Refrigeration system and computer-implemented method

Abstract

A computer-implemented method includes receiving charge data (605) indicative of a loss of charge of refrigerant in a refrigeration system of a refrigerated container. The computer-implemented system includes, when the charge data is indicative that the loss of charge of refrigerant is at a first level above a first loss of charge threshold and below a second loss of charge threshold, causing performance of a first sequence of actions (700a). The computer-implemented method includes, when the charge data is indicative that the loss of charge of refrigerant is at a second level at or above the second loss of charge threshold, causing performance of a second sequence of actions. The second sequence of actions is different to the first sequence of actions (700b).

Description

REFRIGERATION SYSTEM AND COMPUTER-IMPLEMENTED METHODTECHNICAL FIELD

[0001] The present invention relates to computer-implemented methods for controlling refrigerated containers, controllers, refrigerated containers, and vessels comprising refrigerated containers.BACKGROUND

[0002] Cargo is often stored and transported in transport units. Refrigerated transport units can be used to transport perishable goods such as fruit, vegetables, fresh or frozen meat or fish, or other goods, such as medicaments. Some such refrigerated transport units include TEU or 2-TEU containers designed to be shipped on container vessels, and / or refrigerated trucks or trailers. Refrigeration systems of such storage units are designed to be operated at or above a particular level of charge of refrigerant in the refrigeration systems.SUMMARY

[0003] According to a first aspect of the present invention, there is provided a computer- implemented method, comprising: receiving charge data indicative of a loss of charge of refrigerant in a refrigeration system of a refrigerated container; when the charge data is indicative that the loss of charge of refrigerant is at a first level above a first loss of charge threshold and below a second loss of charge threshold, causing performance of a first sequence of actions; and when the charge data is indicative that the loss of charge of refrigerant is at a second level at or above the second loss of charge threshold, causing performance of a second sequence of actions, the second sequence of actions different to the first sequence of actions.

[0004] Refrigeration systems in refrigerated containers may utilise refrigerants that are flammable. In the event of a leak of refrigerant into an internal space of a refrigerated container a hazardous environment can be formed in the internal space, and remedial action may be required. In previously proposed systems, actions such as ventilation of an interior of a container and providing alerts to an operator can be performed where a loss of charge is determined to have occurred. Typically, such actions are simply performed whenever a loss of charge threshold is reached. This can, however, result in unnecessary ventilation of the interior of the container, andcan lead to false positives occurring, for example where factors other than a leak or rupture contribute to the loss of charge in the refrigeration system.

[0005] By performing the first sequence of actions when the charge data is indicative that the loss of charge of refrigerant is at the first level above the first loss of charge threshold and below the second loss of charge threshold, and performing the second set of actions when the charge data is indicative that the loss of charge of refrigerant is at the second level at or above the second loss of charge threshold, increased flexibility may be provided in comparison to a method where a single sequence of actions is performed when a level of charge of refrigerant is over a particular threshold. For example, instead of simply ventilating and / or providing an alarm, a different set of actions, which may provide increased intelligence, may be performed in certain scenarios where it is deemed appropriate to do so, resulting in more robust decision making, and more informed decisions being taken about whether to ventilate and whether and how to alert an operator.

[0006] The refrigerant may be a flammable refrigerant. The computer-implemented method may comprise receiving refrigerant data indicative of a type of the refrigerant, and at least one of the first sequence of actions and the second sequence of actions may be based on the refrigerant data.

[0007] The computer-implemented method may comprise determining, based on the charge data, a level of the loss of charge of the refrigerant, for example determining that the level of the loss of charge is at the first level or at the second level. The computer-implemented method may comprise causing performance of the first sequence of actions or the second sequence of actions based on the respective determined level of the loss of charge of the refrigerant. The computer- implemented method may comprise monitoring the charge data, for example either continuously or intermittently at pre-determined time intervals.

[0008] The charge data may comprise pressure and / or temperature data indicative of respective pressures and / or temperatures internal to and / or external to the refrigerated container. The charge data may comprise or be based on a mass flow rate of refrigerant in the refrigerated container. The charge data may comprise or be based on one or more measured thermofluidic parameters of refrigerant in the refrigeration system and / or of an external fluid associated with an evaporator and / or condenser of the refrigeration system, such as one or more measured temperatures and / or pressures of the refrigerant and / or the external fluid. For instance, a mass flow rate may be monitored using pressure sensors which are already installed in the refrigeration system, thereby making further use of thermofluidic parameters that are already measured in therefrigeration system. This may allow the method to be performed on a refrigeration system without requiring the installation of additional components, such as additional sensors for sensing the thermofluidic parameters, or external components such as gas sensors for detecting the presence of refrigerant outside the refrigeration system, such as in the internal space.

[0009] The computer-implemented method may be performed by a processor of a controller of the refrigeration system, for example a processor located locally to, such as on or in, the refrigerated container. For example, the computer-implemented method may comprise receiving, at the processor, the charge data. The computer-implemented method may comprise the processor causing performance of the first sequence of actions. The computer-implemented method may comprise the processor causing performance of the second sequence of actions. Causing performance of the first and / or second sequence of actions may comprise the processor issuing instructions that cause performance of an action by another component of the refrigeration system and / or another component of the refrigerated container. In such cases, issuance of instructions by the processor can be considered an action. An action of the first sequence of actions and / or an action of the second sequence of actions may be performed by the processor, for example with an internal decision making process of the processor comprising an action.

[0010] The refrigerated container may be an intermodal container, or refrigerated truck or trailer, such as for transporting a cargo. The internal space may be an internal cargo storage space of the refrigerated container.

[0011] Optionally, the first level is indicative of a first priority of remedial action associated with the loss of charge of refrigerant, the second level is indicative of a second priority of remedial action associated with the loss of charge of refrigerant, and the second priority is higher than the first priority. By performing different sequences of actions where the level of charge is associated with a different level of priority of required remedial action, more informed sequences of actions can be taken than for previous systems where ventilation is performed and / or alerts are issued irrespective of a level of charge relative to a threshold.

[0012] The second loss of charge threshold may be, for example, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, or 100%, of a total charge capacity of the refrigeration system.

[0013] The first loss of charge threshold may be, for example, no greater than 75%, no greater than 80%, no greater than 85%, no greater than 90%, no greater than 95%, or less than 100%, of the total charge capacity of the refrigeration system.

