REFRIGERATION CYCLE DEVICE, AND HOT WATER HEATING DEVICE PROVIDED WITH THE SAME

Abstract

 A refrigeration cycle device (1A) according to the present disclosure includes a first temperature sensor (61) for detecting a temperature of refrigerant at an outlet of a bypass channel, a first pressure sensor (51) for detecting a pressure of refrigerant to be sucked into a compressor (21), a second temperature sensor (62) for detecting a discharge temperature of the compressor, and a control device (4). The control device performs control of reducing openings of a main expansion valve (24) and a bypass expansion valve (31), when a degree of superheating of refrigerant at the outlet of the bypass channel (3) is great and a temperature increase value, within a predetermined period of time, of a temperature of refrigerant discharged from the compressor (21) becomes equal to or greater than a predetermined value. Accordingly, an abnormal increase in the discharge temperature at the start of flow of refrigerant through the bypass channel may be suppressed.

Description

BACKGROUND

1. Technical Field

[0001] The present disclosure relates to a refrigeration cycle device that bypasses a part of refrigerant flowing out of a radiator, and that subcools mainstream refrigerant by exchanging heat between the mainstream refrigerant and bypass-flow refrigerant.

2. Description of the Related Art

[0002] For example, Unexamined Japanese Patent Publication No. H10-68553 proposes, with respect to this type of refrigeration cycle device and hot water heating device, providing a subcooling heat exchanger on a downstream side of a radiator of a refrigerant circuit, and subcooling refrigerant flowing out of the radiator by causing expanded refrigerant to flow into the subcooling heat exchanger.

[0003] FIG. 5 shows a conventional refrigeration cycle device described in PTL 1.

[0004] As shown in FIG. 5, refrigeration cycle device 100 includes refrigerant circuit 110 for circulating refrigerant, and bypass channel 120. Refrigerant circuit 110 is configured from compressor 111, radiator 112, subcooling heat exchanger 113, main expansion valve 114, and evaporator 115 which are connected in a circular manner by pipes.

[0005] Bypass channel 120 is branched from refrigerant circuit 110 between subcooling heat exchanger 113 and main expansion valve 114, and is connected to refrigerant circuit 110 between evaporator 115 and compressor 111 via subcooling heat exchanger 113. Also, bypass expansion valve 121 is provided to bypass channel 120, on an upstream side of subcooling heat exchanger 113.

[0006] Furthermore, refrigeration cycle device 100 includes temperature sensor 141 for detecting temperature (compressor discharge pipe temperature) Td of refrigerant which is discharged from compressor 111, temperature sensor 142 for detecting temperature (evaporator inlet temperature) Te of refrigerant flowing into evaporator 115, temperature sensor 143 for detecting, on bypass channel 120, temperature (bypass-side inlet temperature) Tbi of refrigerant flowing into subcooling heat exchanger 113, and temperature sensor 144 for detecting, on bypass channel 120, temperature (bypass-side outlet temperature) Tbo of refrigerant flowing out of subcooling heat exchanger 113.

[0007] Moreover, target temperature Td (target) for the discharge pipe of the compressor is set based on evaporator inlet temperature Te detected by temperature sensor 142. Refrigeration cycle device 100 further includes a main expansion valve controller for controlling main expansion valve 114 so as to cause discharge pipe temperature Td detected by temperature sensor 141 to reach target temperature Td (target), and a bypass expansion valve controller for controlling bypass expansion valve 121 so as to cause difference (Tbo - Tbi) between bypass-side outlet temperature Tbo and bypass-side inlet temperature Tbi at subcooling heat exchanger 113 becomes a predetermined target value.

[0008] However, according to the conventional configuration described above, bypass expansion valve 121 operates to control the temperature difference between the inlet side and the outlet side of bypass channel 120, that is, a degree of superheat at the outlet of bypass channel 120, and is not able to control a refrigerant state at the outlet of bypass channel 120 to be a wet state.

[0009] Accordingly, when bypass expansion valve 121 is opened during heating operation at a time when an ambient temperature is extremely low at -20°C, for example, refrigerant flowing through bypass channel 120 before a flow rate of refrigerant in bypass channel 120 is increased to an appropriate rate is possibly heated to an excessive degree by subcooling heat exchanger 113, and a sucked refrigerant state at compressor 111 may reach an excessively superheated state. This may result in an abnormal increase in a discharge temperature of compressor 111.

