CROSS-REFERENCE(S) TO RELATED APPLICATION(S)

This application claims the benefit of U.S. Provisional Application No. 63/331,372, filed on April 15, 2022, expressly incorporated by reference herein for all purposes.

BACKGROUND

Several countries have legislation regarding how much ammonia can be within a factory. If these amounts are exceeded the penalties can be very tough.

A large ammonia charge will also require larger vessels in the refrigeration plant which both increase cost and space. Accordingly, it would be advantageous to reduce the amount of ammonia charge or any other refrigerant used in refrigeration systems as much as possible.

U.S. Patent No. 5,857,347, incorporated expressly by reference herein for all purposes describes a refrigeration system with an evaporator and separator. A control unit ensures that the evaporator is provided with overfeed, which provides a greater rate of liquid refrigerant to the evaporator than the rate that actually evaporates.

In one embodiment, a refrigeration system and method are disclosed that can lower the refrigerant levels in the separator compared to the '347 patent.

SUMMARY

This disclosure relates to controlling the refrigerant level in a refrigeration system, wherein the refrigeration system includes at least an evaporator connected to a separator, a compressor, and a condenser. The refrigeration system may include a receiver after the condenser. In the present disclosure, the inlet and outlet of the evaporator is connected to the separator, and the separator feeds the suction side of the compressor.

In one embodiment, the aim of the present disclosure is a lower refrigerant charge in the refrigeration system. In one embodiment, the refrigerant charge can be lowered by calculating the instantaneous refrigeration load from a number of measurements, and the refrigerant level in the separator vessel is adapted according to the refrigeration load.

In one embodiment, a refrigeration system includes a compressor, condenser, separator, and evaporator, wherein a condenser inlet is connected to an outlet of the compressor, a separator inlet is connected to an outlet of the condenser, an evaporator inlet is connected to a first outlet of the separator, an evaporator outlet is connected to the separator inlet, and a control unit has instructions stored thereon for executing a method comprising the following steps, repetitively calculating a refrigeration load on the evaporator; and controlling a level target of refrigerant in the separator based on the calculation of the refrigeration load.

In one embodiment, the control unit further comprises instructions for determining a minimum level target and a maximum level target of refrigerant in the separator, and calculating a level target of refrigerant in the separator as a function of the minimum and maximum level targets and refrigeration load.

In one embodiment, the control unit further comprises instructions for calculating a level target based on the calculation of the refrigeration load, wherein the level target is calculated to maintain a constant refrigerant charge within the combined volume of the separator and evaporator.

In one embodiment, the separator is positioned substantially laterally of the evaporator.

In one embodiment, the separator includes at least one analog level meter, and the control unit further comprises instructions for receiving a level measurement from the analog level meter and a step for comparing the measured level to the calculated level target.

In one embodiment, the control unit further comprises instructions for opening or closing an expansion valve connected to the inlet of the separator to control the level of refrigerant in the separator at the calculated level target.

In one embodiment, a calculation of refrigeration load is based on one or more measured variables including air temperature before and after the evaporator, air flow over the evaporator, refrigerant gas flowing out of the evaporator, refrigerant pressure in the evaporator, or any combination of variables.

In one embodiment, the refrigeration load data is obtained from the compressor (in the case the compressor serves only one set of separator/evaporator). Compressors can be fitted with instrumentation to provide signals with this data or the data could be derived from parameters like refrigerant pressure, refrigerant temperature, compressor rpm, compressor displacement, compressor motor input power etc. In one embodiment, the control unit further comprises instructions for overriding controlling the level of refrigerant in the separator based on the refrigeration load when a measured level in the separator is above a predetermined high level limit or below a predetermined low level limit.

In one embodiment, the system further comprises a suction valve between a second outlet of the separator and an inlet of the compressor, and the control unit further comprises instructions for closing the suction valve when a high level of refrigerant or a high rate of level change of refrigerant is detected in the separator.

In one embodiment, the refrigerant is ammonia, propane, carbon dioxide, a chlorofluorocarbon, a hydrochlorofluorocarbon, or a hydrofluorocarbon.

In one embodiment, the control unit further comprises instructions for, for each calculation of refrigeration load, re-calculating a level target for controlling the refrigerant in the separator.

