CN113375351A

CN113375351A - Refrigeration device

Info

Publication number: CN113375351A
Application number: CN202110250583.3A
Authority: CN
Inventors: 伊万·雅克·莱姆巴特; 菲利普·德尔·马塞尔·蒂斯朗
Original assignee: Trane International Inc
Current assignee: Trane International Inc
Priority date: 2020-03-10
Filing date: 2021-03-08
Publication date: 2021-09-10
Also published as: US20210285704A1; EP3879207A1; DK3879207T3; EP3879207B1

Abstract

Disclosed is a refrigeration device comprising a refrigerant circuit, the refrigerant circuit comprising: a compressor including a compressor fan and a motor driving the compressor fan; the condensing device is arranged at the downstream of the compressor and comprises a condenser and a subcooler; an expansion valve disposed downstream of the condensing device; an evaporator provided between the expansion valve and the compressor; a main refrigerant line fluidly connected in a loop series: compressor, condensing equipment, expansion valve and evaporator. A motor cooling line including a motor cooling valve fluidly connects the subcooler to the motor to tap refrigerant from the main refrigerant line to cool the motor, the motor cooling line also being connected to the main refrigerant line at a return point upstream of the compressor fan to return refrigerant to the main refrigerant line at the compressor fan. A bypass line fluidly connects an outlet of the condenser to the expansion valve to bypass the subcooler, the bypass line including a bypass valve to selectively allow refrigerant in the main refrigerant line to bypass the subcooler.

Description

Refrigeration device

Technical Field

The present invention relates to a refrigeration device and a method of operating a refrigeration device.

Background

A refrigeration unit typically includes a compressor, a condenser, an expansion valve, and an evaporator, which are connected in series and through which a refrigerant flows. Ambient air flows over the condenser to cool the pressurized refrigerant in the condenser, and air or water to be cooled flows over the evaporator to transfer heat to the refrigerant in the evaporator, thereby cooling the air.

The components of the compressor may become hot during use and require cooling. The refrigerant from the condenser may be passively driven to the compressor and used to cool components of the compressor. However, under certain conditions, the amount of refrigerant directed to the compressor may be insufficient to cool the components of the compressor. To overcome this problem, previously considered methods of operating refrigeration units have relied on disengaging the most efficient operation.

Disclosure of Invention

According to a first aspect, there is provided a refrigeration device comprising a refrigerant circuit, the refrigerant circuit comprising: a compressor including a compressor fan and a motor driving the compressor fan; a condensing device disposed downstream of the compressor, the condensing device including a condenser and a subcooler; an expansion valve disposed downstream of the condensing device; an evaporator disposed between the expansion valve and the compressor; a main refrigerant line fluidly connecting the compressor, the condensing device, the expansion valve, and the evaporator in a loop series; and a motor cooling line including a motor cooling valve fluidly connecting the subcooler to the motor to divert refrigerant from the main refrigerant line to cool the motor, wherein the motor cooling line is further connected to the main refrigerant line at a return point upstream of the compressor fan to return refrigerant to the main refrigerant line at the compressor fan; wherein the refrigerant circuit further comprises a bypass line fluidly connecting an outlet of the condenser to the expansion valve to bypass the subcooler, wherein the bypass line includes a bypass valve to selectively allow refrigerant in the main refrigerant line to bypass the subcooler.

The compressor may include an inverter. The subcooler may be connected to the inverter by an inverter cooling line including an inverter cooling valve, and wherein the inverter cooling line is further connected to the main refrigerant line at the return point to direct refrigerant from the inverter to the main refrigerant line at the compressor fan.

The refrigeration appliance may include a controller. The controller may be configured to control opening and closing of the bypass valve. The controller may be configured to control opening and closing of the inverter cooling valve. The controller may be configured to control opening and closing of the motor cooling valve. There may be an additional controller integrated with the compressor and configured to control operation of the motor and the inverter and to control opening and closing of the motor cooling valve, the inverter cooling valve, and/or the expansion valve.

The bypass valve may be a regulator valve. The controller may be configured to control the bypass valve to control a flow rate of refrigerant through the bypass valve.

