Patent Application
20250003661
This application claims foreign priority benefits under 35 U.S.C. § 119 from French Patent Application No. 23/06837, filed Jun. 29, 2023, the content of which is hereby incorporated by reference it its entirety.
The present invention relates to a method of managing oil in a multi-compressor refrigeration system using oil level detection devices.
CN212867870U discloses a refrigerant compressor including a compressor casing, an oil sump arranged in a lower part of the compressor casing, and an oil level sensor arrangement positioned in the lower part of the compressor casing and configured to detect an oil level in the oil sump of the refrigerant compressor.
FR3124554A1 teaches about a refrigeration system including a refrigerant compressor with an oil level sensor arrangement, and a controller configured to control operation of the refrigerant compressor based on oil level detected by the oil level sensor arrangement of the refrigerant compressor. The oil level sensor arrangement is configured to provide a low oil level warning signal to the controller if the oil level in the oil sump reaches a predetermined low oil level. The controller is configured to stop the refrigerant compressor, for example without or with a predetermined delay of time, if a low oil level warning signal is provided to the controller.
Between a low oil level warning and stopping a compressor, it is recommended to perform some action in order to avoid the downtime of the compressor. There are active and passive oil management methods.
Active oil management methods monitor the refrigeration system in real time and the oil management is done by using additional valves and/or oil tanks. The control of the operation is based on the valves. Such solutions are complex and expensive.
Passive oil management methods performs oil management operations in a periodically or basically pre-determined way, regardless the actual status of the multi-compressor refrigeration system. Such solutions however noticeably influence the efficiency of the multi-compressor refrigeration system, as they perform oil management operations even if they are not necessary.
Moreover, a detected low oil level could result from oil return issue (oil is trapped in the refrigeration system) or from oil balancing issue between compressors. Depending on the low oil level reason, it is recommended to perform different actions.
EP1605212 discloses an air conditioner and a method for performing oil equalising operation in the air conditioner. The oil equalization may be performed when it is detected that an oil level in the oil reservoir of a particular one of the compressors is lower than a predetermined level. Compressors are connected by an oil equalizing tube to feed surplus oil in each of the compressors to the remaining compressors. An oil equalizing tube opening/closing valve is arranged in the oil equalizing tube. A method for performing an oil equalizing operation involves opening of valves to supply oil from one compressor oil sump to another and pressurizing the lubricant oil by the discharge pressure of one compressor and feeding the pressurized lubricant oil to another compressor.
However, this special design of the oil equalizing tubes leads to increased costs for the multi-compressor device.
It is an object of the present invention to provide an improved method for managing oil in a running multi-compressor refrigeration system which can overcome the drawbacks encountered in conventional multi-compressor refrigeration systems.
Particularly, an object of the present invention is to provide a method for managing oil in a running multi-compressor refrigeration system which is simple and easy to implement, which can provide a robust prevention of running compressor in lack of oil situation, especially if the oil is trapped in the refrigeration system outside the compressor manifold.
According to the invention, there is provided a method for managing oil in a running multi-compressor refrigeration system comprising a controller configured to control operation of the multi-compressor refrigeration system and a multi-compressor device including compressors which are parallelly coupled, a total number of compressors in the multi-compressor device being at least two and each compressor being equipped with an oil sump and an oil level detection device operatively connected to the controller and configured to detect an oil level in the respective oil sump, the oil sumps being connected through a common oil balancing line, the method including:
The method according to the present invention combines robust prevention of running compressor in lack of oil situation, since it monitors the operation of the compressors in in real time (claiming advantages of an active oil management) with an ease of implementation, since it does not require any additional valves, oil balancing lines or oil tanks (claiming advantages of a passive oil management). Moreover, the method according to the present invention imparts an improved efficiency to the multi-compressor refrigeration system, as it performs oil management only if necessary.
The method may also include one or more of the following features, taken alone or in combination.
