GB2553970A

GB2553970A - Refrigeration cycle apparatus

Info

Publication number: GB2553970A
Application number: GB1716734.7A
Authority: GB
Inventors: Saikusa Tetsuji; Obayashi Tomoyoshi; Kadowaki Kimitaka
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2015-04-15
Filing date: 2015-04-15
Publication date: 2018-03-21
Anticipated expiration: 2035-04-15
Also published as: WO2016166845A1; JP6463464B2; GB201716734D0; JPWO2016166845A1; GB2553970B

Abstract

This refrigeration cycle apparatus has: a refrigerant circuit in which a compressor, a condenser, a primary expansion valve, and an evaporator are connected through main piping; an internal heat-exchanger for carrying out heat-exchanging on a refrigerant flowing between the condenser and the primary expansion valve and a refrigerant flowing between the evaporator and the compressor, and introducing the refrigerant flowing out of the evaporator to the intake side of the compressor; an HIC heat-exchanger disposed between the condenser and the internal heat-exchanger and connected in series to the internal heat-exchanger; bypass piping branched between the condenser and the HIC heat-exchanger and guiding the refrigerant to the compressor via the HIC heat-exchanger; and a secondary expansion valve depressurizing the refrigerant introduced into the bypass piping from the condenser to discharge the refrigerant to the HIC heat-exchanger, wherein the HIC heat-exchanger carries out heat-exchange on the refrigerant introduced therein from the condenser through the main piping and the refrigerant introduced therein from the condenser through the secondary expansion valve.

Description

(56) Documents Cited:

JP 2012207843 A JP 2006112708 A

JP 2011179689 A (86) International Application Data:

PCT/JP2015/061603 Ja 15.04.2015 (87) International Publication Data:

WO2016/166845 Ja 20.10.2016 (58) Field of Search:

INT CL F25B

Other: Jitsuyo Shinan Koho 1922-1996, Jitsuyo Shinan Toroku Koho 1996-2015, Kokai Jitsuyo Shinan Koho 1971-2015, Toroku Jitsuyo Shinan Koho 1994-2015 (71) Applicant(s):

Mitsubishi Electric Corporation (Incorporated in Japan)

7-3 Marunouchi 2-chome, Chiyoda-ku, Tokyo 100-8310, Japan (72) Inventor(s):

Tetsuji Saikusa Tomoyoshi Obayashi Kimitaka Kadowaki (74) Agent and/or Address for Service:

Mewburn Ellis LLP

City Tower, 40 Basinghall Street, LONDON, Greater London, EC2V 5DE, United Kingdom (54) Title of the Invention: Refrigeration cycle apparatus Abstract Title: Refrigeration cycle apparatus (57) This refrigeration cycle apparatus has: a refrigerant circuit in which a compressor, a condenser, a primary expansion valve, and an evaporator are connected through main piping; an internal heat-exchanger for carrying out heatexchanging on a refrigerant flowing between the condenser and the primary expansion valve and a refrigerant flowing between the evaporator and the compressor, and introducing the refrigerant flowing out of the evaporator to the intake side of the compressor; an HIC heat-exchanger disposed between the condenser and the internal heat-exchanger and connected in series to the internal heat-exchanger; bypass piping branched between the condenser and the HIC heat-exchanger and guiding the refrigerant to the compressor via the HIC heat-exchanger; and a secondary expansion valve depressurizing the refrigerant introduced into the bypass piping from the condenser to discharge the refrigerant to the HIC heat-exchanger, wherein the HIC heat-exchanger carries out heat-exchange on the refrigerant introduced therein from the condenser through the main piping and the refrigerant introduced therein from the condenser through the secondary expansion valve.

Control device

90a Superheat degree calculating unit 90b Superheat degree determining unit 90c Valve control unit

1/10

FIG 1 /

SO

DEGREE OF-SUPERHCAT

CALCULATION U\l ί

J.

DEGRE	EE-OF-SUPERHEAT
DETE	ERMINATION UNIT

90g

VALVE CONTROL UNIT

I

2/10

FIG. 2

G04a CO2

3/10

PIP⁴ Q rlvj. Ο

4/10

FIG. 4

AMOUNT OF HEAT EXCHANGE OF INTERNAL HEAT EXCHANGER/ TOTAL REFRIGERATION CAPACITY [%]

FIG. 5

AMOUNT OF HEAT EXCHANGE OF INTERNAL HEAT EXCHANGER / TOTAL REFRIGERATION CAPACITY [%]

5/10 ib. Ο

AMOUNT OF HEAT EXCHANGE OF 1!C HEAT EXCHANGER / AMOUNT OF HEAT EXCHANGE OF INTERNAL HEAT EXCHANGER [%]

6/10

FIG. 7

CONTROLLER degree-of-superheatI^

CALCULATION UNIT ~v.

DEGREE-OF-SUPERHEA DETERMINATION UNIT

ΖΖΪΖΖΖΞΖ

-VALVE CONTROL UNI

7/10

CIP β

ΓΙΟ. ο

h

8/10

IG. 9 (7~START~ ) <—

INPUT H

V.

C INLET 'EMPERATURE Thi

INPUT HIC OUTLET TEMPERATURE Tho ψ

CALCULATE FIRST DEGREE OF SUPERHEAT SHh [SHh=Tho-Thi]

S201

S202

S203

REDUCE OPENING

DEGREE OF SUBEXPANSION VALVE

S205

S2O7

—^SET VALUE?—- YesTT ..........................ψ..........................	No		S20S t
INCREASE OPENING		MAINTAIN OPENING
DEGREE OF SUB-		DEGREE OF SUB-
EXPANSION VALVE		EXPANSION VALVE

9/10

TOTAL REFRIGERATION CAPACITY [%]

FIG. 11

10/10

FIG. 12

AMOUNT OF HEAT EXCHANGE OF HIC HEAT EXCHANGER / AMOUNT OF HEAT EXCHANGE OF INTERNAL. HEAT EXCHANGER [%]

DESCRIPTION

Title of Invention

REFRIGERATION CYCLE APPARATUS

Technical Field [0001]

The present invention relates to a refrigeration cycle apparatus, which includes a refrigerant circuit for circulation of refrigerant.

Background Art [0002]

There has been known a related-art refrigeration cycle apparatus which includes an internal heat exchanger configured to exchange heat between refrigerant having flowed out of a condenser and refrigerant having flowed out of an evaporator. Further, as refrigerant to be circulated in the refrigeration cycle apparatus, there has hitherto been used HFO-1234yf (R1234yf) or HFO-1234ze. The internal heat exchanger is considered useful for improvement in refrigeration capacity in a case in which the refrigerant such as HFO-1234yf is used (for example, see Patent Literature 1).

[0003]

In Patent Literature 1, there is proposed a refrigerant cycle including a compressor for compressing refrigerant, a condenser for condensing the compressed refrigerant, pressure-reduction and expansion means for reducing pressure of the condensed refrigerant and expanding the condensed refrigerant, an evaporator for evaporating the pressure-reduced and expanded refrigerant, and an internal heat exchanger for exchanging heat between refrigerant at an exit side of the condenser and refrigerant at an exit side of the evaporator. In the refrigerant cycle, R1234yf is used as refrigerant, and an amount of heat exchange by the internal heat exchanger is set to be equal to or larger than a predetermined value that has been determined beforehand by a simulation or an experiment. Further, a capacity ratio of the predetermined value of the amount of heat exchange by the internal heat exchanger to a total refrigeration capacity of the refrigeration cycle is set to be equal to or larger than 7%.

Citation List

Patent Literature [0004]

Patent Literature 1: Japanese Patent No. 5180680 Summary of Invention Technical Problem [0005]

According to the refrigeration cycle apparatus of Patent Literature 1, the amount of heat exchange in the internal heat exchanger is set to be equal to or larger than 7% of the total refrigeration capacity of the apparatus. Thus, a length of a heat transfer portion of the internal heat exchanger is increased, and refrigerant pressure loss or other loss is increased in a region from the evaporator to a suction port of the compressor. Therefore, there is a problem in that the efficiency is degraded.

[0006]

The present invention has been made to solve the above-mentioned problem, and has an object to provide a refrigeration cycle apparatus, which is reduced in length of a heat transfer portion of an internal heat exchanger and is improved in efficiency in a case of using HFO-1234yf or HFO-1234ze as refrigerant.

