ADAPTIVELY CONTROLLED DEFROST CYCLE TIME FOR AN AIRCRAFT VAPOR CYCLE REFRIGERATION SYSTEM

A defrost cycle time of an aircraft vapor cycle refrigeration system is adaptively controlled. A pressure of refrigerant at an inlet of a compressor of the vapor cycle refrigeration system is sensed. A defrost cycle of the vapor cycle refrigeration system is initiated in response to the sensed pressure being less than a threshold pressure. The defrost cycle is terminated upon expiration of the defrost cycle time. The defrost cycle time is based upon a time duration of the cooling cycle.

BACKGROUND

The present disclosure relates generally to vapor cycle refrigeration systems, and in particular to defrost operations associated with vapor cycle refrigeration systems.

Vapor cycle refrigeration systems, such as those implemented onboard aircraft, typically include an evaporator that converts a liquid refrigerant to a gas, thereby absorbing heat and providing cooling to an airflow. In some applications, the refrigerant employed by the evaporator operates at a temperature below the freezing point of water. As a result, the evaporator through which the refrigerant flows may cause water vapor in the air being cooled to condense and freeze at it passes through the evaporator. Ice buildup within the evaporator both reduces the cooling efficiency of the evaporator and restricts the flow of air through the evaporator.

To prevent the accumulation of ice and/or melt an existing ice buildup, periodic defrost operations of the vapor cycle refrigeration system are often initiated (e.g., on a periodic schedule). Typically, the defrost operations include stopping (or decreasing) the flow of refrigerant through the refrigeration system and allowing unconditioned air to flow through the evaporator to melt the ice. However, initiating the defrost operations too often or for too long can degrade the cooling performance of the system, as conditioned air is not provided by the system during the defrost operations. Similarly, initiating the defrost operations too infrequently or for too little time can also degrade system performance by inadequately removing (or preventing) the accumulation of ice and decreasing the cooling efficiency of the evaporator.

SUMMARY

In one example, a method includes (a) initiating a cooling cycle of a vapor cycle refrigeration system, (b) sensing a pressure of refrigerant at an inlet of a compressor of the vapor cycle refrigeration system during operation of the cooling cycle, and (c) initiating a defrost cycle of the vapor cycle refrigeration system in response to the sensed pressure being less than a threshold pressure. The method further includes (d) terminating the defrost cycle upon expiration of a defrost cycle time that is based upon a time duration of the cooling cycle, and (e) repeating steps (a)-(d).

In another example, a vapor cycle refrigeration system of an aircraft includes an evaporator, a compressor, a pressure sensor, and a controller device that includes at least one processor and computer-readable memory. The evaporator is configured to receive refrigerant and provide cooling to an airflow by evaporating the refrigerant. The compressor is configured to compress the refrigerant and produce flow of the refrigerant through the vapor cycle refrigeration system. The pressure sensor is disposed to sense pressure of the refrigerant at an inlet of the compressor. The controller device is operatively coupled to the pressure sensor and to the compressor. The computer-readable memory of the controller device is encoded with instructions that, when executed by the at least one processor, cause the controller device to (a) initiate a cooling cycle of the vapor cycle refrigeration system by increasing a speed of the compressor, (b) receive an indication of sensed pressure of the refrigerant at the inlet of the compressor from the pressure sensor, and (c) initiate a defrost cycle of the vapor cycle refrigeration system in response to the received indication of the sensed pressure of the refrigerant being less than a threshold pressure. The computer-readable memory is further encoded with instructions that, when executed by the at least one processor, cause the controller device to (d) terminate the defrost cycle upon expiration of a defrost cycle time that is based upon a time duration of the cooling cycle, and (e) repeat steps (a)-(d).

