阅读说明：本技术 对制冷剂至压缩机中的喷射基于闪蒸罐的控制 (Flash tank based control of injection of refrigerant into a compressor ) 是由 埃里克·维南迪 雷米·迪克斯 保罗·基亚拉蒙特 卢卡·马佐拉纳 于 2021-04-22 设计创作，主要内容包括：描述了一种对至制冷循环中的压缩机中的喷射进行控制的方法,其中该方法在制冷循环中执行,该制冷循环至少包括构造成接收制冷剂并使液体制冷剂与蒸气制冷剂分离的闪蒸罐,以及构造成压缩制冷剂的压缩机,其中该压缩机包括用于压缩的装置、吸入口和喷射口,该喷射口在制冷循环的至少一时刻连接至该用于压缩的装置,其中该闪蒸罐经由喷射阀与压缩机的喷射口连接。该方法包括确定闪蒸罐中的压力并基于所确定的闪蒸罐中的压力控制喷射阀。(A method of controlling injection into a compressor in a refrigeration cycle is described, wherein the method is performed in a refrigeration cycle comprising at least a flash tank configured to receive refrigerant and separate liquid refrigerant from vapor refrigerant, and a compressor configured to compress refrigerant, wherein the compressor comprises means for compressing, a suction port, and an injection port connected to the means for compressing at least a moment in the refrigeration cycle, wherein the flash tank is connected with the injection port of the compressor via an injection valve. The method includes determining a pressure in the flash tank and controlling the injection valve based on the determined pressure in the flash tank.)

1. A method of controlling injection into a compressor (2) in a refrigeration cycle (1a, 1b), wherein the method is performed in a refrigeration cycle (1a, 1b), the refrigeration cycle (1a, 1b) comprising at least a flash tank (5) configured to receive a refrigerant and to separate liquid refrigerant from vapor refrigerant, and a compressor (2) configured to compress the refrigerant, wherein the compressor (2) comprises means for compressing, a suction inlet, and an injection outlet connected to the means for compressing at least a moment of the refrigeration cycle, wherein the flash tank (5) is connected to the injection outlet of the compressor (2) via an injection valve (9),

the method comprises the following steps:

determining (102) a pressure in the flash tank (5);

controlling (104) the injection valve (9) based on the determined pressure in the flash tank (5).

2. The method according to claim 1, wherein controlling the injection valve (9) comprises:

closing (206) the injection valve (9) in case the determined pressure in the flash tank (5) is below a first threshold value.

3. The method according to claim 2, wherein controlling the injection valve (9) comprises:

-at least partially opening (210) the injection valve (9) in case the determined pressure in the flash tank (5) is equal to or greater than the first threshold value and below a second threshold value.

4. A method according to claim 3, wherein opening the injection valve (9) comprises:

determining an opening value of the injection valve (9) based on the determined flash tank pressure by means of a proportional integral derivative PID controller; and

setting the opening degree of the injection valve (9) to the determined value.

5. The method according to any one of claims 3 and 4, further comprising:

determining whether the compressor (2) is operating; and

wherein opening the injection valve (9) is performed only if it is determined that the compressor (2) is operating.

6. The method according to any of claims 3-5, wherein controlling the injection valve (9) comprises:

closing (212) the injection valve (9) in case the determined pressure in the flash tank (2) is greater than the second threshold value.

7. The method according to any one of the preceding claims, further comprising:

-determining the pressure at the suction of the compressor (2);

determining whether the pressure at the suction port is below a third threshold; and

in the event that it is determined that the pressure at the suction port is below the third threshold:

-closing the injection valve (9); and

-switching off the compressor (2).

8. The method according to any one of the preceding claims, further comprising:

controlling the compressor (2) based on the determined pressure in the flash tank (5).

9. The method of claim 8, wherein controlling the compressor (2) comprises:

in the event that the determined flash tank pressure is below a fourth threshold, an operating speed for the compressor (2) is determined by the PID controller and the operating speed is set (306) to the determined operating speed.

10. The method of claim 9, wherein controlling the compressor (2) comprises:

unloading (310) the compressor (2) in case the determined flash tank pressure is equal to or greater than the fourth threshold value and lower than a fifth threshold value; and

stopping (312) operation of the compressor (2) in case the determined flash tank pressure is greater than the fifth threshold value.

11. A method according to any of the preceding claims, wherein the compressor (2) comprises a discharge, and wherein the refrigeration cycle (1a, 1b) further comprises a heat rejecting heat exchanger (3) and an expansion device (4), the heat rejecting heat exchanger (3) being connected to the discharge of the compressor (2), the expansion device (4) being arranged between the heat rejecting heat exchanger (3) and the flash tank (5), wherein the method further comprises:

setting (406) an opening of the expansion device (4) to a predetermined value in case the determined flash tank pressure is below a sixth threshold value;

setting (410) the opening of the expansion device (4) to a value determined by a PID controller based on a first heat rejection heat exchanger pressure mode if the determined flash tank pressure is equal to or greater than the sixth threshold and below a seventh threshold;

determining that the pressure in the flash tank (5) is equal to or greater than the seventh threshold and below an eighth threshold, and setting (414) the opening of the expansion device (4) to a value determined by the PID controller based on a second heat rejecting heat exchanger pressure mode; or

Determining that the pressure in the flash tank (5) is equal to or greater than the eighth threshold and below a ninth threshold, and controlling (418) the opening of the expansion device (4) based on a fuzzy adjustment; or

Determining that the pressure in the flash tank (5) is equal to or greater than the ninth threshold and below a tenth threshold, and controlling (422) the opening of the expansion device (4) based on a flash tank pressure adjustment mode; or

Determining if the pressure in the flash tank (5) is equal to or greater than the tenth threshold value and closing (424) the expansion device (4).

12. A method according to claim 11, wherein the first heat rejecting heat exchanger pressure mode comprises controlling the expansion device (4) based on a temperature of refrigerant in the heat rejecting heat exchanger (3).