The refrigeration appliance may include a first pressure sensor arranged to monitor the pressure of refrigerant exiting the subcooler and a second pressure sensor arranged to monitor the pressure in the main refrigerant line at the return point; wherein the controller is arranged to receive a first pressure parameter from the first pressure sensor and a second pressure parameter from the second pressure sensor, and the controller is arranged to control the bypass valve based on the first pressure parameter and the second pressure parameter.

The refrigeration appliance may include a first pressure sensor arranged to monitor a pressure of refrigerant exiting the subcooler, a second pressure sensor arranged to monitor a pressure in a main refrigerant line at an inlet of the compressor, and a third pressure sensor arranged to monitor a pressure in a main refrigerant line at an outlet of the compressor. The controller is arranged to receive a first pressure parameter from the first pressure sensor, a second pressure parameter from the second pressure sensor, and a third pressure parameter from the third pressure sensor. The controller may be arranged to control the bypass valve based on the first pressure parameter, the second pressure parameter and the third pressure parameter.

The compressor may be a dual stage compressor including a first stage compressor fan and a second stage compressor fan, and wherein the return point is located between the first stage compressor fan and the second stage compressor fan.

According to a second aspect, there is provided a method of operating a refrigeration appliance as described above, the method comprising: determining whether there is insufficient refrigerant delivered from the subcooler to the compressor; and in response to determining that there is insufficient refrigerant being delivered from the subcooler to the compressor, controlling the bypass valve to increase the flow of refrigerant through the bypass valve.

The refrigerant delivered from the subcooler to the compressor may relate to refrigerant delivered from the subcooler through a motor cooling line to the compressor motor to cool the motor.

Increasing the flow of refrigerant through the bypass valve may include: opening the bypass valve, or gradually increasing the size of the opening through the bypass valve.

Determining whether there is insufficient refrigerant delivered to the compressor may include: monitoring a first pressure parameter related to a pressure of refrigerant in a main refrigerant line at an outlet of the subcooler; monitoring a second pressure parameter related to the pressure in the main refrigerant line at a return point upstream of the compressor fan; and determining whether there is insufficient refrigerant delivered to the compressor based on the first pressure parameter and the second pressure parameter.

The second pressure parameter may relate to a pressure in the main refrigerant line at a return point between a first stage compressor fan and a second stage compressor fan of the dual stage compressor.

Determining whether there is insufficient refrigerant delivered to the compressor may include: calculating a difference parameter related to a difference between the first pressure parameter and the second pressure parameter; comparing the difference parameter to a first threshold; and determining that insufficient refrigerant is delivered to the compressor if the difference parameter is below the first threshold.

The method may further comprise: a determination is made as to whether excess refrigerant is delivered to the compressor. The method may include: reducing a flow of refrigerant through the bypass valve in response to determining that too much refrigerant is delivered to the compressor.

Reducing the flow of refrigerant through the bypass valve may include: closing the bypass valve, or gradually reducing the size of an opening through the bypass valve.

Determining whether too much refrigerant is delivered to the compressor may include: comparing the difference parameter to a second threshold; and determining that too much refrigerant is delivered to the compressor if the difference parameter is above the second threshold.

The first threshold and the second threshold may be the same.

A person skilled in the art will appreciate that features or parameters described in relation to any one of the above aspects may be applied to any other aspect, except where mutually exclusive. Furthermore, any feature or parameter described herein may be applied to any aspect and/or combined with any other feature or parameter described herein, except where mutually exclusive.

Drawings

Embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 shows a schematic diagram of an exemplary refrigeration appliance; and

fig. 2 and 3 are flow charts illustrating steps of exemplary methods of operating a refrigeration appliance.

Detailed Description

Fig. 1 shows an exemplary refrigeration appliance 10 including a refrigerant circuit. The refrigerant circuit includes a compressor 12, a condensing device 14, an expansion valve 16 and an evaporator 18, which are fluidly connected to each other in series and in the order described above by a main refrigerant line 11, wherein the evaporator is connected to the compressor 12 to form the circuit.

