TECHNICAL FIELD

The present invention relates in general to freight containers and in particular to methods and devices for performance tests of climate-controlled freight containers.

BACKGROUND

Today, transportation of goods worldwide is a huge business, having impact on the daily life of substantially all people around the world. Many products are produced far from the location where they are assumed to be consumed or used, and transportation is therefore crucial. Many products today are sensitive for storage/ transportation times, the environment, and physical exposure of e.g. vibrations or shocks.

Climate-controlled air-freight containers are available since many years. The common basic idea is to produce a climate-controlled flow of air, or other gas, that is entered into the cargo compartment. The cooling action may furthermore be controlled based on different sensor measurements, usually of the temperatures within the systems. For long time, the refrigeration was relying on passive cooling by dry ice, but in recent years, battery-powered refrigeration equipment has become widely used for active cooling.

If a trustable transport of sensitive goods should be performed, there are a lot of different systems that have to work properly. The climate-control units have to operate according to expected performance, the power system has to be charged to a suitable level, the container thermal isolation has to be intact, the distribution of climate-controlled air has to be operable, etc. Ideally, every part or module in a climate-controlled freight container should be controlled before a shipping is initiated, in terms of operability. This could be performed by making tests of every part, either as mounted in the container or demounted therefrom. However, such procedures are far too time consuming for being realistic.

SUMMARY

A general object is to provide efficient and reliable methods and devices for performance checks of climate-controlled freight containers.

The above object is achieved by methods and devices according to the independent claims. Preferred embodiments are defined in dependent claims.

In general words, in a first aspect, a method for testing performance of a climate-controlled freight container comprises cooling down of a cargo compartment of the freight container to a predefined target temperature by use of a cooling system. The cooling system comprises at least two cooling modules. A temperature distribution within the cargo compartment is equalized during a predetermined equalizing period. An individual cooling module test is performed for all the at least two cooling modules, one at a time. The individual cooling module test in turn comprises controlling of the cargo compartment to have a constant temperature during a predetermined period by operating a single cooling module and measuring a power consumption of the single cooling module during the predetermined period.

In a second aspect, a climate-controlled freight container comprises a cargo compartment, a cooling system and a control unit. The cooling system has at least two cooling modules and an air distribution arrangement. The air distribution arrangement is configured to distribute air from the cooling modules around and/or into the cargo compartment and back. The control unit is configured to control an operation of the cooling system. The control unit is configured to instruct the cooling system to cool down the cargo compartment of the freight container to a predefined target temperature. The control unit is further configured to instruct the cooling system to equalize a temperature distribution within the cargo compartment during a predetermined equalizing period. The control unit is further configured to instruct the cooling system to perform an individual cooling module test for all the at least two cooling modules, one at a time. Thereby, as being comprised in the individual cooling module test, the control unit is further configured to instruct the cooling system to operate a single cooling module to control the cargo compartment to have a constant temperature during a predetermined period. The climate-controlled freight container further comprises a power meter, configured to measure a power consumption of the single cooling module during the predetermined period.

One advantage with the proposed technology is an efficient and reliable check of climate-controlled freight containers is provided. Other advantages will be appreciated when reading the detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with further objects and advantages thereof, may best be understood by making reference to the following description taken together with the accompanying drawings, in which:

FIG. 1 illustrates schematically a cross-sectional view of an embodiment of a freight container;

FIG. 2 illustrates a diagram of temperature measurements during an embodiment of a test program;

FIG. 3 illustrates a diagram illustrating an example of a power consumption for the cooling modules during an embodiment of the individual cooling module tests;

FIG. 4 is a flow diagram of steps of an embodiment of a method for testing performance of a climate-controlled freight container;

FIG. 5 is a flow diagram of steps of an embodiment of step S10 of Fig. 4;

FIG. 6 is a flow diagram of steps of an embodiment of step S20 of Fig. 4; and

FIG. 7 is a flow diagram of steps of an embodiment of step S40 of Fig. 4. DETAILED DESCRIPTION

Throughout the drawings, the same reference numbers are used for similar or corresponding elements.

