Patent Application
20250012490
This application claims priority to French Patent Application No. 23/07222, filed on Jul. 6, 2023, which is incorporated by reference herein in its entirety.
The present invention relates to a multi-compressor refrigeration system and a method for balancing oil in a multi-compressor refrigeration system.
A gas turbine engine typically includes a fan section, a compressor section, a combustor section, and a turbine section. Air entering the compressor section is compressed and delivered into the combustion section where it is mixed with fuel and ignited to generate a high-speed exhaust gas flow. The high-speed exhaust gas flow expands through the turbine section to drive the compressor and the fan section.
Good oil balancing is an important issue related to multi-compressor systems.
The most common solutions include providing oil equalization lines between compressors, oil level detecting means in each compressor and pumps for providing oil flow in the oil equalization lines between compressors and a controller to control the operation of the multi-compressor system. The general idea is that once the oil level detection means detect a low oil level in a particular compressor, the controller may operate the respective oil pump located in the respective oil equalization line and pump some oil from the compressor with a high oil level to the compressor with a low oil level.
While these solutions may be sufficient for multi-compressor systems with a relatively small number of compressors (e.g., 2 or 3), it becomes very difficult and, in particular, expensive to implement such solution into multi-compressor systems with higher numbers of compressors. The price of the oil pump contributes to the final cost of a multi-compressor system.
A good oil balancing configuration is usually not difficult to achieve, and can be obtained in most cases by adding passive features (e.g., suction washer, restrictor, etc.) in the suction line. This has a limited impact on pressure drop and overall refrigeration system efficiency. In such cases there is no need for external actuators like oil pumps.
However, when it comes to a bigger multi-compressor refrigeration system, the situation can dramatically change. In trio configurations with passive devices embedded in the suction line, the refrigeration system may experience a pressure drop sufficient to affect the efficiency of the refrigeration system. In these cases, external actuators, like oil pumps, may be very valuable.
DE1915174 A1 discloses an oil level compensation system, wherein each compressor in a multi-compressor system has an oil level sensor and an oil pump. A controller actuates an oil flow based on the output from the oil level sensors from the compressor with a high oil level to the compressor with a low oil level. However, such solutions are complex and expensive, and require as many pumps as compressors.
EP0840870 A1 discloses an oil level control apparatus for controlling the oil level in each compressor of a multi-compressor system. Particularly, each compressor is fluidly connected to an additional oil reservoir, and the oil level control apparatus is able to maintain the oil level within a compressor between a predetermined minimum level and a predetermined maximum level. In the event that the oil level in a compressor drops below the predetermined minimum level, oil is added to said compressor from the additional oil reservoir. In the event that the oil level in a compressor exceeds the predetermined maximum level, oil is returned from the compressor to the additional oil reservoir. However, such solutions are also complex and expensive, and require additional oil reservoir and piping.
CN100516682C discloses a multi-compressors system divided into groups, wherein each group comprises one oil pump and at least two compressors. Such arrangements allow the system to balance oil between groups. However, it does not solve the problem if only a particular compressor in the group needs oil. Therefore, such arrangements may lead to creating excessive oil levels in compressors.
JPH04116349A discloses a multi-compressor system with an oil pump capable of switching over its transfer directions. However, in this arrangement, the oil pump and the compressors are spaced apart by a distance which affects the efficiency of the system. Moreover, this solution does not solve the problem with a high number of compressors in a multi-compressor system. Moreover, an additional oil tank is required, as a direct oil flow between compressors is not possible.
It is an object of the present invention to provide an improved 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 multi-compressor refrigeration system which is simple, reliable and cheap, while ensuring reliable oil balancing even if the multi-compressor system comprises a high number of compressors. According to the invention such a multi-compressor refrigeration system comprises a controller configured to control operation of the multi-compressor refrigeration system, and a multi-compressor device including: at least three compressors which are parallelly coupled, each compressor being equipped with a suction fitting, 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, wherein the compressors in the multi-compressor device are divided into at least two groups, each group including at least one compressor and at least one group including at least two compressors; a common suction line configured to fluidly connect the suction fittings of all compressors of the multi-compressor device; a common oil equalization line configured to fluidly connect the oil sumps of all compressors of the multi-compressor device; an oil pumping device located in the common oil equalization line and operatively connected to the controller, the oil pumping device comprising at least one oil pump; characterized in that the oil pumping device is located between two groups such that one of said two groups is located on a first side of the oil pumping device and the other of said two groups is located on a second side of the oil pumping device, and in that the multi-compressor device further includes at least one valve located in the common oil equalization line and associated with a group including at least two compressors, the at least one valve being operatively connected with the controller and being configured to control an oil flow in the common oil equalization line and between the oil pumping device and at least one compressor of the group associated with the at least one valve, the controller being configured to control operation of the oil pumping device and the at least one valve based on outputs from the oil level detection devices.
