WO2016000750A1 - Procédé de réduction de formation de glace dans une unité de refroidissement - Google Patents

Procédé de réduction de formation de glace dans une unité de refroidissement Download PDF

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Publication number
WO2016000750A1
WO2016000750A1 PCT/EP2014/063881 EP2014063881W WO2016000750A1 WO 2016000750 A1 WO2016000750 A1 WO 2016000750A1 EP 2014063881 W EP2014063881 W EP 2014063881W WO 2016000750 A1 WO2016000750 A1 WO 2016000750A1
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Prior art keywords
defrost
evaporator
return air
frost
ice
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PCT/EP2014/063881
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English (en)
Inventor
Leijn Johannes Sjerp Lukasse
Original Assignee
A.P. Møller A/S
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Publication date
Application filed by A.P. Møller A/S filed Critical A.P. Møller A/S
Priority to PCT/EP2014/063881 priority Critical patent/WO2016000750A1/fr
Publication of WO2016000750A1 publication Critical patent/WO2016000750A1/fr

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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
    • F25D21/00—Defrosting; Preventing frosting; Removing condensed or defrost water
    • F25D21/002—Defroster control
    • F25D21/006—Defroster control with electronic control circuits
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
    • F25D21/00—Defrosting; Preventing frosting; Removing condensed or defrost water
    • F25D21/002—Defroster control
    • F25D21/008—Defroster control by timer

Definitions

  • the present invention relates to a method, a system and a plant for reducing or avoiding ice formation in containers such as intermodal freight containers and the like.
  • the invention relates to a method, a system and a plant for reducing or avoiding ice formation in a cooling unit used to cool a refrigerated storage space container during so-called frozen mode operation.
  • a refrigerated container or a so-called reefer container is a shipping container used for freight transport.
  • the container is cooled or refrigerated for the transportation of temperature- sensitive cargo.
  • a typical reefer container consists of a refrigerated transport volume in connection with a cooling unit that typically relies on external electric power supply.
  • Frozen mode operation of a reefer container is operation at a temperature set point below -5 °C. It is normal that in frozen mode operation at least some frost accumulates on the evaporator.
  • the evaporator is the part of the refrigeration system in which the refrigerant absorbs heat and thereby cools air forced over or through the evaporator. Therefore a defrost controller is provided that periodically interrupts cooling operation to defrost the evaporator or the evaporator coil.
  • a defrost controller normally has two decision moments. The first decision moment is when to initiate a period of defrost operation, i.e. when to initiate the defrost period, and the second decision moment is when to terminate the period of defrost operation, i.e. when to terminate the defrost period.
  • Two situations which may occur in frozen mode operation are the formation of ice on one or more faces of the floor underneath the cargo space, i.e. in the supply air duct, and/or the formation of frost on components in the cooling space above or upstream the evaporator.
  • this space above or upstream the evaporator houses the return air grid, which is arranged to separate the cooling machinery space from the cargo space or transport volume.
  • the return air grid may be susceptible to formation of frost or ice, which formation in turn gives rise to flow wise problems that need to be addressed.
  • the first situation of ice accumulation on the floor underneath the cargo space or transport volume i.e.
  • a conceivable solution to the problem of accumulating ice on the air ducts or elsewhere would be to simply supply heat to locations where ice may accumulate. Ice primarily tends to accumulate on the floor of the refrigerated transport container and on melt water collection guides provided on the inner walls of the cooling space.
  • a solution to the problem of accumulating ice could be to avoid ice formation by supplying sufficient amounts of heat to the mentioned locations during defrost cycles. However, supply of heat to the mentioned locations would then require installation of heating elements in the location where ice is observed to accumulate to a problematic level, i.e. primarily in or close to the supply air duct region.
  • US patent 6,672,086 discloses a frosting cooler that on purpose supplies fog to the cooler. This is done with the object to create and maintain frost on cold products, such as bottles of a beverage stored in the cooler. By this is provided a visual manifestation of the cold condition of the beverage, which is meant to be highly attractive for thirsty consumers.