In one embodiment, a method of controlling a separator and evaporator of a refrigeration system, wherein an evaporator inlet is connected to a first outlet of the separator, and an evaporator outlet is connected to a separator inlet, the method comprises, repetitively calculating a refrigeration load on the evaporator; and controlling a level of refrigerant in the separator based on the calculation of the refrigeration load.

In one embodiment, the method further comprises determining a minimum level target and a maximum level target of refrigerant in the separator; and calculating a level target of refrigerant in the separator as a function of the minimum and maximum level targets and refrigeration load.

In one embodiment, the method further comprises calculating a level target based on the calculation of the refrigeration load, wherein the level target is calculated to maintain a constant refrigerant charge within the combined volume of the separator and evaporator.

In one embodiment, the method further comprises receiving a level measurement from an analog level meter on the separator, and comparing the measured level to the calculated level target.

In one embodiment, the method further comprises opening or closing an expansion valve connected to the inlet of the separator to control the refrigerant level in the separator at the calculated level target.

In one embodiment, a calculation of refrigeration load is based on one or more measured variables including air temperature before and after the evaporator, air flow over the evaporator, refrigerant gas flowing out of the evaporator, refrigerant pressure in the evaporator, or a combination.

In one embodiment, the method further comprises overriding controlling the level of refrigerant in the separator based on the refrigeration load when a measured level in the separator is above a predetermined high level limit or blow a predetermined low level limit.

In one embodiment, the method further comprises closing a suction valve between an outlet of the separator and an inlet of the compressor when a high level of refrigerant or a high rate of level change of refrigerant is detected in the separator

In one embodiment, the refrigerant is ammonia, propane, carbon dioxide, a chlorofluorocarbon, a hydrochlorofluorocarbon, or a hydrofluorocarbon.

In one embodiment, the method further comprises, for each calculation of refrigeration load, re-calculating a level target for controlling the refrigerant in the separator.

This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:

FIGURE 1 is a schematic illustration of a refrigeration system in accordance with one embodiment;

FIGURE 2 is a diagrammatical illustration of a separator vessel in accordance with one embodiment;

FIGURE 3 is a schematic illustration of a refrigeration system control unit in accordance with one embodiment; and

FIGURE 4 is a flow diagram of a control method for a refrigeration system in accordance with one embodiment. DETAILED DESCRIPTION

U.S. Patent No. 5,857,347 describes a refrigeration system with an evaporator and separator. A control unit ensures that the evaporator is provided with overfeed, which provides a greater rate of liquid refrigerant to the evaporator than the rate that actually evaporates.

In one embodiment, compared to the '347 patent, the present disclosure can lower the refrigerant level in the separator up to 55%. The refrigerant charge for a specific refrigeration system (separator, pipes and evaporator(s)) is determined in the design of the refrigeration system. In the present disclosure, the required level to keep the designed refrigerant charge in the separator and evaporator is calculated according to a mathematical algorithm based on measured inputs from the process. At low refrigeration capacities the required level is lower and at higher capacities the refrigerant level is higher in the separator. However, the actual refrigerant charge within the separator and evaporator is the same for both low capacity and high capacity.

The system of the '347 patent maintains a constant level in the separator, whereas in one embodiment, the control unit in the present disclosure maintains a constant refrigerant charge within the evaporator and separator.

In one embodiment, advantages of the present disclosure can include a more even control of liquid feed. The gain is lower wear on valves, compressors, and a more even load on the refrigeration plant.

With the present disclosure, it is possible to have a higher operating level in the separator vessel at full capacity compared to the '347 patent.

In one embodiment, a higher operating level itself may not increase the capacity of the evaporator (if all other parameters are unchanged). To increase capacity you need to add more heat by, for example, increasing food product flow or increasing food product infeed temperature to the freezer. However, an increased operating level increases the possibility to operate at a higher capacity.

In one embodiment, a feature of the present disclosure is to keep the same refrigerant charge in the evaporator/separator during base load and full capacity.

In one embodiment, the refrigerant level in the separator vessel is low at low capacity and higher at high capacities. In one embodiment, a control unit is configured to keep the refrigerant charge in the evaporator, separator, and connecting pipes constant during operating conditions, meaning the refrigerant amount is constant.