Solution to Problem [0007]

According to one embodiment of the present invention, there is provided a refrigeration cycle apparatus, including: a refrigerant circuit in which a compressor, a condenser, a main expansion valve, and an evaporator are connected one another by a main pipe; an internal heat exchanger, which is configured to exchange heat between refrigerant flowing between the condenser and the main expansion valve and refrigerant flowing between the evaporator and the compressor, and is configured to allow the refrigerant flowed out of the evaporator to flow to a suction side of the compressor; an HIC heat exchanger, which is provided between the condenser and the internal heat exchanger and is connected in series to the internal heat exchanger; a bypass pipe, which branches at a portion between the condenser and the HIC heat exchanger and is configured to introduce the refrigerant to the compressor via the HIC heat exchanger; and a sub-expansion valve, which is configured to reduce pressure of the refrigerant flowing into the bypass pipe from the condenser and allow the refrigerant to flow out to the HIC heat exchanger, the HIC heat exchanger being configured to exchange heat between the refrigerant flowing into the HIC heat exchanger from the condenser through the main pipe and the refrigerant flowing into the HIC heat exchanger from the condenser through the sub-expansion valve. Advantageous Effects of Invention [0008]

According to one embodiment of the present invention, the HIC heat exchanger connected in series to the internal heat exchanger exchanges heat between the refrigerant having flowed into the HIC heat exchanger from the condenser through the main pipe and the refrigerant having flowed into the HIC exchanger from the condenser through the bypass pipe. Thus, the amount of heat exchange by the internal heat exchanger can be reduced. Therefore, even in the case of using HFO1234yf or HFO-1234ze as the refrigerant, the length of the heat transfer portion of the internal heat exchanger can be reduced, and the efficiency can be improved.

Brief Description of Drawings [0009] [Fig. 1] Fig. 1 is a system configuration diagram including a refrigerant circuit diagram of a refrigeration cycle apparatus according to Embodiment 1 of the present invention.

[Fig. 2] Fig. 2 is a P-h diagram for illustrating an operation state of the refrigeration cycle apparatus of Fig. 1.

[Fig. 3] Fig. 3 is a flowchart for illustrating a control operation executed by a controller of Fig. 1 during a hot water supply operation.

[Fig. 4] Fig. 4 is a characteristic graph for showing a simulation result of a relationship between a ratio of an amount of heat exchange of an internal heat exchanger to a total refrigeration capacity of the refrigeration cycle apparatus of Fig. 1 and a COP.

[Fig. 5] Fig. 5 is a characteristic graph for showing a relationship between a ratio of an amount of heat exchange of the internal heat exchanger to the total refrigeration capacity of the refrigeration cycle apparatus of Fig. 1 and a first degree of superheat SHh at an outlet of an HIC heat exchanger.

[Fig. 6] Fig. 6 is a characteristic graph for showing a relationship between a ratio of an amount of heat exchange of the HIC heat exchanger to the amount of heat exchange of the internal heat exchanger in the refrigeration cycle apparatus of Fig. 1 and the COP.

[Fig. 7] Fig. 7 is a system configuration diagram including a refrigerant circuit diagram of a refrigeration cycle apparatus according to Embodiment 2 of the present invention.

[Fig. 8] Fig. 8 is a P-h diagram for illustrating an operation state of the refrigeration cycle apparatus of Fig. 7.

[Fig. 9] Fig. 9 is a flowchart for illustrating a control operation executed by a controller of Fig. 7 during a hot water supply operation.

[Fig. 10] Fig. 10 is a characteristic graph for showing a simulation result of a relationship between a ratio of an amount of heat exchange of the internal heat exchanger to a total refrigeration capacity of the refrigeration cycle apparatus of Fig. 7 and the COP.

[Fig. 11] Fig. 11 is a characteristic graph for showing a relationship between a ratio of an amount of heat exchange of the internal heat exchanger to the total refrigeration capacity of the refrigeration cycle apparatus of Fig. 7 and a first degree of superheat SHh at an outlet of the HIC heat exchanger.

[Fig. 12] Fig. 12 is a characteristic graph for showing a relationship between a ratio of an amount of heat exchange of the HIC heat exchanger to the amount of heat exchange of the internal heat exchanger in the refrigeration cycle apparatus of Fig. 7 and the COP.

Description of Embodiments [0010]

Embodiment 1

Fig. 1 is a system configuration diagram including a refrigerant circuit diagram of a refrigeration cycle apparatus according to Embodiment 1 of the present invention. Fig. 1 is an illustration of a state in which a heating operation for raising a temperature of water on a load side is performed.

[0011]

A refrigeration cycle apparatus 100 according to Embodiment 1 includes a compressor 10, a four-way valve 20, a condenser 30, a main expansion valve 80, and an evaporator 60, which are annularly connected one another. Further, in the refrigeration cycle apparatus 100, there are arranged an Heat Inter Changer (HIC) heat exchanger 50 and an internal heat exchanger 70, which are connected one another in series, between the condenser 30 and the main expansion valve 80. Specifically, the refrigeration cycle apparatus 100 includes the refrigerant circuit, the internal heat exchanger 70, and the HIC heat exchanger 50. In the refrigerant circuit, the compressor 10, the condenser 30, the main expansion valve 80, and the evaporator 60 are connected one another by a main pipe 1. The internal heat exchanger 70 is configured to exchange heat between refrigerant flowing between the condenser 30 and the main expansion valve 80 and refrigerant flowing between the evaporator 60 and the compressor 10, and is configured to allow the refrigerant having flowed out of the evaporator to flow to a suction side of the compressor 10.

The HIC heat exchanger 50 is provided between the condenser 30 and the internal heat exchanger 70 and is connected in series to the internal heat exchanger 70.

[0012]

The refrigeration cycle apparatus 100 includes the main pipe 1 being a refrigerant pipe for allowing the refrigerant to circulate through the compressor 10, the four-way valve 20, the condenser 30, the HIC heat exchanger 50, the internal heat exchanger 70, the main expansion valve 80, and the evaporator 60. Further, the refrigeration cycle apparatus 100 includes a bypass pipe 2, which branches from a portion between the condenser 30 and the HIC heat exchanger 50 to introduce the refrigerant to the compressor 10 via the HIC heat exchanger 50. The bypass pipe 2 branches from the main pipe 1 extending from an outlet of the condenser 30 and bypasses part of high-pressure liquid refrigerant having flowed out of the condenser 30 to flow into the main pipe 1. The bypass 2 is connected to the main pipe 1 extending from the internal heat exchanger 70. Further, the refrigeration cycle apparatus 100 includes a sub-expansion valve 40 configured to reduce pressure of the refrigerant flowing into the bypass pipe 2 from the condenser 30 and allow the refrigerant to flow out to the HIC heat exchanger 50. That is, the bypass pipe 2 bypasses part of the high-pressure liquid refrigerant having passed through the condenser 30 to pass through the sub-expansion valve 40 and the HIC heat exchanger 50.

[0013]

More specifically, the compressor 10 is constructed by, for example, a capacitycontrollable inverter compressor, and is configured to suck low-temperature and lowpressure gas refrigerant, compress the refrigerant into high-temperature and highpressure gas refrigerant, and then discharge the refrigerant. The four-way valve 20 is configured to switch directions of the high-temperature and high-pressure gas refrigerant discharged from the compressor 10 and the low-temperature and lowpressure gas refrigerant sucked into the compressor 10. The condenser 30 is constructed by, for example, a plate-type heat exchanger, and is configured to exchange heat between water and the high-temperature and high-pressure gas refrigerant, which has been discharged from the compressor 10 and has passed through the four-way valve 20, so that the high-temperature and high-pressure gas refrigerant rejects heat.

[0014]

The sub-expansion valve 40 is provided to the bypass pipe 2, and is configured to reduce pressure of the high-pressure liquid refrigerant having passed through the condenser 30 so that the high-pressure liquid refrigerant turns into low-pressure twophase refrigerant. The HIC heat exchanger 50 is configured to exchange heat between the high-pressure liquid refrigerant having flowed out of the condenser 30 and passed through the main pipe 1 and the low-pressure two-phase refrigerant reduced in pressure by the sub-expansion valve 40. The evaporator 60 is constructed by, for example, a fin-plate type heat exchanger, and is configured to exchange heat between the refrigerant and the air to evaporate the refrigerant. The internal heat exchanger 70 includes, for example, a double pipe, and is configured to exchange heat between the high-pressure liquid refrigerant having passed through the HIC heat exchanger 50 and the low-pressure gas refrigerant having passed through the evaporator 60. The main expansion valve 80 is configured to reduce pressure of the high-pressure liquid refrigerant having passed through the internal heat exchanger 70 so that the high-pressure liquid refrigerant turns into the lowpressure two-phase refrigerant.

