid flowing into the compressor 110 contains a large amount of liquid working fluid). The working fluid level LL in the condenser 120 E - 2 For example, the low working fluid level LL in the condenser 120 E-2 The working fluid that may be caused to flow from the condenser 120 to the expansion valve 130 may include a gaseous working fluid (eg, include a gaseous working fluid and a liquid working fluid, include a large amount of the gaseous working fluid).

[0051] Figure 3 The expansion valve 130 in the refrigerant circuit 101 is changed to operate in the charge regulating subcooling mode. For example, the controller 190 is configured to operate the expansion valve 130 in the charge regulating subcooling mode. In the charge regulating subcooling mode, the expansion valve 130 is controlled according to the corrected subcooling value. The controller 190 is configured to change from the subcooling mode to the charge regulating subcooling mode based on the detected temperature in the refrigerant circuit 101. In one embodiment, the detected temperature may be the working fluid discharge temperature T of the compressor 110. 2 In one embodiment, the detected temperature may be the process fluid discharge temperature T of evaporator 140. 3 .

[0052] In one embodiment, the expansion valve 130 is configured to Figure 2 Then, Figure 3 The expansion valve 130 in the embodiment can be controlled according to the corrected subcooling value to prevent the working fluid level in the evaporator 140 from reaching a level that causes the liquid working fluid to be carried into the compressor 110. In one embodiment, the expansion valve 130 can be constantly controlled according to the corrected subcooling value, which will prevent the working fluid level in the evaporator 140 from reaching Figure 3 The relatively high working fluid level LL shown E-2The control of the expansion valve 130 will be discussed in more detail below.

[0053] In one embodiment, condenser 120 is a microchannel heat exchanger. Compared to other types of heat exchangers, microchannel heat exchangers can have relatively low working fluid volumes. For example, such relatively low volumes of microchannel condensers may cause previous control schemes of heat transfer loop 101 to cause working fluid to accumulate in evaporator 140, such as Figure 3 For example, when the condenser 120 is a heat exchanger with a relatively small working fluid volume (eg, a microchannel condenser, etc.), control of the expansion valve 130 as described herein can advantageously prevent such undesirable accumulation of working fluid in the evaporator 140.

[0054] Figure 4 1 is a flow chart of a method 1000 for operating an expansion valve in a refrigerant circuit in one embodiment. The refrigerant circuit includes a compressor (e.g., compressor 110), a condenser (e.g., condenser 120), an expansion valve, and an evaporator (e.g., evaporator 140) that are fluidly connected (e.g., in series). In one embodiment, the method 1000 may be used to operate Figure 1-3 The expansion valve 130 in the refrigerant circuit 101. For example, the controller 190 of the refrigerant circuit 101 can use the method 1000 to operate the expansion valve 130. Figure 4 In this document, the term working fluid is abbreviated as "WF" and the term process fluid is understood as "PF". Figure 4 As shown, method 1000 starts at 1010 .

[0055] At 1010, a corrected subcooling value is determined. The corrected subcooling value is based on the condenser working fluid discharge temperature 1005A (eg, the condenser working fluid discharge temperature T 1 ), condenser discharge subcooling set point 1009A, and one or more compressor working fluid discharge temperatures 1005B (e.g., compressor working fluid discharge velocity T 2 ) and the evaporator approach temperature. For example, the corrected subcooling value can be based on the condenser working fluid discharge temperature 1005A (eg, the condenser working fluid discharge temperature T 1 ), condenser discharge subcooling set point 1009A, and one or more of compressor discharge superheat and evaporator approach temperature. The condenser working fluid discharge temperature can be detected using a temperature sensor (e.g., temperature sensor 192A). The evaporator approach temperature can be detected using another temperature sensor (e.g., temperature sensor 192C) and a pressure sensor (e.g., pressure sensor 194C). Figure 3 As shown, determination of the corrected subcooling value 1010 may include 1020 , 1030 , and 1040 .

