Compressor Lubricant Quality Management

Abstract

The present application discloses a heating, ventilation, air conditioning and refrigeration (HVACR) system. The HVACR system includes a refrigerant circuit. The refrigerant circuit includes a compressor, a condenser, an expansion device and an evaporator that are fluidly connected to each other. A controller is electrically connected to the compressor. The controller is configured to prevent the compressor from operating at a speed less than a minimum speed limit. A lubricant separator has an inlet and a plurality of outlets that are fluidly connected between the compressor and the condenser. A first outlet of the plurality of outlets is fluidly connected to the condenser. A second outlet of the plurality of outlets is fluidly connected to one or more components of the compressor to provide lubricant to the one or more components.

Description

Technical Field

[0001] The present disclosure relates generally to a heating, ventilation, air conditioning, and refrigeration (HVACR) system. More specifically, the present disclosure relates to lubricant quality management for a compressor in an HVACR system. Background Art

[0002] Heating, ventilation, air conditioning and refrigeration (HVACR) systems typically include compressors. Compressors, such as but not limited to screw compressors and scroll compressors, utilize bearings to support a rotating shaft. The bearings typically include a lubrication system. If the bearings are not properly lubricated, the bearings may fail and ultimately the compressor may fail before the expected service life of the bearings. Summary of the invention

[0003] The present disclosure relates generally to a heating, ventilation, air conditioning, and refrigeration (HVACR) system. More specifically, the present disclosure relates to lubricant quality management for a compressor in an HVACR system.

[0004] In one embodiment, the HVACR system includes a variable speed compressor. In one embodiment, the variable speed compressor is a positive displacement compressor.

[0005] In one embodiment, the variable speed compressor is a variable speed screw compressor. In one embodiment, the variable speed screw compressor can operate between a minimum speed and a maximum speed. In one embodiment, the minimum speed limit can be set to a value greater than the minimum speed at which the variable speed compressor can operate. For example, the minimum speed limit can be determined for a selected compressor efficiency and bearing size based on the saturated suction temperature and saturated discharge temperature of the selected refrigerant and lubricant.

[0006] In one embodiment, the minimum speed limit may be determined based on the saturated suction temperature, the saturated discharge temperature, and the lubricant temperature. In one embodiment, the lubricant temperature may be a measured value. In one embodiment, the lubricant temperature may be a relative lubricant temperature, which is the difference between the measured lubricant temperature and the saturated discharge temperature.

[0007] In one embodiment, the selected refrigerant includes a refrigerant that has a low discharge superheat and is miscible with the selected lubricant, which results in high lubricant dilution.

[0008] In one embodiment, the selected refrigerant includes a refrigerant having a relatively lower global warming potential (GWP) than R-134a, and the refrigerant can be used as a replacement refrigerant for R-134a.

[0009] In one embodiment, the selected refrigerant may be R1234ze(E), R-513A, R1234yf, or the like.

[0010] In one embodiment, the minimum speed limit is inversely proportional to the bearing size. That is, in one embodiment, as the bearing size decreases, the minimum speed limit increases.

[0011] In one embodiment, the HVACR system includes a lubricant separator. The lubricant separator may include a lubricant tank. In one embodiment, the combination of the lubricant separator and the lubricant tank may reduce the overall complexity of the HVACR system.

[0012] A heating, ventilation, air conditioning and refrigeration (HVACR) system is disclosed. The HVACR system includes a refrigerant circuit. The refrigerant circuit includes a compressor, a condenser, an expansion device and an evaporator that are fluidly connected to each other. The controller is electrically connected to the compressor. The controller is configured to prevent the compressor from operating at a speed less than a minimum speed limit. A lubricant separator has an inlet and a plurality of outlets that are fluidly connected between the compressor and the condenser. A first outlet of the plurality of outlets is fluidly connected to the condenser. A second outlet of the plurality of outlets is fluidly connected to one or more components of the compressor to provide lubricant to the one or more components.

