Refrigeration cycle apparatus

Abstract

The purpose of the present disclosure is to suppress liquid slugging in a refrigeration cycle apparatus provided with an oil separator. A refrigeration cycle apparatus (100) according to one aspect of the present disclosure is provided with a refrigerant circuit, a first oil return pipe (104a), a first solenoid valve (104), a second oil return pipe (105a), a second solenoid valve (105), a pressure detection unit, and a control device (300). The first oil return pipe (104a) forms a connection from an oil separator (102) to a suction pipe of a compressor (101). The second oil return pipe (105a) forms a connection from the oil separator (102) to an inlet pipe of an accumulator (117). The pressure detection unit is provided to each of a first pipe (108) and a second pipe (112), and detects the pressure in each thereof. The control device (300) performs liquid-slugging control by controlling an expansion valve, the first solenoid valve (104), and the second solenoid valve (105) on the basis of pressure data detected by the pressure detection unit, the frequency of the compressor (101), and installation conditions.

Description

Refrigeration cycle equipment

[0001] The present disclosure relates to a refrigeration cycle device that performs liquid return control.

[0002] The refrigeration cycle device disclosed in JP 2008-096019 A (Patent Document 1) is equipped with an oil recovery operation section that operates each indoor unit in a liquid backflow-like mode at a predetermined timing to perform an oil recovery operation to recover lubricating oil remaining in the refrigerant circuit, and terminates the oil recovery operation when liquid backflow is detected on the outdoor unit side. The refrigeration cycle device changes the liquid backflow-like operation time depending on the piping length in order to recover the accumulated lubricating oil.

[0003] Japanese Patent Application Laid-Open No. 2008-096019

[0004] However, when the oil separator's oil return pipe is connected to the compressor's intake pipe, if the refrigeration cycle device disclosed in JP 2008-096019 A (Patent Document 1) is operated with a tendency to return liquid to recover lubricating oil, the liquid refrigerant accumulated in the oil separator will return directly to the compressor, increasing the amount of liquid returned and potentially causing serious damage to the compressor.

[0005] The present disclosure has been made to solve the above-mentioned problems, and an object of the present disclosure is to suppress liquid backflow in a refrigeration cycle device equipped with an oil separator.

[0006] A refrigeration cycle apparatus according to one aspect of the present disclosure includes a refrigerant circuit, a first oil return pipe, a first solenoid valve, a second oil return pipe, a second solenoid valve, a pressure detection unit, and a control device. In the refrigerant circuit, refrigerant circulates through a compressor, an oil separator, a four-way valve, a first pipe, an indoor heat exchanger, a second pipe, a stop valve, an expansion valve, an outdoor heat exchanger, and an accumulator. The first oil return pipe is connected from the oil separator to an intake pipe of the compressor. The first solenoid valve is provided in the first oil return pipe. The second oil return pipe is connected from the oil separator to an inlet pipe of the accumulator. The second solenoid valve is provided in the second oil return pipe. Pressure detection units are provided in each of the first pipe and the second pipe and detect the pressure of each. The control device controls the expansion valve, the first solenoid valve, and the second solenoid valve to perform liquid return control based on pressure data detected by the pressure detection unit, the compressor frequency, and installation conditions.

[0007] According to the refrigeration cycle device of the present disclosure, liquid backflow control is performed by controlling the expansion valve, the first solenoid valve, and the second solenoid valve based on the pressure data detected by the pressure detection unit, the compressor frequency, and the installation conditions, so that liquid backflow can be suppressed in a refrigeration cycle device equipped with an oil separator.

[0008] FIG. 1 is a refrigerant circuit diagram of a refrigeration cycle device according to embodiment 1. FIG. 2 is a functional block diagram for explaining the configuration of a control device of the refrigeration cycle device according to embodiment 1. FIG. 3 is a flowchart for explaining control at start-up of the refrigeration cycle device according to embodiment 1. FIG. 4 is a flowchart for explaining control at start-up of a refrigeration cycle device according to a modified example of embodiment 1. FIG. 5 is a flowchart for explaining control at start-up of a refrigeration cycle device according to a modified example of embodiment 1. FIG. 6 is a refrigerant circuit diagram of a refrigeration cycle device according to embodiment 2. FIG. 7 is a functional block diagram for explaining the configuration of a control device of the refrigeration cycle device according to embodiment 2. FIG. 8 is a flowchart for explaining control at start-up of the refrigeration cycle device according to embodiment 2.

[0009] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and their description will not be repeated in principle.

[0010] Embodiment 1. FIG. 1 is a refrigerant circuit diagram of a refrigeration cycle apparatus 100 according to Embodiment 1. The refrigeration cycle apparatus 100 shown in FIG. 1 is, for example, a multi-air conditioner for a building, and includes an outdoor unit and multiple indoor units. The outdoor unit and each indoor unit are connected by refrigerant piping. Refrigerant piping is broadly classified into long refrigerant piping and short refrigerant piping, as will be described later, and the amount of liquid returned differs depending on whether long refrigerant piping or short refrigerant piping is used in the refrigeration cycle apparatus 100. The refrigeration cycle apparatus 100 of this embodiment will be described using an example having three indoor units as shown in FIG. 1, but the number of indoor units may be one to two, or four or more.