[0056] At 1020, based on the condenser working fluid discharge temperature 1005A, the condenser working fluid saturation temperature 1007A (eg, the saturation temperature of the working fluid discharged from the condenser, the condenser working fluid saturation temperature T Sat-CD ) and the condenser discharge subcooling set point 1009A to determine the subcooling value. The determination 1020 of the subcooling value may include determining a degree of subcooling 1022 of the working fluid discharged from the condenser. At 1022, the degree of subcooling is the difference between the condenser working fluid saturation temperature 1007A and the condenser working fluid discharge temperature 1005A (e.g., degree of subcooling = condenser working fluid saturation temperature 1007A - condenser working fluid discharge temperature 1005A). The condenser working fluid saturation temperature 1007A may be determined based on the pressure of the working fluid entering / discharged from the condenser (e.g., pressure P 1 ). For example, a pressure sensor (e.g., pressure sensor 194A) of the refrigerant circuit can be used to detect the working fluid condenser pressure. For example, a temperature sensor (e.g., temperature sensor 192B) can be used to detect the compressor working fluid discharge temperature.

[0057] The determination 1022 of the subcooling value may include comparing the degree of subcooling (determined at 1022) to the condenser discharge subcooling set point 1009A. For example, the comparison may be the difference between the degree of subcooling and the subcooling set point 1009A (e.g., subcooling value=determined degree of subcooling-subcooling set point 1009A). In one embodiment, the subcooling value at 1022 is the difference between the subcooling at 1022 and the subcooling set point 1009A. In one embodiment, the subcooling set point 1009A is a predetermined subcooling set point. For example, the predetermined subcooling set point 1009A may be a predetermined magnitude of subcooling (e.g., a degree of subcooling of X degrees). In one embodiment, the subcooling set point 1009A may be a variable amount / value based on a predetermined operating chart (e.g., an amount / value determined using a predetermined table, a predetermined operating chart, etc.). The subcooling set point 1009A may be selected for efficient operation of the condenser in the refrigerant circuit. The term "subcooling value" refers to a subcooling-based control value for subcooling regulation of an expansion valve in a refrigerant circuit. The subcooling value and the modified subcooling value may also be referred to as a subcooling control value and a modified subcooling control value, respectively. The method 1000 then proceeds from 1020 to 1030.

[0058] At 1030, a compressor discharge superheat is determined at 1032 and / or an evaporator approach temperature is determined at 1032. In one embodiment, 1030 includes determining the compressor discharge superheat at 1032. In such an embodiment, a modified subcooling value is determined at 1010 based on the condenser working fluid discharge temperature 1005A, the condenser discharge subcooling set point 1009A, and the compressor working fluid discharge temperature 1005B. For example, the modified subcooling value at 1010 is based on the condenser working fluid discharge temperature 1005A, the condenser discharge subcooling set point 1009A, and the compressor discharge superheat.

[0059] The compressor discharge superheat determination 1032 may include comparing the compressor discharge working fluid saturation temperature 1007B (eg, saturation temperature T Sat-CD ) and the compressor working fluid discharge temperature 1005B. For example, the compressor discharge superheat may be the difference between the compressor discharge working fluid saturation temperature 1007B and the compressor working fluid discharge temperature 1005B (e.g., superheat = compressor discharge working fluid saturation temperature 1007B - compressor working fluid discharge temperature 1005B). The compressor discharge working fluid saturation temperature 1007B may be determined based on the pressure of the working fluid discharged from the condenser (e.g., pressure P 2 For example, a pressure sensor of the refrigerant circuit (eg, pressure sensor 194B) may be used to detect the pressure of the working fluid discharged from the compressor.

[0060] In one embodiment, the pressure of the working fluid discharged from the condenser is significantly different from the pressure of the working fluid discharged from the compressor (e.g., P 1 ≠P 2 ), so that each pressure is detected separately. In another embodiment, the pressure drop from the discharge of the compressor to the discharge of the condenser may not be significant (e.g., P 1 is or approximately P 2 ). In one embodiment, the pressure drop from the discharge of the compressor to the discharge of the condenser may be known (e.g., based on previous testing, as a set point, determined based on current operation of the refrigerant circuit, etc.). In such an embodiment, a single pressure sense (e.g., from pressure sensor 192A or pressure sensor 192B) may be used to determine a single saturation temperature for both the condenser working fluid discharge saturation temperature 1007A and the compressor discharge working fluid saturation temperature 1007B.

