JP5259944B2 - Air conditioner - Google Patents

Description

  The present invention relates to a multi-type air conditioner having an oil recovery operation function of recovering lubricating oil that circulates in a refrigerant circuit together with refrigerant discharged from a compressor and stays on the refrigerant circuit side to the compressor.

  In an air conditioner using a refrigerant compression refrigeration cycle, the refrigerant is compressed by a compressor and circulated in the refrigerant circuit to obtain an air conditioning effect. The compressor is filled with lubricating oil for lubricating the sliding portion, and a part of the lubricating oil is discharged from the compressor to the refrigerant circuit together with the compressed refrigerant. The lubricating oil circulates in the refrigerant circuit together with the refrigerant, and then returns to the compressor again. However, some lubricating oil may stay on the refrigerant circuit side. The retention amount of the lubricating oil varies depending on the refrigerant pipe length or operation state of each indoor unit, but is generally considered to increase in proportion to the operation time of the air conditioner.

  As described above, if the amount of lubricating oil staying on the refrigerant circuit side increases, the amount of lubricating oil retained in the compressor will decrease accordingly, affecting the lubricating action of the compressor, and in some cases In addition, the lack of lubricating oil may cause a failure or breakage of the compressor. Therefore, every time the air conditioner is operated for a certain time (for example, 8 hours), the oil recovery operation for forcibly collecting the lubricating oil staying in the refrigerant circuit to the compressor is performed for a certain time (for example, 3 hours). Min). In addition, as the oil recovery operation, the compressor is set to the set rotation speed, the liquid expansion operation is performed with the indoor expansion valve and the outdoor expansion valve set to the respective opening degrees, and the lubricating oil staying in the refrigerant circuit together with the liquid refrigerant is compressed. A method of collecting on the machine side is known.

By the way, in a multi-type air conditioner in which a plurality of indoor units are connected in parallel, especially those installed for building air conditioning have a very long refrigerant piping length, and the refrigerant piping length differs for each indoor unit. In most cases. In this multi-type air conditioner, as described above, even if the oil recovery operation is performed for a certain period of time, the amount of lubricating oil may not return to the compressor as expected, which may result in poor lubrication. is there.
In order to avoid such a situation, during oil recovery operation, it is determined whether the lubricating oil has returned to the compressor based on the suction superheat of the refrigerant sucked into the compressor, and if necessary, oil recovery operation The thing which changed the driving | operation time of this is proposed (for example, refer patent document 1).

  On the other hand, in the multi-type air conditioner as described above, after installing the air conditioner in the field work, it is necessary to additionally charge an appropriate amount of refrigerant corresponding to the refrigerant pipe length of each indoor unit. Since the charge amount of the refrigerant directly affects whether or not the specified air conditioning performance can be obtained, it is necessary to grasp the length of the refrigerant pipe as accurately as possible and additionally charge an appropriate amount of refrigerant corresponding to it. Therefore, a system and a method for detecting the refrigerant pipe length have been proposed (see, for example, Patent Document 2).

Japanese Patent Laid-Open No. 10-288410 JP 2006-183979 A

However, in Patent Document 1, it is determined whether the lubricating oil has returned to the compressor based on the suction superheat of the refrigerant sucked into the compressor, and the state where the suction superheat is equal to or less than a predetermined value. Is continued for a predetermined time or when a predetermined maximum time has elapsed after the start of the oil recovery operation, the oil recovery operation is terminated. For this reason, regardless of the difference in the refrigerant pipe length of the multiple indoor units, the suction superheat of the compressor is reduced by the liquid refrigerant that circulates and returns through the indoor unit having a relatively short refrigerant pipe length, thereby reducing the oil recovery operation time. Will be decided. Therefore, in such a configuration, there is a problem that the indoor unit having a long refrigerant pipe length and the lubricating oil staying on the refrigerant circuit side cannot be sufficiently recovered.
Patent Document 2 proposes a system and method for detecting the refrigerant pipe length, and does not directly disclose or suggest a technique for recovering the lubricating oil staying in the refrigerant circuit by the compressor. Absent.

