Refrigeration cycle

Abstract: In order to magnify capacity control of a refrigeration cycle for an increased efficiency and achievement of compactness, the refrigeration cycle includes a compressor 10, a four-way valve 20, a heat exchanger 30 on a side of a heat source, a liquid receiver 40, a heat exchanger 70 on a side of use, and an electronic expansion valve 60, all of which are connected other by pipes, and comprises a refrigerant circulating in the refrigeration cycle and being a non-azeotropic refrigerant, a second liquid receiver 130 for taking out a refrigerant vapor from an upper portion of the liquid receiver 40 to condense and store the refrigerant, and a pipe 150 connecting the second liquid receiver 130 to the liquid receiver 40 via a shut-off valve 140.

Description: The present invention relates to a refrigeration cycle according to the preamble of claim 1. Such a refrigeration cycle is described in EP 0 838 643 A2. Conventionally, in order to exhibit a capacity conformed to load, a compressor is inverter-driven to change the mass flow rate of a refrigerant circulating in a refrigeration cycle. Another system, in which a non-azeotropic refrigerant is used as a refrigerant and a distiller is used to change the composition of the refrigerant for production of a capacity suitable for load at all times, is known and disclosed in, for example, JP-A-9-196481. In the above-described prior art, the system adapted for capacity control through inverter-driving is difficult to operate at very low and very high speeds of compressor, so that it cannot but entail upper and lower limits in inverter frequency. Therefore, capacity control is effected by making the compressor on/off particularly at low load, thus leading to a poor efficiency. Also, with the system using a distiller, the distiller and a separation circuit thereof are large in scale to make it difficult for the system to be rendered compact in size. EP 0 838 643 A2 refers to a refrigeration cycle using a non-azeotrope refrigerant. The cycle comprises a compressor, a heat-source-side heat exchanger, a use-side heat exchanger, a refrigerant pressure reducing means, a refrigerant receiver disposed between the heat-source-side heat exchanger and the use-side heat exchanger. Further, composition ratio detecting means are arranged for detecting the composition ratio of the refrigerant, operating composition ratio control means disposed between the heat-source-side heat exchanger and the receiver. The control means take out refrigerant gas from the receiver on the basis of the detected composition ratio and adjust the composition ratio according to predetermined values depending on operation parameters. The vapor part of the liquid receiver is connected by a pipe comprising a shut-off valve and a heat exchanger with the vapor portion of the liquid tank which is part of the control means. The liquid portion of the receiver is connected through a shut-off valve and the other side of the heat exchanger with a pipe going to an accumulator on the suction side of the compressor. This pipe is connected through a shut-off valve with the liquid in the refrigerant tank. This system works only in connection with the accumulator. The object of the present invention is to magnify capacity control for an increased efficiency and achievement of compactness, particularly to magnify the capacity on a side of low load to afford an energy-saving operation for a reduction in annual power consumption and adaptation to environment, such as prevention of destruction of ozone layer and an increase in recycle efficiency. In order to solve the above problems, the present invention provides the refrigeration cycle of claim 1 embodiments of which are described in claims 2 to 4. In the refrigeration cycle of the invention, the second liquid receiver is connected to the suction side of the compressor via a second shut-off valve and a pressure reducing mechanism whereby any restrictions as to the positional relationship between the two liquid receivers are excluded. In the preferred refrigeration cycle, the refrigerant vapor is preferably caused to make heat exchange with a refrigerant on a suction side of the compressor to thereby be condensed. The use of a non-azeotropic refrigerant (for example, a HFC refrigerant mixture such as R407C having an ozone layer destruction coefficient of zero) results in that the refrigerant vapor in the liquid receiver contains much low boiling point refrigerant in composition and an amount of the refrigerant stored in the second liquid receiver and containing an abundant amount of low boiling point refrigerant can be changed by the opening and closing actions of the shut-off valve, so that the capacity of an air conditioner can be controlled by changing the composition ratio of a refrigerant circulating in the