REFRIGERATION CYCLE APPARATUS

Abstract

 A refrigeration cycle apparatus includes a refrigerant circuit through which refrigerant is circulated, an economizer circuit branching off from the refrigerant circuit between an intercooler and a main expansion valve or between the intercooler and a condenser and connecting to a compressor via the intercooler, an economizer expansion valve disposed in the economizer circuit, an intermediate pressure sensor configured to detect an intermediate pressure of the refrigerant to be injected into the compressor, a temperature sensor configured to detect a temperature of the refrigerant to be injected into the compressor, a calculating unit configured to calculate an economizer superheat degree that is a difference between a saturated gas temperature corresponding to the detected intermediate pressure and a detection value of the temperature sensor and obtain, on the basis of an operating state of the refrigerant circuit, a target value of the economizer superheat degree, and a flow rate control unit configured to adjust an opening degree of the economizer expansion valve such that the economizer superheat degree matches the target value.

Description

Technical Field

[0001] The present disclosure relates to a refrigeration cycle apparatus including a refrigerant circuit through which refrigerant is circulated.

Background Art

[0002] Some refrigeration cycle apparatus has been known that includes an intermediate heat exchanger in a refrigeration cycle to improve a refrigeration capacity and a coefficient of performance (COP = refrigeration capacity/compressor power consumption) (refer to Patent Literature 1, for example).

[0003] Patent Literature 1 discloses a refrigeration apparatus including an economizer circuit through which part of refrigerant flowing out from a condenser is injected into a compressor via an intermediate heat exchanger and an economizer expansion valve disposed in the economizer circuit. This refrigeration apparatus includes, as an economizer expansion valve, a thermostatic expansion valve and adjusts the opening degree of the economizer expansion valve to keep the degree of superheat of the intermediate heat exchanger constant.

Citation List

Patent Literature

[0004] Patent Literature 1: Japanese Patent No. 5463192

Summary of Invention

Technical Problem

[0005] The refrigeration apparatus disclosed in Patent Literature 1 adjusts the opening degree of the economizer expansion valve such that the degree of superheat of the intermediate heat exchanger is kept constant. In the refrigeration apparatus, its annual efficiency, which is an annual COP evaluation index, cannot be expected to improve.

[0006] The present disclosure has been made to solve the above-described problem and aims to provide a refrigeration cycle apparatus that improves annual efficiency. Solution to Problem

[0007] A refrigeration cycle apparatus according to an embodiment of the present disclosure includes a refrigerant circuit in which a compressor, a condenser, an intercooler, a main expansion valve, and an evaporator are connected by a refrigerant pipe and through which refrigerant is circulated; an economizer circuit branching off from the refrigerant circuit between the intercooler and the main expansion valve or between the condenser and the intercooler and connecting to the compressor via the intercooler; an economizer expansion valve disposed in the economizer circuit; an intermediate pressure sensor disposed in the economizer circuit and configured to detect an intermediate pressure of the refrigerant to be injected into the compressor; a temperature sensor disposed in the economizer circuit and configured to detect a temperature of the refrigerant to be injected into the compressor; a calculating unit configured to calculate an economizer superheat degree that is a difference between a saturated gas temperature corresponding to the intermediate pressure detected by the intermediate pressure sensor and a detection value of the temperature sensor and obtain, on the basis of an operating state of the refrigerant circuit, a target value of the economizer superheat degree; and a flow rate control unit configured to adjust an opening degree of the economizer expansion valve such that the economizer superheat degree matches the target value obtained by the calculating unit.

[0008] A refrigeration cycle apparatus according to another embodiment of the present disclosure includes a refrigerant circuit in which a compressor, a condenser, an intercooler, a main expansion valve, and an evaporator are connected by a refrigerant pipe and through which refrigerant is circulated; an economizer circuit branching off from the refrigerant circuit between the intercooler and the main expansion valve or between the condenser and the intercooler and connecting to the compressor via the intercooler; an economizer expansion valve disposed in the economizer circuit; an intermediate pressure sensor disposed in the economizer circuit and configured to detect an intermediate pressure of the refrigerant to be injected into the compressor; an intercooler high-pressure side outlet temperature sensor disposed between the intercooler and the main expansion valve in the refrigerant circuit and configured to detect a temperature of the refrigerant; a calculating unit configured to calculate a main refrigerant liquid approach temperature that is a difference between a saturated gas temperature corresponding to the intermediate pressure detected by the intermediate pressure sensor and a detection value of the intercooler high-pressure side outlet temperature sensor and obtain, on the basis of an operating state of the refrigerant circuit, a target value of the main refrigerant liquid approach temperature; and a flow rate control unit configured to adjust an opening degree of the economizer expansion valve such that the main refrigerant liquid approach temperature matches the target value obtained by the calculating unit.

