Refrigeration – Automatic control – Of external fluid or means
Patent
1989-12-22
1991-08-20
Tanner, Harry B.
Refrigeration
Automatic control
Of external fluid or means
62187, 62179, 62409, 62411, F25D 1704, F25D 2104
Patent
active
050403788
DESCRIPTION:
BRIEF SUMMARY
During the last years Nofrost refrigerators have entered the market very successfully, since they offer the important advantage of avoiding ice formation in the cooling chamber and, thus, the troublesome defrosting of the ice built-up.
The process is essentially based on the idea that--in a separate section of the refrigerator--air is supercooled at the evaporator of the cooling machine and that this supercooled air is transferred into the actual cooling chamber by a blower until the required mixed temperature is reached and the blower is turned off by a thermostat. The humidity of the exchanged air condenses on the evaporator of the cooling machine, and the usual ice builtup occurs on the evaporator. However, this process does not extend to the actual cooling chamber. The evaporator is defrosted in certain intervals by increasing the temperature, and the melted ice is drained without problem.
Because of the advantages mentioned--no icing and no defrosting--this process has conquered the market in no time.
The main disadvantage of the process is the de-humidification of the air during supercooling and, thus, the extreme low humidity level within the cooling chamber, causing the food in such refrigerators to quickly dry out and lose taste and shelf life, unless the food is packaged airtight.
Subject of the invention is to offer a process which avoids this important disadvantage without losing the advantages of the nofrost process.
The solution to the problem is a system, in which the cold reaches the cooling chamber by means of convectors instead of cold air, and the required temperature is obtained by a controlled supply of fresh air of higher temperature to the cooling chamber. The assumption is that the quantity of cold air reaching the cooling chamber during a certain time period is smaller than the amount of heat which enters during maximum fresh air supply. Otherwise, the temperature would keep decreasing due to the preponderant presence of cold air, possibly below 0.degree. C. with all the icing consequences.
The fresh air supply ensures that the cooling chamber does not get too cold and that the temperature remains in the predetermined range.
The inflow of fresh air is naturally cooled by the convectors, resulting in a loss of cold following its exit from the cooling chamber; thus, it is proposed as per the invention, to lead the cooled exhaust air to a heat exchanger which, for instance, could be assigned to the warm condenser of the cooling machine, so that the cold is again led into the cycle of the cooling machine.
This effect can even be increased by leading the exhaust air, which has been heated in the heat exchanger, within a closed cycle to the cooling chamber as fresh air. The designation fresh air, in this connection, is to be understood as air which is again led into the cooling chamber, whereby a pre-treatment as per the invention is recommended. This pre-treatment can, for instance, consist of warming as described above, or even of cooling. Furthermore, filtering, for instance by using an activated charcoal filter, is appropriate to avoid the effect of odors, in case cigarette smoke or cooking vapors from the kitchen could be absorbed.
A refrigerator as per the invention, thus, requires at least one air inlet duct and one air exhaust duct between the cooling chamber and the fresh air, whereby a blower with temperature control monitors the air exchange. It is of no importance whether the blower is located in the air inlet duct or in the exhaust duct.
When the refrigerator door is opened, warmer ambient air normally enters and it takes some time until the higher temperature is again decreased to the required cooling range. Thus, it is recommended as per the invention to supply an additional air inlet duct for cold air; another blower with temperature control ensures that in such a case cold air instead of fresh air enters the cooling chamber. The temperature control turns the cold air supply off either once the cooling range is reached or close to that range, and the fresh air control sta
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