[0014] Optionally, the second sequence of actions comprises causing ventilation of an internal space of the refrigerated container. By causing ventilation of the internal space of the refrigerated container when the charge data is indicative that the loss of charge of refrigerant is at the second level at or above the second, higher, loss of charge threshold, ventilation of the internal space of the refrigerated container occurs when the loss of charge is relatively high, thereby ensuring removal of a potentially hazardous environment within the internal space of the refrigerated container.

[0015] Causing ventilation of the internal space of the refrigerated container may comprise causing actuation of a valve actuator to open a ventilation valve to enable fluid communication between the internal space of the refrigerated container and an ambient environment of the refrigerated container.

[0016] Causing ventilation of the internal space of the refrigerated container may comprise causing ventilation of the internal space of the refrigerated container for longer than a first predetermined time threshold. The first pre-determined time threshold may, for example, be at least 20 minutes, at least 30 minutes, at least 45 minutes, at least 60 minutes, at least 90 minutes, or at least 120 minutes.

[0017] Optionally, the second sequence of actions comprises receiving location data indicative of a location of a leakage that is a cause of the loss of charge of refrigerant, and when the location data is indicative that the location of the leakage is within the internal space of the refrigerated container, causing ventilation of the internal space of the refrigerated container.

[0018] By accounting for location of the leakage that is a cause of the loss of charge of the refrigerant, ventilation of the internal space of the refrigerated container may only be performed when strictly necessary. For example, if the location of the leakage is external to the internal space of the refrigerated container, then ventilation may be unnecessary, as the refrigerant may already be vented to an ambient atmosphere where weather conditions, such as wind and the like, may enable rapid dispersion of the refrigerant into the atmosphere. In contrast, if the location of the leakage is within the internal space of the refrigerated container, then ventilation may be necessary to mitigate for build-up of a hazardous environment within the internal space of therefrigerated container, and knowledge of the location of the leakage can enable appropriate action to take place.

[0019] The computer-implemented method may comprise determining, for example at the processor of the refrigeration system, the location of the leakage based on the location data. The computer-implemented method may comprise causing the ventilation of the internal space of the refrigerated container based on the determined location.

[0020] The location data may comprise or be based on at least one of: discharge pressure data indicative of a discharge pressure of the refrigeration system; suction pressure data indicative of a suction pressure of the refrigeration system; ambient temperature data indicative of an ambient temperature of an environment external to the refrigerated container; and an internal temperature data indicative of a temperature of the internal space of the refrigerated container.

[0021] Optionally, the second sequence of actions comprises, when the location data is indicative that the location of the leakage is within the internal space of the refrigerated container, causing provision of an internal condition alert indicative of the second level.

[0022] As the second level corresponds to a relatively high loss of charge of refrigerant, providing the internal condition alert, alongside the ventilation of the internal space of the refrigerated container, may alert an operator to the potentially hazardous environment within the internal space of the refrigerated container.

[0023] The internal condition alert may comprise at least one of an audible alert, a visual alert, and a digital alert stored in a log. The audible alert and / or the visual alert may be provided locally to the refrigerated container, for example provided by one or more components of the refrigerated container. Causing provision of the internal condition alert may comprise causing at least one of a transducer to provide an audible alert, and a display device to display a visual signal. Such a display device may comprise, for example, an LED light or a screen.

[0024] The computer-implemented method may comprise causing provision of the internal condition alert for a pre-determined time period. The computer-implemented method may comprise causing provision of the internal condition alert until receiving an operator input requesting cessation of provision of the internal condition alert. The computer-implemented method may comprise causing provision of the internal condition alert until a remedial action, such as a repair of the refrigeration system, occurs and is confirmed and / or detected.

[0025] Optionally, when the location data is indicative that the location of the leakage is external to the internal space of the refrigerated container, the second sequence of actions comprises causing provision of an external condition alert indicative of the second level. Notifying an operator of an external leakage via the external condition alert may enable appropriate remedial action to take place.

[0026] The second sequence of actions may comprise causing provision of the external condition alert without also causing ventilation of the internal space of the refrigerated container. This may enable an operator to be notified that a potential remedial action is required without causing unnecessary ventilation of the internal space of the refrigerated container, which would otherwise cause unnecessary maintenance time and / or cost.

[0027] The external condition alert may comprise at least one of an audible alert, a visual alert, and a digital alert stored in a log. The audible alert and / or the visual alert may be provided locally to the refrigerated container, for example provided by one or more components of the refrigerated container. Causing provision of the external condition alert may comprise causing at least one of a transducer to provide an audible alert, and a display device to display a visual signal. Such a display device may comprise, for example, an LED light or a screen.

[0028] The computer-implemented method may comprise causing provision of the external condition alert for a pre-determined time period. The computer-implemented method may comprise causing provision of the external condition alert until receiving an operator input requesting cessation of provision of the external condition alert. The computer-implemented method may comprise causing provision of the external condition alert until a remedial action, such as a repair of the refrigeration system, occurs and is confirmed and / or detected.

[0029] When the location data is inconclusive as to whether the location of the leakage is external to the internal space of the refrigerated container or within the internal space of the refrigerated container, the computer-implemented method may comprise shifting operation from the second sequence of actions to the first sequence of actions. This may enable, for example, further analysis to take place.

[0030] Optionally, the first sequence of actions comprises receiving valve data indicative of an operational state of a ventilation valve that selectively enables fluid communication between an internal space of the refrigerated container and an ambient atmosphere external to therefrigerated container, and a next subsequent action of the first sequence of actions to the receiving valve data is based on the valve data.

[0031] By accounting for an operational state of the ventilation valve, an informed decision may be taken as to whether to attempt ventilation of the internal space of the refrigerated container to remove any refrigerant from the internal space of the container. The operational state of the ventilation valve may be indicative as to whether the valve is operational or non-operational and / or as to whether a valve actuator of the ventilation valve is operational or non-operational.

[0032] The computer-implemented method may comprise determining, for example at the processor of the refrigeration system, the operational state of the ventilation valve based on the valve data. The computer-implemented method may comprise causing performance of the next subsequent action of the first sequence of actions based on the determined operational state of the ventilation valve.