[0013] A method of controlling a variable speed compressor is also disclosed. The method includes determining, using a controller of the variable speed compressor, a saturated suction temperature and a saturated discharge temperature, and calculating, using the controller of the variable speed compressor, a minimum speed limit of the variable speed compressor based on the saturated suction temperature and the saturated discharge temperature. The controller receives a cooling demand and determines a speed setting of the variable speed compressor based on the cooling demand. In response to determining that the speed setting is less than the calculated minimum speed limit, the controller overrides the speed setting, utilizes the minimum speed limit, and cools to meet the cooling demand.

[0014] A lubricant separator for a heating, ventilation, air conditioning and refrigeration (HVACR) system is also disclosed. The lubricant separator includes a first chamber and a second chamber. A conduit disposed in the first chamber fluidly connects the first chamber to the second chamber. The first chamber includes an inlet for receiving a high-pressure refrigerant / lubricant mixture and an outlet for providing the high-pressure refrigerant. The second chamber receives a lubricant portion of the refrigerant / lubricant mixture through the conduit. The second chamber includes an outlet through which a low-pressure lubricant is provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Reference is made to the accompanying drawings which form a part of this disclosure and which illustrate embodiments in which the systems and methods described herein may be practiced.

[0016] Figure 1is a schematic diagram of a refrigerant circuit according to one embodiment.

[0017] Figure 2A is a flow chart of a method for determining a minimum speed limit for a variable speed compressor according to one embodiment.

[0018] Figure 2B is a flow chart of a method for determining a minimum speed limit for a variable speed compressor according to another embodiment.

[0019] Figure 3 is a flow chart of a method for operating a variable speed compressor to maintain a minimum bearing lubricant film thickness according to one embodiment.

[0020] Figure 4 A schematic diagram illustrating a minimum operating frequency of a variable speed motor in an HVACR system according to one embodiment.

[0021] Figures 5A-5E A schematic diagram illustrating a minimum operating frequency of a variable speed motor in an HVACR system according to one embodiment.

[0022] Like reference numerals refer to like parts throughout. DETAILED DESCRIPTION

[0023] The present disclosure relates generally to a heating, ventilation, air conditioning, and refrigeration (HVACR) system. More specifically, the present disclosure relates to lubricant quality management for a compressor in an HVACR system.

[0024] There is a growing concern about the environmental impact of HVACR refrigerants. For example, since 2011, the European Union has been phasing out refrigerants with a global warming potential (GWP), such as greater than 150, in certain refrigeration systems. HVACR systems can use environmentally friendly HVACR refrigerants with suitable properties, such as density, vapor pressure, heat of vaporization, and suitable chemical properties that meet requirements regarding safety and environmental impact, such as the above-mentioned EU standards. The environmentally friendly HVACR refrigerants are non-flammable or mildly flammable, non-ozone depleting, energy-efficient, low in toxicity, compatible with structural materials, and chemically stable over the life of the equipment.

[0025] Current refrigerants, such as R134a, etc., may have relatively high GWPs. For example, R134a has a GWP of 1,430. Therefore, alternative refrigerants such as, but not limited to, R1234ze(E), R513A, etc. are being applied in HVACR systems.

[0026] When using newer refrigerant compositions (such as, but not limited to, R1234ze(E) and R513A), various problems may arise due to the different properties of the refrigerant compared to existing refrigerants (such as R134a). Generally, refrigerants with lower GWP, such as R1234ze(E), R513A, etc., may be introduced into the lubricant. In some examples, the replacement refrigerant is relatively more miscible in the lubricant than the current refrigerant, resulting in a higher concentration of the refrigerant in the lubricant (e.g., lubricant dilution).

[0027] As a result, portions of the operating map of the compressor of the HVACR system may suffer from higher lubricant dilution and limited bearing viscosity (i.e., limited viscosity of the lubricant and refrigerant mixture at the bearings) due to low discharge superheat. In some examples, the higher lubricant dilution and limited bearing viscosity issues may be more severe when the variable speed compressor is operated at relatively low speeds. Higher lubricant dilution and limited bearing viscosity may result in, for example, reduced bearing life and ultimately compressor failure. In some examples, replacing the refrigerant with R134A may require replacement of mechanical components (e.g., bearings, etc.) in the compressor.

[0028] In other examples, controlling a variable speed compressor to maximize efficiency may result in lubricant dilution issues even with current refrigerants such as R134a.