According to an embodiment of the invention, the method further includes determining, for example through the controller, the number of running compressors in the multi-compressor device.
According to an embodiment of the invention, the method further includes determining, for example through the controller, the total number of compressors in the multi-compressor device.
Advantageously, the method further includes determining, for example through the controller, the percentage of running compressors in the multi-compressor device.
According to an embodiment of the invention, the method further includes:
According to an embodiment of the invention, the predetermined threshold condition is reached if:
Thanks to the above requirements, wrong fault detection of a lack of oil situation in the running compressor may be prevented and the efficiency and reliability of the multi-compressor refrigeration system may be further improved.
According to an embodiment of the invention, the oil balancing action includes keeping the operation of the running compressor for which a lack of oil situation has been detected and stopping the operation of the other running compressor or of all other running compressors, i.e. the other running compressor(s) for which a lack of oil situation has not been detected.
Particularly, if all compressors are running and a lack of oil situation is detected for one of the running compressors, it is assumed that there is an issue with the oil balancing (i.e. there is excessive oil in at least one of the running compressor for which a lack of oil situation has not been detected). In order to overcome this and to balance the oil level in all the compressors, the controller stops the operation of the other running compressor(s). Thanks to that action, the running compressor, for which a lack of oil situation has been detected, may withdraw more oil from the multi-compressor device and therefore increase the oil level in the respective oil sump. In another words, the pressure of the oil free surface of the stopped compressor is increased (reduced pressure drop), and its potential excessive amount of oil is sent to adjacent compressor through the common oil balancing line.
According to an embodiment of the invention, if all compressors are running, the oil balancing action includes keeping the operation of the running compressor for which a lack of oil situation has been detected and stopping the operation of the other running compressor or of all other running compressors, i.e. the other running compressor(s) for which a lack of oil situation has not been detected.
According to an embodiment of the invention, the oil balancing action includes stopping the operation of the running compressor for which a lack of oil situation has been detected and starting the operation of an idle compressor, i.e. an idle compressor for which a lack of oil situation has not been detected, in order to maintain substantially identical the workload of the multi-compressor refrigeration system. Particularly, if not all compressors are running and a lack of oil situation is detected for one of the running compressors, it is assumed that there is an issue with the oil balancing (i.e. there is excessive oil in the compressors for which a lack of oil situation has not been detected). In order to overcome this and to balance the oil level in all the compressors, the controller stops the operation of the running compressor for which a lack of oil situation has been detected, keeps the operation of the running compressor(s) for which a lack of oil situation has not been detected and starts the operation of an idle compressor for which a lack of oil situation has not been detected. Thanks to that action, the multi-compressor refrigeration system maintains the required workload, balances the oil between compressors and protects the compressor in lack of oil situation and allows the compressor in lack of oil situation to recover some oil. Indeed, a suction bypass is created by the common oil balancing line, so some refrigerant charged with oil will still come inside this compressor and fill in oil the compressor oil sump.
According to an embodiment of the invention, if not all compressors are running, and thus if at least one compressor is idle, the oil balancing action includes stopping the operation of the running compressor for which a lack of oil situation has been detected and starting the operation of an idle compressor, i.e. an idle compressor for which a lack of oil situation has not been detected, in order to maintain substantially identical the workload of the multi-compressor refrigeration system.
According to an embodiment of the invention, the oil balancing action includes stopping the operation of all compressors. By doing so, it is possible to use the principle of communicating vessels in order to balance the oil level between the compressors.
According to an embodiment of the invention, the oil returning action includes increasing the workload of the multi-compressor refrigeration system. By increasing the workload of the multi-compressor refrigeration system, an oil boost can be provided and the oil can return to the multi-compressor device and thus to the compressors. Indeed, due to the increase of the workload, the demand for the oil supply is increased, and the oil can be withdrawn from the farther parts of the multi-compressor refrigeration system.