[0015]

In the refrigeration cycle apparatus 100, there is formed the refrigerant circuit for circulation of the refrigerant sequentially through the compressor 10, the condenser 30, the sub-expansion valve 40, the HIC heat exchanger 50, the internal heat exchanger 70, the main expansion valve 80, and the evaporator 60. In the refrigeration cycle apparatus 100, a mixture refrigerant including HFO-1234yf or HFO1234ze is used as the refrigerant.

[0016]

HFO-1234yf or HFO-1234ze being the refrigerant has a global warming potential (GWP) of 4. R410A having hitherto been used has a GWP of 2,090, and

R407C has a GWP of 1,770. That is, HFO-1234yf or HFO-1234ze is a refrigerant which has smaller influence on the global environment than that of R410Aand R407C. [0017]

HFO-1234yf or HFO-1234ze has a characteristic that a discharge temperature from the compressor 10 is less liable to rise as compared to R410Aand R407C. Further, HFO-1234yf or HFO-1234ze has a characteristic that, in the case of the heating operation for raising the temperature of water, when the discharge temperature through rise in degree of suction superheat of the compressor 10 is raised, the condensing pressure at the time of equivalent performance output is reduced, thereby improving the efficiency.

[0018]

Next, with reference to Fig. 1 and Fig. 2, description is made of the hot water supply operation of the refrigeration cycle apparatus 100. Fig. 2 is a P-h diagram for illustrating an operation state of the refrigeration cycle apparatus 100. The vertical axis represents an absolute pressure P [MPa-abs] of the refrigerant, and the horizontal axis represents a specific enthalpy h [kJ/kg], [0019]

The refrigerant being in the state of the low-temperature and low-pressure gas is sucked into the compressor 10 (C01: suction port of compressor 10), is compressed by the compressor 10 into the high-temperature and high-pressure gas, and then is discharged. The high-temperature and high-pressure gas refrigerant having been discharged from the compressor 10 passes through the four-way valve 20 and flows into the condenser 30. The high-temperature and high-pressure gas refrigerant having flowed into the condenser 30 transfers heat to water being a heat exchange medium to turn into the high-pressure liquid refrigerant. The highpressure liquid refrigerant having flowed out of the condenser 30 (C02: outlet of condenser 30) is branched into two directions. One of the branched high-pressure liquid refrigerant flows into the sub-expansion valve 40 through the bypass pipe 2 and is reduced in pressure and expanded to turn into low-temperature and low-pressure two-phase gas-liquid refrigerant (C03: outlet of sub-expansion valve 40). The other of the branched high-pressure liquid refrigerant flows into the HIC heat exchanger 50, exchanges heat (T01) with the low-temperature and low-pressure two-phase gasliquid refrigerant having flowed out of the sub-expansion valve 40 to turn into highpressure subcooled liquid refrigerant, and then flows out (C04a: outlet of HIC heat exchanger 50). The low-temperature and low-pressure two-phase gas-liquid refrigerant having flowed out of the sub-expansion valve 40 exchanges heat (T01) with the high-pressure liquid refrigerant having flowed into the HIC heat exchanger 50 to turn into intermediate-temperature and low-pressure gas refrigerant, and then flows out (C04b: outlet of HIC heat exchanger 50).

[0020]

The high-pressure subcooled liquid refrigerant having flowed out of the HIC heat exchanger 50 flows into the internal heat exchanger 70, exchanges heat (T02) with the low-pressure and low-temperature gas refrigerant having flowed out of the evaporator 60 and passed through the four-way valve 20 to turn into liquid refrigerant having a further large degree of subcooling, and then flows out (C05: outlet of internal heat exchanger 70). The subcooled liquid refrigerant having flowed out of the internal heat exchanger 70 flows into the main expansion valve 80, is reduced in pressure and expanded to turn into the low-pressure two-phase refrigerant, and then flows into the evaporator 60 (C06: inlet of evaporator 60). The low-pressure twophase refrigerant having flowed into the evaporator 60 cools air being a heat exchange medium, is evaporated into the low-temperature and low-pressure gas refrigerant, and then flows out (C07: outlet of evaporator 60).

[0021]

The low-temperature and low-pressure gas refrigerant having flowed out of the evaporator 60 passes through the four-way valve 20 again, flows into the internal heat exchanger 70, exchanges heat (T02) with the high-pressure liquid refrigerant having flowed out of the HIC heat exchanger 50 to turn into the intermediate-temperature and low-pressure gas refrigerant, and then flows out (C08: outlet of internal heat exchanger 70). The intermediate-temperature and low-pressure gas refrigerant having flowed out of the internal heat exchanger 70 merges with the intermediatetemperature and low-pressure gas refrigerant having flowed out of the HIC heat exchanger 50 to turn into a low-pressure gas having a large degree of superheat, and is sucked into the compressor 10 again (C01: suction port of compressor 10).

[0022]

The low-pressure gas before being sucked into the compressor 10 flows to the internal heat exchanger 70 on the suction side of the compressor 10. Therefore, a large length of the heat transfer portion may increase the pressure loss in the low pressure, causing degradation of the efficiency of the refrigeration cycle apparatus

100. A small amount of two-phase refrigerant which is to be bypassed to the suction side of the compressor 10 flows to the bypass pipe 2 on the gas side of the HIC heat exchanger 50. Therefore, there is no influence on the efficiency of the refrigeration cycle apparatus 100 by the pressure loss. Thus, with the refrigeration cycle apparatus 100 including the HIC heat exchanger 50, the length of the heat transfer portion of the internal heat exchanger 70 can be reduced, resulting in improved efficiency. Further, the HIC heat exchanger 50 can be constructed with a pipe thinner than a pipe of the internal heat exchanger 70, thereby being capable of achieving a compact configuration.

[0023]

Next, with reference to Fig. 1, description is made of a control configuration for the refrigeration cycle apparatus 100. The refrigeration cycle apparatus 100 includes a state detection unit and a controller 90. The state detection unit is configured to detect a state of the refrigerant flowing in the refrigerant circuit. The controller 90 is constructed by, for example, a microcomputer such as a DSP, and is configured to control opening degrees of the sub-expansion valve 40 and the main expansion valve 80 based on a result of detection by the state detection unit. The state detection unit includes a pressure sensor 110, an HIC outlet temperature sensor 120, and an evaporator outlet temperature sensor 130. The pressure sensor 110 is configured to detect a suction pressure Ps being a pressure of the gas refrigerant sucked into the compressor 10. The HIC outlet temperature sensor 120 is configured to detect an HIC outlet temperature Tho being a temperature of the gas refrigerant having flowed out of the HIC heat exchanger 50. The evaporator outlet temperature sensor 130 is configured to detect an evaporator outlet temperature The being a temperature of the gas refrigerant having flowed out of the evaporator 60. [0024]

The controller 90 includes a degree-of-superheat calculation unit 90a and a valve control unit 90c. The degree-of-superheat calculation unit 90a is configured to calculate a first degree of superheat being a degree of superheat at the outlet of the

HIC heat exchanger 50 through use of the result of detection by the state detection unit. The valve control unit 90c is configured to control an opening degree of the sub-expansion valve 40 so that the first degree of superheat falls within a preset target range.