[0011] The refrigeration cycle apparatus 100 according to this embodiment includes a compressor 101, an oil separator 102, a four-way valve 103, a first stop valve 106, a first pipe 108, an indoor heat exchanger 110, a second pipe 112, a second stop valve 114, a first expansion valve 115, an accumulator 117, a second expansion valve 118, an outdoor heat exchanger 119, and a control device 300. A refrigerant circuit is formed by circulating the refrigerant through the compressor 101, the oil separator 102, the four-way valve 103, the first pipe 108, the indoor heat exchanger 110, the second pipe 112, the first stop valve 106, the first pipe 108, the indoor heat exchanger 110, the second pipe 112, the second stop valve 114, the first expansion valve 115, the accumulator 117, the second expansion valve 118, and the outdoor heat exchanger 119.

[0012] There are no particular limitations on the type of refrigerant used in the refrigerant circuit of the refrigeration cycle apparatus 100. For example, the refrigeration cycle apparatus 100 may use natural refrigerants such as carbon dioxide, hydrocarbons, or helium, chlorine-free alternative refrigerants such as HFC410A, HFC407C, or HFC404A, or fluorocarbon refrigerants such as R22 or R134a that are used in existing products.

[0013] The compressor 101 draws in low-temperature, low-pressure gas refrigerant, compresses it, and discharges high-temperature, high-pressure gas refrigerant. The refrigerant is circulated within a refrigerant circuit by the compressor 101. The compressor 101 is, for example, an inverter-type compressor whose capacity can be controlled.

[0014] The oil separator 102 is a device for separating the refrigerant from the lubricating oil, and has a first oil return pipe 104a connected to the suction pipe of the compressor 101 and a second oil return pipe 105a connected to the inlet pipe of the accumulator 117. A first solenoid valve 104 is provided in the first oil return pipe 104a, and a second solenoid valve 105 is provided in the second oil return pipe 105a. As will be described later, the control device 300 controls the first solenoid valve 104 and the second solenoid valve 105 based on pressure data of the first pipe 108 and the second pipe 112, the frequency of the compressor 101, and installation conditions, thereby performing liquid return control.

[0015] The four-way valve 103 switches the flow path of the refrigerant discharged from the compressor 101 depending on the operation of the indoor unit. The four-way valve 103 switches to the flow path shown by the solid line in Fig. 1 during heating operation, and switches to the flow path shown by the dashed line in Fig. 1 during cooling operation. The four-way valve 103 may be a combination of a three-way valve or a two-way valve.

[0016] The indoor heat exchanger 110 is, for example, a fin-tube heat exchanger. The indoor heat exchanger 110 exchanges heat between the refrigerant and air supplied by an indoor fan (not shown). The indoor heat exchanger 110 functions as a condenser during heating operation, condensing and liquefying the refrigerant. The indoor heat exchanger 110 also functions as an evaporator during cooling operation, evaporating and gasifying the refrigerant. The refrigeration cycle apparatus 100 is provided with three indoor heat exchangers 110, and three indoor units are installed.

[0017] The first expansion valve 115 and the second expansion valve 118 are, for example, solenoid valves whose opening degrees are variably controlled. The first expansion valve 115 and the second expansion valve 118 are connected in series with the indoor heat exchanger 110 and reduce the pressure of the refrigerant flowing out of the indoor heat exchanger 110 or the refrigerant flowing into the indoor heat exchanger 110 to expand it. The refrigeration cycle apparatus 100 is provided with a HIC (Heat Inter Changer) circuit 116 that increases the amount of refrigerant circulating by injecting a gas-liquid two-phase refrigerant into the compressor when the outside air temperature is low, and the first expansion valve 115 is provided closer to the indoor heat exchanger 110 than the HIC circuit 116.

[0018] The accumulator 117 is provided on the suction side of the compressor 101, and has a function of separating the liquid refrigerant from the gas refrigerant and a function of storing excess refrigerant.

[0019] The outdoor heat exchanger 119 is, for example, a fin-tube heat exchanger. The outdoor heat exchanger 119 exchanges heat between the refrigerant and air supplied by an outdoor fan (not shown). The outdoor heat exchanger 119 functions as a condenser during cooling operation, condensing and liquefying the refrigerant. The outdoor heat exchanger 119 also functions as an evaporator during heating operation, evaporating and gasifying the refrigerant.

[0020] The indoor heat exchanger 110 and the outdoor heat exchanger 119 are connected by a first pipe 108 and a second pipe 112, which are refrigerant pipes. The first pipe 108 and the second pipe 112 are determined to be long refrigerant pipes if they are equal to or longer than a reference length (e.g., 10 m), and are determined to be short refrigerant pipes if they are shorter than the reference length. Because the amount of liquid backflow differs depending on whether long refrigerant pipes or short refrigerant pipes are used for the first pipe 108 and the second pipe 112 of the refrigeration cycle apparatus 100, it is necessary to determine whether the installed first pipe 108 and the second pipe 112 are long refrigerant pipes or short refrigerant pipes.