According to an embodiment of the invention, if the total number of compressors in the multi-compressor is equal to two, the oil returning action includes keeping the operation of the running compressor for which a lack of oil situation has been detected and starting the operation of the idle compressor, i.e. the idle compressor for which a lack of oil situation has not been detected. Therefore, if the total number of compressors in the multi-compressor is equal to two and if one compressor is idle, the oil returning action includes keeping the operation of the running compressor for which a lack of oil situation has been detected and starting the operation of the idle compressor. Particularly, if only one of two compressors is running (50% load) and a lack of oil situation is detected for one of the running compressors, it is assumed that there is an issue with oil return from the refrigeration system to compressors (the oil is trapped in the refrigeration system outside the multi-compressor device). In order to overcome this and to return the oil to the multi-compressor device, and particularly to the compressor for which a lack of oil situation has been detected, the controller starts the operation of the idle compressor.
Thanks to that action, an oil boost can be provided and the oil can return to the multi-compressor device and particularly to the running compressor for which a lack of oil situation has been detected.
According to an embodiment of the invention, if the total number of compressors in the multi-compressor is higher than two, the oil returning action includes stopping the operation of the running compressor for which a lack of oil situation has been detected and starting the operation of at least two idle compressors, and for example of all idle compressors, i.e. the idle compressor(s) for which a lack of oil situation has not been detected. Particularly, if only one compressor is running and all other compressors are idle and a lack of oil situation is detected for the running compressors, it is assumed that there is an issue with the oil return from the refrigeration system to the multi-compressor device (the oil is trapped in the refrigeration system outside the multi-compressor device). In order to overcome this and to return the oil to compressors, the controller stops the running compressor for which a lack of oil situation has been detected and starts all other compressors. Thanks to that action, an oil boost can be provided and the oil can return to the multi-compressor device and particularly to the running compressor for which a lack of oil situation has been detected.
According to an embodiment of the invention, if the total number of compressors in the multi-compressor is higher than two and if only one compressor is running and all other compressors are idle, the oil returning action includes stopping the operation of the running compressor for which a lack of oil situation has been detected and starting the operation of all idle compressors.
According to an embodiment of the invention, the oil returning action includes opening an electronic expansion valve of the multi-compressor refrigeration system in order to increase suction mass flow of the multi-compressor device. By the increased suction mass flow, the oil can be withdrawn from farther parts of the refrigeration system and returned to the multi-compressor device and particularly to the running compressor for which a lack of oil situation has been detected.
According to an embodiment of the invention, the oil returning action additionally includes opening an electronic expansion valve of the multi-compressor refrigeration system in order to increase suction mass flow of the multi-compressor device. Thus, by combining the increase of the suction mass flow and the increase of the workload of the multi-compressor refrigeration system, the oil boost is enhanced.
According to an embodiment of the invention, the method further includes stopping the operation of all compressors, if, after lapse of a third predetermined time period, for example two minutes, from the start of the oil managing action, a lack of oil situation is still detected for the compressor for which a lack of oil situation has previously been detected. In other words, the method further includes stopping the operation of all compressors, if the predetermined threshold condition remains in the respective compressor for a third predetermined time, for example two minutes, from the start of the oil managing action. Particularly, if the lack of oil situation remains after having performed the oil managing action, it is assumed that there a lack of oil trip situation and the controller stops the operation of the whole refrigeration system for safety reasons.
According to an embodiment of the invention, the method further includes going back to the monitoring step, if the lack of oil situation disappears before lapse of the third predetermined time period.
According to an embodiment of the invention, the oil level detection device of each compressor includes an oil level sensor or an oil level switch.
According to an embodiment of the invention, the method further includes providing a low oil level warning, if a lack of oil situation is detected for a running compressor.
According to an embodiment of the invention, each compressor of the multi-compressor device is a scroll compressor.
According to an embodiment of the invention, each oil level detection device is at least partially located in the respective oil sump.
