Systems and Methods for Pumped Refrigerant Economization Superheat Control

This U.S. Non-Provisional Patent Application claims the benefit of U.S. Provisional Patent Application Ser. No. 63/651,617 filed May 24, 2024, the entire disclosure of which is hereby incorporated by reference.

The present disclosure relates to control routines of refrigeration systems, and in particular, to systems and methods pumped refrigerant economization superheat control.

A refrigeration system may implement different control routines to control the temperature of refrigerant as it moves throughout the refrigeration system. For example, in single circuit systems, the liquid temperature is controlled to remain at a fixed setpoint (e.g., 37° Fahrenheit (F)). This level of control is needed in refrigeration systems, where maintaining specific temperatures is essential for the correct operation of the systems. In relatively more complex systems that use multiple circuits and have a staged economization feature, the control strategy may involve the liquid temperature in the upstream circuit being controlled at a first temperature (e.g., 45° F.), while the downstream circuit is maintained at a second temperature (e.g., 37° F.). The staged economization is a method used to improve energy efficiency in refrigeration systems by recovering waste heat and using it for pre-cooling the refrigerant, which reduces the load on the condenser.

This disclosure relates generally to pumped refrigerant systems.

An aspect of the disclosed embodiments includes a superheat control circuit of a refrigeration system. The superheat control circuit comprises: a temperature sensor configured to measure a temperature of a refrigerant of the refrigeration system and generate temperature data associated with the measured temperature of the refrigerant; a pressure sensor configured to measure a pressure of the refrigerant and generate pressure data associated with the measured pressure of the refrigerant; and a controller. The controller configured to: receive the temperature data and the pressure data; calculate, based on the temperature data and the pressure data, a superheat value of the refrigerant; and adjust a speed of a fan of a condenser of the refrigeration system based on the calculated superheat value of the refrigerant.

Another aspect of the disclosed embodiments includes a method for operating a superheat control circuit of a refrigeration system. The method comprises: measuring a temperature of a refrigerant of the refrigeration system; measuring a pressure of the refrigerant; calculating, based on the measured temperature and the measured pressure, a superheat value of the refrigerant; and adjusting, based on calculated superheat value, a speed of a fan of a condenser of the refrigeration system.

Still yet, another aspect of the disclosed embodiments includes a superheat control circuit of a refrigeration system. The superheat control circuit comprises: a temperature sensor configured to measure temperature of refrigerant of the refrigeration system and generate temperature data associated with the measured temperature of the refrigerant; a pressure sensor configured to measure pressure of the refrigerant and generate pressure data associated with the measured pressure of the refrigerant; and a controller configured to receive the temperature data and the pressure data, calculate, based on the temperature data and the pressure data, a superheat value of the refrigerant, and adjust a speed of a fan of a condenser of the refrigeration system based a comparison of the calculated superheat value of the refrigerant and a superheat setpoint.

These and other aspects of the present disclosure are disclosed in the following detailed description of the embodiments, the appended claims, and the accompanying figures.

Those skilled in the art will appreciate and understand that, according to common practice, various features of the drawings discussed below are not necessarily drawn to scale, and that dimensions of various features and elements of the drawings may be expanded or reduced to more clearly illustrate the embodiments of the present disclosure described herein.

The following discussion is directed to various embodiments of the disclosure. Although one or more of these embodiments may be preferred, the embodiments disclosed should not be interpreted, or otherwise used, as limiting the scope of the disclosure, including the claims. In addition, one skilled in the art will understand that the following description has broad application, and the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to intimate that the scope of the disclosure, including the claims, is limited to that embodiment.

The present specification and accompanying drawings disclose one or more embodiments that incorporate the features of the present disclosure. The scope of the present disclosure is not limited to the disclosed embodiments. The disclosed embodiments merely exemplify the present disclosure, and modified versions of the disclosed embodiments are also encompassed by the present disclosure. Embodiments of the present disclosure are defined by the claims appended hereto.

References in the specification to “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

In the discussion, unless otherwise stated, adjectives such as “substantially,” “approximately,” and “about” modifying a condition or relationship characteristic of a feature or features of an embodiment of the disclosure, are understood to mean that the condition or characteristic is defined to be within tolerances that are acceptable for operation of the embodiment for an application for which it is intended.

