SURVEILLANCE OF A PLURALITY OF REFRIGERATED CONTAINERS AND DETERMINATION OF AN INSULATION PARAMETER OF A REFRIGERATED CONTAINER

Abstract

A method is disclosed herein of managing a plurality of refrigerated containers (2), the method comprising the step of surveilling the insulation condition of said containers (2) by repeatedly determining an insulation parameter (Uact, Ucur) of each of the plurality of refrigerated containers (2). Furthermore is disclosed a method to determine an insulation parameter (U.sub.act) of a refrigerated container (2), the method comprising at least the steps of—determining a refrigeration effect (Q.sub.Ref) caused by a refrigeration unit refrigerating the container (2), —calculating an actual rate of energy loss of the container (2) due to heat ingress from the ambient surroundings, —determining an actual temperature difference (ΔT) between the interior (8) of the container (2) and the ambient air, and—determining the actual insulation parameter (U.sub.act) of the container (2) from the ratio of said actual rate of energy loss and said actual temperature difference.

Claims

1. A method of managing a plurality of refrigerated containers, the method comprising the step of surveilling the insulation condition of said containers by repeatedly determining an insulation parameter of each of the plurality of refrigerated containers, wherein the insulation parameter of each of the plurality of containers is determined by means of the set point temperature of that container, the ambient temperature of that container and an energy consumption of that container.

2. The method according to claim 1, further comprising the step of ranking the plurality of containers for suitable use thereof based on the determined insulation parameter or a model insulation parameter of the container.

3. The method according to claim 1, further comprising the step of identifying which of the plurality of containers need maintenance based on the determined insulation parameter or a model insulation parameter of the container.

4. The method according to claim 1, further comprising the step of determining of the placement of each of said plurality of containers in a ship based on the determined insulation parameter or a model insulation parameter.

5. The method according to claim 1, further comprising the step of estimating the lifetime of each container based on the determined insulation parameter or a model insulation parameter of the container.

6. (canceled)

7. (canceled)

8. A method to determine an insulation parameter of a refrigerated container, the method comprising the steps of determining a refrigeration effect caused by a refrigeration unit refrigerating the container, calculating an actual rate of energy loss of the container due to heat ingress from the ambient surroundings, determining an actual temperature difference between the interior of the container and the ambient air, and determining the actual insulation parameter of the container from the ratio of said actual rate of energy loss and said actual temperature difference.

9. The method according to claim 8, where the method of determining an actual insulation parameter is repeatedly performed over time and a current insulation parameter of the container is found from said determined actual insulation parameters of the container.

10. (canceled)

11. The method according to claim 8, further comprising the steps of: determining a difference in insulation parameter between the determined insulation parameter and a model insulation parameter for the container, and updating the model insulation parameter for the container using the determined insulation parameter.

12. (canceled)

13. (canceled)

14. The method according to claim 8, wherein the refrigeration effect released by the refrigeration unit is determined from a current rotational speed and a current intermittence time of a compressor of the refrigeration unit.

15. The method according to claim 8, wherein the refrigeration effect released by the refrigeration unit is determined using at least one of the following parameters: a suction pressure at the inlet of the compressor, and a discharge pressure from the compressor.

16. The method according to claim 8, wherein a consumed power of evaporator fan or fans of an evaporator of the refrigeration unit is calculated and said consumed power is applied to calculating the actual rate of energy loss through the insulated outer walls of the container.

17. The method according to claim 16, wherein a supply voltage and a supply frequency of the evaporator fan or fans are applied to calculating the consumed power of the evaporator fan or fans.

18. The method according to claim 8, wherein the actual insulation parameter is determined when the container is operated in frozen mode at a temperature set point of the interior of the container of ≤−5° C.

19. The method according to claim 8, wherein the actual insulation parameter is determined between defrost cycles of an evaporator of the refrigeration unit and is initiated when the temperature of the interior of the container has been determined to be stable after defrosting of the evaporator.

20. The method according to claim 8, further comprising the step of identifying that the container needs maintenance based on the determined insulation parameter the model insulation parameter of the container.