[0033] The computer-implemented method may comprise receiving, from an actuator sensor, the valve data. The actuator sensor may be configured to monitor one of more parameters of the valve actuator, for example parameters indicative of a position of the valve actuator.

[0034] Optionally, when the valve data is indicative that the ventilation valve is non-operational, the next subsequent action of the first sequence of actions is to wait for performance of a defrost operation of the refrigeration system.

[0035] By waiting for performance of the defrost operation of the refrigeration system, a time period may be provided to determine whether the defrost operation is possible or not. This time period may then also be utilised as part of a time-out procedure of the computer-implemented method. The computer-implemented method may comprise, when the defrost operation is not performed after a pre-determined time period has elapsed whilst waiting for performance of the defrost operation, transitioning the refrigeration system to a receiving state for receiving the charge data. The computer-implemented method may comprise increasing a counter value where such a transition takes place, and where the counter value reaches a pre-determined threshold, at least one of causing ventilation of the internal space of the refrigerated container and causing provision of a counter alert. This may inhibit the computer-implemented method becoming stuck in a loop where the defrost operation is unable to be performed.

[0036] The counter alert may comprise at least one of an audible alert, a visual alert, and a digital alert stored in a log. The audible alert and / or the visual alert may be provided locally to therefrigerated container, for example provided by one or more components of the refrigerated container. Causing provision of the counter alert may comprise causing at least one of a transducer to provide an audible alert, and a display device to display a visual signal. Such a display device may comprise, for example, an LED light or a screen.

[0037] Optionally, when the valve data is indicative that the ventilation valve is operational, the next subsequent action of the first sequence of actions is to cause ventilation of the internal space of the refrigerated container. This may enable any refrigerant to be purged from the internal space of the refrigerated container, for example to avoid build-up of refrigerant before further analysis is performed, thereby enabling the further analysis to be performed safely without risk of a hazardous build-up of refrigerant occurring in the internal space of the refrigerated container. The first sequence of actions may comprise, subsequent to causing ventilation of the internal space of the refrigerated container, to wait for performance of a defrost operation of the refrigeration system.

[0038] Optionally, the first sequence of events comprises, following the next subsequent action of the first sequence of actions, causing performance of a defrost operation of the refrigeration system. By causing performance of the defrost operation, factors such as ice, which may otherwise impact on the charge data or further charge data to be received as part of the computer- implemented method, may be removed, which may enable more accurate determination of the level of the loss of charge of refrigerant.

[0039] Optionally, the first sequence of events comprises, following the performance of the defrost operation of the refrigeration system, causing performance of a determination of a state of the refrigeration system and causing, based on a determined state of the refrigeration system and based on the valve data, provision of a state alert.

[0040] By accounting for both a determined state of the refrigeration system and the valve data a greater certainty may be obtained than relying on the charge data alone, which may ensure that the state alert is only provided where necessary. This may lead to a reduction in maintenance actions and / or costs in comparison to systems where a greater number of false alarms, for example due to less accurate determinations, occur.

[0041] A form of the state alert may depend on the determined state of the refrigeration system and the valve data. For example, the form of the state alert may take a first form when the valve data is indicative that the valve is operational, and a second, different, form, when the valve datais indicative that the valve is non-operational. The state of the refrigeration system may comprise, for example, an indication that the refrigeration system has a leak, or an indication that the refrigeration system has a rupture. The form of the state alert may be different when the refrigeration has a leak compared to when the refrigeration system has a rupture.

[0042] The state alert may comprise at least one of an audible alert, a visual alert, and a digital alert stored in a log. The audible alert and / or the visual alert may be provided locally to the refrigerated container, for example provided by one or more components of the refrigerated container. Causing provision of the state alert may comprise causing at least one of a transducer to provide an audible alert, and a display device to display a visual signal. Such a display device may comprise, for example, an LED light or a screen.

[0043] The computer-implemented method may comprise causing provision of the state alert for a pre-determined time period. The computer-implemented method may comprise causing provision of the state alert until receiving an operator input requesting cessation of provision of the state alert. The computer-implemented method may comprise causing provision of the state alert until a remedial action, such as a repair of the refrigeration system, occurs and is confirmed and / or detected.

[0044] When the determined state indicates a normal operating state of the refrigeration system, and the valve data is indicative that the ventilation valve is operational, the state alert may not be provided.

[0045] Optionally, the computer-implemented method comprises, prior to causing performance of a determination of a state of the refrigeration system, causing an increase in a load on a compressor of the refrigeration system. This may enable more accurate charge data to be obtained than for a system with a lower load on the compressor.

[0046] Causing the increase in the load on the compressor may comprise causing a set-point temperature of the refrigeration system to be lowered.

[0047] Determination of the state of the refrigeration system may be based on at least one of the charge data and further obtained charge data, for example obtained after increasing the load on the compressor of the refrigeration system.

[0048] A second aspect of the present invention provides a data carrier comprising machine readable instructions that, when executed, cause operation of one or more processors of arefrigeration system controller of a refrigeration system of a refrigerated container to perform the computer-implemented method according to the first aspect of the present invention.

[0049] A third aspect of the present invention provides a refrigeration system controller for a refrigeration system of a refrigerated container, the refrigeration system controller configured to perform the computer-implemented method according to the first aspect of the present invention.

[0050] A fourth aspect of the present invention provides a refrigeration system for a refrigerated container, the refrigeration system comprising the refrigeration system controller according to the third aspect of the present invention.

[0051] The refrigeration system may comprise a compressor. The refrigeration system may comprise a heat exchanger. The refrigeration system may comprise at least one temperature sensor, for example at least one temperature sensor in communication with the processor. The refrigeration system may comprise at least one pressure sensor, for example at least one pressure sensor in communication with the processor. The refrigeration system may comprise the ventilation valve and the valve actuator. The refrigeration system may comprise the valve sensor, for example with the valve sensor in communication with the controller.

[0052] A fifth aspect of the present invention provides a refrigerated container comprising the refrigeration system controller according to the third aspect of the present invention or the refrigeration system according to the fourth aspect of the present invention.

