AU2016202855B2

AU2016202855B2 - Refrigeration apparatus

Info

Publication number: AU2016202855B2
Application number: AU2016202855A
Authority: AU
Inventors: Satoshi Ishida; Nobuki Matsui; Tadafumi Nishimura
Original assignee: Daikin Industries Ltd
Current assignee: Daikin Industries Ltd
Priority date: 2011-12-28
Filing date: 2016-05-04
Publication date: 2017-10-26
Anticipated expiration: 2032-12-26
Also published as: BR112014015866A2; AU2012361734A1; EP2806233B1; KR20140103352A; BR112014015866A8; WO2013099898A1; ES2861271T3; JP2013139924A; US20140373564A1; AU2016202855A1; AU2012361734B2; EP2806233A1; JP5447499B2; KR101479458B1; EP2806233A4; CN104024764A; CN104024764B

Abstract

The purpose of the present invention is to carry out superheat control in appropriate fashion, in a refrigeration apparatus that is susceptible to the refrigerant reaching a supercooled state short of the evaporator. During cooling, an indoor expansion valve (41) 5 of the refrigeration apparatus (10) controls expansion of cooling inflowing to an indoor heat exchanger (42), doing so on the basis of a low-pressure target value, and a superheat target value for the outflow side of the indoor heat exchanger (42). A supercooled state of the refrigerant at the inflow side of the indoor heat exchanger (42) is detected by an indoor liquid line temperature sensor (44) and an intake pressure sensor (33). An indoor control 10 apparatus (47), in the case of having determined, on the basis of detection results from the indoor liquid line temperature sensor (44) and the intake pressure sensor (33), that the refrigerant at the inflow side of the indoor heat exchanger (42) is in a supercooled state, makes a settings change to raise the superheat target value from a first superheat target value Tshl to a second superheat target value Tsh2. (, Ci - -------- -- --- ~---------- -- ------------ -- -

Description

REFRIGERATION DEVICE

TECHNICAL FIELD

The present invention relates to a refrigeration apparatus, and in particular to a refrigeration apparatus having a refrigerating circuit that includes an evaporator. CROSS-REFERENCE

This application is a divisional application of Australian Patent Application No. 2012361734 which is a national phase application from International Application No. PCT/JP2012/083565 which claims priority to and benefit of Japanese Patent Application No. 2011-290079 which was filed on 28 December 2011. The full disclosure of these applications is incorporated herein by reference.

BACKGROUNDART

Air conditioning apparatus provided with a refrigerating circuit for circulating a refrigerant, and incorporating a refrigeration device for transferring heat between an indoor heat exchanger and an outdoor heat exchanger in the refrigerating circuit, are known in the prior art. In such an air conditioning apparatus, superheat control is carried out in order to control the degree of superheat of the refrigerant at the outlet of the evaporator, in the manner disclosed, for example, in Patent Literature 1 (Japanese Laid-Open Patent Application 2004-271066), in order to carry out heat exchange in appropriate fashion in the indoor heat exchanger and/or the outdoor heat exchanger.

Demands to conserve energy in order to reduce power consumption by air conditioning apparatus have increased in recent years. For example, one measure for doing so is to adopt a low differential pressure, i.e. a small differential between high pressure and low pressure in the refrigerating cycle. In this sort of air conditioning apparatus, if the system is operated at increased evaporation temperature under conditions of being filled with a large quantity of refrigerant and low outside temperature, the refrigerant may reach a subcooled state short of reaching the indoor heat exchanger, which functions as an evaporator. When a subcooled state occurs in the indoor heat exchanger in this manner, the problem of loss of superheat control of the indoor heat exchanger arises.

Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each claim of this application.

Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

SUMMARY

Disclosed herein is a refrigeration apparatus in which a compressor, a radiator, and an evaporator are connected in order to form a refrigerant circuit through which a refrigerant circulates, the refrigeration apparatus including: an expansion mechanism disposed at an inflow side of the evaporator, the expansion mechanism being arranged and configured to control expansion of refrigerant flowing into the evaporator based on a superheat target value at an outflow side of the evaporator; a detector arranged and configured to detect a subcooled state of the refrigerant at the inflow side of the evaporator; and a control part configured and arranged to cause a setting change to raise the high-pressure target value upon determining based on detection results from the detector that the refrigerant at the inflow side of the evaporator is in a subcooled state.

Also disclosed herein is a refrigeration apparatus in which a compressor, a radiator, and an evaporator are connected in order to form a refrigerant circuit through which a refrigerant circulates, the refrigeration apparatus including: an expansion mechanism disposed at an inflow side of the evaporator, the expansion mechanism being arranged and configured to control expansion of refrigerant flowing into the evaporator based on a superheat target value at an outflow side of the evaporator; a detector arranged and configured to detect a subcooled state of the refrigerant at the inflow side of the evaporator; and a control part configured and arranged to cause a setting change to lower the low-pressure target value upon determining based on detection results from the detector that the refrigerant at the inflow side of the evaporator is in a subcooled state.

Also disclosed herein is a refrigeration apparatus in which a compressor, a radiator, and an evaporator are connected in the stated order to form a refrigerating circuit through which a refrigerant circulates, the apparatus being provided with: an expansion mechanism, furnished to an inflow side of the evaporator, and adapted for controlling expansion of refrigerant inflowing to the evaporator, doing so on the basis of at least one value from among a high-pressure target value of the refrigerant circuit, a low-pressure target value of the refrigerant circuit, and a superheat target value at an outflow side of the evaporator; a detector for detecting a subcooled state of the refrigerant at the inflow side of the evaporator; and a control part configured and arranged to make at least one settings change from among a settings change to raise the high-pressure target value, a settings change to lower the low-pressure target value and a settings change to raise the superheat target value when it is decided on the basis of the detection results from the detector that the refrigerant at the inflow side of the evaporator is in a subcooled state.

In a refrigeration apparatus disclosed herein, in the case that a determination is made that the refrigerant at the inflow side of the evaporator is in a subcooled state, at least one settings change from among a settings change to raise the high-pressure target value, to lower the low-pressure target value, and to raise the superheat target value, is made, thus avoiding a situation in which superheat control of the evaporator is lost, whereby the degree of superheat of the evaporator can be controlled in an appropriate manner.

According to the present disclosure, there is a refrigeration apparatus in which the evaporator is a usage-side heat exchanger; and the control part is configured and arranged to make a settings change to lower the low-pressure target value and/or a settings change to raise the superheat target value when it is decided on the basis of the detection results from the detector that the refrigerant at an inflow side of the usage-side heat exchanger is in a subcooled state.

According to the present disclosure, in a refrigeration apparatus, in the case of a determination that the refrigerant at the inflow side of the usage-side heat exchanger is in a subcooled state, at least one of a settings change to lower the low-pressure target value and a settings change to raise the superheat target value is made, thus avoiding a subcooled state, whereby it is possible to satisfactorily deal with cases in which, due to the large quantity of refrigerant, the refrigerant tends to reach a subcooled state short of the usage- side heat exchanger which functions as an evaporator.