In the following, embodiments of air-freight containers are described. However, even though the present ideas are of most benefit for air freight, the same approaches are also operational for other types of freight containers. Thus, in one preferred embodiment, the freight container is an air-freight container.

For a better understanding of the proposed technology, it may be useful to begin with a discussion of features that are important to consider during testing. First, it can be concluded that the different units and modules have to operate correctly, as they are. Moreover, they also have to operate correctly together, and together with the freight container structure. Most ideally, they also should operate correctly in the interaction with the goods to be transported. However, since there typically is no time or possibility available to make performance tests when the goods have been loaded into the container, tests have to be performed on either empty containers or containers having a dummy load.

This insight has led to the development of a testing scheme for performance of a climate-controlled freight container that comprises at least three phases, and preferably at least four phases. Such a testing scheme will be presented further below. However, in order to have a better idea of how the actual freight container may look like, we will start to briefly present a climate-controlled freight container on which the testing scheme is intended to be operable.

Figure 1 illustrates an embodiment of a climate-controlled flight container 10 in a cross-sectional view. The climate-controlled flight container 10 is defined by a casing 12. The casing 12 encloses a cargo compartment 20 and a control compartment 26. The casing 12 comprises a floor 16, a ceiling 14 and walls 18. The cargo compartment 20 and a control compartment 26 are separated by a partition wall 28.

The climate-controlled flight container 10 also comprises a cooling system 30. The cooling system 30 has in the present embodiment three cooling modules 40, of which one is visible in the figure. However, in other embodiments, the number of cooling modules 40 can be different, but at least two. This gives a higher maximum cooling effect and provides a redundancy if one of the cooling modules 40 fails. The cooling system 30 further comprises an air distribution arrangement 21, which is configured to distribute air from the cooling modules around and/or into the cargo compartment and back. The cooling system 30 is thereby configured for controlling a temperature of the cargo compartment 20 by providing a flow 100 of temperature-controlled air around and/or into the cargo compartment 20 by means of the air distribution arrangement 21. The air distribution arrangement 21 is in this embodiment constituted by the inner parts of the casing and some deliberately provided flow-directing components. The flow 100 of temperature-controlled air is in this embodiment provided in vicinity of the ceiling 14 of the cargo compartment 20.

In this particular embodiment, the distribution of the flow 100 of temperature- controlled air is supported by an upper gas-flow distributer plate 22. The flow 100 of temperature-controlled air is here directed to the space between the ceiling 14 and the upper gas-flow distributer plate 22. The upper gas-flow distributer plate 22 does not cover all the distance to the walls and leaves openings for climate-conditioned gas to flow 108 into the main cargo compartment. Likewise, there is in this particular embodiment also a side gasflow collector plate 24, placed with a small distance to the partition wall 28 separating the cargo compartment 20 from the control compartment 26. Gas leaving the cargo compartment 20 flows beneath the edge of the side gas-flow collector plate 24 and upwards along the partition wall 28 as a return air-flow The control compartment 26 has a cooling module support with three mounting positions, one for each cooling module 40. Three cooling modules 40 are mounted in the cooling module support. Each cooling modules 40 in operation receives air through an input port 42 and provides an air-flow 102 going out from the climate module 40 through an output port 44.

The cooling system 30 comprises or is associated with a surveillance system comprising at least one internal temperature sensor 53A-C arranged for measuring a temperature inside the cargo compartment 20 and/or in an airflow to 104 and/or from 102 the cargo compartment.