Furthermore, it should be understood that spatial descriptions (e.g., “above,” “below,” “up,” “left,” “right,” “down,” “top,” “bottom,” “vertical,” “horizontal,” etc.) used herein are for purposes of illustration only, and that practical implementations of the structures described herein can be spatially arranged in any orientation or manner.

The word “example” is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as “example” is not necessarily to be construed as preferred or advantageous over other aspects or designs. Rather, use of the word “example” is intended to present concepts in a concrete fashion. As used in this application, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or.” That is, unless specified otherwise, or clear from context, “X includes A or B” is intended to mean any of the natural inclusive permutations. That is, if X includes A; X includes B; or X includes both A and B, then “X includes A or B” is satisfied under any of the foregoing instances. In addition, the articles “a” and “an” as used in this application and the appended claims should generally be construed to mean “one or more” unless specified otherwise or clear from context to be directed to a singular form. Moreover, use of the term “an implementation” or “one implementation” throughout is not intended to mean the same embodiment or implementation unless described as such.

Numerous exemplary embodiments are described as follows. It is noted that any section/subsection headings provided herein are not intended to be limiting. Embodiments are described throughout this document, and any type of embodiment may be included under any section/subsection. Furthermore, embodiments disclosed in any section/subsection may be combined with any other embodiments described in the same section/subsection and/or a different section/subsection in any manner.

As described, a refrigeration system may implement different control routines to control the temperature of refrigerant as it moves throughout the refrigeration system. For example, in single circuit systems, the liquid temperature is controlled to remain at a fixed setpoint (e.g., 37° F.). This level of control is needed in refrigeration systems, where maintaining specific temperatures is essential for the correct operation of the systems. In relatively more complex systems that use multiple circuits and have a staged economization feature, the control strategy may involve the liquid temperature in the upstream circuit being controlled at a first temperature (e.g., 45° F.), while the downstream circuit is maintained at a second temperature (e.g., 37° F.). The staged economization is a method used to improve energy efficiency in refrigeration systems by recovering waste heat and using it for pre-cooling the refrigerant, which reduces the load on the condenser.

Nonetheless, as consumer demands evolve, there is an increasing need for even higher efficiency in thermal management systems to accommodate varying operational environments. Controlling superheat from evaporators using condenser fans can significantly enhance energy efficiency. This not only contributes to energy savings but also facilitates a more straightforward and efficient control routine, particularly as supply and return air temperatures fluctuate.

Accordingly, systems and methods, such as those described herein, configured to provide pumped refrigerant economization superheat control, may be desirable. With reference toa schematic of a refrigeration system, depicting the various components of a refrigeration system, is generally illustrated.

The refrigeration systemmay be configured to manage a condenser fan to ensure that refrigerant temperature is maintained at a predetermined superheat setpoint during a pumped refrigerant economization (PRE) process. Superheat, as referenced herein, refers to the temperature of a vapor above its boiling point at a given pressure. In the context of a refrigeration cycle, it measures how much the refrigerant's temperature has risen above its saturation temperature after it has evaporated. The superheat setpoint is the target temperature above the saturation temperature that the system is designed to maintain. The PRE process, as referenced herein, refers to a refrigeration system component that improves energy efficiency by using a pump to circulate refrigerant through an economizer heat exchange. This process may involve pre-cooling the compressed refrigerant before it enters a condenser. In some embodiments, a pump is not required for this control scheme. This control scheme could work for thermosyphons as well.

The refrigeration systemmay include a pump, an evaporator (EVAP), a condenser (COND), a compressor (COMP), and a receiver, along with piping and valves that connect these components. The evaporatorand the compressorare components of the refrigeration systemlocated in an indoor space. Although the refrigeration systemis shown to include the receiver, in some embodiments, the refrigeration systemmay be implemented without a receiver. Additionally, or alternatively, in some embodiments, compressors may be located outside with the condenser (e.g., as is typical for residential heating, ventilation, and air conditioning (HVAC) systems).

The pumpis configured to circulate refrigerant throughout the refrigeration system. For example, the pumpmay move the refrigerant to the evaporatorand from there through the refrigeration system. The evaporatoris a heat exchanger where the refrigerant absorbs heat from the environment being cooled. For example, the evaporatoris configured to cause the refrigerant to evaporate, moving from a liquid to a gas phase, which removes heat from the area being cooled. The compressoris configured to increase the pressure of the refrigerant gas, which also raises its temperature. Compressor and pump operation may be mutually exclusive. For example, the compressor runs when the outdoor temperatures are high and the pump runs when the outdoor temperatures are low enough to support the PRE process. This allows for the refrigerant to release its absorbed heat in the condenser. The condenseris another heat exchanger where the high-pressure refrigerant gas is condensed into a liquid as it releases the heat that was absorbed in the evaporator. The receiveris configured to store the liquid refrigerant that exits the condenserand ensure that the right amount of refrigerant is supplied to the refrigeration system.

