Defrost operation in refrigerated containers

Abstract

A computer-implemented method includes calculating an amount of ice formed on at least part of a refrigeration system of a refrigerated container, and causing, when the amount of ice is greater than a pre-determined threshold, performance of an action.

Description

Defrost Operations in Refrigerated ContainersTECHNICAL FIELD

[0001] The present invention relates to a computer implemented method, a data carrier, a refrigeration system controller, a refrigeration system, a refrigerated container, and a vessel.BACKGROUND

[0002] Cargo is often stored and transported in transport containers. Refrigerated transport containers 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 containers include TEU or 2-TEU containers designed to be shipped on container vessels, and / or refrigerated trucks or trailers.SUMMARY

[0003] According to a first aspect of the present invention, there is provided a computer- implemented method comprising: calculating an amount of ice formed on at least part of a refrigeration system of a refrigerated container; and causing, when the amount of ice is greater than a pre-determined threshold, performance of an action.

[0004] During use of a refrigeration system of a refrigerated container, for example such as a refrigerated shipping container, ice may accumulate on parts of the refrigeration system. Such accumulation of ice can have a detrimental effect on operation of the refrigeration system. It has previously been proposed to perform actions, such as a defrost operation of the refrigeration system, to remove accumulated ice. However, such defrost operations are typically either simply implemented periodically after a pre-determined time period has elapsed, or are implemented in response to temperature sensor data.

[0005] Where defrost operations are implemented periodically after a pre-determined time period has elapsed, unnecessary defrost operations may be caused to occur, which can result in increased energy and / or fuel consumption. This may also have a detrimental effect on cargo contained within the refrigerated container. Similarly, where defrost operations are implemented solely in response to temperature sensor data, transience in temperature sensor data due to other ambient environmental factors can cause unnecessary defrost operations to occur.P24-054PCT1

[0006] By calculating the amount of ice, and causing, when the amount of ice is greater than the pre-determined threshold, performance of the action, more accurate performance of the action may be achieved in comparison to previously proposed methods.

[0007] The computer-implemented method may comprise causing, when the amount of ice is equal to the pre-determined threshold, performance of the action.

[0008] The amount of ice may comprise a mass of ice formed on the at least part of the refrigeration system of the refrigerated container.

[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. The computer-implemented method may comprise the processor calculating the amount of ice. The computer-implemented method may comprise the processor causing performance of the action. Causing performance of the action may comprise the processor issuing one or more instructions that cause performance of the action by another component of the refrigeration system and / or another component of the refrigerated container. In such cases, issuance of instruction(s) by the processor can be considered an action. The action may be performed by the processor, for example with an internal decision-making process of the processor comprising an action.

[0010] The action may comprise a defrost operation of the refrigeration system.

[0011] The defrost operation of the refrigeration system may comprise increasing an operating temperature of the at least part of the refrigeration system, for example to cause ice formed on the at least part of the refrigeration system to melt. The defrost operation of the refrigeration system may comprise increasing an operating temperature of an evaporator of the refrigeration system.

[0012] The action may comprise issuing an alert, for example to an operator of the refrigerated container or an operator of a vessel on which the refrigerated container is located. The alert may be indicative of at least one of the amount of ice, that the defrost operation is required to be performed, and that the defrost operation is currently being performed. The alert may comprise at least one of an audible alert, a visual alert, and a digital alert stored in a log. The audible alertP24-054PCT1and / 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 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.

[0013] The computer-implemented method may comprise: obtaining relative humidity data indicative of a relative humidity within the refrigerated container; and calculating the amount of ice based on the relative humidity data.

[0014] The computer-implemented method may comprise receiving, from a relative humidity sensor located within the refrigerated container, for example within a cargo storage space of the refrigerated container, the relative humidity data. The computer-implemented method may comprise calculating, based on the relative humidity data, a dew point temperature within the refrigerated container. The computer-implemented method may comprise calculating the amount of ice based on the dew point temperature.

[0015] The calculating may comprise calculating an amount of ice formed on an evaporator of the refrigeration system.

[0016] The computer-implemented method may comprise: obtaining return temperature data indicative of a temperature of gas returned to the evaporator from a cargo storage space of the refrigerated container; and calculating the amount of ice based on the return temperature data.