[0010] Accordingly, bypass channel 120 may not be used when the ambient temperature is extremely low, and an increase in the operation efficiency due to use of bypass channel 120 cannot be achieved, and there are problems of poor efficiency and not enough heating capacity.

SUMMARY

[0011] The present disclosure is for solving the conventional problems described above, and its object is to provide a refrigeration cycle device which is capable of increasing the heating capacity and efficiency even at a low ambient temperature by swiftly controlling a refrigeration cycle to an appropriate state.

[0012] To solve the conventional problems described above, a refrigeration cycle device of the present disclosure includes a refrigerant circuit where a compressor, a radiator, a subcooling heat exchanger, a main expansion section, and an evaporator are connected in a circular manner, a bypass channel that is branched from the refrigerant circuit between the radiator and the main expansion section, and that is connected, via the subcooling heat exchanger, to a compression chamber of the compressor or the refrigerant circuit between the evaporator and the compressor, a bypass expansion section that is provided to the bypass channel, on an upstream side of the subcooling heat exchanger, a first temperature sensor that is provided to the bypass channel, and that is for detecting a temperature of refrigerant flowing out of the subcooling heat exchanger, a first saturation temperature detection unit for detecting a saturation temperature of refrigerant to be sucked into the compressor, a second temperature sensor for detecting a temperature of refrigerant discharged from the compressor, and a control device. The control device reduces an opening of each of the main expansion section and the bypass expansion section when the temperature detected by the first temperature sensor becomes higher than the saturation temperature detected by the first saturation temperature detection unit and a temperature increase value of the temperature detected by the second temperature sensor within a predetermined period of time becomes equal to or greater than a predetermined value.

[0013] It is thereby possible to perform detection if a refrigerant mass flow rate of the bypass channel is extremely low, and by increasing amounts of pressure reduction at the main expansion section and the bypass expansion section in such a case, evaporation of refrigerant at the evaporator on a low-pressure side is accelerated. As a result, liquid refrigerant retained on the low-pressure side is moved to a high-pressure side.

[0014] Therefore, the refrigerant at an inlet of the bypass expansion section is changed into a liquid state, and the refrigerant mass flow rate to the bypass channel is swiftly increased, and thus, the refrigerant at an outlet of the bypass channel changes into a saturation state in a short time. An abnormal increase in a discharge temperature of the compressor may thereby be suppressed.

[0015] According to the present disclosure, there may be provided a refrigeration cycle device which is capable of increasing the heating capacity and efficiency even at a low ambient temperature by swiftly controlling a refrigeration cycle to an appropriate state.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] 

FIG. 1 is a schematic configuration diagram of a refrigeration cycle device according to a first exemplary embodiment of the present disclosure;

FIG. 2A is a diagram showing a relationship between an opening of a main expansion section of the refrigeration cycle device and a discharge temperature;

FIG. 2B is a diagram showing a relationship between an opening of a bypass expansion section of the refrigeration cycle device and a discharge temperature;

FIG. 3 is a diagram showing a flowchart of operation control of the refrigeration cycle device;

FIG. 4 is a diagram showing a relationship between an operation time at a time of normal operation of the refrigeration cycle device and changes in states; and

FIG. 5 is a schematic configuration diagram of a conventional refrigeration cycle device.

DETAILED DESCRIPTION

[0017] A refrigeration cycle device according to a first aspect includes a refrigerant circuit where a compressor, a radiator, a subcooling heat exchanger, a main expansion section, and an evaporator are connected in a circular manner, a bypass channel that is branched from the refrigerant circuit between the radiator and the main expansion section, and that is connected, via the subcooling heat exchanger, to a compression chamber of the compressor or the refrigerant circuit between the evaporator and the compressor, a bypass expansion section that is provided to the bypass channel, on an upstream side of the subcooling heat exchanger, a first temperature sensor that is provided to the bypass channel, and that is for detecting a temperature of refrigerant flowing out of the subcooling heat exchanger, a first saturation temperature detection unit for detecting a saturation temperature of refrigerant to be sucked into the compressor, a second temperature sensor for detecting a temperature of refrigerant discharged from the compressor, and a control device. The control device reduces an opening of each of the main expansion section and the bypass expansion section when the temperature detected by the first temperature sensor becomes higher than the saturation temperature detected by the first saturation temperature detection unit and a temperature increase value of the temperature detected by the second temperature sensor within a predetermined period of time becomes equal to or greater than a predetermined value.