According to the present disclosure, there is a refrigeration apparatus in which the detectors include a first detector for detecting the pressure saturation temperature at the inflow side of the usage-side heat exchanger, a second detector for detecting the temperature of the refrigerant at the inflow side of the us age-side heat exchanger, or a third detector for detecting the temperature of the refrigerant at an inflow side of the expansion mechanism and the first detector; and the control part is configured and arranged to determine whether the refrigerant at the inflow side of the usage-side heat exchanger is in a subcooled state, on the basis of a comparison of the detection results from the first detector and the second detector, or a comparison of detection results from the first detector and the third detector.

According to the present disclosure, in a the refrigeration apparatus, a determination as to whether or not the refrigerant at the inflow side of the usage-side heat exchanger is in a subcooled state is made on the basis of a comparison of the detection results from the first detector and the second detector, or a comparison of the detection results from the first detector and the third detector, whereby the determination as to whether a subcooled state exists can be made correctly, even when the refrigerant at the inflow side of the usage-side heat exchanger is subcooled.

According to the present disclosure, there is a refrigeration apparatus in which the third detector is a liquid line temperature sensor disposed to an outflow side of the radiator; and the control part determines whether the refrigerant at the inflow side of the usage-side heat exchanger is in a subcooled state, using a obtained temperature as the temperature of the refrigerant at the inflow side of the expansion mechanism. The obtained temperature is obtained by subtracting a correction value from the detected temperature of the liquid line temperature sensor. And the correction value is equivalent to the thermal loss experienced from the liquid line temperature sensor installation location to the expansion mechanism.

According to the present disclosure, in a refrigeration apparatus, a conventional heat source-side liquid line temperature sensor can be employed in making the determination as to whether the refrigerant at the inflow side of the usage-side heat exchanger is in a subcooled state.

According to the present disclosure, there is a refrigeration apparatus in which the first detector is an intake pressure sensor for detecting pressure at an intake side of the compressor, and the control part is able to calculate the pressure saturation temperature from the pressure detected by the intake pressure sensor.

According to the present disclosure, in a refrigeration apparatus, because the control part is able to calculate the pressure saturation temperature from the pressure detected by the intake pressure sensor, a conventional intake pressure sensor can be employed.

With a refrigeration apparatus described herein, situations in which superheat control of the evaporator is lost are avoided, and control of the degree of superheat of the evaporator can be carried out in an appropriate manner, whereby superheat control may be carried out appropriately in a refrigeration apparatus susceptible to the refrigerant reaching a subcooled state short of the evaporator.

With a refrigeration apparatus described herein, situations in which superheat control of the usage-side heat exchanger is lost are avoided, and control of the degree of superheat of the usage-side heat exchanger can be carried out in an appropriate manner, whereby superheat control may be carried out appropriately in a refrigeration apparatus susceptible to the refrigerant reaching a subcooled state short of the usage-side heat exchanger.

With a refrigeration apparatus described herein, the determination as to whether a subcooled state exists can be made correctly, whereby superheat control carried out appropriately in a refrigeration apparatus in which the refrigerant reaches a subcooled state short of the evaporator.

With a refrigeration apparatus described herein, a conventional heat source-side liquid line temperature sensor can be employed, thereby suppressing the increase in cost.

With a refrigeration apparatus described herein, a conventional intake pressure sensor can be employed, thereby minimizing the increase in cost.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing a refrigerant pipeline system of an air conditioning apparatus that includes a refrigeration apparatus according to an embodiment of the present invention; FIG. 2 is a block diagram showing a control system in the air conditioning apparatus of FIG 1; and FIG. 3 is a graph describing operation of a refrigerating circuit.

DESCRIPTION OF EMBODIMENTS (1) Overall constitution of air conditioning apparatus FIG. 1 shows a refrigerant pipeline system of an air conditioning apparatus that includes a refrigeration apparatus according to an embodiment of the present invention. An air conditioning apparatus 1 is a distributed air conditioning apparatus of refrigerant line design, the apparatus being used for cooling and heating rooms of building through vapor compression refrigerating cycle operation. The air conditioning apparatus 1 is provided with an outdoor air conditioning unit 2 as the heat source unit, a plurality of indoor air conditioning units 4 (in FIG. 1, the two units of an indoor air conditioning unit 4a and an indoor air conditioning unit 4b are shown) as usage units, and a first refrigerant communication line 6 and a second refrigerant communication line 7 as refrigerant communication lines connecting the outdoor air conditioning unit 2 and the indoor air conditioning units 4. A refrigeration apparatus 10 of the air conditioning apparatus 1 is constituted by connecting the outdoor air conditioning unit 2, the indoor air conditioning units 4, and the refrigerant communication lines 6, 7. The refrigeration apparatus 10 has a refrigerant sealed therein, and carries out a refrigerating cycle operation in which the refrigerant is compressed, cooled, decompressed, evaporated by heating, and again is compressed as referred to hereinafter. As the refrigerant, it is possible to employ one selected, for example, from R410A, R407C, R22, R134a, carbon dioxide, or the like. (2) Detailed constitution of air conditioning apparatus (2-1) Indoor air conditioning unit

The indoor air conditioning units are installed by being flush-mounted in or suspended from an interior ceiling of a building or the like, or by being hung from an interior wall surface or the like. The indoor air conditioning units 4 are connected to the outdoor air conditioning unit 2 through the refrigerant communication lines 6, 7, and constitute a part of the refrigeration apparatus 10.

The indoor air conditioning units 4 are described next. In FIG. 1, the two units of the indoor air conditioning unit 4a and the indoor air conditioning unit 4b are shown as the indoor air conditioning units 4, but since each of the indoor air conditioning units 4 is substantially identical in constitution, only the constitution of the indoor air conditioning unit 4a will be described here.

The indoor air conditioning unit 4a has an indoor-side main refrigerant circuit 10a constituting a part of the refrigeration apparatus 10. The indoor-side main refrigerant circuit 10a mainly has an indoor expansion valve 41 serving as a decompressor, and an indoor heat exchanger 42 serving as a us age-side heat exchanger.

The indoor expansion valve 41 is a mechanism for decompression of the refrigerant, and is an electrically driven valve with an adjustable valve opening. The indoor expansion valve 41 is connected at one end thereof to the first refrigerant communication line 6, and at the other end to the indoor heat exchanger 42.

The indoor heat exchanger 42 is, for example, a fin-and-tube heat exchanger of cross-fin type constituted by heat transfer tubes and a multitude of fins. During cooling operations, the heat exchanger functions as an evaporator for the refrigerant, to cool the indoor air, and during heating operations functions as a condenser for the refrigerant, to heat the indoor air. The indoor heat exchanger 42 is connected at one end thereof to the indoor expansion valve 41, and at the other end to the second refrigerant communication line 7.