According to an embodiment of the invention, each compressor includes a compressor casing, and the respective oil sump is arranged in a lower part of said compressor casing.
According to an embodiment of the invention, if the total number of compressors in the multi-compressor device is 5 or above and a half or less of the total number of compressors are running and at least two compressors are running, the oil managing action includes:
According to an embodiment of the invention, the predetermined length of the piping is 10 metres.
The present invention also relates to a multi-compressor refrigeration system comprising:
According to an embodiment of the invention, the multi-compressor refrigeration system further comprises a refrigerant circulation circuit successively including a condenser, an electronic expansion valve, an evaporator and the multi-compressor device connected in series.
According to an embodiment of the invention, the multi-compressor refrigeration system is devoid of opening/closing valves and/or oil tanks.
According to an embodiment of the invention, the compressors may be fixed speed compressors or variable speed compressors.
According to other embodiments of the invention, the compressors may be of other type than scroll compressors, i.e. the compressors may be especially screw compressors or piston compressors.
The following detailed description of two embodiments of the invention is better understood when read in conjunction with the appended drawings being understood, however, that the invention is not limited to the specific embodiments disclosed.
The multi-compressor device 7 includes a plurality of compressors 8 which are parallelly coupled. According to the embodiment shown on
Each compressor 8 includes a compressor casing 9 provided with a suction fitting 11 configured to supply the respective compressor 8 with refrigerant gas to be compressed and a discharge fitting 12 configured to discharge compressed refrigerant gas.
Advantageously, each compressor 8 is a scroll compressor, and includes a compression unit 13 disposed inside the respective compressor casing 9 and configured to compress the refrigerant gas supplied by the respective suction fitting 11. Each compression unit 13 includes a fixed scroll, which is fixed in relation to the respective compressor casing 9, and an orbiting scroll configured to perform an orbiting movement relative to the respective fixed scroll during operation of the respective compressor 8.
Each compressor 8 also includes an oil sump 14 arranged at a lower part of the respective compressor casing 9, and an oil level detection device 15 located in the respective oil sump 14 and configured to detect an oil level in the respective oil sump 14. Each oil level detection device 15 may be an oil level sensor or an oil level switch. Advantageously, each oil level detection device 15 is configured to output a low oil level warning signal if the oil level in the oil sump 14 of the respective compressor 8 reaches a predetermined low oil level value.
The multi-compressor device 7 further includes a common suction line 16 and inlet connection lines 17 each connecting the common suction line 16 to the suction fitting 11 of a respective compressor 8. The multi-compressor device 7 also includes a common discharge line 18 and outlet connection lines 19 each connecting the common discharge line 18 to the discharge fitting 12 of a respective compressor 8.
Furthermore, the multi-compressor device 7 includes a common oil balancing line 20.1 and balancing connection lines 20.2, also named balancing branch lines, each connecting the common oil balancing line 20.1 to an oil balancing connection 20.3 provided on the compressor casing 9 of a respective compressor 8. The common oil balancing line 20.1 and the balancing connection lines 20.2 are particularly configured to fluidly connect the oil sumps 14 of the compressors 8, and thus to allow oil to flow between the compressors 8 and to balance the oil levels within the compressors 8.
The multi-compressor refrigeration system 2 further includes a controller 21 configured to control operation of the multi-compressor refrigeration system 2, and particularly to control operation (starting or stopping) of the compressors 8 and to control which compressor(s) 8 is(are) in operation. The controller 21 may for example includes a microprocessor and a memory. Each oil level detection device 15 is particularly operatively connected to the controller 21.
The method particularly includes:
Particularly, if the lack of oil situation remains after having performed the oil managing action, it is assumed that there a lack of oil trip situation and the controller 21 stops the operation of the whole multi-compressor refrigeration system 2 for safety reasons. However, if the lack of oil situation disappears, that means that the oil managing action has been successful and the oil sump 14 of the compressor 8, for which the lack of oil situation has previously been detected, now includes enough oil.