Due to such an arrangement of the oil pumping device and the at least one valve, it is possible to obtain a simple and cheap multi-compressor system with a very limited number of additional equipment. The present invention obtains reliable oil balancing without interfering with the common suction line and therefore the common suction line may be designed to be fully optimized for maximum efficiency, and thus the overall efficiency of the multi-compressor refrigeration system is improved. Moreover, the cost of a valve is much lower than the cost of an oil pump, so it is beneficial to replace oil pumps with valves.
The multi-compressor refrigeration system may also include one or more of the following features, taken alone or in combination.
According to an embodiment of the invention, the compressors in the multi-compressor device are divided into two groups.
According to an embodiment of the invention, each compressor includes an oil balancing connection, the common oil equalization line being configured to fluidly connect the oil balancing connections of all compressors of the multi-compressor device.
According to an embodiment of the invention, the controller is configured to determine a current amount of oil in each compressor based on outputs from the oil level detection devices.
According to an embodiment of the invention, the controller is configured to: monitor an oil level in the oil sump of each compressor through the respective oil level detection device; detect, for example based on a signal outputted from an oil level detection device, that a low oil level situation, also named lack of oil situation, occurs in a respective compressor, if the oil level in said compressor reaches a predetermined low oil level condition; and perform an oil balancing action if a low oil level situation is detected for a compressor, the oil balancing action including controlling operation of the oil pumping device and the at least one valve so as to transfer oil from the oil sump of at least one compressor of the multi-compressor device for which a low oil level situation has not been detected to the oil sump of the compressor for which a low oil level situation has been detected.
According to an embodiment of the invention, each oil level detection device is configured to output a low oil level warning signal if the oil level in the oil sump of the respective compressor reaches a predetermined low oil level value.
According to an embodiment of the invention, the predetermined low oil level condition is reached for a compressor if a low oil level warning signal is outputted from the respective oil level detection device.
According to an embodiment of the invention, the predetermined low oil level condition is reached for a compressor if: the low oil level warning signal outputted from the respective oil level detection device is continuously outputted for a first predetermined time, and for example for at least ten seconds; or the low oil level warning signal outputted from the respective oil level detection device has switched, i.e. has switched on and off, more than a predetermined number of times, and for example more than ten times, within a second predetermined time, and for example within a minute.
According to an embodiment of the invention, the controller is configured to detect that an excess oil situation occurs in a respective compressor, if the oil level in said compressor reaches a predetermined high oil level condition.
According to an embodiment of the invention, the oil balancing action includes controlling operation of the oil pumping device and the at least one valve so as to transfer oil from the oil sump of at least one compressor of the multi-compressor device for which an excess oil situation has been detected to the oil sump of the compressor for which a low oil level situation has been detected.
According to an embodiment of the invention, the oil balancing action includes: if oil balancing is required between compressors from different groups, controlling operation of the oil pumping device and the at least one valve so as to transfer oil from the oil sump of at least one compressor, for which a low oil level situation has not been detected and belonging to a group different from the group including the compressor for which a low oil level situation has been detected, to the oil sump of the compressor for which a low oil level situation has been detected; if oil balancing is required between compressors from a same group, controlling operation of the oil pumping device and the at least one valve so as to transfer oil from the oil sump of at least one compressor, for which a low oil level situation has not been detected and belonging to the same group as the compressor for which a low oil level situation has been detected, to a temporary oil vessel and then from the temporary oil vessel to the oil sump of the compressor for which a low oil level situation has been detected, wherein the temporary oil vessel is constituted by the oil sump of at least one compressor belonging to a group different from the group including the compressor for which a low oil level situation has been detected.