The indoor air conditioning unit 4a is provided with an indoor fan 43 for drawing indoor air into the unit and supplying it back to the indoors, and is designed to bring about heat exchange between indoor air and the refrigerant flowing through the indoor heat exchanger 42. The indoor fan 43 permits adjustment of the air flow of air supplied to the indoor heat exchanger 42, and the rotation of the fan is driven by an indoor fan motor 43a comprising a DC fan motor or the like. In the indoor fan 43, the indoor fan motor 43a drives, for example, a centrifugal fan and/or a multiblade fan or the like, in order to force air into the indoor heat exchanger 42.

The indoor air conditioning unit 4a is additionally furnished with sensors of various kinds. In specific terms, the unit is furnished with an indoor liquid line temperature sensor 44 comprising a thermistor, and/or with an indoor gas line temperature sensor 45, for measuring the temperature of the refrigerant, from the temperature of the refrigerant line in the vicinity of the indoor heat exchanger 42. The unit is further furnished with an indoor temperature sensor 46; this indoor temperature sensor 46 detects the temperature of indoor air drawn into the indoor air conditioning unit 4 prior to heat exchange taking place. The indoor air conditioning unit 4a further has an indoor control apparatus 47 for controlling the operation of the parts that constitute the indoor air conditioning unit 4a. The indoor control apparatus 47 has a memory and/or a microcomputer or the like, furnished for the purpose of controlling the indoor air conditioning unit 4a, and is designed to exchange control signals or the like with respect to a remote control part (not shown) for individual control of the indoor air conditioning unit 4a, and to exchange control signals or the like with respect to an outdoor control apparatus 30 of the outdoor air conditioning unit 2 via a transmission cable 8a, discussed below. (2-2) Outdoor air conditioning unit

The outdoor air conditioning unit 2 is installed outside a building or the like, and is connected to the indoor air conditioning units 4a, 4b through the first refrigerant communication line 6 and the second refrigerant communication line 7. The outdoor air conditioning unit 2 has a supercooling refrigerant channel 61 that shunts off from the refrigeration apparatus 10 and an outdoor-side main refrigerant circuit 10c constituting a part of the refrigeration apparatus 10. (2-2-1) Outdoor-side main refrigerant circuit

The outdoor-side main refrigerant circuit 10c primarily has a compressor 21, a switchover mechanism 22, an outdoor heat exchanger 23, a first outdoor expansion valve 25, a liquid vapor heat exchanger 27, a liquid-side close off valve 28a, a gas-side close off valve 28b, and an accumulator 29. This outdoor-side main refrigerant circuit 10c primarily has the compressor 21, the switchover mechanism 22, the outdoor heat exchanger 23 as the heat exchanger on the heat source side, the first outdoor expansion valve 25 as a second shutoff mechanism or expansion mechanism on the heat source side, the liquid vapor heat exchanger 27 as a temperature regulating mechanism, the liquid-side close off valve 28a as a first shutoff mechanism, and the gas-side shutoff valve 28b. (*1)

The compressor 21 is a hermetic compressor driven by a compressor motor 21a. The rotation speed of the compressor motor 21a is controlled, for example, by an inverter, and the compressor 21 is constituted such that the operating capacity is variable.

The switchover mechanism 22 is a mechanism for switching the direction of flow of the refrigerant. During cooling operations, it prompts the outdoor heat exchanger 23 to function as a radiator for refrigerant compressed by the compressor 21, and the indoor heat exchanger 42 to function as an evaporator for refrigerant that has cooled in the outdoor heat exchanger 23. For this purpose, the switchover mechanism 22 connects the refrigerant line on the discharge side of the compressor 21 to one end of the outdoor heat exchanger 23, as well as connecting a compressor inlet-side line 29a (including the accumulator 29) to the gas-side close off valve 28b (see the solid lines of the switchover mechanism 22 in FIG. 1). During heating operations, the switchover mechanism 22 prompts the indoor heat exchanger 42 to function as a radiator for refrigerant compressed by the compressor 21, and the outdoor heat exchanger 23 to function as an evaporator for refrigerant that has cooled in the indoor heat exchanger 42. For this purpose, the switchover mechanism 22 connects the refrigerant line on the discharge side of the compressor 21 to the gas-side close off valve 28b, as well as connecting the compressor inlet-side line 29a to one end of the outdoor heat exchanger 23 (see the broken lines of the switchover mechanism 22 in FIG. 1). The switchover mechanism 22 is a four-way valve, for example.

The outdoor heat exchanger 23 is a fin-and-tube heat exchanger of cross-fin type constituted by heat transfer tubes and a multitude of fins, and is connected at one end to the switchover mechanism 22, and at the other end to the first outdoor expansion valve 25.

The outdoor air conditioning unit 2 has an outdoor fan 26 for drawing outside air into the unit, and again discharging it outdoors. The outdoor fan 26 brings about heat exchange between outside air and refrigerant flowing through the outdoor heat exchanger 23.

The first outdoor expansion valve 25 is a mechanism for decompressing the refrigerant in the refrigeration apparatus 10, and is an electrically driven valve having an adjustable valve opening. In order to be able to regulate the pressure and/or flow rate and the like of the refrigerant flowing inside the outdoor-side main refrigerant circuit 10c, the first outdoor expansion valve 25 is situated to the downstream side from the outdoor heat exchanger 23 and to the upstream side from the liquid vapor heat exchanger 27, in the direction of flow of the refrigerant in the refrigeration apparatus 10 during cooling operations, making it possible to shut off passage of the refrigerant as well. One end of the first outdoor expansion valve 25 is connected to the outdoor heat exchanger 23, while the other end is connected to the liquid-side close off valve 28a through the liquid vapor heat exchanger 27, and connected to the liquid side of the indoor heat exchanger 42.

The outdoor air conditioning unit 2 has the outdoor fan 26 as a blower fan for drawing outside air into the unit, and for discharging it to the outdoors after undergoing heat exchange with the refrigerant in the outdoor heat exchanger 23. This outdoor fan 26 is capable of varying the flow rate of air supplied to the outdoor heat exchanger 23, and is, for example, a propeller fan or the like, driven by a motor 26a composed of a DC fan motor or the like.

The liquid vapor heat exchanger 27 is connected between the first outdoor expansion valve 25 and the liquid-side close off valve 28a. The liquid vapor heat exchanger 27 is a pipe heat exchanger of dual pipe structure in which contact is brought about between a shunt line 64, discussed below, and the refrigerant tube through which the refrigerant condensed in the heat source-side heat exchanger flows. In the liquid vapor heat exchanger 27, heat exchange takes place between refrigerant flowing through the refrigeration apparatus 10 from the outdoor heat exchanger 23 towards the indoor air conditioning unit 4, and refrigerant flowing through the supercooling refrigerant channel 61 from the second outdoor expansion valve 62 to the compressor inlet-side line 29a. In so doing, the liquid vapor heat exchanger 27, through this exchange of heat, further cools the refrigerant that has condensed in the outdoor heat exchanger 23 during cooling operations, imparting a high degree of supercooling to the refrigerant destined for the indoor air conditioning unit 4.