refrigeration cycle, and also a refrigerant rectifying column can be dispensed with which serves as separating components of the refrigerant mixture depending upon differences in boiling point among the respective component and which is liable to become large-sized, complicated, and expensive. Therefore, the number of on/off operations of an associated compressor can be decreased by increasing the capacity control range without hindering the compactness of an air conditioner, so that the air conditioner can be enhanced in efficiency and comfort. The refrigerant vapor, in which a low boiling point refrigerant is rich, is taken out from the liquid receiver, and the taken-out refrigerant is condensed and stored or returned to the refrigeration cycle, whereby the refrigerant circulating in the refrigeration cycle is changed in composition and whereby the number of times, in which the compressor is made off, is reduced. Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. Fig. 1 is a schematic diagram showing a refrigeration cycle which is not part of the invention; Fig. 2 is a schematic diagram showing a modified refrigeration cycle of Fig. 1; Fig. 3 is a schematic diagram showing a refrigeration cycle of the invention; Fig. 4 is a schematic diagram showing a modified refrigeration cycle of Fig. 3. In Fig. 1, the reference character A denotes an outdoor unit, and B an indoor unit. The reference numeral 10 denotes a compressor, 20 a four-way valve for switching the flow direction of a refrigerant according to the heating and cooling operations, 30 a heat exchanger on a heat source side, 40 a (first) liquid receiver, 50 a liquid connection pipe, 60 an electronic expansion valve in the indoor unit, 70 a heat exchanger on a use side, 80 a gas connection pipe, 130 a second liquid receiver for storing a condensate containing an abundant amount of a low boiling point liquid, 110 a pipe for directing a refrigerant vapor in the first liquid receiver 40 to a second liquid receiver 130, and 150 a pipe for directing a liquid refrigerant in the second liquid receiver 130 to the first liquid receiver 40, and connected from a lower portion of the liquid receiver 130 to the liquid receiver 40 via a shut-off valve 140. The second liquid receiver 130 is installed above the first liquid receiver 40. Arrows in the drawings indicate the direction, in which a refrigerant flows, solid lines indicating a cooling operation and broken lines indicating a heating operation. Since the refrigerant circulating in the refrigeration cycle is a non-azeotropic refrigerant, a refrigerant vapor accumulating in an upper portion of the first liquid receiver 40 has that composition, in which a low boiling point refrigerant is rich, due to the low boiling point refrigerant being more liable to vaporize than a high boiling point refrigerant. When the shut-off valve 140 is closed, the refrigerant vapor, in which the low boiling point refrigerant is rich, in the first liquid receiver 40 performs heat exchange with the outside air to be stored in the second liquid receiver 130. As a result, the refrigerant circulating in the refrigeration cycle becomes lean in the low boiling point refrigerant and so circulates with a high ratio of the high boiling point refrigerant in composition. When the shut-off valve 140 is opened, due to the second liquid receiver 130 being installed above the first liquid receiver 40, the liquid refrigerant in the second liquid receiver 130 returns to the first liquid receiver 40 through the pipe 150 under gravity. Therefore, the low boiling point refrigerant does not accumulate in the second liquid receiver 130, and so the composition in the refrigeration cycle does not change. As described above, if a liquid refrigerant, in which the low boiling point refrigerant is rich, is stored in the second liquid receiver 130 at low load, a refrigerant of that composition, in which the high boiling point refrigerant is rich, circulates in the main refrigeration cycle. Therefore, the refrigeration cycle can be decreased in capacity and so the on/off operation of the compressor can be reduced for an increased in efficiency. Also, the shut-off valve 140 is opened at high load to permit a refrigerant, in which the low boiling point refrigerant is rich, to be returned to the main refrigeration cycle, so that the refrigerant circulating in the refrigeration cycle is restored with respect to composition to enable increasing the capacity. Fig. 2 shows a modification of the refrigeration cycle of Fig. 1. The reference numeral 120 denotes a heat exchanger for making heat exchange between the refrigerant vapor from the first liquid receiver 40 and a refrigerant sucked into the compressor 10. The refrigerant vapor in the first liquid receiver 40 is liquefied by heat exchange with the outside air in the above-described