[0017] The computer-implemented method may comprise receiving, from a return temperature sensor located upstream of the evaporator, the return temperature data. The computer- implemented method may comprise calculating, based on the return temperature data, the dew point temperature.

[0018] The computer-implemented method may comprise: obtaining supply temperature data indicative of a temperature of gas supplied from the evaporator to the cargo storage space of the refrigerated container; and calculating the amount of ice based on the supply temperature data.

[0019] The computer-implemented method may comprise receiving, from a supply temperature sensor located downstream of the evaporator, the supply temperature data. The supplyP24-054PCT1temperature data may be indicative of a supply temperature of gas supplied from the evaporator into the cargo storage space of the refrigerated container.

[0020] The computer-implemented method may comprise: calculating, based on the supply temperature data and the return temperature data, a humidity ratio differential between a first humidity ratio associated with return gas returned to the evaporator and a second humidity ratio associated with supply gas supplied from the evaporator; and calculating the amount of ice based on the humidity ratio differential.

[0021] The first humidity ratio may be indicative of an amount of water vapour contained within the return gas. The second humidity ratio may be indicative of an amount of water vapour contained within the supply gas. The humidity ratio differential may comprise a humidity ratio difference between the first humidity ratio and the second humidity ratio.

[0022] The computer-implemented method may comprise calculating the humidity ratio differential based on at least one of the return temperature data, the supply temperature data, the dew-point temperature, and the relative humidity data.

[0023] The computer-implemented method may comprise: calculating, based on the humidity ratio differential, a condensation rate of water within the refrigerated container; and calculating the amount of ice based on the condensation rate of water.

[0024] The computer-implemented method may comprise calculating the condensation rate of water based on at least one of a mass flow rate of dry air within the refrigerated container, a volumetric flow rate of dry air within the refrigerated container, a fan speed of an evaporator fan of the refrigeration system, a supplied power to the refrigeration system, and a density of dry air within the refrigerated container. The computer-implemented method may comprise receiving, from a memory, at least one of the volumetric flow rate of dry air within the refrigerated container, the fan speed of the evaporator fan, the supplied power to the refrigeration system, and the density of dry air.

[0025] The computer-implemented method may comprise: obtaining supplementary data indicative of at least one current operational parameter of the refrigeration system and / or the refrigerated container; and causing, when the amount of ice is greater than the pre-determinedP24-054PCT1threshold and when the supplementary data is indicative of the current operational parameter varying from an expected operational parameter, performance of the action.

[0026] The current operational parameter may comprise any one or more of a temperature of the evaporator, a suction gas temperature at a low side of a compressor of the refrigeration system a temperature differential between the return gas and the supply gas, and a running speed of the compressor of the refrigeration system. The expected operational parameter may comprise an operational parameter that would be expected if there were ice-build up below an ice threshold value on the at least part of the refrigeration system. The computer-implemented method may comprise determining whether the temperature of the evaporator is below the pre-determined threshold. The computer-implemented method may comprise receiving, from an evaporator temperature sensor, the evaporator temperature sensor data.

[0027] The computer-implemented method may comprise: receiving saturated temperature data indicative of a saturated temperature of refrigerant within the refrigeration system; and calculating the amount of ice based on the saturated temperature data.

[0028] The computer-implemented method may comprise calculating the humidity ratio differential based on the saturated temperature data. The saturated temperature data may be determined based on a measured saturated pressure of refrigerant within the refrigeration system. The saturated temperature data may be indicative of a saturated temperature of refrigerant within the evaporator.

[0029] The computer-implemented method may comprise: obtaining dew point data indicative of a dew point temperature within the refrigerated container; and calculating the amount of ice based on the dew point data.

[0030] The computer-implemented method may comprise calculating, based on the return temperature data, the dew point data. The computer-implemented method may comprise calculating, based on the relative humidity data, the dew point data.

[0031] The computer-implemented method may comprise calculating, based on the dew point data, the humidity ratio differential.P24-054PCT1

[0032] The computer-implemented method may comprise calculating the amount of ice in realtime, for example during use of the refrigeration system within the refrigerated container, for example during a cooling operation performed by the refrigeration system. The computer- implemented method may comprise dynamically updating the amount of ice, for example at a predetermined sampling interval.

[0033] According to a second aspect of the present invention there is provided 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 system of a refrigerated container to perform the computer-implemented method according to the first aspect of the present invention.