  This invention is made in view of such a situation, Comprising: Lubricating oil stagnated in each indoor unit and its refrigerant circuit side is irrespective of the refrigerant pipe length difference of the indoor unit connected with two or more units. An object is to provide an air conditioner that can be reliably recovered.

In order to solve the above problems, the air conditioning apparatus of the present invention employs the following means.
That is, an air conditioner according to the present invention includes an outdoor unit having a compressor and an outdoor heat exchanger, a plurality of indoor units having an indoor heat exchanger and an indoor expansion valve, and connected in parallel to each other, A refrigerant circuit configured by sequentially connecting an outdoor unit and the compressor of the indoor unit, the outdoor heat exchanger, the plurality of indoor heat exchangers, and an indoor expansion valve by a refrigerant pipe; Oil recovery operation in which the indoor unit is in a liquid back operation, the oil recovery operation is performed to recover the lubricating oil remaining in the refrigerant circuit, and the oil recovery operation is terminated when a liquid back is detected on the outdoor unit side In the air conditioner including the operation unit, the oil recovery operation unit includes a refrigerant pipe length detection unit that detects a refrigerant pipe length of each indoor unit, and a refrigerant pipe length detected by the refrigerant pipe length detection unit. Refrigerant piping that remembers A storage unit, based on the refrigerant pipe length of each indoor unit stored in the refrigerant pipe length memory, and the oil recovery control unit for changing the opening degree of each of the indoor expansion valve during the oil-recovery operation, the It is characterized by having.

  According to the present invention, the oil recovery operation unit includes a refrigerant pipe length detection unit that detects the refrigerant pipe length of each indoor unit, a refrigerant pipe length storage unit that stores the refrigerant pipe length, and each stored indoor unit. And an oil recovery control unit that changes the opening degree of each indoor expansion valve during oil recovery operation based on the refrigerant pipe length of each indoor unit. Based on the refrigerant pipe length, by changing the opening of each indoor expansion valve during oil recovery operation, an appropriate amount of refrigerant flows through each indoor unit, and lubrication that remains in each indoor unit and its refrigerant circuit Oil can be recovered. For this reason, the lubricating oil accumulated in the indoor unit having a long refrigerant pipe length and the refrigerant circuit can be reliably recovered to the compressor side. Accordingly, a predetermined amount of lubricating oil can always be held in the compressor, and the situation where the compressor falls short of the lubricating oil due to the oil rising phenomenon toward the refrigerant circuit side and leads to poor lubrication can be reliably solved.

  In the air conditioner of the present invention, in the above air conditioner, the oil recovery control unit determines a refrigerant pipe length difference between the indoor units, and the refrigerant pipe length is determined based on the refrigerant pipe length difference. The longer the indoor unit, the larger the opening of the indoor expansion valve.

  According to the present invention, the refrigerant pipe length difference of each indoor unit is determined, and based on the refrigerant pipe length difference, the indoor unit having a longer refrigerant pipe length increases the opening of the indoor expansion valve. Therefore, the longer the refrigerant pipe length is, the more the refrigerant can flow and the liquid back can be actively collected to recover the lubricating oil. For this reason, the lubricating oil accumulated in the indoor unit having a long refrigerant pipe length and the refrigerant circuit thereof can also be reliably recovered. Accordingly, it is possible to eliminate the situation where the compressor is short of lubricating oil.

According to the present invention, since they are in different refrigerant pipe length for each indoor unit, based on the refrigerant pipe length of each indoor unit, so that changing the chamber expansion valve during the oil-recovery operation, The indoor unit having a long refrigerant pipe length and the lubricating oil accumulated on the refrigerant circuit side can also be reliably collected on the compressor side. Therefore, a predetermined amount of lubricating oil can always be held in the compressor, and it is possible to reliably eliminate the situation where the compressor falls short of lubricating oil and leads to poor lubrication.

Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
FIG. 1 shows a refrigerant circuit diagram of a multi-type air conditioner 1 according to an embodiment of the present invention. The air conditioner 1 includes a single outdoor unit 2 and a plurality of indoor units 3A, 3B, 3C connected in parallel to the outdoor unit 2. In this embodiment, an example in which three indoor units 3A, 3B, and 3C are connected is shown, but the number of connected indoor units 3A, 3B, and 3C is not limited.

