Abstract:
A cooling system for compartments that keep the relative humidity of products in refrigeration, characterized because it has a contact duct by means of a heat transfer plate, applied to the functioning of a two-door and two-compartment refrigerator with independent temperature regulation between the two compartments, refrigerator and freezer. The compartments are separated and the air is not mixed, thus the refrigerator compartment dehydrates less the food contained therein.

Description:
BACKGROUND OF THE INVENTION 
     Different cooling systems are known in the art of the refrigeration. Thus, for example, it is known that the air temperature within a refrigerator must be at 3° C., which means low levels of the air humidity. In the case of a refrigerator without frost formation (No-Frost) the air circulates from the refrigerator compartment to the evaporator and returns to the refrigerator compartment. The effect of this air circulation, upon passing through the evaporator, which is normally at a temperature well below 0° C., is that it captures the air humidity condensating it in the evaporator and leaves the air returning to the refrigerator very dry. This dry air dehydrates the food contained in the refrigerator and thus a refrigerator that does not dehydrate food must have a cooling system in which the air does not pass to the evaporator in order to avoid getting to temperatures below 0° C. A technique to reach this objective is to manufacture a refrigerator with separated compartments and to equip the freezer with an evaporator and the refrigerator with a cold plate. This solution to the problem of drying food is correct but it has the drawback of being highly complex and costly. 
     Among other known systems, there is the one of the condensation in the frame of the refrigerator door such as the one described in U.S. Pat. No. 4,192,149, in which a refrigerator cabinet is claimed which includes a chamber divided by a mullion between the freezer and the fresh food compartment and each chamber has a front part opened towards the door frame that prevents the condensation of the system. 
     In U.S. Pat. No. 4,250,719, the assembly of a panel in the refrigerator compartment with controlled humidity is described, said assembly includes a storage container with an open upper part and a stationary lid inside the refrigerator to receive the container, and a control mechanism. Through this arrangement, the user can move said mechanism to increase or diminish the amount of ventilation and thus control the humidity inside the container. As can be observed, said control is manual. 
     In U.S. Pat. No. 4,729,613, a modification of the previous patent is described, in which an assembly of container in two removable sections for fresh food within a rigid unitary frame is claimed. 
     The applicant has developed a new cooling system through a contact duct which is applied to the functioning of a two-door and two-compartment refrigerator with independent temperature regulation between the two compartments, refrigerator and freezer. The compartments are separated and the air is not mixed. Thus, the refrigerator compartment dehydrates less the food contained in it. 
     There is also the air circulation system without mixing the air between the two chambers, as would be the case of the two evaporators used on the European market. Said system of two evaporators is the one which is nearest to the objective of not dehydrating food in the refrigerator compartment, but it is a more expensive system. 
     Hereinafter, the invention will be described with reference to FIGS. 1 to  3 . 
    
    
     DESCRIPTION OF THE INVENTION 
     The present invention relates to a new cooling system according to the drawings wherein: 
     FIG. 1 corresponds to a view of a refrigerator cabin in which a two-door and two-compartment refrigerator is shown with independent regulation. 
     FIG. 1 a  corresponds to an embodiment of the heat transfer plate of FIG.  1 . 
     FIG. 2 corresponds to a top view in which the pipe system between the freezer compartment and the refrigerator compartment is shown. 
     FIG. 3 corresponds to a block diagram of the duct system control. 
     FIG. 4 corresponds to the duct system and housing. 
    
    
     According to what has previously been said, the invention relates to refrigerators that include a combination of a refrigerator compartment for fresh food  2 , FIGS. 1 to  3 , and a freezer compartment for freezing food  1 , FIGS. 1 to  3 . Both compartments are cooled by the operation of a conventional system including: compressor, capillary condenser and one or two evaporators  3 , FIGS. 1 and 1 a.  Both compartments are cooled by means of the circulation of air through evaporator  3  and returning said air to both compartments. 
     With regard to the air circulation, one unique impeller fan  4 , FIGS. 1 and 1 a , dividing by means of ducts the air flow to each compartment can be used, or two fan can be available, one for each compartment,  4 ,  5 , FIGS. 1,  1   a . A fan for the freezer, and a flow regulating butterfly, usually known as damper, for the refrigerator can also be used. 
     In order to obtain the above mentioned cooling system, the applicant implemented a new cooling concept of the refrigerator compartment. This new concept was given the name of Duct System  7 . The functioning principle of the Duct consists in passing the air from the refrigerator  2  through a Duct  7  cooled by conduction by means of a heat transfer plate  6  through the Duct wall, without mixing it with the freezer air  1 . In order to reach the objective of cooling the refrigerator  2 , Duct  7  is set to high flow. The amount of heat removed by this air flow from the refrigerator is equal to: 
     