[0018] It is thereby possible to perform determination if a refrigerant mass flow rate of the bypass channel is extremely low, and by increasing amounts of pressure reduction at the main expansion section and the bypass expansion section in such a case, evaporation of refrigerant at the evaporator on a low-pressure side is accelerated. As a result, liquid refrigerant retained on the low-pressure side is moved to a high-pressure side.

[0019] Therefore, the refrigerant at the inlet of the bypass expansion section is changed into a liquid state, and the refrigerant mass flow rate to the bypass channel is swiftly increased, and thus, the refrigerant at the outlet of the bypass channel changes into a saturation state in a short time. An abnormal increase in a discharge temperature of the compressor may thereby be suppressed.

[0020] Accordingly, even when the ambient temperature is extremely low at -20°C, for example, an increased enthalpy difference effect at the evaporator due to heat exchange, at the subcooling heat exchanger, between mainstream refrigerant and refrigerant flowing through the bypass channel, and a pressure drop reduction effect at a refrigerant route on the low-pressure side due to bypassing of the refrigerant from the high-pressure side to the low-pressure side may be utilized. As a result, a higher operation efficiency and sufficient heating capacity may be achieved.

[0021] A second aspect is according to the first aspect, where amounts of reduction of openings of the main expansion section and the bypass expansion section are greater when the temperature increase value is great than when the temperature increase value is small.

[0022] Accordingly, amounts of operation of the main expansion section and the bypass expansion section are controlled according to levels of insufficiency in the amounts of pressure reduction, and thus, the refrigerant state at the inlet of the bypass expansion section may be swiftly liquefied and the refrigerant at the outlet of the bypass channel may be controlled to be in the saturation state in a short time under various load conditions.

[0023] Therefore, the discharge temperature of the compressor may be prevented from rising excessively with respect to a target, and the controllability of the refrigeration cycle and the reliability of the compressor may be further increased.

[0024] A third aspect is according to the first or the second aspect, and further includes a third temperature sensor for detecting a temperature of refrigerant flowing out of the radiator, a second saturation temperature detection unit for detecting a saturation temperature of refrigerant flowing through the radiator, a fourth temperature sensor for detecting a temperature of a use-side heat medium flowing into the radiator, and a fifth temperature sensor for detecting a temperature of the use-side heat medium flowing out of the radiator. The control device ends an operation of reducing the opening of each of the main expansion section and the bypass expansion section when a degree of subcooling that is a temperature difference between the temperature detected by the third temperature sensor and the saturation temperature detected by the second saturation temperature detection unit becomes greater by a predetermined temperature than a temperature difference between the temperature detected by the fourth temperature sensor and the temperature detected by the fifth temperature sensor.

[0025] Therefore, when the degree of subcooling of the refrigerant at the outlet of the radiator exceeds an appropriate value, the operation of closing the main expansion section and the bypass expansion section is ended, and thus, an abnormal increase in the high pressure or an abnormal reduction in the low pressure due to excessive throttling of the expansion section may be suppressed.

[0026] Accordingly, because operation in an inefficient refrigeration cycle due to excessive throttling of the main expansion section and the bypass expansion section may be prevented, the energy efficiency may be further increased.

[0027] A fourth aspect is a hot water heating device provided with the refrigeration cycle device of any one of the first to the third aspects. The present disclosure is applicable not only in the case where the radiator is a refrigerant-air heat exchanger, but also in a case where the radiator is a refrigerant-water heat exchanger.

[0028] In the following, an exemplary embodiment of the present disclosure will be described with reference to the drawings. Additionally, the present disclosure is not to be limited by the exemplary embodiment.

FIRST EXEMPLARY EMBODIMENT

[0029] FIG. 1 is a schematic configuration diagram of a refrigeration cycle device and a hot water heating device according to a first exemplary embodiment of the present disclosure.

[0030] In FIG. 1, refrigeration cycle device 1A includes refrigerant circuit 2 for circulating refrigerant, bypass channel 3, and control device 4.

[0031] As the refrigerant, a non-azeotropic mixed refrigerant such as R407C, a pseudo-azeotropic mixed refrigerant such as R410A, or a single refrigerant such as R32 may be used, for example.

[0032] Refrigerant circuit 2 is configured by compressor 21, radiator 22, subcooling heat exchanger 23, main expansion valve (main expansion section) 24, and evaporator 25 which are connected in a circular manner by pipes.