13. A method according to any one of claims 11 and 12, wherein the second heat rejecting heat exchanger pressure mode (HRHE _ mode2) comprises controlling the expansion device (4) based on the temperature of refrigerant in the heat rejecting heat exchanger (3) and the pressure of refrigerant in the flash tank (5).

14. The method according to any of the claims 11 to 13, wherein the flash tank (5) pressure regulation mode comprises: controlling the expansion device (4) based on a pressure of refrigerant in the flash tank (5).

15. Method according to any of the preceding claims, wherein the refrigeration cycle (1b) comprises a bypass line (11) connected between the flash tank (5) and the suction inlet of the compressor (2), wherein the bypass line (11) comprises a bypass valve (12), and wherein the method further comprises:

determining that the pressure of the flash tank (5) is below an eleventh threshold value and closing (506) the bypass valve (12); or

Determining that the pressure of the flash tank (5) is equal to or greater than the eleventh threshold and below a twelfth threshold, and determining (510), by a PID controller, an opening value of the bypass valve (12) based on the determined flash tank pressure; or

Determining that the pressure of the flash tank (5) is equal to or greater than the twelfth threshold and below a thirteenth threshold, and fully opening (514) the bypass valve (12); or

Determining that the pressure of the flash tank (5) is equal to or greater than the thirteenth threshold value, and setting (516) the opening of the bypass valve (12) to a predetermined value.

Technical Field

The present patent application relates to a method for controlling injection of refrigerant into a compressor in a refrigeration cycle, wherein the refrigeration cycle includes an injection compressor and a flash tank.

Background

Refrigeration systems having a refrigeration cycle are well known in the art. In a typical refrigeration cycle, a refrigerant is circulated through a refrigeration system, wherein the refrigerant undergoes changes in thermodynamic properties in different parts of the refrigeration system. The refrigerant is a fluid, i.e. a liquid or a vapour or a gas, respectively. An example of the refrigerant may be an artificial refrigerant, such as fluorocarbon. However, in recent applications, CO is present due to carbon dioxide₂Environmentally friendly, carbon dioxide CO as a non-artificial refrigerant₂Is becoming more and more important. Changes in thermodynamic properties of a refrigerant may include, for example, changes in temperature, pressure, volume, or enthalpy, where a change in one property may also affect at least one other property at times, or where at least one property may remain constant while another property changes in some cases. The change in thermodynamic properties may be accompanied by a phase change of at least a portion of the refrigerant, such as from liquid to vapor and vice versa.

Refrigerant is used in a refrigeration system to transfer heat in a refrigeration cycle. Thus, heat is typically transferred from one point in the refrigeration cycle to another point in the refrigeration cycle by utilizing a refrigerant. For example, these points in the refrigeration cycle may be represented by heat exchangers. In the first heat exchanger, the refrigerant may receive heat from a source. The source may be, for example, the air of a room whose temperature should be controlled. After being delivered to the second heat exchanger, the refrigerant may reject heat in the second heat exchanger, for example, by transferring heat into the exhaust gas.

Today, refrigeration systems are particularly important for controlling temperature or climate conditions. One particular type of refrigeration system is a compression refrigeration system, sometimes referred to as a Vapor Compression Refrigeration System (VCRS).

As used herein, a refrigeration cycle includes at least a compressor for compressing a refrigerant. The compressed refrigerant may drive a cycle. In addition, such refrigeration cycles typically include a heat exchanger in which heat can be extracted from the compressed refrigerant. Extracting heat from the compressed refrigerant is sometimes referred to as heat rejection because heat is rejected from the refrigeration system. Therefore, this heat exchanger is commonly referred to as a heat rejecting heat exchanger. Further, such a refrigeration cycle generally includes an expansion device in which the pressure of the refrigerant is lowered and thus the temperature is lowered. The expansion device may be, for example, a valve, in particular an expansion valve, or a metering device. Additionally, such refrigeration cycles typically include another heat exchanger that may be used to receive heat from the source. This other heat exchanger is commonly referred to as a heat accepting heat exchanger. The heat accepting heat exchanger is in fluid communication with the compressor such that the refrigerant is directed to the compressor to close the cycle.

In some refrigeration cycles, a compressor is used to drive the refrigeration cycle. Such compressors typically include a suction port and a discharge port and a means for compression. The suction port is configured to receive refrigerant from the refrigeration cycle. For example, the refrigerant may be received from a heat accepting heat exchanger. The suction port is in fluid communication with the compression chamber at least at a first time to provide refrigerant to the means for compressing. In the device for compression, the refrigerant will be compressed to a desired pressure. Compression generally increases the pressure of the refrigerant. This may be accompanied by an increase in the refrigerant temperature. In the case where the compressor may be a scroll compressor, the means for compressing may be formed by a scroll assembly of the scroll compressor.

The means for compressing is in fluid communication with the discharge port of the compressor at least at the second moment in time to provide compressed refrigerant to the discharge port. At the discharge, the compressed refrigerant may be discharged from the compressor at a desired discharge pressure or a desired discharge temperature.

In some refrigeration cycles, the compressor may be an ejector compressor. In addition to the above-described features of the compressor, the ejector compressor also includes an ejector port. The injection port is in fluid communication with a source for providing a refrigerant. The source may be, for example, an economizer. Furthermore, the injection opening is in fluid communication with the means for compressing of the compressor at least at the third moment. With the injection port in fluid communication with the means for compressing, refrigerant is provided from a source to the means for compressing of the compressor. The refrigerant provided from the source to the means for compressing may be referred to as additional refrigerant, injected refrigerant, or fresh refrigerant. In most applications, the injected refrigerant is in a vapor state. However, in certain situations, such as where it is desired to reduce the temperature of the refrigerant in the compressor, it may be advantageous to inject liquid refrigerant in addition to vapor refrigerant.