Advantageously, the predetermined threshold condition is reached if:
Thanks to the above requirements, wrong fault detection of a lack of oil situation in the running compressor 8 may be prevented.
Depending on the actual operation condition of the multi-compressor refrigeration system 2, the oil managing action may take different forms.
The oil managing action includes the following steps:
Particularly, if all compressors 8 are running (i.e. if 100% of the compressors are running), the oil balancing action includes keeping the operation of the running compressor for which a lack of oil situation has been detected and stopping the operation of the other running compressor(s) 8, i.e. the other running compressor(s) for which a lack of oil situation has not been detected.
However, if not all compressors 8 are running (i.e. the percentage of running compressors is different from 100%), and thus if at least one compressor 8 is idle, the oil balancing action includes stopping the operation of the running compressor 8 for which a lack of oil situation has been detected and starting the operation of an idle compressor 8 in order to maintain substantially identical the workload of the multi-compressor refrigeration system 2.
According to the embodiment shown on
Such an increase of the workload of the multi-compressor refrigeration system 2 could be obtained in various ways.
For example, if the total number of compressors 8 in the multi-compressor is equal to two, the oil returning action includes keeping the operation of the running compressor 8 for which a lack of oil situation has been detected and starting the operation of the idle compressor 8, i.e. the idle compressor 8 for which a lack of oil situation has not been detected.
However, if the total number of compressors 8 in the multi-compressor is higher than two, the oil returning action includes stopping the operation of the running compressor 8 for which a lack of oil situation has been detected and starting the operation of all idle compressors 8.
The oil returning action may additionally include opening the electronic expansion valve 5 of the multi-compressor refrigeration system 2 in order to increase suction mass flow of the multi-compressor device 7. By the increased suction mass flow, the oil can be withdrawn from farther parts of the multi-compressor refrigeration system 2 and returned to the multi-compressor device 7 and particularly to the running compressor 8 for which a lack of oil situation has been detected. Thus, by combining the increase of the suction mass flow and the increase of the workload of the multi-compressor refrigeration system 2, the oil boost is enhanced.
Several scenarios of the present method are disclosed hereafter.
If both compressors 8 in the multi-compressor refrigeration system 2 are running and a lack of oil situation is detected for one of the running compressors 8 (e.g. first compressor), it is assumed that there is an issue with the oil balancing (there is excessive oil in the second compressor). In order to overcome this and to balance the oil levels in the compressors 8, the controller 21 stops the operation of the other running compressor 8 (the second compressor), in which the lack of oil situation has not been detected. Thanks to that action, the first compressor may withdraw more oil from the multi-compressor device 7 and therefore increase the oil level in the respective oil sump 14.
If only one of two compressors 8 (e.g. first compressor) is running (50% load) and a lack of oil situation is detected for this running compressor 8 (first compressor), it is assumed that there is an issue with oil return from the multi-compressor refrigeration system 2 to the compressors 8 (the oil is trapped in the system outside the multi-compressor device 7). In order to overcome this and to return the oil to the multi-compressor device 7, and particularly to the compressor 8 for which a lack of oil situation has been detected, the controller 21 starts the operation of the idle compressor 8 (second compressor). Thanks to that action, an oil boost can be provided and the oil can return to the multi-compressor device 7 and particularly to the running compressor 8 for which a lack of oil situation has been detected.
In another embodiment of the invention, in order to overcome the issue with oil return from the multi-compressor refrigeration system 2 to the compressors 8, the controller 21 may open the electronic expansion valve 5 of the refrigeration system in order to increase suction mass flow. Opening the electronic expansion valve 5 of the refrigeration system in order to increase suction mass flow may be also applied additionally to starting the operation of the idle compressor 8, in order to further enhance the oil boost.