In the present embodiment, first internal temperature sensors are placed at different locations in the cargo compartment and may therefore be denotated as cargo compartment temperature sensors 53A. In the present embodiment, two cargo compartment temperature sensors 53A are placed at the side wall 18, two cargo compartment temperature sensors 53 A are placed at the side gas-flow collector plate 24 and one cargo compartment temperature sensor 53A is placed at an edge of the upper gas-flow distributer plate 22. A second internal temperature sensor 53B is placed in the gas-flow 102 going out from the climate control system 30. A third internal temperature sensor 53C is placed in the gas-flow 104 going into the cooling system 30. In other embodiments, other combinations of internal temperature sensors may be provided. A control unit 50 is configured to control an operation of the cooling system 30.

In order to have a thorough control of the cooling operation and the general function of the freight container, a test program is performed. The test program has at least three stages and preferably at least four stages.

A first stage is a pull-down stage. This stage comprises cooling down of the cargo compartment of the freight container to a predefined target temperature by use of a cooling system. This stage preferably starts with the temperature of the cargo compartment being essentially equal to an ambient temperature. Preferably, all cooling modules are operated simultaneously and with a setting for achieving a maximum cooling effect. The pull-down is temperature controlled and the internal temperature sensors are used for achieving the temperature information during this stage. Preferably, a set temperature for the cooling modules is set a couple of degrees lower than the target temperature. The set temperature should be low enough to trig a maximum cooling.

A typical example of temperature measurements during a test program is illustrated in Figure 2. The cool-down stage 201 is illustrated as the first part of the test program. In this particular example, the test program is run on a freight container having 8 internal temperature sensors within the cargo compartment and two additional temperatures sensors for measuring an external or ambient temperature. The curves 211-218 illustrate the different readings of the individual internal temperature sensors, whereas curves 219- 220 indicates the time evolution of the measurements of the two external temperature sensors. The cool-down stage starts at time tO and at time tl, the target temperature, which in this particular case was set to 5.3°C, was reached.

Preferably, the pull-down process is monitored, as in the above discussed figure. A cooling-down time is then measured. The cooling-down time is simply defined as the time from a start of the cooling system until the predefined target temperature is reached. In the example of Figure 2, the cooling-down time is determined to be t _C d = tl - tO. This cooling-down time gives a first indication of the condition of the freight container.

In a preferred embodiment, the cooling-down stage further comprises indicating of a general operation error warning as a response to a coolingdown time exceeding a predetermined limit value. The cooling-down time may give a first hint about if there are any operational errors of the cooling modules and/or if there are any major thermal isolation problems in the freight container.

In a preferred embodiment, a temperature outside the cargo compartment is also measured. This measure can be an estimate of the original cargo compartment temperature and an estimate of the prevailing ambient temperature. Since the cooling-down time at least to a part depends on the original cargo compartment temperature as well as on the prevailing ambient temperature, the predetermined limit value associated with the cool-down stage for indicating a general operation error warning is determined in dependence of the measured outside temperature. However, the detailed reasons for the possible error may be difficult to conclude, since a long cooldown time may depend on several independent factors.

A second stage of the test program is an equalization stage. This stage starts at tO when the pull-down stage is ended or soon after, as illustrated by the reference number 202 in Figure 2. A first reason for running the equalization stage is to provide a freight container with an as uniform temperature distribution as possible, as a preparation for later stages. A second reason for the equalization stage is that it offers possibilities to detect any errors in the air distribution system or local defects in the thermal isolation of the freight container.

In the example illustrated in Figure 2, the equalization stage is performed with only one active cooling module. This insures that the cooling action will be essentially uniform during the equalization stage, removing any possible differences between different cooling modules. The temperatures within the container cargo compartment will stabilize, but since there are some material within the cargo compartment that has to gain the same temperature, this process may take some time. However, eventually, a temperature equilibrium has been established at time t2. In the present example, the target temperature around which this stabilization takes place was selected to 5°C. As mentioned above, the results of the equalization stage may also preferably be used for diagnosing purposes. In a preferred embodiment the equalizing of a temperature distribution within the cargo compartment in turn comprises monitoring temperatures within the cargo compartment during the predetermined equalizing period. The temperatures are measured at at least two different locations within the cargo compartment. More preferably, more temperature sensors are used. In the present example of Figure 2, eight different sensors measuring the internal temperature are used.