       
           Q=KM  ( T   2   −T   1 ) 
       
     
     where T 2 −T 1  is the air temperature differential (entrance temperature minus exit temperature), K is a constant and M is the air mass flow through the Duct. Thus, if the mass flow is large (the larger, the better), the temperature differential is low. If the refrigerator temperature is 3° C., a low temperature differential will permit that the cold air  8  exiting the Duct could be at temperatures around 0° C., but not below zero. This working mode helps keep food moisture because it does not present air cold enough to freeze the humidity of the air in the refrigerator compartment. 
     Contrary to a no-frost refrigerator, the M component is increased in the duct and thus the temperature differential diminishes. The result is the removal of the same amount of heat from the refrigerator but at not so cold air temperatures. 
     Control Description 
     The control  9  of the refrigerator with the Duct System, FIG. 3, is the following. It has two relays: one that controls the compressor and one that handles the thawing resistance. It has two temperature sensors, one for each compartment: refrigerator  2 , FIG. 1, and freezer  1 , FIG.  1 . It also has a 12 V direct current voltage source for two fans,  4  and  5 , FIG. 1, one located in the freezer and the other in the Duct  7 . 
     The temperature regulation of the freezer compartment is ensured by a sensor, located at the entrance of the evaporator  3 , FIG.  1 . The control turns on the compressor upon sensing a temperature above the starting temperature −15° C., and turns off the compressor upon sensing a temperature below the cutoff temperature, −25° C. The same sensor is used to end the thawing period upon reaching a temperature of 5° C. 
     The temperature regulation of the refrigerator compartment is used to operate a fan in the Duct. Said fan switches on when it reaches a temperature above the regulation temperature, about 3.5° C., and switches off when the temperature goes below the regulation temperature, 2.5° C. 
     This very small differential between the switch-on temperature and the switch-off temperature permits a very precise regulation of the temperature within the refrigerator, which is beneficial for food conservation. 
     Finally, the design or setting up of the Duct system  7  is not a critical aspect, i.e., it is functionally operative in all the positions and sizes of the duct shown in FIG.  1  and FIG. 1 a.    
     According to the functioning, hereinbelow some embodiments of the invention are described: 
     Duct I 
     It consists of a Duct  7  made of aluminum sheet on all the floor  6  of the freezer, with air entrance through two about 2-inch diameter holes, near the door. The air exit is through the bottom of the floor with a fan  5  functioning as extractor and in the end near the evaporator  3 . In this option, the following could be observed: 
     The faster the speed of the fan in the Duct, the higher the heat transfer is. The addition of wings or fins  8  to the aluminum sheet  6  for the Duct die increased heat transfer. In the Duct, no ice was created since the air temperature inside the Duct never reaches a level below 0° C. because the air passes very quickly and only cools a little. This was observed even after 36 hours of compressor working time. 
     Duct II 
     It consists of a Duct made on a sheet that separates the evaporator from the freezer. In this case, the air entrance to the duct is through two 2-inch diameter holes located at the sides and bottom of the upper part of the refrigerator. The air exit is located in the central part and the air is extracted by means of a fan. This option offered the following information: 
     The nearness of the Duct with regard to the evaporator which is the lowest temperature zone allows to transfer easily a sufficient amount of cold to the refrigerator, the air that exits the Duct reaches temperatures slightly above zero. This is improved diminishing the Duct size. The vertical form of the Duct allows a natural cold air flow towards the refrigerator, even without operating the fan, because of the chimney effect it generates. 
     Even though no ice is formed in the Duct because temperatures are above 0° C. in the air that circulates through it, the nearness of the duct with regard to the Defrost resistance of the freezer also allows the Duct defrosting. Said version permits a very fast lowering of the refrigerator compartment. 
     Duct III 
     This version of the duct consisted in reducing the duct area to a part of the floor. Only the area necessary to pass the two lateral holes as air entrance to the Duct and an exit hole in the center, all of them in the back p art of the refrigerator, was left. The duct is left at the bottom of the refrigerator because of the nearness of the evaporator which is the coldest zone in the freezer and most remote from the freezer atmosphere. Basically it is the same as Duct  1 , but with only 30% of the area and being remote from the freezer atmosphere. 
     Duct II lowers the refrigerator temperature more quickly but the air flow temperatures are very low, even below zero. Duct I does not diminish the refrigerator temperature as quickly but the air flows in the Duct at temperatures which are not so low, about zero but not below 0° C., which means that it has a lower drying effect on food. 
     In the case of Duct I a theoretical computation of heat transmission through an aluminum sheet was made and it was discovered that with a 0.5 square foot area 100 BTU could be extracted from the refrigerator per hour, taking into account an air flow of 35 cubic feet per minute and an average temperature in the freezer of −15° C. Based on the previous calculation, a one square foot Duct should offer an excess cold capacity for the refrigerator compartment. A Duct design that increases the heat transfer effective area, without increasing the floor area occupied by the Duct, would be a corrugated sheet. With regard to Duct II, because it is nearer the evaporator, it is considered that a 0.5 square foot area is enough. This is the case because the temperatures on the side of the evaporator are lower and because the heat transfer is carried out on both sides. 
     The Duct has near zero temperatures, which means hot temperatures compared to the freezer temperatures. Because of the fact that having the duct near the freezer, as is the case of options I and II, produces an increase of the freezer average temperatures, it is better to have a duct remote from the freezer. A position that would fulfill what has previously been indicated is the location of the duct behind the evaporator because this position has two important advantages: it is near the cold and far from the freezer. However, a duct near the evaporator also presents the problem of producing lower temperatures, similar to what happens in the case of the duct in the vertical position. I is thus defined that the best option for the position of the duct is on the floor, limited to half the floor space and near the evaporator. Another possible alternative would be to position the Duct behind the evaporator with a Duct smaller than the one used for Duct II. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                   
               