According to an embodiment of the invention, the controller is configured to determine the amount of oil that has to be transferred to a compressor for which a low oil level situation has been detected in order to reach a predetermined oil level in said compressor.
According to an embodiment of the invention, the controller is configured to calculate a risk of a low oil level occurrence in a compressor at a given running condition and to control operation of the oil pumping device and the at least one valve based on the calculation.
According to an embodiment of the invention, the controller is configured to control the oil pumping device and the at least one valve in order to deliver more oil to a compressor that has a high risk of a low oil level occurrence and/or to control the oil pumping device and the at least one valve in order not to withdraw oil from a compressor that has a high risk of a low oil level occurrence.
According to an embodiment of the invention, the at least one oil pump includes a volumetric oil pump configured to measure and output an amount of pumped oil.
According to an embodiment of the invention, the oil pump is a variable speed oil pump.
According to an embodiment of the invention, the at least one oil pump includes two one-way oil pumps, for example two one-way volumetric oil pumps, which are connected in parallel.
According to an embodiment of the invention, the at least one oil pump includes a bidirectional oil pump, and for example a bidirectional volumetric oil pump.
According to an embodiment of the invention, the oil pumping device comprises only one bidirectional oil pump. Such a configuration of multi-compressor refrigeration system eases the control of the multi-compressor refrigeration system and substantially reduces its manufacturing cost.
According to an embodiment of the invention, the oil pump is an electromagnetic oil pump, and for example a bidirectional electromagnetic volumetric oil pump. Advantageously, the electromagnetic oil pump comprises a motor, a pumping member and an electromagnetic coupling arranged between the pumping member and the motor. The oil pump provides a static sealing and removes the risk of leakages. Furthermore, the oil pump, enables the multi-compressor refrigeration system to receive suitable certifications for working in highly dangerous conditions, like explosive atmospheres.
According to an embodiment of the invention, the at least one valve includes a normally closed solenoid valve.
According to an embodiment of the invention, the common suction line includes a main suction line and suction branches each connecting the main suction line to the suction fitting of a respective compressor.
According to an embodiment of the invention, the common oil equalization line includes a main oil equalization line and oil equalization branches each connecting the main oil equalization line to the oil sump of a respective compressor, and particularly to an oil balancing connection provided on a compressor casing of a respective compressor and fluidly connected to the respective oil sump. Each oil equalization branch is particularly connected to the main oil equalization line at an oil equalization line branching.
According to an embodiment of the invention, the at least one valve includes a three-way valve located at an oil equalization line branching of the common oil equalization line and configured to control an oil flow between the oil pumping device and two respective oil equalization branches of the common oil equalization line which are fluidly connected at said oil equalization line branching. In other words, said three-way valve may control an oil flow between the oil pumping device and two compressors that are, respectively, fluidly connected to oil equalization branches which are fluidly connected at said oil equalization line branching. Thus, said three-way valve may control an oil flow to more than one compressor.
According to an embodiment of the invention, the at least one valve includes a two-way valve located in an oil equalization branch of the common oil equalization line, which is fluidly connected to a respective compressor, and configured to control an oil flow between the oil pumping device and the respective compressor fluidly connected to said oil equalization branch. In other words, said two-way valve may control an oil flow to only one compressor.
According to an embodiment of the invention, each group includes at least two compressors.
According to said embodiment of the invention, the multi-compressor device includes a plurality of two-way valves each located in a respective oil equalization branch of the common oil equalization line, each two-way valve being operatively connected with the controller and being configured to control an oil flow between the oil pumping device and a respective compressor fluidly connected to said oil equalization branch, the controller being configured to control operation of the oil pumping device and the two-way valves based on outputs from the oil level detection devices.
According to said embodiment of the invention, each oil equalization branch is provided with a respective two-way valve.
According to an embodiment of the invention, at least one compressor of the multi-compressor device comprises at least two oil level detection devices.
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, 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, the multi-compressor refrigeration system further comprises a refrigerant circulation circuit including a condenser, an electronic expansion valve, an evaporator and the multi-compressor device connected in series.