  The outdoor unit 2 includes an inverter-driven compressor 4 that compresses the refrigerant, a four-way switching valve 5 that switches the refrigerant circulation direction, an outdoor heat exchanger 6 that exchanges heat between the refrigerant and the outside air, and outdoor electronics for heating. An expansion valve 7, a receiver 8 that stores liquid refrigerant, a supercooling heat exchanger 9 that provides supercooling to the liquid refrigerant, and a liquid component in the refrigerant gas are separated and only the gas refrigerant is sucked into the compressor 4. And an accumulator 10, which are connected by a refrigerant pipe 11 as is well known, and constitute a refrigerant circuit 12 on the outdoor unit 2 side. The supercooling heat exchanger 9 is a heat exchanger having a double-pipe structure, in which a refrigerant branched from a refrigerant pipe 11 is introduced to the inner pipe side through an electronic expansion valve 13 and flows through the outer pipe side. The refrigerant introduced to the inner tube side is configured to be a gas refrigerant and guided to the inlet side of the accumulator 10.

  The outdoor unit 2 is provided with a gas side operation valve 14 and a liquid side operation valve 15, and the gas extended to the indoor units 3 </ b> A, 3 </ b> B, 3 </ b> C via the gas side operation valve 14 and the liquid side operation valve 15. A pipe 16 and a liquid pipe 17 are connected. A plurality of indoor units 3A, 3B, and 3C are connected to the gas pipe 16 and the liquid pipe 17 in parallel with each other via a branching unit (not shown) and indoor side refrigerant pipes 18A, 18B, and 18C.

  Each of the indoor units 3A, 3B, and 3C includes an indoor heat exchanger 19 that exchanges heat with indoor air, and an indoor electronic expansion valve 20 for cooling, and is disposed in each air conditioning zone or each room. . The lengths of the refrigerant pipes 18A, 18B, and 18C connected to the indoor units 3A, 3B, and 3C differ depending on the arrangement positions of the indoor units 3A, 3B, and 3C. Here, the relationship of 18A> 18B> 18C Has been. The indoor refrigerant pipes 18A, 18B, and 18C are connected to the refrigerant circuit 12 on the outdoor unit 2 side via the gas pipe 16 and the liquid pipe 17, whereby a single-line sealed refrigerant circuit 21 is formed. Composed.

  The air conditioner 1 sets each indoor unit 3A, 3B, 3C to a liquid back operation at a predetermined timing, for example, every predetermined operation time, and stays in the refrigerant circuit 21 mainly in the gas side refrigerant circuit. An oil recovery operation unit 22 is provided that performs an oil recovery operation for recovering the lubricating oil, and terminates the oil recovery operation when a liquid back is detected on the outdoor unit 2 side. Note that the timing of the oil recovery operation is not limited to the above, and the oil recovery operation is performed when the amount of outflow of the lubricating oil is calculated based on a predetermined formula and the accumulated outflow amount reaches a predetermined limit outflow amount. It may be performed at other timing such as. Further, the liquid back operation is possible by setting the indoor electronic expansion valve 20 of each indoor unit 3A, 3B, 3C to a set opening for oil recovery operation. Further, whether or not the liquid is returned to the outdoor unit 2 during the oil recovery operation is determined based on the detected values of the low-pressure pressure sensor 23 and the suction refrigerant temperature sensor 24 provided in the inlet-side refrigerant pipe 11 of the accumulator 10 and the overheating of the suction refrigerant. It can be detected by determining the degree.