[0034] According to a third aspect of the present invention there is provided a refrigeration system controller for a refrigeration system of a refrigerated container, the refrigeration system controller comprising one or more processors configured to perform a computer-implemented method according to the first aspect of the present invention.

[0035] According to a fourth aspect of the present invention there is provided a refrigeration system for a refrigerated container, the refrigeration system comprising the refrigeration system controller according to the third aspect of the present invention.

[0036] The refrigeration system may comprise an evaporator. The evaporator may be located within a cargo storage space of the refrigerated container. The refrigeration system may comprise any one or more of a relative humidity sensor, a return temperature sensor, a supply temperature sensor, and an evaporator temperature sensor. The relative humidity sensor may be configured to sense a relative humidity within a cargo space of a refrigerated container refrigerated by the refrigeration system. The return temperature sensor may be configured to sense a temperature of gas returned to the evaporator from the cargo storage space. The supply temperature sensor may be configured to sense a temperature of gas supplied from the evaporator into the cargo storage space. The evaporator temperature sensor may be configured to sense a temperature of the evaporator coil.

[0037] The refrigeration system controller may be located locally to the refrigerated container, for example on or in the refrigerated container. The refrigeration system controller may be locatedP24-054PCT1remotely from the refrigerated container, for example elsewhere on board a vessel on which the refrigerated container is located, or remote from the vessel, such as on shore.

[0038] According to a fifth aspect of the present invention there is provided 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.

[0039] The refrigerated container may be an intermodal container, or refrigerated truck or trailer, such as for transporting a cargo.

[0040] According to a sixth aspect of the present invention there is provided a vessel 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, or the refrigerated container according to the fifth aspect of the present invention.

[0041] Optional features of aspects of the present invention may be equally applied to other aspects of the present invention, where appropriate.BRIEF DESCRIPTION OF DRAWINGS

[0042] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0043] Figure 1 is a schematic view of a marine vessel;

[0044] Figure 2 is a schematic view of a refrigerated container carried by the marine vessel;

[0045] Figure 3 is a flow diagram illustrating a first example method; and

[0046] Figure 4 is a flow diagram illustrating a second example method.DETAILED DESCRIPTION

[0047] 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 one of the intermodal shipping containers 2 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 theP24-054PCT1storage space 11 , 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 relative humidity sensor 222, 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, a discharge pressure sensor 250, and an evaporator temperature sensor 260.

[0048] The cargo 12 in the storage space 11 is respiring produce. The storage space 11 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 11. 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, and a display 51 with which a user can interact.

[0049] 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 11. The evaporator 140, the evaporator fan 141 , the supply and return temperature sensors 210, 220, and the evaporator temperature sensor 260, 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 second region 15a, and the return temperature sensor 220 is located in the first region 14a. 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 110 and the condenser 120. The relative humidity sensor 222 is located within the storage space 11. 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.P24-054PCT1

[0050] 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.

[0051] The controller 500 is communicatively coupled to the compressor 110, the expansion valve 130, the condenser and evaporator fans 121 , 141 , the supply and return temperature sensors 210, 220, the relative humidity sensor 222, the suction temperature and pressure sensors 230, 240, the discharge pressure sensor 250, and the evaporator temperature sensor 260. 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 11. 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.

[0052] The controller 500 sends a signal to the motor of the compressor 110 to operate the compressor 110 at a given speed. This causes the compressor 110 to provide refrigerant in the form of a high-pressure, high-temperature discharge gas to the condenser 120 (“high” being relative to refrigerant flowing through the evaporator 140). The temperature of the refrigerant is reduced in the condenser 120 through (latent) heat exchange with the external atmosphere. The controller 500 sends a signal to operate the condenser fan 121 , to move the external atmosphere over the coils and fins of the condenser 120. This enhances the rate of heat transfer between the refrigerant and the external atmosphere.

[0053] 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 the refrigerant in a liquid phase and provides the liquid refrigerant to the expansion valve 130. TheP24-054PCT1liquid 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 a signal to operate the evaporator fan 141 to move an atmosphere from the first region 14a across the coils and fins of the evaporator 140 to the second region 15a. This leads to a reduction in pressure in the first region 14a, and an increase in pressure in the second region 15a. This, in turn, causes air to be passed as return air from the storage space 11 into the first region 14a through the first opening 14, across the evaporator 140 into the second region 15a, and as supply air from the second region 15a into the storage space 11 through the second opening 15. 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 11.