[0061] In one embodiment, 1030 includes determining the evaporator approach temperature at 1034. In such an embodiment, the corrected subcooling value is determined at 1010 based on the condenser working fluid discharge temperature 1005A, the condenser discharge subcooling set point 1009A, and the evaporator approach temperature. The evaporator approach temperature is determined by comparing the evaporator discharge working fluid saturation temperature 1007C (e.g., the evaporator discharge working fluid saturation temperature T Sat-E ) and the evaporator process fluid discharge temperature 1005C (e.g., the evaporator process fluid discharge temperature T 3 ). For example, the evaporator approach temperature may be the difference between the evaporator discharge working fluid saturation temperature 1007C and the evaporator process fluid discharge temperature 1005C (e.g., approach temperature = evaporator process fluid discharge temperature 1005C - evaporator discharge working fluid saturation temperature 1007C). ​​The evaporator discharge working fluid saturation temperature 1007C may be determined based on the pressure of the working fluid discharged from the evaporator (e.g., pressure P 3 ). For example, a pressure sensor (e.g., pressure sensor 194C) of the refrigerant circuit may be used to detect the pressure of the working fluid discharged from the compressor. For example, a temperature sensor (e.g., temperature sensor 192C) may be used to detect the process fluid (e.g., the second process fluid PF) discharged from the evaporator. 2 ) temperature.

[0062] In one embodiment, 1030 may include determining the compressor discharge superheat at 1032 and determining the evaporator approach temperature at 1034. In such an embodiment, a corrected subcooling value is determined at 1010 based on the condenser working fluid discharge temperature 1005A, the condenser discharge subcooling set point 1009A, the compressor working fluid discharge temperature 1005B, and the evaporator approach temperature. For example, the corrected subcooling value at 1010 may be based on the condenser working fluid discharge temperature 1005A, the condenser discharge subcooling set point 1009A, the compressor discharge superheat (e.g., as determined at 1032), and the evaporator approach temperature (e.g., as determined at 1034). The method 1000 then proceeds from 1030 to 1040.

[0063] At 1040, the offset is incorporated into the subcooling value. Figure 4 As shown, 1040 includes determining an offset based on the compressor discharge superheat and / or the evaporator approach temperature at 1042. The offset may be an adjustment to the subcooling control of the expansion valve based on the compressor discharge superheat and / or the evaporator approach temperature.

[0064] In one embodiment, the offset is based on the compressor discharge superheat and the compressor discharge superheat setpoint 1009B determined at 1032. The offset can be determined based on comparing the compressor discharge superheat to the compressor discharge superheat setpoint 1009B. For example, the offset 1042 is a function of the difference between the compressor discharge superheat and the compressor discharge superheat setpoint 1009B (e.g., offset=f(compressor discharge superheat-compressor discharge superheat setpoint 1009B)). In such an embodiment, the offset 1042 can be configured such that the absolute value of the offset 1042 increases as the difference between the compressor discharge superheat and the compressor discharge superheat setpoint 1009B increases.

[0065] In one embodiment, the offset is based on the evaporator approach temperature determined at 1034. In one example, the offset is a function of the evaporator approach temperature (e.g., offset = .f(evaporator approach temperature)). The offset 1042 can be configured such that the absolute value of the offset increases as the evaporator approach temperature decreases. In another example, the offset is based on a change in the evaporator approach temperature. The offset can be a function of the change in the evaporator approach temperature over time (e.g., = f(Δ t evaporator approach temperature)). The offset can be configured to change based on how the evaporator approach temperature changes over a predetermined time period (e.g., change in evaporator approach temperature over the previous X minutes, change in a rolling average of evaporator approach temperature over the previous X minutes, etc.). In such an embodiment, the offset 1042 can be configured such that the absolute value of the offset 1042 increases as the evaporator approach temperature increases or as the evaporator approach temperature changes over time.

