Refrigeration cycle apparatus

Abstract

A refrigeration cycle apparatus 100 includes a low-pressure compressor 113, a high-pressure compressor 101, a radiator 103, a gas-liquid separator 107, an expansion valve 109, an expander 105 and an evaporator 111. The low-pressure compressor 113 and the expander 105 are coupled by a shaft 116, and the low-pressure compressor 113 is driven using power recovered by the expander 105 from a refrigerant. The low-pressure compressor 113 and the high-pressure compressor 101 are serially connected by an intermediate-pressure flow path 114. The gas-liquid separator 107 and the intermediate-pressure flow path 114 are connected by the reciprocating flow path 115. The reciprocating flow path 115 is configured to allow the refrigerant to circulate bidirectionally. It is possible to regulate the refrigerant flow rate in the reciprocating flow path 115 by controlling the opening degree of the expansion valve 109.

Description

TECHNICAL FIELD[0001]The present invention relates to a refrigeration cycle apparatus.BACKGROUND ART[0002]As indicated in FIG. 13, a refrigeration cycle apparatus having a first compressor 801a, a radiator 802, an expander 803, a heat absorber 804 and a second compressor 801b is known to be used for an air-conditioner, a water heater or the like (Patent literature 1). The second compressor 801b and the expander 803 are coupled to each other by a rotary shaft 806, and the driving power for the second compressor 801b is supplied from the power generated at the time of the expansion of a refrigerant in the expander 803. This makes it possible to reduce the power to be consumed in the first compressor 801a for increasing the refrigerant pressure to a particular pressure.[0003]In the refrigeration cycle apparatus illustrated in FIG. 13, the rotational speed of the expander 803 and the rotational speed of the second compressor 801b are consistent. In addition, the refrigerant that has bee...

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Benefits of technology

[0011]According to the present invention, in the case where the suction volume of the low-pressure compressor is insufficient compared to the suction volume of the expander, a gas refrigerant is delivered from the gas-liquid separator to the intermediate-pressure flow path through the reciprocating flow path to be drawn into the high-pressure compressor. This establishes the balance of the flow rate in a refrigeration cycle. On the other hand, in the case where the suction volume of the expander is insufficient compared to the suction volume of the low-pressure compressor, a part of the gas refrigerant that has been pre-compressed in the low-pressure compressor is delivered to the gas-liquid separator through the intermediate-pressure flow path and the reciprocating flow path. This establishes the balance of the flow rate in a refrigeration cycle. Whatever the value (design value) of the ratio between the suction volume of the low-pressure compressor and the suction volume of the expander may be, the flow rate balance is established in a refrigeration cycle due to the function of the reciprocating flow path.

[0012]Meanwhile, the pressure inside the gas-liquid separator can be freely adjusted by an expansion valve. By adjusting the pressure inside the gas-liquid separator, it is possible to arbitrarily adjust the refrigerant pressure on the radiator side. For example, if the expansion valve is completely opened under arbitrary operational conditions, the pressure inside the gas-liquid separator is closest to the evaporation pressure of the refrigerant in the evaporator. Then, the pressure difference between the inlet and the outlet of the low-pressure compressor is closest to zero because the gas-liquid separator and the intermediate-pressure flow path are connected by the reciprocating flow path. That is, the compression work of the low-pressure compressor decreases. On the other hand, the pressure difference between the inlet and the outlet of the expander increases, so that the amount of power recovery in the expander increases. The rotational speed of each of the expander and the low-pressure compressor increases based on the relationship expressed by (the amount of power recovery)>(the compression work). This results in a decrease in the refrigerant pressure on the radiator side because the discharge refrigerant flow rate of the expander is excessive with respect to the discharge refrigerant flow rate of the high-pressure compressor. As a result, the amount of power recovery of the expander decreases to be balanced with the compression work of the low-pressure compressor, thereby stabilizing the refrigeration cycle. That is, it is possible to decrease the refrigerant pressure on the radiator side by opening the expansion valve.

[0013]Conversely, the pressure inside the gas-liquid separator is steadily increased by gradually closing the expansion valve. The pressure difference between the inlet and the outlet of the low-pressure compressor increases because the gas-liquid separator and the intermediate-pressure flow path are connected by the reciprocating flow path. That is, the compression work of the low-pressure compressor increases. On the other hand, the pressure difference between the inlet and the outlet of the expander decreases, so that the amount of power recovery of the expander decreases. The rotational speed of each of the expander and the low-pressure compressor decreases based on the relationship expressed by (the amount of power recovery)<(the compression work). This results in an increase in the refrigerant pressure on the radiator side because the discharge refrigerant flow rate of the expander falls short with respect to the discharge refrigerant flow rate of the high-pressure compressor. As a result, the amount of power recovery in the expander increases to be balanced with the compression work of the low-pressure compressor, thereby stabilizing the refrigeration cycle. That is, it is possible to increase the refrigerant pressure on the radiator side by closing the expansion valve.

[0014]In this way, it is possible always to adjust the refrigerant pressure on the radiator side optimally by controlling the opening degree of the expansion valve appropriately and thereby controlling the rotational speed of each of the expander and the low-pressure compressor. Moreover, the entire amount of the refrigerant passes through the expander, so that efficient power recovery is feasible. Even if the refrigerant flows back in the reciprocating flow path (the second circulation state) and a part of the recovered power is consumed for the circulation of the refrigerant, the present invention can achieve an improved energy budget compared to the conventional example (cf. FIG. 14) in which a refrigerant is allowed to flow into a bypass circuit. Accordingly, a refrigeration cycle apparatus including an expander and a low-pressure compressor at an appropriate volume ratio suitable for application can be operated under desirable pressure and temperature conditions in view of energy efficiency.

[0015]Further, the above-described theory is valid whatever the volume ratio between the low-pressure compressor and the expander may be. Therefore, according to the present invention, a low-pressure compressor and an expander can be designed so as to have an arbitrary volume ratio that can minimize their annual power consumption theoretically. That is, the refrigeration cycle apparatus of the present invention has an enhanced degree of design freedom.

Problems solved by technology

However, the constraint for constant density ratio makes it impossible to adjust the density ρexi and the density ρC2i freely, so that efficient operation is difficult to achieve.

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