[0054] 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 a signal from the supply and return temperature sensors 210, 220, the relative humidity sensor 222, the suction temperature and pressure sensors 230, 240, the discharge pressure sensor 250, and the evaporator temperature sensor 260, to control operation of the refrigeration system 100 to provide a particular set temperature, as will be discussed in further detail hereinafter. In some examples, the controller 500 is configured to provide a set temperature difference between the supply and return air temperature sensed by the supply and return temperature sensors 210, 220. This is by sending a signal to the compressor 110 to increase or decrease a load on the compressor 110. The controller 500 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 230, 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.

[0055] The refrigeration system 100 is operable by the controller 500 in a defrost mode of operation. In the defrost mode, the controller 500 sends a signal to the expansion valve 130 to close the expansion valve 130, and sends a signal to the hot gas bypass valve 145 to cause the hot gas bypass valve 145 to open. Closing the expansion valve 130 prevents refrigerant from 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 pointP24-054PCT1downstream of the compressor 110 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 11. In other examples, an electric heater may be located under the evaporator 140, with the electric heater used to melt ice that may have built-up on the evaporator 140. It will be appreciated that such an electric heater may be used additionally to, or alternatively to, the hot gaseous refrigerant being passed through the evaporator 140.

[0056] 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.

[0057] 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.

[0058] Operations of the controller 500 will now be described in more detail. It will be appreciated that the controller 500 includes at least one processor that is configured to perform operations based on instructions stored in non-transient memory.

[0059] In some examples, the controller 500 causes a defrost mode of operation, such as the defrost mode operation described above, to be performed based on an amount of ice that has formed on the evaporator 140. In particular, the controller 500 calculates an amount of ice formed on the evaporator 140, and when the amount of ice is above a threshold value, the controller 500 issues instructions to control the expansion valve 130 and the hot gas bypass valve 145 in the manner described above. The calculation takes place in real-time, whilst the refrigeration system 100 is performing a cooling operation.P24-054PCT1

[0060] To calculate the amount of ice formed on the evaporator 140, the controller 500 receives data from the return air temperature sensor 220 and the relative humidity sensor 222, and calculates a dew point temperature of the storage space 11 .

[0061] The controller 500 calculates a first humidity ratio (of g of water vapour per kg of dry air) based on the dew point temperature. The controller 500 calculates a second humidity ratio (of g of water vapour per kg of dry air) based on a saturated temperature (To) of refrigerant in the refrigeration system 100. The controller 500 then uses the first and second humidity ratios to calculate a humidity ratio differential.

[0062] The controller 500 calculates a density of dry air within the storage space 11 and calculates a volumetric flow rate of dry air within the storage space 11 . The controller 500 calculates a mass flow rate of dry air within the storage space, and calculates a condensation rate of water in the refrigerated container 10. When a surface of the evaporator 140 is cold enough, then the condensation rate of water is equivalent to a build-up rate of ice, and ice forms on the surface of the evaporator 140. The controller 500 can then calculate an amount of ice forming over time.

[0063] When the current amount of ice formed on the surface of the evaporator 140 is over a predetermined threshold value of ice, the controller 500 causes the defrost mode of operation described above to be performed. By calculating the amount of ice, and causing, when the amount of ice is greater than the pre-determined threshold, performance of the defrost mode of operation, more accurate performance of the defrost mode of operation may be achieved in comparison to previously proposed methods.

[0064] For example, where defrost operations are implemented periodically after a predetermined time period has elapsed, unnecessary defrost operations may be caused to occur, which can result in increased energy and / or fuel consumption. This may also have a detrimental effect on cargo contained within the refrigerated container 10. Similarly, where defrost operations are implemented solely in response to temperature sensor data, transience in temperature sensor data due to other ambient environmental factors can cause unnecessary defrost operations to occur.

[0065] A first example method 600 in accordance with the above is illustrated schematically in the flow diagram of Figure 3. The first example method 600 includes calculating 602 an amountP24-054PCT1of ice formed on the evaporator 140, and causing 604, when the amount of ice is greater than or equal to a pre-determined threshold, performance of a defrost operation. When the amount of ice is less than the pre-determined threshold, the controller 500 continues to monitor the build-up of ice and recalculates in the manner described above.