[0021] For this reason, the refrigeration cycle apparatus 100 is provided with pressure sensors 107, 109 at both ends of the first pipe 108, and pressure sensors 111, 113 at both ends of the second pipe 112. The control device 300 calculates the pressure loss in the first pipe 108 and the second pipe 112 based on the pressure data obtained from the pressure sensors 107, 109, 111, 113, and determines whether the first pipe 108 and the second pipe 112 are long refrigerant pipes or short refrigerant pipes. Note that the means for obtaining the pressure data of the first pipe 108 and the second pipe 112 is not limited to the pressure sensors 107, 109, 111, 113, and any pressure detection unit that can obtain similar pressure data may be used.

[0022] Furthermore, the pressure loss (piping pressure loss) in the first pipe 108 and the second pipe 112 is also affected by the elevation difference between the indoor heat exchanger 110 and the outdoor heat exchanger 119. Therefore, it is necessary to calculate the pressure loss (height difference pressure loss) due to the elevation difference between the indoor heat exchanger 110 and the outdoor heat exchanger 119 and to calculate the pipe pressure loss excluding the elevation difference pressure loss. The refrigeration cycle apparatus 100 is provided with a barometer 120 on the indoor heat exchanger 110 side and a barometer 121 on the outdoor heat exchanger 119 side to calculate the elevation difference between the indoor heat exchanger 110 and the outdoor heat exchanger 119. The control device 300 calculates the elevation difference between the indoor heat exchanger 110 and the outdoor heat exchanger 119 from the air pressure data obtained from the barometers 120 and 121, and calculates the pressure loss due to the elevation difference (height difference pressure loss).

[0023] The elevation difference between the installation positions of the indoor heat exchanger 110 and the outdoor heat exchanger 119 does not necessarily have to be calculated based on the atmospheric pressure data obtained from the barometers 120 and 121, and any elevation difference detector capable of similarly obtaining information on the elevation difference between the installation positions may be used. Furthermore, without providing an elevation difference detector, information on the elevation difference between the installation positions of the indoor heat exchanger 110 and the outdoor heat exchanger 119 may be stored in the memory of the control device 300 at the time of installation. Furthermore, if the effect of the elevation difference between the installation positions of the indoor heat exchanger 110 and the outdoor heat exchanger 119 is negligible or can be ignored, or if the effect of the elevation difference between the installation positions of the indoor heat exchanger 110 and the outdoor heat exchanger 119 cannot be eliminated, there is no need to calculate the pressure loss due to the elevation difference (elevation difference pressure loss), and therefore elevation difference detectors such as the barometers 120 and 121 may not be provided.

[0024] The refrigeration cycle apparatus 100 is provided with a first stop valve 106 on the outdoor heat exchanger 119 side of the first pipe 108, and a second stop valve 114 on the outdoor heat exchanger 119 side of the second pipe 112. The control device 300 can also control the opening and closing of the first stop valve 106 and the second stop valve 114.

[0025] When the refrigeration cycle apparatus 100 is in heating operation, high-temperature, high-pressure gas refrigerant discharged from the compressor 101 flows out of the outdoor unit through the four-way valve 103 and into the indoor heat exchanger 110 of each indoor unit through the first pipe 108. The refrigerant that flows into each indoor unit exchanges heat with air supplied by the indoor fan in the indoor heat exchanger 110, condensing and liquefying. At this time, the refrigerant dissipates heat into the air in the space to be air-conditioned, thereby heating the room in which the indoor unit is installed. The refrigerant that flows out of the indoor heat exchanger 110 leaves the indoor unit and flows into the outdoor unit through the second pipe 112.

[0026] The refrigerant that flows into the outdoor unit is decompressed by the second expansion valve 118, becomes a low-temperature gas-liquid two-phase refrigerant, and flows into the outdoor heat exchanger 119. The refrigerant that flows into the outdoor heat exchanger 119 exchanges heat with air supplied by the outdoor fan, evaporates, and gasifies. The refrigerant that flows out of the outdoor heat exchanger 119 passes through the four-way valve 103 and the accumulator 117 and is sucked back into the compressor 101.

[0027] During cooling operation, high-temperature, high-pressure gas refrigerant discharged from the compressor 101 passes through the four-way valve 103 and flows into the outdoor heat exchanger 119. The refrigerant that flows into the outdoor heat exchanger 119 exchanges heat with air supplied by the outdoor fan, condenses, and liquefies. The refrigerant that flows out of the outdoor heat exchanger 119 is decompressed by the second expansion valve 118, becomes a low-temperature gas-liquid two-phase refrigerant, and flows into each indoor unit through the second piping 112.

[0028] The refrigerant that flows into each indoor unit flows into the indoor heat exchanger 110. The refrigerant that flows into the indoor heat exchanger 110 evaporates and gasifies through heat exchange with air supplied by the indoor fan 33. At this time, the refrigerant absorbs heat from the air in the space to be air-conditioned, thereby cooling the room in which the indoor unit is installed.