According to an embodiment of the invention, at least one compressor of the multi-compressor device is a variable speed compressor.
According to an embodiment of the invention, at least one compressor of the multi-compressor device is a fixed speed compressor.
According to other embodiments of the invention, the compressors may be of a type other than scroll compressors, i.e. the compressors may be especially screw compressors or piston compressors.
According to an embodiment of the invention, the multi-compressor refrigeration system uses a low GWP (Global Warming Potential) refrigerant.
The present invention also relates to a method for balancing oil in a multi-compressor refrigeration system comprising a controller configured to control operation of the multi-compressor refrigeration system and a multi-compressor device including at least three compressors which are parallelly coupled, each compressor being equipped with a suction fitting, 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 of all compressors of the multi-compressor device being fluidly connected through a common oil equalization line and the suction fittings of all compressors of the multi-compressor device being fluidly connected through a common suction line, the method including: dividing the compressors in the multi-compressor device into at least two groups, wherein each group includes at least one compressor and at least one group comprises at least two compressors; providing an oil pumping device in the common oil equalization line and between two groups such that one of said two groups is located on a first side of the oil pumping device and the other of said two groups is located on a second side of the oil pumping device, the oil pumping device comprising at least one oil pump; providing at least one valve located in the common oil equalization line, the at least one valve being associated with a group including at least two compressors and being configured to control an oil flow in the common oil equalization line and between the oil pumping device and at least one compressor of the group associated with the at least one valve; monitoring an oil level in the oil sump of each compressor through the respective oil level detection device; detecting that a low oil level situation occurs in a compressor, if the oil level in said compressor reaches a predetermined low oil level condition; performing an oil balancing action if a low oil level situation is detected for a compressor, the oil balancing action including controlling operation of the oil pumping device and the at least one valve so as to transfer oil from the oil sump of at least one compressor of the multi-compressor device for which a low oil level situation has not been detected to the oil sump of the compressor for which a low oil level situation has been detected.
Thanks to the presence of the at least one valve, it is possible to accurately withdraw excess oil from a selected compressor with a high oil level and then to pump the oil to a selected compressor with a low oil level. This way, it is possible to keep the oil level in each compressor at the desired level, which is usually higher than minimum oil level and lower than maximum oil level.
According to an embodiment of the invention, the oil balancing action includes: if oil balancing is required between compressors from different groups, transferring, by controlling operation of the oil pumping device and the at least one valve, oil from the oil sump of at least one compressor, for which a low oil level situation has not been detected and belonging to a group different from the group including the compressor for which a low oil level situation has been detected, to the oil sump of the compressor for which a low oil level situation has been detected; if oil balancing is required between compressors from a same group, transferring, by controlling operation of the oil pumping device and the at least one valve, oil from the oil sump of at least one compressor, for which a low oil level situation has not been detected and belonging to the same group as the compressor for which a low oil level situation has been detected, to a temporary oil vessel and then from the temporary oil vessel to the oil sump of the compressor for which a low oil level situation has been detected, wherein the temporary oil vessel is constituted by the oil sump of at least one compressor belonging to a group different from the group including the compressor for which a low oil level situation has been detected.
This way, it is possible to balance oil within the multi-compressor refrigeration system without additional external oil tanks. When a compressor with a low oil level and a compressor with an excessive oil level are in different groups, the oil pumping device, which is located between the groups, just simply pump oil from the group with the excessive oil to the group with a low oil level. When a compressor with a low oil level and a compressor with an excessive oil level are in the same group, the oil pump first pumps the excessive oil from this group to the other group (e.g., the other group acts like a temporary oil tank), and then back to the group with the compressor with the low oil level.
According to an embodiment of the invention, the method includes dividing a multi-compressor refrigeration system into two groups.
According to an embodiment of the invention, the method includes calculating a risk of a low oil level occurrence in a compressor at a given running condition, and controlling operation of the oil pumping device and the at least one valve based on said calculation, for example in order to deliver more oil to a compressor that has a high risk of a low oil level occurrence, and/or controlling operation of the oil pumping device and the valves in order not to withdraw oil from a compressor that has a high risk of a low oil level occurrence. Advantageously, the method includes selecting at least one oil sump, from which oil is pumped for oil transferring, based on said calculation.
