JP2014001916A - Refrigeration cycle device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a refrigeration cycle device capable of improving COP by appropriately controlling a ratio of a flow rate G and a density ρ of a refrigerant flowing into a compressor and an expander.SOLUTION: The refrigeration cycle device comprises: a first compressor 1 for compressing a refrigerant; a second compressor 2 for further compressing the refrigerant which has been compressed by the first compressor 1; exothermic heat exchangers 5, 12 for cooling the refrigerant which has been compressed by the second compressor 2, through heat exchange with outside air; an expander 11 which is formed coaxially with the first compressor 1 and expands the refrigerant which has been cooled by the exothermic heat exchangers 5, 12; and endothermic heat exchangers 12, 5 for heating the refrigerant expanded by the expander 11. The refrigeration cycle device further comprises: first bypass channels 9, 19 in which the refrigerant cooled by the exothermic heat exchangers 5, 12 is caused to flow into the first compressor 1 after being decompressed partially; and second bypass channels 9, 20 in which the refrigerant cooled by the exothermic heat exchangers 5, 12 is caused to flow into the second compressor 2 after being decompressed partially.

Description

  The present invention relates to a refrigeration cycle apparatus in which a compressor and an expander are coaxially formed. Specifically, the ratio of the flow rate and density of refrigerant flowing into the compressor and the expander is appropriately controlled to improve COP. The present invention relates to a refrigeration cycle apparatus that can be used.

Generally, the compressor displacement to be used in a refrigeration cycle apparatus, the flow rate of refrigerant flowing into the compressor (the compressor flow rate) G ₁ is the density (compressor density) of the refrigerant entering the compressor and [rho _1, It is calculated by the product of the compressor volume (compressor volume) V ₁ and the compressor rotation speed (compressor rotation speed) N ₁ . Further, in the positive displacement expander for use in a refrigeration cycle apparatus, the flow rate of refrigerant flowing into the expander (expander flow) G ₂ is the density of the refrigerant flowing into the expander (expander Density) [rho _2, It is calculated by the product of the volume of the expander (expander volume) V ₂ and the rotation speed (expander speed) N ₂ of the expander. That is, the following expression is established.
Compressor flow rate G ₁ = ρ ₁ × V ₁ × N ₁
Expander flow rate G ₂ = ρ ₂ × V ₂ × N ₂

A refrigeration cycle comprising a positive displacement compressor, a heat dissipation heat exchanger for cooling the refrigerant, a positive displacement expander, and an endothermic heat exchanger for heating the refrigerant, wherein the compressor and the expander are coaxially formed. In the apparatus, the compressor rotational speed N ₁ and the expander rotational speed N ₂ are equal. In addition, since the compressor volume V ₁ and the expander volume V ₂ are determined by design, the ratio (V ₁ / V ₂ ) can be expressed by a constant k. Therefore, such a refrigeration cycle apparatus is
_{G 1 / ρ 1 = k (} G 2 / ρ 2)
It will operate while satisfying the conditional expression.

  However, when the amount of heat exchange in the heat dissipation heat exchanger or the endothermic heat exchanger changes due to a change in the outside air temperature, the flow rate and density of the refrigerant also change accordingly. Then, there is a problem that the refrigeration cycle apparatus does not operate without satisfying the above expression, or an extra load is applied to satisfy the above expression, and the efficiency of the refrigeration cycle apparatus decreases.

  Therefore, in order to solve such a problem, in the conventional refrigeration cycle apparatus, a part of the refrigerant bypasses the expander, and the refrigerant to be bypassed and the refrigerant flowing into the expander are heat-exchanged by an internal heat exchanger. There was something to be made (for example, Patent Document 1). Such a refrigeration cycle apparatus was able to control the refrigerant flow rate that became excessive due to a change in the outside air temperature by bypassing the expander, and to satisfy the above equation.

JP 2007-210242 A

  However, in the conventional refrigeration cycle apparatus, all of the refrigerant that bypasses the expander flows into the compressor, so the flow rate of the refrigerant that bypasses the expander and the flow rate of the refrigerant that flows into the compressor are controlled independently. It was difficult to control the refrigerant flow rate appropriately. For this reason, the efficiency of the refrigeration cycle apparatus may be reduced due to a change in the outside air temperature.

  Accordingly, the problem to be solved by the present invention that addresses such problems is to improve COP by appropriately controlling the ratio between the flow rate and density of the refrigerant flowing into the compressor and the expander. An object of the present invention is to provide a refrigeration cycle apparatus capable of

  In order to solve the above problems, a refrigeration cycle apparatus according to the present invention includes a first compressor that compresses a refrigerant, a second compressor that further compresses the refrigerant compressed by the first compressor, and the second compression. A heat radiation heat exchanger that cools the refrigerant compressed by the machine by heat exchange with the outside air, an expander that is formed coaxially with the first compressor and expands the refrigerant cooled by the heat radiation heat exchanger, and An endothermic heat exchanger that heats the refrigerant expanded by the expander, and a first bypass flow that depressurizes a part of the refrigerant cooled by the radiant heat exchanger and flows into the first compressor And a second bypass flow path for depressurizing a part of the refrigerant cooled by the heat dissipation heat exchanger and flowing into the second compressor.

  According to the refrigeration cycle apparatus according to the present invention, a part of the refrigerant cooled by the heat dissipation heat exchanger is caused to flow into the first compressor and the second compressor through the first bypass channel and the second bypass channel, respectively. Therefore, the flow rate of the refrigerant that bypasses the expander and the flow rate of the refrigerant that flows into the first compressor formed coaxially with the expander can be controlled independently. Thereby, even if it is a case where external temperature changes, the flow volume of the refrigerant | coolant which flows in into an expander and a compressor can be controlled appropriately, and COP of a refrigerating-cycle apparatus can be improved.