Advantageous Effects of Invention

[0009] According to an embodiment of the present disclosure, the target value of a monitored target is set such that a higher COP is achieved at an actual operating load. The opening degree of the economizer expansion valve is thus adjusted more appropriately than in a case where the target value is set to be constant. Annual efficiency is therefore improved.

Brief Description of Drawings

[0010] 

[Fig. 1] Fig. 1 is a refrigerant circuit diagram illustrating an example of a refrigeration cycle apparatus according to Embodiment 1 of the present disclosure.

[Fig. 2] Fig. 2 is a functional block diagram illustrating an exemplary configuration of a controller in Fig. 1.

[Fig. 3] Fig. 3 is an explanatory graph illustrating an example of how to determine a target value of a monitored target on the basis of an operating state of a refrigerant circuit in economizer flow rate control in Embodiment 1 of the present disclosure.

[Fig. 4] Fig. 4 is a flowchart illustrating an operation procedure of the refrigeration cycle apparatus shown in Fig. 1.

[Fig. 5] Fig. 5 is a refrigerant circuit diagram illustrating another exemplary configuration of the refrigeration cycle apparatus according to Embodiment 1 of the present disclosure.

[Fig. 6] Fig. 6 is a refrigerant circuit diagram illustrating an example of a refrigeration cycle apparatus according to Embodiment 2 of the present disclosure.

[Fig. 7] Fig. 7 is a schematic diagram explaining a main refrigerant liquid approach temperature that is a monitored target in economizer flow rate control in Embodiment 2 of the present disclosure.

[Fig. 8] Fig. 8 is a flowchart illustrating an operation procedure of the refrigeration cycle apparatus shown in Fig. 6.

Description of Embodiments

Embodiment 1

[0011] The configuration of a refrigeration cycle apparatus according to Embodiment 1 will be described. Fig. 1 is a refrigerant circuit diagram illustrating an example of the refrigeration cycle apparatus according to Embodiment 1 of the present disclosure. A refrigeration cycle apparatus 1 includes a compressor 2, a condenser 3, an intercooler 4, a main expansion valve 5, an evaporator 6, an economizer circuit 11, and a controller 10. The intercooler 4 includes a high pressure section 4a and a low pressure section 4b. The compressor 2, the condenser 3, the high pressure section 4a of the intercooler 4, the main expansion valve 5, and the evaporator 6 are connected by a refrigerant pipe. A refrigerant circuit 12 through which refrigerant is circulated is thus formed.

[0012]  An evaporating pressure sensor 8a is disposed to a refrigerant outlet of the evaporator 6. The evaporating pressure sensor 8a detects an evaporating pressure of the refrigerant flowing out from the evaporator 6. A condensing pressure sensor 8b is disposed to a refrigerant inlet of the condenser 3. The condensing pressure sensor 8b detects a condensing pressure of the refrigerant flowing into the condenser 3.

[0013] The compressor 2 suctions, compresses, and discharges the refrigerant. The compressor 2 is an inverter-driven compressor whose capacity can be changed by adjusting a rotational frequency. Examples of the compressor 2 include a single-screw compressor and a twin-screw compressor. The compressor 2 may be of any compressor to which the economizer circuit 11 can be connected. The condenser 3 is a heat exchanger that exchanges heat between gas refrigerant discharged from the compressor 2 and, for example, air or water, to cool and condense the gas refrigerant. The evaporator 6 is a heat exchanger that exchanges heat between the refrigerant flowing out from the main expansion valve 5 and, for example, air, water, or brine, to evaporate the refrigerant. The condenser 3 and the evaporator 6 are, for example, fin- and-tube heat exchangers, plate heat exchangers, or shell-and-tube heat exchangers. The main expansion valve 5 reduces the pressure of the refrigerant flowing from the intercooler 4 to expand the refrigerant. The main expansion valve 5 is, for example, an electronic expansion valve.

[0014] The economizer circuit 11 includes an economizer pipe 9 that branches off from the refrigerant circuit between the intercooler 4 and the main expansion valve 5 and connects to the compressor 2 via the low pressure section 4b of the intercooler 4 and an economizer expansion valve 7 disposed in the economizer pipe 9. The economizer expansion valve 7 is disposed between the intercooler 4 and a branch point 15 located between the intercooler 4 and the main expansion valve 5. The economizer expansion valve 7 is, for example, an electronic expansion valve. In the economizer pipe 9, a temperature sensor 13 and an intermediate pressure sensor 8c are arranged between the intercooler 4 and the compressor 2.