Disclosure of Invention

Generally, the system efficiency, expressed in a so-called coefficient of performance (COP), depends on the temperature or pressure difference between the temperature or pressure of the refrigerant in the heat rejecting heat exchanger and the refrigerant in the heat accepting heat exchanger. However, injection conditions (e.g., pressure and temperature) directly affect the efficiency of the system. Therefore, controlling a refrigerant system based solely on the temperature of the refrigerant in the heat rejecting heat exchanger may result in fluctuations in the cooling provided by the refrigeration system or inefficient operation. Accordingly, there is a need in the art for improving the efficiency of refrigeration systems.

This need is overcome by a method for controlling injection into a compressor of a refrigeration cycle according to the present invention.

In general, the present disclosure is directed to a method for controlling injection into a compressor of a refrigeration cycle based on a pressure in a flash tank of the refrigeration cycle, wherein the flash tank is connected to at least an injection port of an injection compressor.

A method according to the invention of controlling injection into a compressor in a refrigeration cycle is performed in a refrigeration cycle comprising at least: a flash tank configured to receive refrigerant and separate liquid refrigerant from vapor refrigerant; and a compressor configured to compress a refrigerant. The compressor comprises means for compression, a suction inlet and an injection port, wherein at least the injection port is connected to the means for compression at least one moment. The means for compressing is configured to receive refrigerant from a suction port and/or a discharge port of the compressor. Further, the means for compressing compresses the refrigerant. In a preferred embodiment, the compressor may be a scroll compressor and the means for compressing may be formed by a scroll assembly of the scroll compressor. Further, the compressor may further include a discharge port, and the means for compressing may be configured to provide compressed refrigerant to the discharge port of the compressor.

Since the present invention relates to the control of refrigerant in a refrigerant cycle of a refrigerant system, the term "connection" is used to describe a connection that enables fluid communication via the connection. In other words, the connection enables exchange of refrigerant between the connected entities.

According to the invention, the flash tank is connected to the injection port of the compressor. Said connection between the flash tank and the injection port is established via the injection valve. The flash tank is configured to separate vapor refrigerant from liquid refrigerant. A connection between the flash tank and the injection port is configured to provide vapor refrigerant from the flash tank to the injection port of the compressor. The vapor refrigerant may be fresh refrigerant for injection into the compressor, in particular into the means for compressing of the compressor.

The method according to the invention comprises determining the pressure in the flash tank. Determining the pressure in the flash tank may be performed continuously, periodically, or triggered by a particular event. In this regard, the specific event may be, for example, a read operation issued by a method for controlling. Determining the pressure in the flash tank may include determining a particular pressure value in the flash tank, or may include determining whether the pressure value exceeds or falls below a threshold value. Additionally, determining the pressure in the flash tank may also include determining a parameter associated with the pressure.

In a preferred embodiment, the inlet of the flash tank may comprise an expansion device, or may be connected to an expansion device within the refrigeration cycle. A corresponding expansion device may be used to expand the refrigerant, thereby reducing its pressure. Expansion of the refrigerant may occur with flashing. Flashing refers to the generation of vapor during the expansion of a saturated liquid. In a flash tank, vapor refrigerant and liquid refrigerant may be separated in the same receiving space within the flash tank. For example, liquid refrigerant may collect at the bottom of the receiving space while vapor refrigerant collects at the top. In this case, determining the pressure in the flash tank may include determining the pressure in the receiving space that collects liquid refrigerant and vapor refrigerant. However, in an example, the flash tank may collect vapor refrigerant and liquid refrigerant in separate chambers. For example, the flash tank may include at least one chamber for collecting vapor refrigerant and at least one other chamber for collecting liquid refrigerant. In this case, determining the pressure in the flash tank may include any one of: determining a pressure within at least one chamber for collecting vapor refrigerant; and determining the pressure in at least one chamber for collecting liquid refrigerant.

According to the invention, the method further comprises controlling the injection valve based on the determined pressure in the flash tank. Controlling the injection valve may include adjusting an amount of injected refrigerant.

Thus, controlling the injection valve may comprise opening or closing the injection valve or partially opening or closing the injection valve. In this regard, partially opening or closing the injection valve may include determining an opening degree of the injection valve and setting the injection valve to the opening degree. The opening may be expressed in percentages, where 100% may refer to a fully open injection valve and 0% may refer to a fully closed injection valve.

In a refrigeration system performing the method according to the invention, the control may be performed by a controller within the system. To this end, the controller may be connected to the component to be controlled. The connections between the controller and other components, such as the injection valve, compressor and/or flash tank, are configured to exchange information. The controller may perform the step of controlling the injection valve by transmitting one or more control signals to the injection valve. The control signal may cause the valve to close or open. In addition, the controller may also provide additional control signals that cause a read operation to be performed to determine the pressure in the flash tank.

The controller may be connected to at least one sensor, wherein the sensor is configured to determine pressure. The at least one sensor may be integrated in the flash tank. In one example, the sensor may be configured to determine a pressure in the flash tank and provide the determined pressure to the controller. In another example, a sensor may be configured to provide data to a controller, wherein the controller is configured to determine the pressure in the flash tank from the data provided by the sensor. In any case, the controller is configured to determine whether and how to perform control based on the determined pressure in the flash tank. For example, the controller may determine how to adjust the amount of injected refrigerant.

In a preferred embodiment, controlling the injection valve may comprise closing the injection valve in case the determined pressure in the flash tank is below a first threshold value. The first threshold may be referred to as a minimum flash tank pressure for injection. The minimum flash tank pressure for injection may depend on the operating conditions of the compressor. In a preferred embodiment, this minimum flash tank pressure for injection is the pressure in the flash tank necessary to provide efficient injection of fresh refrigerant into the compressor. In at least one embodiment, the minimum flash tank pressure for injection is selected to be greater than the pressure at the suction of the compressor. For example, the minimum flash tank pressure for injection is based on the internal characteristics of the compressor. Thus, the minimum flash tank pressure for injection may be a compressor specific value.