[0066] The corrected subcooling value is the result of incorporating the offset into the subcooling value at 1040. Incorporating the offset at 1040 is configured as a modification to the subcooling control of the expansion valve. The offset / modification is configured to cause a decrease in the working fluid level in the evaporator (e.g., from the working fluid level LL C-2 The offset / modification may also increase the working fluid level in the condenser (e.g., increase the working fluid level LL E-2 ). This may advantageously allow a combination of efficiency-based subcooling control and liquid level control in the evaporator.

[0067] In one embodiment, the merging 1040 of the offset is to apply the offset to the subcooling value to produce a modified subcooling value. For example, the subcooling value 1022 and the offset at 1042 are determined separately and then combined (e.g., subcooling value at 1020 + offset 1042, subcooling value at 1020 - offset at 1042, subcooling value at 1020 x offset at 1042, etc.).

[0068] In another embodiment, the incorporation of the offset 1040 is an offset used in the determination of the subcooling value, so that the determined subcooling value is a corrected subcooling value. For example, the incorporation of the offset 1040 can be applying the offset at 1042 to one or more pressures / temperatures used in determining the subcooling value at 1020, so that the subcooling value determined at 1020 is a corrected subcooling value. For example, the offset 1042 is applied to one or more of the condenser working fluid discharge temperature 1005A, the condenser working fluid saturation temperature 1007A, the condenser discharge subcooling set point 1009A, the pressure used to determine the condenser working fluid saturation temperature 1007A, etc. The method 1000 then proceeds from 1010 to 1050.

[0069] At 1050, the expansion valve is adjusted based on the corrected subcooling value determined at 1010. For example, the adjustment at 1050 may include changing the position of the expansion valve based on the corrected subcooling value (e.g., changing the expansion valve position in proportion to the subcooling value). For example, the adjustment at 1050 adjusts the flow of the expansion valve based on the corrected subcooling value (e.g., the flow of the expansion valve is adjusted in proportion to the subcooling value).

[0070] Figure 5 1 is a flow chart of an embodiment of a method 1100 for operating an expansion valve in a refrigerant circuit. The refrigerant circuit includes a compressor (e.g., compressor 110), a condenser (e.g., condenser 120), an expansion valve, and an evaporator (e.g., evaporator 140) that are fluidly connected (e.g., in series). In one embodiment, the method 1100 may be used to operate Figure 1-3 The expansion valve 130 in the refrigerant circuit 101. For example, the controller 190 of the refrigerant circuit 101 can use the method 1100 to operate the expansion valve 130. Figure 5 In this document, the term working fluid is abbreviated as "WF" and the term process fluid is understood as "PF". Figure 5 As shown, method 1100 starts at 1110 .

[0071] At 1110, a corrected subcooling value is determined. At 1110, based on the condenser working fluid discharge temperature 1005A (eg, the condenser working fluid discharge temperature T 1 )), a modified condenser discharge subcooling set point and a compressor working fluid discharge temperature 1005B (e.g., a compressor working fluid discharge temperature T 2 ) to determine the corrected supercooling value. Figure 5 As shown, determining a corrected subcooling value 1110 may include 1122 , 1131 , and 1141 .

[0072] At 1122, the subcooling of the working fluid discharged from the condenser is determined. The subcooling at 1122 is determined based on the condenser working fluid discharge temperature 1005A and the condenser working fluid saturation temperature 1007A. For example, the subcooling can be determined based on the condenser working fluid discharge temperature 1005A and the condenser working fluid saturation temperature 1007A. Figure 4 The subcooling is determined at 1122 in a manner similar to the subcooling determined at 1022 .

[0073] At 1131, a modified condenser discharge subcooling set point is determined. Determining the modified condenser discharge subcooling set point at 1131 includes determining the compressor discharge superheat at 1132. The compressor discharge superheat 1132 is determined based on the compressor working fluid discharge temperature 1005B and the compressor discharge working fluid saturation temperature 1007B. For example, the compressor discharge superheat can be determined at 1132 in the same manner as described above. Figure 4 The compressor discharge superheat determined at 1032 is discussed in a similar manner.