In another example, a controller device for a vapor cycle refrigeration system of an aircraft includes at least one processor and computer-readable memory. The computer-readable memory is encoded with instructions that, when executed by the at least one processor, cause the controller device to (a) initiate a cooling cycle of the vapor cycle refrigeration system, (b) receive an indication of a sensed pressure of refrigerant at an inlet of a compressor of the vapor cycle refrigeration system, and (c) initiate a defrost cycle of the vapor cycle refrigeration system in response to the indication of the sensed pressure being less than a threshold pressure. The computer-readable memory is further encoded with instructions that, when executed by the at least one processor, cause the controller device to (d) determine a time duration of the cooling cycle, (e) adjust a defrost cycle time based on the time duration of the cooling cycle to determine an adjusted defrost cycle time, (f) terminate the defrost cycle upon expiration of the adjusted defrost cycle time, and (g) repeat steps (a)-(f).

DETAILED DESCRIPTION

As described herein, a duration of a defrost cycle of a vapor cycle refrigeration system is adaptively controlled. A pressure of refrigerant at an inlet of a system compressor is sensed. Defrost operations of the vapor cycle refrigeration system are initiated in response to the sensed pressure being less than a threshold pressure. Accordingly, rather than require multiple sensors to measure, for example, temperature and/or differential pressure of refrigerant or airflow at an evaporator, a system implementing techniques of this disclosure can initiate defrost operations to prevent and/or mitigate ice buildup within the evaporator based on a single pressure sensor at an inlet of the compressor. The use of a single pressure sensor can significantly reduce cost and complexity while increasing reliability of the system. Moreover, a duration of the defrost cycle is iteratively adapted based on a time duration of a preceding cooling cycle and/or a number of consecutive successful and unsuccessful operating cycles. As such, the techniques described herein adaptively control (e.g., increase and decrease) the duration of the defrost cycle to account for varying environmental and system conditions, such as changing temperature and humidity of the operational environment, to better approximate an optimal defrost cycle time duration.

FIG. 1is a schematic block diagram illustrating aircraft vapor cycle refrigeration system10including controller12that adaptively controls a defrost cycle time based on a time duration of a cooling cycle of vapor cycle refrigeration system10. As illustrated inFIG. 1, vapor cycle refrigeration system10further includes condenser14, expansion orifice16, flash tank18, throttling valve19, evaporator20, compressor22, heat sink inlet temperature sensor THSI, compressor suction temperature sensor TCS, compressor suction pressure sensor PCS, compressor discharge temperature sensor TCD, compressor discharge pressure sensor PCD, compressor speed sensor N, and compressor motor current sensor I. The arrowed lines extending between condenser14, expansion orifice16, flash tank18, throttling valve19, evaporator20, and compressor22indicate a flow and direction of refrigerant circulated in vapor cycle refrigeration system12. Vapor cycle refrigeration system10can be part of, e.g., an air conditioning pack of a cooling system of an aircraft.

As illustrated inFIG. 1, refrigerant is supplied to compressor22in vapor form from both flash tank18and evaporator20. Compressor22is driven by a compressor motor (not illustrated), a speed of which is controlled by controller12to compress the refrigerant to a higher pressure and supply the compressed refrigerant in vapor form to condenser14. Operation of compressor22to compress the refrigerant drives a flow of refrigerant through vapor cycle refrigeration system10. A greater operational speed of compressor22(e.g., a greater rotational speed of a shaft of compressor22) increases the compression generated by compressor22and the corresponding flow of refrigerant. Similarly, a lesser operational speed of compressor22decreases the compression generated by compressor22and the corresponding flow of refrigerant.