[0029] Typically, lubricants used with R134a replacement refrigerants encounter higher lubricant dilution issues.The lubricant may include any suitable lubricant that is miscible with the selected replacement refrigerant.

[0030] Generally, higher lubricant dilution may become a problem when the exhaust superheat becomes relatively low. For example, higher lubricant dilution may occur when the exhaust superheat temperature is less than or about 8°C.

[0031] In one embodiment, a minimum speed limit may be set for a variable speed compressor to limit or avoid reaching operating conditions where higher lubricant dilution and limited bearing viscosity become problematic. Thus, existing mechanical components (e.g., bearings, etc.) may be utilized. Providing a minimum speed limit for a variable speed compressor may, for example, control the linear speed of rotation of the bearings (mean diameter multiplied by speed). Thus, bearing life may be improved. In one embodiment, the minimum speed limit may be selected based on saturated suction and discharge temperatures in conjunction with the compressor frame size. In one embodiment, the compressor frame size may include bearing size and compressor efficiency.

[0032] In one embodiment, the compressor for the HVACR system is a screw compressor. In one embodiment, the screw compressor is a variable speed screw compressor capable of operating at various speeds between a minimum speed and a maximum speed.

[0033] According to one embodiment, a minimum speed for the variable speed compressor may be selected based on the discharge superheat.

[0034] In one embodiment, a minimum speed for the variable speed compressor may be selected based on the saturated suction temperature and the saturated discharge temperature.

[0035] Figure 1 1 is a schematic diagram of a refrigerant circuit 10 according to one embodiment. The refrigerant circuit 10 generally includes a compressor 12, a condenser 14, an expansion device 16, an evaporator 18, and a lubricant separator 150.

[0036] The refrigerant circuit 10 is an example and may be modified to include additional components. For example, in one embodiment, the refrigerant circuit 10 may include other components such as, but not limited to, an economizer heat exchanger, one or more flow control devices, a receiver tank, a dryer, a suction liquid heat exchanger, etc.

[0037] The refrigerant circuit 10 may be generally applied in various systems for controlling environmental conditions (eg, temperature, humidity, air quality, etc.) in a space (commonly referred to as a conditioned space). Examples of such systems include, but are not limited to, HVACR systems, transport refrigeration systems, and the like.

[0038] The compressor 12, condenser 14, expansion device 16, and evaporator 18 are fluidly connected via refrigerant lines 20, 22, 24. In one embodiment, the refrigerant lines 20, 22, and 24 may alternatively be referred to as refrigerant pipes 20, 22, and 24, or the like.

[0039] In one embodiment, the refrigerant circuit 10 can be configured as a cooling system (eg, an air conditioning system) capable of operating in a cooling mode. In one embodiment, the refrigerant circuit 10 can be configured as a heat pump system capable of operating in both a cooling mode and a heating / defrost mode.

[0040] The refrigerant circuit 10 may operate according to known principles and may be configured to heat or cool a gaseous process fluid (eg, a heat transfer medium or fluid such as, but not limited to, air, etc.), in which case the refrigerant circuit 10 may generally represent an air conditioner or heat pump.

[0041] In operation, the compressor 12 compresses a working fluid (e.g., a heat transfer fluid such as a refrigerant) from a relatively low pressure gas (e.g., suction pressure) to a relatively high pressure gas (e.g., discharge pressure). In one embodiment, the compressor 12 may be a positive displacement compressor. In one embodiment, the positive displacement compressor may be a screw compressor, a scroll compressor, a reciprocating compressor, etc. In one embodiment, the compressor 12 may be a centrifugal compressor.

[0042] The relatively high pressure gas is also at a relatively high temperature, and the gas is discharged from the compressor 12 and flows to the condenser 14 through the refrigerant line 20. The working fluid flows through the condenser 14 and dissipates heat to the process fluid (such as water, air, etc.), thereby cooling the working fluid. The cooled working fluid, which is now liquid, flows to the expansion device 16 via the refrigerant line 22. The expansion device 16 reduces the pressure of the working fluid. As a result, a portion of the working fluid is converted into a gaseous state. The "expansion device" may also be referred to as an expander. In one embodiment, the expander may be an expansion valve, an expansion plate, an expansion container, an orifice, etc., or other such type of expansion mechanism. It should be understood that the expander may be any type of expander used in the art to expand the working fluid to reduce the temperature of the working fluid.