The refrigeration systemmay include a condenser fan, a controller, a temperature sensor, and a pressure sensor. The condenser fanis configured to assist in the heat exchange process occurring at the condenserby blowing air across condenser coils of the condenser, helping to dissipate the heat more quickly. For example, the speed of the condenser fancan be varied to control the rate at which heat is removed. Controlleris configured to monitor superheat of the refrigerant and compare it to a superheat setpoint.

In some embodiments, the controllermay be a Proportional-Integral-Derivative (PID) controller, a type of feedback control loop. A PID controller is designed to maintain a desired setpoint by adjusting the control variable, such as the speed of the condenser fan or a pump, based on the difference between the desired setpoint and the measured variable.

For example, at the evaporator, refrigerant absorbs heat, which causes the refrigerant to boil and evaporate. As described, superheat refers to additional heat that the refrigerant gas absorbs above its boiling point while still in the evaporator. The refrigerant, now a superheated vapor, is drawn into the compressor. When the compressor is not running, the vapor bypasses the compressor (e.g., a small portion moves through the compressor). The compressoris configured to compress the superheated vapor, which further increases the pressure and temperature. The high-temperature, high-pressure superheated vapor then flows into the condenser. In the condenser, the refrigerant releases the heat it absorbed in the evaporatorduring the superheating process. As it cools, it condenses into a high pressure liquid.

The condenser fanis configured to remove heat from the refrigerant by passing air over condenser coils of the condenser. The controlleris further configured to adjust a speed of the condenser fanto control the temperature of the refrigerant, ensuring it condenses properly and exits the condenser at the correct temperature and pressure. The temperature sensoris configured to measure the temperature of the refrigerant prior to it entering the condenserand provide the temperature data to the controller. The pressure sensoris configured to measure the pressure of the refrigerant prior to it entering the condenserand provide the pressure data to the controller. Pressure can affect the temperature at which the refrigerant evaporates and condenses.

The controllermay then use the temperature and pressure data to adjust the speed of the condenser fanaccordingly. For example, in some embodiments, the controllerreceives temperature and pressure data, calculates, based on the temperature data and the pressure data, a superheat value of the refrigerant (e.g., a difference between the actual temperature of refrigerant vapor at a certain point and the saturation temperature of the refrigerant), and compares the calculated superheat value to a predefined setpoint (such as a superheat setpoint). More specifically, a superheat value is the temperature of a vapor above its boiling point at a given pressure. In the context of a refrigeration cycle, superheat value measures how much the refrigerant's temperature has risen above the refrigerant's saturation temperature after the refrigerant has evaporated. The superheat setpoint is the target temperature above the saturation temperature that the system is designed to maintain.

If the superheat value is higher or lower than the predefined setpoint, the controller determines how much adjustment of the fan speed of the condenser fanis needed to bring the superheat value to the predefined setpoint. Based on the calculations, the controllermay provide a command to an actuator connected to the condenser fan. The actuator may increase the speed of the condenser fanto increase the rate of heat removal from the condenser, causing the refrigerant temperature and pressure to lower. In contrast, the actuator may lower the speed of the condenser fanto lower the rate of heat removal from the condenser, causing the refrigerant temperature and pressure to increase.

In some embodiments, condenser fan speed may be controlled by superheat entering the condenser at a setpoint (e.g., of 5±1° F.). This will allow for the most efficient condenser fan operation. This also allows for sensible cooling of the refrigerant in the discharge/vapor line.

generally illustrates a schematic of a refrigeration system, depicting the various components of a refrigeration system. In some embodiments, the temperature and pressure of the refrigerant can be measured at various points in the refrigeration system. For example, in, the fan speed of the condenser fanis regulated based on the superheat level—specifically, the temperature and pressure of the refrigerant vapor as it exits (e.g., after the refrigerant exits) the evaporatorand enters (e.g., before the refrigerant enters) the compressor. A temperature sensoris configured to measure the temperature of the refrigerant, and a pressure sensoris configured to measure the pressure of the refrigerant.