The compressor 12 is in this example a two-stage compressor including a first stage compressor fan 20 and a second stage compressor fan 22. In other examples, the compressor may have only one stage, or the compressor may have more than two stages.

The compressor 12 includes a motor 24, the motor 24 being configured to drive the first stage compressor fan 20 and the second stage compressor fan 22. The motor 24 is connected to an inverter 26, the inverter 26 being configured to control the speed of the motor 24.

The condensation device 14 is arranged downstream of the compressor 12 and comprises two condensation stages. In the first stage, the condensing unit 14 includes a condenser 28, and in the second stage, the condensing unit 14 includes a subcooler 30. A subcooler 30 is disposed downstream of the condenser 28.

An expansion valve 16 is disposed downstream of the condensing device 14, and an evaporator 18 is disposed between the expansion valve 16 and the compressor 12.

A check valve 32 is disposed between the compressor 12 and the condensing device 14, the check valve 32 being configured to ensure that refrigerant flows from the compressor 12 to the condenser 28, and not allow refrigerant to flow in the opposite direction from the condenser 28 to the compressor 12.

A cooling line 34 fluidly connects subcooler 30 directly to compressor 12 to provide subcooled refrigerant to compressor 12 to cool compressor 12. In this example, the cooling line 34 taps the subcooled refrigerant from the main refrigerant line 11 connecting the subcooler 30 to the expansion valve 16 and directs the tapped refrigerant to the compressor 12.

Within compressor 12, cooling line 34 is split into a motor cooling line 36 and an inverter cooling line 38. A motor cooling line 36 fluidly connects the subcooler 30 to the motor 24 such that the subcooled refrigerant is directed to the motor 24 and allowed to expand to cool the motor 24 by heat transfer. An inverter cooling line 38 fluidly connects subcooler 30 to inverter 26 such that subcooled refrigerant is directed to inverter 26 and allowed to expand to cool the inverter by heat transfer.

The motor cooling line 36 includes a motor cooling valve 37, the motor cooling valve 37 configured to control a flow of refrigerant through the motor cooling line 36 to the motor 24. The inverter cooling line 38 includes an inverter cooling valve 39, and the inverter cooling valve 39 is configured to control the flow rate of the refrigerant to the inverter 26 through the inverter cooling line 38.

The motor cooling line 36 and the inverter cooling line 38 are in turn connected to the main refrigerant line 11 at a return point 40 between the first stage compressor fan 20 and the second stage compressor fan 22, so that the tapped refrigerant in the motor cooling line 36 and the inverter cooling line 38 rejoins the main refrigerant line 11 after being used to cool the motor 24 and the inverter 26, respectively. The maximum possible refrigerant flow through the motor cooling line 36 and the inverter cooling line 38 (i.e., if the motor cooling valve 37 and the inverter cooling valve 39 are fully open) depends on the pressure of the refrigerant in the main refrigerant line 11 at the return point 40 and the pressure of the refrigerant in the main refrigerant line 11 at the outlet of the subcooler 30. The pressure at the return point 40 must be at least a threshold amount lower than the pressure at the outlet of the subcooler 30 in order to passively drive the subcooled refrigerant through the motor cooling line 36 and the inverter cooling line 38 to the return point 40 (i.e., there must be a sufficiently high pressure differential to drive the refrigerant through the motor cooling line 36 and the inverter cooling line 38).

The threshold amount may be an absolute threshold, or may depend on the load on the compressor 12.

In examples where the compressor is a single stage compressor including one compressor fan, the motor cooling line and the inverter cooling line may be connected to the main refrigerant line upstream of the compressor fan (i.e., the return point may be located upstream of the compressor fan).

The outlet of the condenser 28 is also fluidly connected to the main refrigerant line 11 upstream of the expansion valve 16 by a bypass line 42. The bypass line 42 is arranged to allow at least some of the refrigerant in the main refrigerant line 11 to bypass the subcooler 30 such that some refrigerant flows directly from the condenser 28 to the main refrigerant line 11 between the subcooler 30 and the expansion valve 16.