[0053] A sixth aspect of the present invention provides a vessel comprising the controller according to the third aspect of the present invention, or the refrigeration system according to the fourth aspect of the present invention, or the refrigerated container according to the sixth aspect of the present invention.BRIEF DESCRIPTION OF DRAWINGS

[0054] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0055] Figure 1 shows a schematic view of a marine vessel transporting intermodal storage containers;

[0056] Figure 2 shows a schematic view of a refrigerated container transported on the marine vessel;

[0057] Figure 3 shown an example process performed by a controller of the refrigerated container; and

[0058] Figure 4 shows an example computer-implemented method performed by the controller.DETAILED DESCRIPTION

[0059] Figure 1 shows a marine vessel 1 , which here is a container vessel transporting intermodal shipping containers 2. Figure 2 shows an example refrigerated container 10 that is transported on the marine vessel 1. The refrigerated container 10 has a storage space 11 , cargo 12 in the storage space 11 , a compartment 13 adjacent to the storage space 1 1 , first and second flow vents 14, 15, an air vent 16, and a user interaction module 50. The refrigerated container 10 also has a refrigeration system 100, supply and return air temperature sensors 210, 220, a vent valve 280, and a controller 500. The refrigeration system 100 comprises, in a series fluidic connection, a compressor 110, a condenser 120, a liquid receiver 135, an expansion valve 130 and an evaporator 140. The refrigeration system 100 comprises a hot gas bypass valve 145 in a parallel fluidic connection with the evaporator 120 and the expansion valve 130. The refrigeration system 100 also comprises an evaporator fan 141 , a condenser fan 121 , a suction temperature sensor 230, a suction pressure sensor 240, and a discharge pressure sensor 250.

[0060] In the example described herein, the cargo 12 in the storage space 11 is respiring produce. The storage space 1 1 is separated from the compartment 13 by a wall. The compartment 13, and the first and second flow vents 14, 15 are openings in the wall, the openings fluidically connecting the compartment 13 and the storage space 1 1. The first flow vent 14 is higher up the wall than the second flow vent 15, relative to a base 18 of the refrigerated container 10. In this way, the first flow vent 14 opens into a first region 14a of the compartment 13, and the second flow vent 15 opens into a second region 15a of the compartment 13, below the first region 14a. The air vent 16 is an opening between the compartment 13, specifically the first region 14a, and an external atmosphere surrounding the refrigerated container 10. The user interaction module 50 is located on an outer wall of the refrigerated container 10, and comprises the controller 500, a display 51 with which a user can interact.

[0061] The compressor 110, the condenser 120, the condenser fan 121 , the expansion valve 130 and the hot gas bypass valve 145 are located on an external wall of the refrigerated container 10, external to the compartment 13 and the storage space 1 1 . The evaporator 140, the evaporator fan 141 , and the supply and return temperature sensors 210, 220 are located in the compartment 13. Specifically, the evaporator 140 and evaporator fan 141 are located between the first and second regions 14a, 15a, the supply temperature sensor 210 is located in the first region 14a, and the return temperature sensor 220 is located in the second region 15a. The suction temperature and pressure sensors 230, 240 are located in a suction line between the compressor 110 and the evaporator 140, and the discharge pressure sensor 250 is located in a discharge line between the compressor 1 10 and the condenser 120. The vent valve 280 comprises a vent valve actuator 281 and a solid member that is movable by the vent valve actuator 281 to selectively block and unblock the air vent 16.

[0062] The refrigeration system 100 comprises flammable refrigerant, specifically 1234yf refrigerant, but other refrigerants may be used in other examples. The compressor 110 is a variable-speed compressor with a motor that varies a speed of the compressor 110. The expansion valve 130 is an electronic expansion valve with a valve port defining an opening through the expansion valve 130, and a motor that varies an opening degree of the valve port. The evaporator 140 and condenser 120 are fin-and-tube heat exchangers having serpentine coils that carry refrigerant and fins in contact with the coils. The condenser and evaporator fans 121 , 141 have variable-speed motors that vary a speed of the condenser and evaporator fans 121 , 141. The condenser and evaporator fans 121 , 141 are orientated to pass air across the coils and fins of the condenser 120 the evaporator 140. The liquid receiver 135 is a refrigerant storage tank that receives refrigerant from the condenser 120 and stores the refrigerant in a liquid state. The liquid receiver 135 provides a buffer for changes in refrigerant charge and / or changes in an amount of refrigerant circulating in the refrigeration system with changing load.

[0063] The controller 500 is communicatively coupled to the compressor 1 10, the expansion valve 130, the condenser and evaporator fans 121 , 141 , the first and second supply and return temperature sensors 210, 220, the supply temperature and pressure sensors 230, 240, and the discharge pressure sensor 250. The controller 500 is configured to control operation of the components of the refrigeration system 100 to provide air at a set temperature to the storage space 1 1 . A person skilled in the art of refrigeration systems will understand the general principles of operation of refrigeration systems; however, for the avoidance of doubt, one mode of operation of the refrigeration system 100 is described here.

[0064] The controller 500 sends signals to the motor of the compressor 1 10 to operate the compressor 1 10 at a given speed. This causes the compressor to provide refrigerant in the form of a high-pressure, high-temperature discharge gas to the condenser 120 (“high” relative to refrigerant flowing through the evaporator 140). The refrigerant in the present example is R1234yf, but in other examples any other suitable refrigerant may be used. The temperature of the refrigerant is reduced in the condenser 120 through (latent) heat exchange with the external atmosphere. The controller 500 sends signals to operate the compressor fan 121 , to move the external atmosphere over coils and fins of the condenser 120. This enhances the rate of heat transfer between the refrigerant and the external atmosphere.

[0065] Cooling of the refrigerant in the condenser 120 causes condensation of the refrigerant, and liquid refrigerant is provided to the liquid receiver 135. The liquid receiver 135 stores refrigerant in a liquid phase and provides the liquid refrigerant to the expansion valve 130. The liquid refrigerant is expanded through the valve port in the expansion valve 130. This reduces a temperature and pressure of the refrigerant and provides a vaporous gas-liquid refrigerant mixture, which is then passed through the evaporator 140. The controller 500 sends signals to operate the evaporator fan 141 to move an atmosphere from the second region 15a across the coils and fins of the evaporator 140 to the first region 14a. This leads to a reduction in pressure in the second region 15a, and an increase in pressure in the first region 14a. This, in turn, causes air to be passed as return air from the storage space 1 1 into the second region 15a through the second opening 15, across the evaporator 140 into the first region 14a, and as supply air from the first region 14a into the storage space 11 through the first opening 14. Heat carried in the return air from the storage space 11 is thus passed to the refrigerant in the evaporator 140, which is cooler than the supply air due to expansion of the refrigerant in the expansion valve 130. The cooler supply air is then passed into the storage space 11 to reduce a temperature in the storage space 1 1 .