[0033] In the present exemplary embodiment, sub-accumulator 26 and main accumulator 27 for performing gas-liquid separation are provided between evaporator 25 and compressor 21. Also, refrigerant circuit 2 is provided with four-way valve 28 for switching between normal operation and defrosting operation.

[0034] In the present exemplary embodiment, refrigeration cycle device 1A is heating unit of a hot water heating device which uses hot water generated by the heating unit for heating, and radiator 22 is a heat exchanger for heating water by exchanging heat between refrigerant and water.

[0035] Specifically, supply pipe 71 and recovery pipe 72 are connected to radiator 22, and water is supplied to radiator 22 through supply pipe 71, and water (hot water) heated by radiator 22 is recovered through recovery pipe 72.

[0036] Hot water recovered through recovery pipe 72 is sent to a heater such as a radiator directly or through a hot water tank, and heating is thus performed.

[0037] In the present exemplary embodiment, bypass channel 3 is branched from refrigerant circuit 2 between subcooling heat exchanger 23 and main expansion valve 24, and is connected, via subcooling heat exchanger 23, to refrigerant circuit 2 between sub-accumulator 26 and main accumulator 27, between evaporator 25 and compressor 21.

[0038] Moreover, bypass expansion valve (bypass expansion section) 31 is provided to bypass channel 3, on an upstream side of subcooling heat exchanger 23.

[0039] Furthermore, refrigerant circuit 2 is provided with first pressure sensor 51 for detecting pressure (suction pressure) Ps of refrigerant to be sucked into compressor 21, second temperature sensor 62 for detecting temperature (discharge temperature) Td of refrigerant discharged from compressor 21, second pressure sensor 52 for detecting pressure (condensing pressure) Pc of refrigerant flowing out of radiator 22, and third temperature sensor 63 for detecting temperature (radiator outlet temperature) Tco of refrigerant flowing out of radiator 22.

[0040] Furthermore, bypass channel 3 is provided with first temperature sensor 61 for detecting temperature (bypass channel outlet temperature) Tbo of refrigerant flowing out of subcooling heat exchanger 23.

[0041] On the other hand, supply pipe 71 is provided with fourth temperature sensor 64 for detecting temperature (inflow water temperature) Twi of water flowing into radiator 22. Recovery pipe 72 is provided with fifth temperature sensor 65 for detecting temperature (outflow water temperature) Two of water flowing out of radiator 22.

[0042] Moreover, control device 4 controls a rotational speed of compressor 21, switching of four-way valve 28, and openings of main expansion valve 24 and bypass expansion valve 31 based on detection values detected by first pressure sensor (first saturation temperature detection unit) 51, second pressure sensor (second saturation temperature detection unit) 52, first temperature sensor 61, second temperature sensor 62, third temperature sensor 63, fourth temperature sensor 64, and fifth temperature sensor 65, for example.

[0043] In normal operation, refrigerant that is discharged from compressor 21 is sent to radiator 22 through four-way valve 28. In defrosting operation, refrigerant that is discharged from compressor 21 is sent to evaporator 25 through four-way valve 28. In FIG. 1, a flow direction of refrigerant in the normal operation is indicated by an arrow.

[0044] First, a change in a state of refrigerant in the normal operation of refrigeration cycle device 1A of the present exemplary embodiment will be described with reference to FIG. 1.

[0045] High-pressure refrigerant that is discharged from compressor 21 flows into radiator 22, and releases heat to water passing through radiator 22. High-pressure refrigerant flowing out of radiator 22 flows into subcooling heat exchanger 23, and is subcooled by low-pressure refrigerant whose pressure is reduced by bypass expansion valve 31. High-pressure refrigerant flowing out of subcooling heat exchanger 23 is dispensed to main expansion valve 24 side and to bypass expansion valve 31 side.

[0046] High-pressure refrigerant that is dispensed to main expansion valve 24 side is expanded by having its pressure reduced by main expansion valve 24, and then flows into evaporator 25. Low-pressure refrigerant flowing into evaporator 25 absorbs heat from air at evaporator 25.

[0047] For its part, high-pressure refrigerant that is dispensed to bypass expansion valve 31 side is expanded by having its pressure reduced by bypass expansion valve 31, and then flows into subcooling heat exchanger 23. Low-pressure refrigerant flowing into subcooling heat exchanger 23 is heated by high-pressure refrigerant flowing out of radiator 22. Then, low-pressure refrigerant flowing out of subcooling heat exchanger 23 merges with low-pressure refrigerant flowing out of evaporator 25, and is sucked into compressor 21 again.