Condenser14condenses the compressed vapor refrigerant received from compressor22to liquid form using cooling liquid and/or gaseous flow supplied through the heat sink inlet. Heat from the compressed refrigerant is transferred from the refrigerant to the cooling liquid and/or gaseous flow supplied to condenser14through the heat sink inlet and is carried away from vapor cycle refrigeration system10via the heat sink outlet. The condensed, liquid refrigerant is supplied from condenser14to expansion orifice16. As the liquid refrigerant passes through expansion orifice16, a rapid pressure reduction of the liquid refrigerant occurs causing an evaporation of a portion of the refrigerant and resulting in two-phase refrigerant (i.e., liquid phase and vapor phase) that is supplied to flash tank18where phase separation occurs through, e.g., gravity separation. Expansion orifice16can be a fixed orifice configured to cause the pressure reduction in the refrigerant. In some examples, expansion orifice16can be implemented as a valve, the position of which is controlled via, e.g., controller12to cause and/or control the pressure reduction of the refrigerant.

Vapor-form refrigerant is supplied from flash tank18to compressor22. Liquid refrigerant, cooled by both the heat transfer in condenser14and the rapid pressure reduction in expansion orifice16, is supplied to throttling valve19. A position of throttling valve19, sometimes referred to as an expansion valve, is controlled by a motor (not illustrated) via commands from controller12to cause an additional rapid pressure reduction of the liquid refrigerants as it passes through throttling valve19, thereby causing an evaporation of a portion of the refrigerant (having a further cooling effect on the refrigerant) and resulting in a two-phase refrigerant (i.e., liquid phase and vapor phase) that is supplied to evaporator20.

Evaporator20cools inlet air as it is passed through evaporator20through an evaporation process in which the liquid refrigerant is converted (i.e., evaporated) from the liquid state to a mostly or entirely gaseous state. The evaporation process absorbs heat from the inlet air, thereby cooling the inlet air and providing conditioned air for, e.g., a cabin, galley, or other air conditioning system. The evaporated refrigerant is supplied from evaporator20to compressor22. As such, vapor cycle refrigeration system10provides a closed-loop cycle of refrigerant in which heat is transferred from an inlet air supply to the refrigerant to provide cooled, conditioned air, and rejected from vapor cycle refrigeration system10via the heat sink inlet and the heat sink outlet at condenser14.

As inlet air passes through evaporator20and is cooled by the evaporation process of the refrigerant to provide the conditioned air, water vapor present in the inlet air can freeze, thereby causing ice to accumulate within evaporator20. The accumulation of ice within evaporator20can degrade the cooling efficiency of evaporator20by hindering the transfer of heat from the inlet air to the refrigerant. This reduced heat transfer efficiency in evaporator20caused by the accumulation of ice can further reduce the refrigerant temperature. Due to the two-phase refrigerant heat transfer that occurs in evaporator20as refrigerant is evaporated by the transfer of heat from the inlet air, the pressure of the refrigerant within evaporator20is correlated with the refrigerant temperature within evaporator20. That is, as the temperature of refrigerant within evaporator20decreases, the pressure of the refrigerant within evaporator20also decreases. Similarly, as the temperature of refrigerant within evaporator20increases, the pressure of the refrigerant within evaporator20also increases. Accordingly, controller12implementing techniques of this disclosure monitors a pressure of the refrigerant downstream of evaporator20via compressor suction pressure sensor PCS. Controller12initiates a defrost cycle of vapor cycle refrigeration system10based on the measured refrigerant pressure from compressor suction pressure sensor PCSand adaptively controls (e.g., adjusts) a time duration of the defrost cycle based on a time duration of a preceding cooling cycle, as is further described below.

Controller12can be any electronic device that is operationally coupled (e.g., electrically and/or communicatively coupled) to components of vapor cycle refrigeration system10to control real-time operation of the components of the system and to receive inputs from various sensors positioned throughout vapor cycle refrigeration system10. As illustrated inFIG. 1, controller12is operationally connected to receive inputs from compressor suction temperature sensor TCS, compressor discharge temperature sensor TCD, heat sink inlet temperature sensor THSI, compressor suction pressure sensor PCS, compressor discharge pressure sensor PCD, compressor speed sensor N, and compressor motor current sensor I. In addition, controller12is operationally connected to control components of vapor cycle refrigeration system10, such as condenser14, throttling valve19, evaporator20, and compressor22.