Further, controlling the injection valve may include at least partially opening the injection valve if the flash tank pressure is equal to or greater than a first threshold and may be below a second threshold. The second threshold is greater than the first threshold and may be a maximum flash tank pressure for refrigerant injection. If the pressure in the flash tank exceeds the maximum flash tank pressure for injection, the refrigerant may be injected into the compressor at a pressure that is too high, which may either damage the compressor or result in a too high discharge pressure of the compressed refrigerant that may result in a reduced COP. Accordingly, controlling the injection valve may further include closing the injection valve in the event the determined pressure in the flash tank is greater than the second threshold.

In at least some embodiments, opening the injection valve may include determining a value for an opening degree of the injection valve based on the determined flash tank pressure and setting the opening degree of the injection valve to the determined value. The determined value may be represented by a percentage. Further, the determination may be performed by the controller using a closed-loop algorithm. Examples of the closed-loop algorithm may be a proportional-integral-derivative (PID) control algorithm, a fuzzy logic algorithm, or a Z-transform. Thus, the controller that can perform this determination can be a PID controller, a fuzzy logic controller, or a Z converter. However, those skilled in the art will appreciate that other types of controllers may be used. The closed-loop controller may be a controller performing the method according to the invention or may be a component within a controller performing the method according to the invention or may be connected to said controller. The use of a closed loop controller for the determination has the following advantages: closed loop controllers are generally cheap and easy to implement and do not require extensive maintenance work.

In at least some of the foregoing embodiments, the opening of the injection valve is performed only if it is determined that the compressor is operating. In these embodiments, the method may further include determining whether the compressor is operating. Determining whether the compressor is operating may include determining that the compressor is operating normally, which means that the compressor is not operating in a fault condition. In the event that the compressor is not running or is not running properly, then the controller may also decide to close the injection valve.

In another preferred embodiment, the method may include determining a pressure at an injection port of the compressor. Further, the method may include determining whether the pressure at the injection port is greater than a third threshold. The third threshold may be a maximum injection pressure. In the event that it is determined that the pressure at the injection port is greater than the third threshold, then the method may include closing the injection valve and stopping operation of the compressor. If the pressure at the injection port exceeds the maximum injection pressure, the pressure of the refrigerant received by the compressor at the injection port is already too high to allow proper injection into the compressor. This method step therefore represents a safety adjustment, since the operation of the compressor can be stopped in order to avoid damage to the compressor due to the increased pressure.

In another preferred embodiment, the method may further comprise controlling the compressor. While this control may regulate the operation of the compressor, it is to be understood that the operation of the compressor may also be regulated by other control operations. For example, the operation of the compressor may be controlled by the pressure at the suction inlet of the compressor, and may be adjusted based on the flash tank pressure in the event that the flash tank pressure becomes too high.

Controlling the compressor may also include adjusting an operating condition of the compressor. The operating condition of the compressor may be determined by the capacity of the compressor. In this regard, for example, the capacity of the compressor may be defined as the amount of compressed refrigerant provided per time interval. As will be understood by those skilled in the art, the adjustment of the capacity of the compressor may be performed by adjusting the operating speed of the compressor, as the adjustment is directly related to the amount of compressed refrigerant provided in each time interval. For example, the higher the speed at which the compressor is operated, the higher the amount of compressed refrigerant provided by the compressor in each time interval.

In a preferred embodiment, the method may comprise: in the event that the determined flash tank pressure is below the fourth threshold, controlling the compressor may include determining an operating speed of the compressor and setting the operating speed to the determined operating speed. The fourth threshold may be referred to as the flash tank pressure for compressor unloading.

In the event that the determined flash tank pressure is equal to or greater than the fourth threshold and below the fifth threshold, then controlling the compressor may include unloading the compressor. Thus, the fifth threshold may be equal to the second threshold, which may be referred to as a maximum pressure for refrigerant injection. Unloading the compressor may include minimizing the capacity of the compressor. Although the capacity of the compressor is reduced to a minimum, the operation of the compressor is not stopped. According to the invention, the compressor is unloaded when it is in the pressure range between the fourth threshold value and the fifth threshold value. Within this pressure range, unloading will be performed regardless of the pressure at the suction of the compressor.

If the determined flash tank pressure is greater than the fifth threshold, the method may further include stopping operation of the compressor. This may improve the safe operation of the compressor, since if the flash tank pressure is too high, which may result in too high an injection pressure and possibly damage the compressor, the operation of the compressor may be stopped.

In another preferred embodiment, the compressor comprises a discharge, the refrigeration cycle in which the method is performed further comprising a heat rejecting heat exchanger connected to the discharge of the compressor and a second expansion device arranged between the heat rejecting heat exchanger and the flash tank. The second expansion device may be referred to as a high pressure valve. The method may further comprise: in the case where the determined flash tank pressure is below the sixth threshold, the opening of the second expansion device is set to a predetermined value. The predetermined value may be determined based on a characteristic of a compressor used in a refrigeration cycle. In one embodiment, the predetermined value may correspond to a fully open second expansion device. The sixth threshold may be a minimum allowable flash tank pressure necessary for proper operation of the flash tank. The predetermined value may be a value known to provide acceptable refrigerant performance under standard conditions.

Further, the method may comprise: in the event that the determined flash tank pressure is equal to or greater than the sixth threshold and below the seventh threshold, the opening of the second expansion device is set to a value determined by the PID controller based on the first heat rejection heat exchanger pressure mode (HRHE _ mode 1). The first rejecting heat exchanger pressure mode indicates that the second expansion device is controlled based on the temperature of the refrigerant in the heat rejecting heat exchanger in order to reach a desired pressure and thereby a high COP in the heat rejecting heat exchanger. For example, the desired pressure may be a set point specified by an operator or set during manufacture, or may be an optimal pressure associated with an optimal COP. The optimum pressure may depend on the operating conditions of the compressor or other system characteristics, such as compressor efficiency or heat exchanger efficiency. The desired pressure may be determined by the controller. In one embodiment, the controller detects a temperature of the refrigerant at an outlet of the heat rejecting heat exchanger. Thus, the controller may be configured to measure the temperature itself, or may be configured to receive the temperature from the sensor. Based on the determined temperature at the outlet of the heat rejecting heat exchanger, the controller adjusts the opening degree of the second expansion device in order to maintain a high pressure in the heat rejecting heat exchanger, which optimizes the COP. The relationship between the temperature of the refrigerant at the outlet of the heat rejecting heat exchanger and the pressure of the refrigerant in the heat rejecting heat exchanger depends at least in part on the thermodynamic properties of the refrigerant used. For example, the pressure of the refrigerant in the heat rejecting heat exchanger may depend on at least one of the following parameters: a temperature of the refrigerant in the heat rejecting heat exchanger, a pressure of the refrigerant in the heat accepting heat exchanger, and an injection pressure.