[0048] According to the configuration of refrigeration cycle device 1A of the present exemplary embodiment, the pressure of refrigerant to be sucked into compressor 21 when the ambient temperature is low is reduced and an amount of refrigerant circulation is reduced, and thus, reduction in the heating capacity of radiator 22 may be prevented.

[0049] To realize the above, it is important that an enthalpy difference at evaporator 25 is increased by subcooling. In addition, it is also important to suppress an amount of gas-phase refrigerant with low heat absorption effect which flows through a low-pressure part of refrigerant circuit 2 by causing refrigerant to flow through bypass channel 3, and to thereby reduce a pressure drop in the low-pressure part of refrigerant circuit 2.

[0050] If a pressure drop in the low-pressure part of refrigerant circuit 2 is reduced, pressure of refrigerant that is sucked into compressor 21 is increased by this amount and a specific volume is reduced, and the amount of refrigerant circulation is thereby increased.

[0051] Furthermore, if the enthalpy difference at evaporator 25 is increased, even if a mass flow rate of refrigerant passing through evaporator 25 is reduced by causing refrigerant to pass through bypass channel 3, an amount of heat absorption at evaporator 25 may be maintained.

[0052] That is, if the degree of subcooling of refrigerant and the mass flow rate of refrigerant through bypass channel 3 are maximized, a maximum effect to increase the heat capacity of radiator 22 and a maximum effect to increase a coefficient of performance of refrigeration cycle device 1A may be achieved.

[0053] However, in the case of utilizing the effect of causing refrigerant to flow through bypass channel 3 when the ambient temperature is extremely low at -20°C, for example, or when a use-side load is small, there is a problem that the discharge temperature of compressor 21 is abnormally increased before the flow rate of refrigerant flowing through bypass channel 3 becomes appropriate.

[0054] Accordingly, to increase the efficiency of an appliance by utilizing, under various conditions, the capacity increase effect achieved by causing refrigerant to flow through bypass channel 3, it is important to suppress the abnormal increase in the discharge temperature of compressor 21.

[0055] Accordingly, in the present exemplary embodiment, at the time of normal operation (especially, at the start of bypassing), control device 4 reduces the openings of main expansion valve 24 and bypass expansion valve 31 by main expansion valve operation opening Otm and bypass expansion valve operation opening Otb calculated based on amount of change Atd, respectively, when bypass channel outlet temperature Tbo becomes higher than suction saturation temperature Ts calculated based on suction pressure Ps by predetermined temperature Tm or more and amount of change Atd in discharge temperature Td within a predetermined period of time becomes equal to or greater than predetermined amount of change Am.

[0056] Furthermore, control device 4 ends an operation of reducing the openings of main expansion valve 24 and bypass expansion valve 31 when degree of subcooling Sc calculated based on a difference between condensed saturation temperature Tc calculated based on condensing pressure Pc and radiator outlet temperature Tco becomes greater, by predetermined temperature difference Dm or more, than water temperature difference Dw calculated based on a difference between outflow water temperature Two and inflow water temperature Twi.

[0057] Moreover, predetermined openings by which control device 4 operates main expansion valve 24 and bypass expansion valve 31 in a closing direction is set as shown in FIG. 2, for example. That is, setting is performed such that the faster the speed of increase in the discharge temperature, the greater the amount of pressure reduction, and thus, an excessive increase in the discharge temperature may be suppressed.

[0058] Next, a control specification at the time of normal operation of refrigeration cycle device 1A of the present exemplary embodiment will be specifically described with reference to the flowchart shown in FIG. 3.