The oil recovery operation unit 22 includes a refrigerant pipe length detection unit 26 that detects the pipe lengths of the refrigerant pipes 18A, 18B, and 18C connected to the indoor units 3A, 3B, and 3C, and a refrigerant pipe length storage unit 27 that stores the refrigerant pipes. Is provided. The invention of the above-mentioned Patent Document 2 (Japanese Patent Laid-Open No. 2006-183979) filed by the present applicant can be used for detecting the refrigerant pipe length. In this refrigerant pipe length detection method, the suction pressure of the compressor 4 (detected by the low-pressure sensor 23) and the saturation pressure of the indoor heat exchanger 18 (the indoor heat exchanger) when the cooling operation is performed. The pressure loss of the low-pressure gas pipes (respective refrigerant pipes 18A, 18B, 18C and the gas pipe 16) is calculated from the refrigerant temperature detected by the temperature sensor 25 provided at 18 and based on the pressure loss. Thus, the pipe length of the low-pressure gas pipe is obtained from the following Darcy's formula (Darcy's Formula).
ΔP = λ (Δx / D) · (ρu 2/2)
Here, λ is Darcy's pipe friction coefficient, Δx is the pipe length of the low-pressure gas pipe, D is the pipe inner diameter, ρ is the specific gravity of the refrigerant, and u is the average flow velocity. Darcy's pipe friction coefficient λ, pipe inner diameter D, refrigerant specific gravity ρ, and average flow velocity u are acquired in advance. The average flow velocity u is that the discharge flow rate of the compressor 4 to calculate the average flow rate of the refrigerant flowing through the refrigerant circuit 21, which is calculated by dividing the flow path cross-sectional area of the refrigerant pipe ([pi] D ^2/4) it can.

The detection of the refrigerant pipe length is not limited to the above method. For example, after the cooling operation is performed and the state becomes stable, the opening of the expansion valve is forcibly changed, and the compressor Of course, other known methods such as calculating the refrigerant pipe length from the elapsed time until the discharge gas temperature from the gas reaches a predetermined temperature may be used.
The refrigerant pipe length detection by the refrigerant pipe length detector 26 detects the refrigerant pipe length after the air conditioner 1 is installed in order to additionally fill the refrigerant pipe with an amount corresponding to the refrigerant pipe length. What is necessary is just to memorize | store by the pipe length memory | storage part 27, and to use it at the time of oil collection | recovery driving | operation.

The oil recovery operation unit 22 also includes the lengths of the refrigerant pipes 18A, 18B, and 18C of the indoor units 3A, 3B, and 3C stored in the refrigerant pipe length storage unit 27 when the oil recovery operation is performed at the above timing. Based on (actually, the length of the low pressure gas pipe obtained by adding the length of the gas pipe 16 to this), an oil recovery control unit 28 that changes the operation time of the oil recovery operation is provided.
The oil recovery control unit 28 is configured to control the operation time during the oil recovery operation as follows in accordance with the control flow shown in FIG. The control flow of FIG. 2 is a flowchart of a reference example of the present invention in which the operation end time of the oil recovery operation is changed based on the refrigerant pipe length difference.

  In the oil recovery control unit 28, first, based on the detection result of the refrigerant pipe length, the refrigerant pipe length (Lmax) of the farthest indoor unit 3A having the longest refrigerant pipe 18A and the latest indoor unit 3C having the shortest refrigerant pipe 18C. It is determined whether or not the difference from the refrigerant pipe length (Lmin) is greater than a set pipe length difference Llim (for example, 40 m) (S1). If the refrigerant pipe length difference is smaller than the set pipe length difference Llim, the control shifts to normal control, and when the oil recovery operation is performed and the liquid back is detected on the outdoor unit 2 side, the refrigerant pipe length is determined based on the refrigerant pipe length. The oil recovery operation is terminated after the changed operation time Tk of the oil recovery operation (for example, after 30 seconds). When the refrigerant pipe length difference is larger than the set pipe length difference Llim, the end condition of the oil recovery operation is changed (S2).

  The change in the end condition of the oil recovery operation is determined based on the refrigerant pipe length difference (Lmax−Lmin) as to how much the operation end time of the oil recovery operation is delayed (S3). If the refrigerant pipe length difference (Lmax−Lmin) is within a set range (for example, 40 m <Lmax−Lmin ≦ 60 m), the operation end time is delayed from the specified end time by, for example, 30 seconds, and the oil recovery operation time is set to 30 seconds. Increase the length (S4). When the refrigerant pipe length difference (Lmax−Lmin) exceeds a set range (for example, 60 m), the operation end time is delayed from the specified end time by, for example, 60 seconds, and the oil recovery operation time is increased by 60 seconds ( S5). Then, the oil recovery operation unit 22 of the outdoor unit 2 side controller stores the operation end condition changed as described above (S6), thereby shifting to normal control and executing the oil recovery operation.

