DUAL TEMPERATURE REFRIGERATION SYSTEM

Description

TECHNICAL FIELD

This disclosure relates to refrigeration systems, and more specifically, to dual temperature refrigeration systems.

BACKGROUND

Refrigeration systems are used to cool spaces such as refrigerators, freezers, coolers, and display cases. Display cases are used for the storage, preservation, and presentation of products, including food products. To facilitate the preservation of the products, temperature-controlled cases often include one or more refrigeration systems for maintaining a display area of the case at a desired temperature. Refrigeration systems rely on refrigeration cycles of a refrigerant that alternately absorbs and rejects heat to cool an internal volume of the display case. As a result of the cooling, the food products are typically maintained in a chilled state, which reduces a likelihood of spoilage for future retrieval and consumption.

SUMMARY

Implementations of the present disclosure include a refrigeration system that includes one or more compressors, a gas cooler/condenser, a receiver tank, one or more evaporators, an expansion valve, a sensor, and a controller. The one or more compressors compress a working fluid. The gas cooler/condenser is fluidly coupled to the one or more compressors. The receiver tank is fluidly coupled to the gas cooler/condenser. The one or more evaporators are fluidly coupled to the receiver tank and the one or more compressors. The expansion valve is fluidly coupled to and disposed between the receiver tank and the one or more evaporators. The sensor is coupled to the one or more evaporators. The controller is coupled to the sensor and the expansion valve. The controller receives sensor feedback from the sensor and performs operations, including determining, as a function of the sensor feedback, that a discharge air temperature of an airflow circulated through the one or more evaporators satisfies a discharge air temperature threshold. The discharge air temperature is cooled by the working fluid in the one or more evaporators. The operations also includes controlling, as a function of determining that the discharge air temperature satisfies the discharge air temperature threshold, the expansion valve to maintain or switch a mode of operation of the one or more evaporators. The modes of operation include a first temperature mode and a second temperature mode.

In some implementations, the controlling includes controlling the expansion valve based only on the discharge air temperature while maintaining a superheat temperature of the working fluid within a superheat range.

In some implementations, the one or more evaporators are one or more dual temperature evaporators and the first temperature mode is medium temperature mode and the second temperature is low temperature mode.

In some implementations, the refrigeration system is void of pressure-regulating valves at an outlet of the one or more evaporators.

In some implementations, the expansion valve includes an electronic expansion valve (EEV) and controlling the expansion valve includes controlling the expansion valve using pulse width modulation. In some implementations, the controller controls the EEV to maintain, in the first temperature mode, a discharge air setpoint of between 30 and 38 degrees Fahrenheit while maintaining a superheat of the working fluid within a superheat range. In some implementations, the superheat range is between 2 and 9 degrees Fahrenheit. In some implementations, the controller controls the EEV to maintain, in the second temperature mode, a discharge air setpoint of between −20 and 32 degrees Fahrenheit while maintaining a superheat of the working fluid within a superheat range.

In some implementations, the one or more evaporators include one or more display cases. Each of the one or more display cases includes a single dual temperature evaporator coil configured to operate in low temperature mode and medium temperature mode.

In some implementations, the controller maintains, in a medium temperature defrost mode of the one or more evaporators and as a function of determining that the discharge air temperature satisfies a second discharge air temperature threshold, the expansion valve closed to passively de-ice the one or more evaporators.

In some implementations, a suction line that is coupled to an outlet of the one or more evaporators is arranged to operate with the working fluid at temperatures of between −20 and 45 degrees Fahrenheit.

In some implementations, the one or more compressors include at least one low-temperature compressor and at least one medium temperature compressor.

Implementations of the present disclosure also include a refrigeration system controller that includes one or more hardware processors and a computer storage medium communicatively coupled to the one or more hardware processors. The computer storage medium includes instructions that, when executed by the one or more hardware processors, cause the one or more hardware processors to perform operations that include receiving sensor feedback that includes a discharge air temperature of an airflow circulated within an evaporator case, through one or more evaporators, and cooled by working fluid in the one or more evaporator. The operations also include determining that the discharge air temperature satisfies a discharge air temperature threshold. The operations also include changing, as a function of the determination, an operation parameter of one or more expansion valves to regulate an amount of the working fluid circulated into the one or more evaporators to change the one or more evaporators between a first temperature mode and a second temperature mode.

In some implementations, the first temperature mode includes medium temperature mode in which items stored within the evaporator case are at a temperature of between 30 and 40 degrees Fahrenheit, and the second temperature mode includes low temperature mode in which the items stored within the evaporator case are at a temperature of between −20 and 32 degrees Fahrenheit.

In some implementations, the changing includes opening or closing the expansion valve based on the discharge air temperature using pulse width modulation while maintaining superheat of the working fluid within a superheat range to prevent the working fluid to exit the one or more evaporators in liquid form.