[0059] Moreover, FIG. 4 includes diagrams showing relationships between operation time at the time of normal operation of refrigeration cycle device 1A of the present exemplary embodiment and changes in the states. In FIG. 4(a), a vertical axis shows a rotational speed of the compressor. A horizontal axis shows time. A target rotational speed is reached after a lapse of a predetermined time. Additionally, also in FIGS. 4(b) to 4(f), horizontal axes show time as in FIG. 4(a). In FIG. 4(b), a vertical axis shows the openings of the expansion valves. A solid line shows the opening of the main expansion valve, and a broken line shows the opening of the bypass expansion valve. In FIG. 4(c), a vertical axis shows a bypass channel mass flow rate. A solid line shows the bypass channel mass flow rate according to the present exemplary embodiment, and a broken line shows the bypass channel mass flow rate according to conventional control (technique). In FIG. 4(d), a vertical axis shows a degree of superheat at the bypass channel outlet. A solid line shows the degree of superheat at the bypass channel outlet according to the present exemplary embodiment, and a broken line shows the degree of superheat at the bypass channel outlet according to the conventional control (technique). In FIG. 4(e), a vertical axis shows the discharge temperature of the compressor. A solid line shows the discharge temperature of the compressor according to the present exemplary embodiment, and a broken line shows the discharge temperature of the compressor according to the conventional control (technique). Also, a dashed-dotted line shows a target temperature, and a dashed-two dotted line shows an upper limit temperature according to a compressor specification. In FIG. 4(f), a vertical axis shows the degree of subcooling of refrigerant at an outlet of a condenser. A solid line shows the degree of subcooling of refrigerant at the outlet of the condenser according to the present exemplary embodiment, and a broken line shows a temperature difference of hot water between an outlet and an inlet of the radiator.

[0060] First, control device 4 detects suction pressure Ps, condensing pressure Pc, bypass outlet temperature Tbo, discharge temperature Td, radiator outlet temperature Tco, inflow water temperature Twi, and outflow water temperature Two by first pressure sensor 51, second pressure sensor 52, first temperature sensor 61, second temperature sensor 62, third temperature sensor 63, fourth temperature sensor 64, and fifth temperature sensor 65, respectively (step S1).

[0061] Next, control device 4 calculates suction saturation temperature Ts at the pressure of refrigerant to be sucked into compressor 21, based on suction pressure Ps detected by first pressure sensor 51 (step S2). Calculation of suction saturation temperature Ts is performed by using a refrigerant property formula.

[0062] Then, control device 4 compares bypass channel outlet temperature Tbo and suction saturation temperature Ts against each other, and determines whether Tbo is higher than Ts by predetermined temperature Tm set in advance or more (step S3).

[0063] In the case where bypass channel outlet temperature Tbo is not higher than suction saturation temperature Ts by predetermined temperature Tm or more (NO in step S3), control device 4 determines that the flow rate of refrigerant in bypass channel 3 is appropriate, and shifts to normal control.

[0064] On the other hand, in the case where bypass channel outlet temperature Tbo is higher than suction saturation temperature Ts by predetermined temperature Tm or more (YES in step S3), control device 4 determines that the flow rate of refrigerant in bypass channel 3 is not enough, and then, calculates amount of change Atd in the discharge temperature based on discharge temperature Td detected by second temperature sensor 62 (step S4).

[0065] Amount of change Atd in the discharge temperature is determined based on a difference between currently detected discharge temperature Td(n) and discharge temperature Td(n-1) which was detected a specific time earlier.

[0066] Next, control device 4 determines whether amount of change Atd in the discharge temperature which has been calculated is greater than predetermined amount of change Am set in advance or more (step S5).

[0067] In the case where amount of change Atd in the discharge temperature is less than predetermined amount of change Am (NO in step S5), control device 4 determines that the speed of increase in the discharge temperature is slow and that the temperature will not be increased abnormally, and shifts to normal control.

[0068] On the other hand, in the case where amount of change Atd in the discharge temperature is equal to or greater than predetermined amount of change Am (YES in step S5), control device 4 determines that the speed of increase in the discharge temperature is fast and that the discharge temperature may possibly reach an upper limit value, and proceeds to step S6.

[0069] In step S6, water temperature difference Dw is calculated based on the difference between outflow water temperature Two and inflow water temperature Twi.

[0070] Then, condensed saturation temperature Tc of refrigerant at the outlet of radiator 22 is calculated based on condensing pressure Pc detected by second pressure sensor 52, and degree of subcooling Sc is calculated based on a difference between condensed saturation temperature Tc and radiator outlet temperature Tco (step S7).

[0071] Then, control device 4 compares degree of subcooling Sc and water temperature difference Dw against each other, and determines whether Sc is greater than Dw by predetermined temperature difference Dm or more (step S8).

[0072] In the case where degree of subcooling Sc is greater than water temperature difference Dw by predetermined temperature difference Dm or more (YES in step S8), control device 4 determines that the state of refrigerant at the outlet of radiator 22 is a liquid state and that liquid refrigerant is not retained on the low-pressure side, and shifts to normal control.