Controller12can include one or more processors and computer-readable memory encoded with instructions that, when executed by the one or more processors, cause controller12to operate in accordance with techniques described herein. Examples of the one or more processors include any one or more of a microprocessor, a controller, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other equivalent discrete or integrated logic circuitry. Computer-readable memory of controller12can be configured to store information with controller12during operation. The computer-readable memory can be described, in some examples, as computer-readable storage media. In some examples, a computer-readable storage medium can include a non-transitory medium. The term “non-transitory” can indicate that the storage medium is not embodied in a carrier wave or a propagated signal. In certain examples, a non-transitory storage medium can store data that can, over time, change (e.g., in RAM or cache). Computer-readable memory of controller12can include volatile and non-volatile memories. Examples of volatile memories can include random access memories (RAM), dynamic random access memories (DRAM), static random access memories (SRAM), and other forms of volatile memories Examples of non-volatile memories can include magnetic hard discs, optical discs, floppy discs, flash memories, or forms of electrically programmable memories (EPROM) or electrically erasable and programmable (EEPROM) memories.

Compressor suction temperature sensor TCSand compressor suction pressure sensor PCSare positioned at or near an upstream inlet of compressor22to measure a temperature and pressure of refrigerant entering the upstream (or suction) inlet of compressor22. Compressor discharge temperature sensor TCDand compressor discharge pressure sensor PCDare positioned at or near a downstream outlet of compressor22to measure a temperature and pressure of refrigerant exiting the downstream (or discharge) outlet of compressor22. Compressor speed sensor N and compressor current sensor I are integral to or positioned adjacent to compressor22. Compressor speed sensor N is configured to sense an operational speed of compressor22, such as a rotational speed of a shaft of compressor22. Compressor current sensor I is configured to sense an amount of electrical current draw of compressor22from a power source integral to or remote from vapor cycle refrigeration system10. Heat sink inlet temperature sensor THSIis positioned at or near the heat sink inlet of condenser14to sense a temperature of the cooling liquid and/or gaseous flow through the heat sink inlet.

In operation, controller12initiates a cooling cycle of vapor cycle refrigeration system10by increasing an operational speed of compressor22to start the flow of refrigerant through vapor cycle refrigeration system10. During the cooling cycle, refrigerant flowing through evaporator20absorbs heat from inlet air to provide cooled, conditioned air to a consuming system, such as an aircraft cabin, galley, or other cooling system. Controller12monitors the pressure sensed via compressor suction pressure sensor PCSand initiates a defrost cycle in response to the sensed pressure being less than a threshold pressure, such as a defined minimum pressure stored in computer-readable memory of controller12that is less than normal operational refrigerant pressures of vapor cycle refrigeration system10. A value of the threshold pressure can based on an operating state (or flight condition) of an aircraft that includes vapor cycle refrigeration system10, such as an on-ground operating state, an in-flight operating state, or other operating states. Controller12decreases the operational speed of compressor22(or halts compressor22) to decrease or stop the flow of refrigerant during the defrost cycle. Accordingly, during the defrost cycle, unconditioned inlet air passes through evaporator20and warms internal components of evaporator20to melt accumulated ice that could degrade the efficiency of heat transfer from the inlet air to refrigerant within evaporator20. In addition, controller12adaptively controls the duration of the defrost cycle based on a time duration of a preceding cooling cycle. For instance, controller12can increase a duration of the defrost cycle in response to determining that the time duration of a preceding cooling cycle is less than a threshold time duration, such as a desired minimum continuous runtime of vapor cycle refrigeration system10in a cooling cycle without entering a defrost cycle (e.g., ten minutes, fifteen minutes, thirty minutes, one hour, or other minimum continuous cooling cycle runtimes). Controller12can decrease the duration of the defrost cycle in response to determining that the time duration of the preceding cooling cycle is greater than the threshold time duration. The defrost cycle time can, in certain examples, be based on an operating state (or flight condition) of an aircraft that includes vapor cycle refrigeration system10, such as an on-ground operating state, an in-flight operating state, or other operating states. In some examples, controller12can compare the duration of the defrost cycle to a maximum defrost cycle time duration to differentiate between an inadequate defrost cycle duration and, e.g., a system fault condition. For instance, if the desired minimum continuous cooling cycle runtime is not achieved when the defrost cycle time is greater than or equal to the maximum defrost cycle time duration, controller12can identify a fault condition of vapor cycle refrigeration system10due to, e.g., low refrigerant charge, a fault condition of throttling valve19, or other fault conditions. Controller12can output an indication identifying that the fault condition is present for, e.g., annunciation at a display device or other consuming system.