[0043] The working fluid, now in a mixed state of liquid and gas, flows to the evaporator 18 via the refrigerant line 22. The working fluid flows through the evaporator 18 and absorbs heat from the process fluid (e.g., water, air, etc.), heating the working fluid and converting it to a gaseous state. The gaseous working fluid then returns to the compressor 12 via the refrigerant line 24. The above process continues when the refrigerant circuit is operating in, for example, a cooling mode (e.g., when the compressor 12 is enabled).

[0044] The refrigerant circuit 10 may include a lubricant separator 150 disposed between the compressor 12 and the condenser 14. The lubricant separator 150 is fluidly connected to the outlet of the compressor 12 via the refrigerant line 20. The lubricant separator 150 is fluidly connected to the compressor 12 to provide lubricant to various components (e.g., bearings, etc.) of the compressor 12 via the lubricant return line 28a and optionally via the second lubricant return line 28b. It should be understood that the number of lubricant return lines 28a, 28b may be selected based on, for example, which components of the compressor are provided with lubricant.

[0045] Figure 2A is a method for determining a variable speed compressor (e.g., Figure 1Flowchart of method 50 for determining a minimum speed limit for compressor 12 in a compressor 12. The method 50 may be specific to a selected compressor size. The selected compressor size and corresponding execution of method 50 may be based on, for example, the size of bearings in the compressor and the efficiency requirements of the compressor. According to one embodiment, method 50 may be performed by a controller of the compressor (e.g., Figure 1 In one embodiment, the method 50 may be performed for a series of compressors, and the determined minimum speed limit may be included in the control of the compressors. Figure 3 An example of a control method for compressor 12 is shown and described.

[0046] At 52, the suction pressure of the HVACR system is measured. The suction pressure in combination with the selected refrigerant (e.g., R-134a, R1234ze(E), R-513A, etc.) can be used to determine the saturated suction temperature. In one embodiment, the suction temperature can be optionally measured, although assumptions must be made regarding the amount of superheat, which may make the determination less accurate than using the suction pressure.

[0047] At 54, the discharge pressure for the HVACR system is measured. The discharge pressure in combination with the selected refrigerant (e.g., R-134a, R1234ze(E), R-513A, etc.) can be used to determine the saturated discharge temperature. In one embodiment, the discharge temperature can alternatively be measured, although assumptions must be made regarding the amount of superheat, which may make the determination less accurate than using the discharge pressure.

[0048] In 56, the minimum speed limit of the variable speed compressor is determined using the selected saturated suction temperature and the selected saturated discharge temperature. The minimum speed limit is generally dependent on the refrigerant, lubricant, bearing size in the compressor, and compressor performance. In one embodiment, as the bearing size decreases, the minimum speed limit increases. The determination of the minimum speed limit can be determined, for example, by testing or modeling the discharge temperature of the variable speed compressor (associated with the bearing cavity temperature of the bearing in the variable speed compressor) and performing surface fitting to determine the minimum speed limit equation. Typically, when the bearing reaches a pitch speed less than or equal to or approximately equal to 300,000 mm / min, a minimum speed limit may be required to prevent higher lubricant dilution and / or loss of bearing lubricant film. Therefore, a pitch speed less than or equal to or approximately equal to 300,000 mm / min can be considered a lower speed, while a pitch speed greater than 300,000 mm / min can be considered a higher speed.

[0049] refer to Figure 4 , shows an example of a minimum motor frequency determined according to method 50 according to one embodiment. Figure 4Indicates the selected bearing size. It should be understood that Figure 4 The minimum motor frequency curve in FIG. 1 depends on the selected refrigerant (e.g., R1234ze(E), etc.), the bearing size, and the selected lubricant. In the figure, the x-axis shows the saturated suction temperature (°F), and the y-axis shows the saturated discharge temperature (°F). The motor frequency is represented by various shades from relatively low to relatively high. As shown in the figure, the minimum motor frequency at a lower saturated suction temperature and saturated discharge temperature is relatively lower than the minimum motor frequency at a relatively higher saturated suction temperature and saturated discharge temperature.