[0073] On the other hand, in the case where degree of subcooling Sc is not greater than water temperature difference Dw by predetermined temperature difference Dm or more (NO in step S8), control device 4 determines that subcooling of refrigerant at the outlet of radiator 22 is not enough and that refrigerant is retained on the low-pressure side, and proceeds to step S9.

[0074] In step S9, operation opening Otm of main expansion valve 24 and operation opening Otb of bypass expansion valve 31 are calculated based on calculated amount of change Atd in the discharge temperature. A calculation method of each of operation openings Otm and Otb may be set as a function of amount of change Atd in the discharge temperature in the manner of Otm = fm(Atd) or Otb = fb(Atd), for example.

[0075] Then, control device 4 operates main expansion valve 24 in the closing direction by opening Otm, and operates bypass expansion valve 31 in the closing direction by opening Otb.

[0076] That is, in the present exemplary embodiment, as shown in FIG. 4(b), control device 4 performs control of reducing the openings of main expansion valve 24 and bypass expansion valve 31 by predetermined openings, when the degree of superheating of refrigerant at the outlet of bypass channel 3 is great and a temperature increase value, within a predetermined period of time, of a temperature of refrigerant discharged from compressor 21 becomes equal to or greater than a predetermined value. Furthermore, the predetermined openings are set to be greater as the temperature increase value within a predetermined period of time becomes greater.

[0077] In this state, control device 4 reduces the openings of main expansion valve 24 and bypass expansion valve 31, and thus, evaporation of refrigerant at evaporator 25 is accelerated, and refrigerant retained, in a low dryness state, at low-pressure parts such as sub-accumulator 26 and main accumulator 27 is moved to the high-pressure side.

[0078] Accordingly, refrigerant at the outlet of radiator 22 is liquefied, the refrigerant mass flow rate to bypass channel 3 side is swiftly increased, and refrigerant at the outlet of bypass channel 3 is controlled to be in a saturation state. Therefore, as shown in FIG. 4(e), an abnormal increase in the discharge temperature of compressor 21 is suppressed.

[0079] As described above, even when the ambient temperature is extremely low at -20°C, for example, an increased enthalpy difference effect at evaporator 25 due to heat exchange, at subcooling heat exchanger 23, between mainstream refrigerant and bypass refrigerant due to bypassing, and a pressure drop reduction effect at a refrigerant route on the low-pressure side due to bypassing of refrigerant may be utilized, and thus, a higher operation efficiency and sufficient heating capacity may be achieved.

[0080] Moreover, because the discharge temperature may be prevented from being excessively increased, the controllability of the refrigeration cycle and the reliability of compressor 21 may be further increased.

[0081] Furthermore, as shown in FIG. 4(b), control device 4 performs control to end the operation of reducing the opening of each of main expansion valve 24 and bypass expansion valve 31 by a predetermined opening, when the degree of subcooling of refrigerant at the outlet of radiator 22 becomes greater, by a predetermined value or more, than the temperature difference between water flowing out of radiator 22 and water flowing into radiator 22.

[0082] Accordingly, in the case where the degree of subcooling of refrigerant at the outlet of radiator 22 exceeds an appropriate value, the operation of closing main expansion valve 24 and bypass expansion valve 31 is ended, and thus, an abnormal increase in the high pressure or an abnormal reduction in the low pressure due to excessive throttling of the expansion section may be suppressed.

[0083] Therefore, because operation in an inefficient refrigeration cycle due to excessive throttling of the main expansion section and the bypass expansion section may be prevented, the energy efficiency may be further increased.

[0084] That is, by normally operating refrigeration cycle device 1A according to the flowchart of the present exemplary embodiment shown in FIG. 3, refrigerant at the outlet of radiator 22 is liquefied in a short time and the refrigerant mass flow rate to bypass channel 3 side is swiftly increased, and thus, the state of refrigerant at the outlet of bypass channel 3 is controlled to be in the saturation state in a short time as shown by dot a" in FIG. 4(d). Accordingly, as shown in FIG. 4(e), an abnormal increase in the discharge temperature of compressor 21 may be suppressed.

[0085] Furthermore, an appropriate value of the degree of subcooling of refrigerant at the outlet of radiator 22 is determined based on the temperature difference between water flowing out of radiator 22 and water flowing into radiator 22, and the closing operation is ended before the amount of pressure reduction at the expansion value becomes excessively great, and thus, an abnormal increase in discharge pressure or an abnormal reduction in the suction pressure may be suppressed.