[0066] Heat transfer with the supply air flowing over the evaporator 140 causes the refrigerant to evaporate in the evaporator 140, to provide low-temperature, low pressure suction gas to the compressor. The controller 500 receives signals from the supply and return temperature sensors 210, 220, the suction pressure and temperature sensors 230, 240, and the discharge temperature sensor 250 to control operation of the refrigeration system 100 to provide a particular set temperature. Specifically, the controller 500 is configured to provide a set temperature difference between the supply and return air temperature sensed by the supply and return temperaturesensors 210, 220. This is by sending signals to the compressor 110 to increase or decrease a load on the compressor 110. The controller then controls the expansion valve 130 to provide a target level of superheat, which is a measure of how much a suction temperature, as measured by the suction temperature sensor, exceeds a saturation temperature of the refrigerant (i.e., a temperature above which the refrigerant is purely gaseous) at a suction pressure, as measured by the suction pressure sensor 240.

[0067] The refrigeration system 100 is operable by the controller 500 in a defrost mode of operation. In the defrost mode, the controller 500 sends signals to the expansion valve 130 to close the expansion valve 130, and sends signals to the hot gas bypass valve 145 to cause the hot gas bypass valve 145 to open. Closing the expansion valve 130 prevents refrigerant flowing through the condenser 120 and the expansion valve 130. Opening the hot gas bypass valve 145 causes refrigerant to flow through a hot gas bypass line that extends from a point downstream of the compressor 1 10 and upstream of the condenser 120 to a point downstream of the expansion valve 130 and upstream of the evaporator 140. This causes hot gaseous refrigerant discharged from the compressor 110 to bypass the condenser 120 and expansion valve 130 and instead to be passed through the evaporator 140. This, in turn, causes heating of the evaporator 140, which melts ice that may have built-up on the evaporator 140. Such ice may build up during operation of the refrigeration system 100 to cool the storage space 1 1 .

[0068] An operator can utilise the user interaction module 50 to modify how the controller 500 controls the refrigeration system 100, such as to start or stop cooling operations, to switch between different cooling modes, e.g., with different set-point temperatures, and / or to receive information and alerts about the state of the refrigeration system 100.

[0069] It is emphasised that the foregoing description is a simplified example operation of the refrigeration system 100, provided merely for ease of understanding, and that in other examples the refrigeration system 100 may operate in other suitable ways and / or with other components, as will be evident to the skilled reader.

[0070] Operations of the controller 500 will now be described in more detail, with particular reference to Figure 3. The controller 500, and specifically a processor of the controller 500, performs a process 600 that includes the controller 500 monitoring 605 “charge data” in the refrigeration system 100. The charge data monitored by the controller 500 includes suction temperatures and suction pressures sensed by the suction temperature and pressure sensors230, 240, discharge pressure as measured by the discharge pressure sensor 250, as well as supply and return air temperatures measured by the supply and return air temperature sensors 210, 220.

[0071] The charge data is then used by the controller 500 to estimate 610 a level of loss of charge of refrigerant in the refrigeration system 100. Techniques for estimating the level of the loss of charge are described in international patent application publication no. WO2023057463A1 (here “P1”), and so will not be described in detail here. In brief, one method involves determining, using the measured suction pressure and measured discharge pressure, along with physical properties of the expansion valve 130 and refrigerant, an expansion valve mass flow rate, which is a flow rate of refrigerant through the expansion valve 130. The method also comprises determining, using based on an operating speed of the compressor and physical properties of the compressor 110 and refrigerant, a compressor mass flow rate, which is a mass flow rate of refrigerant through the compressor 1 10. A difference or ratio between the compressor mass flow rate and the expansion valve mass flow rate is determined, and the estimation of the level of loss of refrigerant charge is based on a comparison between this difference and a threshold. Another method disclosed in P1 involves comparing a cooling capacity of the refrigeration system to an expected or theoretical cooling capacity based on physical properties of the evaporator 140. It will be appreciated that such methods are merely examples, and that other methods of estimating the loss of charge may be used in other examples. For instance, some examples may employ techniques described in international patent application publication no. WO2023084127A1 (here “P2”). Moreover, in other examples, the refrigeration system 100 may comprise any other suitable sensors and / or components for performing the methods disclosed in P1 and / or P2.

[0072] If the estimated level of loss of charge exceeds a lower threshold but is below an upper threshold, the controller 500 performs a diagnosis sequence of actions 700a. If the estimated level of the loss of charge is at or above the upper threshold, the controller 500 performs a rupture sequence of actions 700b. In the present example, the lower threshold is 56% of a total charge capacity of refrigerant in the refrigeration system, and the upper threshold is 100% of a total charge capacity of refrigerant in the refrigeration system.

[0073] Starting with the diagnosis sequence of actions 700a, the controller 500 first determines 615 a status of the vent valve actuator 281 . This is by the controller 500 receiving a feedback signal from a position sensor of the actuator, the feedback signal representing a position of the vent valve actuator 281 .

[0074] If the feedback signal indicates that the actuator is has moved as expected in response to an instruction to open the vent valve 280, the controller 500 concludes that the vent valve actuator 281 is operational then performs a pre-defrost ventilation operation 620. This is achieved by the controller 500 sending a signal to the vent valve 280 to operate the actuator and open the air vent 16. The controller 500 also sends a signal to the evaporator fan 141 to cause the evaporator fan to operate at full speed. This forces air from the storage space 11 and the compartment 13 towards and through the air vent 16 and into the external atmosphere surrounding the refrigerated container 10. This, in turn, causes refrigerant that has leaked from the refrigeration system 100 into the compartment 13 and / or storage space to pass out of the refrigerated container 10 along with the air, thereby preventing a build-up of refrigerant in the compartment 13 and / or storage space 11 that could lead to a hazardous environment within the refrigerated container 10. The controller 500 ventilates for twenty minutes, to ensure adequate removal of refrigerant in the compartment 13 and / or storage space 1 1 .