[0050] Figure 2B is a method for determining a variable speed compressor (e.g., Figure 1 Flowchart of method 60 for determining a minimum speed limit for compressor 12 in a compressor 12. The method 60 may be specific to a selected compressor size and a selected lubricant and refrigerant combination. The selected compressor size and corresponding execution of method 60 may be based on, for example, the size of the bearings in the compressor, the efficiency of the compressor, and the solubility of the lubricant and refrigerant mixture. According to one embodiment, the method 60 may be executed by a controller of the compressor (e.g., Figure 1 In one embodiment, the method 60 may be performed for a series of compressors, and the determined minimum speed limit may be included in the control of the compressors. Figure 3 An example of a control method for compressor 12 is shown and described.

[0051] At 62, the suction pressure for the HVACR system is measured. This suction pressure in combination with the selected refrigerant (e.g., R-134a, R1234ze(E), R-513A, etc.) can be used to determine the saturated suction temperature. In one embodiment, the suction temperature can be optionally measured, although assumptions must be made regarding the superheat, which may make the determination less accurate than using the suction pressure.

[0052] At 64, the discharge pressure of the HVACR system is measured. The combination of the discharge pressure and the selected refrigerant (e.g., R-134a, R1234ze(E), R-513A, etc.) can be used to determine the saturated discharge temperature

[0053] At 66, the lubricant temperature of the compressor 12 is measured. In one embodiment, the lubricant temperature may be assumed rather than measured. In such an embodiment, the lubricant temperature may be assumed to be the same as the saturated discharge temperature. The lubricant temperature may be used to determine a relative lubricant temperature. The relative lubricant temperature may be based on the lubricant temperature and the saturated discharge temperature. For example, the relative lubricant temperature may be the difference between the measured lubricant temperature and the saturated discharge temperature. The lubricant temperature may provide a relative lubricant temperature. Figure 2A The method 50 provides a more accurate perspective on operating conditions in HVACR systems.

[0054] In 68, the selected saturated suction temperature, the selected saturated discharge temperature, and the lubricant temperature are used to determine the minimum speed limit of the variable speed compressor. In one embodiment, the lubricant temperature used in 68 is the relative lubricant temperature rather than the measured lubricant temperature. The minimum speed limit generally depends on the refrigerant, the lubricant, the bearing size in the compressor, and the compressor performance. In one embodiment, as the bearing size decreases, the minimum speed limit increases. The determination of the minimum speed limit, for example, can be determined by testing or modeling the discharge temperature of the variable speed compressor (associated with the bearing cavity temperature of the bearing in the variable speed compressor) and performing surface fitting to determine the minimum speed limit equation to determine the minimum speed limit. Typically, when the bearing reaches a pitch speed of less than or equal to or approximately equal to 40,000 mm / min to equal to or approximately equal to 550,000 mm / min, a minimum speed limit may be required to prevent dilution loss of the lubricating film at the bearing. Therefore, a pitch speed of less than or equal to or approximately equal to 150,000 mm / min can be considered a lower speed, while a pitch speed greater than 400,000 mm / min can be considered a higher speed.

[0055] In another embodiment, the minimum compressor speed may be known, in which case the minimum compressor speed may be modified. Figure 2B The method in to determine another variable, such as but not limited to the lubricant temperature, the exhaust temperature, etc. In such an embodiment, Figure 2B The method can be used, for example, to control the discharge temperature or the lubricant temperature.

[0056] Reference Figures 5A-5E , showing a relative lubricant temperature of 5°F ( Figure 5A )、12°F( Figure 5B )、20°F( Figure 5C )、30°F( Figure 5D ) and 40°F( Figure 5E ) is an example of the minimum motor frequency. Figures 5A to 5E Indicates the selected bearing size. It should be understood that Figures 5A to 5EThe minimum motor frequency curve in depends on the selected refrigerant (e.g., R134a, etc.), the bearing size, and the selected lubricant. In the figure, the saturated suction temperature (°F) and the saturated discharge temperature (°F) are plotted relative to the minimum motor frequency. The motor frequency is represented from relatively low to relatively high. As shown in the figure, the minimum motor frequency at a lower saturated suction temperature, a saturated discharge temperature, and a lower relative lubricant temperature is relatively lower than the minimum motor frequency at a higher saturated suction temperature, a saturated discharge temperature, and a higher relative lubricant temperature. As the saturated suction temperature and the saturated discharge temperature increase, the lubricant viscosity can generally increase. However, in one embodiment, there may be a point where the lubricant viscosity decreases as the saturated suction temperature and the saturated discharge temperature increase.