In some implementations, the one or more evaporators includes one or more dual temperature evaporators. The refrigeration system controller is part of a refrigeration system including one or more sensors, one or more compressors, and a gas cooler/condenser, and the receiving includes receiving the sensor feedback from the one or more sensors. In some implementations, the refrigeration system is void of pressure-regulating valves between the one or more evaporators and the one or more compressors. In some implementations, the expansion valve includes an electronic expansion valve (EEV) and controlling the expansion valve includes controlling the expansion valve using pulse width modulation to maintain, in the first temperature mode, a discharge air setpoint of between 30 and 38 degrees Fahrenheit while maintaining a superheat of the working fluid within a superheat range. In some implementations, the superheat range is between 3 and 6 degrees Fahrenheit.

Implementations of the present disclosure also include a method that includes receiving, from one or more sensors of a refrigeration system and by a controller, sensor feedback. The refrigeration system includes one or more evaporators, a working fluid, and one or more expansion valves. The working fluid flows through the one or more evaporators. The one or more expansion valves each reside upstream of each of the one or more evaporators. The sensor feedback includes a discharge air temperature of an airflow circulated through the one or more evaporators and cooled by the working fluid in the one or more evaporators. The method also includes determining, by the controller, that the discharge air temperature satisfies a discharge air temperature threshold. The method also includes controlling, as a function of the determination and by the controller, an operation parameter of the one or more expansion valves, thus regulating an amount of the working fluid flowed into the one or more evaporators to change the one or more evaporators between a first temperature mode and a second temperature mode.

Particular implementations of the subject matter described in this specification can be implemented so as to realize one or more of the following advantages. For example, the refrigeration system of the present disclosure saves time and resources by allowing evaporators to switch between low temperature and medium temperature mode, which provides flexibility of storage, energy efficiency, space saving, etc. Additionally, the refrigeration system of the present disclosure controls the temperature of the evaporators as a function of discharge airflow, allowing the system to be simple in design and void of additional components such as pressure-regulating valves, solenoid valves, electronic regulating valves, multiple braze joints, alternate piping paths to bypass pressure-regulating valves in low cooling mode, and dedicated heat exchangers for each cooling mode. Moreover, low temperature and medium temperature evaporators can have the same construction and specification, both being capable of operating in dual temperature and thus allowing the display case building process to be streamlined, improving economies of scale, and reducing the amount of models or stock keeping units (SKUs) offered for sale. Additionally, the uniformity of design of the evaporators can help streamline and simplify the installation and maintenance process and reduce installation and maintenance errors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a refrigeration system according to implementations of the present disclosure.

FIG. 2 is a block diagram of an example control logic according to implementations of the present disclosure.

FIG. 3 is a flow chart of an example refrigeration method.

FIG. 4 is a schematic illustration of an example control system or controller for a refrigeration system.

DETAILED DESCRIPTION

The refrigeration system of the present disclosure can be used to provide cooling for temperature-controlled display devices in a supermarket or similar facility. Advantageously, the refrigeration system has dual temperature evaporators and a control system that allows the refrigeration system to be selectively switched (e.g., by simply pressing a button) between a low temperature mode and medium temperature mode. For example, a human operator can change the cooling mode of the refrigeration system based on market needs, without the need of physically replacing equipment or entire display cases.

The control system includes an electronic expansion valve (EEV) that is controlled based on a discharge air temperature setpoint, which allows precise cooling mode control of the evaporator without the need of additional equipment. For example, controlling an EEV based on discharge air temperature allows a single dual temperature evaporator coil to switch between medium temperature mode and low temperature mode without the need of pressure-regulating valves, different defrosting processes, or superheat-based control logic.

The refrigeration system 100 can be, for example, a commercial CO₂ refrigeration system, an ammonia refrigeration system, or a propane (e.g., R290) refrigeration system. In some aspects, the refrigeration system 100 can be direct expansion type system (e.g., DX type system) that evaporates a liquid in an evaporator at a certain pressure and cools forced air. As shown, the refrigeration system 100 is a booster system with two sets of compressors 14, 24. However, the refrigeration system 100 can also be a single pressure system with only one set of compressors 14.

In some aspects, the refrigeration system 100 includes a first refrigeration assembly 10 and second refrigeration assembly 20. For example, the first refrigeration assembly can operate, in standard mode of the refrigeration system 100, as a medium temperature refrigeration assembly 10 and the second refrigeration assembly as a low temperature refrigeration assembly 20. In the standard mode of the refrigeration system 100, the first refrigeration assembly 10 includes one or more medium temperature compressors 14 (e.g., a set of transcritical compressors) and one or more evaporators 12 operating in medium temperature mode. The low temperature refrigeration assembly 10 includes one or more low temperature compressors 24 (e.g., a set of subcritical compressors) and one or more evaporators 22 operating in low temperature mode. The refrigeration system 100 also includes expansion valves 11, 21 and fluid control valves 27, 29, 31, 33.