Further, the method may comprise: in the event that the determined pressure in the flash tank is equal to or greater than the seventh threshold and below the eighth threshold, the opening of the second expansion device is set to a value determined by the PID controller based on the second heat rejection heat exchanger pressure mode (HRHE _ mode 2). The eighth threshold may be equal to the fourth threshold. The second heat rejecting heat exchanger pressure mode represents control of the second expansion device based on a temperature of refrigerant in the heat rejecting heat exchanger and a pressure of refrigerant in the flash tank. The second heat rejecting heat exchanger pressure mode thereby addresses the increased flash tank pressure level by decreasing the opening of the second expansion device. This may reduce the flash tank pressure. Further, this may allow to achieve a flash tank pressure suitable for injecting refrigerant into the compressor.

Further, the method may comprise: in a case where the determined flash tank pressure is equal to or greater than the eighth threshold and lower than the ninth threshold, the opening of the second expansion device is controlled based on the fuzzy adjustment. The ninth threshold may be equal to the second threshold.

Further, the method may comprise: in a case where the determined pressure in the flash tank is equal to or greater than the ninth threshold value and lower than the tenth threshold value, the opening degree of the second expansion device is controlled based on a flash tank pressure adjustment mode (FT _ mode). The tenth threshold may be referred to as the maximum allowable flash tank pressure. The flash tank pressure regulation mode represents control of the second expansion device based on the pressure of the refrigerant in the flash tank. Thus, the flash tank pressure adjustment mode takes into account the further increased flash tank pressure and adjusts the second expansion device to receive a flash tank pressure suitable for injection. The flash tank pressure is the main condition for the adjustment, since it is higher than the pressure range where the second heat rejecting heat exchanger pressure mode is used.

Further, the method may include closing the second expansion device if the determined pressure in the flash tank is equal to or greater than a ninth threshold.

In another preferred embodiment, the refrigeration cycle in which the method is carried out also comprises a so-called bypass line connected between the flash tank and the suction inlet of the compressor. Thus, the bypass line may be used to provide refrigerant from the flash tank to the compressor. In one example, the bypass line may be connected to the vapor collection chamber of the flash tank. Further, the bypass line may include a bypass valve. The bypass valve may function to expand the refrigerant. Expanding the refrigerant through the bypass valve may be used to reduce the pressure of the refrigerant. In these embodiments, the method may include closing the bypass valve if the determined pressure in the flash tank is below an eleventh threshold. An eleventh threshold may be a minimum flash tank pressure for bypass adjustment.

Further, the method may comprise: in a case where the determined flash tank pressure is equal to or greater than an eleventh threshold value and lower than a twelfth threshold value, a value of an opening degree of the bypass valve is determined based on the determined flash tank pressure. The twelfth threshold may be equal to the fourth threshold. The opening degree may be determined by a PID controller.

Further, the method may comprise: in the event that the determined flash tank pressure is equal to or greater than the twelfth threshold and below the thirteenth threshold, the bypass valve is fully opened. The thirteenth threshold may be equal to the second threshold.

Further, the method may comprise: in the case where the determined flash tank pressure is equal to or greater than the twelfth threshold value, the opening degree of the bypass valve is set to a predetermined value. Thus, the predetermined value may be set by a user according to the characteristics of the refrigerant and the refrigerant system. In order to set the predetermined value to an appropriate value, the predetermined value represents an opening degree at which the flash tank pressure is reduced without providing too high a pressure to the suction port of the compressor.

The thresholds described throughout this application may be independent of the operating conditions of the refrigeration system in at least some embodiments. However, in other embodiments, at least one of the thresholds may depend on the operating conditions of the refrigeration system. For example, the third threshold may depend on at least one of a pressure of refrigerant in the heat rejecting heat exchanger, a pressure of refrigerant in the heat accepting heat exchanger, or an ambient temperature. In this case, the controller performing the method according to the present invention may comprise logic for adaptively adjusting the third threshold value based on the operating conditions of the refrigeration system. Because the third threshold may be the maximum injection pressure, the dependence of the third threshold on the operating conditions of the refrigeration system may improve the flexibility of the control, may result in a higher COP and increased reliability of the compressor, and may also protect the compressor from failure.

The following description and the annexed drawings set forth in detail certain illustrative aspects of the system. These aspects are indicative, however, of but a few of the various ways in which the principles of various embodiments may be employed and the described embodiments are intended to include all such aspects and their equivalents.

Drawings

In the drawings, like reference numerals generally refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention.

In the following description, various embodiments of the present invention will be described with reference to the following drawings, in which:

FIGS. 1a, 1b show schematic diagrams of an exemplary refrigeration system for flash tank based control of injection of refrigerant into a compressor;

fig. 2 shows a diagram of the effect of refrigerant injection on the optimum heat rejecting heat exchanger pressure;

3a, 3b, 3c show block diagrams of the inputs and outputs of a controller that may be used in connection with the present invention;

FIG. 4 shows a flow chart of a method of controlling injection into a compressor according to an embodiment of the present invention;

FIG. 5 illustrates a decision diagram of a preferred embodiment of a method of controlling injection into a compressor, wherein the decision diagram relates to controlling an injection quantity into the compressor;

FIG. 6 illustrates a decision diagram of a preferred embodiment of a method of controlling injection into a compressor, wherein the decision diagram relates to controlling operating conditions of the compressor;

FIG. 7 shows a decision diagram for a preferred embodiment of a method of controlling injection into a compressor, wherein the decision diagram relates to control of a second expansion device arranged between a heat rejecting heat exchanger and a flash tank;

fig. 8 shows a diagram representing a transition from the second heat rejecting heat exchanger pressure mode to the flash tank pressure control mode for the second expansion device;

fig. 9 shows a decision diagram of a preferred embodiment of a method of controlling injection into a compressor, wherein the decision diagram relates to controlling a bypass valve for bypassing refrigerant from a flash tank to a suction inlet of the compressor.