[0015] As described above, the intercooler 4 includes the high pressure section 4a and the low pressure section 4b. The refrigerant on a high-pressure side between the condenser 3 and the main expansion valve 5, or high-pressure side refrigerant, flows through the high pressure section 4a. The economizer expansion valve 7 reduces the pressure of part of the high-pressure side refrigerant, and the part of the refrigerant flows through the low pressure section 4b. The refrigerant flowing out from the low pressure section 4b is refrigerant having an intermediate pressure in the entire refrigeration cycle, or intermediate pressure refrigerant. The intercooler 4 exchanges heat between the high-pressure side refrigerant and the intermediate pressure refrigerant to cool the high-pressure side refrigerant. The temperature sensor 13 detects the temperature of the refrigerant to be injected into the compressor 2. The intermediate pressure sensor 8c detects the intermediate pressure of the refrigerant to be injected to the compressor 2.

[0016] The configuration of the controller 10 in Fig. 1 will be described below. Fig. 2 is a functional block diagram illustrating an exemplary configuration of the controller in Fig. 1. As illustrated in Fig. 1, the controller 10 incudes a memory 31 storing a program and a central processing unit (CPU) 32 that executes a process in accordance with the program. As the CPU 32 executes the program, a refrigeration cycle control unit 33, a calculating unit 34, and a flow rate control unit 35 are involved in the refrigeration cycle apparatus 1 as illustrated in Fig. 2.

[0017] The refrigeration cycle control unit 33 adjusts the rotational frequency of the compressor 2 and the opening degree of the main expansion valve 5 on the basis of detection values of the evaporating pressure sensor 8a and the condensing pressure sensor 8b. The calculating unit 34 calculates, as a monitored target in economizer flow rate control, an economizer superheat degree ΔTesh that is the difference between a saturated gas temperature Tesa corresponding to the intermediate pressure and a refrigerant temperature Te detected by the temperature sensor 13. Furthermore, the calculating unit 34 determines a target value of the economizer superheat degree ΔTesh on the basis of an operating state of the refrigerant circuit 12. The economizer superheat degree ΔTesh is calculated by the mathematical formula of ΔTesh = (Te - Tesa).

[0018] Although, in Embodiment 1, a case is described where the calculating unit 34 determines a target value on the basis of, as an operating state of the refrigerant circuit 12, a compression ratio of the compressor 2, the operating state of the refrigerant circuit 12 used as the basis to determine the target value is not limited to the compression ratio. In the case where the target value is determined on the basis of, as an operating state of the refrigerant circuit 12, the compression ratio of the compressor 2, the calculating unit 34 calculates the compression ratio of the compressor 2 from an evaporating pressure detected by the evaporating pressure sensor 8a and a condensing pressure detected by the condensing pressure sensor 8b. The compression ratio is calculated by the mathematical formula of compression ratio = (condensing pressure/evaporating pressure). As the compression ratio is greater, compression work increases, and an operating load increases accordingly. As the compression ratio is less, compression work decreases, and an operating load decreases accordingly. The compression ratio is used as an index representing the operating load. The flow rate control unit 35 adjusts the opening degree of the economizer expansion valve 7 such that the economizer superheat degree ΔTesh, which is a monitored target, matches the target value.

[0019] The target value of the monitored target in economizer flow rate control will described below. A COP at a rated condition has been mainly used as an index of energy conservation in a refrigeration cycle apparatus. The rated condition is an operating condition at 100% operating load. Attention has recently been focused on annual efficiencies as indices close to actual operating conditions. Examples of the annual efficiencies include an integrated part load value (IPLV).

[0020]  The Air-Conditioning and Refrigeration Institute (ARI) defines Expression (1) to calculate an integrated part load value IPLV_us.

[0021] In Expression (1), A is a COP at 100% load, B is a COP at 75% load, C is a COP at 50% load, and D is a COP at 25% load.

[0022] As expressed by Expression (1), the integrated part load value is calculated by summing multiple COPs associated with different operating loads. In Expression (1), the coefficient of each term represents a ratio to annual operating time. For example, when Tz denotes the annual operating time, operating time at 100% operating load is 0.01 × Tz (hour). Each coefficient is a weight for the operating load in the annual operating time. With reference to Expression (1), operating time at 75% load accounts for 42% of the annual operating time and operating time at 50% load accounts for 45% of the annual operating time. In Expression (1), greater weights are assigned to these two operating conditions.

[0023] The Japan Refrigeration and Air Conditioning Industry Association (JRAIA) also defines an integrated part load value, which is an index similar to American integrated part load value IPLV_us. Expression (2) is a mathematical formula representing the integrated part load value defined by JRAIA.