All or some of the second group of evaporators 22 are dual temperature evaporators. For example, each evaporator 22 includes a refrigerated case 50 and a single evaporator coil 41 (only one display case and coil shown for simplicity) that can operate in both medium temperature mode and low temperature mode. In some aspects, medium temperature mode refers to the temperature of the stored items (e.g., perishables) being below room temperature but above, though potentially close to, their freezing temperature. For example, the temperature of the items stored in medium temperature mode can be between 30 and 40 degrees Fahrenheit. The medium temperature mode is typically used in applications that require moderate cooling, such as chilling foods in a display case, but typically without freezing them.

In some aspects, low temperature mode refers to the temperature of the stored items being below their freezing point. For example, the temperature of the items stored in low temperature mode can be between −20 and 32 F. The low temperature mode is typically used in applications that require temperatures below freezing (e.g., freezing food products or maintaining them frozen in a display case).

The medium temperature evaporators 12 can include, for example, refrigerated display cases that display medium-temperature merchandise such as non-frozen products. The low temperature evaporators 22 can include, for example, refrigerated display cases that display low-temperature merchandise such as frozen products.

In some aspects, the evaporators 12, 22 reside at one location (e.g., inside a grocery store), with the rest of the components (except some pipes) of the system 100 residing at a remote location (e.g., in a remote mechanical room). In some cases, the system 100 is a self-contained system or is part of a self-contained display case.

The medium temperature evaporators 12 are fluidly coupled to the compressors 14 through a first medium/low temperature fluid line 13 (e.g., suction line). The low temperature evaporators 22 are fluidly coupled to the compressors 24 through a second medium/low temperature fluid line 23. The low temperature fluid lines 23 can operate in both medium and low temperature modes, withstanding medium as well as low temperatures of the working fluid 5. For example, the fluid lines 23 are designed to operate with the working fluid at temperatures of between −30 and 45 degrees Fahrenheit.

The low temperature compressors 24 are fluidly connected to the medium temperature compressors 14 through a third fluid line 25. The evaporators 12, 22 are fluidly coupled to a receiver tank 6 through a fourth fluid line 9. The refrigeration system circulates a working fluid 5 such as carbon dioxide (CO₂) or ammonia. However, it is contemplated that other refrigerants can be used without departing from the teachings of the present disclosure.

The refrigeration system 100 also includes a high side heat exchanger 2 (also referred to as gas cooler 2, condenser 2, or gas cooler/condenser 2), the receiver tank 6 (e.g., a flash tank or refrigerant liquid vapor separator) fluidly coupled to the heat exchanger 2, an oil separator 3, and a control system 16. The heat exchanger 2 is fluidly coupled to the medium temperature compressors 14 through a discharge line 7. In some aspects, the refrigeration system 100 can have a split gas cooler configuration instead of a single gas cooler configuration. Moreover, the heat exchanger 2 can be both a gas cooler and condenser or include two units: a gas cooler and a condenser.

In some aspects, the expansion valves 11, 21 are mechanical expansion valves or electronic expansion valves (EEV) controlled by the control system 16. In some aspects, the EEVs are stepper valves or pulse valves. The stepper valves can be programmed to close 100% when the discharge air satisfies the setpoint (e.g., an upper or lower limit of a temperature range), and open when the discharge air satisfies a differential temperature (e.g., the other of the upper or lower limit of the temperature range). The expansion valves 11, 21 reside between the receiver tank 6 and the medium and low temperature evaporators 12, 22. Specifically, each of the first expansion valves 11 is fluidly coupled to an inlet of a respective medium temperature evaporator 12, and each of the second expansion valves 21 is fluidly coupled to an inlet of a respective low temperature evaporator 22. The expansion valves 11, 21 meter and expand the working fluid 5 before the working fluid 5 reaches the evaporators 12, 22. Additionally, the system can include other sensors that sense parameters of other components of the system 100 such as the gas cooler/condenser 2 or the compressors 14, 24.

The refrigeration system 100 also includes evaporator sensors 19. The evaporator sensors 19 are electrically connected to the control system 16. In some aspects, the evaporator sensors 19 are temperature sensors. The evaporator sensors 19 are attached to low temperature evaporators 22. Specifically, each of the evaporator sensors 19 is coupled to a respective low temperature evaporator 22. The evaporator sensors 19 sense the discharge air temperature of the air in the evaporators 22. For example, the evaporator sensors 19 can be attached to the discharge side of the evaporator coil 41 of each case 50 to sense the temperature of the discharge air.