It is a block diagram which shows embodiment of the refrigerating-cycle apparatus by this invention. It is a Mollier diagram which shows the refrigerating cycle of the said embodiment. It is a graph which shows the relationship between the refrigerant | coolant temperature of an expander inlet, and the opening degree of a 1st valve means. It is a graph which shows the relationship between the refrigerant temperature of an expander inlet, and the opening degree of an expansion valve. It is a graph which shows the relationship between a high voltage | pressure and COP for every heat radiation heat exchanger exit temperature. It is a graph which shows the relationship between the opening degree of a 1st valve means, and a high voltage | pressure. It is a graph which shows the relationship between the opening degree of an expansion valve, and high pressure. It is a graph which shows the relationship between the heat exchanger outlet temperature and the optimum high pressure.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
First, the configuration of the refrigeration cycle apparatus according to the present embodiment and the state of the refrigerant in each part will be described with reference to FIGS. 1 and 2. FIG. 1 is a configuration diagram showing an embodiment of a refrigeration cycle apparatus according to the present invention. This refrigeration cycle apparatus is an air conditioning facility that uses CO ₂ as a refrigerant, and can be used for both cooling and heating by switching the flow path of the refrigerant, as shown in FIG. The first compressor 1, the second compressor 2, the outdoor unit 5, the internal heat exchanger 10, the expander 11, the indoor unit 12, the expansion valve 17, the first flow path 19, and the second And a flow path 20. Hereinafter, the present embodiment will be described along a refrigerant flow path (hereinafter referred to as “cooling cycle”) when the refrigeration cycle apparatus is used for cooling.

The first compressor 1 is a positive displacement compressor including a reciprocating compressor, a swash plate compressor, a screw compressor, a scroll compressor, and the like. The flow rate (compressor flow rate) G ₁ of the refrigerant compressed by the first compressor ₁ is the density (compressor density) ρ _{1 of} the refrigerant flowing into the first compressor ₁ and the volume of the refrigerant taken in by the first compressor 1. (Compressor volume) V ₁ and the number of rotations of the first compressor 1 (compressor rotation number) N ₁ are obtained. That is,
Compressor flow rate G ₁ = Compressor density ρ ₁ × Compressor volume V ₁ × Compressor rotation speed N ₁
Holds. The first compressor 1 is driven by an expander 11 formed coaxially.

When the refrigerant is compressed by the first compressor 1, the state of the refrigerant changes along the isoenthalpy line from A to B in FIG. This refrigerant merges with and mixes with a refrigerant (second refrigerant) flowing in from the second flow path 20 described later at the junction P ₄ , and changes to the state C. The refrigerant that has changed to the state C flows into the second compressor 2 provided downstream of the first compressor 1.

  The second compressor 2 can be arbitrarily selected from known compressors and is not limited to a positive displacement compressor, and may be a turbo compressor including a centrifugal compressor and an axial flow compressor. Good. The second compressor 2 is driven by, for example, a motor 3 and rotates independently of the first compressor 1.

  When the refrigerant is compressed by the second compressor 2, the state of the refrigerant changes from C to D in FIG. The refrigerant that has changed to the state D flows into the outdoor unit 5 (radiation heat exchanger) through the four-way valve 4 provided downstream of the second compressor 2.

  The four-way valve 4 switches between a refrigerant flow path when using cooling and a refrigerant flow path when using heating (hereinafter referred to as “heating cycle”). This switching is performed by energizing a built-in electromagnetic coil. Is called. As shown in FIG. 1, the solid line part in the four-way valve 4 is a flow path in the four-way valve 4 when cooling is used, and the broken line part is a flow path in the four-way valve 4 when heating is used.

  At the time of cooling use, the refrigerant flows into the outdoor unit 5 provided downstream through the solid line portion in the four-way valve 4. When passing through the four-way valve 4, the state of the refrigerant remains the same as D in FIG.

  The outdoor unit 5 functions as a heat dissipation heat exchanger in the present invention when cooling is used, and cools the refrigerant by exchanging heat with the outside air.

  When the refrigerant is cooled by the outdoor unit 5 (radiation heat exchanger), the state of the refrigerant changes from D to E in FIG. This refrigerant flows into the internal heat exchanger 10 through the bridge circuit 6 provided downstream of the outdoor unit 5.

  The bridge circuit 6 includes four check valves 7a to 7d that are connected in an annular shape, and the refrigerant on the high-pressure side (states D, E, and F in FIG. 2) and the low-pressure side (the state in FIG. 2) in the refrigeration cycle. The cooling cycle and the heating cycle are automatically switched using the pressure difference between the refrigerants G and H). More specifically, when the cooling circuit is used, the bridge circuit 6 opens the check valves 7a and 7b and closes the check valves 7c and 7d to form a cooling cycle. This is because the high pressure side (state E) refrigerant flows into the check valve 7a and the low pressure side (state G) refrigerant flows into the check valve 7b, so that the check valves 7c and 7d become the check valve 7a. This is because it is pressed from the side and does not open. In this way, by arranging the bridge circuit 6 downstream of the heat dissipation heat exchanger (the outdoor unit 5 when using the cooling or the indoor unit 12 when using the heating), in any case of using the cooling and heating, The refrigerant can be caused to flow into the expander 11 from the same direction.