[0057] Figure 3 According to one embodiment, a method for operating a variable speed compressor (e.g., Figure 1 Flow chart of a method 100 for maintaining a minimum bearing lubricant film thickness in a compressor 12 in a compressor 12. The method 100 generally includes operating an HVACR system (e.g., Figure 1 The refrigerant circuit 10 in the embodiment of the present invention.

[0058] The method 100 begins at 102. At 102, a controller (e.g., a thermostat, etc.) determines a cooling demand. The cooling demand may be determined based on a thermostat, one or more sensors in the conditioned space, a building automation system, and / or an HVACR system (e.g., Figure 1 The cooling demand is determined by the settings of a controller of the refrigerant circuit 10 shown in FIG.

[0059] At 104, the controller determines a variable speed compressor setting based on the cooling demand. In one embodiment, this may include a target speed setting for the compressor 12. In one embodiment, this may include a speed setting for the compressor 12 that is less than a target speed for the compressor 12. In one embodiment, the target speed may be a maximum speed.

[0060] At 106, the controller 26 determines whether the determined variable speed compressor setting is less than a minimum speed limit (e.g., as in Figure 2A determined in method 50 or Figure 2B determined in method 60 ).

[0061] At 108 , the controller sets one or more cooling settings for the HVACR system based on the cooling demand and the variable speed compressor setting determined at 104 .

[0062] At 110, if the variable speed compressor setting determined at 104 is less than the minimum speed limit (e.g., as in Figure 2AMethod 50 discussed in or Figure 2B 60 ), the controller 26 overrides the variable speed compressor setting (eg, determined at 104 ) to utilize the minimum speed limit and provide cooling in accordance with the cooling demand.

[0063] Implementation method:

[0064] Any one of Examples 1-8 can be combined with any one of Examples 9-13 and 14-21. Any one of Examples 9-13 can be combined with any one of Examples 14-21.

[0065] Example 1. The present application provides a heating, ventilation, air conditioning and refrigeration (HVACR) system, comprising: a refrigerant circuit, the refrigerant circuit comprising: a compressor, a condenser, an expansion device and an evaporator fluidly connected to each other; a controller electrically connected to the compressor, the controller being configured to prevent the compressor from operating at a speed less than a minimum speed limit, wherein the controller is configured to determine the minimum speed limit based on a saturated suction temperature, a saturated discharge temperature and a lubricant temperature.

[0066] Embodiment 2. The HVACR system of embodiment 1, wherein the lubricant temperature is a relative lubricant temperature, the relative lubricant temperature being a difference between a measured lubricant temperature and the saturated discharge temperature.

[0067] Embodiment 3. The HVACR system of any one of embodiments 1 or 2, wherein the controller is configured to override the cooling setting when the cooling setting corresponds to an operating speed of the compressor that is below a minimum speed limit.

[0068] Embodiment 4. The HVACR system according to any one of embodiments 1-3, wherein the compressor is a variable speed screw compressor.

[0069] Embodiment 5. The HVACR system of embodiment 4, wherein the minimum speed limit is for a bearing pitch speed of less than or approximately equal to 40,000 mm / min to equal to or approximately equal to 550,000 mm / min.

[0070] Embodiment 6. The HVACR system according to any one of embodiments 1-5, wherein the HVACR system uses R134a as the refrigerant.

[0071] Embodiment 7. The HVACR system according to any one of embodiments 1-6, wherein the HVACR system uses a refrigerant having a relatively lower GWP than R134a.

[0072] Embodiment 8: The HVACR system according to any one of embodiments 1-7, wherein the HVACR system uses R1234ze(E) or R513A as the refrigerant.