With the above configuration, the present embodiment provides the following operational effects.
During normal air-conditioning operation, a part of the lubricating oil discharged from the compressor 4 together with the refrigerant gas circulates in the refrigerant circuit 21 together with the refrigerant gas, and then returns to the compressor 4 again. Some of them stay in the indoor units 3A, 3B, 3C and their refrigerant pipes 18A, 18B, 18C, mainly gas side refrigerant pipes. The oil recovery operation is started at a predetermined timing, for example, when the operation time has passed for a predetermined time, or when the amount of lubricant flowing out reaches the limit amount.
In the oil recovery operation, the indoor electronic expansion valve 20 of each indoor unit 3A, 3B, 3C is set to a set opening degree for oil recovery operation by a cooling cycle, and a liquid back operation is performed and liquid is returned to the outdoor unit 2 side. As a result, the lubricating oil staying in the indoor units 3A, 3B, 3C, the refrigerant pipes 18A, 18B, 18C, and the like is washed away with the refrigerant flow and recovered to the compressor 4 side.

When the liquid is returned to the outdoor unit 2 side, this is detected and the oil recovery operation is terminated. Whether or not the liquid is backed by the outdoor unit 2 is detected by obtaining the degree of superheat of the suction refrigerant from the detection values of the low pressure sensor 23 and the suction refrigerant temperature sensor 24 provided in the inlet side refrigerant pipe 11 of the accumulator 10. Is possible. The oil recovery operation is ended after a predetermined time, in this embodiment, 30 seconds after the liquid back is detected on the outdoor unit 2 side.
In general, when the refrigerant pipe length is long, the pressure loss increases, so that the differential pressure that can be taken before and after the expansion valve also decreases, and the refrigerant flow rate decreases, so that the return of oil becomes worse. Further, when the refrigerant pipe length is long, the heat loss in the refrigerant pipe is large, and the refrigerant approaches an overheated state while flowing in the pipe even in the liquid back state. The oil is more likely to return when it is backed up, but the return of oil becomes worse when overheated.

  Therefore, in this reference example, the refrigerant pipe length difference (Lmax−Lmin) of each of the indoor units 3A, 3B, 3C that is detected in advance by the refrigerant pipe length detection unit 26 and stored in the refrigerant pipe length storage unit 27 is set. When compared with the pipe length difference Llim (for example, 40 m) (S1 in FIG. 2) and less than 40 m, as described above, the oil recovery operation is terminated when 30 seconds have elapsed after the liquid back detection. If the refrigerant pipe length difference (Lmax−Lmin) is 40 m or more, the end condition of the oil recovery operation is changed.

  The end condition of the oil recovery operation is determined based on whether or not the refrigerant pipe length difference between the indoor unit 3A and the indoor unit 3C is in a range of 40 m <Lmax−Lmin ≦ 60 m (S3 in FIG. 2). In the case of 40 m to 60 m, the oil recovery operation time is extended by 30 seconds (S4 in FIG. 2), and the oil recovery operation is terminated when 60 seconds have elapsed after detecting the liquid back on the outdoor unit 2 side. If the refrigerant pipe length difference exceeds 60 m, the oil recovery operation time is extended by 60 seconds (S5 in FIG. 2), and 90 seconds have elapsed after the liquid back is detected on the outdoor unit 2 side. The oil recovery operation is terminated. As described above, even if the refrigerant pipe length is different for each of the indoor units 3A, 3B, and 3C, the operation time during the oil recovery operation is changed based on the refrigerant pipe length of each of the indoor units 3A, 3B, and 3C. An appropriate oil recovery operation time commensurate with the long indoor unit 3A can be secured. For this reason, the lubricating oil staying in each indoor unit 3A, 3B, 3C and its refrigerant circuit can be reliably recovered.