In the cooling use, refrigerant cooled state E in the outdoor unit 5, passes through the check valve 7a, is branched at the branch point P ₁ which is provided on the downstream of the refrigerant pipe. When passing through the check valve 7a, the state of the refrigerant does not change as E in FIG.

The refrigerant pipe has a refrigerant flow path (hereinafter referred to as “main flow path”) 8 communicating with the expander 11 and a refrigerant flow path (hereinafter referred to as “sub flow path” bypassing the expander 11 at the branch point P _1. Branch to 9). Therefore, the refrigerant cooled by the outdoor unit 5 is divided into the refrigerant flowing into the main flow path 8 (hereinafter referred to as “main refrigerant”) and the refrigerant flowing into the sub flow path 9 (hereinafter referred to as “sub-flow”) at the branch point P _1. It is branched into two, called “refrigerant”.

First, the main flow path 8 will be described. On the downstream of the main channel 8 of the branch point P _1, the internal heat exchanger 10 is provided. The internal heat exchanger 10 is provided across both the main channel 8 and the auxiliary flow channel 9 which is branched at the branch point P _1, by heat exchange with the primary refrigerant and the secondary refrigerant, the primary refrigerant Cool and heat the secondary refrigerant.

  As the main refrigerant is cooled by the internal heat exchanger 10, the state of the main refrigerant changes from E to F in FIG. Thus, by cooling the main refrigerant by the internal heat exchanger 10, the degree of supercooling of the main refrigerant can be increased. Thereby, the efficiency of the refrigeration cycle apparatus can be improved. The refrigerant that has changed to the state F flows into the expander 11 provided downstream of the internal heat exchanger 10 on the main flow path 8.

The expander 11 is a positive displacement type, is formed coaxially with the first compressor 1, and rotates together with the first compressor 1. Therefore, the rotation speed N 1 of the first compressor ₁ and the rotation speed N ₂ of the expander 11 are equal. Here, the flow rate of the refrigerant (expander flow rate) G ₂ expanded by the expander 11 is the density of the refrigerant flowing into the expander 11 (expander density) ρ ₂ and the volume of refrigerant taken by the expander 11 (expander). Volume) V ₂ and the rotation speed of the expander 11 (expander speed) N ₂ . That is,
Expander flow rate G ₂ = Expander density ρ ₂ × Expander volume V ₂ × Expander rotation speed N ₂
Holds. As described above, the compressor flow rate G1 compressed by the first compressor ₁ is
Compressor flow rate G ₁ = Compressor density ρ ₁ × Compressor volume V ₁ × Compressor rotation speed N ₁
It is expressed. Furthermore, when the compressor rotational speed N ₁ = expander rotational speed N ₂ and the compressor volume V ₁ / expander volume V ₂ is expressed by a constant k, the refrigeration cycle apparatus of the present invention is
_{G 1 / ρ 1 = k (} G 2 / ρ 2)
It operates while satisfying the condition.

  The refrigerant that has flowed into the expander 11 expands, and the state of the refrigerant changes from F to G in FIG. The refrigerant in the state G passes through the bridge circuit 6 (check valve 7b) and flows into the indoor unit 12 provided downstream.

  The indoor unit 12 is an endothermic heat exchanger according to the present invention during cooling use, and cools the inside air and heats the refrigerant by exchanging heat between the inside air and the refrigerant.

  When the refrigerant is heated in the indoor unit 12, the state of the refrigerant changes from G to H in FIG. The refrigerant in the state H passes through the solid line portion of the four-way valve 4 and flows into the third compressor 13 provided downstream. Note that when passing through the four-way valve 4, the state of the refrigerant remains unchanged as H in FIG.

  The third compressor 13 is a compressor that compresses the refrigerant heated by the indoor unit 12, and can be arbitrarily selected from known compressors. The third compressor 13 is not limited to a positive displacement compressor, and may be a turbo compressor including a centrifugal compressor and an axial flow compressor. The third compressor 13 is driven by a motor 14 that is different from a motor (not shown) that drives the first compressor 1, and rotates independently of the first compressor 1. The third compressor 13 may be formed coaxially with the second compressor 2, and in this case, the third compressor 13 is preferably driven by a common motor.

  When the refrigerant is compressed by the third compressor 13, the state of the refrigerant changes from H to I in FIG. Thereby, the pressure of the refrigerant flowing into the first compressor 1 is increased. The refrigerant changed to the state I flows into the auxiliary heat exchanger 15 provided downstream of the third compressor 13.

The auxiliary heat exchanger 15 is a heat exchanger that cools the refrigerant compressed by the third compressor 13 by heat exchange with the outside air, and includes a fan 16. During cooling use, the refrigerant is cooled by the auxiliary heat exchanger 15 to reduce the degree of superheat of the refrigerant flowing into the first compressor 1, and the slope of the isoenthalpy line from state A to state B in FIG. It can be made smaller than the vertical axis of FIG. Thereby, the efficiency of the refrigeration cycle apparatus can be improved. Moreover, it is preferable not to perform heat exchange in the auxiliary heat exchanger 15 when heating is used. Specifically, it is preferable to provide a refrigerant flow path (not shown) that stops the fan 16 or bypasses the auxiliary heat exchanger 15 so that the refrigerant does not pass through the auxiliary heat exchanger 15. This prevents the degree of superheat of the refrigerant flowing into the first compressor 1 from becoming small. Therefore, it can prevent that the heating effect by the heat exchange in a thermal radiation heat exchanger (indoor unit 12) falls. Further, the density ρ ₁ of the refrigerant flowing into the first compressor 1 can be adjusted by controlling the rotational speed of the fan 16 of the auxiliary heat exchanger 15.