The bypass line 42 includes a bypass valve 44, the bypass valve 44 configured to be selectively opened and closed to control the flow of refrigerant through the bypass line 42.

The controller 50 is connected to the bypass valve 44, the motor cooling valve 37, the inverter cooling valve 39, and the expansion valve 16. The controller 50 is configured to selectively open and close the valves, thereby controlling the flow of refrigerant through the refrigerant circuit. In some examples, there may be an additional controller integrated with the compressor and configured to control the motor cooling valve and the inverter cooling valve. The controller 50 or an additional controller may also control the operation of the inverter and the compressor in use.

The bypass valve 44, motor cooling valve 37, inverter cooling valve 39, and expansion valve 16 are, in this example, regulator valves, such that the controller 50 can vary the size of the opening of each valve to precisely control the flow of refrigerant through the valves. In other examples, the valves may be binary valves that may be selectively opened and closed, but that do not control the size of the opening, and thus do not directly control the flow through the valves. In some examples, the valve may be any combination of a binary valve and a regulator valve.

Thus, the controller 50 is configured in this example to control the bypass valve 44, the motor cooling valve 37, the inverter cooling valve 39 and the expansion valve 16 so as to precisely control the flow of refrigerant through the bypass line 42, the motor cooling line 36, the inverter cooling line 38 and the main refrigerant line 11 in use.

In this example, the refrigeration device 10 further comprises a first pressure sensor 52, the first pressure sensor 52 being arranged to monitor the pressure of the refrigerant in the main refrigerant line 11 at the outlet of the subcooler 30. The refrigeration device 10 further comprises a second pressure sensor 54 and a third pressure sensor 55, the second pressure sensor 54 being arranged to monitor the main control upstream (i.e. at the inlet) of the first compressor fan 20The third pressure sensor 55 is arranged to monitor the pressure in the refrigerant line 11 downstream (i.e. at the outlet) of the second compressor fan 22. The controller 50 calculates the pressure of the refrigerant at the return point 40 based on the pressure monitored by the second pressure sensor 54 and the pressure monitored by the third pressure sensor 55. Will return the refrigerant pressure (p) at point 40_r) The calculation is as follows: refrigerant pressure (p) at inlet of first compressor fan 20₁) Multiplied by the refrigerant pressure (p) at the outlet of the second compressor fan₂) The square root of the product of (i.e.,

)。

in an example where the compressor is a single stage compressor having one compressor fan, the second pressure sensor may be arranged to monitor the pressure in the main refrigerant line upstream of the compressor fan, and the third pressure sensor may be absent. In other examples, the sensor may be any sensor capable of outputting a parameter indicative of refrigerant pressure, such as a temperature sensor. In other examples, there may be a pressure sensor arranged to directly monitor the pressure at the return point 40.

The controller 50 is arranged to monitor a first pressure parameter received from a first pressure sensor 52, which first pressure parameter is related to the pressure of the refrigerant in the main refrigerant line 11 downstream of the subcooler 30 or the pressure of the refrigerant at the cooling line 34. The controller is arranged to monitor a second pressure parameter received from the second pressure sensor 54, which second pressure parameter is related to the pressure of the refrigerant in the main refrigerant line 11 at the return point 40. The controller 50 is configured to control the bypass valve 44 based on the first pressure parameter and the second pressure parameter. This process will be described in more detail below with reference to fig. 2 and 3.

The refrigeration device may further comprise a temperature sensor arranged to monitor the refrigerant temperature at the outlet of the condenser, the refrigerant temperature at the outlet of the subcooler, and/or the refrigerant temperature downstream of the expansion means.

Normal with the refrigeration appliance 10 closed at the bypass valve 44Operating under conditions such that all of the refrigerant passes through the subcooler 30. The vaporized refrigerant is compressed in the compressor 12 to pressurize the refrigerant, thereby increasing the temperature of the refrigerant. For example, for an outdoor ambient temperature of 35 ℃, the vaporized refrigerant may enter the compressor at a pressure of about 2.7bar (270kPa) and a temperature of 6 ℃, and exit the compressor at a pressure of about 10bar (1000kPa) and a temperature of 50 ℃. Thus, the pressure at the return point 40 is calculated as:

the refrigerant exits compressor 12 in a vapor phase.