As such, controller12controls a time duration of defrost operations to adapt to changing environmental and system conditions, such as temperature and/or moisture content of the inlet air. The adaptive control can help to ensure that a duration of the defrost cycle is sufficient to prevent accumulation of ice within evaporator20that could prevent continuous runtime in a cooling cycle that is less than a prescribed minimum time duration while preventing excessive defrosting that could degrade the overall cooling performance of vapor cycle refrigeration system10.

FIGS. 2A and 2Bare flow diagrams illustrating example operations to adaptively control a defrost cycle time based on a time duration of a cooling cycle of a vapor cycle refrigeration system. For purposes of clarity and ease of discussion, the example operations ofFIGS. 2A and 2Bare described together within the context of vapor cycle refrigeration system10ofFIG. 1.

A cooling cycle of vapor cycle refrigeration system10is initiated (Step24). For example, controller12can command operation of compressor22to start a flow of refrigerant through vapor cycle refrigeration system10. Vapor cycle refrigeration system10operates in a cooling cycle mode (Step26). During the cooling cycle mode, operation of compressor22causes refrigerant to flow through evaporator20where heat from inlet air is absorbed by the refrigerant, thereby producing a cooled, conditioned airflow for one or more consuming systems.

Pressure of the refrigerant is sensed at an inlet of compressor22during operation of the cooling cycle (Step28). For example, compressor suction pressure sensor PCSsenses pressure of refrigerant downstream of evaporator20at or near an inlet of compressor22and transmits the sensed pressure to controller12via one or more electrical and/or communicative connections. Controller12determines whether the sensed pressure at the inlet of compressor22is less than a threshold pressure (Step30). For example, controller12can store a predetermined minimum pressure threshold that is less than normal operational pressures of refrigerant within vapor cycle refrigeration system10. The threshold pressure can, in certain examples, be based on an operating state (or flight condition) of an aircraft that includes vapor cycle refrigeration system10, such as an on-ground operating state, an in-flight operating state, or other operating states. A pressure of refrigerant sensed by compressor suction pressure sensor PCSthat is less than the threshold pressure can correspond to a temperature of refrigerant within evaporator20that is indicative of the accumulation of ice within evaporator20. In response to determining that the sensed pressure at the inlet of compressor22is not less than the threshold pressure (“NO” branch of Step30), controller12continues to cause vapor cycle refrigeration system10to operate in the cooling cycle mode (Step26).

In response to determining that the sensed pressure at the inlet of compressor22is less than the threshold pressure (“YES” branch of Step30), controller12determines whether the duration of the cooling cycle of vapor cycle refrigeration system10is greater than a threshold time duration (Step32). For example, controller12can store a threshold time duration corresponding to a desired minimum continuous runtime of vapor cycle refrigeration system10in a cooling cycle without entering a defrost cycle (e.g., fifteen minutes or other threshold durations of time). The threshold time duration can, in some examples, be based on an operating state (or flight condition) of an aircraft that includes vapor cycle refrigeration system10, such as an on-ground operating state, an in-flight operating state, or other operating states. Controller12can measure a duration of the preceding cooling cycle, such as by determining a difference between a time when the immediately-preceding cooling cycle was initiated (e.g., at Step24) and a time when the sensed pressure at the inlet of compressor22was determined to be below the threshold pressure (e.g., at the “YES” branch of Step30).