[0066] It will be appreciated that, in other examples, additional or alternative actions may be performed when the calculated amount of ice is greater than the pre-determined threshold value. In some examples, the controller 500 may cause issuance of an alert to an operator of the refrigerated container 10 or an operator of the marine vessel 1. The alert may be indicative of at least one of the amount of ice, that the defrost operation is required to be performed, and that the defrost operation is currently being performed. The alert can be any of an audible alert, a visual alert, and a digital alert stored in a log. For example, the alert may be displayed at the user interaction module 50 via the display 51 .

[0067] In some examples, the pre-determined threshold can be 12kg of ice formed on the surface of the evaporator 140. An additional criterion may be that the controller 500 cannot trigger the defrost mode of operation if less than a certain period, such as 2.5 hours, has passed since a previous defrost mode of operation. In some examples, the operator may be allowed to trigger a defrost mode of operation (this may be referred to as a defrost on demand operation) where the calculated amount of ice is over a temperature dependent threshold value, for example by utilising the user interaction module 50. The temperature dependent threshold value may be 2.5kg when the return gas temperature is less than -5 degrees Celsius, and may be 4kg when the return gas temperature is greater than -5 degrees Celsius. The operator may be inhibited from triggering the defrost mode of operation when less than 2.5 hours has passed since a previous defrost mode of operation.

[0068] In some examples, the operator may be allowed to trigger the defrost mode of operation where the calculated amount of ice is over 60% of a threshold limit, more than 2.5 hours has passed since a previous defrost mode of operation, the compressor speed is more than 30% above a calculated average stable speed in a stable period, a deforest mode of operation has been run between turn on of the refrigeration system 100 and the current time, and the defrost mode of operation has been run since a last change of temperature set point and the current time.

[0069] From the above, it will be appreciated that other operational parameters can be utilised alongside the calculated ice amount for the defrost mode of operation to be enabled. SuchP24-054PCT1operational parameters can include any of a temperature of the evaporator 140, a suction gas temperature at a low side of the compressor 110, a temperature differential between the return gas and the supply gas, and a running speed of the compressor 110. In such examples, the current operational parameter can be compared to an expected operational parameter, and when both the calculated amount of ice is above the pre-determined threshold value, and the current operational parameter doesn’t meet the expected operational parameter, a defrost operation can be performed. The expected operational parameter is an operational parameter that would be expected if there were ice-build up below the pre-determined threshold value on the evaporator 140.

[0070] In some examples, additionally or alternatively to causing a defrost mode of operation to be performed based on the calculated amount of ice, the controller 500 operates to ensure the cargo 12 is stored in the storage space 11 at a desired relative humidity value.

[0071] To achieve this, the controller 500 receives a desired relative humidity value, with the desired relative humidity value input via the user interaction module 50. The controller 500 receives data from the return air temperature sensor 220 and the relative humidity sensor 222, and calculates a dew point temperature of the storage space 11.

[0072] The controller 500 calculates a temperature differential between the actual relative humidity and the desired relative humidity. The controller 500 then uses the temperature differential to calculate the desired evaporation temperature of the refrigeration system 100.

[0073] Once the controller 500 has the desired evaporation temperature, the controller 500 controls the refrigeration system 100 such that the current relative humidity moves toward, and then matches, the desired relative humidity value. This is achieved by reducing a surface temperature of the evaporator 140 such that water condenses, or freezes if the temperature is low enough, on the surface and is removed from the air within the refrigerated container 10. It will be appreciated that if, as a result, there is sufficient ice build-up on the surface of the evaporator 140, then the controller 500 can cause performance of the defrost mode of operation, as discussed above.

[0074] By actually determining the desired evaporation temperature based on the desired relative humidity, instead of simply decreasing the evaporation temperature until the desired relative humidity is reached, increased accuracy of relative humidity within the refrigerated container 10P24-054PCT1may be achieved. This may, in turn, lead to improved cargo storage, and less wastage of cargo compared to other methods where cargo has been stored at an incorrect or undesirable relative humidity.

[0075] A second example method 700 in accordance with the above is illustrated schematically in the flow diagram of Figure 4. The second example method 700 includes obtaining 702 a desired relative humidity value indicative of a desired relative humidity within the cargo storage space 11. The second example method 700 includes determining 704, based on the desired relative humidity value, a desired evaporation temperature of the refrigeration system 100. The second example method 700 includes controlling 706, based on the desired evaporation temperature, the refrigeration system 100.