According to an embodiment of the invention, the method includes outputting a low oil level warning signal from an oil level detection device and to the controller, if the oil level in the oil sump of the respective compressor reaches a predetermined low oil level value.
According to an embodiment of the invention, the method includes calculating a risk of a low oil level occurrence in a compressor at a given running condition and operating the oil pumping device and the at least one valve based on that calculation.
According to an embodiment of the invention, wherein the oil pumping device and the at least one valve deliver more oil to a compressor that has a high risk of a low oil level occurrence and/or the oil pumping device and the at least one valve block the transfer of oil from a compressor that has a high risk of a low oil level occurrence.
The following detailed description of two embodiments of the invention is better understood when read in conjunction with the appended drawings. However, it should be understood that the invention is not limited to the specific embodiments disclosed.
The multi-compressor device 7 comprises at least three 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. The multi-compressor refrigeration system 2 may use a low GWP (Global Warming Potential) refrigerant as 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. However, according to another embodiment of the invention, the compressors 8 may be of other type than scroll compressors, such as screw compressors or piston compressors, for example.
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 configured to fluidly connect the suction fittings 11 of all compressors 8 of the multi-compressor device 7. The common suction line 16 includes a main suction line 17 and suction branches 18 each connecting the main suction line 17 to the suction fitting 11 of a respective compressor 8. The multi-compressor device 7 also includes a common discharge line 19 configured to fluidly connect the discharge fittings 12 of all compressors 8 of the multi-compressor device 7. The common discharge line 19 includes a main discharge line 21 and discharge branches 22 each connecting the main discharge line 21 to the discharge fitting 12 of a respective compressor.
Furthermore, the multi-compressor device 7 includes a common oil equalization 23 line configured to fluidly connect the oil sumps 14 of all compressors 8 of the multi-compressor device 7. The common oil equalization line 23 particularly includes a main oil equalization line 24 and oil equalization branches 25 each connecting the main oil equalization line 24 to the oil sump 14 of a respective compressor 8, and particularly to an oil balancing connection 26 provided on the compressor casing 9 of a respective compressor 8 and fluidly connected to the respective oil sump 14. Each oil equalization branch 25 is connected to the main oil equalization line 24 at an oil equalization line branching connection 26.
The compressors in the multi-compressor device 7 are divided into two groups, each group including at least one compressor 8 and at least one group including at least two compressors 8. According to the embodiment shown on
The multi-compressor device 7 further includes an oil pumping device 27 located in the common oil equalization line 23 and between the two groups of compressors 8 such that one of said two groups is located on a first side of the oil pumping device 27 and the other of said two groups is located on a second side of the oil pumping device 27. According to the embodiment shown on
According to the embodiment shown on
The multi-compressor refrigeration system 2 further includes a controller 31 configured to control operation of the multi-compressor refrigeration system 2, and particularly to control operation (starting or stopping) of the compressors 8. The controller 31 may for example include a microprocessor and a memory.
The controller 31 is operatively connected to each oil level detection device 15, to the oil pumping device 27 and to each valve 29. The controller 31 is configured to control operation of the oil pumping device 27 and the valves 29 based on outputs from the oil level detection devices 15.
The method particularly includes: monitoring an oil level in the oil sump 14 of each compressor 8 through the respective oil level detection device 15; detecting, through the controller 31 and based on a signal outputted from an oil level detection device 15, that a low oil level situation (or lack of oil situation) occurs in a respective compressor 8, if the oil level in said compressor 8 reaches a predetermined low oil level condition; and performing an oil balancing action if a low oil level situation is detected for a compressor 8, the oil balancing action including: if oil balancing is required between compressors from different groups, controlling operation of the oil pumping device 27 and the valves 29 so as to transfer oil from the oil sump 14 of at least one compressor 8, for which a low oil level situation has not been detected and belonging to a group different from the group including the compressor 8 for which a low oil level situation has been detected, to the oil sump 14 of the compressor 8 for which a low oil level situation has been detected; if oil balancing is required between compressors 8 from a same group, controlling operation of the oil pumping device 27 and the valves 29 so as to transfer oil from the oil sump 14 of at least one compressor 8, for which a low oil level situation has not been detected and belonging to the same group as the compressor 8 for which a low oil level situation has been detected, to a temporary oil vessel and then from the temporary oil vessel to the oil sump 14 of the compressor 8 for which a low oil level situation has been detected, wherein the temporary oil vessel is constituted by the oil sump 14 of at least one compressor 8 belonging to a group different from the group including the compressor 8 for which a low oil level situation has been detected.
