Refrigeration – Automatic control – Refrigeration producer
Reexamination Certificate
2002-04-18
2003-06-24
Esquivel, Denise L. (Department: 3744)
Refrigeration
Automatic control
Refrigeration producer
C062S513000
Reexamination Certificate
active
06581397
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a refrigerating device using a working medium containing an R32 refrigerant (chemical formula: CH
2
F
2
) and particularly to a refrigerating device which copes with a low GWP (global warming potential), is energy-saving and inexpensive, and is capable of protecting the ozone layer and achieving recycling.
BACKGROUND ART
Hitherto, a refrigerating device of the heat pump type using a HCFC (hydrochlorofluorocarbon) refrigerant is known. The refrigerating device has a refrigerant circuit having a compressor, a condenser, a motor operated valve, and an evaporator connected sequentially in the shape of a loop and has a supercooling heat exchanger disposed between the condenser and the motor operated valve. A gas refrigerant from the supercooling heat exchanger is returned to a liquid injection of the compressor and the suction side of the compressor. However the refrigerating device has a problem of deterioration of the COP (coefficient of performance) owing to decrease in the circulation amount of the refrigerant caused by by-passing of the refrigerant. The HCFC refrigerants have a problem of deteriorating the environment of the earth because they have a high ozone-layer destruction coefficient and a high GWP (global warming potential).
Thus it is conceivable to use the R32 refrigerant as a low-GWP HFC refrigerant capable of realizing a high COP without destroying the ozone layer. However in its physical properties, the R32 refrigerant has a higher discharge temperature than the HCFC refrigerants. Thus the R32 refrigerant has a problem that it deteriorates oil for the refrigerating device so that the reliability deteriorates.
In a conventional apparatus using R22, when a dryness of the refrigerant at the suction side of a high-pressure dome type compressor is 0.97, the discharge temperature reaches 90° C. In the case of a low-pressure dome type compressor, when a dryness of the refrigerant at its suction side is 0.97, the discharge temperature reaches 70° C.
The R32 refrigerant has a low pressure loss and its COP (coefficient of performance) can be improved, whereas in its physical properties, its discharge temperature rises to a temperature higher than the discharge temperatures of R22, R410, and R407 by 15° C. in theory and by 10-15° C. in actual measurement. Thus in an apparatus using R22, R410 or R407, merely replacing such a refrigerant with R32 and changing the refrigeration oil to an oil compatible with R32 would lead to a problem of deterioration in reliability and performance.
Regarding the reliability, there is a fear that when the compressor is heated to a high temperature, deterioration of a material and oil proceeds and its long-term reliability deteriorates. In particular, because a compressor motor deteriorates (the demagnetizing force decreases) greatly owing to temperature, attention should be paid to a DC motor in dependence on a material that is used therefor.
Regarding the performance, supposing that the discharge-pipe temperature, the manner of controlling the refrigerant by using sensors, and the manner of controlling electric current are same as before, the R32 refrigerant has a problem of deteriorating the performance of the refrigerating device and reducing its operation area.
DISCLOSURE OF THE INVENTION
Therefore, it is an object of the present invention to provide a refrigerating device capable of optimizing the discharge temperature of a compressor without deteriorating the efficiency of the compressor by using a working medium containing an R32 refrigerant, so that the COP and reliability of the refrigerating device is improved.
In order to accomplish the above object, a refrigerating device according to the present invention comprises:
a refrigerant circuit having a compressor, a condenser, a main pressure-reducing means, and an evaporator connected in a loop;
a supercooling heat exchanger disposed between the condenser and the main pressure-reducing means;
a by-pass pipe by which a gas side of the refrigerant circuit and a liquid side thereof are connected through the supercooling heat exchanger; and
a supercooling pressure-reducing means disposed at the by-pass pipe upstream of the supercooling heat exchanger, wherein:
the refrigerating device uses an R32 refrigerant or a mixed refrigerant containing the R32 refrigerant at at least 70 wt %; and
the refrigerating device further comprises:
a discharge temperature sensor detecting a discharge temperature of the compressor;
a discharge temperature determination part determining the discharge temperature detected by the discharge temperature sensor; and
a control part controlling the supercooling pressure-reducing means, based on a result of determination made by the discharge temperature determination part, to control an amount of the refrigerant flowing through the by-pass pipe.
According to the refrigerating device, after the R32 refrigerant (or the mixed refrigerant containing R32 at at least 70 wt %) discharged from the compressor is condensed by the condenser, the refrigerant is pressure-reduced by the main pressure-reducing means. Then the refrigerant vaporizes in the evaporator and returns to the suction side of the compressor. At this time, the refrigerant pressure-reduced by the supercooling pressure-reducing means flow from the liquid side of the refrigerant circuit to the gas side thereof at the downstream side of the evaporator by the by-pass pipe through the supercooling heat exchanger. The supercooling heat exchanger supercools the refrigerant flowing from the condenser to the main pressure-reducing means. The discharge temperature determination part determines the discharge temperature detected by the discharge temperature sensor. Based on the result of the determination, the control parts controls the supercooling pressure-reducing means to adjust the amount of the refrigerant flowing through the by-pass pipes to a large amount or a small amount, according as the discharge temperature is high or low. Thus, when the discharge temperature is high, the discharge temperature can be decreased by increasing the amount of the refrigerant flowing through the by-pass pipes. Accordingly, even if the R32 refrigerant (or the mixed refrigerant containing R32 at at least 70 wt %) which is higher, due to its physical property, in the discharge temperature than the HCFC refrigerants is used, it is possible to optimize the discharge temperature without deteriorating the efficiency and thus improve the COP and the reliability. A motor operated valve may be used as the supercooling pressure-reducing means. Then, the opening of the motor operated valve is controlled to control a by-pass refrigerant amount. Further a solenoid operated valve and a capillary may be combined to provide the supercooling pressure-reducing means to control the by-pass refrigerant amount by opening and closing of the solenoid operated valve.
In one embodiment, when the discharge temperature determination part determines that the discharge temperature exceeds a set upper-limit value, the control part controls the supercooling pressure-reducing means to increase the amount of the refrigerant flowing through the by-pass pipe, and to decrease the amount of the refrigerant flowing through the by-pass pipe when the discharge temperature determination part determines that the discharge temperature is smaller than a set lower-limit value.
According to the refrigerating device, when the discharge temperature determination part determines that the discharge temperature exceeds a set upper-limit value, the control part controls the supercooling pressure-reducing means to increase the amount of the refrigerant flowing through the by-pass pipe. On the other hand, when the discharge temperature determination part determines that the discharge temperature is smaller than the set lower-limit value, the control part controls the supercooling pressure-reducing means to decrease the amount of the refrigerant flowing through the by-pass pipe. Thereby optimum control of the discharge temperature can be
Shibaike Koji
Taira Shigeharu
Tanaka Jun-ichirou
Birch & Stewart Kolasch & Birch, LLP
Daikin Industries Ltd.
Esquivel Denise L.
Norman Marc
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