The refrigeration system illustrated in FIGURE 1 comprises a compressor 1, a condenser 2, a receiver 3, and an evaporator 4, each having at least one inlet and an outlet. It should be understood that FIGURE l is a simplified diagram of the refrigeration system that includes the features of the present disclosure, and omits items such as auxiliary equipment, valves, instrumentation, and the like that are common on refrigeration systems. The refrigeration system further comprises a separator 5 having an inlet 6 and a first and a second outlet 7 and 8, respectively.

The first bottom outlet 7 of the separator 5 is connected to the inlet 9 of the evaporator 4. The outlet 10 of the evaporator 4 is connected to the middle inlet 6 of the separator 5. The second top outlet 8 of the separator 5 is connected to the inlet 11 of the compressor 1. The outlet 12 of the compressor 1 is connected to the inlet 13 of the condenser 2. The outlet 14 of the condenser 2 is connected to the inlet 15 of the receiver 3. Finally, the outlet 16 of the receiver 3 is connected to the inlet 6 of the separator 5 via a pipe 17 connecting the outlet 10 of the evaporator 4 with the inlet 6 of the separator 5. In one embodiment, the outlet 16 of the receiver 3 is connected to the separator 5 via a pipe 50 that does not mix with the evaporator 4 outlet.

In one embodiment, the separator 5 is positioned in a space which is cooled by the evaporator 4. This eliminates the need for insulating the separator 5. In one embodiment, the separator is positioned substantially laterally of the evaporator. This allows the separator 5 to feed the evaporator liquid refrigerant based on the head pressure on the refrigerant in the separator 5.

FIGURE 2 is an illustration of the separator 5. In one embodiment, the separator 5 comprises a container 19 formed as a substantially cylindrical shell 20 with rounded end caps 21 and 22. The separator 5 has a first pipe forming the inlet 6 at a midsection, a second pipe forming the first outlet 7 in the bottom end cap 21, and a third pipe forming the second outlet 8 in the top end cap 22.

As shown from FIGURE 1, in one embodiment of the separator 5, the first inlet pipe 6 may be connected via pipe 17 to the outlet 10 of the evaporator 4 so as to receive the mixture of liquid and vapor refrigerant therefrom. Optionally, in one embodiment, the outlet 10 of the evaporator 6 is connected to the inlet pipe 6, and the refrigerant from the receiver 3 enters the separator 5 through a separate pipe 50.

Further, in one embodiment, the inlet pipe 6 is directed tangentially into the container 19 such that the incoming mixture of liquid and vapor refrigerant will follow helical paths. Inside the cylindrical inner wall of the container 19, a foraminous partition 23 is provided, preferably a metallic net having a plurality of holes, openings or perforations. This foraminous partition 23 has a smaller width or diameter than the shell of the container 19 such that there is a small gap between the partition 23 and the inner surface of the container 19.

In operation, the mixture of the vapor and liquid components of the refrigerant received from the evaporator 4 is ejected into the separator 5 towards the inner side of the foraminous partition 23. The liquid component follows a spiral or helical path penetrating the foraminous partition 23. It then flows downwards in the gap between the inner surface of the container 19 and the foraminous partition 23. The vapor component of the refrigerant does not penetrate the foraminous partition 23 but forms a helical flow upwards in the container 19 and will be evacuated through the top outlet pipe. Hereby, a most efficient separation of the vapor and liquid components of the refrigerant outputted from the evaporator is possible.

Above the opening of the inlet pipe a splash shield 24 is mounted so as to prevent liquid drops from moving upwards instead of downwards in the separator 5.

Above the bottom outlet 7 of the container 19 and below the desired level of the liquid refrigerant therein, a vortex limiter 25 is provided so as to reduce the risk of introducing vapor refrigerant into the liquid refrigerant in the lower section of the container 19.

In embodiments, the refrigerant can include ammonia, propane, carbon dioxide, a chlorofluorocarbon, a hydrochlorofluorocarbon, or a hydrofluorocarbon.