Detailed Description

The following detailed description refers to the accompanying drawings that show, by way of illustration, specific details in which embodiments of the invention may be practiced.

The word "exemplary" is used herein to mean "serving as an example, instance, or illustration. Any embodiment or design described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments or designs.

Fig. 1a shows a schematic diagram of a refrigeration system 1a, the refrigeration system 1a being used for flash tank based control of injection of refrigerant into a compressor 2 of the refrigeration system 1 a. The refrigeration system 1a includes: a compressor 2, the compressor 2 including a suction port, a discharge port, and a jet port; a heat rejecting heat exchanger 3 downstream of the compressor 2; a first expansion device 6 downstream of the heat rejecting heat exchanger 3; and a heat accepting heat exchanger 7 downstream of the first expansion device 6 and upstream of the compressor 2.

Further, the refrigeration system 1a includes a second expansion device 4 and a flash tank 5. The second expansion device 4 is arranged downstream of the heat rejecting heat exchanger 3 and upstream of the first expansion device 6. The second expansion device 4 is adapted to expand the refrigerant after leaving the heat rejecting heat exchanger 3. Therefore, the pressure and temperature of the refrigerant can be reduced.

A flash tank 5 is connected downstream of the second expansion device 4 and upstream of the first expansion device 6. In the refrigeration system 1a depicted in fig. 1, the flash tank 5 comprises two separate chambers 5a, 5 b. However, it is also possible that the flash tank separates the liquid refrigerant and the vapor refrigerant in the same accommodation space.

The two separation chambers 5a, 5b comprise a chamber 5a for collecting vapour or flash gas and a chamber 5b for collecting liquid. The liquid collection chamber 5b comprises at least one outlet. The connection between the flash tank 5 and the first expansion device 6 is established via at least one of the at least one outlet of the liquid collection chamber 5b of the flash tank 5.

The vapour collection chamber 5a of the flash tank 5 comprises at least one outlet. The at least one outlet of the vapor collection chamber 5a is connected to an injection path 8, the injection path 8 connecting the at least one outlet of the vapor collection chamber 5a to an injection port of the compressor 2. The injection path 8 includes an injection valve 9.

Further, the refrigeration system 1a comprises a controller 10, the controller 10 being configured to control at least one of the injection valve 9 and the compressor 2 based on the determined pressure in the flash tank 5. Further, the controller 10 may also control the first expansion device 6 and/or the second expansion device 4. Fig. 1a indicates the connections for exchanging control signals by means of dashed lines. Although fig. 1a shows dashed lines between the controller 10 and the injection valve 9, the first expansion device 6, the second expansion device 4, the compressor 2 and the flash tank 5, those skilled in the art will appreciate that these dashed lines are shown for illustrative purposes only. The controller 10 may be connected to any subset of the aforementioned components of the refrigeration cycle. With respect to the connection between the controller 10 and the flash tank 5, it should be noted that the controller 10 may be connected to a sensor within the flash tank 5, wherein the sensor may be a pressure sensor. Further, in some examples, multiple controllers may be employed in a refrigeration system. Each of these multiple controllers may control any subset of the expansion device, compressor, and flash tank, as previously described with respect to controller 10.

Fig. 1b shows a schematic diagram of a refrigeration system 1b, the refrigeration system 1b being used for flash-tank based control of injection of refrigerant into a compressor 2 of the refrigeration system 1 b. The refrigeration system 1b differs from the refrigeration system 1a in that a bypass path 11 connects the injection path 8 between the flash tank 5 and the injection valve 9 to the suction port of the compressor 2. The bypass path 11 includes a bypass valve 12. In another example not depicted in the drawings, it is also possible that the bypass path 11 is directly connected to the flash tank 5. As depicted in fig. 1b, the controller 10 may also be configured to control the bypass valve 12.

With respect to the refrigeration systems 1a, 1b depicted in fig. 1a, 1b, it is noted that the elements of the refrigeration systems 1a, 1b, which are depicted as separate components in fig. 1a, 1b or any other figure of the present application, may be comprised in the same housing or may form a circulating component capable of performing the operations of the separate components depicted in fig. 1a, 1 b. As an example, the second expansion device 4 may be integrated into the flash tank 5. As such, there are many different configurations that combine or configure the individual components depicted in fig. 1a, 1 b. Moreover, it is possible to include additional components not depicted in the embodiment examples.

Fig. 2 shows a diagram of the effect of refrigerant injection on the optimum heat rejecting heat exchanger pressure. In detail, fig. 2 depicts the dependence on the pressure (p) of the refrigerant in the heat rejecting heat exchanger_c) Coefficient of performance (COP). Thus, the solid line 50 represents the curve for the COP of the refrigeration system with the injection valve closed, while the dashed line 55 represents the curve for the COP of the same refrigeration system with the injection valve open. In a refrigeration system, the operating conditions are controlled in order to achieve the highest COP. Without refrigerant injection, the COP depends on the temperature of the refrigerant in the heat rejecting heat exchanger. However, the injection of refrigerant directly affects the efficiency of the system. The effect depends on the injection conditions, such as the pressure of the injected refrigerant or the temperature of the injected refrigerant. It can be seen that the injection not only improves the overall COP. The injection also moves the maximum value of COP to a lower pressure of the refrigerant in the heat rejecting heat exchanger. The maximum of the corresponding curve represents the optimum heat rejecting heat exchanger pressure. When refrigerant injection into the compressor is used, this is most importantThe preferred pressure is lower.

