EP0455633A4

EP0455633A4 - High humidity storage container

Info

Publication number: EP0455633A4
Application number: EP19890903051
Authority: EP
Inventors: Steven C. Morris
Original assignee: Commonwealth Scientific and Industrial Research Organization CSIRO; Minister for Agriculture and Rural Affairs for State of New South
Current assignee: Commonwealth Scientific and Industrial Research Organization CSIRO; Minister for Agriculture and Rural Affairs for State of New South
Priority date: 1989-02-02
Filing date: 1989-03-03
Publication date: 1992-04-15
Also published as: NZ232188A; WO1990008925A1; CA2009243A1; EP0455633A1; KR920701761A

Abstract

A refrigeration unit (1) used on bulk containers for perishable foodstuffs which cycles water obtained by condensation from the refrigeration cooling coil (2) through a fine water spray (9) into the air on the cold side of the cooling coil (2) while circulating the air through the container. The relative humidity of the circulating air on the warm side of the cooling coil is measured (10) and the water spray (9) controlled according to the measured relative humidity.

Description

"HIGH HUMIDITY STORAGE CONTAINER"

This invention relates to a high humidity refrigerated enclosure and means to control the humidity in a refrigerated enclosure. BACKGROUND ART

During the transportation of vegetables their quality can be better retained when kept refrigerated. Further, refrigeration in a humid environment, say above 901 relative humidity, further retains quality by helping to prevent the loss of moisture content of the vegetables. Vegetable transportation is therefore frequently carried out in refrigerated bulk containers, and more recently in such containers where the atmosphere within the container is modified in order to maintain a high humidity.

The present invention sets about to provide an effective high humidity refrigerated enclosure such as a refrigerated storage room or a refrigerated transport room container. DISCLOSURE OF THE INVENTION

Accordingly, in one broad form, the present invention can be said to provide means to control the humidity in a refrigerated enclosure comprising: a condensate collector adapted to be positioned relative to a cooling coil present in the refrigerated enclosure so as to collect condensate produced on the coil during cooling operation of the refrigerated enclosure; a condensate storage unit in liquid connection with the collector unit so as to receive and store the condensate; a water spray device which in operation draws water from the condensate storage unit and delivers the water in a spray into the moving air at the exit side of the coil; and a control unit adapted to measure the relative humidity of the air at the entry side of the coil and to - 2 -

control the water spray so as to maintain the measured relative humidity within a preset range.

According to another aspect the present invention provides a refrigerated enclosure including: a cooling coil; a condensate collector positioned relative to the coil so as to collect condensate produced on the coil during cooling operation of the refrigerated enclosure; a condensate storage unit in liquid connection with the collector unit so as to receive and store the condensate; an air circulation device which in operation causes air to circulate from an entry side of the coil, past the coil to an exit side of the coil and thence through the enclosure; a water spray device which in operation draws water from the condensate storage unit and delivers the water in a spray into the moving air at the exist side of the coil; and a control unit measuring the relative humidity of the air at the entry side of the coil and controlling the water spray so as to maintain the measured relative humidity within a preset range.

A further broad aspect of the invention provides a humidity modified refrigerating unit including: an air passage with an inlet adapted to receive circulating air from a volume to be refrigerated and an outlet adapted to return the circulating air into said volume; a cooling coil intermediate and fixed generally across the cross-section of said air passage; a condensate collector positioned relative to the coil so as to collect condensate produced on the coil during cooling operations; a condensate storage unit in liquid connection with, or being an integral part of, the collector unit so as to receive and store the condensate; an air circulation device which in operation causes the circulating air to move from said inlet, past the coil and to discharge through said outlet; a water spray device which in operation draws water from the condensate storage unit and delivers a water spray into the moving air at the outlet side of the coil; and a control unit measuring the relative humidity of the circulating air at the inlet side of the coil and controlling the water spray so as to maintain the measured relative humidity within a preset range or at about a preset level.

