DESCRIPTION

Technical Field

The present invention relates to a method and to an arrangement for simulating the shuttering of fans when defrosting refrigerating batteries, for example when defrosting refrigerating batteries which generate re¬ frigeration air in the refrigeration compartment of a closed, insulated transport container.

Background Art

When defrosting a refrigeration battery of a refrigera¬ tion compartment in a closed, insulated transport con¬ tainer, the refrigeration battery is heated subseguent to interrupting the supply of refrigerant for vapouriza- tion in the system evaporator. In order to prevent the heated air from leaving the refrigeration battery and continuing into the refrigeration compartment, a fan shuttering device may be mounted in connection with the fan used to generate the flow of cold air during refrig¬ eration. The fan shuttering device may, for instance, consist of thin metal plates or shutters which function to close the fan openings on the refrigerator side when the fan is switched off and thus stationary. The con- struction of mechanical fan shuttering devices often exhibits limitations in the form of unreliable shutter¬ ing functions.

Disclosure of the Invention

With the intention of shortening the time.taken to

defrost refrigerating batteries and, at the same time, to achieve greater reliability in the actual defrosting of said batteries without needing to use mechanical fan shutters, there is proposed a method and an arrangement for simulating a fan shutter function in which the fans which direct warm air onto the refrigeration battery are operated over short time periods during the actual defrosting operation. The warm air formed when defrost¬ ing the battery rises and collects above the refrigera- tor. This warm air is blown repeatedly downwards by the fans and is pressed back, through the refrigeration battery during said short time periods, the heated air moving forwards and backwards through said battery so as to improve defrosting of said battery without influenc- ing the temperature in the refrigeration compartment to any appreciable extent. Water and ice flakes loosely seated on the refrigeration battery surfaces are thrown from the battery and do not consume energy during con¬ tinued defrosting of the battery.

Brief Description of the Drawing

The single Figure of the accompanying drawing is a simple illustration of a closed insulated cargo contain- er equipped with a control unit and a refrigerating plant.

Best Mode of Carrying Out the Invention

The Figure is a simple illustration of the construction of an insulated transport container 1 having a refrig¬ eration compartment 2 and a refrigeration unit 3, 4. The refrigeration compartment 2 is cooled by blowing cold air through the refrigeration compartment 2 by means of a fan, said air being cooled in a refrigeration battery 3. Cooling of the refrigeration .compartment is

effected by passing cooled or chilled air into the compartment through inlet openings 5 provided in the compartment floor and exiting said air through exhaust openings 6 provided at the top of one end wall of the compartment. Cooled air is caused to pass through the refrigeration compartment during said cooling process. The refrigeration units 3, 4 are placed on one side of the refrigeration compartment 2 in the insulated cargo container 1 and consist of one or more electric fans 4 and a refrigeration battery 3. The refrigeration bat¬ tery 3 is connected to an external refrigeration plant 7, which supplies the battery 3 with coolant. Defrost¬ ing of the refrigeration battery 3 can be effected with hot gas taken from the refrigeration plant 7 and caused to flow through the battery 3, said battery then func¬ tioning as a condenser. Alternatively, the battery 3 may be heated electrically during the defrosting pro¬ cess.

An external control unit 8 is connected to the external refrigeration plant 7 which coacts with the battery 3 , and also to the electrically operated fan 4. The values of prevailing system state parameters, such as the real values prevailing in the refrigeration compartment, are delivered to the external control unit by a measuring device 9 and are there processed and compared with the set point values of said parameters stored in the exter¬ nal control unit, which then adjusts the flow of refrig¬ erant in response to a prevailing refrigerant require- ment. The external control unit 8 is thus able to initiate defrosting of the battery. The unit first interrupts the delivery of liquid refrigerant to the refrigeration battery, which in normal refrigerating conditions functions as an evaporator. The battery 3 is then heated electrically over a time period T_ . Alter¬ natively, the battery may be heated by passing "hot

gas", hot gaseous refrigerant, through the battery 3 over said time period. As the battery is heated, warm air will be formed and collected in a space 10 above the battery 3. The warm air rises up through a fan opening 11 and up into a cooling space 12. Upon termination of the time period T _x , the fan 4 is again run for a short period. The warm air in the cooling space 3 and in the space above the battery is then moved back through the battery 3 and fills a cavity 13 located beneath said battery. This backflow of air will cause loose ice flakes and water to be blown from the battery. When the fan 4 is stopped, heating of the battery 3 for defrost¬ ing pur-poses is continued over a time period T ₂ and the air is transported back to the refrigeration battery and to the space 10 above said battery and to the space 12 above said fan through the chimney effect created. Subsequent to termination of the time period T ₂ , the fan 4 is again started-up for a brief moment, causing the warm air above the battery to be again forced back through said battery. The procedure of heating the battery and running the fan for short time periods is continued until the battery is completely defrosted. During defrosting of the battery, which may take from 60 to 80 minutes, the fans may be driven for 2-3 seconds on each said occasion and the duration of the fan driving times (T _l T ₂ ...) may vary between 5 and 15 minutes at a constant- or decreasing fan.speed.

When practicing the invention method, the air that has been heated in the refrigeration battery does not disap¬ pear into the cargo space, but is moved backwards and forwards through the refrigerator. Water and ice flakes which sit loosely on the refrigerator surfaces are thrown from the refrigerator and do not consume energy during continued defrosting of the battery. The tem¬ perature of the air beneath the battery can be

accurately determined upon completion of a defrosting operation.