[0074] At 1131, an adjusted condenser discharge subcooling setpoint is determined based on the compressor discharge superheat (as determined at 1132) and the compressor discharge superheat setpoint 1009A. In the method 1100, the condenser discharge subcooling setpoint is the adjusted condenser discharge subcooling setpoint determined at 1131. For example, the adjusted condenser discharge subcooling setpoint at 1111 is a condenser discharge subcooling setpoint that varies based on the compressor discharge superheat (e.g., a variable setpoint that varies with the compressor discharge superheat). The modified condenser discharge subcooling setpoint may also be referred to as a variable condenser discharge subcooling setpoint.

[0075] For example, at 1131, an adjusted condenser discharge subcooling setpoint is determined based on the difference between the compressor discharge superheat (determined at 1132) and the compressor discharge superheat setpoint 1009B. In one embodiment, at 1132, an adjusted condenser discharge subcooling setpoint is determined by adjusting the condenser discharge subcooling setpoint 1009A based on the difference between the compressor discharge superheat (determined at 1132) and the compressor discharge superheat setpoint 1009B. In one embodiment, the adjusted condenser discharge subcooling setpoint at 1111 may be a variable discharge subcooling setpoint (e.g., a variable value) that varies / adjusts with the difference between the compressor discharge superheat (determined at 1111) and the compressor discharge superheat setpoint 1009B.

[0076] At 1141, a corrected subcooling value is determined based on the subcooling of the WF discharged from the condenser (as determined at 1122) and the adjusted condenser discharge subcooling set point (as determined at 1131). For example, the corrected subcooling value may be determined at 1141 based on comparing the subcooling to the adjusted condenser discharge subcooling set point. The method 1110 then proceeds to 1150.

[0077] At 1150, the expansion valve is adjusted based on the corrected subcooling value determined at 1110. For example, based on Figure 5 The modified subcooling value determined at 1110 may be used to adjust the expansion valve at 1150 similarly to the adjustment based on Figure 4 The corrected subcooling value determined at 1010 is used to adjust the expansion valve at 1050.

[0078] exist Figure 5 In method 1100 of the present invention, an offset based on the compressor discharge superheat is incorporated into a corrected subcooling value by adjusting the condenser discharge subcooling set point, on which the (corrected) subcooling value is based. Method 1100 is an example of incorporating an offset into a subcooling value by an offset applied to the condenser discharge subcooling set point 1009A, such that the resulting determined subcooling value is a corrected subcooling value. It should be understood that method 1100 can be modified to adjust the subcooling value based on the evaporator approach temperature (e.g., at Figure 4 The evaporator approach temperature determined at 1034 in (i) is used to determine an adjusted subcooling condenser discharge subcooling set point as an alternative to or in addition to the compressor discharge superheat.

[0079] The subcooling value may also be referred to as a subcooling control value, and the modified subcooling value may be referred to as a modified subcooling control value. For example, the subcooling value is based on adjusting the expansion valve to control / adjust the subcooling of the working fluid discharged from the condenser so that it is at a desired subcooling (e.g., at a condenser discharge subcooling set point). In one embodiment, Figure 4 The subcooling value at 1010 in may be a base value for controlling the expansion valve when the refrigerant circuit is operating at a desired temperature / working fluid level. In one embodiment, Figure 5 The adjustment of the adjusted condenser discharge subcooling at 1131 can be zero or approximately zero so that when the refrigerant circuit is operating at a desired temperature / working fluid level, the corrected subcooling value at 1141 can be a base value. For example, the offset at 1032 and the adjustment of the condenser discharge subcooling set point at 1131 can be configured to be set to zero when the working fluid in the evaporator is at a desired level (e.g., at working fluid level LL E-1) does not change the subcooling value. For example, when the compressor discharge superheat is equal to the compressor superheat set point and / or the evaporator approach temperature is at or approximately constant, the modified subcooling value can be equal to the subcooling value (such as the base subcooling value).

[0080] It should be understood that in another embodiment Figure 4 Method 1000 and Figure 5 The method 1100 may be based on Figure 1-3 The HVACR system 100 and the refrigerant circuit 101 in the embodiment of the present invention are modified as described above. For example, the method 1000 and / or the method 1100 may include using the temperature sensors 192A, 192B, 192C and / or the pressure sensors 194A, 194B to detect the temperature and pressure of the working fluid in the refrigerant circuit 101.