The refrigerant passes through the condensing device 14, where the refrigerant first passes through a condenser 28 to condense the refrigerant by heat transfer to the ambient air in the condensing device 14. The refrigerant exits the outlet of the condenser 28 in liquid form. The refrigerant then passes through a subcooler 30 where the refrigerant is further cooled. There is a pressure loss of the refrigerant through the condenser 28 and subcooler 30 due to the large mass flow in the small passages. For example, refrigerant may enter the condenser at 10bar (1000kPa) (the same pressure as the refrigerant leaving the compressor 12), and 0.5bar (50kPa) of pressure may be lost across the condenser 28. Passing the condensate through the subcooler 30 may further lose 1.5bar (150kPa) of pressure, causing the condensate to exit the subcooler 30 at a pressure of 8bar (800kPa), which leaves a pressure differential of 2.8bar (280kPa) between the return point 40 and the outlet of the subcooler 30, which 2.8bar is sufficient to flow the refrigerant through the motor cooling line 36 and the inverter cooling line 38 by opening the respective motor cooling valve 37 and the inverter cooling valve 39.

Then, the refrigerant flows through the expansion valve 16, and the refrigerant is caused to expand in the expansion valve 16. This reduces the pressure and thus the temperature of the refrigerant further, so that the refrigerant is cooler than the temperature of the water or air to be cooled. For example, the pressure of the refrigerant downstream of the expansion valve 16 may be 2.7bar (270kPa), and the temperature of the refrigerant downstream of the expansion valve 16 may be 6 ℃.

The opening in the expansion valve 16 may be variable such that the pressure drop of the refrigerant passing through the expansion valve, and thus the temperature drop of the refrigerant passing through the expansion valve, may be varied. The size of the opening can be controlled to ensure that the temperature of the refrigerant leaving the expansion valve 16, and thus entering the evaporator 18, is maintained constant so that the refrigeration capacity of the refrigeration unit 10 is maintained constant.

The refrigerant downstream of the expansion valve 16 is then led to an evaporator 18, where heat is exchanged between the air or water to be cooled and the cooled refrigerant at the evaporator 18. The refrigerant evaporates so that the refrigerant leaves the evaporator 18 in a vapor phase and the air is cooled.

During use, the motor 24 and the inverter 26 are heated and must be cooled. The controller 50 controls the motor cooling valve 37 and the inverter cooling valve 39 to control the flow of sub-cooled refrigerant to the motor 24 and the inverter 26, respectively.

Under operating conditions where the ambient temperature is low (e.g., 0 ℃), the flow rate of refrigerant from the subcooler 30 to the compressor 12 may not be sufficient to cool the motor 24 and the inverter 26 even if the motor cooling valve 37 and the inverter cooling valve 39 are fully open. In such operating conditions, the bypass valve 44 may be opened to enable a greater supply of refrigerant to the compressor, as explained below.

Fig. 2 and 3 are flow charts illustrating methods of operating the exemplary refrigeration unit 10 to adjust the amount of refrigerant delivered to the compressor 12 as needed. This method may be used when the refrigeration appliance 10 is experiencing an abnormal condition.

This situation may occur, for example, when the ambient temperature is low, e.g., 10 ℃. The compressor outlet pressure may be 5.8bar (580kPa), the refrigerant pressure downstream of the expansion valve 16 may be 2.7bar (270kPa), and the refrigerant temperature at the compressor inlet may be 30 ℃. Thus, the pressure at the return point 40 is