  • the cooler has the ability to deliver moisture to the products within the cooler so that frosting may be produced in environments where there is low humidity in the ambient air without freezing the liquid contained by the bottle.
  • the cooler is operated to control and to protect the frost on the products, once formed.
  • the document discloses a design which prevents frost formation on objects in the air flow pathway between the product volume and the evaporator by just omitting or repositioning those components.
  • the mentioned specification does not describe a return air grid. Secondly it places the one or more evaporator fans such that air first hits the evaporator coil and then the fan, which is an effective way to avoid frost formation on the fan, though it leads to reduced refrigeration capacity and increased energy consumption.
  • the first problem to be solved is how to prevent formation of ice underneath the cargo space or transport volume, i.e. in the supply air duct.
  • the second problem to be solved is how to prevent formation of frost or ice on components in the cooling space above or upstream the evaporator, and in particular on the return air grid.
  • Another problem to be solved by the present invention is ice accumulation on the floor in the reefer machinery space.
  • the method includes the steps of:
  • predefined indicators to predetermined conditions related to temperature and/or time, where the predetermined conditions represent conditions in which substantially all frost and/or ice has melted from a return air grid 42 positioned in the return air flow in between the transport volume 45 and a cooling space 41, and
  • a multi-purpose refrigerated transport container that is suited to carry temperature-sensitive cargo may also be used for the transportation of a very moist load in frozen mode without risk of damaging the cargo and without requiring any hardware modifications.
  • the return air grid 42 as well as the supply air duct 46 in a standard refrigerated container are not visible and not easily accessible once the container is filled with cargo. This is why the formation of frost and ice in those locations can neither easily be seen nor mechanically removed.
  • the supply air duct underneath the cargo space is only accessible through the transport volume. Therefore the procedure to salvage what is left of the cargo in the kind of situations which are addressed by the present invention, if the situation is noticed at all, is to first break the customs seal at the door locks, open the doors and then repack the cargo into another refrigerated container, and sort out the customs-related paper work due to change of refrigerated container identification number and new customs seal.
  • the abovementioned highly undesirable procedure can be avoided.
  • the avoidance of this procedure is highly desirable by all stakeholders involved in the shipment of frozen cargo in a refrigerated transport container.
  • it is sometimes attempted to unload at least part of the cargo and then try to remove the accumulated ice and frost mechanically. Obviously it is impossible to do when the container is stowed in a cargo hold, typically in-between cell guides, on board a container vessel.
  • the method for defrost termination control includes application of predetermined conditions that, empirically or not, represent conditions in which substantially all frost and/or ice has melted also from the at least one evaporator fan 10 and/or from the evaporator 16 and/or from all other components above or upstream the evaporator 16 and/or from anyone of a return air temperature sensor 5 and a defrost temperature sensor 17 arranged inside the cooling space 41.
  • the method for defrost termination control includes determining one or both of the predefined indicators, which is temperature, by a temperature sensor preferably arranged at the height of the at least one evaporator fan or above or, alternatively or not, by a temperature sensor positioned in the cooling space optionally at a position higher than the highest point of the evaporator or, as a further alternative, by at least one temperature sensor arranged on either side of the return air grid 42.
  • a protective recess may be provided in the inner wall or ceiling of the refrigerated transport container so as to house a temperature sensor when positioned on the transport volume side of the return air grid.
  • This recess offers protection to the temperature sensor, so as to facilitate simplified and efficient loading or related management of the refrigerated transport container without running the risk of damaging or even destroying sensitive measurement equipment. In particular, this is of value when one or more temperature sensors are housed on the transport volume side of the return air grid 42.
  • the protective function of the recess can be utilised on either sides of the return air grid 42 or anywhere in the refrigerated transport container where measurement equipment is to be installed.
  • the method for defrost termination control may utilise that one of the predefined indicators may be time elapsed since start of defrost.