When the refrigerant is cooled by the auxiliary heat exchanger 15, the state of the refrigerant changes from I to J in FIG. The refrigerant in the state J is mixed merges with another refrigerant at the meeting point P ₃ to be described later. The state of the refrigerant changes from J to A in FIG. 2 and flows into the first compressor 1 again.

Next, the subchannel 9 will be described. The sub-flow channel 9 is a common part of the first bypass flow channel and the second bypass flow channel in the present invention, and is a downstream branch point P from the branch point P ₁ that branches the refrigerant cooled by the heat dissipation heat exchanger 5. It communicates to ₂ . An expansion valve 17 is provided on the sub-flow channel 9 as decompression means for decompressing the refrigerant. The expansion valve 17 is provided between the branch point P ₁ and the internal heat exchanger 10 on the sub-flow channel 9, the secondary refrigerant branched at the branch point P ₁ makes expanded (decompressed). Although the opening degree of the expansion valve 17 can be controlled according to the state of the refrigerant circulating in the refrigeration cycle apparatus, it is preferable to maintain a constant opening degree.

  When the auxiliary refrigerant is expanded by the expansion valve 17, the state of the auxiliary refrigerant changes from E to K in FIG. The refrigerant in the state K (gas-liquid coexistence state) flows into the refrigerant tank 18 provided downstream of the expansion valve 17.

  The refrigerant tank 18 is provided between the expansion valve 17 and the internal heat exchanger 10, and stores at least a part of the liquid-phase refrigerant among the gas-liquid coexisting refrigerant expanded by the expansion valve 17. The liquid-phase refrigerant stored in the refrigerant tank 18 serves as a buffer for the refrigerant flow rate. Therefore, the appropriate range of the amount of the refrigerant sealed in the refrigeration cycle apparatus can be widened. Moreover, even if it is a case where a refrigerant | coolant leaks from a refrigeration cycle apparatus, the fall of a performance can be suppressed.

  The auxiliary refrigerant that has passed through the refrigerant tank 18 flows into the internal heat exchanger 10 provided downstream of the refrigerant tank 18. As described above, the internal heat exchanger 10 is provided so as to straddle both the main flow path 8 and the sub flow path 9 and exchanges heat between the main refrigerant and the sub refrigerant. Therefore, a part of the sub refrigerant expanded by the expansion valve 17 is heated by the internal heat exchanger 10 by heat exchange with the main refrigerant.

When the sub refrigerant is heated in the internal heat exchanger 10, the state of the refrigerant changes from K to L in FIG. The sub refrigerant in the state L is branched into _two at a branch point P ₂ provided on the refrigerant pipe downstream of the internal heat exchanger 10.

The branch point P <b> ₂ is a point where the sub flow path 9 is branched into the first flow path 19 and the second flow path 20. The secondary refrigerant heated by the internal heat exchanger 10, at the branch point P _2, a first refrigerant flowing into the first flow path 19, and a second refrigerant flowing into the second flow channel 20, two Branch off.

The first flow path 19 is a refrigerant flow path that constitutes the first bypass flow path of the present invention together with the sub flow path 9, so that at least part of the sub refrigerant (first refrigerant) flows into the first compressor 1. In addition, the refrigerant pipe between the indoor unit 12 and the first compressor 1 is connected at a junction P ₃ , and in this embodiment, the refrigerant pipe is connected between the auxiliary heat exchanger 15 and the first compressor 1. Has been.

  A first valve means 21 is provided on the first flow path 19. The first valve means 21 is a valve that adjusts the flow rate of the first refrigerant, and an expansion valve is used. The opening degree of the first valve means 21 is controlled in accordance with the state of the refrigerant circulating in the refrigeration cycle apparatus, thereby adjusting the flow rate of the first refrigerant. More specifically, after the cooling by the outdoor unit 5, the opening degree of the first valve means 21 (the first opening degree) is changed according to the refrigerant temperature (expander inlet temperature) and pressure (high pressure) before flowing into the expander 11. 1 valve means opening degree) is controlled. The temperature and pressure of the refrigerant are measured by a temperature sensor and a pressure sensor (both not shown) provided between the internal heat exchanger 10 and the expander 11.

When the first refrigerant expands in the first valve means 21, the state of the refrigerant changes from L to M in FIG. First refrigerant expanded includes a refrigerant state J cooled by the auxiliary heat exchanger 15, it is mixed and joins at the joining point P _3. The mixed refrigerant enters the state A and flows into the first compressor 1 again.

The second flow path 20 is a refrigerant flow path that constitutes the second bypass flow path of the present invention together with the sub flow path 9, so that at least a part of the sub refrigerant (second refrigerant) flows into the second compressor 2. to, and is connected at the joining point P ₄ to the refrigerant pipe between the first compressor 1 and the second compressor 2. A second valve means 22 is provided on the second flow path 20. The 2nd valve means 22 is a valve which prevents the back flow of the 2nd refrigerant, for example, can use a check valve. The flow rate of the second refrigerant changes according to the opening degree of the first valve means 21.

The second refrigerant, after passing through the second valve means 22, and the refrigerant in the state B, which is compressed by the first compressor 1 are mixed and joins at the joining point P _4. The mixed refrigerant enters the state C and flows into the second compressor 2 again.