[0029] The refrigerant flowing out of the indoor heat exchanger 110 flows into the outdoor unit through the first pipe 108. The refrigerant flowing into the outdoor unit passes through the four-way valve 103 and the accumulator 117 and is sucked into the compressor 101 again.

[0030] Next, Fig. 2 is a functional block diagram for explaining the configuration of the control device 300 of the refrigeration cycle apparatus 100 according to Embodiment 1. As shown in Fig. 2, the control device 300 has a calculation unit 301 and a storage unit 302. Specifically, the calculation unit 301 controls the operation of the refrigeration cycle apparatus 100 by executing an operation program stored in the storage unit 302.

[0031] The calculation unit 301 is a processor that can read and execute programs (for example, an OS and an operating program) stored in the storage unit 302. The calculation unit 301 executes various programs read from the storage unit 302.

[0032] The storage unit 302 is configured by, for example, a nonvolatile storage device such as a ROM, a flash memory, etc. In addition to an OS for realizing basic functions, the storage unit 302 stores an operation program for controlling the operation of the refrigeration cycle apparatus 100, pressure data detected by a pressure detection unit 305, information on the elevation difference of the installation position detected by an elevation difference detection unit 306, etc.

[0033] The control device 300 is connected to a pressure detection unit 305, an elevation difference detection unit 306, the first solenoid valve 104, the second solenoid valve 105, the first expansion valve 115, the second expansion valve 118, the first stop valve 106, and the second stop valve 114. The pressure detection unit 305 includes, for example, pressure sensors 107, 109, 111, and 113 shown in FIG. 1 . The elevation difference detection unit 306 includes, for example, barometer 120 and barometer 121 shown in FIG. 1 . The control device 300 can control the compressor 101, the four-way valve 103, the indoor fan of the indoor heat exchanger 110, the outdoor fan of the outdoor heat exchanger 119, and the like, although not shown.

[0034] Next, the startup control of the refrigeration cycle apparatus 100 will be described. In multi-type refrigeration cycle apparatuses with an oil separator, it is common to return the oil separated in the oil separator to the compressor's suction pipe via an oil return pipe to improve oil return. However, refrigerant pipes connecting the outdoor unit and the indoor unit can be broadly divided into long refrigerant pipes and short refrigerant pipes, and the causes of liquid backflow differ between long and short refrigerant pipes. When long refrigerant pipes are used, high pressure rises due to excessive capacity in the indoor heat exchanger are less likely to occur, and liquid backflow is more likely to occur from the refrigerant circuit side that passes through the accumulator. Therefore, the accumulator functions to prevent liquid backflow.

[0035] On the other hand, when using short refrigerant piping, the time it takes for the refrigerant discharged from the compressor to travel through the piping and reach the indoor heat exchanger is shorter than with long refrigerant piping when the compressor starts up, and there is a high possibility that the indoor heat exchanger will not be able to process all of the refrigerant, causing a high-pressure rise due to excessive capacity. As a result, the high-low pressure difference increases, and the liquid refrigerant accumulated in the oil separator is returned directly from the oil separator to the oil return piping connected to the compressor's suction piping, increasing the amount of liquid backflow and potentially damaging the compressor.

[0036] Therefore, in the refrigeration cycle apparatus 100 according to this embodiment, in addition to the first oil return pipe 104a connected from the oil separator 102 to the suction pipe of the compressor 101, a second oil return pipe 105a connected to the inlet pipe of the accumulator 117 is provided, and when short refrigerant pipes are used, liquid refrigerant accumulated in the oil separator 102 flows through the second oil return pipe 105a from the time the compressor 101 is started until the compressor 101 stabilizes. Therefore, even when short refrigerant pipes are used in the refrigeration cycle apparatus 100, the liquid refrigerant accumulated in the oil separator 102 is not directly returned to the compressor 101, preventing an increase in the amount of liquid return that would damage the compressor 101.

[0037] Specific control will be described using a flowchart. FIG. 3 is a flowchart illustrating control during startup of the refrigeration cycle apparatus 100 according to the first embodiment. First, the control device 300 starts the compressor 101 (step S101). Next, a process is performed to determine whether the first pipe 108 and the second pipe 112 are short refrigerant pipes or long refrigerant pipes. To this end, the control device 300 acquires a pipe pressure loss ΔPl from pressure data obtained from the pressure sensors 107, 109, 111, and 113 (step S102). Furthermore, the control device 300 uses the pipe pressure loss ΔPl acquired in step S102 to estimate the pipe lengths of the first pipe 108 and the second pipe 112 using the Darcy-Weisbach equation (step S103).

[0038] The Darcy-Weisbach equation is expressed as Equation 1: ΔPl = λ × L / d × (ρ × U ２) / 2 (Equation 1) where ΔPl is the pressure loss [Pa], λ is the friction coefficient of the piping [-], L is the piping length [m], and ρ is the density of the refrigerant [kg / m ３ ], U is the average flow velocity [m / s], and d is the inner diameter of the pipe [m]. The average flow velocity U can be calculated by calculating the average flow rate of the refrigerant circulating in the refrigerant circuit and dividing it by the flow path cross-sectional area of ​​the refrigerant pipe.