[0024] In Expression (2), A is a COP at 100% load, B is a COP at 75% load, C is a COP at 50% load, and D is a COP at 25% load.

[0025] With reference to Expression (2), the weight varies by operating load in a manner similar to the integrated part load value IPLV_US defined by ARI. In Expression (2), however, some of the same operating loads as those in Expression (1) are assigned weights different from those in Expression (1). For example, in Expression (2), 75% load accounts for 47% of annual operating time and is assigned the greatest weight.

[0026]  A typical refrigeration cycle apparatus is operated at a rated condition in a very short time of a year, and is in a part-load operation in 90% or more of annual operating time. Most part-load operations are at loads of from 75% to 50% of full load. A part-load operation differs from a full-load operation in refrigerant circulation flow rate and operating compression ratio. The COP also changes. The above-described integrated part load value obtained in consideration of such an actual operating situation has attracted attention. In other words, the integrated part load value is an index in which importance is placed on COPs at part load conditions.

[0027] In Embodiment 1, for the economizer superheat degree ΔTesh, which is the monitored target in economizer flow rate control, a target value associated with the greatest integrated part load value calculated using the mathematical formula expressed by Expression (2) can be obtained in advance. With reference to Expression (2), 75% load of the four operating loads accounts for 47% of the annual operating time and is assigned the greatest weight. Attention can be paid to an operating load assigned the greatest weight.

[0028] An operating condition of interest is not limited to the operating load assigned the greatest weight. Attention may be paid to two or more operating loads selected in order from greatest weight to smallest weight. Operating conditions of interest may be all of the four operating loads included in Expression (2). The number of operating conditions of interest may be any number. For example, the calculating unit 34 may calculate, at each of the operating conditions, a compression ratio of the compressor 2 that is obtained when a value associated with a maximum COP is set, and obtain a target value of a monitored target associated with each compression ratio in advance, for example, in a break-in period of the refrigeration cycle apparatus 1. The calculating unit 34 stores information representing the relationship between the compression ratios and the target values of the monitored target in the memory 31.

[0029]  The calculating unit 34 may obtain, with respect to four operating conditions corresponding to the four operating loads included in the mathematical formula of Expression (2), compression ratios of the compressor 2 and target values of the monitored target associated with the respective compression ratios. In this case, the calculating unit 34 can estimate compression ratios at operating conditions other than the four operating conditions and target values associated with these compression ratios on the basis of the relationship between the compression ratios at the four operating conditions and the target values.

[0030] Fig. 3 is an explanatory graph illustrating an example of how to determine a target value of a monitored target on the basis of an operating state of the refrigerant circuit in economizer flow rate control in Embodiment 1 of the present disclosure. Fig. 3 illustrates a case where a compression ratio, which is one of operating states of the refrigerant circuit 12, is used as a reference for target value determination. In the graph shown in Fig. 3, the horizontal axis represents the compression ratio and the vertical axis represents the target value of the monitored target. In Embodiment 1, the vertical axis shown in Fig. 3 represents the target value of the economizer superheat degree ΔTesh.

[0031] Fig. 3 illustrates points representing target values of the economizer superheat degree ΔTesh associated with the compression ratios at four conditions: a condition Cond1 in which a maximum COP at 100% load is achieved; a condition Cond2 in which a maximum COP at 75% load is achieved; a condition Cond3 in which a maximum COP at 50% load is achieved; and a condition Cond4 in which a maximum COP at 25% load is achieved. An approximate curve connecting the four points is represented by a dashed line. From the approximate curve, the calculating unit 34 can estimate target values associated with compression ratios that are not relevant to the four points. The calculating unit 34 can draw an approximate curve, as illustrated in Fig. 3, on the basis of data representing target values of a monitored target associated with at least two conditions.

[0032] The calculating unit 34 may determine target values associated with operating conditions other than the four operating conditions corresponding to the four operating loads included in the mathematical formula of Expression (2) as follows. The calculating unit 34 divides the range of compression ratios into four subranges on the basis of the relationship between the compression ratios obtained at the four operating conditions and the target values such that one of the four compression ratios corresponding to the above-described four operating conditions is included in each subrange. Then, the calculating unit 34 sets values of the four compression ratios corresponding to the above-described four operating conditions to respective target values of the compression ratios in the subranges. In this case, when a target value of a calculated compression ratio is unknown, the calculating unit 34 identifies a subrange including the calculated compression ratio out of subranges into which the range of compression ratios is divided, and determines a target value set in the identified subrange as a target value of a compression ratio. Although the case where target values associated with the four operating conditions are obtained has been described above, the number of operating conditions of interest may be any number.