The accumulator 29 is situated on the compressor inlet-side line 29a, between the switchover mechanism 22 and the compressor 21. (2-2-2) Supercooling refrigerant channel

The supercooling refrigerant channel 61 is constituted by a refrigerant line running through the liquid vapor heat exchanger 27 from the second outdoor expansion valve 62 and towards the compressor inlet-side line 29a between the switchover mechanism 22 and the accumulator 29. The second outdoor expansion valve 62 is a mechanism for decompressing the refrigerant in the supercooling refrigerant channel 61, and is an electrically driven valve with an adjustable valve opening. The second outdoor expansion valve 62 is furnished to the supercooling refrigerant channel 61, and is situated at a location after the supercooling refrigerant channel 61 shunts off from the line leading from the first outdoor expansion valve 25 to the liquid-side close off valve 28a, but before entering the liquid vapor heat exchanger 27.

The liquid vapor heat exchanger 27 is furnished with the shunt line 64 as a cooling source. The main refrigerant circuit is the section of the refrigeration apparatus 10 excluding the supercooling refrigerant channel 61. The supercooling refrigerant channel 61 is connected to the main refrigerant circuit in such a way that the refrigerant branched between the liquid vapor heat exchanger 27 and the first outdoor expansion valve 25 is returned to the inlet side of the compressor 21. The refrigerant shunted into the supercooling refrigerant channel 61 is decompressed, and thereafter introduced into the liquid vapor heat exchanger 27. The refrigerant shunted into the supercooling refrigerant channel 61 then passes from the outdoor heat exchanger 23 to the first refrigerant communication line 6 where it undergoes heat exchange with the refrigerant fed to the indoor expansion valve 41, and is then returned to the inlet side of the compressor 21.

Seen in greater detail, the supercooling refrigerant channel 61 has the shunt line 64, a junction line 65, and the second outdoor expansion valve 62. The shunt line 64 is connected in such a way that a portion of the refrigerant fed from the first outdoor expansion valve 25 to the indoor expansion valve 41 is shunted at a location between the outdoor heat exchanger 23 and the liquid vapor heat exchanger 27. The junction line 65 is connected to the inlet side of the compressor 21, in such way as to return to the inlet side of the compressor 21 from the outlet on the supercooling refrigerant channel side of the liquid vapor heat exchanger 27. The second outdoor expansion valve 62 is composed of an electrically driven expansion valve, and functions as a communication line expansion mechanism for regulating the flow rate of the refrigerant flowing through the supercooling refrigerant channel 61. In so doing, the refrigerant fed from the outdoor heat exchanger 23 to the indoor expansion valve 41 is cooled in the liquid vapor heat exchanger 27, by the refrigerant flowing through the supercooling refrigerant channel 61 subsequent to decompression by the second outdoor expansion valve 62. That is, the liquid vapor heat exchanger 27 carries out capability control by regulating the valve opening of the second outdoor expansion valve 62.

As discussed below, the supercooling refrigerant channel 61 functions as a communication line connecting a section of the inlet side of the compressor 21, and a section between the liquid-side close off valve 28a and the first outdoor expansion valve 25 in the refrigeration apparatus 10.

The liquid-side close off valve 28a and the gas-side close off valve 28b are valves furnished to the connection ports to the outdoor units/pipelines (specifically, the first refrigerant communication line 6 and the second refrigerant communication line 7). The liquid-side close off valve 28a is connected to the liquid vapor heat exchanger 27, while the gas-side close off valve 28b is connected to the switchover mechanism 22, and can shut off the passage of refrigerant thereby. (2-2-3) Outdoor control device and various sensors

The outdoor air conditioning unit 2 has the outdoor control apparatus 30 for controlling operations of the parts that constitute the outdoor air conditioning unit 2. The outdoor control apparatus 30 has a memory and a microcomputer furnished for the purpose of controlling the outdoor air conditioning unit 2, and/or an inverter circuit or the like for controlling the motor 26a, and is designed to be capable of exchanging control signals and the like with respect to the indoor control apparatus 47 of the indoor air conditioning units 4a, 4b via the transmission cable 8a. That is, an air conditioning control apparatus 8 for controlling operation of the entire air conditioning apparatus 1 is constituted by the indoor control apparatus 47 and the transmission cable 8a connecting the outdoor control apparatus 30 and the indoor control apparatus 47.

The outdoor air conditioning unit 2 is furnished with sensors of various kinds. The refrigerant line on the discharge side of the compressor 21 is furnished with a discharge pressure sensor 31 for detecting the compressor discharge pressure, and with a discharge temperature sensor 32 for detecting the compressor discharge temperature. The compressor inlet-side line 29a is furnished with an intake temperature sensor 34 for detecting the temperature of the gas refrigerant drawn into the compressor 21, and with an intake pressure sensor 33 for detecting the compressor intake pressure. The outdoor control apparatus 30 is constituted in such a way as to control the operating capacity of the compressor 21, and has a target low-pressure value representing a target value for the intake pressure of the compressor 21 during cooling operations, and a target high-pressure value representing a target value for the discharge pressure of the compressor 21 during heating operations. During cooling operations, the operating capacity of the compressor 21 is controlled in such a way that the intake pressure sensor 33 reaches the target low-pressure value, and during heating operations, the operating capacity of the compressor 21 is controlled in such a way that the discharge pressure sensor 31 reaches the target high-pressure value.

The outlet at the main refrigerant circuit side of the liquid vapor heat exchanger 27 is furnished with a liquid line temperature sensor 35 for detecting the refrigerant temperature (specifically, the liquid line temperature). The outside air inlet side of the outdoor air conditioning unit 2 is furnished with an outside air temperature sensor 36 for detecting the temperature of the outside air (specifically, the outside air temperature) inflowing to the interior. The junction line 6 of the supercooling refrigerant channel 61 leading from the liquid vapor heat exchanger 27 to the low-pressure refrigerant line between the switchover mechanism 22 and the accumulator 29 is furnished with a bypass temperature sensor 63 for detecting the temperature of the refrigerant flowing through the outlet at the supercooling refrigerant channel side of the liquid vapor heat exchanger 27. The discharge temperature sensor 32, the intake temperature sensor 34, the liquid line temperature sensor 35, the outside air temperature sensor 36, and the bypass temperature sensor 63 are composed of thermistors. (2-3) Refrigerant communication lines