In response to determining that the duration of the cooling cycle of vapor cycle refrigeration system10is not greater than the threshold time duration (“NO” branch of Step32), controller12determines whether the time duration of the defrost cycle is greater than (or equal to) a maximum defrost cycle time duration stored at, e.g., computer-readable memory of controller12(Step34). In response to determining that the time duration of the defrost cycle is greater than (or equal to) the maximum defrost cycle time duration (“YES” branch of Step34), controller12exits operation of the cooling and defrost cycles of vapor cycle refrigeration system10(e.g., shuts down vapor cycle refrigeration system10by decreasing an operational speed of or stopping operation of compressor22) and outputs an indication of a fault condition of vapor cycle refrigeration system10(Step36). That is, a defrost cycle time duration that is greater than the maximum defrost cycle time duration can indicate a fault condition of vapor cycle refrigeration system due to, e.g., low refrigerant charge, a fault condition of throttling valve19, or other fault conditions. As such, controller12can identify and output an indication of the presence of a fault condition of vapor cycle refrigeration system10based at least in part on the time duration of a preceding cooling cycle.

In response to determining that the defrost cycle time duration is not greater than (or equal to) the maximum defrost cycle time duration (“NO” branch of Step34), controller12increases the time duration of the defrost cycle (Step38). For example, controller12can store (e.g., in computer-readable memory) an initial baseline defrost cycle time duration, such as three minutes, five minutes, or other time durations. Controller12can increase the defrost cycle time duration from the baseline duration, such as by an amount of thirty seconds, one minute, or other increased time durations to arrive at an adjusted defrost cycle time duration. Controller12can increase the defrost cycle time duration from the baseline duration during, e.g., a first iteration of the operations ofFIGS. 2A and 2B, and can increase the defrost cycle time duration from the adjusted defrost cycle time duration during subsequent iterations of the operations ofFIGS. 2A and 2B. In some examples, controller12can increase the defrost cycle time by an amount that is proportional to a difference between the threshold time duration and the time duration of the preceding cooling cycle.

In response to determining that the duration of the cooling cycle of vapor cycle refrigeration system10is greater than the threshold time duration (“YES” branch of Step32), controller12determines whether the defrost cycle time duration is less than (or equal to) a minimum defrost cycle time duration stored at, e.g., computer-readable memory of controller12(Step40). In response to determining that the defrost cycle time duration is less than (or equal to) the minimum defrost cycle time duration (“YES” branch of step40), controller12continues to operate the defrost cycle using the minimum defrost cycle time duration by, e.g., setting the defrost cycle time duration as the minimum defrost cycle time duration (Step42).

In response to determining that the defrost cycle time duration is not less than (or equal to) the minimum defrost cycle time duration (“NO” branch of Step40), controller12decreases the time duration of the defrost cycle (Step44) to arrive at an adjusted defrost cycle time. Controller12can decrease the defrost cycle time from a baseline defrost cycle time duration during, e.g., a first iteration of the operations ofFIGS. 2A and 2B. Controller12can decrease the defrost cycle time from the adjusted defrost cycle time during, e.g., subsequent iterations of the operations ofFIGS. 2A and 2B. In some examples, controller12can decrease the defrost cycle time by an amount that is proportional to a difference between the threshold time duration and the time duration of the preceding cooling cycle.