[0033] The operating state of the refrigerant circuit 12 used as the basis to determine a target value may be a parameter other than the compression ratio. For example, the operating state of the refrigerant circuit 12 may be a pressure difference Pd (condensing pressure - evaporating pressure) between a high pressure and a low pressure in the refrigerant circuit 12 instead of the compression ratio. The calculating unit 34 determines a target value of a monitored target on the basis of the pressure difference Pd. Furthermore, the memory 31 may store target determination information used to identify a target value associated with an optimum integrated part load value IPLV for each of the range of condensing pressures and the range of evaporating pressures, and the calculating unit 34 may determine a target value on the basis of a detected condensing pressure and a detected evaporating pressure with reference to the target determination information. Additionally, the rotational frequency may be used to determine a target value.

[0034] An operation of the refrigeration cycle apparatus 1 according to Embodiment 1 will be described below. Fig. 4 is a flowchart illustrating an operation procedure of the refrigeration cycle apparatus shown in Fig. 1. During operation of the refrigeration cycle apparatus 1, the controller 10 reads detection values of various sensors at predetermined intervals. The calculating unit 34 calculates an economizer superheat degree ΔTesh from a refrigerant temperature Te detected by the temperature sensor 13 and a saturated gas temperature Tesa corresponding to an intermediate pressure detected by the intermediate pressure sensor 8c.

[0035] Then, the calculating unit 34 calculates a compression ratio on the basis of an evaporating pressure detected by the evaporating pressure sensor 8a and a condensing pressure detected by the condensing pressure sensor 8b. The calculating unit 34 determines a target value Tset1 of the economizer superheat degree ΔTesh on the basis of the calculated compression ratio (step S101). For example, the calculating unit 34 determines the target value Tset1 with reference to the graph shown in Fig. 3. The graph shown in Fig. 3 is stored in the memory 31.

[0036] The flow rate control unit 35 compares the calculated economizer superheat degree ΔTesh with the target value Tset1 (step S102). When the economizer superheat degree ΔTesh is less than the target value Tset1 as a result of comparison in step S102, the flow rate control unit 35 reduces the opening degree of the economizer expansion valve 7 (step S103). A reduction in the opening degree of the economizer expansion valve 7 leads to a reduction in intermediate pressure and a reduction in flow rate of the refrigerant flowing through the economizer circuit 11. As a result, a temperature of gas refrigerant to be injected rises, so that the economizer superheat degree ΔTesh rises and approaches the target value Tset1.

[0037]  When the economizer superheat degree ΔTesh is greater than the target value Tset1 as a result of comparison in step S102, the flow rate control unit 35 increases the opening degree of the economizer expansion valve 7 to reduce the economizer superheat degree ΔTesh (step S104). An increase in the opening degree of the economizer expansion valve 7 leads to an increase in intermediate pressure and an increase in flow rate of the refrigerant flowing through the economizer circuit 11. As a result, a temperature of gas refrigerant to be injected decreases, so that the economizer superheat degree ΔTesh decreases and approaches the target value Tset1.

[0038] When the economizer superheat degree ΔTesh is substantially equal to the target value Tset1 as a result of comparison in step S102, the flow rate control unit 35 keeps the opening degree of the economizer expansion valve 7 (step S105). As described above, the amount and temperature of the refrigerant to be injected into the compressor 2 are automatically adjusted to optimum values, at which a higher COP is achieved, in response to an operating load.

[0039] In the refrigeration cycle apparatus 1 according to Embodiment 1, the connection configuration of the economizer circuit 11 is not limited to that illustrated in Fig. 1. Fig. 5 is a refrigerant circuit diagram illustrating another exemplary configuration of the refrigeration cycle apparatus according to Embodiment 1 of the present disclosure. Fig. 5 illustrates a refrigeration cycle apparatus 1a in which the economizer circuit 11 branches off from the refrigerant circuit between the intercooler 4 and the condenser 3 and connects to the compressor 2 via the economizer expansion valve 7 and the low pressure section 4b of the intercooler 4. The economizer expansion valve 7 is disposed between the intercooler 4 and a branch point 15a located between the intercooler 4 and the condenser 3.

[0040] The refrigeration cycle apparatus 1 according to Embodiment 1 calculates the economizer superheat degree ΔTesh as a monitored target. The refrigeration cycle apparatus 1 determines a target value of the economizer superheat degree ΔTesh on the basis of an operating state of the refrigerant circuit 12 and adjusts the opening degree of the economizer expansion valve 7 such that the economizer superheat degree ΔTesh matches the target value.

[0041] In Embodiment 1, the target value of the economizer superheat degree, which is the monitored target, is set such that a higher COP is achieved at an actual operating load. The opening degree of the economizer expansion valve is thus adjusted more appropriately than in a case where the target value is set to be constant. Annual efficiency is therefore improved.