21. (canceled)

22. (canceled)

23. The method according to claim 8, further comprising the step of estimating the lifetime of a container based on the determined insulation parameter or the model insulation parameter of the container.

24. A method of estimating a respiration rate of chilled, respiring commodities stored in a refrigerated container having insulated outer walls, the method comprising the steps of: determining an insulation parameter of the insulated outer walls of the container by means of the method according to claim 8, determining a refrigeration effect released by a refrigeration unit refrigerating the container, determining an actual temperature difference between the interior the container and the ambient air, calculating an actual rate of energy loss through the insulated outer walls of the container from said insulation parameter and said actual temperature difference, and estimating the respiration rate from said determined refrigeration effect and the calculated actual rate of energy loss.

25. The method according to claim 24, wherein said commodities comprise one or more of: fresh fruits, vegetables, bulbs, live plants and cut flowers.

26-29. (canceled)

30. The method according to claim 24, wherein the respiration rate is estimated when the container is operated at a temperature set point of the interior of the container in the range of −1° C., to 20° C.

31. (canceled)

32. (canceled)

Description

[0069] Examples of how the present disclosure may be carried out are illustrated in the enclosed drawing of which

[0070] FIG. 1 is a perspective cutaway view of a part of an insulated wall of a refrigerated container,

[0071] FIG. 2 is a cross-section of a refrigerated container, and

[0072] FIG. 3 is a flow chart illustrating the process of determining the insulation parameter of the container and employing it for various purposes.

[0073] The insulated wall 1 of a refrigerated container 2 may typically comprise the layers shown in FIG. 1, where on the outside of the container 2 a corrugated steel sheet 3 provides the outermost layer. On the inside, an inner layer 4 is provided made from e.g. aluminium sheets or glass fibre reinforced polymer sheets. Optionally, a plywood layer 5 may be provided under the inner layer 4. Between the outer layer 3 and the inner layer 4, an insulating material 6 such as insulating foam of polyurethane and vertical U-shaped steel beams 7 connecting the inner 4 and outer layers 3 of the container.

[0074] In the cross-section of a refrigerated container 2 shown in FIG. 2, the temperature T.sub.box inside the container and T.sub.ambient are indicated. At the storage space 8 inside the container 2, the commodities to be refrigerated are to be kept. The atmosphere in the storage space 8 is cooled by means of the evaporator 12 delivering the refrigeration effect Q.sub.Ref by evaporation of the liquid refrigerant received from the compressor 13. The evaporator fans 9 drive a flow of air from the storage space 8 of the container 2 and past the evaporator 12 in order to cool the air, which is returned to the storage space 8. The amount of water condensing at the evaporator 12 is determined by the condensation sensor 11.

[0075] Air exchange between the surroundings of the container 2 and the storage space 8 inside the container for the purpose of controlling the content of the atmosphere inside the container in the storage space 8, in particular the CO.sub.2 contents, is controlled by means of the fresh air ventilators 10.

[0076] A controller 14 is arranged to control the operation of the various parts of the equipment in the refrigerated container 2.

[0077] An example of how the methods disclosed herein is provided below with reference to the flow chart in FIG. 3. The insulation parameter U of the standard refrigerated intermodal container is from the manufacturing of the new container known to have a value of 43 W.Math.K±1. When the container is operated for storing of commodities that have a temperature set point for storage of e.g. −18° C. or less, the actual insulation parameter U.sub.act is determined in step 15. At such low temperatures, the stored commodities do not generate heat from respiration and the fresh air ventilators 10 are not operated. The actual insulation parameter U.sub.act is determined between defrost cycles at a time where the temperature T.sub.box inside the storage space 8 is stable.

[0078] The refrigeration effect Q.sub.Ref of the evaporator 12 may be calculated from the mass flow of refrigerant multiplied by the difference between the specific enthalpy of the refrigerant before it reaches the evaporator and the specific enthalpy of the refrigerant after leaving the evaporator.