[0039] The control device 300 determines whether the pipe lengths of the first pipe 108 and the second pipe 112 calculated in step S103 are less than a reference length (e.g., 10 m) (step S104). If the pipe lengths of the first pipe 108 and the second pipe 112 are less than the reference length (YES in step S104), the control device 300 determines that the first pipe 108 and the second pipe 112 are short refrigerant pipes (step S105).

[0040] Next, the control device 300 closes the first solenoid valve 104 and opens the second solenoid valve 105 (step S106). This allows the refrigeration cycle device 100 to flow the liquid refrigerant accumulated in the oil separator 102 through the second oil return pipe 105a instead of the first oil return pipe 104a, thereby preventing an increase in the amount of liquid returned and damaging the compressor 101, and ensuring the reliability of the compressor 101.

[0041] Next, the control device 300 determines whether the frequency of the compressor 101 is higher than the reference frequency (step S107). If the frequency of the compressor 101 is lower than the reference frequency (NO in step S107), the control device 300 returns the process to step S106.

[0042] On the other hand, if the frequency of the compressor 101 is higher than the reference frequency (YES in step S107), the control device 300 closes the second expansion valve 118 (step S108). Furthermore, the control device 300 determines whether the discharge superheat (discharge SH) is higher than 10 degrees (step S109). If the discharge superheat (discharge SH) is 10 degrees or less (NO in step S109), the control device 300 returns the process to step S108.

[0043] The control device 300 determines that the compressor 101 has stabilized when the frequency of the compressor 101 is greater than a reference frequency and the discharge superheat (discharge SH) is greater than 10 degrees. Whether the compressor 101 has stabilized may be determined when the frequency of the compressor 101 is greater than the reference frequency. Alternatively, the control device 300 may determine that the compressor 101 has stabilized based on a value other than the frequency and the discharge superheat (discharge SH) of the compressor 101. For example, the determination may be based on the elapsed time since the compressor 101 was started.

[0044] If the discharge superheat (discharge SH) is greater than 10 degrees (YES in step S109), the control device 300 opens the first solenoid valve 104 and closes the second solenoid valve 105 (step S110). This allows the refrigeration cycle device 100 to return the liquid refrigerant accumulated in the oil separator 102 to the compressor 101 via the first oil return pipe 104a, thereby improving oil return performance. Note that the control device 300 opens the first solenoid valve 104 and closes the second solenoid valve 105 when the discharge superheat (discharge SH) is greater than 10 degrees, but may also open the first solenoid valve 104 and close the second solenoid valve 105 when the frequency of the compressor 101 becomes greater than the reference frequency.

[0045] Returning to step S104, if the piping lengths of the first piping 108 and the second piping 112 are equal to or longer than the reference length (NO in step S104), the control device 300 determines that the first piping 108 and the second piping 112 are long refrigerant piping (step S111). The control device 300 opens the first solenoid valve 104 and closes the second solenoid valve 105 (step S112). This allows the refrigeration cycle apparatus 100 to return the liquid refrigerant accumulated in the oil separator 102 to the compressor 101 via the first oil return piping 104a, thereby improving oil return performance.

[0046] Next, the control device 300 closes the second expansion valve 118 (step S113). The control device 300 determines whether the discharge superheat (discharge SH) is greater than 10 degrees (step S114). If the discharge superheat (discharge SH) is 10 degrees or less (NO in step S114), the control device 300 returns the process to step S113. On the other hand, if the discharge superheat (discharge SH) is greater than 10 degrees (YES in step S113), the control device 300 ends the startup process.

[0047] The installation conditions for the refrigeration cycle apparatus 100 include information on whether the first pipe 108 and the second pipe 112 are short or long refrigerant pipes, as well as information on the elevation difference between the indoor heat exchanger 110 and the outdoor heat exchanger 119. If the indoor heat exchanger 110 and the outdoor heat exchanger 119 are installed at different elevations, pressure loss due to the elevation difference between the installation positions will occur in addition to pipe pressure loss. Therefore, the pressure loss calculated from the pressure data of the pressure sensors 107, 109, 111, and 113 also includes pressure loss due to the elevation difference between the installation positions. To accurately estimate the pipe lengths of the first pipe 108 and the second pipe 112, it is necessary to exclude the pressure loss due to the elevation difference between the installation positions from the pressure loss calculated from the pressure data. Therefore, a control for eliminating the pressure loss due to the elevation difference between the installation positions of the indoor heat exchanger 110 and the outdoor heat exchanger 119 will be described using a flowchart. 4 and 5 are flowcharts for explaining the control at the time of start-up of the refrigeration cycle apparatus 100 according to the modification of the first embodiment.