  In particular, in this reference example, the refrigerant pipe length difference of each indoor unit 3A, 3B, 3C is judged, and the operation end time is changed during the oil recovery operation based on the refrigerant pipe length difference. When it is determined that the pipe length difference is large, the end time of the oil recovery operation can be delayed and the operation time can be lengthened by a time corresponding to the difference. For this reason, the lubricating oil accumulated in the indoor unit 3A having a long refrigerant pipe length and the refrigerant pipe 18A can be reliably recovered to the compressor 4 side. Accordingly, a predetermined amount of lubricating oil can always be held in the compressor 4, and the situation where the compressor 4 falls short of the lubricating oil due to the oil rising phenomenon toward the refrigerant circuit 21 side and causes poor lubrication is surely eliminated. be able to.

In the above reference example, when the refrigerant pipe length difference is equal to or larger than the set pipe length difference, the operation time of the oil recovery operation is changed to two stages, but may be changed to three stages or more or continuously. It may be changed.
Moreover, although the operation time at the time of oil collection | recovery operation is changed based on the refrigerant | coolant piping length difference of each indoor unit 3A, 3B, 3C, it is not restricted to this but various modifications are considered as follows.
First, based on the refrigerant pipe length detection result of each indoor unit 3A, 3B, 3C, the distribution state of the refrigerant pipe length is judged, and when there are many indoor units whose refrigerant pipe length is longer than the average refrigerant pipe length The oil recovery operation end time is delayed and the oil recovery operation time is lengthened by the time corresponding thereto. As a result, similarly to the above-described embodiment, the indoor unit having a long refrigerant pipe length and the lubricating oil accumulated in the refrigerant pipe can be reliably recovered to the compressor 4 side. Therefore, a sufficient amount of lubricating oil can always be ensured in the compressor 4, and the poor lubrication due to the lack of lubricating oil can be reliably eliminated.

Second, based on the refrigerant pipe length detection result of each indoor unit 3A, 3B, 3C, the refrigerant pipe lengths of all the indoor units 3A, 3B, 3C are integrated, and based on the integrated refrigerant pipe length, the integrated refrigerant When it is determined that the pipe length is longer than the reference pipe length, the end time of the oil recovery operation is delayed by a time corresponding to the length, and the oil recovery operation time is lengthened. Also by this, the same effect as the reference example can be obtained.
On the other hand, in each of the above reference examples, the end time of the oil recovery operation is delayed according to the indoor unit having a longer refrigerant pipe length based on the refrigerant pipe length of each indoor unit 3A, 3B, 3C, and the oil recovery operation time is reduced. On the contrary, a reference oil recovery operation time is set corresponding to the indoor unit 3A having a long refrigerant pipe length, and the oil recovery operation is started for the indoor unit 3C having a short refrigerant pipe length. You may make it change time . That is, the oil recovery operation is sequentially started from the indoor unit 3A having a long refrigerant pipe length, and the indoor unit 3C having a long refrigerant pipe length is delayed for the indoor unit 3C having a short refrigerant pipe length by delaying the start time of the oil recovery operation. Increases the oil recovery operation time and shortens the oil recovery operation time for the indoor unit 3C having a short refrigerant pipe length.

  Thus, an appropriate oil recovery operation time is ensured for each of the indoor units 3A, 3B, and 3C, and the lubricating oil accumulated in the long refrigerant pipe 3A and the refrigerant pipe 18A can be reliably collected. Accordingly, a predetermined amount of lubricating oil can always be held in the compressor 4, and the situation where the compressor 4 falls short of the lubricating oil due to the oil rising phenomenon toward the refrigerant circuit 21 side and causes poor lubrication is surely eliminated. be able to.

In this reference example , the operation time changed during the oil recovery operation is not limited to the above, and can be set as appropriate. However, since the oil recovery operation is a liquid back operation, it is desirable to limit the maximum operation time in consideration of the capacity of the accumulator 10 and the like.

Next, an embodiment of the present invention will be described with reference to FIG.
This embodiment differs in the structure of the oil collection | recovery control part 38 with respect to the above-mentioned reference example . The other points are the same as in the reference example, and thus the description thereof is omitted.
The oil recovery control unit 38 of this embodiment changes the opening time of each indoor electronic expansion valve 20 based on the refrigerant pipe length of each indoor unit 3A, 3B, 3C instead of changing the operation time during the oil recovery operation. The configuration is to be changed.
The oil recovery control unit 38 controls the opening degree of each indoor electronic expansion valve 20 during the oil recovery operation as follows according to the control flow shown in FIG.

