Method for managing oil in a multi-compressor refrigeration system and multi-compressor refrigeration system having a common oil equalization line provided with an oil pumping device

Abstract

A method for managing oil in a multi-compressor refrigeration system comprising a controller; a multi-compressor device including at least two compressors which are parallelly coupled, each compressor being equipped with a suction fitting and an oil sump, suction fittings of all compressors being fluidly connected by a common suction line and oil sumps of all compressors being fluidly connected by a common oil equalization line; and an oil pumping device including an oil pump located in the common oil equalization line. The method including monitoring an operating parameter of the oil pump; and performing an oil returning action if the operating parameter of the oil pump reaches a predetermined value, wherein the oil returning action includes retrieving oil from the multi-compressor refrigeration system to the multi-compressor device.

1 . A method for managing 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 two compressors which are parallelly coupled, each compressor being equipped with a suction fitting and an 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, wherein the multi-compressor refrigeration system further includes 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 and being configured to perform an oil balancing action between oil sumps of the multi-compressor device, the method including:
 monitoring an operating parameter of the at least one oil pump, and   performing an oil returning action if the operating parameter of the at least one oil pump reaches a predetermined value, wherein the oil returning action includes retrieving oil from the multi-compressor refrigeration system to the multi-compressor device.   
     
     
         2 . The method as recited in  claim 1 , wherein the oil returning action includes increasing the workload of the multi-compressor refrigeration system. 
     
     
         3 . The method as recited in  claim 2 , wherein the oil returning action includes controlling the multi-compressor refrigeration system to operate at a full system workload. 
     
     
         4 . The method as recited in  claim 1 , wherein the oil returning action includes controlling the multi-compressor refrigeration system to restart the multi-compressor device with a different operational configuration. 
     
     
         5 . The method as recited in  claim 4 , wherein the oil returning action includes changing ON/OFF configurations of the compressors in the multi-compressor device. 
     
     
         6 . The method as recited in  claim 1 , wherein each compressor is equipped with an oil level detection device operatively connected to the controller and configured to detect an oil level in the respective oil sump, the method further including:
 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 running compressor, if the oil level in said running compressor reaches a predetermined low oil level condition, and   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 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.   
     
     
         7 . The method as recited in  claim 6 , wherein the multi-compressor device includes at least three compressors which are parallelly coupled, the method further 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 the 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, and   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,   wherein 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 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.   
     
     
         8 . The method as recited in  claim 7 , wherein if oil balancing is required between compressors from different groups, the oil balancing action includes transferring, by controlling operation of the oil pumping device and the at least one valve with the controller, oil from the oil sump of at least one compressor, for which a low oil level situation has not been detected and which belongs 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, and if oil balancing is required between compressors from a same group, the oil balancing action includes transferring, by controlling operation of the oil pumping device and the at least one valve with the controller, oil from the oil sump of at least one compressor, for which a low oil level situation has not been detected and which belongs 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. 
     
     
         9 . The method as recited in  claim 6 , further comprising determining a current amount of oil in each compressor based on outputs from the oil level detection devices. 
     
     
         10 . The method as recited in  claim 6 , further comprising determining an 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. 
     
     
         11 . The method as recited in  claim 1 , wherein the operating parameter of the at least one oil pump is a start frequency of the at least one oil pump to perform an oil balancing action, said start frequency corresponding to a number of times, in a predetermined period of time, the at least one oil pump has been started to perform an oil balancing action. 
     
     
         12 . The method as recited in  claim 11 , wherein the predetermined period of time is from 1 minute to 5 minutes. 
     
     
         13 . The method as recited in  claim 11 , wherein the predetermined value of the operating parameter of the at least one oil pump is at least 2 starts of the at least one oil pump in the predetermined period of time. 
     
     
         14 . The method as recited in  claim 1 , wherein the at least one oil pump includes a variable speed oil pump. 
     
     
         15 . The method as recited in  claim 14 , wherein the operating parameter of the at least one oil pump is an oil flowrate of the at least one oil pump. 
     
     
         16 . The method as recited in  claim 15 , wherein the predetermined value of the operating parameter being the oil flowrate is between 4 L/min and 10 L/min. 
     
     
         17 . A system, comprising:
 a controller configured to control operation of a multi-compressor refrigeration system; and   a multi-compressor device including
 at least two compressors which are parallelly coupled, each compressor being equipped with a suction fitting and an oil sump, 
 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, and 
 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 and being configured to perform an oil balancing action between oil sumps of the multi-compressor device, 
   wherein the controller is configured to monitor an operating parameter of the at least one oil pump and perform an oil returning action if the operating parameter of the at least one oil pump reaches a predetermined value, wherein the oil returning action includes retrieving oil from the multi-compressor refrigeration system to the multi-compressor device.   
     
     
         18 . The multi-compressor refrigeration system as recited in  claim 17 , wherein each compressor is equipped with an oil level detection device operatively connected to the controller and configured to detect an oil level in the respective oil sump, the controller being configured to monitor an oil level in the oil sump of each compressor through the respective oil level detection device, detect that a low oil level 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 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. 
     
     
         19 . The multi-compressor refrigeration system as recited in  claim 18 , wherein the multi-compressor device includes at least three compressors which are parallelly coupled and 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, the oil pumping device being 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. 
     
     
         20 . The multi-compressor refrigeration system as recited in  claim 19 , wherein the multi-compressor device 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.