[0048] First, the control device 300 starts the compressor 101 (step S201). Next, the control device 300 determines whether there is a difference in elevation between the indoor heat exchanger 110 and the outdoor heat exchanger 119 (step S202). The control device 300 acquires air pressure data from the barometers 120 and 121, which are provided to determine the difference in elevation between the indoor heat exchanger 110 and the outdoor heat exchanger 119. When the first pipe 108 and the second pipe 112 are installed such that there is a difference in elevation between the indoor heat exchanger 110 and the outdoor heat exchanger 119, the pressure loss due to the difference in elevation between the installation positions is expressed by Equation 2.

[0049] ΔPh = ρgh (Equation 2) Here, ΔPh is the pressure loss [Pa] due to the difference in elevation of the installation position, and ρ is the density of the refrigerant [kg / m ３ ], g is the gravitational acceleration [m / s ２ ], and h is the elevation difference [m] of the installation positions. The elevation difference h of the installation positions can be obtained from atmospheric pressure data from the barometers 120 and 121. The method of obtaining the elevation difference h of the installation positions is not limited to the atmospheric pressure data from the barometers 120 and 121, and an elevation difference detection unit using another method of obtaining the elevation difference of the installation positions may also be used. Furthermore, the elevation difference h of the installation positions may be stored in advance in the memory unit 302 when the indoor heat exchanger 110 and the outdoor heat exchanger 119 are installed.

[0050] If there is a difference in elevation between the indoor heat exchanger 110 and the outdoor heat exchanger 119 (YES in step S202), the control device 300 calculates the pressure loss ΔPh due to the difference in elevation h between the installation locations (step S203). The control device 300 calculates the piping pressure loss ΔPl (= ΔP - ΔPh) by excluding the pressure loss ΔPh due to the difference in elevation h between the installation locations (altitude difference pressure loss) from the pressure loss ΔP calculated from the pressure data of the pressure sensors 107, 109, 111, and 113 (step S204). The control device 300 acquires the piping pressure loss ΔPl calculated in step S204 (step S205). This allows the piping lengths of the first piping 108 and the second piping 112 to be estimated with high accuracy from the piping pressure loss ΔPl that does not include the pressure loss ΔPh due to the difference in elevation h between the installation locations.

[0051] Steps S206 to S217 shown in Fig. 4 are the same as the processing of steps S103 to S114 shown in Fig. 3, and therefore detailed description thereof will not be repeated. Returning to step S202, if there is no difference in elevation between the installation positions of indoor heat exchanger 110 and outdoor heat exchanger 119 (NO in step S202), control device 300 acquires piping pressure loss ΔPl from pressure data obtained from pressure sensors 107, 109, 111, and 113 (step S218 shown in Fig. 5). Steps S218 to S230 shown in Fig. 5 are the same as the processing of steps S102 to S114 shown in Fig. 3, and therefore detailed description thereof will not be repeated.

[0052] Embodiment 2. Because refrigerant has the property of easily moving toward lower temperatures, when the indoor temperature is higher than the outdoor temperature, a state known as refrigerant stagnation occurs, in which refrigerant accumulates in large-volume outdoor heat exchangers, compressors, etc. In this embodiment, a description is given of startup control in a refrigeration cycle device that takes refrigerant stagnation into consideration.

[0053] Fig. 6 is a refrigerant circuit diagram of a refrigeration cycle apparatus 100A according to embodiment 2. Fig. 7 is a functional block diagram for explaining the configuration of a control device 300 of the refrigeration cycle apparatus 100A according to embodiment 2. The configuration of the refrigeration cycle apparatus 100A according to embodiment 2 is the same as the configuration of the refrigeration cycle apparatus 100 described in embodiment 1, and therefore the same components are designated by the same reference numerals and detailed description thereof will not be repeated.

[0054] In the refrigeration cycle apparatus 100A, in order to grasp the state of refrigerant stagnation, the outdoor heat exchanger 119 is provided with a thermistor 122, and the indoor heat exchanger 110 is provided with a thermistor 123. The thermistors 122 and 123 are included in a temperature detection unit 307 shown in Fig. 7. When the temperature difference between the indoor temperature and the outdoor temperature detected by the temperature detection unit 307 is equal to or greater than a reference temperature (for example, 10°C), the control device 300 determines that refrigerant stagnation has occurred on the outdoor unit side.

[0055] The liquid return control at startup that takes refrigerant stagnation into consideration will be specifically described using a flowchart. Figures 8 and 9 are flowcharts for explaining the control at startup of the refrigeration cycle apparatus 100A according to the second embodiment. The flowcharts shown in Figures 8 and 9 are based on the premise that the refrigeration cycle apparatus 100A is operating in heating mode. First, the control device 300 acquires the outdoor temperature and the indoor temperature using the thermistor 122 and the thermistor 123 (step S301). The control device 300 determines whether the indoor temperature is higher than the outdoor temperature and whether the temperature difference between the indoor temperature and the outdoor temperature is greater than a reference temperature (indoor temperature - outdoor temperature > reference temperature) (step S302).