Accordingly, controller12can adjust the defrost cycle time by increasing (in Step38) or decreasing (in Step44) the defrost cycle time based on the time duration of the cooling cycle. Controller12initiates the defrost cycle of vapor cycle refrigeration system10(Step46). Controller12terminates the defrost cycle (Step48) upon expiration of the determined defrost cycle time (i.e., the adjusted defrost cycle time determined in one of Step38and Step44). Controller12can initiate the defrost cycle by decreasing an operational speed of compressor22(or halting compressor22) to slow or stop a flow of refrigerant through vapor cycle refrigeration system10, thereby enabling unconditioned inlet air to flow through evaporator20to warm internal components of evaporator20and mitigate the accumulation of ice within evaporator20. Controller12can terminate the defrost cycle by, e.g., increasing the operational speed of compressor22to increase or start the flow of refrigerant through vapor cycle refrigeration system10and initiate a subsequent cooling cycle (Step24).

Accordingly, vapor cycle refrigeration system10implementing techniques of this disclosure can adaptively control the duration of a defrost cycle, thereby accounting for varying environmental and system conditions and increasing overall cooling efficiency of the system. Moreover, the techniques can enable such adaptive control based on a single pressure sensor PCSdisposed downstream of evaporator20at an inlet of compressor22, thereby decreasing the cost, weight, and complexity of implementation of the adaptive control techniques.

Discussion of Possible Embodiments

A method includes (a) initiating a cooling cycle of a vapor cycle refrigeration system, (b) sensing a pressure of refrigerant at an inlet of a compressor of the vapor cycle refrigeration system during operation of the cooling cycle, and (c) initiating a defrost cycle of the vapor cycle refrigeration system in response to the sensed pressure being less than a threshold pressure. The method further includes (d) terminating the defrost cycle upon expiration of a defrost cycle time that is based upon a time duration of the cooling cycle, and (e) repeating steps (a)-(d).

The method of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations, operations and/or additional components:

The method can further include adjusting the defrost cycle time based on the time duration of the cooling cycle.

Adjusting the defrost cycle time based on the time duration of the cooling cycle can include increasing the defrost cycle time in response to determining that the time duration of the cooling cycle is less than a threshold time duration.

Adjusting the defrost cycle time based on the time duration of the cooling cycle can include decreasing the defrost cycle time in response to determining that the time duration of the cooling cycle is greater than a threshold time duration.

Adjusting the defrost cycle time based on the time duration of the cooling cycle can include adjusting the time duration of the cooling cycle by an amount that is proportional to a difference between a threshold time duration and the time duration of the cooling cycle.

Adjusting the defrost cycle time can include adjusting the defrost cycle time from a baseline defrost cycle time based on a difference between the time duration of the cooling cycle and a threshold time duration.

Initiating the defrost cycle can include reducing an operational speed of the compressor of the vapor cycle refrigeration system, and wherein initiating the cooling cycle can include increasing the operational speed of the compressor.

A vapor cycle refrigeration system of an aircraft includes an evaporator, a compressor, a pressure sensor, and a controller device that includes at least one processor and computer-readable memory. The evaporator is configured to receive refrigerant and provide cooling to an airflow by evaporating the refrigerant. The compressor is configured to compress the refrigerant and produce flow of the refrigerant through the vapor cycle refrigeration system. The pressure sensor is disposed to sense pressure of the refrigerant at an inlet of the compressor. The controller device is operatively coupled to the pressure sensor and to the compressor. The computer-readable memory of the controller device is encoded with instructions that, when executed by the at least one processor, cause the controller device to (a) initiate a cooling cycle of the vapor cycle refrigeration system by increasing a speed of the compressor, (b) receive an indication of sensed pressure of the refrigerant at the inlet of the compressor from the pressure sensor, and (c) initiate a defrost cycle of the vapor cycle refrigeration system in response to the received indication of the sensed pressure of the refrigerant being less than a threshold pressure. The computer-readable memory is further encoded with instructions that, when executed by the at least one processor, cause the controller device to (d) terminate the defrost cycle upon expiration of a defrost cycle time that is based upon a time duration of the cooling cycle, and (e) repeat steps (a)-(d).

The vapor cycle refrigeration system of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations, operations and/or additional components:

The computer-readable memory of the controller device can be further encoded with instructions that, when executed by the at least one processor, cause the controller device to adjust the defrost cycle time based on the time duration of the cooling cycle.