[0025]

More specifically, the controller 90 includes the degree-of-superheat calculation unit 90a, a degree-of-superheat determination unit 90b, and the valve control unit 90c. The degree-of-superheat calculation unit 90a is configured to calculate a first degree of superheat SHh being the degree of superheat at the gas outlet of the HIC heat exchanger 50 by calculating a saturation temperature f(Ps) corresponding to a suction pressure Ps detected by the pressure sensor 110 and subtracting the saturation temperature f(Ps) from the HIC outlet temperature Tho detected by the HIC outlet temperature sensor 120. The degree-of-superheat determination unit 90b is configured to determine, through comparison between the first degree of superheat SHh calculated by the degree-of-superheat calculation unit 90a and a first set value being a preset allowable lower limit, whether or not the first degree of superheat SHh is smaller than the first set value. The valve control unit 90c is configured to control the opening degrees of the sub-expansion valve 40 and the main expansion valve 80 based on a result of determination by the degree-of-superheat determination unit 90b. [0026]

The degree-of-superheat determination unit 90b has a function of determining, through comparison between the first degree of superheat SHh and a second set value being a preset allowable upper limit, whether or not the first degree of superheat SHh is larger than the second set value when the degree-of-superheat determination unit 90b determines that the first degree of superheat SHh is equal to or larger than the first set value. The valve control unit 90c reduces the opening degree of the sub-expansion valve 40 when the degree-of-superheat determination unit 90b determines that the first degree of superheat SHh is smaller than the first set value. Further, when the degree-of-superheat determination unit 90b determines that the first degree of superheat SHh is larger than the second set value, the valve control unit 90c increases the opening degree of the sub-expansion valve 40. When the degree-of-superheat determination unit 90b determines that the first degree of superheat SHh is equal to or smaller than the second set value, the valve control unit 90c maintains the opening degree of the sub-expansion valve 40. That is, in Embodiment 1, the target range is set to a range of equal to or larger than the first set value and equal to or smaller than the second set value.

[0027]

Further, the degree-of-superheat calculation unit 90a has a function of calculating a second degree of superheat SHe being a degree of superheat at an outlet of the evaporator 60 by subtracting the saturation temperature f(Ps) corresponding to the suction pressure Ps from the evaporator outlet temperature The detected by the evaporator outlet temperature sensor 130. The degree-of-superheat determination unit 90b has a function of determining, through comparison between the second degree of superheat SHe calculated by the degree-of-superheat calculation unit 90a and a preset third set value (target value), whether or not the second degree of superheat SHe is smaller than the third set value. When the degree-of-superheat determination unit 90b determines that the second degree of superheat SHe is smaller than the third set value, the valve control unit 90c reduces the opening degree of the main expansion valve 80. When the degree-of-superheat determination unit 90b determines that the second degree of superheat SHe is equal to or larger than the third set value, the valve control unit 90c increases the opening degree of the main expansion valve 80. That is, the valve control unit 90c is configured to control the opening degree of the main expansion valve 80 so that the second degree of superheat SHe becomes equal to a sixth set value being a target value.

[0028]

Next, with reference to Fig. 1 and Fig. 3, description is made of a procedure of opening and closing control for the main expansion valve 80 and the sub-expansion valve 40, which is executed by the controller 90, during the hot water supply operation. Fig. 3 is a flowchart for illustrating the control operation by the controller 90 during the hot water supply operation.

[0029]

First, the degree-of-superheat calculation unit 90a inputs the suction pressure Ps detected by the pressure sensor 110 (Fig. 3: Step S101) and inputs the HIC outlet temperature Tho detected by the HIC outlet temperature sensor 120 (Fig. 3: Step S102). The degree-of-superheat calculation unit 90a calculates the first degree of superheat SHh at the gas outlet of the HIC heat exchanger 50 by calculating the saturation temperature f(Ps) corresponding to the suction pressure Ps and subtracting the calculated saturation temperature f(Ps) from the HIC outlet temperature Tho (Fig. 3: Step S103).

[0030]

The degree-of-superheat determination unit 90b determines, through comparison between the first degree of superheat SHh calculated by the degree-ofsuperheat calculation unit 90a and the first set value, whether or not the first degree of superheat SHh is smaller than the first set value (Fig. 3: Step S104). When the degree-of-superheat determination unit 90b determines that the first degree of superheat SHh is smaller than the first set value (Fig. 3: Step S104/Yes), the valve control unit 90c reduces the opening degree of the sub-expansion valve 40 to suppress the amount of heat exchange of the HIC heat exchanger 50 (Fig. 3: Step S105). When the degree-of-superheat determination unit 90b determines that the first degree of superheat SHh is equal to or larger than the first set value (Fig. 3: Step S104/No), the valve control unit 90c determines, through comparison between the first degree of superheat SHh and the second set value, whether or not the first degree of superheat SHh is larger than the second set value (Fig. 3: Step S106). [0031]

Next, the degree-of-superheat determination unit 90b determines, through comparison between the first degree of superheat SHh calculated by the degree-ofsuperheat calculation unit 90a and the second set value, whether or not the first degree of superheat SHh is larger than the second set value (Fig. 3: Step S106). When the degree-of-superheat determination unit 90b determines that the first degree of superheat SHh is larger than the second set value (Fig. 3: Step S106/Yes), the valve control unit 90c increases the opening degree of the sub-expansion valve 40 to increase the amount of heat exchange of the HIC heat exchanger 50 (Fig. 3: Step S107). When the degree-of-superheat determination unit 90b determines that the first degree of superheat SHh is equal to or smaller than the second set value (Fig. 3: Step S106/No), the valve control unit 90c maintains a current opening degree of the sub-expansion valve 40 (Fig. 3: Step S108). That is, the valve control unit 90c is configured to control the opening degree of the sub-expansion valve 40 so that the first degree of superheat falls within the target range of equal to or larger than the first set value and equal to or smaller than the second set value.

[0032]

Next, the degree-of-superheat calculation unit 90a inputs the evaporator outlet temperature The detected by the evaporator outlet temperature sensor 130 (Fig. 3: Step S109). The degree-of-superheat calculation unit 90a calculates the second degree of superheat SHe at the outlet of the evaporator 60 by subtracting the saturation temperature f(Ps) corresponding to the suction pressure Ps from the evaporator outlet temperature The input from the evaporator outlet temperature sensor 130 (Fig. 3: Step S110). The degree-of-superheat determination unit 90b determines, through comparison between the second degree of superheat SHe calculated by the degree-of-superheat calculation unit 90a and the third set value, whether or not the second degree of superheat SHe is smaller than the third set value (Fig. 3: Step S111).

[0033]

When the degree-of-superheat determination unit 90b determines that the second degree of superheat SHe is smaller than the third set value (Fig. 3: Step S111/Yes), the valve control unit 90c reduces the opening degree of the main expansion valve 80 to suppress the amount of heat exchange of the evaporator 60 (Fig. 3: Step S112). When the degree-of-superheat determination unit 90b determines that the second degree of superheat SHe is equal to or larger than the third set value (Fig. 3: Step S111/No), the valve control unit 90c increases the opening degree of the main expansion valve 80 to increase the amount of heat exchange of the evaporator 60 (Fig. 3: Step S113).

[0034]

Fig. 4 is a characteristic graph for showing a simulation result of a relationship between a ratio of the amount of heat exchange of the internal heat exchanger 70 to a total refrigeration capacity of the refrigeration cycle apparatus 100 (hereinafter simply referring to as total refrigeration capacity) and a COP. With reference to Fig. 4, description is made of a region in which a value of the coefficient of performance (COP) of the refrigeration cycle apparatus 100 is favorable. In the case of Fig. 4, a peak value is given when the ratio of the amount of heat exchange of the internal heat exchanger 70 to the total refrigeration capacity is about 4%. When the length of the heat transfer portion of the internal heat exchanger 70 is excessively small, that is, when the ratio of the amount of heat exchange of the internal heat exchanger 70 to the total refrigeration capacity is smaller than a predetermined lower limit amount, the degree of suction superheat of the compressor 10 is reduced, and the rise in discharge temperature of the compressor 10 is reduced, with the result that the COP is reduced. When the length of the heat transfer portion of the internal heat exchanger 70 is excessively large, that is, when the ratio of the amount of heat exchange of the internal heat exchanger 70 to the total refrigeration capacity is larger than a predetermined upper limit amount, the refrigerant pressure loss on the lowpressure gas side of the internal heat exchanger 70 is increased, with the result that the COP is reduced.

[0035]

As shown in Fig. 4, when the ratio of the amount of heat exchange of the internal heat exchanger 70 to the total refrigeration capacity falls within a range of equal to or larger than 2.4% and smaller than 7%, the refrigeration cycle apparatus 100 can be operated in the region in which a value of the COP is favorable. In Embodiment 1, the region in which a value of the COP is favorable is a region in which the COP is equal to or larger than 100%. That is, in the refrigeration cycle apparatus 100, the length of the heat transfer portion of the internal heat exchanger 70 is set so that the ratio of the amount of heat exchange of the internal heat exchanger 70 to the total refrigeration capacity is equal to or larger than 2.4% and smaller than 7%.