[0056] If the indoor temperature is higher than the outdoor temperature and the temperature difference between the indoor temperature and the outdoor temperature is greater than the reference temperature (YES in step S302), the control device 300 determines that refrigerant stagnation is occurring (step S303). Next, the control device 300 starts the compressor 101 (step S304). The control device 300 acquires the piping pressure loss ΔPl from the pressure data obtained from the pressure sensors 107, 109, 111, and 113 (step S305). The control device 300 uses the piping pressure loss ΔPl acquired in step S305 to estimate the piping lengths of the first piping 108 and the second piping 112 using the Darcy-Weisbach equation (step S306).

[0057] The control device 300 determines whether the pipe lengths of the first pipe 108 and the second pipe 112 estimated in step S306 are less than a reference length (e.g., 10 m) (step S307). If the pipe lengths of the first pipe 108 and the second pipe 112 are less than the reference length (YES in step S307), the control device 300 determines that the first pipe 108 and the second pipe 112 are short refrigerant pipes (step S308).

[0058] Next, the control device 300 opens the first solenoid valve 104 and the second solenoid valve 105 (step S309). In the refrigeration cycle apparatus 100A, when the first pipe 108 and the second pipe 112 are short refrigerant pipes and refrigerant stagnation occurs during startup, there is a risk that the refrigerant stagnation on the outdoor unit side will suddenly flow into the indoor heat exchanger 110, causing the indoor heat exchanger 110 to become over-capacitated. Therefore, in the refrigeration cycle apparatus 100A, both the first solenoid valve 104 and the second solenoid valve 105 are opened during startup to increase the amount of liquid refrigerant returned from the oil separator 102 to the first oil return pipe 104a and the second oil return pipe 105a, thereby preventing the refrigerant stagnation on the outdoor unit side from suddenly flowing into the indoor heat exchanger 110. Therefore, in the refrigeration cycle device 100A, even when short refrigerant piping is used, the risk of the indoor heat exchanger 110 becoming over-capacitated can be reduced while preventing an increase in the amount of liquid backflow that would damage the compressor 101.

[0059] Next, the control device 300 determines whether the frequency of the compressor 101 is greater than the reference frequency (step S310). If the frequency of the compressor 101 is equal to or less than the reference frequency (NO in step S310), the control device 300 returns the process to step S309.

[0060] On the other hand, if the frequency of the compressor 101 is greater than the reference frequency (YES in step S310), the control device 300 closes the second expansion valve 118 (step S312). Furthermore, the control device 300 determines whether the discharge superheat (discharge SH) is greater than 10 degrees (step S312). If the discharge superheat (discharge SH) is 10 degrees or less (NO in step S312), the control device 300 returns the process to step S311.

[0061] If the discharge superheat (discharge SH) is greater than 10 degrees (YES in step S312), the control device 300 opens the first solenoid valve 104 and closes the second solenoid valve 105 (step S313). This allows the refrigeration cycle apparatus 100A to return the liquid refrigerant accumulated in the oil separator 102 to the compressor 101 through the first oil return pipe 104a, thereby improving oil return performance.

[0062] Returning to step S307, if the piping lengths of the first piping 108 and the second piping 112 are equal to or greater than the reference length (NO in step S307), the control device 300 determines that the first piping 108 and the second piping 112 are long refrigerant piping (step S314). Next, the control device 300 closes the first stop valve 106 (step S315). Furthermore, the control device 300 performs the cooling operation (step S316). The control device 300 determines whether a reference time has elapsed since the cooling operation was performed (step S317). If the reference time has not elapsed since the cooling operation was performed (NO in step S317), the control device 300 returns the process to step S316 and continues the cooling operation.

[0063] In the refrigeration cycle apparatus 100A, if the first pipe 108 and the second pipe 112 are long refrigerant pipes, the refrigerant that has accumulated on the outdoor unit side may liquid-back into the accumulator 117, reducing the separation efficiency of the accumulator 117. Therefore, in the refrigeration cycle apparatus 100A, the first stop valve 106 is closed at startup to perform cooling operation, thereby controlling the removal of refrigerant from the outdoor unit side, thereby reducing the possibility of a reduction in the separation efficiency of the accumulator 117.

[0064] Next, the control device 300 opens the first solenoid valve 104 and closes the second solenoid valve 105 (step S318). This allows the refrigeration cycle apparatus 100A to return the liquid refrigerant accumulated in the oil separator 102 to the compressor 101 via the first oil return pipe 104a, thereby improving oil return performance. Furthermore, the control device 300 closes the second expansion valve 118 (step S319). The control device 300 determines whether the discharge superheat (discharge SH) is greater than 10 degrees (step S320). If the discharge superheat (discharge SH) is 10 degrees or less (NO in step S320), the control device 300 returns the process to step S319. On the other hand, if the discharge superheat (discharge SH) is greater than 10 degrees (YES in step S320), the control device 300 ends the startup process.

[0065] Returning to step S302, if the temperature difference between the indoor temperature and the outdoor temperature is equal to or less than the reference temperature (NO in step S302), control device 300 determines that refrigerant stagnation has not occurred (step S321 shown in FIG. 9). Steps S322 to S335 shown in FIG. 9 are the same as the processes in steps S101 to S114 shown in FIG. 3, and therefore detailed description thereof will not be repeated.