The control system 16 controls, as a function of feedback received from at least one of the sensors 19, one or more of the expansion valves 21. Specifically, the control system 16 uses the discharge air temperature sensed by the sensors 19 to adjust a cooling temperature of the evaporators 21 and/or change a mode of operation of the refrigeration system second refrigeration assembly 20. For example, the control system 16 controls, based only on discharge air temperature, the expansion valves 21 to increase or decrease a flow of working fluid 5 into the evaporators 22, maintaining the temperature of the discharge air at a predetermined discharge air setpoint.

When the refrigeration system 100 operates as a standard booster system, the first group of evaporators 12 operate in medium temperature mode and the second group of evaporators 22 operates in low temperature mode. However, the control system 16 can change the mode of operation of any evaporator 22 connected to the low temperature compressors 24. For example, by controlling the respective expansion valves 21, the control system 16 can change the second group of evaporators 22 from low temperature to medium temperature mode or back to low temperature mode from medium temperature mode.

In some aspects, although the first group of evaporators 12 can be limited to operating in medium temperature mode due to being connected to the medium temperature compressors 14, the construction of the first group and second group of evaporators 12, 22 can be the same or substantially the same. For example, the medium temperature refrigerated cases 40, evaporator coils, and EEVs 11 of the medium temperature evaporators 12 can have the same construction and specifications as the refrigerated cases 50, evaporator coils 41, and EEVs 21 of the low temperature evaporators 22.

In some aspects, the refrigerated cases 40, 50 have a defrost unit 39 to de-freeze the evaporators. In some aspects, the medium temperature cases 40 can all have identical defrost schedules, identical saturation suction temperatures (SST), e.g., the lowest prevailing medium temperature compressor SST, and can all function without pressure regulating valves. In some aspects, the SST is defined as the temperature at which a working fluid 5 changes state from liquid to vapor at a given pressure, e.g., at the pressure inside the evaporator 12, 22.

During normal operation, the second refrigeration assembly 20 generally works as in a standard booster system, flowing the working fluid 5 directly from the dual temperature evaporators 22 (acting as low temperature evaporators) to the low temperature compressors 24. However, the control system 16 allows any discrete, individual dual temperature case 50 within the second refrigeration assembly 20 to be changed from low temperature mode to medium temperature mode without the complexity of added valves, piping, or pressure regulating valves that artificially raise the saturated suction temperature of the evaporators 22.

In some aspects, to change the dual temperature evaporators 22 between low and medium temperature modes, the control system 16 does not operate the EEVs 21 in constant run mode (as done in conventional systems or with mechanical expansion valves operate). Rather, the control system 16 selectively controls each EEV 21, closing it down when the discharge air-temperature of its respective case 50 achieves the target setpoint. Measurements in the suction line 23 exiting any evaporator 12, 22 provide the control system 16 with feedback on the superheat value. In some aspects, the superheat value is defined as the difference between the measured temperature of working fluid 5 minus its temperature of saturation. The control system 16 can holds the superheat temperature value within a desired range (e.g., 4 to 6 degrees Fahrenheit above the SST of the working fluid 5) to prevent liquid reaching the compressors while also optimizing refrigerant to boil at a consistent rate that matches and uses the entire available length of passageways (i.e. copper tubes, aluminum tubes, micro-channels, steel tubes, etc.) within the evaporator.

In some aspects, unlike conventional refrigeration systems, the discharge air temperature measured by sensor 19 is a direct input (not just monitored for other purposes) to the control system 16 to modulate the expansion valve 21. Specifically, conventional refrigeration systems typically rely on producing a different and stable SST at each given evaporator for each different discharge air value. For example, in conventional refrigeration systems, the compressor can provide a pressure corresponding to −20 degrees Fahrenheit to a case evaporator requiring −20 degrees Fahrenheit for its SST, which can add complexity to the system because such control process requires using dedicated regulating valves in each evaporator to increase the pressure of the working fluid in each evaporator to provide another evaporator with the required SST value (e.g., −15 F, −10F, 24 F, 26F, 28 F, 30 F, etc.). This can add complexity and points of failure to a refrigeration systems. In contrast, in the refrigeration system 100 of the present disclosure, the superheat value is kept within a tight range but the true control feedback for modulating the EEV (e.g., opening and adjusting the amount open of the EEV as percentage of full scale/closing) is the discharge air temperature of the air 42.

In some aspects, the control system 16 is a controller implemented as a computer system electrically coupled (e.g., with cables or wirelessly) to the sensors 19 and expansions valves 11, 21. Such computer system includes one or more processors and a computer-readable medium storing instructions executable by the one or more processors to perform the operations described here. In some implementations, the control system 16 is implemented as processing circuitry, firmware, software, or combinations of them.

The control system 16 is electrically coupled to the sensor 19 and the expansion valves 11, 21. The control system 16 receives sensor feedback (e.g., a temperature of the discharge air) from the sensors 19 and controls, as a function of determining that the sensor feedback satisfies a threshold, the respective expansion valve 21. The control system 16 operates the expansion valves 21 to (i) maintain one or more of the dual temperature evaporators 22 operating in the low temperature mode or medium temperature mode, (ii) to switch a mode of operation of one or more of the evaporators 22 between the first temperature mode or second temperature mode, or (iii) increase a superheat temperature of the working fluid 5 in one or more of the evaporators 22 if the superheat temperature reaches a fail-safe threshold.