In Figure 2, it can be seen that there are some differences in readings between the different temperature sensors, i.e. between the curves 211-218. If these differences are small, as is the case in the diagram of Figure 2, this indicates a homogeneous distribution of the cooled air within the cargo compartment. A seen in Figure 2, all temperatures are typically within 1-2 °C from each other, which has to be considered as an admitted variation. From Figure 2, it can also be seen that the temperatures vary more in the beginning of the equalizing stage but become stable after a certain time. This initial transient course is caused by the cooling of the interior parts of the cargo compartment. If the tests are preformed with cargo in the cargo compartment, this transient time will be much longer.

Indications of possible errors in the freight container functions may be found in different way. If there is some malfunctioning part in the air distribution system, e.g. blocked channels, non-efficient fans or missing distributor or collection plates, an even distribution of the temperature within the cargo compartment may very well be obtained, but the time until this equilibrium state is reached may take longer time than expected for a well operating system. Also, if the thermal isolation of the freight container is not intact, e.g. if there exist local defects in the isolation material or if the door is not properly sealed when being shut. Vacuum isolated panels (VIP) are today often used for thermal isolation purposes and unfortunately it is not uncommon that such panels are damaged during transport handling of the freight container. A punctured wall will lose a significant part of its isolating properties. Such local defects in the thermal isolation will probably result in an equilibrium condition where different parts of the cargo compartment present somewhat differing temperatures.

Therefore, in one embodiment, the monitoring of the temperatures further comprises determination of a highest temperature difference between temperatures at the at least two locations at an end of the predetermined equalizing period. If this difference is large, this may indicate that there are some local isolation problems.

In another alternative or complementing embodiment, the monitoring further comprises determining of a duration of a transient time until the temperatures at the at least two locations reaches a steady-state temperature. The transient time thus indicates the time when the cargo compartment still is not in an equilibrium state, but where changes in temperatures still are occurring. Long transient times may indicate some problems in the air distribution system.

Preferably, for both embodiments above, they are followed by a possible error indication, if deviations from the normal behavior is detected. In other words, the monitoring further comprises indication of a suspected air distribution failure and/or local isolation damage as a response to that the highest temperature difference exceeds a predetermined value and/or the transient time exceeds a predetermined time limit.

When the cargo compartment of the freight container has reached the equilibrium state at the end of the equalization stage at t2, the third stage is started. In this third, individual module test stage 203, an individual cooling module test is performed for all cooling modules, one at a time. By making these tests sequentially, the operation of each individual cooling module can be distinguished. A difference in performance between the different individual cooling modules can thereby be detected. In a preferred embodiment, the performance test will be based on energy consumption that is necessary for the cooling modules to maintain a constant temperature. The individual cooling module test thus in turn comprises controlling of the cargo compartment to have a constant temperature during a predetermined period by operating a single cooling module. A power consumption of the single cooling module is measured during this predetermined period.

In the particular tests illustrated in Figure 2, the predetermined time for each cooling module to operate on its own was set to 30 minutes. However, other durations can also be used.

The monitoring of the power consumption is preferably also followed up. To this end, in a preferred embodiment, the individual cooling module test further comprises evaluation of a variance in power consumption for each individual cooling module, as illustrated by the short, dotted lines.

This evaluation may be performed in different ways. One possibility is to calculate a total power consumption for each individual cooling module, as well as an average power consumption for all cooling modules. If the different cooling modules all are operating according to the expectations, all individual cooling modules should have essentially the same power consumption and therefore also the same power consumption as the average over all modules.

In one embodiment, the individual cooling module test further comprises indicating of a suspected cooling module failure in a first cooling module as a response to that the variance in power consumption of the first cooling module exceeds a predetermined value and / or that the total power consumption for the first cooling module differs from the average power consumption by more than a predetermined fraction.