embodiment, but it does not liquefy under the condition that the outside air is high in temperature. Hereupon, when the refrigerant vapor is caused to make heat exchange with a refrigerant on a suction side of the compressor where the refrigerant is always made low in temperature, the refrigerant is changed in composition independently of the outside air temperature to make the capacity variable. Fig. 3 shows a refrigerant cycle of the invention, in which the pipe 150 communicated to the liquid in the second liquid receiver 130 is connected to the compressor suction side via the shut-off valve 140 and a capillary 180. In the embodiment shown in Fig. 1 or 2, gravity is used to remove the liquid refrigerant in the second liquid receiver 130, so that there is imposed a restriction that a liquid level in the second liquid receiver 130 should be higher than that in the first liquid receiver 40. In the refrigerant cycle of Fig. 3, however, the liquid refrigerant stored in the second liquid receiver 130 is returned to the compressor suction side through the capillary by virtue of a pressure difference, and so the positional relationship between the first and second liquid receivers becomes free of any restrictions. While the pipe 150 connects to an suction pipe this side of the heat exchanger 120 in Fig. 3, it may be also connected to the suction pipe that side of the heat exchanger 120 and between the compressor 10 and the heat exchanger 120. When the circulating refrigerant should not be changed in composition, the shut-off valve 140 is opened to remove the liquid refrigerant in the second liquid receiver 130 in the embodiment shown in Fig. 3. Consequently, the refrigerant vapor in the first liquid receiver 40 will bypass the compressor 10. Fig. 4 shows a modification of Fig. 3, wherein a pipe for providing communication between the liquid in the first liquid receiver 40 and the liquid in the second liquid receiver 130 is provided with a shut-off valve 190 for communication. Since the refrigerant preserved in the second liquid receiver 130 varies greatly in amount, the first liquid receiver 40 must be enlarged by a magnitude conformed to the varying amount of the refrigerant. When no change is to be made in composition, the shut-off valve 190 is opened to permit a surplus refrigerant to be accumulated in both of the first liquid receiver 40 and the second liquid receiver 130, so that the first liquid receiver 40 need not be enlarged and so can be advantageously made small-sized. Also, when some change is to be made in composition, the shut-off valve 190 is closed to prevent the liquid refrigerants in the first liquid receiver 40 and the second liquid receiver 130 from mixing with each other, so that the refrigerant can be made variable in composition.

Claims: A refrigeration cycle comprising a non-azeotropic refrigerant to circulate therein and connected by pipes (50, 80) a compressor (10), a four-way valve (20) for switching the flow direction of the refrigerant according to the heating and cooling operations, a heat exchanger (30) on a heat-source-side, a first liquid receiver (40), a heat exchanger (70) on the use side, and an electronic expansion valve (60), a second liquid receiver (130) for storing a condensate containing an abundant amount of low boiling point liquid of the refrigerant, connected with the first liquid receiver (40) by a pipe (110) for directing refrigerant vapor in the first liquid receiver (40) to the second liquid receiver (130) and a further pipe (150) connecting the lower portion of the second liquid receiver (130) with the suction side of the compressor (10) via a shut-off valve (140), characterized by a pressure reducing mechanism (180) in the further pipe (150) connecting the lower portion of the second liquid receiver (130) with the suction side of the compressor (10) via the shut-off valve (140). Refrigeration cycle according to claim 1, characterized by a further heat exchanger (120) for exchanging heat between the pipe on the suction side of the compressor (10) and the pipe (110) connecting the upper portions of the two liquid receivers (40, 130). Refrigeration cycle according to claim 2, characterized in that the pipe (150) with the pressure reducing means (180) enters the pipe on the suction side of the compressor (10) upstream of the further heat exchanger (120). Refrigeration cycle according to one of the preceding claims, characterized by a shut-off valve (190) in a pipe connecting the liquids in the two liquid receivers (130, 40).

Inventors: MATSUMURA KENJI, NAKAYAMA SUSUMU, MATSUMURA, KENJI, NAKAYAMA, SUSUMU, Matsumura, Kenji, Shimizu Works, Nakayama, Susumu, Shimizu Works
Applicants: HITACHI AIR CONDITIONING SYS, HITACHI AIR CONDITIONING SYSTEMS CO., LTD.
Application year: 2001
Main classification: F25B13
IPC codes: F25B1, C09K5, F25B13, F25B41