  • This indicator has the benefit of providing a further option of terminating a defrost and/or controlling the effects that a defrost has on frost and/or ice melting from essential components in a refrigerated transport container.
  • further advantages of the indicator are related to the option of measuring temperature as a function of elapsed time according to the below.
  • the method for defrost termination control may include that one of the predefined indicators may be a function of temperatures logged since defrost initiation. This has the benefit of providing a further option of terminating a defrost after that an indication can be determined that represent conditions in which substantially all frost and/or ice has melted from other components than only the evaporator.
  • the method for defrost termination control comprises the step of: automatically controlling whether to terminate a defrost when substantially all frost and/or ice has melted from an evaporator 16 or from a return air grid 42 positioned in the return air flow in between the transport volume and a cooling space 41.
  • This has the advantage of avoiding unnecessarily long defrost periods, while reducing or even eliminating the need for manual input and assistance, and thus the need for an operator.
  • a container such as an intermodal shipping container, provided with means for defrosting according to the present application is provided.
  • the present invention provides a method and means for addressing the root cause of the problem of ice formation instead of just trying to counter the effects of the ice formation. Alleviating the root cause of the problem of ice formation in a refrigerated transport container requires complete understanding of a chain of events that leads to the ice formation.
  • the sequence of steps leading to ice formation in a refrigerated transport container is as follows: in a fourth step, the supply air duct 46 ices up, after in a third step the one or more melt water collection guides 21 ice up, after frost is still melting when defrost cycles terminate in a second step, after this frost first accumulated in locations above the evaporator in a first step.
  • the locations above the evaporator in particular, but not exclusively, concern the return air grid 42.
  • the previously mentioned chain of events does usually not occur in frozen mode shipments, but nevertheless, incidentally it does and then oftentimes with considerable detrimental effects. It especially occurs, as mentioned, in shipments with a very moist load, such as brine frozen fish, in particular brine frozen tuna, which still needs to be cooled down after loading, so as not to deteriorate during transportation.
  • the here proposed solution calls upon prolonged defrost cycles and relying on natural convection, i.e. the fact that hot air rises, to transport heat applied to the evaporator further up into the unit, and only terminate defrost cycles when substantially all frost accumulated in locations above the evaporator, including the return air grid, has melted. This explains the targeting especially to the second step in the chain of events mentioned above.
  • the method according to the present invention enables a selection of cases where it is necessary to call upon prolonged defrost cycles as follows: either an operator sets an input to the controller at the start of a shipment with very moist load which still needs to be cooled down after loading cargo into the container or an automated algorithm detects the need for a prolonged defrost cycle.
  • This automated detection could be based on observed abnormal behaviour of the refrigeration unit, one of these abnormal behaviours being the detection of remarkably rapid frost formation on the evaporator, resulting in a need for unusually frequent defrosting.
  • Such remarkably rapid frost formation leaves behind particular patterns that can be detected by various detection techniques, including measurement of return air
  • Figure 1 schematically illustrates a simplified longitudinal sectional view of a refrigerated transport container in accordance with an aspect of the present disclosure.
  • Figure 2 illustrates a return air temperature trajectory of a defrost cycle where the return air grid is frosted at the start of the cycle.
  • Figure 3 illustrates a flow chart of the method according to the present disclosure for reducing or avoiding formation of ice.
  • Figure 4 illustrates a flow chart of a method to automatically control when to apply existing defrost termination methods to terminate when all frost has melted from the evaporator (here called 'evaporator defrosts') and when to apply the prolonged defrost according to the present disclosure to terminate a defrost when substantially all frost has melted from the return air grid (here called 'return air grid defrosts').
  • ice indicates frozen water, a brittle transparent crystalline solid.
  • frost is meant small white or bright crystals formed when water vapour deposits from water-saturated air. Frost is formed when solid surfaces are cooled to below the so-called dew point of the adjacent air as well as below the freezing point of water. A flow of warm air melts ice much slower than frost due to the much smaller surface to volume ratio of ice.