With the same pressure drop across the condenser 28 and subcooler 30, and a total pressure drop of 2bar (200kPa), the pressure at the outlet of the subcooler 30 is: 5.8bar-2bar 3.8bar (380kPa) such that the return is madeThe pressure difference between the return point 40 and the outlet of the subcooler 30 will be-0.2 bar (-20 kPa). In this case, even if the motor cooling valve 37 and the inverter cooling valve 39 are fully opened, no refrigerant is transmitted to the motor 24 and the inverter 26 for cooling. In this case, the low temperature of the ambient air means that there is a large pressure loss across the condenser 28 and the subcooler 30, such that even with the motor cooling valve 37 and the inverter cooling valve 39 fully open, the pressure differential between the cooling line 34 and the return point 40 is insufficient to drive enough refrigerant to the motor 24 and the inverter 26. As a result, the cooling of the motor 24 and the inverter 26 may be insufficient, such that these components may overheat, potentially leading to damage or failure. As described above, the pressure differential between the cooling line 34 and the return point 40 may be increased by opening the bypass valve 44. This allows refrigerant to bypass the subcooler 30 so that there is less pressure drop between the outlet of the condenser 28 and the cooling line 34.

Fig. 2 illustrates a method 200 of operating the refrigeration unit 10 to overcome these conditions.

In step 202, the method determines whether there is insufficient refrigerant being delivered to the compressor 12 from the main refrigerant line downstream of the subcooler 30 (e.g., insufficient to cool the motor 24 and inverter 26).

If it is determined that there is not sufficient refrigerant being delivered to the compressor 12, the method proceeds to step 204, where in step 204 the bypass valve 44 is controlled to open to increase the flow of refrigerant through the bypass valve 44. Increasing the flow of refrigerant through the bypass valve 44 decreases the flow of refrigerant through the subcooler 30 such that the pressure of the refrigerant in the main refrigerant line 11 between the subcooler 30 and the expansion valve 16 increases. This is because less refrigerant experiences a pressure loss across the subcooler 30.

Increasing the pressure of the refrigerant in the main refrigerant line 11 at the cooling line 34 means that the pressure difference between the refrigerant line 34 and the return point 40 increases, so that more refrigerant is driven through the motor cooling line 36 and the inverter cooling line 38.

In this example, the bypass valve 44 is a regulator valve, and in step 204, the bypass valve 44 is gradually opened, and the method returns to step 202 to determine if there is still insufficient refrigerant being delivered to the compressor 12. This creates a negative feedback loop. In other examples, the bypass valve may be controlled to open a particular amount depending on the degree of refrigerant starvation to the compressor 12.

If sufficient refrigerant is supplied to the compressor 12, the method determines in step 206 whether excess refrigerant is delivered to the compressor. If too much refrigerant is not being delivered, and there is not an insufficiency of the refrigerant being delivered, then the level of refrigerant being delivered is at the desired set point. The method then proceeds to step 208, where in step 208 no change is made to the bypass valve 44, and the method returns to step 202.

If it is determined that too much refrigerant is being delivered to the compressor 12, the method proceeds to step 210 to reduce the flow of refrigerant through the bypass valve 44 (e.g., by reducing the size of the opening in the bypass valve 44, or closing the bypass valve 44). If the bypass valve 44 has been closed, the refrigeration appliance 10 may return to normal operation in which the bypass valve 44 is closed. The method then returns to step 202.

Fig. 3 details an exemplary method of determining whether insufficient refrigerant, too much refrigerant, or just enough refrigerant is delivered to the compressor 12. This is determined by monitoring the pressure differential from the cooling line 34 to the return point 40. Ideally, the pressure differential will fall within a set range or at a set point where it will be determined that there is just enough refrigerant delivered to the compressor 12. The set range may be an absolute range of acceptable pressure differences, or the set range may vary and may be calculated based on the load on the compressor 12.

In the method described below, the controller 50 is configured to maintain the pressure difference within a set range defined between a lower threshold and an upper threshold.

In examples where the threshold value is dependent on the load on the compressor 12, the controller 50 may determine the threshold value in real time by monitoring the compressor load and looking up the corresponding threshold value from a look-up table. In other examples, the threshold may be calculated using a formula based on compressor load. For example, the minimum threshold pressure at 30% compressor load may be 0.2bar (20kPa), whereas the minimum threshold pressure at 100% compressor load may be as high as 1bar (100kPa) several times.

In step 220, the method includes monitoring a first pressure parameter related to the pressure of refrigerant in the main refrigerant line 11 at the outlet of the subcooler 30. This may be monitored by the first pressure sensor 52.