[0081] aspect:

[0082] Any of aspects 1-12 may be combined with any of aspects 13-20.

[0083] Aspect 1. A method for operating an expansion valve in a refrigerant circuit, wherein the refrigerant circuit includes a fluidically connected compressor, a condenser, an expansion valve and an evaporator, and the refrigeration circuit includes a working fluid, the method comprising: determining a corrected subcooling value based on a condenser working fluid discharge temperature, a condenser discharge subcooling set point, and one or more compressor discharge temperatures and an evaporator approach temperature; and adjusting the expansion valve according to the corrected subcooling value.

[0084] Aspect 2. The method of aspect 1, wherein determining the corrected subcooling value comprises modifying the subcooling value to incorporate an offset based on one or more of the compressor discharge temperature and the evaporator approach temperature.

[0085] Aspect 3. A method according to aspect 2, wherein modifying the subcooling value to incorporate the offset includes applying the offset to at least one of the subcooling of the working fluid discharged from the condenser, the condenser discharge subcooling set point, the condenser discharge working fluid saturation temperature, the pressure of the working fluid discharged from the cooler, and the condenser working fluid discharge temperature.

[0086] Aspect 4. The method according to any one of aspects 2-3, wherein the offset is configured to reduce the working fluid level in the evaporator and increase the working fluid level in the condenser.

[0087] Aspect 5. A method according to any one of aspects 1-4, wherein the condenser discharge subcooling set point is an adjusted discharge subcooling set point, and the determination of the corrected subcooling value includes determining the adjusted discharge subcooling set value based on one or more of the compressor discharge temperature and the evaporator approach temperature, and the corrected subcooling value is based on the condenser working fluid discharge temperature and the adjusted condenser discharge subcooling set point.

[0088] Aspect 6. A method according to any one of aspects 1-5, wherein the corrected subcooling value is based on the condenser working fluid discharge temperature, the condenser discharge subcooling set point, the compressor discharge temperature and the compressor discharge superheat set point.

[0089] Aspect 7. A method according to any one of aspects 1-6, wherein the corrected subcooling value is based on the condenser discharge subcooling set point, the compressor discharge superheat set point, the subcooling of the working fluid discharged from the condenser, and the superheat of the working fluid discharged from the compressor.

[0090] Aspect 8. The method according to any one of aspects 5-7, wherein determining the corrected subcooling value includes determining the subcooling value based on the condenser working fluid discharge temperature and the condenser discharge subcooling set point.

[0091] Aspect 9. A method according to aspect 8, wherein determining the subcooling value includes determining the degree of subcooling of the working fluid discharged from the condenser, the degree of subcooling being the difference between the condenser working fluid discharge temperature and the saturation temperature of the working fluid discharged from the condenser.

[0092] Aspect 10. A method according to any one of aspects 1 to 9, wherein the expansion valve is adjusted according to the corrected subcooling value so that the position of the expansion valve changes in proportion to the corrected subcooling value.

[0093] Aspect 11. A method according to any one of aspects 1 to 10, wherein the corrected subcooling value is determined based on the condenser working fluid discharge temperature, the condenser discharge subcooling set value and the evaporator approach temperature.

[0094] Aspect 12. A method according to any one of aspects 1 to 11, wherein the corrected subcooling value is determined based on changes in the condenser working fluid discharge temperature, the condenser discharge subcooling set point, and the evaporator approach temperature.

[0095] Aspect 13. The method according to any one of Aspects 1-12 further includes: detecting the condenser working fluid discharge temperature using a first temperature sensor; and detecting the compressor discharge temperature or the evaporator working fluid discharge temperature using a second temperature sensor.