[0066] The embodiments disclosed herein are intended to be combined appropriately within the scope of compatibility. The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present disclosure is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0067] 100, 100A refrigeration cycle device, 101 compressor, 102 oil separator, 103 four-way valve, 104 first solenoid valve, 104a first oil return pipe, 105 second solenoid valve, 105a second oil return pipe, 106 first stop valve, 107, 109, 111, 113 pressure sensor, 108 first pipe, 110 indoor heat exchanger, 112 second pipe, 114 second stop valve, 115 first expansion valve, 117 accumulator, 118 second expansion valve, 119 outdoor heat exchanger, 120, 121 barometer, 122, 123 thermistor, 300 control device, 301 calculation unit, 302 memory unit, 305 pressure detection unit, 306 elevation difference detection unit, 307 temperature detection unit.

Claims

1. A refrigeration cycle device comprising: a refrigerant circuit in which refrigerant circulates through a compressor, an oil separator, a four-way valve, a first pipe, an indoor heat exchanger, a second pipe, a stop valve, an expansion valve, an outdoor heat exchanger, and an accumulator; a first oil return pipe connected from the oil separator to the intake pipe of the compressor; a first solenoid valve provided on the first oil return pipe; a second oil return pipe connected from the oil separator to the inlet pipe of the accumulator; a second solenoid valve provided on the second oil return pipe; pressure detection units provided on each of the first pipe and the second pipe for detecting the pressure of each pipe; and a control device for controlling the expansion valve, the first solenoid valve, and the second solenoid valve to perform liquid return control based on pressure data detected by the pressure detection unit, the frequency of the compressor, and installation conditions.

2. The refrigeration cycle device of claim 1, wherein the installation conditions include information on the lengths of the first pipe and the second pipe, and the control device calculates the pressure loss of the first pipe and the second pipe based on the pressure data detected by the pressure detection unit, and determines from the calculated pressure loss whether the lengths of the first pipe and the second pipe are less than a reference length.

3. The refrigeration cycle device according to claim 2, wherein the installation conditions further include information on the difference in elevation between the installation positions of the indoor heat exchanger and the outdoor heat exchanger, and the control device calculates the pressure loss by excluding the pressure loss due to the difference in elevation.

4. A refrigeration cycle device as described in claim 3, wherein the control device has a memory unit that stores information on the elevation difference, and calculates the pressure loss due to the elevation difference from the information on the elevation difference stored in the memory unit.

5. A refrigeration cycle device as described in claim 3, further comprising an elevation difference detection unit provided in each of the first pipe and the second pipe to detect the elevation difference, and wherein the control device determines the pressure loss due to the elevation difference from the elevation difference detected by the elevation difference detection unit.

6. A refrigeration cycle device as described in any one of claims 2 to 5, wherein the control device closes the first solenoid valve and opens the second solenoid valve during a period from when the compressor is started until the compressor stabilizes, when the piping lengths of the first piping and the second piping are less than the reference length.

7. A refrigeration cycle device as described in any one of claims 2 to 6, wherein the control device controls the first solenoid valve and the second solenoid valve taking into account information on whether refrigerant stagnation is occurring in the outdoor heat exchanger.

8. A refrigeration cycle device as described in claim 7, further comprising a temperature detection unit in each of the outdoor heat exchanger and the indoor heat exchanger, and wherein the control device determines that refrigerant stagnation is occurring on the outdoor unit side when the indoor temperature is higher than the outdoor temperature detected by the temperature detection unit and the temperature difference between the indoor temperature and the outdoor temperature is greater than a reference temperature.

9. A refrigeration cycle device as described in any one of claims 7 or 8, wherein the control device operates the refrigeration cycle device in heating operation, opens the first solenoid valve and closes the second solenoid valve when the piping lengths of the first pipe and the second pipe are equal to or longer than the reference length and no refrigerant stagnation occurs in the outdoor heat exchanger.

10. A refrigeration cycle device as described in claim 7 or claim 8, further comprising a first stop valve arranged between the four-way valve and the first pipe, and a second stop valve arranged between the second pipe and the expansion valve, wherein the control device operates the refrigeration cycle device in heating operation, and when the piping lengths of the first pipe and the second pipe are equal to or longer than the reference length and refrigerant stagnation has occurred in the outdoor heat exchanger, closes the first stop valve and operates the refrigeration cycle device in cooling operation to eliminate refrigerant stagnation that has occurred in the outdoor heat exchanger.

11. A refrigeration cycle device as described in claim 7 or claim 8, wherein the control device operates the refrigeration cycle device in heating operation, closes the first solenoid valve and opens the second solenoid valve when the piping lengths of the first piping and the second piping are less than the reference length and no refrigerant stagnation occurs in the outdoor heat exchanger.

12. A refrigeration cycle device as described in claim 7 or claim 8, wherein the control device operates the refrigeration cycle device in heating operation, and when the piping lengths of the first piping and the second piping are less than the reference length and refrigerant stagnation occurs in the outdoor heat exchanger, opens the second solenoid valve and opens the first solenoid valve.

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