In some aspects, the sensor feedback is a temperature of the discharge air in the dual temperature evaporators 22. Alternatively, the feedback can be a pressure of the discharge air or another parameter from which the control system 16 can determine the discharge air temperature. The discharge air temperature refers to the temperature of the airflow circulated through an evaporator and cooled by the evaporator's working fluid that flows through its coil. For example, the discharge air is the cold air 42 that is expelled from the evaporator coil 41 after the evaporator coil 41 has removed heat from the air 42 that flows across the coil 41.

The control system 16 compares the discharge air temperature to a discharge air temperature threshold. If the control system 16 determines that the discharge air temperature satisfies the threshold, the control system 16 selectively controls the desired EEV 21 to maintain or switch a mode of operation of the selected evaporator 22. The control system 16 can operate just one or one group of expansion valves 21 to change the temperature mode of one or more evaporators 22.

In some aspects, the control system 16 controls the expansion valves 21 based only on the discharge air temperature. In other words, the control system 16 does not use other parameters or sensor feedback to control the expansion valves 21. Specifically, the control system 16 controls the expansion valves 21 to regulate the temperature of the refrigerated items based on the discharge air temperature instead of the superheat temperature or the SST of the working fluid. Thus, the refrigeration system 100 can be void of pressure-regulating valves at the outlet of the evaporators 22, relying only on the expansion valves 21 to regulate the temperature of the working fluid.

In some aspects, the control system 16 determines the superheat temperature of the working fluid 5 at the evaporators 12, 22 to prevent liquid from flowing to the compressors 14, 24, the control system 16 can floats (e.g., ignores for regular operation until a threshold is satisfied) a superheat temperature of the working fluid as long as the superheat temperature is above a fail-safe threshold. The fail-safe threshold helps prevent the superheat temperature from getting low enough to where there is risk of liquid refrigerant exiting the evaporator and reaching the compressor. In other words, the control system 16 can use the superheat temperature of the working fluid 5 only to control the expansion valve 11, 21 to prevent working fluid 5 in its liquid phase from flowing to the compressors 14, 24. The fail-safe threshold is, for example, a superheat temperature above a superheat temperature at which at least some of the working fluid 5 could exit the one or more evaporators 12, 22 in liquid form. For example, the superheat fail-safe threshold can be between 3 and 6 degrees Fahrenheit. Specifically, the superheat threshold can be 3 degrees Fahrenheit in low temperature mode, 6 degrees Fahrenheit in medium temperature mode.

In some aspects, the system 100 includes multiple parallel rack systems 101 with multiple evaporators 12, 22. In one example, if a single display case 50 is being fed by a low temperature rack refrigerant while most of the display cases on the circuit are low temperature, the system 100 can easily control the valves 21 to change the mode of operation of the display case 50.

For example, when in low temperature mode, the controller 16 turns off the flow of refrigerant when the discharge air satisfies a setpoint, which can be around −12 degrees Fahrenheit. The controller can turn the flow back on when the discharge air satisfies a temperature differential (e.g., a differential of 8 degrees Fahrenheit), which can be at around −4 degrees Fahrenheit. The system 100 can continue to operate between these two points while controlling the optimal setpoint superheat so as the entire coil is being utilized and all of the products are getting the same amount of cooling.

When a human operator switches the cooling mode of the single display case 50 to medium temperature, the only change done by the case controller 16 can be the off setpoint of that particular case, while the differential temperature stays the same. For example, the setpoint can go from −12 degrees Fahrenheit to 27 degrees Fahrenheit, having the same differential temperature of 8 degrees Fahrenheit. Specifically, the discharge air can go to 35 degrees Fahrenheit and then the system can turn the flow back on until the discharge air temperature reaches 27 degrees Fahrenheit. This allows the system 100 to defrost the evaporator at every cycle, since air flow exiting the evaporator is 35 degrees Fahrenheit (and the cycle can be around 12 minutes). Thus, the system 100 allows individual evaporators to be easily switched between low and medium temperature more while constantly defrosting the coil, since the only change is the case setpoint.

In some aspects, the control system 16 controls (e.g., modulates) the expansion valve using pulse width modulation (PWM). The PWD technique allows the controller to adjust the supply of voltage and power to the expansion valves 11, 21, allowing the expansion valves 11, 21 to be finely and accurately controlled, which results in precise flow control. Thus, the control system 16 can finely tune and control the cooling temperature of the evaporators 12, 22 to maintain the discharge air temperature at a desired setpoint.