In operation, the mixture of liquid and vapor refrigerant from the evaporator 4 is thrown against the partition 23 with a certain minimum speed that gives the necessary centrifugal force to ensure the desired separation. The size of the openings in the partition 23, the viscosity of the liquid refrigerant and the distance between the partition 23 and the inner surface of the container 19 are other design criteria that influence the efficiency of the separation. The result is that the liquid component of the refrigerant is dropping down in the gap between the inner surface of the container 19 and the partition 23 while the vapor component of the refrigerant will flow helically upwards through the center of the container 19. Any droplets entrained by this helical flow will be thrown by centrifugal force out towards that part of the partition 23 that is positioned above the inlet 6 to the separator 5 and thus be trapped by the partition 23 so as to flow down in the gap between the partition 23 and the inner surface of the container 19.

It should be noted that the feeding in of fresh refrigerant into the separator 5 is via the end of the pipe 29 opening within the pipe 17 towards the inlet 6 of the separator 5. Thereby, any vapor component of the fresh refrigerant will be separated in the same way as the vapor component of the mixture returned from the evaporator 4. The fresh refrigerant also helps the circulation between the evaporator 4 and the separator 5. Optionally, in one embodiment, the outlet 10 of the evaporator 6 is connected to the inlet pipe 6, and the refrigerant from the receiver 3 enters the separator 5 through a separate pipe 50.

The vortex limiter 25, preferably having the form of a mesh cross, reduces vortex movement of incoming circulating liquid refrigerant and thereby simplifies the control of the level of the liquid refrigerant in the separator 5. Further, a vortex can be avoided at the bottom of the separator in order to ensure an even feed of liquid refrigerant to the evaporator, since a vortex could reduce the driving force and in extreme situations jeopardize the function of the evaporator.

In the present disclosure, the refrigeration system can include one or more analog level sensers 27. An analog sensor can provide continuous and instantaneous measurements of the refrigerant level in the separator 5. In one embodiment, the analog sensor 27 can be placed on a bypass line on the side wall of the separator 5.

In one embodiment, the refrigeration system may also include instruments to measure the conditions relating to the evaporator 4 and separator 5. Temperature sensor 31 measures the temperature of the medium being cooled after the evaporator 4. Temperature sensor 33 measures the temperature of the medium being cooled before the evaporator 4. Temperature sensor 32 can measure the temperature of the refrigerant from the separator 5. Temperature sensor 32 can be positioned on the evaporator 4 itself, on the outlet or return pipe therefrom or within the evaporator 4 below the liquid level therein.

Instrument 34 can measure the flow of the air passing over the evaporator 5. Instrument 34 can indirectly measure the air flow by determining the fan speed. Instrument 35 can measure the refrigerant flow out of the separator 5. Instrument 36 can measure the pressure of the refrigerant in the evaporator 5 or separator 5.

The refrigeration system also comprises a control unit 26 illustrated in detail in FIGURE 3. The control unit 26 is connected to the instruments 31-36. Instruments 31-36 send measurements to the control unit 26, which are then processed by the control unit 26. The control unit 26 provides an output signal to the expansion valve 28 based on the received measurements.

The above described embodiment may be modified in several ways.

As an example, the outlet of the condenser 2 and receiver 3 could be connected directly to the separator 5 via a further, separate inlet positioned above the liquid refrigerant level therein. The outlet of the condenser 2 and receiver 3 could even be connected into the pipe leading from the first outlet of the separator 5 to the inlet of the evaporator 4.

In FIGURE 1, the condenser 2 and receiver 3 constitutes a one-stage refrigeration system. However, a two-stage refrigeration system may also be used. Further, the condenser 2 and receiver 3 may comprise a closed economizer or an open economizer. Thus, the structure of the compressor 1 as well as the condenser 2 and receiver 3 may be varied within the scope of the invention.

Also, the evaporator 4 may take several forms and be used for cooling different fluids, such as a gas, e.g. air, as well as a liquid. The cooled fluid may be used for freezing, e.g. in a food freezing plant, but also for cooling, e.g. in an air conditioning system.

FIGURE 3 is one embodiment of the control unit 26. The control unit 26 can be implemented in one or more computing devices.

A computing device includes at least one processor and a system memory connected by a communication bus. Depending on the exact configuration and type of device, the system memory may be volatile or nonvolatile memory, such as read only memory ("ROM"), random access memory ("RAM"), EEPROM, flash memory, a hard drive, solid state drive, CD ROM, DVD, or other disk storage, magnetic cassettes, magnetic tape, magnetic disk storage, and/or the like.