The computer-readable memory of the controller device can be further encoded with instructions that, when executed by the at least one processor, cause the controller device to adjust the defrost cycle time based on the time duration of the cooling cycle by increasing the defrost cycle time in response to determining that the time duration of the cooling cycle is less than a threshold time duration.

The computer-readable memory of the controller device can be further encoded with instructions that, when executed by the at least one processor, cause the controller device to adjust the defrost cycle time based on the time duration of the cooling cycle by decreasing the defrost cycle time in response to determining that the time duration of the cooling cycle is greater than a threshold time duration.

The computer-readable memory of the controller device can be further encoded with instructions that, when executed by the at least one processor, cause the controller device to adjust the defrost cycle time by an amount that is proportional to a difference between a threshold time duration and the time duration of the cooling cycle.

The computer-readable memory of the controller device can be further encoded with instructions that, when executed by the at least one processor, cause the controller device to adjust the defrost cycle time from a baseline defrost cycle time based on a difference between the time duration of the cooling cycle and a threshold time duration.

The computer-readable memory of the controller device can be further encoded with instructions that, when executed by the at least one processor, cause the controller device to initiate the defrost cycle by reducing an operational speed of the compressor, and wherein the computer-readable memory of the controller device can be further encoded with instructions that, when executed by the at least one processor, cause the controller device to initiate the cooling cycle by increasing the operational speed of the compressor.

A controller device for a vapor cycle refrigeration system of an aircraft includes at least one processor and computer-readable memory. The computer-readable memory is encoded with instructions that, when executed by the at least one processor, cause the controller device to (a) initiate a cooling cycle of the vapor cycle refrigeration system, (b) receive an indication of a sensed pressure of refrigerant at an inlet of a compressor of the vapor cycle refrigeration system, and (c) initiate a defrost cycle of the vapor cycle refrigeration system in response to the indication of the sensed pressure being less than a threshold pressure. The computer-readable memory is further encoded with instructions that, when executed by the at least one processor, cause the controller device to (d) determine a time duration of the cooling cycle, (e) adjust a defrost cycle time based on the time duration of the cooling cycle to determine an adjusted defrost cycle time, (f) terminate the defrost cycle upon expiration of the adjusted defrost cycle time, and (g) repeat steps (a)-(f).

The controller device of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations, operations and/or additional components:

The computer-readable memory can be further encoded with instructions that, when executed by the at least one processor, cause the controller device to: determine that the time duration of the cooling cycle is less than a threshold time duration; and increase the defrost cycle time by increasing the defrost cycle time in response to determining that the time duration of the cooling cycle is less than the threshold time duration.

The computer-readable memory can be further encoded with instructions that, when executed by the at least one processor, cause the controller device to: determine that the time duration of the cooling cycle is greater than a threshold time duration; and decrease the defrost cycle time by increasing the defrost cycle time in response to determining that the time duration of the cooling cycle is greater than the threshold time duration.

The computer-readable memory can be further encoded with instructions that, when executed by the at least one processor, cause the controller device to: determine a difference between the time duration of the cooling cycle and a threshold time duration; and adjust the defrost cycle time by an amount that is proportional to the determined difference between the time duration of the cooling cycle and the threshold time duration.

The computer-readable memory can be further encoded with instructions that, when executed by the at least one processor, cause the controller device to: determine a difference between the time duration of the cooling cycle and a threshold time duration; and adjust the defrost cycle time from a baseline defrost cycle time based on a the determined difference between the time duration of the cooling cycle and the threshold time duration.

The computer-readable memory can be further encoded with instructions that, when executed by the at least one processor, cause the controller device to: initiate the defrost cycle by reducing an operational speed of the compressor of the vapor cycle refrigeration system; and initiate the cooling cycle by increasing the operational speed of the compressor.