If all compressors 8 are running and a lack of oil situation is detected for one of the running compressors 8 (e.g. first compressor), it is assumed that there is an issue with the oil balancing (there is excessive oil in the second compressor and/or third compressor). In order to overcome this and to balance the oil levels in the compressors 8, the controller 21 keeps the operation of the first compressor and stops the operation of all other compressors 8 (second compressor and third compressor). Thanks to that action, the first compressor may withdraw more oil from the multi-compressor device 7 and therefore increase the oil level in the respective oil sump 14.
If two compressors 8 are running (e.g. first compressor and second compressor) and one compressor 8 is idle (e.g. third compressor) and a lack of oil situation is detected for one of the running compressors (e.g. first compressor), it is assumed that there is an issue with the oil balancing (there is excessive oil in the second compressor and third compressor). In order to overcome this and to balance the oil levels in the compressors 8, the controller 21 changes the ON/OFF configuration of the multi-compressor refrigeration system 2 while keeping the same workload. Specifically, the controller 21 stops the operation of the first compressor, keeps the operation of the other running compressor 8 (second compressor) and starts the operation of the idle compressor 8 (third compressor). Thanks to that action, the multi-compressor refrigeration system 2 maintains the required workload and balances the oil levels in the compressors.
If only one compressor 8 is running (e.g. first compressor) and all other compressors 8 are idle (e.g. second compressor and third compressor) and a lack of oil situation is detected for the running compressor 8 (first compressor), it is assumed that there is an issue with the oil return from the multi-compressor refrigeration system 2 to the compressors 8. In order to overcome this and to return the oil to the compressors, the controller 21 stops the running compressor 8 for which a lack of oil situation has been detected (first compressor) and starts all other compressors 8 (second compressor and third compressor). Thanks to that action, an oil boost can be provided and the oil can return to the multi-compressor device 7 and particularly to the first compressor.
If only two compressors 8 are running and all other compressors 8 are idle and a lack of oil situation is detected for one of the running compressors 8, it is assumed that there might be an issue with the oil balancing or an issue with the oil return. In order to overcome this, the controller 21 may first perform the oil balancing action for a fourth predetermined time period. If the lack of oil situation does not disappear before lapse of the fourth predetermined time period for one of the running compressors 8, the controller 21 may then perform the oil returning action.
The oil balancing action and the oil returning action may be performed as described above in relation to other scenarios.
In general and as shown in
“Short piping” system relates to “monobloc” systems with all components of the refrigerant circuit (an evaporator, a condenser, a compressor and an expansion valve) being located on the same compact frame. The dimension of the circuit between the evaporator and the compressor is about 2 metres and the dimension of the circuit between the condenser and the compressor is also about 2 metres.
“Long piping” (“split”) system relates to systems with several smaller units within a refrigeration system connected by a refrigerant pipe. In other words, in “long piping” systems at least one heat exchanger unit (an evaporator or a condenser) is located separately from the unit with a compressor. The distance between the units may be up to 30 metres.
In another embodiment of the invention, in order to overcome the issue with oil return from the multi-compressor refrigeration system 2 to the compressors 8, the controller 21 may open the electronic expansion valve 5 of the refrigeration system in order to increase suction mass flow. Opening the electronic expansion valve 5 of the refrigeration system in order to increase suction mass flow may be also applied additionally to starting the operation of the idle compressors 8, in order to further enhance the oil boost.
Regardless the scenarios, if, after the start of the oil managing action, the lack of oil situation remains for two minutes, then there is a lack of oil trip situation and the controller 21 stops the operation of the whole multi-compressor refrigeration system 2 by stopping the operation of all compressors 8.
In other scenarios than described above, no oil managing action is needed.
Of course, the invention is not restricted to the embodiments described above by way of non-limiting examples, but on the contrary it encompasses all embodiments thereof.
While the present disclosure has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this disclosure may be made without departing from the spirit and scope of the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 23/06837 | Jun 2023 | FR | national |