[0096] Aspect 14. A refrigerant circuit for a heating, ventilation, air conditioning and refrigeration system, comprising: a compressor for compressing a working fluid; a condenser for condensing the working fluid compressed by the compressor; an expansion valve for expanding the working fluid condensed by the condenser; an evaporator for evaporating the working fluid expanded by the expansion valve; a controller for the refrigerant circuit, the controller being configured to: determine a corrected subcooling value based on a condenser working fluid discharge temperature, a condenser discharge subcooling set point, and one or more compressor discharge temperatures and an evaporator approach temperature; and adjust the expansion valve according to the corrected subcooling value.

[0097] Aspect 15. A refrigerant circuit according to aspect 14, wherein the controller is configured to incorporate an offset into a subcooling value, the offset being based on one or more of the compressor discharge temperature and the evaporator approach temperature in order to determine the corrected subcooling value.

[0098] Aspect 16. The refrigerant circuit of aspect 15, wherein the offset is configured to reduce the working fluid level in the evaporator and increase the working fluid level in the condenser.

[0099] Aspect 17. A refrigerant circuit according to any one of Aspects 15-16, wherein the corrected subcooling value is determined based on the condenser working fluid discharge temperature, the condenser discharge subcooling set point, the compressor discharge temperature and the compressor discharge superheat set point.

[0100] Aspect 18. A refrigerant circuit according to any one of Aspects 14-17, wherein the corrected subcooling value is determined based on the condenser discharge subcooling set point, the compressor discharge superheat set point, the subcooling of the working fluid discharged from the condenser, and the superheat of the working fluid discharged from the compressor.

[0101] Aspect 19. A refrigerant circuit according to any one of aspects 14-18, wherein the controller is configured to determine the corrected subcooling value, including the controller determining the subcooling value based on the condenser working fluid discharge temperature and the condenser discharge subcooling set point.

[0102] Aspect 20. A refrigerant circuit according to any one of aspects 14-19, wherein the corrected subcooling value is determined based on the condenser working fluid discharge temperature, the condenser discharge subcooling set point and the evaporator approach temperature.

[0103] Aspect 21. The refrigerant circuit according to any one of Aspects 14-20 further includes: a first temperature sensor, the controller being configured to use the first temperature sensor to detect the condenser working fluid discharge temperature; and a second temperature sensor, the controller being configured to use the second temperature detector to detect the compressor working fluid discharge temperature or the evaporator working fluid discharge temperature.

[0104] The terms used herein are intended to describe specific embodiments and are not restrictive. Unless expressly stated otherwise, the terms "a", "an", and "said / the" also include plural forms. The terms "include" and / or "comprise" used in this specification specify the presence of the features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations and / or elements. In one embodiment, "connected" and "connected" described herein may refer to "directly connected" and "directly connected".

[0105] With respect to the foregoing description, it should be understood that changes in detail may be made without departing from the scope of the present disclosure, especially in the construction materials used and the shape, size and arrangement of the components. This specification and the described embodiments are exemplary only, with the true scope and spirit of the present disclosure being indicated by the following claims.

Claims

1. A method for operating an expansion valve in a refrigerant circuit, characterized in that The refrigerant circuit includes a compressor, a condenser, an expansion valve, and an evaporator in fluid connection, the refrigeration circuit contains a working fluid, and the method includes: determining a modified subcooling value based on the condenser working fluid discharge temperature, the condenser discharge subcooling set point, and one or more of the compressor discharge temperature and the evaporator approach temperature; and The expansion valve is adjusted based on the corrected subcooling value.

2. The method according to claim 1, characterized in that Determining the corrected subcooling value includes modifying the subcooling value to incorporate an offset based on one or more of a compressor discharge temperature and an evaporator approach temperature.

3. The method according to claim 2, characterized in that Modifying the subcooling value to incorporate the offset includes applying the offset to at least one of the subcooling of the working fluid discharged from the condenser, the condenser discharge subcooling set point, the condenser discharge working fluid saturation temperature, the pressure of the working fluid discharged from the condenser, and the condenser working fluid discharge temperature.

4. The method according to claim 2, characterized in that: The offset is configured to decrease the working fluid level in the evaporator and increase the working fluid level in the condenser.