               
                 COMPARATIVE TABLE FOR DUCT SYSTEM 
               
             
          
           
               
                   
                 DUCT I 
                 DUCT II 
                 DUCT III 
               
               
                   
                   
               
             
          
           
               
                 Cold Capacity 
                 Medium 
                 High 
                 Low 
               
               
                 Refrigerator 
               
               
                 Air Temperature 
                 About 3° C. 
                 Below 0° C. 
                 About 3° C. 
               
               
                 in the Duct 
               
               
                 Lowering 
                 Medium 
                 Fast 
                 Slow 
               
               
                 Temperature Time 
               
               
                 Cold Capacity 
                 Good 
                 Good 
                 Better 
               
               
                 Freezer 
               
               
                 Construction 
                 Very simple 
                 Simpler 
                 Simple 
               
               
                 Ease 
               
               
                 Defrost 
                 Not required 
                 Uses the same 
                 Not required 
               
               
                   
                   
                 resistance 
               
               
                 Ice formation 
                 No ice 
                 Slight 
                 No ice 
               
               
                 in the Duct 
                 formation 
                   
                 formation 
               
               
                   
               
             
          
         
       
     
     Based on the above comparative table it can be seen that a Duct on the floor, limited to the back part of the freezer and near the evaporator and, if necessary, with a corrugated sheet with ribs or fins on both size is the best possible option that would permit not to dry food in the refrigerator compartment. 
     From what has just been said, the conclusion is that the present invention shows the practicability of using a duct as a way of removing heat from the refrigerator compartment, without there being a communication between the air of the refrigerator compartment and the air of the freezer compartment. The cold source is the compressor-condenser-capillary-evaporator refrigeration system. In the case of the freezer, the temperature regulator element is the compressor operation. In the of the refrigerator, the temperature regulator element is the Duct fan. The regulation mode between both compartment is independent. 
     The Duct system is a solution that is very economical because it is simple and it is a solution that competes against the European system of cold plate in the refrigerator compartment, system which is more expensive. 
     It is thus believed that the operation and construction of the present invention will be apparent from the foregoing description. While the method, apparatus and system shown and described have been characterized as being preferred, it will be readily apparent that various changes and modifications could be made therein without departing from the scope of the invention as defined in the following claims.