Besides providing longer term storage of vegetables under high humidity in a refrigerated enclosure a particular preferred form of the invention provides a method of curing potatoes and like curable vegetables comprising the storage of the vegetables in a refrigerated enclosure as described above for a predetermined time period while maintaining the interior temperature and humidity at about predetermined levels. BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be explained by way of example and in reference to the accompanying drawing which schematically represents a sectional view of a high humidity refrigeration storage plant for a container as provided by the present invention. BEST MODE OF CARRYING OUT THE INVENTION

The refrigeration plant 1 is contained in an integral unit which is easily attached to, or carried within, a suitable storage or transport container (not shown). The plant includes cooling coils 2 which are part of a conventional heat pump used in cooling air circulating about the container. The cooling coils 2 extend generally - 4 -

across a portion of an air duct 4 in which further reside air circulation fans 3. The air circulation fans 3 force the passage of air upwardly through the air duct 4 drawing the air in at an air entry point 5 connected to the container interior and forcing the exit of the air out through an air exit side 6 to return back to the container.

During normal cooling processes condensation gathers on the cooling coils 2. A condensate collector 7 is placed under the cooling coils 2 so as to collect runoff condensate. The condensate collector 7 is sufficiently sized to further act as a condensate reservoir holding a predetermined volume of condensate before it commences drainage through the overflow tube 8. Typically a 10-15 litre volume is practical but larger volumes might be necessary in some plants while smaller volumes might be feasible in others.

A water atomizer 9 is positioned within the air duct 4 at the air exit side 6 of the cooling coils 2. The atomizer 9 is supplied with compressed air and draws water from the condensate collector/reservoir 7 in order to produce a water-air mist of fine water droplets within the cold part of the circulating air flow, so that the droplet size (Mean Number Diameter) is about 20 microns or less. The water flow rate during misting is in the range 10-30 mis per minute.

Where the atomiser is positioned vertically above the reservoir by substantial amount it may be necessary to deliver pressured water to the atomiser by a suitable pump so as to ensure satisfactory operation. Sprays other than atomisers might also be used.

The air and water lines feeding the atomiser are enveloped in insulation so as to prevent their partial or complete freezing which would adversely affect atomiser operation.

A relative humidity sensor 10 is positioned on the warm side of the cooling coils 2, that is on the air entry side 5 of the coils 2, the sensor 10 being connected to a humidity controller 11 which in turn processes the sensor 10 information and controls accordingly air supply to the atomizer 9 so as to maintain the sensed relative humidity within a predetermined range. A relative humidity range of a few percent within the range 88-98% (depending upon the performance of sensor 10) is practical,

Thus water moisture content normally lost from the circulating air at the cooling coils 2 is trapped within the condensate collector/reservoir 7 and recycled via the fine water mist produced by the atomizer 9 in a manner controlled by the humidity controller 11 so as to ensure the humidity in general within the container is maintained at some predetermined level.

To ensure effective cyclic operation the controller 11 has a programmed hysterisis of about 2-4% rel. humidity. Thus for a set point rel. humidity of say 96%, the atomiser will commence operation whenever the sensed rel. humidity falls below say 93% and will cease operation whenever it exceeds 96%.

It has been found that some vegetables, for example potato and sweet potato, will "cure" if maintained for a period of time, preferably a number of days, within a particular temperature and relative humidity environment. Except for the special case when temperatures are elevated for "curing" to about 25°C, the best storage conditions for horticultural crops are at as low a temperature as possible for the crop being stored, typically 1 to 5°C and at a high relative humidity e.g. above 90% and more preferably above 95%. Therefore it is preferable that the high humidity refrigeration plant be capable of maintaining the internal atmosphere of the refrigerated enclosure at adjustable levels within a predetermined range of temperatures and/or rel. humidities. Clearly the invention can also be used to modify an existing refrigerated container or refrigerated room design, so as to enable maintenance of a high or controlled humidity atmosphere. Further, all components excepting the water atomiser and sensor can be placed internally or externally to the refrigerated enclosure and it is not restricted to a vertically upward air flow past the coils. Alternative arrangements such as proprietary downdraft refrigeration plant may be equally well adapted to receive the humidity control unit.