In step 222, the method includes monitoring a second pressure parameter related to the pressure of the refrigerant in the main refrigerant line 11 at the return point 40 (i.e., between the first stage compressor fan 20 and the second stage compressor fan 22). This may be monitored with the second pressure sensor 54. In examples where the compressor is a single stage compressor having only one compressor fan, the second pressure parameter may be related to the pressure of refrigerant in the main refrigerant line upstream of the compressor fan.

The method determines whether there is not enough refrigerant, just enough refrigerant, or too much refrigerant to deliver to the compressor 12 in steps 224 through 234 based on the first and second pressure parameters.

In step 224, the method includes calculating a difference parameter related to a difference between the first pressure parameter and the second pressure parameter. The difference parameter will indicate the pressure difference of the refrigerant between the outlet of the subcooler 30 (i.e., the cooling line 34) and the return point 40 of the compressor.

In step 226, the difference parameter is compared to a lower threshold and a determination is made whether the difference parameter is below the lower threshold. If the difference parameter is below the lower threshold, then it is determined in step 228 that the pressure differential between the subcooler 30 and the return point 40 is not high enough that insufficient refrigerant is delivered to the compressor 12 to cool it. If the difference parameter is not below the lower threshold (i.e., the difference parameter is above the lower threshold), the method proceeds to step 230.

In step 230, the difference parameter is compared to a second upper threshold and a determination is made whether the difference parameter is above the upper threshold. If the difference parameter is above the upper threshold, then it is determined in step 232 that too much refrigerant is being delivered to the compressor 12. If the difference parameter is less than or equal to the upper threshold, the difference parameter must be within the set range so that it is determined in step 234 that there is just enough refrigerant delivered to the compressor 12.

In examples where the desired pressure differential is a set point rather than a set range, the upper and lower thresholds may be the same, such that a determination is made that sufficient refrigerant is delivered to the compressor only if the difference parameter is equal to the threshold or set point. In such an example, if the difference parameter is above the threshold, it is determined that too much refrigerant is delivered to the compressor, and if the difference parameter is below the threshold, it is determined that not enough refrigerant is delivered to the compressor.

In this example, the controller 50 implementing the method controls the bypass valve 44 in a negative feedback loop to gradually increase or decrease the flow through the bypass valve 44 to maintain the cooling of the compressor 12 at a desired point.

Although it has been described that the determination of whether there is insufficient or excessive refrigerant delivered to the compressor is based on the monitored pressures at the outlet of the subcooler 30 and at the return point 40, this may be determined by other means, such as by monitoring the flow of fluid through the cooling line, the motor cooling line and/or the inverter cooling line, or by monitoring the temperature of the motor 24 and the temperature of the inverter 26 to infer that there is insufficient refrigerant if the motor temperature rises above a threshold.

It will be understood that the present invention is not limited to the above-described embodiments, and various modifications and improvements may be made without departing from the concepts described herein. Any feature may be used alone or in combination with any other feature or features unless mutually exclusive, and the disclosure extends to and includes all combinations and subcombinations of one or more features described herein.

Claims

1. A refrigeration device comprising a refrigerant circuit, the refrigerant circuit comprising:

a compressor including a compressor fan and a motor driving the compressor fan;

a condensing device disposed downstream of the compressor, the condensing device including a condenser and a subcooler;

an expansion valve disposed downstream of the condensing device;

an evaporator disposed between the expansion valve and the compressor;

a main refrigerant line fluidly connected in a loop series: the compressor, the condensing device, the expansion valve, and the evaporator; and

a motor cooling line including a motor cooling valve fluidly connecting the subcooler to the motor to split refrigerant from the main refrigerant line to cool the motor, wherein the motor cooling line is further connected to the main refrigerant line at a return point upstream of the compressor fan to return refrigerant to the main refrigerant line at the compressor fan;

wherein the refrigerant circuit further comprises a bypass line fluidly connecting an outlet of the condenser to the expansion valve to bypass the subcooler, wherein the bypass line includes a bypass valve to selectively allow refrigerant in the main refrigerant line to bypass the subcooler.