  • the present disclosure is generally referring to a standard refrigerated transport container, and the mentioned features are normally present in standardised refrigerated containers irrespective of type.
  • the construction of other typical cooling units or refrigeration units used in connection with refrigerated transport containers may differ in some respects without departing from the scope of the claims related to this invention.
  • FIG. 1 a simplified longitudinal sectional view of a refrigerated space is schematically illustrated in the form of a refrigerated transport container.
  • FIG 1 illustrates an example of a refrigerated transport container 1 comprising a front section having a cooling or refrigeration unit or system 40 and a load/cargo section or transport volume 45.
  • the transport volume 45 of the refrigerated transport container 1 comprises a commodity load e.g. comprising a plurality of stackable transport cartons or crates 35 arranged within the transport volume 45 such as to leave appropriate clearance at a ceiling and a floor structure for sufficient air flow passages above and beneath the commodity load.
  • the cooling unit 40 in this example comprises a so-called vapour compression refrigeration circuit and a cooling space 41.
  • the refrigeration circuit comprises at least a compressor 6, a condenser 7 with one or more condenser fans 9, an expansion device or throttle valve 8, an evaporator 16 with one or more evaporator fans 10.
  • the compressor 6 and the condenser 7 with the one or more condenser fans 9 are typically situated outside the insulated enclosure of the transport container 1.
  • the evaporator 16 may also comprise a so-called defrost temperature sensor 17 measuring the temperature of the external surface of the evaporator 16.
  • the cooling space 41 is situated inside the insulated enclosure of the refrigerated transport container 1.
  • the cooling space 41 is normally separated from the transport volume 45 by a panel.
  • the upper part of the panel includes a so-called return air grid 42, which is perforated.
  • a return air flow 50 is drawn from the transport volume 45 into the cooling space 41.
  • a supply air flow 55 is expelled into the transport volume 45 through the supply air duct 46, situated in the lower end of the cooling space 41.
  • the air flow through the cooling space is maintained by one or more evaporator fans 10.
  • one or more evaporator fans 10 circulate air through the cooling space 41 and the transport volume 45.
  • a return air grid 42 marks the entrance for air from the transport volume 45 into the cooling space 41.
  • air successively passes a return air grid 42, the return air temperature sensor 5, the air-flow- maintaining one or more evaporator fans 10, the evaporator coil 16 with in or right on top of it the defrost temperature sensor 17, possibly one or more electric heater elements 20, the defrost melt water collection guides 21, and supply air temperature sensor(s) 25 situated in the supply air duct, after which air is supplied to the T-bar floor of the refrigerated transport volume 45.
  • Defrost temperature sensor 17 measures the air-side surface temperature of the evaporator or a representative thereof.
  • the return air grid 42 has a precautionary function to avoid that objects, e.g. loose packaging materials or human fingers, hit the rotating evaporator fans during operation.
  • the one or more defrost melt water collection guides 21 are situated underneath the evaporator 16 and the possible heating unit 20.
  • This defrost melt water collection guide 21 comprises a sequence of drain gutters or drip trays, collecting defrost melt water dripping off the evaporator or parts in the cooling space above the evaporator and guiding it to a so-called drain pan, which at the lower-end has an opening connected to the drain line, through which melt water is then expelled to the outside of the container.
  • a control system comprises a programmed microprocessor or equivalent, which controls amongst others the compressor 6 and the heating unit 20 in accordance with a control algorithm defined by a set of microprocessor program instructions.
  • the control system may additionally comprise a user interface, for example an LCD display and a keypad, where an operator or ship technician can enter or modify certain parameter values of the control algorithm such as a set point temperature of the refrigerated transport container 1, to mention only one parameter among a plurality of variable parameters.
  • a user interface for example an LCD display and a keypad, where an operator or ship technician can enter or modify certain parameter values of the control algorithm such as a set point temperature of the refrigerated transport container 1, to mention only one parameter among a plurality of variable parameters.
