Refrigeration – Processes – Defrosting or frost inhibiting
Patent
1997-05-02
1998-09-15
Tanner, Harry B.
Refrigeration
Processes
Defrosting or frost inhibiting
62155, 62234, F25D 2100
Patent
active
058063218
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a method for defrosting a refrigeration system, in which a supply arrangement supplies at least one cooling surface with refrigerant and as required a defrosting process is initiated at specific intervals; for implementing the method, the invention also relates to a control unit for a refrigeration system having at least one cooling surface, the unit having an output for switching on and switching off a flow of refrigerant passing through the cooling surface in dependence on the refrigerating chamber temperature.
Such a method and control apparatus are known, for example, from DE 40 06 468 C1. A refrigerator thermostat controls the switching on and off of a compressor (on-off operation). The thermostat switches the compressor off at a lower limit temperature and does not switch it on again until the cooling surface (evaporator) of the refrigerator reaches an upper limit value, which normally lies in the positive temperature range. In this mode of operation a heavy formation of frost or ice is not expected, so that there is no need for enforced defrosting. If, however, the refrigerator is set to a low temperature and, for example, is heavily overburdened as a result of frequent opening of the door or the placing of a large quantity of goods in the refrigerator for cooling, the lower limit temperature is not reached, and the compressor runs continuously for a very long period which leads to the formation of frost and ice on the cooling surface. For that reason a timer is provided, which switches the compressor off after a fixed time and carries out enforced full defrosting. The temperature in the refrigerator rises for a short time during this defrosting. This is tolerated, however, because otherwise with an iced-up evaporator an elevated temperature would occur constantly because of the insulation effect of the iced-up evaporator.
Similar problems arise with other known refrigeration systems too, in which defrosting has to be carried out from time to time because refrigerant is supplied to the cooling surface constantly or at least for relatively long periods of time.
SUMMARY OF THE INVENTION
The invention is based on the problem of being able to carry out de-icing of the cooling surface by defrosting at longer intervals than previously, wherein it is also possible for convenient times for defrosting to be selected.
That problem is solved by the method according to the invention in that partial defrosting is carried out at relatively short intervals and full defrosting is carried out at longer intervals.
Partial defrosting is effected when a layer of frost has formed on the cooling surface. It is caused by the temperature of the cooling surface assuming a value above zero for a short time. The frost layer is not removed in this process. On the contrary, it is converted into a solid layer of ice by fusing of a substantial part of the ice crystals. This layer is a much better conductor of heat than the layer of frost and takes up considerably less volume. This is especially important if the cooling surface has fins between which air flows, the quantity of air being substantially reduced by an increasingly thicker layer of frost but not by this solid ice layer. As operation continues, additional frost forms on the solid ice, and in turn can be converted into solid ice by partial defrosting. The refrigeration system can therefore continue normal operation for a relatively long time before full defrosting has to be carried out.
The efficiency of the refrigeration system is high. Firstly, with partial defrosting the cooling surface is brought only for a short time to a low positive temperature value. Secondly, the layer of ice to be thawed on the cooling surface assists in largely maintaining the desired temperature during the defrosting period.
It has proved beneficial for the shorter intervals to be from one to two hours. In this way the layer of frost has still not achieved a substantial insulating effect before the frost melts partially.
On the other ha
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patent: 5315835 (1994-05-01), Park
Bendtsen Christian
Schmidt Frede
Danfoss A/S
Tanner Harry B.
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