  When the refrigeration cycle apparatus configured as described above is used as heating, the indoor unit 12 functions as a heat dissipation heat exchanger of the present invention, and the outdoor unit 5 functions as an endothermic heat exchanger of the present invention. In this case, the refrigerant compressed by the second compressor 2 flows into the indoor unit 12 through the broken line portion of the four-way valve 4. In the bridge circuit 6, the check valves 7c and 7d are opened and the check valves 7a and 7b are closed to form a heating cycle. This is because when the high-pressure side refrigerant flows into the check valve 7c and the low-pressure side refrigerant flows into the check valve 7d, the check valves 7a and 7b are pressed from the check valve 7c side and do not open. It is.

Next, control of the refrigerant flow rate in the refrigeration cycle apparatus configured as described above will be described with reference to FIGS.
The refrigeration cycle apparatus according to the present invention is controlled so as to satisfy the expression G ₁ / ρ ₁ = k (G ₂ / ρ ₂ ) as described above. This control becomes possible by adjusting the opening degree of the first valve means 21, the opening degree of the expansion valve 17, or the heat exchange amount by the auxiliary heat exchanger 16.

(Design points of refrigeration cycle equipment)
In the refrigeration cycle apparatus according to the present embodiment, the pressure (high pressure) in the high-pressure side states D, E and F is 10 MPa, the pressure in the low-pressure side G and H (low pressure) is 2.649 MPa, and the third compressor output (state) I) is 4 MPa, first valve means opening (flow rate) is 50%, expansion valve opening (flow rate) is 10%, radiant heat exchanger inlet temperature (state D) is 25 ° C., expander inlet temperature (state F) ) Is 18.4 ° C,
Compressor flow rate G ₁ = 95%
Compressor density ρ ₁ = 91 m ³ / kg
Expander flow rate G ₂ = 90%
Expander density ρ ₂ = 868 m ³ / kg
Constant k (= V ₁ / V ₂ ) = 10.0
(See FIG. 2). Compressor flow rate G ₁ and the compressor density [rho _1, the refrigerant flowing into the first compressor 1, that is, the flow rate and density of the refrigerant in A of FIG. 2, the expander flow G ₂ and the expander density [rho ₂ is It is the flow volume and density of the refrigerant | coolant which flows in into the expander 11, ie, the refrigerant | coolant in F of FIG. To obtain these values, between the internal heat exchanger 10 and the expander 11, and a merging point P ₃ between the first compressor 1, a sensor for measuring the temperature and pressure of the refrigerant ( (Not shown) is provided. Incidentally, the compressor flow rate G ₁ and the expander flow G ₂ are, for convenience, shown as a percentage of total refrigerant circulating through the refrigeration cycle apparatus.

In this design condition,
G ₁ / ρ ₁ = 95/91 = 1.04
k (G ₂ / ρ ₂ ) = 10.0 (90/868) = 1.04
Thus, G ₁ / ρ ₁ = k (G ₂ / ρ ₂ ) holds.

(Control of refrigerant flow rate and density)
Here, when the expander inlet temperature decreases from 18.4 ° C. to 14.6 ° C., for example,
Compressor density ρ ₁ = 90 m ³ / kg
Expander density ρ ₂ = 892 m ³ / kg
Therefore, if the refrigerant flow rate is not controlled,
G ₁ / ρ ₁ = 95/90 = 1.06
k (G ₂ / ρ ₂ ) = 10.0 (90/892) = 1.01
Therefore, G ₁ / ρ ₁ = k (G ₂ / ρ ₂ ) does not hold, and the efficiency of the refrigeration cycle apparatus decreases. If the expander inlet temperature rises from 18.4 ° C to 22.2 ° C,
Compressor density ρ ₁ = 92 m ³ / kg
Expander density ρ ₂ = 840 m ³ / kg
Therefore, if the refrigerant flow rate is not controlled,
G ₁ / ρ ₁ = 95/92 = 1.03
k (G ₂ / ρ ₂ ) = 10.0 (90/840) = 1.07
Therefore, G ₁ / ρ ₁ = k (G ₂ / ρ ₂ ) does not hold, and the efficiency of the refrigeration cycle apparatus is also lowered.

(1) Control by the first valve means 21 As described above, when the expander inlet temperature changes, the opening degree of the first valve means 1 is controlled in accordance with the change in the expander inlet temperature, and the refrigeration cycle apparatus Efficiency can be improved. FIG. 3 is a graph showing the relationship between the expander inlet temperature and the opening degree of the first valve means 1. As shown in FIG. 3, when the expander inlet temperature is 14.6 ° C., the compressor flow rate G ₁ is reduced by changing the first valve means opening from 50% to 14%,
G ₁ / ρ ₁ = 91/90 = 1.01
k (G ₂ / ρ ₂ ) = 10.0 (90/892) = 1.01
Thus, G ₁ / ρ ₁ = k (G ₂ / ρ ₂ ) can be satisfied. When the expander inlet temperature is 22.2 ° C., the compressor flow rate G ₁ is increased by changing the first valve means opening from 50% to 93%,
G ₁ / ρ ₁ = 99/92 = 1.07
k (G ₂ / ρ ₂ ) = 10.0 (90/840) = 1.07
Thus, G ₁ / ρ ₁ = k (G ₂ / ρ ₂ ) can be satisfied.

  As shown in FIG. 3, the higher the expander inlet temperature, the larger the first valve means opening degree. Thus, the efficiency of the refrigeration cycle apparatus can be improved by controlling the opening degree of the first valve means 21 in accordance with the expander inlet temperature. Further, even if the opening degree of the first valve means 21 is changed, the flow rates of the main refrigerant and the sub refrigerant are not changed. Therefore, the degree of supercooling of the main refrigerant (the refrigerant flowing into the expander 11) can be reliably increased.