[0073] Embodiment 9, a method for controlling a variable speed compressor, comprising: using a controller of the variable speed compressor to determine a saturated suction temperature, a saturated discharge temperature and a lubricant temperature; and using the controller of the variable speed compressor to calculate a minimum speed limit of the variable speed compressor based on the saturated suction temperature, the saturated discharge temperature and the lubricant temperature; receiving a cooling demand through the controller; determining a speed setting of the variable speed compressor based on the cooling demand; in response to determining that the speed setting is less than the calculated minimum speed limit, overwriting the speed setting and utilizing the minimum speed limit and cooling to meet the cooling demand.

[0074] Embodiment 10. The method of embodiment 9, wherein, in response to determining that the speed setting is greater than a minimum speed limit, cooling is performed based on the speed setting to meet the cooling requirement.

[0075] Embodiment 11. The method according to one of embodiments 9 or 10, wherein the calculation is based on saturated suction temperature, saturated discharge temperature, lubricant temperature, bearing size and compressor efficiency.

[0076] Embodiment 12: The method according to any one of embodiments 9-11, wherein the variable speed compressor uses R1234ze(E) as the refrigerant.

[0077] Embodiment 13. A method according to any one of embodiments 9-12, wherein the minimum speed limit is for a bearing pitch speed of less than or approximately equal to 40,000 mm / min to equal to or approximately equal to 550,000 mm / min.

[0078] Embodiment 14. A heating, ventilation, air conditioning and refrigeration (HVACR) system, comprising: a refrigerant circuit, the refrigerant circuit including: a fluidly connected compressor, a condenser, an expansion device and an evaporator; a controller electrically connected to the compressor, the controller configured to prevent the compressor from operating at a speed less than a minimum speed limit.

[0079] Embodiment 15. The HVACR system of embodiment 14, wherein the lubricant temperature is a relative lubricant temperature, the relative lubricant temperature being the difference between the measured lubricant temperature and the saturated discharge temperature.

[0080] Embodiment 16. The HVACR system of any of Embodiments 14 or 15, wherein the controller is configured to override the cooling setting when the cooling setting corresponds to an operating speed of the compressor that is below a minimum speed limit.

[0081] Embodiment 17. The HVACR system of any one of embodiments 14-16, wherein the compressor is a variable speed screw compressor.

[0082] Embodiment 18. The HVACR system of embodiment 17, wherein the minimum speed limit is for a bearing pitch speed of less than or about 40,000 mm / min to equal to or about 550,000 mm / min.

[0083] Embodiment 19. The HVACR system according to any one of embodiments 14 to 18, wherein the HVACR system uses R134a as the refrigerant.

[0084] Embodiment 20. The HVACR system of any one of embodiments 14-19, wherein the HVACR system uses a refrigerant having a relatively lower GWP than R134a.

[0085] Embodiment 21. The HVACR system according to any one of embodiments 14-20, wherein the HVACR system uses R1234ze(E) or R513A as the refrigerant.

[0086] The terms used in this specification are intended to describe specific embodiments and are not intended to be limiting. Unless otherwise expressly stated, the terms "a", "an" and "the" also include plural forms. When the terms "include" and / or "comprise" are used in this specification, it specifies the presence of the features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements and / or components.

[0087] With respect to the foregoing description, it should be understood that detailed changes may be made without departing from the scope of the present disclosure, especially in the construction materials adopted and the shapes, sizes and arrangements of the components. This specification and the described embodiments are exemplary only, and the true scope and spirit of the present disclosure are indicated by the appended claims.

Claims

1. A heating, ventilation, air conditioning and refrigeration system, characterized in that: include: A refrigerant circuit, the refrigerant circuit comprising: a fluidly connected variable speed compressor, condenser, expansion device, and evaporator; A controller is electrically connected to the variable speed compressor, the controller being configured to determine a speed setting for the variable speed compressor based on a cooling demand and to prevent the variable speed compressor from operating at a speed less than a minimum speed limit based on a saturated suction temperature, a saturated discharge temperature, and a lubricant temperature.

2. The heating, ventilation, air conditioning and refrigeration system according to claim 1, characterized in that: The lubricant temperature is a relative lubricant temperature, which is a difference between a measured lubricant temperature and the saturated discharge temperature.