2. The refrigeration appliance of claim 1, wherein the compressor includes an inverter, and wherein the subcooler is connected to the inverter by an inverter cooling line including an inverter cooling valve, and wherein the inverter cooling line is further connected to the main refrigerant line at the return point to direct refrigerant from the inverter to the main refrigerant line at the compressor fan.

3. The refrigeration appliance according to claim 1 or 2, comprising a controller configured to control the opening and closing of the bypass valve.

4. The refrigeration appliance according to claim 2, comprising a controller configured to control opening and closing of the bypass valve, wherein the controller is configured to control opening and closing of the inverter cooling valve.

5. The refrigeration appliance according to claim 3 or 4, wherein the bypass valve is a regulator valve, and wherein the controller is configured to control the bypass valve to control the flow of refrigerant through the bypass valve.

6. Refrigeration appliance according to any of claims 3 to 5, comprising a first pressure sensor arranged to monitor the pressure of the refrigerant leaving the subcooler and a second pressure sensor arranged to monitor the pressure in the main refrigerant line at the return point;

wherein the controller is arranged to receive a first pressure parameter from the first pressure sensor and a second pressure parameter from the second pressure sensor, and the controller is arranged to control the bypass valve based on the first pressure parameter and the second pressure parameter.

7. The refrigeration appliance according to any one of claims 3 to 5, comprising a first pressure sensor arranged to monitor the pressure of refrigerant exiting the subcooler, a second pressure sensor arranged to monitor the pressure in the main refrigerant line at the inlet of the compressor, and a third pressure sensor arranged to monitor the pressure in the main refrigerant line at the outlet of the compressor;

wherein the controller is arranged to receive a first pressure parameter from the first pressure sensor, a second pressure parameter from the second pressure sensor, and a third pressure parameter from the third pressure sensor, and wherein the controller is arranged to control the bypass valve based on the first pressure parameter, the second pressure parameter, and the third pressure parameter.

8. The refrigeration appliance according to any of the preceding claims, wherein the compressor is a dual stage compressor comprising a first stage compressor fan and a second stage compressor fan, and wherein the return point is located between the first stage compressor fan and the second stage compressor fan.

9. The refrigeration appliance according to any one of claims 3 to 8, wherein the controller is configured to control the opening and closing of the motor cooling valve.

10. A method of operating a refrigeration device according to any preceding claim, the method comprising:

determining whether there is insufficient refrigerant from the subcooler to be delivered to the compressor; and

controlling the bypass valve to increase a flow rate of refrigerant through the bypass valve in response to determining that insufficient refrigerant is delivered from the subcooler to the compressor.

11. The method of claim 10, wherein determining whether there is insufficient refrigerant delivered to the compressor comprises:

monitoring a first pressure parameter related to a pressure of refrigerant in the main refrigerant line at an outlet of the subcooler;

monitoring a second pressure parameter related to pressure in the main refrigerant line at a return point upstream of a compressor fan; and

determining whether there is insufficient refrigerant delivered to the compressor based on the first pressure parameter and the second pressure parameter.

12. The method of claim 11, wherein the second pressure parameter relates to a pressure in the main refrigerant line at a return point between a first stage compressor fan and a second stage compressor fan of a two stage compressor.

13. The method of claim 11 or 12, wherein determining whether there is insufficient refrigerant delivered to the compressor comprises:

calculating a difference parameter related to a difference between the first pressure parameter and the second pressure parameter;

comparing the difference parameter to a first threshold; and

if the difference parameter is below the first threshold, it is determined that insufficient refrigerant is delivered to the compressor.

14. The method of any of claims 10 to 13, wherein the method further comprises: determining whether an excess of refrigerant is delivered to the compressor; and reducing a flow rate of refrigerant through the bypass valve in response to determining that too much refrigerant is delivered to the compressor.

15. The method of claim 14, wherein determining whether too much refrigerant is delivered to the compressor comprises:

comparing the difference parameter to a second threshold; and

if the difference parameter is above the second threshold, it is determined that excess refrigerant is delivered to the compressor.