[0036]

Fig. 5 is a characteristic graph for showing a relationship between the ratio of the amount of heat exchange of the internal heat exchanger 70 to the total refrigeration capacity and the first degree of superheat SHh at the outlet of the HIC heat exchanger 50. With reference to Fig. 5, description is made of an adjustment method for the ratio of the amount of heat exchange of the internal heat exchanger 70 to the total refrigeration capacity. As shown in Fig. 5, through control of the first degree of superheat SHh at the outlet of the HIC heat exchanger 50, the ratio of the amount of heat exchange of the internal heat exchanger 70 to the total refrigeration capacity can be controlled. In Embodiment 1, in order to set the ratio of the amount of heat exchange of the internal heat exchanger 70 to the total refrigeration capacity to fall within the range of equal to or larger than 2.4% and smaller than 7%, the first set value being the allowable lower limit of the first degree of superheat SHh is set to 15 degrees Celsius, and the second set value being the allowable upper limit of the first degree of superheat SHh is set to 44 degrees Celsius. That is, the valve control unit 90c is configured to control the opening degree of the sub-expansion valve 40 so that the first degree of superheat SHh has a value within the target range.

[0037]

Fig. 6 is a characteristic graph for showing a relationship between the ratio of the amount of heat exchange of the HIC heat exchanger 50 to the amount of heat exchange of the internal heat exchanger 70 in the refrigeration cycle apparatus 200 and the COP. With reference to Fig. 6, description is made of a relationship between the amounts of heat exchange by the HIC heat exchanger 50 and the internal heat exchanger 70 and the region in which a value of the COP of the refrigeration cycle apparatus 100 is favorable.

[0038]

With regard to the flow of the refrigerant during the heating operation, the HIC heat exchanger 50 is provided upstream, and the internal heat exchanger 70 is provided downstream. Therefore, when the amount of heat exchange of the HIC heat exchanger 50 is increased, the temperature of the high-pressure liquid refrigerant flowing into the internal heat exchanger 70 is reduced. That is, there is a relationship in which the amount of heat exchange of the internal heat exchanger 70 is reduced when the amount of heat exchange of the HIC heat exchanger 50 increases, and as shown in Fig. 6, a peak value of the COP is present with respect to the ratio of the amount of heat exchange of the HIC heat exchanger 50 to the amount of heat exchange of the internal heat exchanger 70.

[0039]

In Embodiment 1, the ratio of the amount of heat exchange of the HIC heat exchanger 50 to the amount of heat exchange of the internal heat exchanger 70 is set so as to be equal to or larger than 160% and equal to or smaller than 700%. With such setting, the refrigeration cycle apparatus 100 can be operated in the range in which a value of the COP is favorable as shown in Fig. 6.

[0040]

As described above, the refrigeration cycle apparatus 100 according to Embodiment 1 employs the following configuration. That is, the refrigeration cycle apparatus 100 includes the HIC heat exchanger 50 connected in series to the internal heat exchanger 70, and the HIC heat exchanger 50 exchanges heat between the high-pressure refrigerant flowing into the HIC heat exchanger 50 from the condenser 30 through the main pipe 1 and the two-phase refrigerant flowing into the HIC heat exchanger 50 from the condenser 30 through the sub-expansion valve 40 on the bypass pipe 2. Thus, the amount of heat exchange of the internal heat exchanger 70 can be reduced. Therefore, the operation in the region with high COP can be achieved without setting an irrelevantly large length of the heat transfer portion of the internal heat exchanger 70, which may cause the refrigeration pressure loss on the suction side of the compressor 10. That is, with the refrigeration cycle apparatus 100, the amount of heat exchange by the internal heat exchanger 70 can be reduced. Therefore, in the case of using HFO-1234yf or HFO-1234ze as the refrigerant, the length of the heat transfer portion of the internal heat exchanger 70 can be reduced, and the efficiency can be improved. In addition, the valve control unit 90c has a configuration of controlling the opening degree of the main expansion valve 80 so that the second degree of superheat is set to the preset target value (third set value). Therefore, the influence of the control for the sub-expansion valve 40 on the evaporator 60 side can be suppressed to minimum.

[0041]

Hitherto, the internal heat exchanger has a long double-pipe configuration, and hence there is a problem in that the productivity is degraded. However, with the refrigeration cycle apparatus 100, the length of the heat transfer portion of the internal heat exchanger 70 can be reduced, resulting in improved productivity. Further, the bypass pipe 2 passing through the HIC heat exchanger 50 has a configuration in which a small amount of two-phase refrigerant flows therein. Therefore, the influence of the pressure loss on the efficiency of the refrigeration cycle apparatus 200 is suppressed. Thus, with the refrigeration cycle apparatus 200 including the HIC heat exchanger 50, the length of the heat transfer portion of the internal heat exchanger 70 can be reduced, resulting in improved efficiency. Further, the HIC heat exchanger 50 can be constructed with use of a pipe thinner than a pipe of the internal heat exchanger 70. Therefore, the apparatus can be reduced in size. Further, the reduction in size with use of the thin pipe for the HIC heat exchanger 50 can reduce the dimension of the equipment as compared to the related-art configuration, thereby being capable of achieving improvement in ease of installation, reduction in weight of the equipment, and reduction in cost.

[0042]

In addition, the refrigeration cycle apparatus 100 of Embodiment 1 has a configuration of using HFO-1234yf or HFO-1234ze having a small global warming potential, thereby being capable of reducing the influence on the global environment. [0043]

Embodiment 2

Next, with reference to Fig. 7 to Fig. 12, description is made of a configuration and an operation of a refrigeration cycle apparatus according to Embodiment 2 of the present invention. Fig. 7 is a system configuration diagram including a refrigerant circuit diagram of a refrigeration cycle apparatus 200 according to Embodiment 2.

Fig. 7 is an illustration of a state in which a heating operation for raising the temperature of water on a load side is performed. The members which are the same as those of Embodiment 1 described above are denoted by the same reference symbols.

[0044]

The refrigeration cycle apparatus 200 includes a compressor 15. The compressor 15 is constructed by, for example, a capacity-controllable inverter compressor, and is configured to suck and compress low-temperature and lowpressure gas refrigerant to form the compressed refrigerant into high-temperature and high-pressure gas refrigerant, and then discharge the refrigerant. The compressor 15 includes an injection port (not shown) and an intermediate chamber (not shown).

In a compression step, refrigerant having an intermediate pressure (intermediatepressure refrigerant), having flowed into the bypass pipe 2, and having flowed out of the HIC heat exchanger 50 is injected through the injection port into the intermediate chamber. That is, the gas refrigerant having flowed out of the HIC heat exchanger 50 is injected through the injection port into the intermediate chamber provided in a pressure chamber of the compressor 15.

[0045]

Next, with reference to Fig. 7 and Fig. 8, description is made of a hot water supply operation of the refrigeration cycle apparatus 200. Fig. 8 is a P-h diagram for illustrating an operation state of the refrigeration cycle apparatus 200. The vertical axis represents an absolute pressure P [MPa-abs] ofthe refrigerant, and the horizontal axis represents a specific enthalpy h [kJ/kgj.

[0046]

The refrigerant being in the state of the low-temperature and low-pressure gas (C11: outlet of internal heat exchanger 70) is sucked into the compressor 15, is compressed by the compressor 15 into the high-temperature and high-pressure gas, and then is discharged. The high-temperature and high-pressure gas refrigerant having been discharged from the compressor 15 passes through the four-way valve and flows into the condenser 30. The high-temperature and high-pressure gas refrigerant having flowed into the condenser 30 transfers heat to water being a heat exchange medium to turn into high-pressure liquid refrigerant. The high-pressure liquid refrigerant having flowed out of the condenser 30 (C12: outlet of condenser 30) is branched into two directions. One of the branched high-pressure liquid refrigerant flows into the sub-expansion valve 40 through the bypass pipe 2 and is reduced in pressure and expanded to turn into intermediate-temperature and intermediatepressure two-phase gas-liquid refrigerant (C13: outlet of sub-expansion valve 40).