Those of ordinary skill in the art and others will recognize that system memory typically stores data and/or program modules that are immediately accessible to and/or currently being operated on by the processor. In this regard, the processor may serve as a computational center of the computing device by supporting the execution of instructions. In this disclosure "engine" refers to logic embodied in hardware, circuitry, or software instructions, which can be written in a programming language, such as C, C++, COBOL, JAVA™, PHP, Perl, HTML, CSS, JavaScript, VBScript, ASPX, Microsoft.NET™, Go, and/or the like. An engine may be compiled into executable programs or written in interpreted programming languages. Software engines may be callable from other engines or from themselves. Generally, the engines described herein refer to logical modules that can be merged with other engines, or can be divided into subengines. The engines can be stored in any type of computer-readable medium or computer storage device and be stored on and executed by one or more general purpose computers, thus creating a special purpose computer configured to provide the engine or the functionality thereof.

The control unit 26 includes a refrigeration load engine 40. The refrigeration load engine 40 is used for calculating an estimate of the heat load being applied to the evaporator 4. As shown, the refrigeration load engine 40 can use one or more inputs from instruments 31 to 36 for calculating refrigeration load. The refrigeration load engine 40 can rely on at least one instrument to calculate an estimate of the instantaneous refrigeration load on the evaporator 4. The instruments can provide, for example, measured variables including air temperature before and after the evaporator, air flow over the evaporator, refrigerant gas flowing out of the separator, refrigerant pressure in the evaporator, or any combination of variables. In one embodiment, the refrigeration load is calculated repetitively during the operation of the refrigeration system, so as to provide continuous estimate of the refrigeration load as the heat load on the evaporator 4 can be continuously changing over time. The refrigeration load can be calculated in units of BTU/hr or Watts (W), and the like.

The control unit 26 includes a level target engine 42. In one embodiment, the level target engine 42 uses the calculated refrigeration load to determine a level target of refrigerant in the separator 5.

In one embodiment, a level target is based on a linear function. For example, a linear function can be described by a plot of minimum to maximum designed refrigeration load versus the minimum to maximum designed refrigerant level. The function can be stored as a two-dimensional Table having the level target values correlated to the refrigeration load values. In one embodiment, the level target is calculated to maintain a substantially constant refrigerant charge in the combined volumes of the evaporator/separator. Such calculation can take into consideration, for example, thermodynamic equations relating to the amounts of refrigerant in the system, refrigerant density, the heats of capacity, the heats of vaporization, and other thermodynamic quantities.

The control unit 26 may include a level control engine 44. The level control engine 44 uses the level target supplied by the level target engine 42. The level control engine 44 continuously receives a measured level of refrigerant in the separator 5 from an instrument, such as the analog level sensor 27. The analog level sensor can be placed on a bypass line of the separator 5. The level control engine 44 compares the level target from the level target engine 42 with the measured level and processes the difference into a signal that can be used to control the expansion valve 28. For example, when the measured level is below the level target, the level control engine 44 sends a signal to open the expansion valve 28 and increase the flow of refrigerant into the separator 5. When the measured level is above the level target, the level control engine 44 sends a signal to close the expansion valve 28 to reduce the flow of refrigerant into the separator 5. The strength of the signal that determines the position of the expansion valve 28 will vary based on the difference, the controller gain, and other factors.

In one embodiment, the level control engine 44 has an override function that prevents the level of refrigerant from exceeding a maximum permissible high level limit or falling below a minimum permissible low level limit in the separator 5. The permissible high and low level limits can be used to prevent equipment damage or prevent unsafe operating conditions. In the case of a high level limit being reached or exceeded, the level control engine 44 can fully close the expansion valve, for example, until such time as the level of refrigerant in the separator falls to safe operating level. In the case of a reaching or falling below a low level limit, the level control engine 44 can fully open the expansion valve, for example, until such time as the level of refrigerant in the separator reaches a safe operating level.