[0042] In Embodiment 1, the calculating unit 34 sets the target value at which a maximum COP is achieved at an operating load corresponding to, for example, a frequency or a compression ratio. The refrigeration cycle apparatus 1 can improve the integrated part load value by exercising economizer flow rate control in response to an actual operating load such that a higher COP is achieved.

[0043] In this case, the calculating unit 34 may estimate a target value associated with a compression ratio on the basis of the different operating loads, included in the mathematical formula used to calculate the integrated part load value, to determine the target value. In this case, the calculating unit 34 can also determine optimum estimated target values of a monitored target associated with operating conditions other than the different operating loads included in the mathematical formula.

[0044] Furthermore, the calculating unit 34 may divide the range of compression ratios into subranges on the basis of compression ratios at the different operating loads included in the mathematical formula used to calculate the integrated part load value and determine a target value for each subrange.

[0045] Furthermore, when the calculating unit 34 determines a target value, the calculating unit 34 may use an operating load assigned the greatest weight or may use two or more operating loads selected from the different operating loads in order from greatest weight to smallest weight. In this case, as the number of operating loads used as the basis to determine target values of compression ratios is small, the calculating unit 34 can determine target values of a monitored target more quickly.

Embodiment 2

[0046] In Embodiment 1 described above, the economizer superheat degree is used for economizer flow rate control. Embodiment 2 illustrates a case where a temperature of the refrigerant at a high-pressure side refrigerant outlet of the intercooler is used for economizer flow rate control. In Embodiment 2, the same components as those of the refrigeration cycle apparatus according to Embodiment 1 are designated by the same reference signs and a detailed description of these components is omitted.

[0047] In the refrigerant circuit shown in Fig. 1, part of the refrigerant flowing through the refrigerant circuit 12 is diverted to the economizer circuit 11 and flows through the low pressure section 4b of the intercooler 4. The refrigerant flowing through the low pressure section 4b of the intercooler 4 cools the refrigerant flowing through the high pressure section 4a of the intercooler 4. Thus, the refrigerant flowing through the economizer circuit 11 reduces the temperature of the refrigerant flowing through the high pressure section 4a of the intercooler 4. In Embodiment 1, the temperature and pressure of the refrigerant flowing through the economizer circuit 11 are detected and used to adjust the opening degree of the economizer expansion valve 7. In contrast, in Embodiment 2, a change in temperature of the refrigerant at the high-pressure side refrigerant outlet of the intercooler 4 is detected and used to adjust the opening degree of the economizer expansion valve 7.

[0048] The configuration of a refrigeration cycle apparatus according to Embodiment 2 will be described below. Fig. 6 is a refrigerant circuit diagram illustrating an example of the refrigeration cycle apparatus according to Embodiment 2 of the present disclosure. A refrigeration cycle apparatus 1b according to Embodiment 2 includes an intercooler high-pressure side outlet temperature sensor 14 disposed at a high-pressure side refrigerant outlet of the intercooler 4. The refrigeration cycle apparatus 1b shown in Fig. 6 includes no temperature sensor 13, which is illustrated in Fig. 1. In an exemplary configuration illustrated in Fig. 6, the intercooler high-pressure side outlet temperature sensor 14 is disposed between the branch point 15 and the main expansion valve 5. The intercooler high-pressure side outlet temperature sensor 14 detects the temperature of liquid refrigerant flowing through the refrigerant circuit 12 and flowing out from the intercooler 4.

[0049] In Embodiment 2, the calculating unit 34 calculates a main refrigerant liquid approach temperature ΔTsca, which is the difference between a refrigerant temperature Tm detected by the intercooler high-pressure side outlet temperature sensor 14 and a saturated gas temperature Tesa corresponding to an intermediate pressure. The main refrigerant liquid approach temperature ΔTsca is calculated by the mathematical formula of ΔTsca = (Tm - Tesa). In Embodiment 2, the main refrigerant liquid approach temperature ΔTsca is a monitored target used in economizer flow rate control.

[0050] Fig. 7 is a schematic diagram explaining the main refrigerant liquid approach temperature, which is a monitored target in economizer flow rate control in Embodiment 2 of the present disclosure. Fig. 7 is a p-h diagram in which the vertical axis represents the pressure and the horizontal axis represents the specific enthalpy. Fig. 7 schematically illustrates the main refrigerant liquid approach temperature ΔTsca.