[0075] Following the pre-defrost ventilation operation 620, the controller 50 performs a defrost operation 625 to defrost the evaporator 140. This is by the controller 500 operating the refrigeration system 100 in the defrost mode, whereby the controller 500 sends a signal to the expansion valve 130 to cause the expansion valve 130 to close and sends a signal to the hot gas bypass valve 145 to cause the hot gas bypass valve 145 to open. This, in turn, causes heating of the evaporator, and causes ice that may have built-up on the evaporator 140 coils and / or fins to melt. It will be appreciated that, in other examples, the defrost operation may be performed in any other suitable manner. For instance, the controller 500 may operate the compressor 1 10 in reverse so that the evaporator 140 functions as a condenser that transfers heat to the air moved by the evaporator fan 141 in a “heating mode”. In any event, defrosting the evaporator 140 reduces an impact of ice build-up on an accuracy of the estimation of the level of the loss of charge. In particular, such a build-up affects an ability of the evaporator 140 to transfer heat from the supply air to the refrigerant, thereby reducing an efficiency of the evaporator 140 and impacting a “cooling capacity” provided by the evaporator 140. This may, in turn, affect an estimation of the level of loss of charge, particularly when the estimation is based on a comparison between expected and actual cooling capacity of the evaporator, potentially leading to false positives. By defrosting the evaporator 140, a more accurate determination of the level of loss of charge may be determined.

[0076] If, when determining 615 the status of the vent valve actuator 681 , the controller 500 determines that the vent valve actuator 681 is non-operational, or faulty (e.g., the feedback signalindicates that the actuator has not moved, or has not moved as expected), the controller 500 instead performs the defrost operation 625 without first performing the pre-defrost ventilation operation 620.

[0077] After performing the defrost operation 625, the controller 500 operates 630 the refrigeration system at a lower set-point temperature. This is by the controller 500 sending instructions to the compressor to increase a load on the compressor 1 10 (i.e., to increase a speed of the variable-speed motor of the compressor 110). By increasing the load on the compressor 110, a mass flow rate of refrigerant through both the compressor 110 and the expansion valve 130 is increased. This, in turn, provides more favourable conditions in the refrigeration system for estimating the level of loss of charge. This is because, when the load is increased, the compressor 110 can operate more continuously, and thereby the system runs stable for an extended period of time. This allows for more continuous and undisturbed data to be collected and analysed by the controller 500. In addition, the requested higher capacity (increased load) leads to a higher mass flow rate in the system, meaning more refrigerant is needed to fill the condenser 120 and evaporator 140 coils. As a consequence, a liquid level of refrigerant stored in the liquid receiver 135 drops. In a situation where insufficient refrigerant is charged (e.g. due to leak), this will cause detectable disturbances in the system behaviour, as it is not ensured that liquid is fed to the expansion valve 130, thereby affecting flow and superheat control.

[0078] The controller 500 then monitors 635 further charge data that is sensed while operating the refrigeration system 100 at the lower set-point temperature, and, following the monitoring of further charge data, determines 640 a state of the refrigeration system 100. Determining the state of the refrigeration system includes re-estimating the level of loss of charge, based on the further charge data, and determining whether the vent valve actuator 281 was faulty. It will be appreciated that by defrosting the evaporator 140, reducing the set-point temperature, and increasing the load on the compressor 1 10, the re-estimation may be more accurate than the initial estimation of loss of charge of refrigerant.

[0079] If the controller 500 concludes that there has been no loss of charge above the first threshold, the controller 500 operates the refrigeration system 100 as normal to achieve a target set-point temperature for the cargo 15, and returns to monitoring 605 the charge data. If the controller 500 concludes that there has been a loss of charge above the first threshold, and that the vent valve actuator 281 is operational, then the controller 50 transmits 645 a low-priority alert signal to the display 51 , to cause the display 51 to display a low-priority alert. The low-priority alertindicates visibly on the display 51 that there has been a loss of charge of refrigerant, but that there is likely no hazardous buildup of refrigerant in the compartment 13 and / or storage space 11 (in this case because the compartment 13 and storage space 1 1 have been ventilated). An operator can then take remedial action to address the loss of charge at a suitable time. The controller 500 continues to operate the refrigeration system 100 to cool the storage space 1 1 in the event of a loss of charge that is above the first threshold but below the second threshold.

[0080] If the controller 500 instead concludes that there has been a leak and that the air vent actuator 681 is non-operational, the controller 500 transmits 260 a high-priority alert signal to the display 51 to cause the display 51 to display a high-priority alert. The high-priority alert (which, as will be described below, is a part of the rupture sequence of actions 700b), notifies a user that there is has been a loss of charge, and that there is a potentially hazardous environment within the compartment 13 and / or storage space 1 1 (in this case because the pre-defrost ventilation operation 620 could not be performed). Due to the potentially hazardous environment in the compartment and / or storage space whilst the high-priority alert is displayed, normal operation of the refrigeration system 100 is inhibited, and the controller 500 instead performs a pump-down operation 665. To perform the pump-down operation 665, the controller 500 sends a signal to close the expansion valve 130 and operate the compressor 110 to move refrigerant from a low- pressure side of the refrigeration system 100 extending between the expansion valve 130 and the compressor 1 10 and comprising the evaporator 140, to a high-pressure side of the refrigeration system 100 extending between the compressor 110 and the expansion valve 130 and comprising the condenser 120. It will be appreciated (e.g., from Figure 1 and the description above) that the high-pressure side is external to the compartment 13 and storage space 11 , and so performance of the pump-down operation 665 inhibits any potential further loss of refrigerant from the high-pressure side into the compartment 13 and / or storage space 1 1. An operator can then take remedial action as appropriate (ideally as soon as possible) to repair the refrigeration system 100 and / or refrigerated container 10.