(2) Control by auxiliary heat exchanger 15 When the expander inlet temperature changes, the amount of heat exchange in the auxiliary heat exchanger 15 is controlled according to the change of the expander inlet temperature, and the refrigeration cycle apparatus Efficiency can be improved. For example, when the input temperature of the expander is lower than the design point (18.4 ° C.), the compressor density ρ ₁ is increased by increasing the number of rotations of the fan 16 and increasing the amount of heat exchange in the auxiliary heat exchanger 15. Can be increased, the value of G ₁ / ρ ₁ can be decreased, and G ₁ / ρ ₁ = k (G ₂ / ρ ₂ ) can be satisfied. Conversely, when the input temperature of the expander rises above the design point (18.4 ° C.), the compressor density ρ is reduced by lowering the rotational speed of the fan 16 and reducing the heat exchange amount in the auxiliary heat exchanger 15. ₁ can be reduced, the value of G ₁ / ρ ₁ can be increased, and G ₁ / ρ ₁ = k (G ₂ / ρ ₂ ) can be satisfied. Such control is performed only when cooling is used.

(3) Control by expansion valve 17 Furthermore, when the expander inlet temperature changes, the opening degree of the expansion valve 17 is controlled in accordance with the change in the expander inlet temperature to improve the efficiency of the refrigeration cycle apparatus. Can do. FIG. 4 is a graph showing the relationship between the expander inlet temperature and the opening degree of the expansion valve 17. As shown in FIG. 4, when the expander inlet temperature is 14.6 ° C., the compressor flow rate G ₁ is decreased and the expander flow rate G ₂ is decreased by changing the opening degree of the expansion valve from 10% to 3%. Increased,
G ₁ / ρ ₁ = 98.5 / 90.4 = 1.09
k (G ₂ / ρ ₂ ) = 10.0 (97/893) = 1.09
Thus, G ₁ / ρ ₁ = k (G ₂ / ρ ₂ ) can be satisfied. Further, when the expander inlet temperature is 22.2 ° C., the expansion valve opening G is increased from 10% to 17%, so that the compressor flow rate G ₁ increases and the expander flow rate G ₂ decreases.
G ₁ / ρ ₁ = 91/92 = 0.99
k (G ₂ / ρ ₂ ) = 10.0 (83/840) = 0.99
Thus, G ₁ / ρ ₁ = k (G ₂ / ρ ₂ ) can be satisfied. As shown in FIG. 4, the expansion valve opening increases as the expander inlet temperature increases. Incidentally, changing the expansion valve, with the change of the compressor flow rate G ₁ and the expander flow G _2, also changes the compressor density [rho ₁ and the expander density [rho _2.

  The control of the refrigerant flow rate / density described above is preferably performed in the order of control by the first valve means 21, control by the auxiliary heat exchanger 15, and control by the expansion valve 17. Such an order makes it difficult to change the pressure of the refrigerant.

(High pressure control)
In general, regarding the refrigeration cycle apparatus, it is known that the high pressure (optimum high pressure) at which the COP (coefficient of performance) is highest varies depending on the temperature of the refrigerant discharged from the heat dissipation heat exchanger (heat dissipation heat exchanger outlet temperature). ing. In this embodiment, as shown in FIG. 5, when the expander 11 having an efficiency of 81% is used in the refrigeration cycle apparatus, when the radiant heat exchanger outlet temperature is 35 ° C., about 8.5 MPa is 40 ° C. In this case, the optimum high pressure is about 10 MPa, and at 45 ° C., about 11 MPa is the optimum high pressure. Therefore, in the present embodiment, high pressure control is performed in accordance with the outlet temperature of the heat dissipation heat exchanger. In order to obtain the outlet temperature of the radiant heat exchanger, between the radiant heat exchanger (the outdoor unit 5 when using the cooling or the indoor unit 12 when using the heating) and the internal heat exchanger 10, especially the bridge circuit 6 and the internal A sensor (not shown) for measuring the temperature and pressure of the refrigerant is provided between the heat exchanger 10.

(1) Control by the first valve means 21 FIG. 6 is a graph showing the relationship between the opening degree of the first valve means and the high pressure. As shown in FIG. 6, the higher the first valve means opening, the higher the high pressure, and the higher the first valve means opening, the lower the high pressure. For example, when the outlet temperature of the heat dissipation heat exchanger is 45 ° C., the optimum high pressure is about 11 MPa (see FIG. 5). Therefore, the opening degree of the first valve means is adjusted to about 30%, so that the COP becomes maximum.

(2) Control by expansion valve 17 FIG. 7 is a graph showing the relationship between the expansion valve opening and the high pressure. As shown in FIG. 7, the smaller the expansion valve opening, the higher the high pressure, and the larger the expansion valve opening, the lower the high pressure. For example, when the outlet temperature of the heat dissipation heat exchanger is 45 ° C., the optimum high pressure is about 11 MPa (see FIG. 5). Therefore, the opening degree of the expansion valve is adjusted to about 8%, so that the COP becomes maximum.

  FIG. 8 is a graph showing the relationship between the heat exchanger outlet temperature and the optimum high pressure when the expander efficiency is 49%, 64% and 81%. As shown in FIG. 8, regardless of the efficiency of the expander 11, the relationship between the radiant heat exchanger outlet temperature and the optimum high pressure is substantially constant. Therefore, the above high-pressure control can be applied regardless of the efficiency of the expander used in the refrigeration cycle apparatus.