[0076] Although described above with the controller 500 located on the refrigerated container 10, it will be appreciated that in some examples the controller 500 may instead be located remotely from the refrigerated container 10. In such examples, the calculations discussed herein may be performed remotely from the refrigerated container 10, for example at a bridge of the marine vessel 1. This may allow for increased processing power and relatively simplicity at the refrigerated container 10. Additionally, or alternatively, the controller 500 may obtain at least one of the calculated values above from memory, instead of calculating the value in real-time. For example, any of the density of dry air, the volumetric flow rate of dry air, and the mass flow rate of dry air, may be obtained by the controller 500 from memory.

[0077] Furthermore, whilst particular threshold values have been mentioned above, it will be appreciated that in practice such thresholds may vary. For example, thresholds may vary depending on any of a type of refrigerant in the refrigeration system 100, a size of the evaporator 140, and a type of the cargo 12.

[0078] 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.P24-054PCT1

Claims

CLAIMS:

1. A computer-implemented method comprising: calculating an amount of ice formed on at least part of a refrigeration system of a refrigerated container; and causing, when the amount of ice is greater than a pre-determined threshold, performance of an action.

2. The computer-implemented method according to Claim 1 , wherein the action comprises a defrost operation of the refrigeration system.

3. The computer-implemented method according to Claim 1 or Claim 2, wherein the computer-implemented method comprises: obtaining relative humidity data indicative of a relative humidity within the refrigerated container; and calculating the amount of ice based on the relative humidity data.

4. The computer-implemented method according to any one of Claims 1 to 3, wherein the calculating comprises calculating an amount of ice formed on an evaporator of the refrigeration system.

5. The computer-implemented method according to Claim 4, wherein the computer- implemented method comprises: obtaining return temperature data indicative of a temperature of gas returned to the evaporator from a cargo storage space of the refrigerated container; and calculating the amount of ice based on the return temperature data.

6. The computer-implemented method according to Claim 5, wherein the computer- implemented method comprises: obtaining supply temperature data indicative of a temperature of gas supplied from the evaporator to the cargo storage space of the refrigerated container; and calculating the amount of ice based on the supply temperature data.

7. The computer-implemented method according to Claim 6, wherein the computer- implemented method comprises:P24-054PCT1calculating, based on the supply temperature data and the return temperature data, a humidity ratio differential between a first humidity ratio associated with return gas returned to the evaporator and a second humidity ratio associated with supply gas supplied from the evaporator; and calculating the amount of ice based on the humidity ratio differential.

8. The computer-implemented method according to Claim 7, wherein the computer- implemented method comprises: calculating, based on the humidity ratio differential, a condensation rate of water within the refrigerated container; and calculating the amount of ice based on the condensation rate of water.

9. The computer-implemented method according to any one of Claims 4 to 8, wherein the computer-implemented method comprises: obtaining supplementary data indicative of at least one current operational parameter of the refrigeration system and / or the refrigerated container; and causing, when the amount of ice is greater than the pre-determined threshold and when the supplementary data is indicative of the current operational parameter varying from an expected operational parameter, performance of the action.

10. The computer-implemented method according to any one of Claims 1 to 9, wherein the computer-implemented method comprises: receiving saturated temperature data indicative of a saturated temperature of refrigerant within the refrigeration system; and calculating the amount of ice based on the saturated temperature data.

11. The computer-implemented method according to any one of Claims 1 to 10, wherein the computer-implemented method comprises: obtaining dew point data indicative of a dew point temperature within the refrigerated container; and calculating the amount of ice based on the dew point data.

12. 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 systemP24-054PCT1of a refrigerated container to perform the computer-implemented method according to any one of Claims 1 to 11.

13. A refrigeration system controller for a refrigeration system of a refrigerated container, the refrigeration system controller comprising one or more processors configured to perform the computer-implemented method according to any one of Claims 1 to 11.

14. A refrigeration system for a refrigerated container, the refrigeration system comprising the refrigeration system controller according to Claim 13.

15. A refrigerated container comprising the refrigeration system controller according to Claim13, or the refrigeration system according to Claim 14.

16. A vessel comprising the refrigeration system controller according to Claim 13, or the refrigeration system according to Claim 14, or the refrigerated container according to Claim 15.P24-054PCT1

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