  • Frozen mode operation is, as mentioned, operation at a set point of -5 °C or colder. It is normal that in frozen mode operation some frost accumulates on the evaporator. Therefore a defrost controller periodically interrupts cooling operation with a defrost cycle to defrost the evaporator coil. For one defrost cycle a defrost controller has two decision moments: when to initiate a defrost period and when to terminate a period of defrost operation.
  • control system When the control system indicates a need to start a defrost cycle it stops the evaporator fan or fans 10. It also stops the supply of liquid refrigerant to the evaporator 16 through the expansion device 8. Moreover, it starts the supply of heat to the evaporator through either the possibly present heating unit 20 and/or by changing the refrigerant flow path in such a way that hot refrigerant gas leaving the compressor 6 is lead to flow into the refrigerant side of evaporator 16.
  • Common defrost termination logics aim to terminate a period of defrost operation right after all frost has melted off the evaporator ('evaporator defrost'). Typically this is achieved by applying two termination criteria, terminating a defrost cycle when at least one of them is met.
  • the two usual termination criteria are: when a set maximum defrost duration lapses or when the defrost temperature sensor 17 reaches a predetermined defrost termination temperature set point with a value well above 0 °C, for example +18 °C.
  • the time-criterion is to be tuned in such a way that the defrost temperature sensor criteria is decisive.
  • the defrost temperature sensor is to be positioned in the part of the evaporator where frost and ice usually melts last.
  • frost forms on locations in the cooling space 41 above or upstream the evaporator 16. This especially happens in shipments of very moist cargo which still needs to be cooled down after loading into the container.
  • the return air grid 42 frosts up heavily, thus impairing air circulation through the transport volume 45 and starting a not-so-obvious chain of events causing ice accumulation in the supply air duct. It is believed that frost formation on the return air grid only occurs when there exists super-cooled fog and/or ice crystals present in the return air flow, which might happen in very moist cargo, which cargo still needs to be cooled down after having been loaded into the container.
  • 'evaporator defrost' termination procedure terminates a defrost cycle prematurely.
  • the defrost cycle then terminates too early for the removal of frost or ice accumulated above the evaporator coil, with the return air grid being the highest location where frost may accumulate. If some frost or ice has accumulated above the evaporator coil then some of it will still be melting while the typical procedure terminates the defrost cycle.
  • the control system or unit according to the present invention applies 'return air grid defrosts', i.e. prolonged defrost cycles by postponing the defrost termination decision until substantially all frost and ice has melted from the evaporator 16 and components higher up in the cooling space 41, including the return air grid 42.
  • One aspect of the invention is how to prolong the defrost cycles.
  • Another related aspect is the decision when to apply prolonged defrost cycles. As previously mentioned, by means of the present invention, it is achieved that ideally the entire cooling space 41 stays free of ice.
  • Figure 2 illustrates a return air temperature trajectory typically of a defrost cycle where the return air grid is frosted at the start of the cycle. This curve has been recorded by a return air temperature sensor 5, but any other temperature sensor positioned in the cooling space at a position higher than the highest point of the evaporator would record a comparable temperature trajectory.
  • the defrost starts at time 0.
  • phase A is the period where return air temperature hardly rises, despite supplying heat to the evaporator.
  • phase A return air temperature rises only slowly because most sensible heat supplied to the evaporator 16 is converted to latent heat by the frost melting off the evaporator.
  • phase B When return the air temperature reaches 0 °C frost starts to melt off the return air temperature sensor 5, and most sensible heat reaching the return air temperature sensor 5 is converted into latent heat, resulting in a reduction of the slope of the return air temperature curve to approximately 0 °C/min in phase C. As soon as the return air temperature sensor 5 is frost free the slope of the return air temperature curve increases again, see phase D. Because the return air grid 42 is blocked with frost the heat stays locked up in the cooling space.
  • defrost' typically terminates at the end of phase A or in the beginning of phase B, i.e. when substantially all frost has melted from the evaporator 16.
  • measured return air temperature as a predefined indicator, and comparing it to predetermined conditions, one could terminate a defrost after there is indication that substantially all frost and/or ice has melted from other components than only the evaporator.