Advantageously, the controller 31 is configured to determine a current amount of oil in each compressor 8 based on outputs from the oil level detection devices 15, and the amount of oil that has to be transferred to a compressor 8 for which a low oil level situation has been detected in order to reach a predetermined oil level in said compressor 8. Based on that, the controller 31 may operate the oil pumping device 27 to pump the exact amount of oil needed for the compressor 8 for which a low oil level situation has been detected.
According to an embodiment of the invention, the predetermined low oil level condition is reached for a compressor 8 if a low oil level warning signal is outputted from the respective oil level detection device 15, i.e. if the oil level in the oil sump 14 of the respective compressor 8 reaches the predetermined low oil level value.
Advantageously, the method further includes detecting, through the controller 31 and based on a signal outputted from an oil level detection device 15, that an excess of oil situation occurs in a respective compressor 8, if the oil level in said compressor 8 reaches a predetermined high oil level condition. According to such an embodiment of the invention, the oil balancing action including: if oil balancing is required between compressors 8 from different groups, controlling operation of the oil pumping device 27 and the valves 29 so as to transfer oil from the oil sump 14 of at least one compressor 8, for which an excess of oil situation has been detected and belonging to a group different from the group including the compressor 8 for which a low oil level situation has been detected, to the oil sump 14 of the compressor 8 for which a low oil level situation has been detected; if oil balancing is required between compressors 8 from a same group, controlling operation of the oil pumping device 27 and the valves 29 so as to transfer oil from the oil sump 14 of at least one compressor 8, for which an excess of oil situation has been detected and belonging to the same group as the compressor 8 for which a low oil level situation has been detected, to a temporary oil vessel and then from the temporary oil vessel to the oil sump 14 of the compressor 8 for which a low oil level situation has been detected, wherein the temporary oil vessel is constituted by the oil sump 14 of at least one compressor 8 belonging to a group different from the group including the compressor 8 for which a low oil level situation has been detected.
According to an embodiment of the invention, the predetermined high oil level condition is reached for a compressor 8 if a high oil level warning signal is outputted from the respective oil level detection device 15, i.e. if the oil level in the oil sump 14 of the respective compressor 8 reaches a predetermined high oil level value.
According to an embodiment of the invention, the method further includes calculating a risk of a low oil level occurrence in a compressor 8 at a given running condition, and controlling operation of the oil pumping device 27 and the valves 29 based on that calculation in order to deliver more oil to a compressor 8 that has a high risk of a low oil level occurrence, and/or controlling operation of the oil pumping device 27 and the valves 29 in order not to withdraw oil from a compressor 8 that has a high risk of a low oil level occurrence.
Several scenarios of the method for balancing oil in the multi-compressor refrigeration system 2 of
In scenario 1, there is a need of oil transfer between two different groups of compressors 8, and the oil should be transferred from the second group, which comprises two compressors 8 (named second and third compressors), to the first group, which comprises only one compressor 8 (named first compressor).
In such situation, the oil balancing action includes opening the valve 29 associated with the second compressor (or with the third compressor) and operating the oil pump 28 to start pumping oil in a direction from the second group to the first group, and more particularly from the second compressor (or the third compressor) in the second group to the first compressor in the first group. Once the oil level detection device 15 located in the oil sump 14 of the first compressor detects that the oil level in said oil sump 14 has reached the predetermined oil level, the oil balancing action includes stopping the operation of the oil pump 28 and closing the valve 29 associated with the second compressor (or with the third compressor).
It may happen that the amount of oil in the second compressor (or the third compressor) is not sufficient for the first compressor to reach the predetermined oil level. In such situation, the oil balancing action additionally includes operating the oil pump 28 and the valves 29 to transfer oil also from the third compressor (or the second compressor) to the first compressor.