By such a procedure, it may be possible to detect the existence and identity of a malfunctioning cooling device. The modular design of the cooling system then makes it easy to simply exchange this failing cooling module for a welloperating one before an actual shipping is made.

It is an advantage that the individual cooling module test is planned to take place in the test program just after the equalization stage, since the individual cooling module tests then are initiated from well-defined conditions.

In Figure 2, the temperature readings during the individual module test stage are constant, which is a first proof of that all cooling modules are operating well enough to meet the requirements of keeping the temperatures constant. However, it is the power consumption readings that will reveal any minor problems. Figure 3 illustrates such power consumption 221-223 for the cooling modules during the individual cooling module tests. As can be seen, all cooling modules have essentially the same power consumption, indicating that they all are operating in a same way, and then also probably in the expected manner.

Returning back to Figure 2, there is also a fourth stage 204; a pull-up stage. This stage is not absolutely necessary to perform, but since no additional cooling operations or additional hardware is needed, it is preferred to also include this fourth stage into the test program.

The pull-up stage is basically a passive test of the isolation performance inside the container. At time t3, the cooling action of the cooling modules is shut down, however, the fans for distributing air into the container, which typically are situated in the cooling modules, are operated at a medium rate, sufficient to maintain the equalized temperature distribution within the cargo compartment. The container will passively warm up due to the heat conduction through the walls. This passive warming-up of the cargo compartment is then monitored, by following the temperature readings from the internal temperature sensors. As seen in Figure 2, the warming up process starts with a rapid increase, which successively will be slower and eventually the temperature inside the cargo compartment will reach the ambient temperature. The rate with which the temperature increases gives information about the total thermal isolation of the freight container. Any damaged VIP or any leaking door etc., will contribute to the temperature increase. In particular, the initial warming-up rate will be strongly influenced by any isolation fault. Typically, the first 1-2 hours are the most important to monitor.

In one embodiment, the monitoring further comprises indication of a suspected cargo compartment isolation failure as a response to an initial warming-up rate exceeding a predetermined limit value.

As in the case of the pull-down stage, the temperature rise in the pull-up stage will be dependent on the ambient temperature, at least to certain degree. Therefore, in a preferred embodiment, the monitoring further comprises measuring of a temperature outside the cargo compartment. The predetermined limit value is then determined in dependence of the measured temperature.

Besides the test scheme stages described here above, additional stages can be added. It is, however, important that the performing of the individual cooling module tests starts from a well-characterized temperature distribution within the cargo compartment.

The performance test described above could be performed by manually initiated operations. However, since all procedures are easily performed in an automated way, the performance test could easily be provided as a preprogrammed test procedure. Since the total test takes some time to perform, the automated tests could by advantage be performed during the night.

Figure 4 is a flow diagram of steps of an embodiment of a method for testing performance of a climate-controlled freight container. In step S10, a cargo compartment of the freight container is cooled down to a predefined target temperature by use of a cooling system. The cooling system comprises at least two cooling modules.

In one preferred embodiment, as illustrated in Figure 5, the step S10 of cooling down a cargo compartment in turn comprises the step S12, in which a coolingdown time from a start of the cooling system until the predefined target temperature is reached is measured. In a further preferred embodiment, in step S16, a general operation error warning is indicated as a response to a cooling-down time exceeding a limit value.

In one further preferred embodiment, the step S10 of cooling down a cargo compartment further also comprises the step S14, in which a temperature outside the cargo compartment is measured. By doing this, the limit value of step S16 can be determined in dependence of this measured temperature.

Returning to Figure 4, in step S20, a temperature distribution within the cargo compartment is equalized during a predetermined equalizing period.