The refrigerant communication lines 6, 7 are refrigerant lines constructed on-site during installation of the outdoor air conditioning unit 2 and the indoor air conditioning units 4 at the installation site. The first refrigerant communication line 6 is connected to the outdoor air conditioning unit 2 and the indoor air conditioning units 4a, 4b; this refrigerant line, during cooling operation, feeds liquid refrigerant having reached a high degree of supercooling in the liquid vapor heat exchanger 27, to the indoor expansion valve 41 and the indoor heat exchanger 42, and during heating operation feeds liquid refrigerant having been condensed in the indoor heat exchanger 42 to the outdoor heat exchanger 23 of the outdoor air conditioning unit 2. The second refrigerant communication line 7 is connected to the outdoor air conditioning unit 2 and the indoor air conditioning units 4a, 4b; this refrigerant line, during cooling operation, feeds gas refrigerant having evaporated in the indoor heat exchanger 42 to the compressor 21 of the outdoor air conditioning unit 2, and during heating operation feeds gas refrigerant having been compressed in the compressor 21 to the indoor heat exchanger 42 of the indoor air conditioning units 4a, 4b. (2-4) Air conditioning control apparatus FIG. 2 shows a control block diagram of the air conditioning apparatus 1. As shown in FIG. 2, the air conditioning control apparatus 8, which serves as control means for controlling the various operations of the air conditioning apparatus 1, is constituted by the indoor control apparatus 47 and the outdoor control apparatus 30 which are hooked up through the transmission cable 8a. The air conditioning control apparatus 8 receives detection signals from the various sensors 31-36, 44-46, 63, and on the basis of these detection signals controls the various pieces of equipments 21, 22, 25, 26, 41, 43, 62. (3) Operation of air conditioning apparatus

Next, the basic operations of the air conditioning apparatus 1 according to the present embodiment will be described. The air conditioning control apparatus 8 performs control in the various operations described below. (3-1) Cooling operation

In an air conditioning apparatus that operates at a low differential pressure whereby there is only small differential between high pressure and low pressure in the refrigerating cycle, when the system is operated, for example, at increased evaporation temperature under conditions of being filled with a large quantity of refrigerant and low outside air temperature, the refrigerant may reach a subcooled state short of reaching the indoor heat exchanger 42, which functions as the evaporator. In the following description, operation at times when the refrigerant has not reached subcooled state short of reaching the indoor heat exchanger 42 is termed a normal cooling operation, and operation at times when refrigerant has reached subcooled state short of reaching the indoor heat exchanger 42 is termed an abnormal cooling operation, to distinguish the two in the description. (3-1-1) Normal cooling operation

During a cooling operation, the switchover mechanism 22 enters the state shown by the solid lines in FIG. 1, specifically, a state in which the discharge side of the compressor 21 is connected to the gas side of the outdoor heat exchanger 23, and the inlet side of the compressor 21 is connected to the gas side of the indoor heat exchanger 42 through the gas-side close off valve 28b and the second refrigerant communication line 7. During the cooling operation, the first outdoor expansion valve 25 enters the completely open state, and the liquid-side close off valve 28a and the gas-side close off valve 28b enter the open state.

The indoor expansion valves 41 are designed to regulate the valve opening in such a way that a degree of superheat of the refrigerant at the outlet of the indoor heat exchanger 42 (specifically, the gas side of the indoor heat exchanger 42) becomes steadily a first superheat target value Tshl.

For example, in FIG. 3, a point C at pressure PI is at the inflow side of the indoor expansion valve 41, and a point B at pressure P2 is at the outflow side of the indoor expansion valve 41. The degree of superheat of the refrigerant at the outlet of each of the indoor heat exchangers 42 is detected in the indoor control apparatus 47, by subtracting the refrigerant temperature Th2 detected by the indoor liquid line temperature sensor 44 from the refrigerant temperature Thl detected by the indoor gas line temperature sensor 45.

At this time, from the fact that indoor unit liquid line pressure saturation temperature Tein does not exceed the refrigerant temperature Th2 detected by the indoor liquid line temperature sensor 44 (Tein < Th2), it is determined in the indoor control apparatus 47 that a subcooled state does not exist short of reaching the indoor heat exchanger 42. This indoor unit liquid line pressure saturation temperature Tein may be obtained, for example, through conversion of intake pressure LP of the compressor 21 detected by the intake pressure sensor 33, to saturation temperature corresponding to evaporation temperature Te.

The second outdoor expansion valve 62 regulates the valve opening in such a way as to bring the degree of superheat of the refrigerant in the outlet at the supercooling refrigerant channel side of the liquid vapor heat exchanger 27 to a superheat target value (hereinafter termed superheating control). The degree of superheat of the refrigerant in the outlet at the supercooling refrigerant channel side of the liquid vapor heat exchanger 27 is detected by converting the intake pressure of the compressor 21 detected by the intake pressure sensor 33 to a saturation temperature corresponding to evaporation temperature, and subtracting this saturation temperature of the refrigerant from the refrigerant temperature detected by the bypass temperature sensor 63.

With the refrigeration apparatus 10 in this state, operating the compressor 21, the outdoor fan 26, and the indoor fan 43 prompts low-pressure gas refrigerant to be drawn into the compressor 21 and compressed, becoming high-pressure gas refrigerant. Thereafter, the high-pressure gas refrigerant is fed through the switchover mechanism 22 and into the outdoor heat exchanger 23, where it undergoes heat exchange with outside air supplied by the outdoor fan 26, and condenses to become high-pressure liquid refrigerant. Then, after this high-pressure liquid refrigerant has passed through the first outdoor expansion valve 25, it flows into the liquid vapor heat exchanger 27, where it undergoes heat exchange with the refrigerant flowing through the supercooling refrigerant channel 61, becoming further cooled to a subcooled state. At this time, a portion of the high-pressure liquid refrigerant condensed in the outdoor heat exchanger 23 is shunted into the supercooling refrigerant channel 61, and after being decompressed by the second outdoor expansion valve 62, is returned to the inlet side of the compressor 21. Here, the refrigerant passing through the second outdoor expansion valve 62 is decompressed to close to the intake pressure of the compressor 21, causing a portion to evaporate. Then, the refrigerant flowing from the outlet of the second outdoor expansion valve 62 of the supercooling refrigerant channel 61 towards the inlet side of the compressor 21 passes through the liquid vapor heat exchanger 27, and undergoes heat exchange with the high-pressure liquid refrigerant fed to the indoor air conditioning unit 4 from the outdoor heat exchanger 23 in the main refrigerant circuit side.

The high-pressure liquid refrigerant in the subcooled state is fed to the indoor air conditioning unit 4 through the liquid-side close off valve 28a and the first refrigerant communication line 6.

The high-pressure liquid refrigerant fed to the indoor air conditioning unit 4 is decompressed by the indoor expansion valve 41 to close to the intake pressure of the compressor 21, becoming a low-pressure refrigerant having a gas-liquid two-phase state, which is fed to the indoor heat exchanger 42, undergoes heat exchange with indoor air in the indoor heat exchanger 42, and evaporates to become low-pressure gas refrigerant.