  • a condition in which substantially all frost and/or ice has melted from the at least one evaporator fan 10 is when return air temperature exceeds a value well above 0 °C, for example 2 °C, which is well beyond phase C in Figure 2.
  • a condition when substantially all frost has melted from a return air grid 42 and all other components above the evaporator 16 inside the cooling space 41 is when return air temperature during the last e.g. 5 minutes has been larger than e.g. 1 °C and during that period the slope of the return air temperature curve has always been positive but not steep, e.g. averaged over the e.g. 5 minutes between 0 and e.g. 1 °C/min, a slope typical of phase F in Figure 2.
  • predetermined condition One would then typically use prior experiences to tune the pre-set maximum defrost duration to the worst case frost formation. For the case of Figure 2 a pre-set maximum defrost duration of 34 minutes would be an effective predetermined condition.
  • Figure 3 is a flow chart illustrating exemplified steps executed by a microprocessor- implemented defrosts termination control method or algorithm or program of a control system of a refrigerated transport container.
  • the procedure in Figure 3 is to be called on a frequent basis during a defrost cycle, e.g. not less than once per 5 minutes but preferably not less than once per 5 seconds.
  • the flow chart shown in Figure 3 provides one example of the operation of a defrost termination procedure according to a 'return air grid defrost' type 300.
  • the name 'return air grid defrost' type refers to a method for comparing predefined indicators to predetermined conditions related to temperature and/or time, where the predetermined conditions represent conditions in which substantially all frost and/or ice has melted from a return air grid 42 positioned in the return air flow in between the transport volume and a cooling space 41, and terminating the defrost cycle by switching off the heat supply when one or more of the predefined indicators meet the predetermined conditions.
  • step 302 The algorithm starts in step 302 and proceeds to step 303 where it is determined whether the current defrost was initiated less than e.g. 34 minutes ago. If the test in step 303 is no (N) the method applies a timer-based defrost termination by proceeding to step 312. In step 312 the method terminates the current defrost cycle by switching off the heat supply to the evaporator, and the cooling system reverts to freezing operation. If the test in step 303 is yes (Y) the method proceeds to step 304. In step 304 the method checks if the return air temperature has risen till above e.g. 2 °C. If the test in step 304 is no (N) the return air grid may still be frosted and the method reverts to step 303.
  • step 304 If the test in step 304 is yes (Y) the return air temperature sensor is free of frost and the method proceeds to step 306.
  • step 306 the method checks if the return air temperature has been above e.g. 1 °C for more than e.g. 5 minutes. If the test in step 306 is no (N) it is too early to test if the return air
  • step 306 the method checks if the slope of the return air temperature trajectory has always been positive during the last e.g. 5 minutes. If the test in step 308 is no (N) phase E (see Figure 2) is part of the last 5 minutes and it is still too early to decide if the return air grid is completely free of frost, hence the method reverts to step 303.
  • the test in step 308 can only be yes (Y) if the return air temperature resided in phase D or F (see Figure 2) during the last 5 minutes, not if phase E has been part of the last 5 minutes.
  • step 308 If the test in step 308 is yes (Y) the method proceeds to step 310.
  • step 310 the method checks if the average slope of the return air temperature curve over the last 5 minutes has been less than e.g. 1 °C/min to discriminate between phase D and F (see Figure 2). If the test in step 310 is no (N) the return air temperature curve is apparently still in phase D (see Figure 2) and the method therefore reverts to step 303. If the test in step 310 is yes (Y) the method proceeds to step 312 to terminate the defrost cycle, because the return air temperature curve is in phase F (see Figure 2) and substantially all frost has melted off the return air grid.
  • frost formation on components higher than the evaporator 16 is rare, it would be a waste of energy to let every defrost last until predefined indicators meet predetermined conditions, indicating that the return air grid is free of frost. Usually it would be fine to apply an
  • a defrost termination type controller that decides when to use a 'return air grid defrost', i.e. when to let a defrost last until predefined indicators meet predetermined conditions, indicating that the return air grid is free of frost. This can be controlled manually, e.g. through the unit controller's keypad, by letting a human operator set an input flag to the controller.