In one preferred embodiment, as illustrated in Figure 6, the step S20 of equalizing a temperature distribution within the cargo compartment in turn comprises the step S22, in which temperatures at at least two locations within the cargo compartment are measured during the predetermined equalizing period. Prefer ably, in step S24. a highest temperature difference between temperatures at the at least two locations at an end of the predetermined equalizing period is determined. Preferably, in step S26, a duration of a transient time until the temperatures at the at least two locations reache a steady-state temperature is determined. Preferably, in step S28, a suspected air distribution failure is indicating as a response to the results of at least one of steps S24 and S26. One of the criteria, based on the results of step S24 is that the highest temperature difference exceeds a predetermined value. The other criteria, based on step S26, is that the transient time exceeds a predetermined time limit. Returning to Figure 4, in step S30, an individual cooling module test for all the at least two cooling modules are performed, one at a time. The individual cooling module test in turn comprises step S32, in which the cargo compartment is controlled to have a constant temperature during a predetermined period by operating a single cooling module. The individual cooling module test also comprises step S34, in which a power consumption of the single cooling module is measured during the predetermined period.

In one preferred embodiment, individual cooling module test S30 further comprises step S36, in which a variance in power consumption is evaluated for each individual cooling module. In one preferred embodiment, individual cooling module test S30 further comprises step S37, in which a total power consumption for each individual cooling module is calculated, as well as an average power consumption for all cooling modules. Preferably, the individual cooling module test S30 further comprises step S38, in which a suspected cooling module failure in a first cooling module is indicatied as a response to at least one of two criteria. A first criteria, based on the results of step S36, is that the variance in power consumption of the first cooling module exceeds a predetermined value. The other criteria, based on the results of step S37, is that the total power consumption for the first cooling module differs from the average power consumption by more than a predetermined fraction.

In a preferred embodiment, the method for testing performance of a climate- controlled freight container comprises the further step S40, in which a passive warming-up of the cargo compartment is monitored.

In a further preferred embodiment, as illustrated in Figure 7, the step S40 of monitoring comprises the further step S44, in which a suspected cargo compartment isolation failure is indicated as a response to an initial warming- up rate exceeding a limit value. Preferably, in step S42, a temperature outside the cargo compartment is measured. Thereby, the limit value in step S44 may be determined in dependence of that measured temperature. As for the physical implementation allowing the test schedule to be performed, preferably autonomously, Figure 1 is again referenced. As was mentioned above, a control unit 50 is configured to control an operation of the cooling system 30. This control unit 50 can also be utilized for managing the test schedule.

To this end, the control unit 50 is configured to instruct the cooling system 30 to cool down the cargo compartment 20 of the freight container 10 to a predefined target temperature. The control unit 50 is further configured to instruct the cooling system 30 to equalize a temperature distribution within the cargo compartment during a predetermined equalizing period. The control unit 50 is further configured to instruct the cooling system 30 to perform an individual cooling module test for all the at least two cooling modules, one at a time. The control unit 50 being further configured, as comprised in the individual cooling module test, to instruct the cooling system 30 to operate a single cooling module to controlling the cargo compartment to have a constant temperature during a predetermined period. The freight container 10 further comprises a power meter 80. The power meter is configured to measure a power consumption of the single cooling module during the predetermined period. This can be achieved by having one power meter 80 per cooling module, measuring the power consumption of just that cooling module. However, it is also feasible to have one power meter 80 measuring the total power consumption of all cooling modules. Since the cooling modules are operated sequentially, the power consumption of each individual cooling module can be distinguished. The power meter 80 is communicationally connected to the control unit 50.

Preferably, the control unit 50 is further configured to evaluate a variance in power consumption for each individual cooling module measured by the power meter. Preferably, the control unit 50 is further configured to calculate a total power consumption for each individual cooling module, as well as an average power consumption for all cooling modules. Preferably, the control unit 50 is further configured to indicate a suspected cooling module failure in a first cooling module as a response to that the variance in power consumption of the first cooling module exceeds a predetermined value and / or that the total power consumption for the first cooling module differs from the average power consumption by more than a predetermined fraction.

In one preferred embodiment, the control unit 50 is further configured to monitoring a passive warming-up of the cargo compartment 20. Preferably, the control unit 50 is further configured to indicate, during or after the monitoring, a suspected cargo compartment isolation failure as a response to an initial warming-up rate exceeding a limit value.