Fig. 3a, 3b, 3c show block diagrams of the inputs and outputs of a controller that can be used in connection with the present invention.

In fig. 3a, a controller, represented by block "CTRL", receives as input the flash tank pressure and controls at least one of the injection valve EVI and the compressor CMP. In fig. 3a, the output arrow of the compressor CMP is shown in dashed lines to illustrate that the controller may perform injection valve control, compressor control, or both.

In fig. 3b, the controller receives flash tank pressure as an input and controls at least one of the injection valve EVI, the compressor CMP, the bypass valve or the second expansion device HPV. Similar to fig. 3a, the dashed lines indicate that the controller can output any combination of four output controls.

In fig. 3c, the controller receives as inputs the flash tank pressure, the temperature at the heat rejecting heat exchanger GCT, the pressure at the heat rejecting heat exchanger GCP and the pressure at the suction port SCP and controls at least one of the injection valve EVI, the compressor CMP, the bypass valve or the second expansion device HPV. Similar to fig. 3a, 3b, the dashed lines indicate that the controller can output any combination of four output controls.

Fig. 4 shows a flow chart of a method of controlling injection into a compressor according to an embodiment of the invention. The method 100 may be performed by a controller in a refrigeration cycle (e.g., the controller 10 as depicted in fig. 1a, 1 b). The method 100 includes the step of determining 102 a pressure in the flash tank 5. Determining the pressure in the flash tank 5 may include determining the pressure in the vapor collection chamber 5 a.

Further, the method 100 comprises the steps of: the injection valve 9 is controlled 104 based on the determined pressure in the flash tank 5.

Fig. 5 shows a decision diagram 200 of a preferred embodiment of a method of controlling injection into a compressor, wherein the decision diagram relates to controlling an amount of injection into the compressor. The amount injected into the compressor is controlled by controlling the injection valve (referred to as EVI). This determination may be performed by a controller, such as controller 10.

The method begins at step 202 by determining a flash tank pressure or receiving a determined flash tank pressure at step 202. In fig. 5, the flash tank pressure is referred to as FTP.

At step 204, it is determined whether the flash tank pressure is below a first threshold. In the event that the pressure is below the first threshold, the method continues to step 206, where injection valve EVI is closed at step 206. Otherwise, in the event that the pressure is not below the first threshold, the method continues to step 208.

At step 208, it is determined whether the flash tank pressure is greater than or equal to a first threshold and below a second threshold. In the event that the flash tank pressure is greater than or equal to the first threshold value and below the second threshold value, the method continues to step 210 where injection valve EVI is opened in step 210. In an example, injection valve EVI may be fully opened at step 210. In the event that the flash tank pressure is not greater than or equal to the first threshold value and is below the second threshold value, the method continues to step 212 where injection valve EVI is closed in step 212.

In the event that the method reaches one of steps 206, 210 or 212, the method may continue again to step 202 by determining or receiving the flash tank pressure FTP. In this case, the method may determine or receive an updated value for the flash tank pressure FTP.

Fig. 6 shows a decision diagram 300 of a preferred embodiment of a method of controlling injection into a compressor, wherein the decision diagram relates to controlling the operating conditions of the compressor. The operating condition of the compressor is referred to as CMP in fig. 6. This determination may be performed by a controller, such as controller 10.

The method begins at step 302 by determining or receiving a determined flash tank pressure at step 302. In fig. 6, the flash tank pressure is referred to as FTP.

At step 304, it is determined whether the flash tank pressure is below a fourth threshold. In the event that the pressure is below the fourth threshold, the method continues to step 306 where the operating condition of the compressor is calculated by the PID controller based on the pressure at the suction port at step 306. Otherwise, in the event that the flash tank pressure is not below the fourth threshold, the method continues to step 308.

At step 308, it is determined whether the flash tank pressure is greater than or equal to the fourth threshold and below the fifth threshold. If this is the case, the method continues to step 310 where the compressor is unloaded at step 310. Otherwise, the method continues to step 312, where the compressor stops its operation at step 312.

In the event that the method reaches one of steps 306, 310 or 312, the method may continue again to step 302 by determining or receiving the flash tank pressure FTP. In this case, the method may determine or receive an updated value for the flash tank pressure FTP.

Fig. 7 shows a decision diagram 400 of a preferred embodiment of a method of controlling injection into a compressor, wherein the decision diagram relates to the control of a second expansion device arranged between a heat rejecting heat exchanger and a flash tank. The second expansion means is referred to as the high pressure valve HPV in fig. 7. This determination may be performed by a controller, such as controller 10.

The method begins at step 402 by determining or receiving a determined flash tank pressure at step 402. In fig. 7, the flash tank pressure is referred to as FTP.

At step 404, it is determined whether the flash tank pressure is below a sixth threshold. In case the pressure is below the sixth threshold, the method continues to step 406, where the high pressure valve HPV is opened by a predetermined opening degree. The predetermined value may be determined based on a characteristic of a compressor used in a refrigeration cycle. In one embodiment, the predetermined value may correspond to a fully open second expansion device. The sixth threshold may be a minimum allowable flash tank pressure, which is necessary for proper operation of the flash tank. The predetermined value may be a value known to provide acceptable refrigerant performance under standard conditions. Otherwise, in the event that the pressure is not below the sixth threshold, the method continues to step 408.

At step 408, it is determined whether the flash tank pressure is greater than or equal to the sixth threshold and below the seventh threshold. In the event that the flash tank pressure is greater than or equal to the sixth threshold and below the seventh threshold, the method continues to step 410 where the PID controller calculates the opening of the high pressure valve HPV based on the first heat rejection heat exchanger pressure mode (HRHE _ mode 1). The first rejecting heat exchanger pressure mode represents a control of the second expansion device based on the temperature of the refrigerant in the heat rejecting heat exchanger in order to achieve an optimal pressure in the heat rejecting heat exchanger and thus an optimal COP. In the event that the flash tank pressure is not greater than or equal to the sixth threshold and is below the seventh threshold, the method continues to step 412.