Further, in some embodiments, the refrigeration systemmay continuously monitor the temperature and pressure conditions and adjust the fan speed accordingly. This allows for the refrigeration systemto adapt as the load on the refrigeration systemchanges or as other environmental conditions vary. This superheat control method improves efficiency. This improvement in efficiency comes from the condenserbeing able to turn down more quickly to meet the superheat setpoint. This cost savings would be further increased if the system utilized staged economization (i.e., two circuits).

generally illustrates a schematic of a refrigeration system including a staged economization feature. Similar to, refrigeration systeminalso includes a condenser fan speed control circuit, which includes the condenser fan, the controller, the temperature sensor, and the pressure sensor.

Refrigeration systemalso includes a pump speed control circuit including controller, Call-For-Cooling (CFC), and Electronic Expansion Valve (EEV). In some embodiments, a Thermal Expansion Valve (TEV) and a solenoid valve bypassing around the TEV may be used in place of an Electronic Expansion Valve (EEV). Controlleris configured to adjust the speed of the pumpto meet cooling demands, CFC, dictated by customer requirements. EEV or solenoid is set to a fixed position (such as fully open) to reduce the pump head pressure, allowing the pump to operate more efficiently, likely at a lower power level. These controls enhance the efficiency of refrigeration systemby optimizing the refrigerant temperature and pressure throughout the refrigeration cycle.

To help further illustrate, controllermay receive a signal that cooling is required from CFC. This may be triggered by a thermostat or a temperature sensor in the indoor spacethat needs to be cooled. This signal indicates that the indoor temperature has risen above the desired setpoint. In response to the CFC, controllermay adjust the speed of the pump. If more cooling is needed, the speed of the pumpincreases to circulate more refrigerant though refrigeration system. Conversely, if less cooling is needed, the speed of the pumpdecreases.

Additionally, a position of EEVmay be set to a fixed position or sizing of solenoid valve, which could be fully open or another specific setting, to ensure that the refrigerant flow is maximized or optimized as required. By fixing the position of EEV, refrigeration systemhelps to minimize the resistance against which the pumphas to work.

In some embodiments, while operating in PRE, experiencing a loss of superheat at the evaporators exit may need to be prevented.generally illustrates what occurs if a loss of superheat occurs in a refrigeration system. In particular,depicts a refrigeration system during normal operation, anddepicts a refrigeration system during the loss of superheat. As illustrated in, if a loss of superheat occurs, Net Positive Suction Head Available (NPSHa), at the pump inlet will fall below, Net Positive Suction Head Required, (NPSHr) and flow will be lost. To prevent the loss of superheat at the exit of the evaporator, the supply fan and pump may need to be throttled accordingly. The pump speed can decrease as quickly as possible without issue. However, when the pump speed is being increased it may need to be throttled to prevent loss of super-heat as the evaporate exits. The supply fan can be increased as quickly as possible without issue. However, when the supply fan speed is being decreased it may need to be throttled to prevent loss of super-heat as the evaporate exits.

In some embodiments, if too much heat is being rejected from the discharge/vapor line due to either poor insulation, long indoor sections, high temperatures (from chases) superheat could be lost at the evaporators exit. To address this, the controlleror controllerofcan be configured to adjust condenser fan speed controls to a superheat setpoint (e.g., of 5±1° F.) at the lowest location reading the lowest measurement, and switching between either entering the condenser or exiting the evaporator with a hysteresis to prevent erratic switch overs.

In some embodiments, a control approach for a refrigeration system that adjusts the refrigerant temperature setpoint dynamically, based on superheat, may be implemented. The control approach may also include adapting the setpoint based on various factors, such as ambient air temperature, return and supply air temperatures, and airflow across an evaporator. The control approach may involve a Proportional-Integral control algorithm and a computational process that could adjust the setpoint based on data recorded over a predetermined time period (e.g., the last minute). For example, the control approach may include: recording the data from the predetermined time period (such as over the last minute), taking the minimum value of the superheat from this data, and applying this value to a mapping function to adjust the setpoint. The controlleror controllermay implement the control approach.