  • This defrost termination type flag would then have two values: e.g.
  • defrost termination type flag has the value 'evaporator defrost' then a defrost terminates according to current procedures when predefined indicators indicate that the evaporator is substantially free of frost, else a defrost terminates when predefined indicators indicate that the return air grid is substantially free of frost. It is then the responsibility of the operator to decide a priori if during a shipment conditions may be such that frost is formed at the return air grid. It would then be natural to automatically reset this defrost termination type flag to its default value 'evaporator defrost' when indicators indicate that a new shipment starts, e.g.
  • an automatic controller decides whether to apply an 'evaporator defrost' or a 'return air grid defrost'. This could be done in multiple ways.
  • return grid frosting may especially occur in temperature pull-down situations, i.e. in the first period after power up of a unit, and when moisture load is high, i.e. when there is a frequent need for defrosting.
  • the flow chart shown in Figure 4 provides one example of the operation of an automatic defrost termination type control algorithm 400.
  • the procedure would be called right at initiation of a defrost cycle.
  • the algorithm then starts in step 402 and proceeds to step 404 where it is tested whether the current defrost is the first defrost since the most recent power up of the cooling unit, i.e. whether there is a good chance that the unit operates in a temperature pull-down situation. If the test in step 404 is yes (Y) the method proceeds to step 414, i.e. it decides to apply a 'return air grid defrost' where it is ensured that the defrost only terminates when the return air grid is substantially frost free.
  • step 414 the defrost termination type 'return air grid defrost' terminates a defrost according to the logic outlined in the flow chart in Figure 3. If the test in step 404 is no (N) the method proceeds to step 405, where it is tested whether the last defrost terminated less than e.g. 3 hours ago, i.e. whether the moisture load is exceptionally high and hence the risk of return air grid frosting is high. If the test in step 405 is yes (Y) the method proceeds to step 414. If the test in step 405 is no (N) the method proceeds to step 406, where it is tested whether the last defrost type was a 'return air grid defrost', i.e.
  • a defrost terminated when predefined indicators indicated that the return air grid was substantially free of frost. If the test in step 406 is yes (Y) the method analyses the data collected during this preceding defrost for signs of frost on the return air temperature sensor and/or return air grid. The method first proceeds to step 408, where it is tested whether the duration of phase C (see Figure 2) in the last defrost lasted longer than e.g. 3 minutes. If the test in step 408 is yes (Y) there was frost at the return air temperature sensor during the previous defrost and the method proceeds to step 414.
  • step 408 If the test in step 408 is no (N) the return air temperature sensor was free of frost at the start of the preceding defrost and the method proceeds to step 410, where it is tested whether phase E (see Figure 2) was longer than 0 minutes, i.e. whether a period occurred where the slope of the return air temperature curve was negative due to a return air grid opening up. If the test in step 410 is yes (Y) the return air grid was frosted at the start of the previous defrost and the method decides to again use a defrost of the type 'return air grid defrost' by proceeding to step 414.
  • phase E see Figure 2
  • step 410 If the test in step 410 is no (N) there is no indication that the preceding defrost removed frost from other locations than the evaporator, hence there is no need for a 'return air grid defrost' and the method proceeds to step 412.
  • step 412 the defrost termination type 'evaporator defrost' terminates a defrost when substantially all frost has melted off the evaporator, using current practice logic.
  • step 406 If the test in step 406 is no (N), i.e. the last defrost was an 'evaporator defrost', the method proceeds to step 416. In step 416 it is tested whether all last e.g.
  • step 416 determines whether the defrost termination type 'evaporator defrost'. If the test in step 416 is no (N) the method proceeds to step 412, and hence again calls upon a defrost termination type 'evaporator defrost'. If the test in step 416 is yes (Y) the method proceeds to step 414, this provides a sort of safety net by ensuring that at least 1 in every e.g. 6 defrosts is only terminated when substantially all frost has melted from a return air grid. Other flow charts of the same spirit could achieve comparable results.