[0079] The electric effect Q.sub.evaporator_fans consumed by the evaporator fans 9 and the electrical effect Q.sub.internal_electrical_consumed consumed by other minor equipment in the container 2 are determined in order to be able to determine the heat balance for the container and thereby the rate of heat inflow Q.sub.heat_ingress into the container 2:

Q.sub.heat_ingress=Q.sub.Ref−Q.sub.evaporator_fans−Q.sub.internal_electrical_consumed

[0080] With the measurement of the temperature T.sub.box inside the storage space 8 and of the ambient temperature T.sub.ambient, the temperature difference can be determined

ΔT=T.sub.ambient−T.sub.box

[0081] The actual insulation parameter U.sub.act for the container can now be determined from the following:

U.sub.act=Q.sub.heat_ingress/ΔT

[0082] However, since the specific circumstances for determining the actual insulation parameter for the container, are subject to variations, it is advantageous to determine the actual insulation parameter U.sub.act for the container repeatedly over time, i.e. over weeks or months, and based on those values determine a current value for the insulation parameter U.sub.cur for the container from a moving average value of the determined actual insulation parameters in step 16. A model value of the insulation parameter for the container 2 is stored in the controller 14 of the container 2, starting with the factory standard of 43 W.Math.K from new and may be updated when a current insulation parameter has been determined in step 17.

[0083] The updated model insulation parameter may be employed to determine the best use of the container and to decide for repair (step 20) in case the insulation parameter U.sub.model exceeds a threshold value of e.g. 65 W.Math.K or even scrapping of the container as discussed previously. Also, the updated model insulation parameter U.sub.model may be used to rank the container for use, such as deep freezing of commodities for low values of U.sub.model or chilling of commodities at temperatures above 0° C. for containers of higher values of U.sub.model, see step 22, or for determine the most suitable containers for particular placement in a ship in step 23. Also, the expected lifetime of the container may be reevaluated, see step 21. However, an important use of the updated model insulation parameter U.sub.model for the container is to calculate a precise estimate of the respiration heat generated by chilled commodities stored in the refrigerated container, i.e. commodities such as fresh fruits, vegetables, bulbs, live plants and cut flowers, which are stored at temperatures where respiration takes place and heat, CO.sub.2 and water vapour are generated in accordance with the formulas provided above in step 19. The heat balance for the container is calculated with the purpose of determining the respiration heat rate Q.sub.respiration and for that, the updated model insulation parameter U.sub.model for the container is used together with the temperature difference ΔT to determine the heat ingress Q.sub.heat_ingress.

[0084] Thus, the full heat balance equation for a refrigerated container with chilled commodities with respiration and ventilation is:

Q.sub.Ref=Q.sub.evaporator_fans+Q.sub.internal_electrical_consumed+Q.sub.heating elements+Q.sub.respiration+Q.sub.condensation+Q.sub.ventilation+Q.sub.heat_ingress

[0085] Q.sub.Ref may be calculated from the mass flow of the refrigerant as discussed previously, alternatively it may be determined from data for the rotational speed of the compressor, the current intermittence time of the compressor, often combined with the suction pressure at the inlet of the compressor and/or the discharge pressure from the compressor.

[0086] Q.sub.evaporator_fans is the consumed power of the evaporator fans 9.

[0087] Q.sub.internal_electrical_consumed is consumed power of inside located electrical consumers for instance gas sensors, power electronics etc.

[0088] Q.sub.heating elements is the consumed electrical power of heating elements placed inside the container.

[0089] Q.sub.condensation is found from the mass flow of water vapour condensated inside the container as determined by the condensation sensor 11 and the specific latent heat of water, i.e. the specific enthalpy of vaporization.

[0090] Q.sub.ventilation is found from the ventilation rate, the temperature difference ΔT and the specific heat capacity for air.

[0091] Q.sub.heat_ingress may be determined from the temperature difference ΔT and the model insulation parameter U.sub.model.

[0092] Q.sub.respiration can then be found, which generally provides information about the present condition of the commodities, and more specifically can be used to determine the rate of generation of CO.sub.2 from the respiration as discussed previously, which may be employed in step 24 to control the ventilation rate of the interior storage space 8 of the container 2.