The other of the branched high-pressure liquid refrigerant flows into the HIC heat exchanger 50, exchanges heat (T11) with the intermediate-temperature and intermediate-pressure two-phase gas-liquid refrigerant having flowed out of the subexpansion valve 40 to turn into high-pressure subcooled liquid refrigerant, and then flows out (C14a: outlet of HIC heat exchanger 50). The intermediate-temperature and intermediate-pressure two-phase gas-liquid refrigerant having flowed out of the sub-expansion valve 40 exchanges heat (T11) with the high-pressure liquid refrigerant having flowed into the HIC heat exchanger 50 to turn into heating gas (C14b: outlet of HIC heat exchanger 50), and then is injected into the intermediate pressure of the compressor 15 (C15: intermediate pressure merging portion).

[0047]

The high-pressure subcooled liquid refrigerant having flowed out of the HIC heat exchanger 50 flows into the internal heat exchanger 70, exchanges heat (T12) with the low-pressure and low-temperature gas refrigerant having flowed out of the evaporator 60 and passed through the four-way valve 20 to turn into liquid refrigerant having a further large degree of subcooling, and then flows out (C16: outlet of internal heat exchanger 70). The subcooled liquid refrigerant having flowed out of the internal heat exchanger 70 flows into the main expansion valve 80, is reduced in pressure and expanded to turn into the low-pressure two-phase refrigerant, and then flows into the evaporator 60 (C17: inlet of internal heat exchanger 70). The lowpressure two-phase refrigerant having flowed into the evaporator 60 cools air being a heat exchange medium, is evaporated into the low-temperature and low-pressure gas refrigerant, and then flows out (C18: outlet of evaporator 60).

[0048]

The low-temperature and low-pressure gas refrigerant having flowed out of the evaporator 60 passes through the four-way valve 20 again, flows into the internal heat exchanger 70, exchanges heat (T12) with the high-pressure liquid refrigerant having flowed out of the HIC heat exchanger 50 to turn into the gas refrigerant having a large degree of superheat, and is sucked into the compressor 15 again.

[0049]

The low-pressure gas before being sucked into the compressor 10 flows in the main pipe 1 being the gas side of the internal heat exchanger 70. Therefore, a large pipe length may increase the pressure loss at the low pressure to cause degradation of the efficiency of the refrigeration cycle apparatus 200. A small amount of twophase refrigerant which is to be bypassed to the suction side of the compressor 10 flows to the bypass pipe 2 on the gas side of the HIC heat exchanger 50. Therefore, there is no influence on the efficiency of the refrigeration cycle apparatus 200 by the pressure loss. Thus, the HIC heat exchanger 50 can be constructed with a pipe thinner than a pipe of the internal heat exchanger 70, thereby being capable of achieving a compact configuration.

[0050]

Next, with reference to Fig. 7, description is made of a control configuration for the refrigeration cycle apparatus 200. The refrigeration cycle apparatus 200 includes a state detection unit and a controller 190. The state detection unit is configured to detect a state of the refrigerant flowing in the refrigerant circuit. The controller 190 is configured to control the opening degrees of the sub-expansion valve 40 and the main expansion valve 80 based on a result of detection by the state detection unit. The state detection unit of Embodiment 2 includes the pressure sensor 110, the HIC outlet temperature sensor 120, an HIC inlet temperature sensor 210, a suction temperature sensor 230. The pressure sensor 110 is configured to detect a suction pressure Ps being a pressure of the gas refrigerant to be sucked into the compressor 10. The HIC outlet temperature sensor 120 is configured to detect an HIC outlet temperature Tho being a temperature of the gas refrigerant having flowed out of the HIC heat exchanger 50. The HIC inlet temperature sensor 210 is configured to detect an HIC inlet temperature Thi being a temperature of the gas refrigerant flowing into the HIC heat exchanger 50. The suction temperature sensor 230 is configured to detect a suction temperature Ts being a temperature of the gas refrigerant having flowed out of the internal heat exchanger 70 to be sucked into the compressor 15.

[0051]

The controller 190 includes a degree-of-superheat calculation unit 190a, a degree-of-superheat determination unit 190b, and a valve control unit 190c. The degree-of-superheat calculation unit 190a is configured to calculate the first degree of superheat SHh being the degree of superheat at the gas outlet of the HIC heat exchanger 50 by subtracting the HIC inlet temperature Thi detected by the HIC inlet temperature sensor 210 from the HIC outlet temperature Tho detected by the HIC outlet temperature sensor 120. The degree-of-superheat determination unit 190b is configured to determine, through comparison between the first degree of superheat SHh calculated by the degree-of-superheat calculation unit 190a and a fourth set value being a preset allowable lower limit, whether or not the first degree of superheat SHh is smaller than the fourth set value. The valve control unit 190c is configured to control the opening degrees of the sub-expansion valve 40 and the main expansion valve 80 based on a result of determination by the degree-of-superheat determination unit 190b.

[0052]

The degree-of-superheat determination unit 190b has a function of determining, through comparison between the first degree of superheat SHh and a fifth set value being a preset allowable upper limit, whether or not the first degree of superheat SHh is larger than the fifth set value when the degree-of-superheat determination unit 190b determines that the first degree of superheat SHh is equal to or larger than the fourth set value. The valve control unit 190c reduces the opening degree of the subexpansion valve 40 when the degree-of-superheat determination unit 190b determines that the first degree of superheat SHh is smaller than the fourth set value. Further, when the degree-of-superheat determination unit 190b determines that the first degree of superheat SHh is larger than the fifth set value, the valve control unit 190c increases the opening degree of the sub-expansion valve 40. When the degree-of-superheat determination unit 190b determines that the first degree of superheat SHh is equal to or smaller than the fifth set value, the valve control unit 190c maintains the opening degree of the sub-expansion valve 40. That is, in Embodiment 2, the target range is set to the range of equal to or larger than the fourth set value and equal to or smaller than the fifth set value.

[0053]

Further, the degree-of-superheat calculation unit 190a has a function of calculating a third degree of superheat SHs being a degree of superheat at the suction port of the compressor 15 by calculating a saturation temperature f(Ps) corresponding to the suction pressure Ps detected by the pressure sensor 110 and subtracting the saturation temperature f(Ps) from the suction temperature Ts detected by the suction temperature sensor 230. The degree-of-superheat determination unit 190b has a function of determining, through comparison between the third degree of superheat SHs calculated by the degree-of-superheat calculation unit 190a and a preset sixth set value (target value), whether or not the third degree of superheat SHs is smaller than the sixth set value. When the degree-of-superheat determination unit 190b determines that the third degree of superheat SHs is smaller than the sixth set value, the valve control unit 190c reduces the opening degree of the main expansion valve 80. When the degree-of-superheat determination unit 190b determines that the third degree of superheat SHs is equal to or larger than the sixth set value, the valve control unit 190c increases the opening degree of the main expansion valve 80. That is, the valve control unit 190c is configured to control the opening degree of the main expansion valve 80 so that the third degree of superheat SHs becomes equal to the sixth set value being a target value.

[0054]

Next, with reference to Fig. 7 and Fig. 9, description is made of a procedure of opening and closing control for the main expansion valve 80 and the sub-expansion valve 40, which is executed by the controller 190, during the hot water supply operation. Fig. 9 is a flowchart for illustrating the control operation by the controller 190 during the hot water supply operation.

[0055]

First, the degree-of-superheat calculation unit 190a inputs the HIC inlet temperature Thi detected by the HIC inlet temperature sensor 210 (Fig. 9: Step S201) and inputs the HIC outlet temperature Tho detected by the HIC outlet temperature sensor 120 (Fig. 9: Step S202). The degree-of-superheat calculation unit 190a calculates the first degree of superheat SHh at the gas outlet of the HIC heat exchanger 50 by subtracting the HIC inlet temperature Thi from the HIC outlet temperature Tho (Fig. 9: Step S203).

[0056]

The degree-of-superheat determination unit 190b determines, through comparison between the first degree of superheat SHh calculated by the degree-ofsuperheat calculation unit 190a and the fourth set value, whether or not the first degree of superheat SHh is smaller than the fourth set value (Fig. 9: Step S204). When the degree-of-superheat determination unit 190b determines that the first degree of superheat SHh is smaller than the fourth set value (Fig. 9: Step S204/Yes), the valve control unit 190c reduces the opening degree of the sub-expansion valve 40 to suppress the amount of heat exchange of the HIC heat exchanger 50 (Fig. 9: Step S205).