[0051] An operation of the refrigeration cycle apparatus 1b according to Embodiment 2 will be described below. Fig. 8 is a flowchart illustrating an operation procedure of the refrigeration cycle apparatus shown in Fig. 6. In Embodiment 2, the memory 31 stores a graph used to determine a target value of the main refrigerant liquid approach temperature ΔTsca, which is the monitored target. The graph is, for example, the graph shown in Fig. 3.

[0052]  During operation of the refrigeration cycle apparatus 1b, the controller 10 reads detection values of the various sensors at predetermined intervals. The calculating unit 34 calculates a main refrigerant liquid approach temperature ΔTsca from a refrigerant temperature Tm detected by the intercooler high-pressure side outlet temperature sensor 14 and a saturated gas temperature Tesa corresponding to an intermediate pressure detected by the intermediate pressure sensor 8c. The calculating unit 34 calculates a compression ratio by using detection values of the evaporating pressure sensor 8a and the condensing pressure sensor 8b. The calculating unit 34 determines, on the basis of the calculated compression ratio, a target value Tset2 of the main refrigerant liquid approach temperature ΔTsca (step S201). The calculating unit 34 determines the target value Tset2 with reference to the graph shown in Fig. 3.

[0053] The flow rate control unit 35 compares the calculated main refrigerant liquid approach temperature ΔTsca with the target value Tset2 (step S202). When the main refrigerant liquid approach temperature ΔTsca is less than the target value Tset2 as a result of comparison in step S202, the flow rate control unit 35 reduces the opening degree of the economizer expansion valve 7 (step S203). A reduction in the opening degree of the economizer expansion valve 7 leads to a reduction in intermediate pressure and a reduction in flow rate of the refrigerant flowing through the economizer circuit 11. As a result, an amount of heat exchanged between the high-pressure side refrigerant and the low-pressure side refrigerant in the intercooler decreases, so that the refrigerant temperature Tm rises. Thus, the main refrigerant liquid approach temperature ΔTsca increases and approaches the target value Tset2.

[0054] When the main refrigerant liquid approach temperature ΔTsca is greater than the target value Tset2 as a result of comparison in step S202, the flow rate control unit 35 increases the opening degree of the economizer expansion valve 7 to reduce the main refrigerant liquid approach temperature ΔTsca (step S204). An increase in the opening degree of the economizer expansion valve 7 leads to an increase in intermediate pressure and an increase in flow rate of the refrigerant flowing through the economizer circuit 11. As a result, an amount of heat exchanged between the high-pressure side refrigerant and the low-pressure side refrigerant in the intercooler increases, so that the refrigerant temperature Tm decreases. Thus, the main refrigerant liquid approach temperature ΔTsca decreases and approaches the target value Tset2.

[0055] When the main refrigerant liquid approach temperature ΔTsca is substantially equal to the target value Tset2 as a result of comparison in step S202, the flow rate control unit 35 keeps the opening degree of the economizer expansion valve 7 (step S205). As described above, the amount and temperature of the refrigerant to be injected into the compressor 2 are automatically adjusted to optimum values, at which a higher COP is achieved, in response to an operating load.

[0056] In Embodiment 2, the target value of the main refrigerant liquid approach temperature ΔTsca is not limited to those in the graph shown in Fig. 3. The target value of the main refrigerant liquid approach temperature ΔTsca may be obtained from the relationship between the COPs at the four operating loads included in the mathematical formula of Expression (2) and the compression ratios of the compressor 2. Furthermore, a COP used as the basis to determine the target value may be a COP associated with an operating load assigned the greatest weight of the four operating loads included in the mathematical formula of Expression (2) or may be estimated from two or more COPs selected in order from greatest weight to smallest weight.

[0057] In the refrigeration cycle apparatus 1b according to Embodiment 2, the main refrigerant liquid approach temperature ΔTsca is calculated, a target value of the main refrigerant liquid approach temperature ΔTsca is determined on the basis of a compression ratio, and the opening degree of the economizer expansion valve 7 is adjusted such that the main refrigerant liquid approach temperature ΔTsca matches the target value.

[0058]  In Embodiment 2, the target value of the main refrigerant liquid approach temperature is set such that a higher COP is achieved at an actual operating load. The opening degree of the economizer expansion valve is thus adjusted more appropriately than in the case where the target value is set to be constant. Annual efficiency is therefore improved.

[0059] Although the economizer circuit 11 in Embodiment 2 described above has the same connection configuration as in Fig. 1, the economizer circuit 11 may have the same connection configuration as in Fig. 5. Furthermore, the forms of the components described in Embodiments 1 and 2 are intended to be illustrative only and are not intended to be limited to those described in these embodiments and illustrated in the drawings. Additionally, pressure levels are not determined in relation to a particular absolute value but are relatively determined depending on, for example, a state and an operation of the refrigeration cycle apparatus.