This low-pressure gas refrigerant is fed to the outdoor air conditioning unit 2 through the second refrigerant communication line 7, and is again drawn into the compressor 21 through the liquid-side close off valve 28b and the switchover mechanism 22. In this way, the air conditioning apparatus 1 carries out a cooling operation in which the outdoor heat exchanger 23 functions as a condenser for the refrigerant compressed in the compressor 21, and the indoor heat exchanger 42 functions as an evaporator for refrigerant fed through the first refrigerant communication line 6 and the indoor expansion valve 41 after being condensed in the outdoor heat exchanger 23. (3-1-2) Abnormal cooling operation

The switch from normal cooling operation to abnormal cooling operation is made when it has been determined in the indoor control apparatus 47 that a subcooled state exists short of reaching the indoor heat exchanger 42. The indoor control apparatus 47 determines a subcooled state to exist short of reaching the indoor heat exchanger 42, when the indoor unit liquid line pressure saturation temperature Tein exceeds the refrigerant temperature Th2 detected by the indoor liquid line temperature sensor 44 (Tein > Th2). A state in which the indoor unit liquid line pressure saturation temperature Tein exceeds the refrigerant temperature Th2 detected by the indoor liquid line temperature sensor 44 refers to a state of operation in a refrigerating cycle like that shown in FIG. 3. That is, the state is one in which an enthalpy hB of the refrigerant at the point B subsequent to expansion by the indoor expansion valve 41 is lower than an enthalpy hA at point A at which a saturated liquid line LI intersects an evaporating pressure P2 in FIG. 3. In such a state, the refrigerant inflowing to the indoor heat exchanger 42 is subcooled; therefore, if superheat control is performed on the basis of the temperature differential before and after the indoor heat exchanger 42, the actual degree of superheat will be misdetected. As a result, the two-phase state of the refrigerant at the outlet of the indoor heat exchanger 42 will be erroneously recognized as being a superheated state, and the temperature of the refrigerant in the two-phase state will remain unchanged despite regulating the valve opening of the indoor expansion valve 41 to a greater or lesser degree, leading to a loss of control.

Accordingly, when the indoor control apparatus 47 has determined that Tein > Th2, it performs valve opening regulation of the indoor expansion valve 41 while switching the target value for the degree of superheat of the refrigerant from the first superheat target value Tshl to the second superheat target value Tsh2. Here, the second superheat target value Tsh2 is greater than the first superheat target value Tshl (Tsh2 > Tshl).

By evaluating the degree of supercooling which may occur at the inlet of the indoor heat exchanger 42, and changing to the second superheat target value Tsh2 which has been set to higher temperature than the first superheat target value Tshl, the refrigerant at the outlet of the indoor heat exchanger 42 can be transformed to superheated refrigerant in a reliable manner during superheating control, so that diminished controllability can be prevented.

However, operation of the system when the target value for the degree of superheat has been changed to the second superheat target value Tsh2 leads to a drop in efficiency. Therefore, upon entering a state permitting return to the first superheat target value Tshl, the indoor control apparatus 47 returns the target value for the degree of superheat to the first superheat target value Tshl. In specific terms, for example, the indoor control apparatus 47, at the point in time of detecting that the indoor unit liquid line pressure saturation temperature Tein is lower than the refrigerant temperature Th2 detected by the indoor liquid line temperature sensor 44 by a preset temperature β (a few degrees (e.g., 3°C)), changes the target value for the degree of superheat from the second superheat target value Tsh2 to the first superheat target value Tshl. That is, the target value for the degree of superheat is switched at the point in time that the condition Tein < Th2 - β is satisfied. This temperature β is a margin for preventing hunting. (3-2) Heating operation

During heating operation, the switchover mechanism 22 enters the state shown by the broken lines in FIG. 1, specifically, a state in which the discharge side of the compressor 21 is connected to the gas side of the indoor heat exchanger 42 through the gas-side close-off valve 28b and the second refrigerant communication line 7, and the inlet side of the compressor 21 is connected to the gas side of the outdoor heat exchanger 23. The valve opening of the first outdoor expansion valve 25 is regulated in order to decompress the refrigerant inflowing to the outdoor heat exchanger 23, down to a pressure such that evaporation is possible in the outdoor heat exchanger 23 (i.e., to evaporation pressure). The liquid-side close off valve 28a and the gas-side close off valve 28b are in the open state. The valve opening of the indoor expansion valve 41 is regulated such that the degree of supercooling of the refrigerant at the outlet of the indoor heat exchanger 42 becomes the supercooling target value steadily. The degree of supercooling of the refrigerant at the outlet of the indoor heat exchanger 42 is detected by converting the discharge pressure of the compressor 21 detected by the discharge pressure sensor 31 to saturation temperature corresponding to the condensation temperature, and subtracting the refrigerant temperature detected by the indoor liquid line temperature sensor 44 from the this refrigerant saturation temperature.

With the refrigeration apparatus 10 in this state, operating the compressor 21, the outdoor fan 26, and the indoor fan 43 prompts low-pressure gas refrigerant to be drawn into the compressor 21 and compressed, becoming high-pressure gas refrigerant which is fed to the indoor air conditioning unit 4 through the switchover mechanism 22, the gas-side close off valve 28b, and the second refrigerant communication line 7.

In the indoor heat exchanger 42, the high-pressure gas refrigerant fed to the indoor air conditioning unit 4 undergoes heat exchange with the indoor air and is condensed to become high-pressure liquid refrigerant, which is then decompressed according to the valve opening of the indoor expansion valve 41 during passage through the indoor expansion valve 41.

The refrigerant having passed through the indoor expansion valve 41 is fed to the outdoor air conditioning unit 2 through the first refrigerant communication line 6, and after further decompression through the liquid-side close off valve 28a, the liquid vapor heat exchanger 27, and the first outdoor expansion valve 25, flows into the outdoor heat exchanger 23. The low-pressure refrigerant in a gas-liquid two-phase state inflowing to the outdoor heat exchanger 23 undergoes heat exchange with outdoor air supplied by the outdoor fan 26, and evaporates to become low-pressure gas refrigerant, which is again drawn into the compressor 21 through the switchover mechanism 22.

Control of operations such as the above is carried out by the air conditioning control apparatus 8 (the indoor control apparatus 47, the outdoor control apparatus 30, and the transmission cable 8a connecting these), which carries out normal operations including cooling operations and heating operations. (4) Features of refrigeration apparatus (4-1) In the refrigeration apparatus 10 according to the present embodiment, during cooling operations, the compressor 21, the outdoor heat exchanger 23 (example of a radiator), and the indoor heat exchanger 42 (example of an evaporator) are connected in the stated order to form the indoor-side main refrigerant circuit 10a and the outdoor-side main refrigerant circuit 10c (example of a refrigerating circuit) for circulating the refrigerant. The indoor expansion valve 41 (example of an expansion mechanism) furnished to the inflow side of the indoor heat exchanger 42 controls expansion of refrigerant inflowing to the indoor heat exchanger 42, doing so on the basis of the superheat target value at the outflow side of the indoor heat exchanger 42. The indoor liquid line temperature sensor 44 and the intake pressure sensor 33 (example of detectors) detect the subcooled state of the refrigerant at the inflow side of the indoor heat exchanger 42. The indoor control apparatus 47 (example of a control part), in the case of a determination, made on the basis of the detection results from the indoor liquid line temperature sensor 44 and the intake pressure sensor 33, that the refrigerant at the inflow side of the indoor heat exchanger 42 is in a subcooled state, makes a settings change to raise the superheat target value from the first superheat target value Tshl to the second superheat target value Tsh2.