At step 412, it is determined whether the flash tank pressure is greater than or equal to the seventh threshold and below the eighth threshold. In the event that the flash tank pressure is greater than or equal to the seventh threshold value and below the eighth threshold value, the method continues to step 414 where the PID controller calculates the opening of the high pressure valve HPV based on the second heat rejection heat exchanger pressure mode (HRHE _ mode 2). The second heat rejecting heat exchanger pressure mode represents control of the second expansion device based on a temperature of refrigerant in the heat rejecting heat exchanger and a pressure of refrigerant in the flash tank. In the event that the flash tank pressure is not greater than or equal to the seventh threshold value and is below the eighth threshold value, the method continues to step 416.

At step 416, it is determined whether the flash tank pressure is greater than or equal to the eighth threshold and below the ninth threshold. In case the flash tank pressure is greater than or equal to the eighth threshold and below the ninth threshold, the method continues to step 418, at which step 418 the opening of the high pressure valve HPV is calculated by fuzzy adjustment based on the pressure of the refrigerant in the heat rejecting heat exchanger (hrep) and the flash tank pressure. Thereby, the pressure of the refrigerant in the heat rejecting heat exchanger may be, for example, the pressure the refrigerant has at the outlet of the heat rejecting heat exchanger or the pressure in the heat rejecting heat exchanger. In the event that the flash tank pressure is not greater than or equal to the eighth threshold value and is below the ninth threshold value, the method continues to step 420.

At step 420, it is determined whether the flash tank pressure is greater than or equal to a ninth threshold and below a tenth threshold. In case the flash tank pressure is greater than or equal to the ninth threshold value and lower than the tenth threshold value, the method continues to step 422, at which step 422 the opening degree of the high pressure valve HPV is calculated based on the flash tank pressure adjustment mode (FT _ mode). The flash tank pressure regulation mode represents control of the second expansion device based on the pressure of the refrigerant in the flash tank. In case the flash tank pressure is not greater than or equal to the ninth threshold value and is lower than the tenth threshold value, the method continues to step 424, at step 424 the high pressure valve HPV is closed.

In the event that the method reaches one of steps 406, 410, 414, 418, 422 or 424, the method may continue again to step 402 by determining or receiving the flash tank pressure, FTP. In this case, the method may determine or receive an updated value for the flash tank pressure FTP.

Fig. 8 shows a graph representing an exemplary transition from the second heat rejection heat exchanger pressure mode to the flash tank pressure control mode for the second expansion device. In detail, fig. 8 depicts the percentage of adjustment between the second heat rejection heat exchanger pressure mode (HRHE _ mode2) and the flash tank pressure adjustment mode (FT _ mode). Thus, solid line 450 depicts the use of HRHE _ mode2, while dashed line 455 depicts the use of FT _ mode. In the event that the flash tank pressure is below the eighth threshold of flash tank pressure, then control is based solely on HRHE _ mode2, per step 414 of FIG. 7. In the event that the flash tank pressure exceeds the ninth threshold of flash tank pressure, control is based entirely on FT _ mode, per step 422 of FIG. 7.

In the case where the flash tank pressure is between the eighth threshold and the ninth threshold, then control is performed based on a combination of HRHE _ mode2 and FT _ mode. This is represented by a falling curve 450 and a rising curve 455. Thus, the pressure phase between the eighth threshold and the ninth threshold corresponds to the transition region from HRHE _ mode2 to FT _ mode. In this regard, it should be appreciated that the course of the curves 450, 455 in the transition region are shown for exemplary purposes only. The course of the curves 450, 455 need not be linear. Alternatively, the control may be performed based on fuzzy control, as described with respect to step 418 of fig. 7, which may result in different routes of the curves 450, 455.

Fig. 9 illustrates a decision diagram 500 of a preferred embodiment of a method of controlling injection into a compressor, wherein the decision diagram relates to controlling a bypass valve for bypassing refrigerant from a flash tank to a suction inlet of the compressor. The bypass valve is referred to in FIG. 7 as BPV. This determination may be performed by a controller, such as controller 10.

The method begins at step 502 where a flash tank pressure is determined or received at step 502. In fig. 7, the flash tank pressure is referred to as FTP.

At step 504, it is determined whether the flash tank pressure is below an eleventh threshold. In the event that the pressure is below the eleventh threshold, the method continues to step 506 where the bypass valve BPV is closed at step 506. Otherwise, in the event that the flash tank pressure is not below the eleventh threshold, the method continues to step 508.

At step 508, it is determined whether the flash tank pressure is greater than or equal to an eleventh threshold and below a twelfth threshold. In the event that the flash tank pressure is greater than or equal to the eleventh threshold value and below the twelfth threshold value, the method continues to step 510 where the PID controller calculates the opening of the bypass valve BPV based on the flash tank pressure FTP at step 510. Otherwise, in the event that the flash tank pressure is not greater than or equal to the eleventh threshold and is below the twelfth threshold, the method continues to step 512.

At step 512, it is determined whether the flash tank pressure is greater than or equal to a twelfth threshold and below a thirteenth threshold. In the event that the flash tank pressure is greater than or equal to the twelfth threshold and below the thirteenth threshold, the method continues to step 514 where the bypass valve BPV is fully opened at step 514. Otherwise, the method continues to step 516, where the opening of the bypass valve is set to a predetermined value at step 516. The predetermined value may be set by a user according to the characteristics of the refrigerant system and the refrigerant. To set an appropriate value for the predetermined value representing the opening at which the flash tank pressure is reduced without providing too high a pressure to the suction inlet of the compressor.

In the event that the method reaches one of steps 506, 510, 514 or 516, the method may continue again to step 502 by determining or receiving the flash tank pressure, FTP. In this case, the method may determine or receive an updated value for the flash tank pressure FTP.

What has been described above includes examples of one or more implementations. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the aforementioned embodiments, but one of ordinary skill in the art may recognize that many further combinations and permutations of various embodiments are possible. Accordingly, the described embodiments are intended to embrace all such alterations, modifications and variations that fall within the scope of the appended claims.