In a preferred embodiment, the freight container 10 further comprises a temperature meter 82, configured for measuring a temperature outside the cargo compartment 20. In this embodiment, the temperature meter 82 is located within the control compartment 26, which is believed to follow the ambient temperature relatively close. Alternatively or as a complement, a temperature meter 82 may also be provided outside the casing 12. Preferably, such outside temperature meters are recessed into the outer surface of the freight container 10 in order to avoid transport damages. The temperature meter 82 is communicationally connected to the control unit 50. Thereby, the control unit 50 may determine the limit value used for evaluating the warming-up rate in dependence of the measured temperature outside the cargo compartment 20.

As was described above, first internal temperature sensors 53A are placed at different locations in the cargo compartment 20. At least two such cargo compartment temperature sensors 53A are provided. Thereby, temperatures at at least two locations within the cargo compartment can be measured during the predetermined equalizing period. The cargo compartment temperature sensors 53A are communicationally connected to the control unit 50. Therefore, preferably, the control unit 50 is further configured to determine a highest temperature difference between temperatures at the at least two locations at an end of the predetermined equalizing period. Preferably, the control unit 50 is further configured to determine a duration of a transient time until the temperatures at the at least two locations reaches a steady-state temperature. Preferably, the control unit 50 is further configured to indicate a suspected air distribution failure as a response to that the highest temperature difference exceeds a predetermined value and / or that the transient time exceeds a predetermined time limit.

In one preferred embodiment, the control unit 50 is further configured to measure a cooling-down time from a start of the cooling system until the predefined target temperature is reached. Preferably, the control unit 50 is further configured to indicate a general operation error warning as a response to a cooling-down time exceeding a limit value. If the freight container 10 has a temperature meter 82 configured for measuring a temperature outside the cargo compartment, this limit value may be determined in dependence of the measured temperature outside the cargo compartment.

In one aspect of the present technology, it is also possible to use the pull-up stage as a main performance test. This pull-up stage has by necessity to follow a pull-down stage, with or without any failure analysis. Preferably, also an equalizing stage precedes the pull-up stage in order to ensure a homogeneous temperature distribution within the cargo compartment.

In other words, one embodiment of a method for testing performance of a climate-controlled freight container comprises the steps of cooling down a cargo compartment of the freight container to a predefined target temperature by use of a cooling system and- monitoring a passive warming-up of the cargo compartment. Preferably, the method additionally comprises the step of indicating a suspected cargo compartment isolation failure as a response to an initial warming-up rate exceeding a first limit value. Also preferably, the step of monitoring further comprises measuring of a temperature outside the cargo compartment, whereby the first limit value is determined in dependence of the measured temperature. Analogously, an embodiment of a climate-controlled freight container comprises a cargo compartment, a cooling system and a control unit. The cooling system has at least one cooling module and an air distribution arrangement, configured to distribute air from the cooling module(s) around and / or into the cargo compartment and back. The control unit is configured to control an operation of the cooling system. The control unit is configured to instruct the cooling system to cool down the cargo compartment of the freight container to a predefined target temperature. The control unit is further configured to monitoring a passive warming-up of the cargo compartment. Preferably, the control unit is further configured to, during or after the monitoring, indicate a suspected cargo compartment isolation failure as a response to an initial warming-up rate exceeding a first limit value. Also preferably, the climate-controlled freight container further comprises a temperature meter, configured for measuring a temperature outside the cargo compartment. The first limit value can then be determined in dependence of the measured temperature.

The embodiments described above are to be understood as a few illustrative examples of the present invention. It will be understood by those skilled in the art that various modifications, combinations and changes may be made to the embodiments without departing from the scope of the present invention. In particular, different part solutions in the different embodiments can be combined in other configurations, where technically possible. The scope of the present invention is, however, defined by the appended claims.