Because a settings change to raise the superheat target value is made in cases of a determination that the refrigerant at the inflow side of the indoor heat exchanger 42 is in a subcooled state, situations in which superheat control of the indoor heat exchanger 42 is lost are avoided, and control of the degree of superheat of the indoor heat exchanger 42 can be carried out in an appropriate manner. Therefore, superheat control may be carried out appropriately in the refrigeration apparatus 10 which is susceptible to the refrigerant reaching a subcooled state short of the indoor heat exchanger 42. In particular, it is possible to satisfactorily deal with cases in which, due to the large quantity of refrigerant, the refrigerant tends to reach a subcooled state short of the indoor heat exchanger 42 (example of a usage-side heat exchanger) which functions as an evaporator. (4-2) The intake pressure sensor 33 is a first detector for detecting the pressure saturation temperature at the inflow side of the indoor heat exchanger 42 (the usage-side heat exchanger), and the indoor liquid line temperature sensor 44 is a second detector for detecting the temperature of the refrigerant at the inflow side of the indoor heat exchanger 42. The indoor control apparatus 47 (the control part), on the basis of whether or not the indoor unit liquid line pressure saturation temperature Tein exceeds the refrigerant temperature Th2 detected by the indoor liquid line temperature sensor 44 (example of a comparison of detection results from the first detector and the second detector), determines whether the refrigerant at the inflow side of the indoor heat exchanger 42 is in a subcooled state. Therefore, the determination as to whether a subcooled state exists can be made correctly, even when the refrigerant at the inflow side of the indoor heat exchanger 42 is subcooled.

Because the indoor liquid line temperature sensor 44 of conventional design can be employed as the second detector for making the determination as to whether the refrigerant at the inflow side of the indoor heat exchanger 42 (the usage-side heat exchanger) is in a subcooled state, increase in cost can be minimized. Likewise, because the intake pressure sensor 33 of conventional design can be employed as the first detector for making the determination as to whether the refrigerant at the inflow side of the indoor heat exchanger 42 is in a subcooled state, increase in cost can be suppressed. (5) Modification examples

(5-1) Modification example A

For the refrigeration apparatus 10 of the aforedescribed embodiment, there was described a case in which, during cooling operations, when determined that the indoor heat exchanger 42 (the evaporator) is in a subcooled state, the indoor control apparatus 47 raises the superheat target value; however, the settings may instead be changed in such a way that the outdoor control apparatus 30 lowers the low-pressure target value when the indoor control apparatus 47 has determined that a subcooled state exists. In the case of the refrigeration apparatus 10, the low-pressure target value is the indoor unit liquid line pressure saturation temperature Tein. In such a case, the air conditioning control apparatus 8 would be the control part. In the above manner, from the detection results of the indoor liquid line temperature sensor 44 and the intake pressure sensor 33, the air conditioning control apparatus 8 changes the low-pressure target value from a first low-pressure target value PL1 to a second low-pressure target value PL2 which is lower. That is PL1 > PL2.

Once the low-pressure target value is changed to the lower second low-pressure target value PL2 which is lower than the first low-pressure target value PL1, the superheat target value is unchanged, thereby producing a large pressure drop in the indoor expansion valve 41 and a drop in evaporation pressure. Therefore, the state of the refrigerant at time B1 having passed through the indoor expansion valve 41 changes to a gas-liquid two-phase state to the downstream side of the indoor expansion valve 41 (the inflow side of the indoor heat exchanger 42) in association with the drop in evaporation pressure, for example, to P3 as shown in FIG. 3, whereupon control of the degree of superheat may proceed.

In the case of being set to the second low-pressure target value L2, the indoor control apparatus 47 operates, for example, at a low-pressure target upper limit value [such that] the indoor unit liquid line pressure saturation temperature Tein target value equals the indoor unit liquid line pressure Th2. During operation under these conditions, in the case of a drop in low pressure (Tein) related to the load factor or the like, the system will automatically depart from the aforedescribed judgment condition, and transition to normal control. That is, the indoor control apparatus 47 detects that the indoor unit liquid line pressure saturation temperature Tein is equal to or less than the temperature Th2 detected by the indoor liquid line temperature sensor 44 (Tein < Th2), and on the basis of the detected result changes the low-pressure target value from the second low-pressure target value PL2 to the first low-pressure target value PL1.

(5-2) Modification example B

In the refrigeration apparatus 10 of the aforedescribed embodiment, during cooling operations, when the indoor unit liquid line pressure saturation temperature Tein exceeds the refrigerant temperature Th2 detected by the indoor liquid line temperature sensor 44 (Tein > Th2), the inflow side of the indoor heat exchanger 42 is determined to be in a subcooled state; however, the outdoor unit liquid line inlet temperature T1 can also be employed to make this determination. The outdoor unit liquid line inlet temperature T1 is the temperature detected, for example, by the liquid line temperature sensor 35 (example of a third detector). Taking the heat loss component into consideration, the indoor control apparatus 47 determines that the inflow side of the indoor heat exchanger 42 is in a subcooled state, when the condition Tein > T1 - a is met. Then, when this condition is met, the indoor control apparatus 47 changes the superheat target value from the first superheat target value Tshl to the second superheat target value Tsh2, or changes the low-pressure target value from the first low-pressure target value PL1 to the second low-pressure target value PL2. a is a value relating to heat loss, derived empirically or the like, and is a value of about 3°C, for example.

Switching of the superheat target value and/or switching of the low-pressure target value performed by the indoor control apparatus 47 when it has been determined that the inflow side of the indoor heat exchanger 42 is in a subcooled state is accomplished in the same manner as in the aforedescribed embodiment and modification example B.

Likewise, the determination as to whether the inflow side of the indoor heat exchanger 42 has transitioned from a subcooled state to a non-subcooled state, making it acceptable to return to the original superheat target value and/or low-pressure target value, is made employing the outdoor unit liquid line inlet temperature Tl. That is, at the point in time it is detected that the condition Tein < Tl - a - β is met, the superheat target value is changed from the second superheat target value Tsh2 to the first superheat target value Tshl, or the low-pressure target value is changed from the second low-pressure target value PL2 to the first low-pressure target value PL1.

In this way, because the liquid line temperature sensor 35 (example of a heat source-side liquid line temperature sensor) of conventional design can be employed as the third detector for making the determination as to whether the refrigerant at the inflow side of the indoor heat exchanger 42 (the usage-side heat exchanger) is in a subcooled state, increase in cost can be minimized. Likewise, because the intake pressure sensor 33 of conventional design can be employed as the first detector for making the determination as to whether the refrigerant at the inflow side of the indoor heat exchanger 42 is in a subcooled state, increase in cost can be minimized.