  In the oil recovery control unit 38, as shown in FIG. 3, the refrigerant pipe 18A is the longest based on the detection result of the refrigerant pipe length detected by the refrigerant pipe length detection unit 26 and stored in the refrigerant pipe length storage unit 27. Whether or not the difference between the refrigerant pipe length (Lmax) of the farthest indoor unit 3A and the refrigerant pipe length (Lmin) of the latest indoor unit 3C having the shortest refrigerant pipe 18C is larger than the set pipe length difference Llim (for example, 40 m). Is determined (S11). If the refrigerant pipe length difference is smaller than the set pipe length difference Llim, the control shifts to normal control, the above oil recovery operation is performed, and when a liquid back is detected on the outdoor unit 2 side, the oil recovery operation is performed 30 seconds later. Is terminated. When the refrigerant pipe length difference is larger than the set pipe length difference Llim, the operating conditions of the oil recovery operation, that is, the opening degrees of the indoor electronic expansion valves 20 of the indoor units 3A, 3B, 3C are as follows. Will be changed.

First, the average length of the refrigerant pipes 18A, 18B, 18C of each indoor unit 3A, 3B, 3C (actually, the length of the low-pressure gas pipe obtained by adding the length of the gas pipe 16 to this) (Abbreviated and referred to as “Lave” hereinafter) is calculated by Lave = (Lmax−Lmin) / 2 (S12). Next, the refrigerant pipe lengths (Li: i = 1 to 1) of all the indoor units 3A, 3B, and 3C are compared with the average length Lave (S13), and it is determined whether Li> Lave. (S14). As a result, if Li is large (Yes), it is continuously determined whether Li> Lave + 20 (S15). If Li is small (No), it is continuously determined whether Li> Lave-20. (S16).
Here, the above “+20” and “−20” are “X pulses” corresponding to the opening degree to be changed with respect to the set opening degree of each indoor electronic expansion valve 20 during the oil recovery operation. In some cases, for example, “X = + 20 pulses” and “X = −20 pulses” are used.

  Next, if Li> Lave + 20 is compared and Li is large (Yes), the indoor electronic expansion valve 20 of the indoor unit is, for example, a set opening degree + 40 pulses, and the opening degree is larger by 40 pulses than the set opening degree. (S17). Moreover, when Li is small (No), the indoor electronic expansion valve 20 of the indoor unit is set to, for example, a set opening degree + 20 pulses, and is set to an opening degree that is 20 pulses larger than the set opening degree (S18). On the other hand, when Li> Lave-20 is a comparison result and Li is large (Yes), the indoor electronic expansion valve 20 of the indoor unit is set to, for example, a set opening degree −20 pulses, and only 20 pulses from the set opening degree. A small opening is set (S19). Moreover, when Li is small (No), the indoor electronic expansion valve 20 of the indoor unit is set to, for example, a set opening degree −40 pulses, and is set to an opening degree that is smaller than the set opening degree by 40 pulses (S20). .

As described above, the opening degree of each indoor electronic expansion valve 20 is determined, an opening degree change command is issued to each indoor electronic expansion valve 20 (S21), and each indoor electronic expansion valve 20 is set to the opening degree. Oil recovery operation is carried out. Then, when the oil recovery operation is executed and the liquid back is detected on the outdoor unit 2 side as described above, the oil recovery operation is terminated after 30 seconds. In addition, as a method of changing the opening command value of each indoor electronic expansion valve 20, the following two methods are conceivable, and any method may be used.
(1) The changed opening degree of each indoor electronic expansion valve 20 is transmitted to each indoor unit 3A, 3B, 3C, and each indoor unit 3A, 3B, 3C stores the information and also stores it during oil recovery operation. In addition, the opening degree of each indoor electronic expansion valve 20 is corrected individually.
(2) At the time of oil recovery operation, the opening degree command of each indoor electronic expansion valve 20 corrected by the outdoor unit 2 is forcibly corrected with respect to each indoor unit 3A, 3B, 3C.