[0086] Additionally, in FIG. 1, first pressure sensor 51 is provided between a position of refrigerant circuit 2 joined to bypass channel 3 and main accumulator 27, but this is not restrictive. First pressure sensor 51 may be provided at any position of refrigerant circuit 2 as long as the position is between evaporator 25 and compressor 21. Alternatively, first pressure sensor 51 may be provided to bypass channel 3, on a downstream side of subcooling heat exchanger 23.

[0087] Furthermore, in the present exemplary embodiment, the suction saturation temperature is calculated by first pressure sensor 51, but this is not restrictive. Temperatures of parts of refrigerant circuit 2 and bypass channel 3 where low-pressure two-phase refrigerant passes through may be detected to be used instead of the suction saturation temperature.

[0088] Furthermore, bypass channel 3 does not necessarily have to be branched from refrigerant circuit 2 between subcooling heat exchanger 23 and main expansion valve 24, and may alternatively be branched from refrigerant circuit 2 between radiator 22 and subcooling heat exchanger 23.

[0089] Furthermore, a part for connecting bypass channel 3 does not necessarily have to be a suction pipe of compressor 21, and in the case of a compressor provided with an injection mechanism, bypass channel 3 may be connected to an injection port, for example.

[0090] Moreover, in FIG. 1, second pressure sensor 52 is provided to refrigerant circuit 2 between radiator 22 and subcooling heat exchanger 23, but this is not restrictive. Second pressure sensor 52 may be provided at any position of refrigerant circuit 2 as long as the position is between a discharge pipe of the compressor and the main expansion valve. In the case where a pressure drop in a pipe is great, a value compensated to the degree of pressure drop may be used as a detection value.

[0091] Moreover, the main expansion section and the bypass expansion section of the present disclosure do not necessarily have to be expansion valves, and may be expanders for recovering power from expanding refrigerant. In this case, the rotational speed of such an expander may be controlled by changing a load by an electrical generator connected to the expander, for example.

[0092] The present disclosure is particularly advantageous for a hot water heating device which generates hot water by a refrigeration cycle device, and which uses the hot water for heating.

Claims

1. A refrigeration cycle device comprising:

a refrigerant circuit where a compressor, a radiator, a subcooling heat exchanger, a main expansion section, and an evaporator are connected in a circular manner;

a bypass channel that is branched from the refrigerant circuit between the radiator and the main expansion section, and that is connected, via the subcooling heat exchanger, to a compression chamber of the compressor or the refrigerant circuit between the evaporator and the compressor;

a bypass expansion section that is provided to the bypass channel, on an upstream side of the subcooling heat exchanger;

a first temperature sensor that is provided to the bypass channel, and that is for detecting a temperature of refrigerant flowing out of the subcooling heat exchanger;

a first saturation temperature detection unit for detecting a saturation temperature of refrigerant to be sucked into the compressor;

a second temperature sensor for detecting a temperature of refrigerant discharged from the compressor; and

a control device,

wherein the control device reduces an opening of each of the main expansion section and the bypass expansion section when the temperature detected by the first temperature sensor becomes higher than the saturation temperature detected by the first saturation temperature detection unit and a temperature increase value of the temperature detected by the second temperature sensor within a predetermined period of time becomes equal to or greater than a predetermined value.

2. The refrigeration cycle device according to claim 1, wherein amounts of reduction of the openings of the main expansion section and the bypass expansion section are greater when the temperature increase value is great than when the temperature increase value is small.

3. The refrigeration cycle device according to claim 1 or 2, further comprising:

a third temperature sensor for detecting a temperature of refrigerant flowing out of the radiator;

a second saturation temperature detection unit for detecting a saturation temperature of refrigerant flowing through the radiator;

a fourth temperature sensor for detecting a temperature of a use-side heat medium flowing into the radiator; and

a fifth temperature sensor for detecting a temperature of the use-side heat medium flowing out of the radiator,

wherein the control device ends an operation of reducing the opening of each of the main expansion section and the bypass expansion section, when a degree of subcooling that is a temperature difference between the temperature detected by the third temperature sensor and the saturation temperature detected by the second saturation temperature detection unit becomes greater by a predetermined temperature than a temperature difference between the temperature detected by the fourth temperature sensor and the temperature detected by the fifth temperature sensor.

4. A hot water heating device comprising the refrigeration cycle device according to any one of claims 1 to 3.

Drawing