  The high pressure control described above is preferably performed in the order of control by the first valve means 21 and control by the expansion valve 17. Such an order makes it difficult to change the pressure of the refrigerant.

  According to this embodiment, the refrigeration cycle apparatus includes the first compressor 1 that compresses the refrigerant, the second compressor 2 that further compresses the refrigerant compressed by the first compressor 1, and the second compressor 2. A radiant heat exchanger that cools the compressed refrigerant by heat exchange with the outside air (outdoor unit 5 when used in cooling) and a refrigerant that is formed coaxially with the first compressor 1 and cooled by the radiant heat exchanger 5 ( An expander 11 that expands the main refrigerant), and an endothermic heat exchanger that heats the refrigerant (main refrigerant) expanded in the expander 11 (the indoor unit 12 when using the cooling), and a heat dissipation heat exchanger A first bypass flow path (sub-flow path 9 and first flow path 19) that decompresses a part of the refrigerant cooled in 5 (first refrigerant of the sub-refrigeration) and flows into the first compressor 1; A part of the refrigerant (second refrigerant among the sub refrigerants) cooled by the heat radiating heat exchanger 5 is decompressed. In order to further include a second bypass channel (sub-channel 9 and second channel 20) that flows into the second compressor 2, the flow rate and expansion of the refrigerant (first refrigerant) that flows into the first compressor 1 The flow rate of the refrigerant (main refrigerant) flowing into the machine 11 can be controlled independently. Therefore, even when the outside air temperature changes, the ratio between the flow rate and density of the refrigerant flowing into the first compressor 1 and the expander 11 can be appropriately controlled, and the COP of the refrigeration cycle apparatus is improved. Can be made.

  Further, according to the present embodiment, the refrigeration cycle apparatus is provided between the radiant heat exchanger 5 and the expander 11 in the refrigerant (main refrigerant) cooled by the radiant heat exchanger 5 and the sub-flow channel 9. Since the internal heat exchanger 10 that exchanges heat with the refrigerant (sub refrigerant) decompressed by the expansion valve 17 is further provided, the degree of cooling of the refrigerant (main refrigerant) flowing into the expander 11 can be increased. . Further, the conventional refrigeration cycle apparatus controls the ratio of the flow rate and density of the refrigerant flowing into the expander and the compressor, so that the refrigerant bypasses the expander in accordance with the change in the outside air temperature (the auxiliary in the present invention). Although it was necessary to change the flow rate of the refrigerant), this is not necessary according to the refrigeration cycle according to the present embodiment. This is because the ratio between the flow rate and density of the refrigerant flowing into the expander 11 and the compressor 1 can be controlled by changing the flow rates of the first refrigerant and the second refrigerant. Therefore, according to this embodiment, compared with the conventional refrigeration cycle apparatus, the flow rate of the sub refrigerant can be ensured, and the cooling degree of the refrigerant flowing into the expander 11 can be reliably increased. Thereby, the COP of the refrigeration cycle apparatus can be improved.

Further, according to this embodiment, a first bypass passage and the second bypass passage, a part of the downstream from the branch point P ₁ for branching the refrigerant cooled by the radiator heat exchanger 5 (the auxiliary flow channel 9 ) Is common, the configuration of the refrigerant piping is simplified.

  Further, according to the present embodiment, the refrigeration cycle apparatus depressurizes the refrigerant cooled by the heat dissipation heat exchanger 5 in the common part (sub-passage 9) of the first bypass passage and the second bypass passage. Since the pressure reducing means (expansion valve 17) and the internal heat exchanger 10 are sequentially provided, the pressure reducing means and the internal heat exchanger 10 can be shared, and the number of parts can be reduced. Thereby, a refrigeration cycle apparatus can be manufactured at low cost.

  Further, according to the present embodiment, the first bypass flow path includes the first valve means 21 that adjusts the flow rate of the refrigerant downstream (the first flow path 19) of the common portion (sub flow path 9), and the second Since the bypass flow path includes the second valve means 22 for preventing the reverse flow of the refrigerant downstream (second flow path 20) of the common portion (sub flow path 9), by controlling only the first valve means 21, The flow rates of the first refrigerant and the second refrigerant can be controlled.

  In addition, according to the present embodiment, the refrigeration cycle apparatus has an internal heat exchange with the decompression means (expansion valve 17) provided in the common part (sub-passage 9) of the first bypass passage and the second bypass passage. Since the refrigerant tank 18 that stores the liquid-phase refrigerant is further provided between the storage unit 10 and the liquid-phase refrigerant, the liquid-phase refrigerant stored here serves as a buffer and widens an appropriate range of the amount of the refrigerant sealed in the refrigeration cycle apparatus. can do. Moreover, even if it is a case where a refrigerant | coolant leaks from a refrigeration cycle apparatus, the fall of a performance can be suppressed.

  Further, according to the present embodiment, the refrigeration cycle apparatus further includes the third compressor 13 that compresses the refrigerant heated by the endothermic heat exchanger 12 between the endothermic heat exchanger 12 and the first compressor 1. Therefore, the auxiliary refrigerant heated by the internal heat exchanger 10 can be returned to the intermediate pressure (pressure between high pressure and low pressure) increased by the third compressor 13. Thereby, the efficiency of the refrigeration cycle apparatus can be improved.

  Moreover, according to this embodiment, the auxiliary heat exchanger 15 that cools the refrigerant compressed by the third compressor 13 by heat exchange with the outside air is provided between the third compressor 13 and the first compressor 1. Furthermore, since it is provided, the degree of superheat can be reduced during cooling use, and the efficiency of the refrigeration cycle apparatus can be improved.