It may also happen that the controller 31 determines a high risk of a low oil level occurrence for the second compressor (or the third compressor). In such situations, the oil balancing action will include controlling operation of the oil pump 28 and the valves 29 in order to transfer oil from the other compressor 8 with high oil level, i.e. from the third compressor (or the second compressor).
It is also envisaged by the present invention, to transfer oil from more than one oil sump 14 at the same time.
In this scenario, oil should be transferred from the first group to the second group. Since the first group comprises only one compressor 8, the oil will be transferred from the first compressor to the second compressor and/or the third compressor.
In such situations, the oil balancing action includes opening the valve 29 associated with the second compressor (and/or with the third compressor) and operating the oil pump 28 to start pumping oil in the direction from the first group to the second group, and more particularly from the first compressor in the first group to the second compressor (and/or the third compressor) in the second group. Once the oil level detection device 15 located in the oil sump 14 of the second compressor (and/or the third compressor) detects that the oil level in said oil sump 14 has reached the predetermined oil level, the oil balancing action includes stopping the operation of the oil pump 28 and closing the valve 29 associated with the second compressor (and/or with the third compressor).
In this scenario, oil should be transferred within the same group. In order to achieve this, an intermediate step is introduced. In an embodiment, the excessive oil level has been detected in the second compressor and there is the low oil level detected in the third compressor.
Firstly, the oil balancing action includes controlling operation of the oil pump 28 and the valves 29 associated with the second and third compressors in order to transfer the excessive oil from the second compressor to a temporary oil vessel constituted by the oil sump 14 of the first compressor. Particularly, the oil balancing action includes opening the valve 29 associated with the second compressor and operating the oil pump 28 to pump oil from the second group to the first group, and particularly from the oil sump 14 of the second compressor to the oil sump 14 of the first compressor. Once a sufficient amount of oil has been transferred to the oil sump 14 of the first compressor, the oil balancing action includes stopping operation of the oil pump 28 and closing the valve 29 associated with the second compressor.
Then, the oil balancing action includes opening the valve 29 associated with the third compressor and operating the oil pump 28 to pump oil from the first group to the second group, namely from the oil sump 14 of the first compressor to the oil sump 14 of the third compressor. Once the oil level detection device 15 located in the oil sump 14 of the third compressor detects that the oil level in said oil sump 14 has reached the predetermined oil level, the oil balancing action includes stopping the operation of the oil pump 28 and closing the valve 29 of the third compressor.
It is also envisaged by the present invention, that the controller 31 may operate the oil pump 28 and the valves 29 to transfer oil to a compressor 8 even if a low oil level situation has not been detected for said compressor 8 at that moment because said compressor 8 is about to reach a given running condition where it has a high risk of a low oil level occurrence. In such situations, the method may include controlling, through the controller 31, the oil pump 28 and the valves 29 to transfer some additional oil to such a compressor 8 before said compressor 8 reaches the said running condition.
The first compressor and the second compressor, which belong to the first group, are on one side of the oil pump 28, and the third compressor and the fourth compressor, which belong to the second group, are on the other side of the oil pump 28.
The oil balancing operation for the multi-compressor refrigeration system 2 according to the second embodiment of the invention is very similar to the one described above for the first embodiment of the invention, and will thus not be disclosed hereafter. In this situation, the oil may be transferred at the same time to/from two compressors 8.
The oil balancing operation for the multi-compressor refrigeration system 2 according to the third embodiment of the invention is very similar to the one described above for the first embodiment of the invention, and will thus not be disclosed hereafter. In this situation, the oil may be transferred at the same time to/from three compressors 8.
Replacing two two-way valves with a three-way valve simplifies the multi-compressor refrigeration system 2 according to the invention and also reduces the overall cost.
It is also envisaged by the present invention to replace two-way valves with three-way valves in the second and third embodiments of the invention described above.
It is also envisaged by the present invention, that such oil pumping device 27 may replace oil pumping devices 27 in other embodiments described above.
Based on the embodiments described above, a person skilled in the art may easily implement the present invention into a multi-compressor refrigeration system 2 comprising any number of compressors 8. Moreover, a person skilled in the art may easily combine features described in relation to different embodiments, unless clearly stated otherwise.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 23/07222 | Jul 2023 | FR | national |