Additionally or alternatively, a suction valve 38 can be placed on the second outlet of the separator 5 that leads to the suction side of the compressor 1. In one embodiment, the level control engine 44 will close the suction valve 38 when a high level of refrigerant or a high rate of level change of refrigerant is detected in the separator 5. Referring to FIGURE 4, one embodiment of a method 50 of controlling the flow of refrigerant in a refrigeration system having at least one evaporator and one separator is illustrated.

In block 52, the separator and evaporator are charged with refrigerant based on the design criteria. In one embodiment, the refrigeration system is operated so as to maintain the amount of refrigerant charge within the separator and evaporator substantially constant. "Substantially constant" when used in reference to the amount of refrigerant charge can mean no more than 50% deviation, or 45% deviation, or 40% deviation, or 35% deviation, or 30% deviation, or 25% deviation, or 20% deviation, or 15% deviation, or 10% deviation, or 5% deviation. During charging, the evaporator 4 and separator 5 will simultaneously experience a heat load.

In block 58, the refrigeration load on the evaporator is continuously calculated by the control unit 26. Here, the refrigeration load can be calculated every second, or a fraction of a second, or may even perform a calculation after tens of seconds or minutes. Continuous calculation of the refrigeration load can also happen instantaneously or in real time as conditions change. The aim is to repetitively calculate the refrigeration load to provide the ideal target level in the separator 5.

In block 60, the level target is calculated by the control unit 26 based on the refrigeration load. In one embodiment, there are several functions to calculate the level target, including a function based on a linear relationship between the minimum to maximum refrigeration load and the minimum to maximum separator level. In one embodiment, the level target is based on a function that determines a level target that is calculated to maintain a substantially constant refrigerant charge within the evaporator 4/separator 5 system.

In block 62, the instantaneous or actual level in the separator 5 is measured via the analog sensor 27.

In block 64, the measured level is compared to the calculated level target generated in block 60 by the level target engine 42.

Block 66 is a decision block that determines whether the measured level has exceeded a high level limit or fallen below a low level limit in the separator 5. Block 68 is entered if either a high level or low level limit is exceeded. In block 68, the control unit 26 takes one or more corrective actions to correct the level in the separator when either a high level limit or low level limit is exceeded. Specifically, the level control engine 44 is configured to control the expansion valve 28 or the suction valve 38 as described in association with FIGURE 3 above.

Block 70 is entered when neither a high level nor low level limit is exceeded in the separator 5. In block 70, the control unit 26 sends a signal to the expansion valve 28 depending on whether the measured level is less than or greater than the level target. The level target is calculated by the level target engine 42 based on a number or predetermined functions described in association with FIGURE 3 above.

After block 70, the method returns to block 58 to repetitively calculate the refrigeration load and set a new target level if necessary.

The method of operating the evaporator/ separator can have several advantages. The liquid feed can be controlled to be even and proportional to the refrigeration load.

The analog sensor makes it possible for the same separator to be used for several different load conditions and evaporators. This saves design time and adds flexibility. Instead of an analog sensor, a number of digital level switches can also be used to measure the level but it is preferred to use an analog sensor.

The system operates to raise the refrigerant level at high capacity and lower the refrigerant level at low capacity. This will allow a wider range of operating capacities, and in particular higher operating capacities for a specified evaporator/separator assembly. The refrigerant charge will be significantly smaller compared to a system that is controlled at a fixed level.

In one embodiment, the opening degree of the refrigerant from the liquid feed can be proportionally controlled to the actual need to provide an even liquid feed rate proportional to the refrigeration capacity. Even feed conditions are beneficial for the refrigeration plant operation to reduce wear and increase efficiency.

Representative embodiments according to the disclosure include, but are not limited, to the following.

In one embodiment, a refrigeration system comprises a compressor, condenser, separator, and evaporator, wherein; a condenser inlet is connected to an outlet of the compressor; a separator inlet is connected to an outlet of the condenser; an evaporator inlet is connected to a first outlet of the separator; an evaporator outlet is connected to the separator inlet; and a control unit having instructions stored thereon for executing a method comprising the following steps, repetitively calculating a refrigeration load on the evaporator; and controlling a level target of refrigerant in the separator based on the calculation of the refrigeration load.

In one embodiment, the control unit further comprises instructions for, determining a minimum level target and a maximum level target of refrigerant in the separator; and calculating a level target of refrigerant in the separator as a function of the minimum and maximum level targets and refrigeration load.