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  • Engineering & Computer Science (AREA)
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  • Combustion & Propulsion (AREA)
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  • Defrosting Systems (AREA)

Abstract

La présente invention concerne un procédé, un dispositif, et un programme informatique servant à commander la fin du dégivrage dans un récipient de transport réfrigéré (1). Le récipient comprend un volume de transport (45), une unité de refroidissement (40) comprenant au moins un évaporateur (16), une soufflante d'évaporateur (10), et une unité de commande de refroidissement. Le dégivrage est réalisé en envoyant de la chaleur vers l'évaporateur, ce qui est commandé au moyen d'un système de commande avec une unité de traitement. Le procédé comprend les étapes suivantes : la comparaison d'indicateurs prédéfinis avec des conditions prédéterminées concernant la température et/ou le temps, les conditions prédéterminées représentant des conditions dans lesquelles sensiblement tout le givre et/ou toute la glace ont fondu depuis une grille d'air de retour (42) positionnée dans le flux d'air de retour entre le volume de transport et un espace de refroidissement (41) ; et l'arrêt du cycle de dégivrage en coupant l'alimentation de chaleur lorsqu'un ou plusieurs indicateurs prédéfinis correspondent aux conditions prédéterminées.
PCT/EP2014/063881 2014-06-30 2014-06-30 Procédé de réduction de formation de glace dans une unité de refroidissement WO2016000750A1 (fr)

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20170184333A1 (en) * 2015-12-29 2017-06-29 Maersk Line A/S Method of deciding when to terminate a defrosting cycle within a refrigerated container
WO2019243561A1 (fr) * 2018-06-22 2019-12-26 Danfoss A/S Procédé d'arrêt de dégivrage d'évaporateur à l'aide de mesures de température d'air
US10696139B2 (en) 2016-03-07 2020-06-30 Carrier Corporation Return air intake grille de-icing method
US11365919B2 (en) 2018-07-06 2022-06-21 Danfoss A/S Apparatus for removing non-condensable gases from a refrigerant
US11619431B2 (en) 2018-04-13 2023-04-04 Carrier Corporation Method of defrosting a multiple heat absorption heat exchanger refrigeration system

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Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20170184333A1 (en) * 2015-12-29 2017-06-29 Maersk Line A/S Method of deciding when to terminate a defrosting cycle within a refrigerated container
US9933199B2 (en) * 2015-12-29 2018-04-03 Maersk Line A/S Method of deciding when to terminate a defrosting cycle within a refrigerated container
US10696139B2 (en) 2016-03-07 2020-06-30 Carrier Corporation Return air intake grille de-icing method
US11619431B2 (en) 2018-04-13 2023-04-04 Carrier Corporation Method of defrosting a multiple heat absorption heat exchanger refrigeration system
WO2019243561A1 (fr) * 2018-06-22 2019-12-26 Danfoss A/S Procédé d'arrêt de dégivrage d'évaporateur à l'aide de mesures de température d'air
EP3587962A1 (fr) * 2018-06-22 2020-01-01 Danfoss A/S Procédé pour terminer le dégivrage d'un évaporateur à l'aide de mesures de température de l'air
CN112219075A (zh) * 2018-06-22 2021-01-12 丹佛斯有限公司 通过使用空气温度测量来终止蒸发器除霜的方法
CN112219075B (zh) * 2018-06-22 2022-05-31 丹佛斯有限公司 通过使用空气温度测量来终止蒸发器除霜的方法
US11549734B2 (en) 2018-06-22 2023-01-10 Danfoss A/S Method for terminating defrosting of an evaporator by use of air temperature measurements
US11365919B2 (en) 2018-07-06 2022-06-21 Danfoss A/S Apparatus for removing non-condensable gases from a refrigerant

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