[0081] As noted above, if the controller 500 initially estimates 610 that the level of loss of charge exceeds the second threshold, the controller 500 performs the rupture sequence of actions 700b. In the rupture sequence 700b of actions, the controller 500 first determines 650 a location of the rupture, or leak, that has caused the loss of charge. This is by stopping operation of the refrigeration system 100, closing the expansion valve 130, and monitoring the suction and discharge pressures represented by signals received from the suction and discharge pressure sensors 240, 250. If the rupture is in the high-pressure side, the discharge pressure will reducetowards a pressure in the external atmosphere. If the rupture is in the low-pressure side, the suction pressure will increase or decrease depending on the operating pressure in the refrigeration system 100 at the moment prior to the leak. If the pressure in the compartment 13 is below the ambient air pressure (typically 1 bar, absolute), then the refrigerant will leak out of the refrigeration system 100 if the operating pressure in the refrigeration system 100 was above that with an equivalent saturated temperature of -26.36 °C, which is the normal boiling point of R1234yf. For lower temperatures, the pressure of the surrounding air in the compartment 13 is larger than that in the low-pressure side of the refrigeration system 100 and the air will leak into the refrigeration system 100, until the pressure difference has been equalized and all flow stops.

[0082] If the controller 500 determines that the leak is internal to the compartment 13, from a rupture in the low-pressure side of the refrigeration system 100, the controller proceeds to simultaneously transmit 660 the high-priority alert to the display 51 and performs a rupture ventilation operation 655 to ventilate the compartment 13 and storage space 1 1. The compartment 13 and storage space 1 1 are ventilated for two hours, by operating the vent valve actuator 281 and evaporator fan 141 as described above. The high-priority alert signal is the same as that issued following the determination 640 in the diagnosis sequence of actions 700a that a leak has occurred and the vent valve 280 is non-operational. However, in that case, because the vent valve 280 is non-operational, no ventilation of the compartment 13 or storage space 11 is performed simultaneously performed.

[0083] If the controller 500 instead determines 650 that the leak is external to the compartment 13, from the high-pressure side of the refrigeration system 100, then the controller 500 sends the low-priority signal to the display 51 , and the low-priority alert is displayed on the display 51 . This is because an external leak would likely not lead to a hazardous environment in the compartment 13, and so ventilating the compartment 13 and raising a warning of a potential hazardous environment (as with the high-priority alert) is not required.

[0084] It will be appreciated from the foregoing disclosure that the controller 500 is able to perform different sequences of actions depending on the severity of the loss of charge, the location of a rupture, and the availability of ventilation apparatus. In particular, the controller 500 performs the diagnosis sequence of actions 700a when the estimated loss of charge is significant enough to warrant further investigation, but small enough that the loss of charge may be due to a leak that is slow enough to pose minimal risk of a hazardous build-up of refrigerant in the compartment 13 and / or the storage space 1 1 . Such a low estimated loss of charge may alternatively be the result of factors other than a leak, and so may present a “false alarm” situation. The diagnosis sequenceof actions 700a therefore seeks to corroborate the loss of charge estimation whilst at the same time mitigating the effects of a potential leak of refrigerant into the compartment 13 and / or storage space 1 1 .

[0085] The rupture sequence of actions 700b, in contrast to the diagnosis sequence of actions 700a, is instead initiated when the estimated loss of charge is comparatively high, which is indicative of a rupture (rather than a gradual leak) in the refrigeration system 100. The rupture sequence 700b therefore prioritises mitigation of the effects of such a leak and raises suitable alarms.

[0086] Figure 4 shows an example computer-implemented method 700 performed by the controller 500 (specifically by the processor of the controller) described above. The method 700 comprises receiving 710 charge data indicative of a loss of charge of refrigerant in the refrigeration system 100. The method 700 comprises, when the charge data is indicative that the loss of charge (L) of refrigerant is at a first level (L1 ) above the lower threshold (T1 ) and below upper threshold (T2), causing 720 performance of the diagnosis sequence of actions 700a. The method 700 comprises, when the charge data is indicative that the loss of charge (L) of refrigerant is at a second level (L2) at or above the upper loss of charge threshold (T2), causing 730 performance of the rupture sequence of actions 700b, which as described above is different to the first sequence of actions 700a.

[0087] Whilst not shown in the Figures, the user interaction module 50 comprises a non-transitory computer-readable storage medium. The non-transitory computer-readable storage medium stores instructions 630, if executed by the processor of the controller 610, cause the processor to perform the method 700 described above with reference to Figure 4.

[0088] Example embodiments of the present invention have been discussed, with particular reference to the examples illustrated. However, it will be appreciated that variations and modifications may be made without departing from the scope of the invention as defined by the appended claims.

[0089] For instance, whilst the lower threshold described above is 56% of a total charge capacity of refrigerant in the refrigeration system, and the upper threshold is 100% of a total charge capacity of refrigerant in the refrigeration system, these thresholds may be any other suitable values as appropriate to specific applications of the invention. For example, the lower threshold may be no greater than 45%, no greater than 50%, no greater than 60%, no greater than 75%,no greater than 80%, no greater than 85%, no greater than 90%, no greater than 95%, or less than 100%, of the total charge capacity of the refrigeration system. The second loss of charge threshold may be, for example, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, or 100%, of a total charge capacity of the refrigeration system.

[0090] Moreover, whilst the controller 500 is configured to perform the pre-ventilation operation by ventilating the refrigerated container 10 for twenty minutes, in other examples, the controller 500 may ventilate the refrigerated container 10 for at least ten minutes, at least twenty minutes, at least thirty minutes, at least forty five minutes, at least sixty minutes, or at least ninety minutes. Similarly, whilst the controller 500 is configured to perform the rupture ventilation operation 655 by ventilating the refrigerated container 10 for two hours, in other examples the rupture ventilation operation 655 may be performed by ventilating the refrigerated container 10 for up to thirty minutes, up to one hour, up to two hours, or more than two hours.

[0091] In some examples, the controller 500 is configured to wait before performing the defrost operation 265. This allows a time period to be provided to determine whether the defrost operation 265 is possible or not. If the defrost operation is not possible for any reason, then the controller 500 may perform a time-out procedure. In the time-out procedure, the controller 500 returns to monitoring 605 the charge data. If the controller 500 subsequently enters the diagnosis sequence of actions 700a again, the controller 500 increases a counter value. If the controller 500 again times out when waiting for the defrost operation 265 to begin, this process is repeated, and the counter value is increased again. When the counter value reaches 3, the controller 500 causes ventilation of the compartment 13 and the storage space 11 in a manner as described above, as a precaution, and also issues a counter alert signal to the display 51 . The display 51 then displays a counter alert, informing an operator that the defrost operation 265 was not possible.