[0057]

When it is determined that the first degree of superheat SHh is equal to or larger than the fourth set value (Fig. 9: Step S204/No), the degree-of-superheat determination unit 190b determines, through comparison between the first degree of superheat SHh and the fifth set value, whether or not the first degree of superheat SHh is larger than the fifth set value (Fig. 9: Step S206). When the degree-ofsuperheat determination unit 190b determines that the first degree of superheat SHh is larger than the fifth set value (Fig. 9: Step S206/Yes), the valve control unit 190c increases the opening degree of the sub-expansion valve 40 to increase the amount of heat exchange of the HIC heat exchanger 50 (Fig. 9: Step S207). When the degree-of-superheat determination unit 190b determines that the first degree of superheat SHh is equal to or smaller than the fifth set value (Fig. 9: Step S206/No), the valve control unit 190c maintains a current opening degree of the sub-expansion valve 40 (Fig. 9: Step S208). That is, the valve control unit 190c is configured to control the opening degree of the sub-expansion valve 40 so that the first degree of superheat falls within the target range of equal to or larger than the fourth set value and equal to or smaller than the fifth set value.

[0058]

Next, the degree-of-superheat calculation unit 190a inputs the suction pressure Ps detected by the pressure sensor 110 (Fig. 9: Step S209) and inputs the suction temperature Ts detected by the suction temperature sensor 230 (Fig. 9: Step S210). The degree-of-superheat calculation unit 190a calculates the third degree of superheat SHs at the suction port of the compressor 15 by calculating the saturation temperature f(Ps) corresponding to the suction pressure Ps and subtracting the saturation temperature f(Ps) from the suction temperature Ts (Fig. 9: Step S211). [0059]

The degree-of-superheat determination unit 190b determines, through comparison between the third degree of superheat SHs calculated by the degree-ofsuperheat calculation unit 190a and the sixth set value, whether or not the third degree of superheat SHs is smaller than the sixth set value (Fig. 9: Step S212).

When the degree-of-superheat determination unit 190b determines that the third degree of superheat SHs is smaller than the sixth set value (Fig. 9: Step S212/Yes), the valve control unit 190c reduces the opening degree of the main expansion valve 80 to suppress the amount of heat exchange of the evaporator 60 (Fig. 9: Step S213). When the degree-of-superheat determination unit 190b determines that the third degree of superheat SHs is equal to or larger than the sixth set value (Fig. 9: Step S212/No), the valve control unit 190c increases the opening degree of the main expansion valve 80 to increase the amount of heat exchange of the evaporator 60 (Fig. 9: Step S214).

[0060]

Fig. 10 is a characteristic graph for showing a simulation result of a relationship between a ratio of an amount of heat exchange of the internal heat exchanger 7 to a total refrigeration capacity of the refrigeration cycle apparatus 200 and a COP. With reference to Fig. 10, description is made of a region in which a value of the COP of the refrigeration cycle apparatus 200 is favorable. As shown in Fig. 10, in the refrigeration cycle apparatus 200, a peak value of the COP is present around a region in which the ratio of the amount of heat exchange of the internal heat exchanger 70 to the total refrigeration capacity is 5.5%. That is, when the length of the heat transfer portion of the internal heat exchanger 70 is excessively small, the degree of suction superheat of the compressor 10 is reduced, and the rise in discharge temperature of the compressor 10 is reduced, with the result that the COP is reduced. When the length of the heat transfer portion of the internal heat exchanger 70 is excessively large, the refrigerant pressure loss on the low-pressure gas side of the internal heat exchanger 70 is increased, with the result that the COP is reduced.

[0061]

As shown in Fig. 10, when the ratio of the amount of heat exchange of the internal heat exchanger 70 to the total refrigeration capacity falls within a range of smaller than 7%, the refrigeration cycle apparatus 200 can be operated in the region in which a value of the COP is favorable. Also in Embodiment 2, the region in which a value of the COP is favorable is a region in which the COP is larger than 100%.

That is, in the refrigeration cycle apparatus 200, the length of the heat transfer portion of the internal heat exchanger 70 is set so that the ratio of the amount of heat exchange of the internal heat exchanger 70 to the total refrigeration capacity is smaller than 7%.

[0062]

Fig. 11 is a characteristic graph for showing a relationship between the ratio of the amount of heat exchange of the internal heat exchanger 70 to the total refrigeration capacity of the refrigeration cycle apparatus 200 and the first degree of superheat SHh at the outlet of the HIC heat exchanger 50. With reference to Fig. 11, description is made of an adjustment method for the ratio of the amount of heat exchange of the internal heat exchanger 70 to the total refrigeration capacity. As shown in Fig. 11, through control of the first degree of superheat SHh at the outlet of the HIC heat exchanger 50, the ratio of the amount of heat exchange of the internal heat exchanger 70 to the total refrigeration capacity can be controlled. In Embodiment 2, in order to set the ratio of the amount of heat exchange of the internal heat exchanger 70 to the total refrigeration capacity to be smaller than 7%, the valve control unit 190c is configured to control the opening degree of the sub-expansion valve 40 so that the first degree of superheat SHh has a value equal to or smaller than 15 degrees Celsius being the target range.

[0063]

Fig. 12 is a characteristic graph for showing a relationship between the ratio of the amount of heat exchange of the HIC heat exchanger 50 to the amount of heat exchange of the internal heat exchanger 70 in the refrigeration cycle apparatus 200 and the COP. With reference to Fig. 12, description is made of a relationship between the amounts of heat exchange by the HIC heat exchanger 50 and the internal heat exchanger 70 and the region in which a value of the COP of the refrigeration cycle apparatus 200 is favorable.

[0064]

With regard to the flow of the refrigerant during the heating operation, the HIC heat exchanger 50 is provided upstream, and the internal heat exchanger 70 is provided downstream. Therefore, when the amount of heat exchange of the HIC heat exchanger 50 is increased, the temperature of the high-pressure liquid refrigerant flowing into the internal heat exchanger 70 is reduced. That is, there is a relationship in which the amount of heat exchange of the internal heat exchanger 70 is reduced when the amount of heat exchange of the HIC heat exchanger 50 increases, and as shown in Fig. 12, a peak value of the COP is present with respect to the ratio of the amount of heat exchange of the HIC heat exchanger 50 to the amount of heat exchange of the internal heat exchanger 70.

[0065]

In Embodiment 2, the ratio of the amount of heat exchange of the HIC heat exchanger 50 to the amount of heat exchange of the internal heat exchanger 70 is set so as to be equal to or larger than 125% and equal to or smaller than 280%. With such setting, the refrigeration cycle apparatus 200 can be operated in the range in which a value of the COP is favorable as shown in Fig. 12.

[0066]

As described above, the refrigeration cycle apparatus 200 according to Embodiment 2 employs the following configuration. That is, the refrigeration cycle apparatus 200 includes the HIC heat exchanger 50 connected in series to the internal heat exchanger 70, and the HIC heat exchanger 50 exchanges heat between the refrigerant flowing into the HIC heat exchanger 50 from the condenser 30 through the main pipe 1 and the refrigerant flowing into the HIC heat exchanger 50 from the condenser 30 through the sub-expansion valve 40 on the bypass pipe 2. Thus, the amount of heat exchange of the internal heat exchanger 70 can be reduced. Therefore, the operation in the region with high COP can be achieved without setting an irrelevantly large length of the heat transfer portion of the internal heat exchanger 70, which may cause the refrigeration pressure loss on the suction side of the compressor 10. That is, with the refrigeration cycle apparatus 200, the amount of heat exchange of the internal heat exchanger 70 can be reduced. Therefore, in the case of using HFO-1234yf or HFO-1234ze as the refrigerant, the length of the heat transfer portion of the internal heat exchanger 70 can be reduced, and the efficiency can be improved. In addition, the valve control unit 190c has a configuration of controlling the opening degree of the main expansion valve 80 so that the third degree of superheat is set to the preset target value (sixth set value). Therefore, the influence of the control for the sub-expansion valve 40 on the evaporator 60 side can be suppressed to minimum.

[0067]

With the refrigeration cycle apparatus 200, the length of the heat transfer portion of the internal heat exchanger 70 can be reduced, resulting in improved productivity. Further, the bypass pipe 2 passing through the HIC heat exchanger 50 has a configuration in which a small amount of two-phase refrigerant flows therein. Therefore, the HIC heat exchanger 50 can be constructed with use of a pipe thinner than a pipe of the internal heat exchanger 70, thereby being capable of achieving reduction in size. Further, the reduction in size with use of the thin pipe for the HIC heat exchanger 50 can reduce the dimension of the equipment as compared to the related-art configuration, thereby being capable of achieving improvement in ease of installation, reduction in weight of the equipment, and reduction in cost. In addition, the refrigeration cycle apparatus 100 of Embodiment 2 has a configuration of using HFO-1234yf or HFO-1234ze having a small global warming potential, thereby being capable of reducing the influence on the global environment.