5. The method according to claim 1, characterized in that The condenser discharge subcooling set point is an adjusted discharge subcooling set point, and determining the corrected subcooling value includes determining the adjusted discharge subcooling set point based on one or more of the compressor discharge temperature and the evaporator approach temperature, and the corrected subcooling value is based on the condenser working fluid discharge temperature and the adjusted condenser discharge subcooling set point.

6. The method according to claim 1, characterized in that The modified subcooling value is based on the condenser working fluid discharge temperature, the condenser discharge subcooling set point, the compressor discharge temperature, and a compressor discharge superheat set point.

7. The method according to claim 1, characterized in that The modified subcooling value is based on the condenser discharge subcooling set point, the compressor discharge superheat set point, the subcooling of the working fluid discharged from the condenser, and the superheat of the working fluid discharged from the compressor.

8. The method according to claim 7, characterized in that Determining the corrected subcooling value includes determining a subcooling value based on the condenser working fluid discharge temperature and the condenser discharge subcooling set point.

9. The method according to claim 8, characterized in that The determining of the subcooling value includes determining a degree of subcooling of the working fluid discharged from the condenser, the degree of subcooling being a difference between a discharge temperature of the condenser working fluid and a saturation temperature of the working fluid discharged from the condenser.

10. The method according to claim 1, characterized in that The expansion valve is adjusted according to the corrected subcooling value so that the position of the expansion valve changes in proportion to the corrected subcooling value.

11. The method according to claim 1, characterized in that: The modified subcooling value is determined based on the condenser working fluid discharge temperature, the condenser discharge subcooling set point, and the evaporator approach temperature.

12. The method according to claim 1, characterized in that The modified subcooling value is determined based on changes in the condenser working fluid discharge temperature, the condenser discharge subcooling set point, and the evaporator approach temperature.

13. The method according to claim 1, characterized in that Further including: Using a first temperature sensor to detect the discharge temperature of the condenser working fluid; and The compressor discharge temperature or the evaporator working fluid discharge temperature is detected by a second temperature sensor.

14. A refrigerant circuit for a heating, ventilation, air conditioning and refrigeration system, characterized in that: include: A compressor for compressing a working fluid; a condenser for condensing the working fluid compressed by the compressor; an expansion valve for expanding the working fluid condensed by the condenser; an evaporator for evaporating the working fluid expanded by the expansion valve; A controller for the refrigerant circuit, the controller being configured to: determining a corrected subcooling value based on a condenser working fluid discharge temperature, a condenser discharge subcooling set point, and one or more of a compressor discharge temperature and an evaporator approach temperature; and The expansion valve is adjusted according to the corrected subcooling value.

15. The refrigerant circuit according to claim 14, characterized in that The controller is configured to incorporate an offset into a subcooling value, the offset being based on one or more of the compressor discharge temperature and the evaporator approach temperature, in order to determine the corrected subcooling value.

16. The refrigerant circuit according to claim 15, characterized in that The offset is configured to decrease the working fluid level in the evaporator and increase the working fluid level in the condenser.

17. The refrigerant circuit according to claim 14, characterized in that The modified subcooling value is determined based on the condenser working fluid discharge temperature, the condenser discharge subcooling set point, the compressor discharge temperature, and a compressor discharge superheat set point.

18. The refrigerant circuit according to claim 14, characterized in that The modified subcooling value is determined based on the condenser discharge subcooling set point, the compressor discharge superheat set point, a subcooling degree of the working fluid discharged from the condenser, and a superheat degree of the working fluid discharged from the compressor.

19. The refrigerant circuit according to claim 14, characterized in that: The controller is configured to determine the corrected subcooling value, including the controller determining the subcooling value based on the condenser working fluid discharge temperature and the condenser discharge subcooling set point.

20. The refrigerant circuit according to claim 14, characterized in that The modified subcooling value is determined based on the condenser working fluid discharge temperature, the condenser discharge subcooling set point, and the evaporator approach temperature.

21. The refrigerant circuit according to claim 14, characterized in that Further including: a first temperature sensor, the controller being configured to detect the condenser working fluid discharge temperature using the first temperature sensor; and A second temperature sensor, the controller is configured to detect the compressor working fluid discharge temperature or the evaporator working fluid discharge temperature using the second temperature sensor.

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