FIG. 2 shows a control logic diagram 200 of the refrigeration control system 16 (shown in FIG. 1). In some aspects, the control system 16 controls the expansion valves to maintain, in the medium temperature mode, a discharge air setpoint of, for example, between 30 and 38 degrees Fahrenheit while also maintaining superheat at, for example, between 4 and 8 degrees Fahrenheit (e.g., 6 degrees Fahrenheit). In some aspects, the control system 16 controls the expansion valves to maintain, in the low temperature mode, a discharge air setpoint of, for example, between −20 and 30 degrees Fahrenheit while floating the superheat temperature above, for example, between 2 and 5 degrees Fahrenheit (e.g., 3 degrees Fahrenheit).

In some aspects, the control strategy and overall system 100 effectively enables any evaporator 12, 22 to run even though they are connected to a lower (e.g., significantly lower) rack suction. For example, a refrigerated case 50 seeing an SST of −15 degrees Fahrenheit could achieve an average discharge air temperature of 33 degrees Fahrenheit, which in traditional systems would require a change to SST of 28 degrees Fahrenheit for proper operation. As such, the refrigeration system 100 is void of dedicated piping runs, multiple pressure regulation valves, and solenoids required to change the SST for proper operation.

Furthermore, if the refrigeration system 100 requires different temperatures for each display case, the control system 16 simply controls the EEVs 21 as a function of discharge air temperature such that all the display cases 50 see the same or substantially the same suction temperature, such as the coldest temperature (e.g., 26 degrees Fahrenheit), achieve each needed application throughout the many connected display cases 50 despite their array of dissimilar temperature requirements. In contrast, traditional refrigeration systems would have to manage multiple suction groups via pressure regulating valves, additional copper piping, etc. Moreover, if cases 40 were built specifically for a medium temperature application without an active defrost method such as hot gas or electric defrost can benefit from the system 100 because all the cases 40 can be ran, regardless of multitude applications or temperature requirements (e.g., floral, deli, dairy, fresh meat), from the single (i.e., coldest) SST of the medium temperature compressors.

Moreover, if a number of cases 50 on the low temperature compressors 24 are changed to medium temperature mode, the control system 16 could be programmed track and change the number of compressors 24 running. Alternatively, if the compressors 24 are variable speed compressors 24, the control system 16 can adjust the speed of one or more variable speed compressors 24, so as to reflect changed demand in refrigeration load. For example, a dual temperature display case can typically require half the refrigeration load (i.e. BTU/H, tons of refrigeration, etc.) when in medium temperature mode as compared to low temperature mode. The control system 16 can slow down one or more of the low-temperature compressors 24 to save energy and match the new connected load that it is calculating and tracking.

As shown in FIG. 2, the control system 16 controls the refrigeration system 100 based on inputs and decisions made with respect to those inputs. In the first step 201, the refrigeration control system 16 starts the process and, in step two 202, the control system 16 receives feedback (e.g., discharge air temperature) from the temperature sensors. In step three 204, the control system determines the mode of operation in which the refrigeration system 100 is to operate.

In the next step 206, if the mode of operation is a medium temperature mode, the system 16 determines whether the discharge air temperature (T) is greater than or equal to T1. T1 can be, for example, between 35 and 40 degrees Fahrenheit (e.g., 38 degrees Fahrenheit). If the discharge air temperature is not greater than or equal to T1, in the next step 208, the system 16 determines whether the discharge air temperature is less than or equal to T2. T2 can be, for example, between 25 and 35 degrees Fahrenheit (e.g., 30 degrees Fahrenheit). If the discharge air temperature is not less than or equal to T2, the system 16 goes back to the second step 202 of receiving sensor feedback. If the discharge air temperature is less than or equal to T2, in the next step 210, the system 16 shuts off the EEV 11, 21 to stop the flow of working fluid and thus increase the cooling temperature. Then, the system 16 goes back to the second step 202 of receiving sensor feedback.

If the system 16 determines that the discharge air temperature is greater than or equal to T1, in the next step 212, the system 16 opens the EEV 11, 21 to increase the flow of working fluid and thus reduce the cooling temperature.

In the next step 214, the system 16 determines whether the superheat temperature is less than or equal to T3. T3 can be, for example, between 2 and 4 degrees Fahrenheit (e.g., 3 degrees Fahrenheit). If the superheat temperature is less than or equal to T3, the system 16 moves to step 211 to throttle the EEV 11, 21, and thus increase the superheat temperature. For example, if the discharge air temperature is within the range of discharge air temperatures requiring cooling, the EEV 11, 21 can decrease the flowrate of the refrigerant to bring the superheat back within the intended range without completely stopping the flow of refrigerant. Thus, throttling the EEV can help maintain the superheat at the desired range to prevent liquid from reaching the compressors, while also maintaining the discharge air temperature at the desired range.