Reference Signs List

[0060] 1, 1a, 1b refrigeration cycle apparatus 2 compressor 3 condenser 4 intercooler 4a high pressure section 4b low pressure section 5 main expansion valve 6 evaporator 7 economizer expansion valve 8a evaporating pressure sensor 8b condensing pressure sensor 8c intermediate pressure sensor 9 economizer pipe 10 controller 11 economizer circuit 12 refrigerant circuit 13 temperature sensor 14 intercooler high-pressure side outlet temperature sensor 15, 15a branch point 31 memory 32 CPU 33 refrigeration cycle control unit 34 calculating unit 35 flow rate control unit

Claims

1. A refrigeration cycle apparatus comprising:

a refrigerant circuit in which a compressor, a condenser, an intercooler, a main expansion valve, and an evaporator are connected by a refrigerant pipe and through which refrigerant is circulated;

an economizer circuit branching off from the refrigerant circuit between the intercooler and the main expansion valve or between the condenser and the intercooler and connecting to the compressor via the intercooler;

an economizer expansion valve disposed in the economizer circuit;

an intermediate pressure sensor disposed in the economizer circuit and configured to detect an intermediate pressure of the refrigerant to be injected into the compressor;

a temperature sensor disposed in the economizer circuit and configured to detect a temperature of the refrigerant to be injected into the compressor;

a calculating unit configured to calculate an economizer superheat degree that is a difference between a saturated gas temperature corresponding to the intermediate pressure detected by the intermediate pressure sensor and a detection value of the temperature sensor and obtain, from an operating state of the refrigerant circuit, a target value of the economizer superheat degree; and

a flow rate control unit configured to adjust an opening degree of the economizer expansion valve such that the economizer superheat degree matches the target value obtained by the calculating unit.

2. A refrigeration cycle apparatus comprising:

a refrigerant circuit in which a compressor, a condenser, an intercooler, a main expansion valve, and an evaporator are connected by a refrigerant pipe and through which refrigerant is circulated;

an economizer circuit branching off from the refrigerant circuit between the intercooler and the main expansion valve or between the condenser and the intercooler and connecting to the compressor via the intercooler;

an economizer expansion valve disposed in the economizer circuit;

an intermediate pressure sensor disposed in the economizer circuit and configured to detect an intermediate pressure of the refrigerant to be injected into the compressor;

an intercooler high-pressure side outlet temperature sensor disposed between the intercooler and the main expansion valve in the refrigerant circuit and configured to detect a temperature of the refrigerant;

a calculating unit configured to calculate a main refrigerant liquid approach temperature that is a difference between a saturated gas temperature corresponding to the intermediate pressure detected by the intermediate pressure sensor and a detection value of the intercooler high-pressure side outlet temperature sensor and obtain, from an operating state of the refrigerant circuit, a target value of the main refrigerant liquid approach temperature; and

a flow rate control unit configured to adjust an opening degree of the economizer expansion valve such that the main refrigerant liquid approach temperature matches the target value obtained by the calculating unit.

3. The refrigeration cycle apparatus of claim 1 or 2, wherein the calculating unit is configured to set, to the target value, a value at which a maximum coefficient of performance is achieved at an operating load corresponding to the operating state of the refrigerant circuit.

4. The refrigeration cycle apparatus of claim 3, wherein the calculating unit is configured to estimate the target value associated with the operating state of the refrigerant circuit from different operating loads in a mathematical formula representing an integrated part load value calculated from coefficients of performance associated with the different operating loads.

5. The refrigeration cycle apparatus of claim 3, wherein the calculating unit is configured to divide, into subranges, a range of the operating states of the refrigerant circuit associated with different operating loads in a mathematical formula representing an integrated part load value calculated from coefficients of performance associated with the different operating loads, and determine the target value for each of the subranges.

6. The refrigeration cycle apparatus of claim 3, wherein, in a mathematical formula representing an integrated part load value calculated from coefficients of performance associated with the different operating loads, the calculating unit is configured to select an operating load assigned a greatest weight from different operating loads to estimate the target value, or select two or more operating loads from the different operating loads in order from greatest weight to smallest weight to estimate the target value.

7. The refrigeration cycle apparatus of any one of claims 1 to 6, further comprising:

an evaporating pressure sensor disposed to a refrigerant outlet of the evaporator and configured to detect an evaporating pressure of the refrigerant; and

a condensing pressure sensor disposed to a refrigerant inlet of the condenser and configured to detect a condensing pressure of the refrigerant,

wherein the calculating unit is configured to calculate the operating state of the refrigerant circuit with the evaporating pressure detected by the evaporating pressure sensor and the condensing pressure detected by the condensing pressure sensor.

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