[0068]

The above-mentioned embodiments are suitable specific examples of the refrigeration cycle apparatus, and the technical scope of the present invention is not limited to those embodiments. For example, in Embodiments 1 and 2 described above, the mixture refrigerant including HFO-1234yf or HFO-1234ze is exemplified as the refrigerant to be used in the refrigeration cycle apparatus 100 and 200. However, the refrigerant is not limited to the above-mentioned mixture refrigerant. For example, a single refrigerant of HFO-1234yf or HFO-1234ze may be used. Further, as the mixture refrigerant including HFO-1234yf or HFO-1234ze, there may be used a mixture refrigerant in which HFO-1234yf or HFO-1234ze is mixed with R32. Further, the detection result for use in the calculation of the first degree of superheat is not limited to the detection result given by the respective sensors exemplified in the Embodiments 1 and 2. For example, the calculation method of Embodiment 1 may be adopted in Embodiment 2, and the calculation method of Embodiment 2 may be adopted in Embodiment 1. Further, the controller 90 of Embodiment 1 may perform the determination processing with use of the third degree of superheat, and the controller 190 of Embodiment 2 may perform the determination processing with use of the second degree of superheat.

Reference Signs List [0069] main pipe 2 bypass pipe 10,15 compressor 20 four-way valve 30 condenser 40 sub-expansion valve50 HIC heat exchanger 60 evaporator 70 internal heat exchanger 80 main expansion valve 90,190 controller 90a, 190a degree-of-superheat calculation unit 90b, 190b degreeof-superheat determination unit 90c, 190c valve control unit 100, 200 refrigeration cycle apparatus 110 pressure sensor 120 HIC outlet

130 evaporator outlet temperature sensor 210 HIC inlet 230 suction temperature sensor Ps suction pressure

SHh first degree of superheat SHe second degree of superheat SHs third degree of superheat The evaporator outlet temperature Thi HIC inlet temperature Tho HIC outlet temperature Ts suction temperature f(Ps) saturation temperature temperature sensor temperature sensor

Claims

CLAIMS [Claim 1]

A refrigeration cycle apparatus, comprising:

a refrigerant circuit in which a compressor, a condenser, a main expansion valve, and an evaporator are connected one another by a main pipe;

an internal heat exchanger configured to exchange heat between refrigerant flowing between the condenser and the main expansion valve and refrigerant flowing between the evaporator and the compressor, and configured to allow the refrigerant flowed out of the evaporator to flow to a suction side of the compressor;

an HIC heat exchanger, provided between the condenser and the internal heat exchanger and connected in series to the internal heat exchanger;

a bypass pipe branching at a portion between the condenser and the HIC heat exchanger and configured to introduce the refrigerant to the compressor via the HIC heat exchanger; and a sub-expansion valve, which is configured to reduce a pressure of the refrigerant flowing into the bypass pipe from the condenser and allow the refrigerant to flow out to the HIC heat exchanger, the HIC heat exchanger being configured to exchange heat between the refrigerant flowing into the HIC heat exchanger from the condenser through the main pipe and the refrigerant flowing into the HIC heat exchanger from the condenser through the sub-expansion valve.

[Claim 2]

The refrigeration cycle apparatus of claim 1, further comprising: a state detection unit configured to detect a state of the refrigerant flowing in the refrigerant circuit; and a controller configured to control an opening degree of the sub-expansion valve based on a result of detection by the state detection unit, wherein the controller comprises a degree-of-superheat calculation unit configured to calculate a first degree of superheat being a degree of superheat at an outlet of the HIC heat exchanger with use of a result of the detection by the state detection unit, and a valve control unit configured to control the opening degree of the subexpansion valve so that the first degree of superheat falls within a preset target range. [Claim 3]

The refrigeration cycle apparatus of claim 2, wherein the state detection unit comprises a pressure sensor configured to detect a suction pressure being a pressure of the refrigerant to be sucked into the compressor, and an HIC outlet temperature sensor configured to detect an HIC outlet temperature being a temperature of the refrigerant flowed out of the HIC heat exchanger, and wherein the degree-of-superheat calculation unit calculates the first degree of superheat by calculating a saturation temperature from the suction pressure detected by the pressure sensor and subtracting the saturation temperature from the HIC outlet temperature detected by the HIC outlet temperature sensor.

[Claim 4]

The refrigeration cycle apparatus of claim 2, wherein the state detection unit comprises an HIC outlet temperature sensor configured to detect an HIC outlet temperature being a temperature of the refrigerant flowed out of the HIC heat exchanger, and an HIC inlet temperature sensor configured to detect an HIC inlet temperature being a temperature of the gas refrigerant flowing into the HIC heat exchanger, and wherein the degree-of-superheat calculation unit calculates the first degree of superheat by subtracting the HIC inlet temperature detected by the HIC inlet temperature sensor from the HIC outlet temperature detected by the HIC outlet temperature sensor.

[Claim 5]

The refrigeration cycle apparatus of any one of claims 2 to 4, wherein the state detection unit comprises a pressure sensor configured to detect a suction pressure being a pressure of the refrigerant to be sucked into the compressor, and an evaporator outlet temperature sensor configured to detect an evaporator outlet temperature being a temperature of the refrigerant flowed out of the evaporator, wherein the degree-of-superheat calculation unit is configured to calculate a second degree of superheat being a degree of superheat at an outlet of the evaporator based on results of detection by the pressure sensor and the evaporator outlet temperature sensor, and wherein the valve control unit is configured to control an opening degree of the main expansion valve, and control the opening degree of the main expansion valve so that the second degree of superheat is set to a preset target value.

[Claim 6]

The refrigeration cycle apparatus of any one of claims 2 to 4, wherein the state detection unit comprises a pressure sensor configured to detect a suction pressure being a pressure of gas refrigerant to be sucked into the compressor, and a suction temperature sensor configured to detect a suction temperature being a temperature of the gas refrigerant flowed out of the internal heat exchanger to be sucked into the compressor, wherein the degree-of-superheat calculation unit is configured to calculate a third degree of superheat being a degree of superheat at a suction port of the compressor based on results of detection by the pressure sensor and the suction temperature sensor, and wherein the valve control unit is configured to control an opening degree of the main expansion valve, and control the opening degree of the main expansion valve so that the third degree of superheat is set to a preset target value.

[Claim 7]

The refrigeration cycle apparatus of any one of claims 2 to 6, wherein the target range is set so that a ratio of an amount of heat exchange of the internal heat exchanger to a total refrigeration capacity is set to be smaller than 7%.

[Claim 8]

The refrigeration cycle apparatus of claim 7, wherein the target range is set so that the ratio of the amount of the heat exchange of the internal heat exchanger to the total refrigeration capacity is set to be larger than
2.4%.

[Claim 9]

The refrigeration cycle apparatus of any one of claims 1 to 8, wherein the bypass pipe is connected to the main pipe extending from an outlet of the internal heat exchanger.

[Claim 10]

The refrigeration cycle apparatus of any one of claims 1 to 8, wherein the compressor comprises an injection port through which the refrigerant flowed into the bypass pipe and flowed out of the HIC heat exchanger is injected.

[Claim 11]

The refrigeration cycle apparatus of claim 9, wherein a ratio of an amount of heat exchange of the HIC heat exchanger to an amount of heat exchange of the internal heat exchanger is set so as to be equal to or larger than 160% and equal to or smaller than 700%.

[Claim 12]

The refrigeration cycle apparatus of claim 10, wherein a ratio of an amount of heat exchange of the HIC heat exchanger to an amount of heat exchange of the internal heat exchanger is set so as to be equal to or larger than 125% and equal to or smaller than 280%.

[Claim 13]

The refrigeration cycle apparatus of any one of claims 1 to 12, wherein a single refrigerant including HFO-1234yf or HFO-1234ze or a mixture refrigerant including

HFO-1234yf or HFO-1234ze is used as the refrigerant to be circulated in the main pipe and the bypass pipe.