  Note that the refrigeration cycle apparatus according to the present invention may not include the four-way valve 4, the bridge circuit 6, the third compressor 13, the auxiliary heat exchanger 15, and the refrigerant tank 18. In this case, the refrigeration cycle apparatus is used as either one of cooling or heating and can be manufactured at low cost. Conversely, the refrigeration cycle apparatus may include four or more compressors.

In the present embodiment, CO ₂ is used as the refrigerant, but other known refrigerants such as alternative chlorofluorocarbons may be used. For example, when an alternative chlorofluorocarbon is used as the refrigerant, a condenser can be used as the heat dissipating heat exchanger in the present invention, and an evaporator can be used as the endothermic heat exchanger.

Further, the refrigeration cycle apparatus according to the present invention may not include the internal heat exchanger 10, and the internal heat exchanger 10 may be provided at a position different from that of the present embodiment. For example, the internal heat exchanger 10, the first flow path 19 above (between the branching point _{P 2} and the confluence _{P 3)} or the second channel 20 above (between the branching point _{P 2} and the confluence _{P 4)} Or may be provided upstream of the branch point P ₁ , that is, between the radiant heat exchanger 5 and the branch point P ₁ .

  In addition, the first bypass channel and the second bypass channel according to the present invention may be any one that depressurizes the refrigerant cooled by the heat dissipation heat exchanger and allows the refrigerant to flow into the first compressor 1 and the second compressor 2, respectively. Therefore, they may be provided as completely separate channels. In this case, there is no sub-channel 9 in the present embodiment, the first channel 19 and the second channel 20 correspond to the first bypass channel and the second bypass channel, and the first channel 19 and the second channel A pressure reducing means (expansion valve) is provided in each path 20. Even if the first bypass channel and the second bypass channel are common as in the present embodiment, the downstream of the common part, that is, on the first channel 19 and the second channel 20 Each may be provided with a decompression means (expansion valve).

Further, in the present embodiment, the first passage 19 and second passage 20, the first valve means 21 and the second valve means 22 are provided respectively, the first refrigerant to the branching point P ₂ in place A linear three-way valve that can adjust the flow ratio between the second refrigerant and the second refrigerant may be provided.

DESCRIPTION OF SYMBOLS 1 ... 1st compressor, 2 ... 2nd compressor, 3 ... Motor, 4 ... Four-way valve, 5 ... Outdoor unit, 6 ... Bridge circuit, 7a-7d ... Check valve, 8 ... Main flow path, 9 ... Side flow 10: internal heat exchanger, 11: expander, 12: indoor unit, 13: third compressor, 14: motor, 15: auxiliary heat exchanger, 16 ... fan, 17 ... expansion valve, 18 ... refrigerant tank , 19 ... first flow path, 20: second flow path, 21 ... first valve means, 22 ... second valve means, _{P 1, 2 ...} branch point, _{P 3, 4 ...} confluence, G 1 _... compressor Flow rate, G ₂ ... expander flow rate, ρ ₁ ... compressor density, ρ ₂ ... expander density, V ₁ ... compressor volume, V ₂ ... expander volume, k ... constant

Claims (8)

A first compressor for compressing the refrigerant;
A second compressor for further compressing the refrigerant compressed by the first compressor;
A heat dissipation heat exchanger that cools the refrigerant compressed by the second compressor by heat exchange with outside air; and
An expander that is coaxially formed with the first compressor and expands the refrigerant cooled by the heat dissipation heat exchanger;
An endothermic heat exchanger for heating the refrigerant expanded by the expander;
Comprising
A first bypass flow path that decompresses a part of the refrigerant cooled by the heat dissipation heat exchanger and flows into the first compressor;
A second bypass flow path for depressurizing a part of the refrigerant cooled by the heat dissipation heat exchanger and flowing into the second compressor;
A refrigeration cycle apparatus further comprising:   Between the heat dissipation heat exchanger and the expander, a refrigerant cooled by the heat dissipation heat exchanger, and a refrigerant reduced in pressure at least one of the first bypass flow path and the second bypass flow path, The refrigeration cycle apparatus according to claim 1, further comprising an internal heat exchanger for heat exchange.   The first bypass flow path and the second bypass flow path share a part downstream from a branch point where the refrigerant cooled by the heat radiating heat exchanger is branched. The refrigeration cycle apparatus described.   The common part of the first bypass flow path and the second bypass flow path is sequentially provided with a decompression means for decompressing the refrigerant cooled by the radiant heat exchanger and the internal heat exchanger. The refrigeration cycle apparatus according to claim 3. The first bypass flow path includes a first valve means for adjusting a flow rate of the refrigerant downstream of the common part,
5. The refrigeration cycle apparatus according to claim 3, wherein the second bypass flow path includes second valve means for preventing a reverse flow of the refrigerant downstream of the common portion.   A refrigerant tank for storing liquid phase refrigerant is further provided between the pressure reducing means provided in the common part of the first bypass channel and the second bypass channel and the internal heat exchanger. The refrigeration cycle apparatus according to any one of claims 3 to 5, wherein   The third compressor for compressing the refrigerant heated by the endothermic heat exchanger is further provided between the endothermic heat exchanger and the first compressor. The refrigeration cycle apparatus according to item 1.   The auxiliary heat exchanger which cools the refrigerant compressed by the 3rd compressor by heat exchange with the outside air between the 3rd compressor and the 1st compressor. The refrigeration cycle apparatus according to 7.