Further, in some embodiments, the control approach may include a setpoint modifier which could be a linear mapping function. For example,depicts graphically how the setpoint modifier may function. In, the x-axis, labeled “SH” for superheat and the y-axis shows the modification to the refrigerant temperature setpoint. As depicted in, the plot indicates how the refrigerant temperature setpoint may be adjusted based on the superheat value. For instance, with continued reference to, if the superheat is high enough, a refrigerant temperature setpoint (SP) may be increased, and if the superheat (SH) is lower than a given threshold, the current refrigerant temperature SP may be decreased to ensure correct PRE operation. Additionally, ±0.9 R deadband on the plot represents a range around the setpoint within which no adjustment to the control output would be made. In some embodiments, an allowed operational interval for the refrigerant temperature SP may be implemented (e.g., minimum and maximum operation values) to ensure there would be no numerical issues with the controller and allows the operation range to be controlled by a qualified user.

In some embodiments, another control approach may be implemented that involves fully switching from refrigerant temperature SP to superheat control (e.g., PRE mode, condenser fan operation). This control approach can involve continuous operation or discrete operation. For example, in one instance of continuous operation, a PID controller may continuously control superheat at a fixed setpoint.

provides a visual illustration of how different control mechanisms cooperate to ensure stable PRE operation as a function of the superheat. As an illustrative example, in, if the SH is lower than 9K (Rankine), the EEV valve will start to close to increase the SH. There may also be a mechanism which dynamically sets a maximum allowed EEV opening during the operation to ensure correct PRE functioning. In addition, with continued reference to, if the SH is above 9 R, EEV is used to control the differential pressure (DP) across the pump to keep a certain pressure increase. If SH setpoint is set to 14.4 R for the condenser, energy will be saved while keeping the operation of the PRE mode stable (e.g., no unwanted intervention in the EEV operation).

In the case of colder ambient air temperature, the use of fixed refrigerant temperature setpoint approach could yield extremely high superheat values. By controlling the superheat, the refrigerant temperature may be controlled indirectly. With lower superheat, higher refrigerant temperature could be achieved by lower condenser fan speeds in case of same ambient air temperature. Lower fan speed translates to lower energy consumption, while maintaining the quality of the PRE operation (e.g., required heat load delivered). By controlling the SH directly, changing ambient air temperature, return and supply air temperature, and air flow is dynamically being reacted to.

illustrates a stepped approach to modifying the condenser fan speed based on the superheat level. In case of a discrete approach, this approach may involve replacing the PID controller with a step approach. This control approach would modify the condenser fan speed also as a function of superheat but in a discrete manner. For example, this approach may involve steps or specific points at which the condenser fan speed and the EEV are adjusted in response to changes in superheat. For example, with reference to, there is an increase in fan speed as the superheat rises above a setpoint, with a 50% proportional band indicating that when the superheat is within 50% of the target, the fan speed increases to 100% rate of change, represented in by the Increment Area in. Conversely, there is a decrease in fan speed as the superheat falls below the setpoint, with the fan speed change rate reaching 0% as the superheat reaches the setpoint,, represented in by the Decrement Area in. In some embodiments, the ramping may not be symmetrical (e.g., increasing more rapidly than it decreases); the control response may be tailored to a refrigeration system's needs.

In some embodiments, another control approach may be implemented. This control approach of the PRE operation may involve: an evaporator controlled independently (e.g., by return air temperature); pump is controlled by CFC (e.g., PID output to control the supply air temperature); differential pressure is controlled by the EEV valve; minimum superheat is controlled by the EEV valve and complimentary logic to limit the maximum opening of the EEV; a condenser fan speed is controlled by the superheat value (high superheat allow for lower condenser ramping, thereby, causing lower energy consumption).

Each of the above listed control approaches can sufficiently support the PRE operation regime. Different methods could be used for units of different types (e.g., number of circuits), size (e.g., capacity), geographical installation location, etc.

is a flowchart generally illustrated a methodfor a PRE superheat control routine, according the principles of the present disclosure. At, the methodmeasures a temperature of refrigerant of a refrigeration system.

At, the method, measures a pressure of the refrigerant.

At, the method, calculates a superheat of the refrigerant based on the measured temperature and the measured pressure.

At, the method, adjusts a speed of a fan of a condenser of the refrigeration system based on calculated superheat value.

generally illustrates a processor-based computer systemthat may be used to implement various embodiments described herein, such as any of the embodiments described in the above and in reference to. For example, the processor-based computer systemmay be used to implement any of the components of the refrigeration systemand the refrigeration systemas described above in reference to. The description of the processor-based computer systemprovided herein is provided for purposes of illustration and is not intended to be limiting. Embodiments may be implemented in further types of computer systems, as would be known to persons skilled in the relevant art(s).