If the superheat temperature is not less than or equal to T3, in the next step 215, the system 16 determines if the superheat temperature is greater than or equal to T3′. If the superheat temperature is greater than or equal to T3′, the system 16 returns to step 212 to open the EEV 11, 21, and thus lower the superheat temperature. If the superheat temperature is not greater than or equal to T3′, the system 16 returns to the second step 202 to receive sensor feedback. T3′ can be, for example, between 5 and 9 degrees Fahrenheit (e.g., 6 degrees Fahrenheit).

Thus, in medium temperature mode, the controller meters the refrigerant liquid into the evaporator coil by cycling the EEV 11, 21 infrequently compared to an EEV cycled in conventional systems, which, because of the use of pressure regulating valves and a superheat setpoint to control the EEV, cycle the EEV more frequently.

Alternatively, in step 216, if the mode of operation is a low temperature mode, the system 16 determines whether the discharge air temperature is greater than or equal to T4. T4 can be, for example, between −3 and 3 degrees Fahrenheit (e.g., 0 degrees Fahrenheit). If the discharge air temperature is not greater than or equal to T4, in the next step 218, the system 16 determines whether the discharge air temperature is less than or equal to T5. T5 can be, for example, between −30 and −10 degrees Fahrenheit (e.g., −20 degrees Fahrenheit). If the discharge air temperature is not less than or equal to T5, the system 16 goes back to the second step 202 of receiving sensor feedback. If the discharge air temperature is less than or equal to T5, in the next step 220, the system 16 shuts off the EEV 11, 21 to stop the flow of working fluid and thus increase the cooling temperature. Then, the system 16 goes back to the second step 202 of receiving sensor feedback.

If the system 16 determines that the discharge air temperature is greater than or equal to T4, in the next step 222, the system 16 opens the EEV to increase the flow of working fluid and thus reduce the cooling temperature.

In the next step 224, the system 16 determines whether the superheat temperature is less than or equal to T6. T6 can be, for example, between 2 and 4 degrees Fahrenheit (e.g., 3 degrees Fahrenheit). If the superheat temperature is less than or equal to T6, the system 16 goes to step 221 to throttle the EEV 11, 21, and thus increase the superheat temperature. If the superheat temperature is not less than or equal to T6, in the next step 225, the system 16 determines if the superheat temperature is greater than or equal to T6′. If the superheat temperature is greater than or equal to T6′, the system 16 returns to step 222 to open the EEV 11, 21, and thus lower the superheat temperature. If the superheat temperature is not greater than or equal to T6′, the system 16 returns to the second step 202 to receive sensor feedback. T6′ can be, for example, between 5 and 9 degrees Fahrenheit (e.g., 6 degrees Fahrenheit).

Additionally, the control system 16 can passively unfreeze the evaporators. For example, the control system 16 can compare the discharge air temperature to a second discharge air threshold that, when met, indicates that the evaporator needs to be de-iced. When such threshold is met, the control system 16 shuts off the expansion valve (or maintains the expansion valve closed) to passively de-ice or defrost the evaporators. This allows the coil to be defrosted without using different defrost processes (e.g., different fail-safe times, different methods, or different frequency of defrosts for different cooling modes). For example, as the expansion valve 11, 21 is shut while the discharge air is warming past 32 degrees Fahrenheit, the air de-ices and defrost the coil while still extracting heat (e.g., until the air reaches 30 degrees Fahrenheit) from the displayed products of the case. In some cases, each refrigerated cases can use a heater (active defrost) or hot gas from the compressor discharge (active defrost) to deice the coils in low and medium temperature mode.

The controller 16 can also be provided with the needed control logic or instructions to use the active defrost infrastructure only when a dual temperature evaporator is in low temperature mode, and to use the passive defrost method when that same evaporator is in medium temperature mode. It is also possible to defrost the evaporators on a fixed schedule, as is particularly advantageous for active defrost via heaters, so that the electricity consumed can transpire at an ‘off-peak’ time of day for a lower electricity bill, or to coordinate and balance loads from three-phase panels. For example, a first group of display cases 50 (e.g., display cases A, B, and C) can be defrosted once per day at 11:00 PM and a second group of display cases 50 (e.g., display cases D, E, F) can be defrosted at 1:00 AM each day.

Thus, the refrigeration system 100 of the present disclosure controls case temperature by shutting off flow once the discharge setpoint has been achieved. In some aspects, the system 100 does not turn on the flow again until the discharge air temperature reaches a certain temperature that guarantees all of the ice accumulated on the coil has been melted and thus operates the evaporator at the most efficient heat transfer. For example, the controller can be set to regulate at 5 degrees Fahrenheit superheat, discharge air setpoint of 29 degrees Fahrenheit (which is when the flow stops), and then differential of 6 degrees Fahrenheit (which means that the flow turns back on at 36 degrees Fahrenheit), which allows the coil to be frost free. If the case has a mechanical expansion valve, then the mechanical valve can still be set at a low superheat value and the case controller can cycle a solenoid valve to stop the flow at the setpoint and not start the flow until the discharge air reaches a temperate of minimum 36 degrees Fahrenheit.