3. The heating, ventilation, air conditioning and refrigeration system according to claim 1, characterized in that: The controller is configured to override the cooling setting when the cooling setting corresponds to an operating speed of the variable speed compressor that is below a minimum speed limit.

4. The heating, ventilation, air conditioning and refrigeration system according to claim 1, characterized in that: The compressor is a variable speed screw compressor.

5. The heating, ventilation, air conditioning and refrigeration system according to claim 4, characterized in that: The minimum speed limit is for bearing pitch speeds of less than 40,000 mm / min to 550,000 mm / min.

6. The heating, ventilation, air conditioning and refrigeration system according to claim 1, characterized in that: The heating, ventilation, air conditioning and refrigeration system uses R134a as the refrigerant.

7. The heating, ventilation, air conditioning and refrigeration system according to claim 1, characterized in that: The heating, ventilation, air conditioning and refrigeration system uses a refrigerant having a relatively lower GWP than R134a.

8. The heating, ventilation, air conditioning and refrigeration system according to claim 1, characterized in that: The heating, ventilation, air conditioning and refrigeration system uses R1234ze(E) or R513A as refrigerant.

9. A method for controlling a variable speed compressor, characterized in that: include: Using a controller of the variable speed compressor, determining a saturated suction temperature, a saturated discharge temperature, and a lubricant temperature; calculating, using a controller of the variable speed compressor, a minimum speed limit of the variable speed compressor based on the saturated suction temperature, the saturated discharge temperature, and the lubricant temperature; Receiving a cooling demand through the controller; determining a speed setting for the variable speed compressor based on the cooling demand; as well as In response to determining that the speed setting is less than the calculated minimum speed limit, overriding the speed setting and utilizing the minimum speed limit and cooling to satisfy the cooling demand.

10. The method according to claim 9, characterized in that In response to determining that the speed setting is greater than the minimum speed limit, cooling is performed based on the speed setting to meet the cooling demand.

11. The method according to claim 9, characterized in that The calculation is based on the saturated suction temperature, the saturated discharge temperature, the lubricant temperature, bearing size, and compressor efficiency.

12. The method according to claim 9, characterized in that The variable speed compressor uses R1234ze(E) or R513a as the refrigerant.

13. The method according to claim 9, characterized in that The minimum speed limit is for bearing pitch speeds of less than 40,000 mm / min to 550,000 mm / min.

14. A heating, ventilation, air conditioning and refrigeration system, characterized in that: include: A refrigerant circuit, the refrigerant circuit comprising: A variable speed compressor, a condenser, an expansion device, and an evaporator fluidly connected to each other; and a controller electrically connected to the variable speed compressor, the controller configured to determine a speed setting for the variable speed compressor based on a cooling demand and to prevent the variable speed compressor from operating at a speed less than a minimum speed limit, wherein the controller is configured to determine the minimum speed limit based on bearing size, efficiency of the variable speed compressor, a saturated suction temperature, a saturated discharge temperature, and a lubricant temperature.

15. The heating, ventilation, air conditioning and refrigeration system according to claim 14, characterized in that The lubricant temperature is the relative lubricant temperature, which is the difference between the measured lubricant temperature and the saturated discharge temperature.

16. The heating, ventilation, air conditioning and refrigeration system of claim 14, wherein: The controller is configured to override the cooling setting when the cooling setting corresponds to an operating speed of the variable speed compressor that is below a minimum speed limit.

17. The heating, ventilation, air conditioning and refrigeration system of claim 14, wherein: The variable speed compressor is a variable speed screw compressor.

18. The heating, ventilation, air conditioning and refrigeration system of claim 17, wherein: The minimum speed limit is for bearing pitch speeds of less than 40,000 mm / min to 550,000 mm / min.

19. The heating, ventilation, air conditioning and refrigeration system of claim 14, wherein: The heating, ventilation, air conditioning and refrigeration system uses R134a as the refrigerant.

20. The heating, ventilation, air conditioning and refrigeration system of claim 14, wherein: The heating, ventilation, air conditioning and refrigeration system uses a refrigerant having a relatively lower GWP than R134a.

21. The heating, ventilation, air conditioning and refrigeration system of claim 14, wherein: The heating, ventilation, air conditioning and refrigeration system uses R1234ze(E) or R513A as refrigerant.

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