In one embodiment, the control unit further comprises instructions for, calculating a level target based on the calculation of the refrigeration load, wherein the level target is calculated to maintain a constant refrigerant charge within the combined volume of the separator and evaporator.

In one embodiment, the separator is positioned substantially laterally of the evaporator.

In one embodiment, the separator includes at least one analog level meter, and the control unit further comprises instructions for receiving a level measurement from the analog level meter and a step for comparing the measured level to the calculated level target.

In one embodiment, the control unit further comprises instructions for, opening or closing an expansion valve connected to the inlet of the separator to control the level of refrigerant in the separator at the calculated level target.

In one embodiment, a calculation of refrigeration load is based on one or more measured variables including air temperature before and after the evaporator, air flow over the evaporator, refrigerant gas flowing out of the evaporator, refrigerant pressure in the evaporator, or any combination of variables.

In one embodiment, a calculation of refrigeration load is obtained from the compressor.

In one embodiment, a calculation of refrigeration load is calculated by the control unit using signals from the compressor, wherein the signals include one or more of refrigerant pressure, refrigerant temperature, compressor rpm, compressor displacement, compressor motor input power, or a combination thereof. In one embodiment, the control unit further comprises instructions for, overriding controlling the level of refrigerant in the separator based on the refrigeration load when a measured level in the separator is above a predetermined high level limit or below a predetermined low level limit.

In one embodiment, the refrigeration system further comprises a suction valve between a second outlet of the separator and an inlet of the compressor, and the control unit further comprises instructions for, closing the suction valve when a high level of refrigerant or a high rate of level change of refrigerant is detected in the separator.

In one embodiment, the refrigerant is ammonia, propane, carbon dioxide, a chlorofluorocarbon, a hydrochlorofluorocarbon, or a hydrofluorocarbon.

In one embodiment, the control unit further comprises instructions for, for each calculation of refrigeration load, re-calculating a level target for controlling the refrigerant in the separator.

In one embodiment, a method of controlling a separator and evaporator of a refrigeration system, wherein an evaporator inlet is connected to a first outlet of the separator, and an evaporator outlet is connected to a separator inlet, the method comprising: repetitively calculating a refrigeration load on the evaporator; and controlling a level of refrigerant in the separator based on the calculation of the refrigeration load.

In one embodiment, the method further comprises, determining a minimum level target and a maximum level target of refrigerant in the separator; and calculating a level target of refrigerant in the separator as a function of the minimum and maximum level targets and refrigeration load.

In one embodiment, the method further comprises calculating a level target based on the calculation of the refrigeration load, wherein the level target is calculated to maintain a constant refrigerant charge within the combined volume of the separator and evaporator.

In one embodiment, the method further comprises receiving a level measurement from an analog level meter on the separator and comparing the measured level to the calculated level target. In one embodiment, the method further comprises opening or closing an expansion valve connected to the inlet of the separator to control the refrigerant level in the separator at the calculated level target.

In one embodiment, a calculation of refrigeration load is based on one or more measured variables including air temperature before and after the evaporator, air flow over the evaporator, refrigerant gas flowing out of the evaporator, refrigerant pressure in the evaporator, or a combination.

In one embodiment of the method, a calculation of refrigeration load is obtained from the compressor.

In one embodiment of the method, a calculation of refrigeration load is calculated by the control unit using signals from the compressor, wherein the signals include one or more of refrigerant pressure, refrigerant temperature, compressor rpm, compressor displacement, compressor motor input power, or a combination thereof.

In one embodiment, the method further comprises overriding controlling the level of refrigerant in the separator based on the refrigeration load when a measured level in the separator is above a predetermined high level limit or blow a predetermined low level limit.

In one embodiment, the method further comprises closing a suction valve between an outlet of the separator and an inlet of the compressor when a high level of refrigerant or a high rate of level change of refrigerant is detected in the separator

In one embodiment, the refrigerant is ammonia, propane, carbon dioxide, a chlorofluorocarbon, a hydrochlorofluorocarbon, or a hydrofluorocarbon.

In one embodiment, the method further comprises, for each calculation of refrigeration load, re-calculating a level target for controlling the refrigerant in the separator.

While illustrative embodiments have been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.