In some aspects, when the system 100 is in medium temperature mode and running off of a low temperature pressure, the coil can require a high frequency of defrosts. This can be due to the high dewpoint in the case and the low temp of the coil, thus forming large amounts of ice on the evaporator. However, the system 100 can run a defrost every cycle by simply changing or controlling the discharge air setpoint. Thus, with 10-minute cycles, for example, the system 100 can get as much as 144 defrosts per day.

In some aspects, the system 100 does not need more than one defrost per day and does not need extra timed defrosts. Additionally, the defrost schedule does not need to be changed when changing from low temperature to medium temperature, since the one defrost procedure per day setup for low temperature also works for medium temperature (because the case is constantly defrosted when in medium temperature mode). Additionally, the refrigeration system 100 can prevent oil logging by allowing the evaporator to warm up and keeping the superheat low. For example, when the case reaches the upper end of the superheat range, the expansion valve can open 100%, thus providing a large flow rate for a few minutes to push the oil that may have accumulated outside of the evaporator. It can also be possible for the controller to keep track of the case types and quantity that are switched from low temperature mode to medium temperature mode. In such cases, thee controller can provide direct feedback to a variable speed low temperature compressor of the rack and adjust its output to the lower overall connected load that is realized from the cases that are now in medium temperature mode instead of low temperature mode.

FIG. 3 shows a flow chart of an example method (300) of cooling a display case with a dual temperature evaporator. The method includes receiving, by a controller and from one or more sensors of a refrigeration system (e.g., the refrigeration system 100 in FIG. 1), sensor feedback (305). The sensor feedback includes a discharge air temperature of an airflow circulated through the one or more evaporators and cooled by the working fluid in the one or more evaporators. The method also includes determining, by the controller, that the discharge air temperature satisfies a discharge air temperature threshold (310). The method also includes controlling, as a function of the determination and by the controller, an operation parameter of the one or more expansion valves, regulating an amount of the working fluid flowed into the one or more evaporators to change the one or more evaporators between a first temperature mode and a second temperature mode (315).

FIG. 4 is a schematic illustration of an example control system or controller 400 for a refrigeration system with dual temperature evaporators according to the present disclosure. For example, the controller 400 can include or be part of the control system 16 in FIG. 1. The controller 400 is intended to include various forms of digital computers, such as printed circuit boards (PCB), processors, digital circuitry, or otherwise. Additionally, the system can include portable storage media, such as, Universal Serial Bus (USB) flash drives. For example, the USB flash drives may store operating systems and other applications. The USB flash drives can include input/output components, such as a wireless transmitter or USB connector that may be inserted into a USB port of another computing device.

The controller 400 includes a processor 410, a memory 420, a storage device 430, and an input/output device 440. Each of the components 410, 420, 430, and 440 are interconnected using a system bus 450. The processor 410 is capable of processing instructions for execution within the controller 400. The processor may be designed using any of a number of architectures. For example, the processor 410 may be a CISC (Complex Instruction Set Computers) processor, a RISC (Reduced Instruction Set Computer) processor, or a MISC (Minimal Instruction Set Computer) processor.

In one implementation, the processor 410 is a single-threaded processor. In another implementation, the processor 410 is a multi-threaded processor. The processor 410 is capable of processing instructions stored in the memory 420 or on the storage device 430 to display graphical information for a user interface on the input/output device 440.

The memory 420 stores information within the controller 400. In one implementation, the memory 420 is a computer-readable medium. In one implementation, the memory 420 is a volatile memory unit. In another implementation, the memory 420 is a non-volatile memory unit.

The storage device 430 is capable of providing mass storage for the controller 400. In one implementation, the storage device 430 is a computer-readable medium. In various different implementations, the storage device 430 may be a floppy disk device, a hard disk device, an optical disk device, or a tape device.

The input/output device 440 provides input/output operations for the controller 400. In one implementation, the input/output device 440 includes a keyboard and/or pointing device. In another implementation, the input/output device 440 includes a display unit for displaying graphical user interfaces.

Although the following detailed description contains many specific details for purposes of illustration, it is understood that one of ordinary skill in the art will appreciate that many examples, variations and alterations to the following details are within the scope and spirit of the disclosure. Accordingly, the exemplary implementations described in the present disclosure and provided in the appended figures are set forth without any loss of generality, and without imposing limitations on the claimed implementations.

Although the present implementations have been described in detail, it should be understood that various changes, substitutions, and alterations can be made hereupon without departing from the principle and scope of the disclosure. Accordingly, the scope of the present disclosure should be determined by the following claims and their appropriate legal equivalents.