Claims

CLAIMS: -

1. Means to control the humidity in a refrigerated enclosure comprising: a condensate collector adapted to be positioned relative to a cooling coil present in the refrigerated enclosure so as to collect condensate produced on the coil during cooling operation of the refrigerated enclosure; a condensate storage unit in liquid connection with the collector unit so as to receive and store the condensate; a water spray device which in operation draws water from the condensate storage unit and delivers the water in a spray into the moving air at the exit side of the coil; and a control unit adapted to measure the relative humidity of the air at the entry side of the coil and to control the water spray so as to maintain the measured relative humidity within a preset range.

2. Means as defined in claim 1, wherein the condensate collector and condensate storage unit are an integral condensate collector/storage unit of 10 to 15 litre liquid capacity.

3. A means as defined in claim 2, wherein the water spray device is an air powered atomiser.

4. A refrigerated enclosure including: a cooling coil; a condensate collector positioned relative to the coil so as to collect condensate produced on the coil during cooling operation of the refrigerated enclosure; a condensate storage unit in liquid connection with the collector unit so as to receive and store the condensate; an air circulation device which in operation causes air to circulate from an entry side of the coil, past the coil to an exit side of the coil and thence through the - 8 -

enclosure ; a water spray device which in operation draws water from the condensate storage unit and delivers the water in a spray into the moving air at the exist side of the coil; and a control unit measuring the relative humidity of the air at the entry side of the coil and controlling the water spray so as to maintain the measured relative humidity within a preset range.

5. A refrigerated enclosure as defined in claim 4, wherein the condensate collector and condensate storage unit are an integral condensate collector/storage unit of 10 to 15 litre liquid capacity.

6. A refrigerated enclosure as defined in claim 5, wherein the water spray device is an air powered atomiser.

7. A humidity modified refrigerating unit including: an air passage with an inlet adapted to receive circulating air from a volume to be refrigerated and an outlet adapted to return the circulating air into said volume; a cooling coil intermediate and fixed generally across the cross-section of said air passage; a condensate collector positioned relative to the coil so as to collect condensate produced on the coil during cooling operations; a condensate storage unit in liquid connection with, or being an integral part of, the collector unit so as to receive and store the condensate; an air circulation device which in operation causes the circulating air to move from said inlet, past the coil and to discharge through said outlet; a water spray device which in operation draws water from the condensate storage unit and delivers a water spray into the moving air at the outlet side of the coil; and a control unit measuring the relative humidity of the circulating air at the inlet side of the coil and controlling the water spray so as to maintain the measured relative humidity within a preset range or at about a preset level.

8. A refrigerating unit as defined in claim 7, wherein the air passage is a generally vertical air duct and the air circulation device is at least one air compressor causing vertically upward air movement within the air duct during compressor operation.

9. A refrigerating unit as defined in claim 7, wherein the condensate collector and the condensate storage unit are an integral generally funnel shaped receptacle of 10-15 litres liquid capacity fixed generally vertically below, and proximate to, the cooling coil.

10. A refrigerating unit as defined in claim 9, wherein the control unit includes a physically separate, but electrically connected, sensor positioned within the air duct at the inlet side of the cooling coil and is adapted to produce an electrical signal responsive to, and indicative of, the relative humidity of air surrounding the sensor.

11. A refrigerating unit as defined in claim 10, wherein the water spray device is an air driven atomiser and wherein said control unit affects said controlling the water spray by controlling pressured air supplied to said atomiser.

12. A refrigerating unit as defined in claim 11 wherein the control unit connects the pressured air to the atomiser when the signal from the sensor indicates a relative humidity below a preset lower level and isolates the pressured air from the atomiser when the sensor signal indicates a relative humidity above a preset upper level.

13. A refrigerating unit defined in claim 12, constructed integrally with, or attached rigidly to, a container to be - 10 -

refrigerated and with said inlet and outlet being connected to the internal volume of the container at vertically separated locations therein.

14. A method of curing curable vegetables comprising the loading of the vegetables in a refrigerated enclosure as defined in claim 4 for a predetermined time period while maintaining the interior temperature and relative humidity at about predetermined levels.

15. A method as defined in claim 14, wherein the predetermined time period is a number of days, the predetermined temperature level is approximately 25°C and the predetermined relative humidity level is between 88% and 98%.