[0092] The process 600 described above involves the controller 500 sending the high- and low- priority alert signals to the display 51 . In other examples, it will be appreciated that the controller 500 may also, or alternatively, transmit the high- and / or low-priority alert signals to any one or more of: a remote server; a computer-readable memory; an audio transducer of the user interaction module 50; and a visual and / or audible beacon associated with the refrigerated container 10. Transmitting the signals to the remote server may cause suitable alerts to be issued by the remote server to remote personnel, such as personnel on the marine vessel 1 during transport of the refrigerated container 10. This may allow remedial action to be taken sooner. Transmitting the signals to the computer-readable memory may cause the signals to be recordedin the memory, such as to record details of the loss of charge and / or the status of the refrigerated container 10 in a log. Transmitting the signal to the audio transducer may cause the audio transducer to issue an audible alert, which may alert personnel local to the refrigerated container 10 of the loss of charge. Similarly, transmitting the signal to the audible and / or visual beacon may cause the beacon to issue an audible and / or visual alert, such as an alarm and / or flashing light, to local personnel, or to remote personnel if the beacon is remote from the refrigerated container. In some examples, the controller 500 is configured to send the low-priority alert signal only to the display 51 , and the high-priority alert signal to the beacon. This may cause the beacon to draw the attention of personnel only in the event of a major rupture or failure of the vent valve 280 that inhibits ventilation. In some examples, the beacon is a combined device which flashes light and emits an audible alarm, and is positioned behind the condenser fan 120 for protection and to reduce unwanted interference. In other examples, the beacon comprises separate audio and visual components and / or could be positioned elsewhere, such as integrated into a door that opens into the storage space 1 1 .

[0093] Finally, it will be appreciated that the present description analogously applies to other types of storage unit, including refrigerated trucks or trailers, and storage units for storing the cargo 15 in in a ripening warehouse or other facility. The cargo 15 in the illustrated example is fresh or frozen produce. This may include respirating and / or ripenable produce, such as fruit and vegetables, and / or non-respirating fresh produce, meat and / or fish. In other examples, the storage unit 10 may be for transporting any other suitable cargo 15, for example medicaments, such as vaccines. It will be appreciated that the cargo 15 may be any other suitable cargo 15, and may advantageously be cargo 15 that requires, or benefits from, being stored in an atmosphere-controlled space.

Claims

CLAIMS:1 . A computer-implemented method comprising: receiving charge data indicative of a loss of charge of refrigerant in a refrigeration system of a refrigerated container; when the charge data is indicative that the loss of charge of refrigerant is at a first level above a first loss of charge threshold and below a second loss of charge threshold, causing performance of a first sequence of actions; and when the charge data is indicative that the loss of charge of refrigerant is at a second level at or above the second loss of charge threshold, causing performance of a second sequence of actions, the second sequence of actions different to the first sequence of actions.

2. The computer-implemented method according to Claim 1 , wherein the first level is indicative of a first priority of remedial action associated with the loss of charge of refrigerant, the second level is indicative of a second priority of remedial action associated with the loss of charge of refrigerant, and the second priority is higher than the first priority.3 The computer-implemented method according to either Claim 1 or Claim 2, wherein the second sequence of actions comprises causing ventilation of an internal space of the refrigerated container.

4. The computer-implemented method according to Claim 3, wherein the second sequence of actions comprises receiving location data indicative of a location of a leakage that is a cause of the loss of charge of refrigerant, and when the location data is indicative that the location of the leakage is within the internal space of the refrigerated container, causing ventilation of the internal space of the refrigerated container.

5. The computer-implemented method according to Claim 4, wherein the second sequence of actions comprises, when the location data is indicative that the location of the leakage is within the internal space of the refrigerated container, causing provision of an internal condition alert indicative of the second level.

6. The computer-implemented method according to Claim 4 or Claim 5, wherein, when the location data is indicative that the location of the leakage is external to the internal space of therefrigerated container, the second sequence of actions comprises causing provision of an external condition alert indicative of the second level.

7. The computer-implemented method according to any one of the preceding claims, wherein the first sequence of actions comprises receiving valve data indicative of an operational state of a ventilation valve that selectively enables fluid communication between an internal space of the refrigerated container and an ambient atmosphere external to the refrigerated container, and a next subsequent action of the first sequence of actions to the receiving valve data is based on the valve data.

8. The computer-implemented method according to Claim 7, wherein when the valve data is indicative that the ventilation valve is non-operational, the next subsequent action of the first sequence of actions is to wait for performance of a defrost operation of the refrigeration system.

9. The computer-implemented method according to either Claim 7 or Claim 8, wherein when the valve data is indicative that the ventilation valve is operational, the next subsequent action of the first sequence of actions is to cause ventilation of the internal space of the refrigerated container.

10. The computer-implemented method according to either Claim 8 or Claim 9, wherein the first sequence of events comprises, following the next subsequent action of the first sequence of actions, causing performance of a defrost operation of the refrigeration system.11 . The computer-implemented method according to Claim 10, wherein the first sequence of events comprises, following the performance of the defrost operation of the refrigeration system, causing performance of a determination of a state of the refrigeration system and causing, based on a determined state of the refrigeration system and based on the valve data, provision of a state alert.

12. The computer-implemented method according to Claim 1 1 , wherein the computer- implemented method comprises, prior to causing performance of a determination of a state of the refrigeration system, causing an increase in a load on a compressor of the refrigeration system.

13. A data carrier comprising machine readable instructions that, when executed, cause operation of one or more processors of a refrigeration system controller of a refrigeration systemof a refrigerated container to perform the computer-implemented method according to any one of the preceding claims.

14. A refrigeration system controller for a refrigeration system of a refrigerated container, the refrigeration system controller configured to perform the computer-implemented method according to any one of Claims 1 to 12.

15. A refrigeration system for a refrigerated container, the refrigeration system comprising the refrigeration system controller according to Claim 14.

16. A refrigerated container comprising the refrigeration system controller according to Claim 14, or the refrigeration system according to Claim 15.

17. A vessel comprising the controller according to Claim 14, or the refrigeration system according to Claim 15, or the refrigerated container according to Claim 16.

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