  As described above, even if the refrigerant pipe length is different for each of the indoor units 3A, 3B, and 3C, based on the refrigerant pipe length of each of the indoor units 3A, 3B, and 3C, By changing the opening, an appropriate amount of refrigerant corresponding to the length of the refrigerant pipe is supplied to each indoor unit 3A, 3B, 3C to perform a liquid back operation, and each indoor unit 3A, 3B, 3C and its refrigerant pipe The lubricating oil staying in 18A, 18B, 18C can be recovered. For this reason, the lubricating oil accumulated in the indoor unit 3A having a long refrigerant pipe length and the refrigerant pipe 18A can be reliably recovered to the compressor 4 side.

In particular, the refrigerant pipe length difference of each indoor unit 3A, 3B, 3C is judged, and based on the refrigerant pipe length difference, the opening degree of the indoor expansion valve 20 is increased as the indoor unit 3A has a longer refrigerant pipe length. As a result, the indoor unit 3A having a longer refrigerant pipe length can recover the lubricating oil by flowing more refrigerant and actively liquid back.
Therefore, also in the present embodiment, the predetermined amount of lubricating oil can always be held in the compressor 4 by the reliable recovery of the lubricating oil from the refrigerant circuit 21 side , and the compressor 4 falls into a shortage of lubricating oil and lubricates. It is possible to reliably eliminate the situation that leads to defects.

  In the above embodiment, the various sensors such as the low pressure sensor 23, the intake refrigerant temperature sensor 24, the heat exchange temperature sensor 25, etc. are normally used as they are, as they are already installed in this type of air conditioner 1. Well, there is no need to install a new one. Of course, the refrigerant pipe length detection unit 26 can also be used as a refrigerant pipe length detection system installed to supplement the refrigerant.

It is a refrigerant circuit block diagram of the air conditioning apparatus which concerns on one Embodiment of this invention. It is a control flowchart figure of the oil collection | recovery control part of the air conditioning apparatus which concerns on the reference example of this invention. It is a control flowchart figure of the oil collection | recovery control part of the air conditioning apparatus which concerns on one Embodiment of this invention.

DESCRIPTION OF SYMBOLS 1 Air conditioning apparatus 2 Outdoor unit 3A, 3A, 3C Indoor unit 4 Compressor 6 Outdoor heat exchanger 11, 18A, 18B, 18C Refrigerant piping 16 Gas piping 17 Liquid piping 19 Indoor heat exchanger 20 Indoor electronic expansion valve 21 Refrigerant circuit 22 Oil recovery operation part 26 Refrigerant pipe length detection part 27 Refrigerant pipe length storage part 28, 38 Oil recovery control part

Claims (2)

An outdoor unit having a compressor and an outdoor heat exchanger;
A plurality of indoor units having an indoor heat exchanger and an indoor expansion valve and connected in parallel to each other;
A refrigerant circuit configured by sequentially connecting the compressor of the outdoor unit and the indoor unit, the outdoor heat exchanger, the plurality of indoor heat exchangers, and an indoor expansion valve by a refrigerant pipe;
Each indoor unit is set in a liquid back operation at a predetermined timing, an oil recovery operation is performed to recover the lubricating oil staying in the refrigerant circuit, and the oil recovery is performed when a liquid back is detected on the outdoor unit side. In an air conditioner equipped with an oil recovery operation unit that terminates operation,
The oil recovery operation unit includes a refrigerant pipe length detection unit that detects a refrigerant pipe length of each indoor unit,
A refrigerant pipe length storage unit for storing the refrigerant pipe length detected by the refrigerant pipe length detection unit;
An oil recovery control unit that changes the opening of each indoor expansion valve during the oil recovery operation based on the refrigerant pipe length of each indoor unit stored in the refrigerant pipe length storage unit. An air conditioner characterized by. The oil recovery control unit determines the refrigerant pipe length difference between the indoor units, and based on the refrigerant pipe length difference, increases the opening of the indoor expansion valve as the indoor unit has a longer refrigerant pipe length. The air conditioning apparatus according to claim 1 .

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