(5-3) Modification example C

While the aforedescribed embodiment and the aforedescribed modification example A described a case in which the indoor heat exchanger 42 functions as the evaporator during cooling operations, the present invention can be applied also to cases in which the refrigerant at the inflow side of the outdoor heat exchanger 23 tends to reach a subcooled state during heating operations.

In the outdoor control apparatus 30, it can be determined whether or not a subcooled state has arisen at the inflow side of the outdoor heat exchanger 23, from the low pressure Tein and the outdoor unit liquid line inlet temperature Tl, by detecting whether or not the condition Tein > Tl - a is being met.

As heating operations involve setting a high-pressure target value, when it is determined that a subcooled state has arisen at the inflow side of the outdoor heat exchanger 23, the high-pressure target value is changed from a first high-pressure target value HP1 to a second high-pressure target value HP2. In this case, the second high-pressure target value HP2 is set higher than the first high-pressure target value HP1 (HP2 > HP1).

In the same manner as in the aforedescribed embodiment and modification examples A and B, when it is detected that the condition Tein < Ti - a - β is met, the high-pressure target value returns to the normal state. That is, when it is determined that a subcooled state no longer exists at the inflow side of the outdoor heat exchanger 23, the high-pressure target value is changed from the second high-pressure target value HP2 to the first high-pressure target value HP1.

(5-4) Modification example D

While the aforedescribed embodiment described a case in which the indoor air conditioning unit 4 is constituted by connecting the two indoor air conditioning units 4a, 4b, it would be acceptable to instead connect a single indoor air conditioning unit, or three or more. In the case of connecting multiple indoor air conditioning units, indoor air conditioning units constituted differently may be connected.

(5-5) Modification example E

The aforedescribed embodiment described a case in which the superheat target value is changed to the second superheat target value Tsh2 which is set to a higher temperature than the first superheat target value Tshl. However, a plurality of different superheat target values can be set as the second superheat target values. For example, a constitution whereby a third superheat target value Tsh3 higher than the second superheat target value Tsh2 is provided, employing the second superheat target value Tsh2 when a degree of supercooling Tsc meets the condition 0 < Tsc < Tscl is met, and employing the third superheat target value Tsh3 when the degree of supercooling Tsc meets the condition Tscl < Tsc is met, can be adopted. Moreover, a relational expression of the second superheat target value Tsh2 and the degree of supercooling Tsc may be prepared in advance, and the degree of supercooling evaluated at the inlet of the indoor heat exchanger 42, changing the second superheat target value Tsh2 to a higher temperature than the first superheat target value Tshl, according to the extent of the degree of supercooling. The relational expression of the second superheat target value Tsh2 and the degree of supercooling Tsc may be selected, for example, through prior experimentation and/or test operation or the like, as appropriate.

REFERENCE SIGNS LIST 10 Refrigeration apparatus 21 Compressor 23 Outdoor heat exchanger 30 Outdoor control apparatus 32 Discharge temperature sensor 33 Intake pressure sensor 41 Indoor expansion valve 42 Indoor heat exchanger 44 Indoor liquid line temperature sensor 47 Indoor control apparatus

CITATION LIST PATENT LITERATURE

[Patent Literature 1] Japanese Laid-Open Patent Application 2004-271066

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:-

1. A refrigeration apparatus in which a compressor, a radiator, and an evaporator are connected in order to form a refrigerant circuit through which a refrigerant circulates, the refrigeration apparatus including: an expansion mechanism disposed at an inflow side of the evaporator, the expansion mechanism being arranged and configured to control expansion of refrigerant flowing into the evaporator based on a superheat target value at an outflow side of the evaporator; a detector arranged and configured to detect a subcooled state of the refrigerant at the inflow side of the evaporator; and a control part configured and arranged to cause a setting change to raise the high-pressure target value upon determining based on detection results from the detector that the refrigerant at the inflow side of the evaporator is in a subcooled state.
2. A refrigeration apparatus in which a compressor, a radiator, and an evaporator are connected in order to form a refrigerant circuit through which a refrigerant circulates, the refrigeration apparatus including: an expansion mechanism disposed at an inflow side of the evaporator, the expansion mechanism being arranged and configured to control expansion of refrigerant flowing into the evaporator based on a superheat target value at an outflow side of the evaporator; a detector arranged and configured to detect a subcooled state of the refrigerant at the inflow side of the evaporator; and a control part configured and arranged to cause a setting change to lower the low-pressure target value upon determining based on detection results from the detector that the refrigerant at the inflow side of the evaporator is in a subcooled state.
3. The refrigeration apparatus according to claim 1 or 2, wherein the control part is further configured to return the at least one setting change to an original setting when a subcooled state no longer exists after the setting change has been made.
4. The refrigeration apparatus according to claim 3, wherein the control part is further configured to furnish a margin to preventing hunting between a value when determining that a subcooled state exists in a case where the setting change is to be effected, and a value when determining that a departure has been made from a subcooled state in a case of changing is restored to the original setting.
5. The refrigeration apparatus according to any one of claims 1 to 4, wherein the evaporator is a usage-side heat exchanger; and the detector includes a first detector arranged and configured to detect pressure saturation temperature at the inflow side of the usage-side heat exchanger, and one of a second detector arranged and configured to detect temperature of the refrigerant at the inflow side of the usage-side heat exchanger, and a third detector arranged and configured to detect temperature of the refrigerant at an inflow side of the expansion mechanism; and the control part is further configured and arranged to determine whether the refrigerant at the inflow side of the usage-side heat exchanger is in a subcooled state based on a comparison of detection results from the first detector and the second detector, or a comparison of detection results from the first detector and the third detector.
6. The refrigeration apparatus according to claim 5, wherein the third detector is a liquid line temperature sensor disposed at an outflow side of the radiator; and the control part is further configured to determine whether the refrigerant at the inflow side of the usage-side heat exchanger is in a subcooled state using an obtained temperature as the temperature of the refrigerant at the inflow side of the expansion mechanism, the obtained temperature being obtained by subtracting a correction value from the detected temperature of the liquid line temperature sensor, and the correction value being equivalent to a thermal loss experienced from the liquid line temperature sensor installation location to the expansion mechanism.
7. The refrigeration apparatus according to claim 1, wherein the control part is configured and arranged to cause a setting change to raise the high-pressure target value from a first discharge pressure target value to a second discharge pressure target value, which is higher than the first discharge pressure target value, upon determining based on detection results from the detector that the refrigerant at the inflow side of the evaporator is in the subcooled state.
8. The refrigeration apparatus according to claim 2, wherein the control part is configured and arranged to cause a setting change to lower the low-pressure target value for intake pressure from a first intake pressure target value to a second intake pressure target value, which is lower than the first intake pressure target value, upon determining based on detection results from the detector that the refrigerant at the inflow side of the evaporator is in the subcooled state.