Multi-compressor refrigeration system having a common oil equalization line provided with an oil pumping device

Abstract

The multi-compressor refrigeration system comprising a controller and a multi-compressor device including at least three compressors which are coupled in parallel, each compressor equipped with an oil sump and an oil level detection device, the compressors divided into two groups each including at least one compressor; suction fittings of the compressors that are fluidly connected by a common suction line and oil sumps that are fluidly connected by a common oil equalization line. The multi-compressor device includes an oil pumping device located in the common oil equalization line and between the two groups, and at least one valve located in the common oil equalization line and configured to control an oil flow between the oil pumping device and at least one compressor of a group associated with the at least one valve.

What is claimed is: 
     
         1 . 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, wherein the compressors in the multi-compressor device are divided into a first group including at least one compressor and a second group including at least two compressors;   a common suction line configured to fluidly connect the suction fittings of the compressors;   a common oil equalization line configured to fluidly connect the oil sumps of the compressors;   an oil pumping device located in the common oil equalization line and operatively connected to the controller, the oil pumping device having at least one oil pump;   wherein one of the first and second groups of compressors is located on a first side of the oil pumping device and the other of the first and second groups of compressors is located on a second side of the oil pumping device, and the multi-compressor device further includes at least one valve located in the common oil equalization line and associated with the second group, 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 second group, 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.   
     
     
         2 . The multi-compressor refrigeration system as recited in  claim 1 , wherein the controller is configured to determine a current amount of oil in each compressor based on outputs from the oil level detection devices. 
     
     
         3 . The multi-compressor refrigeration system as recited in  1 , wherein the controller is configured to:
 monitor an oil level in the oil sump of each compressor through the respective oil level detection device;   detect a low oil level situation in a respective compressor based on the oil level in said compressor reaching a predetermined low oil level condition; and   perform an oil balancing action in response to detecting a low oil level situation, the oil balancing action including controlling operation of the oil pumping device and the at least one valve to transfer oil from the oil sump of at least one compressor 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.   
     
     
         4 . The multi-compressor refrigeration system as recited in  claim 1 , wherein the controller is configured to detect that an excess oil situation in a respective compressor based on the oil level in said compressor reaching a predetermined high oil level condition. 
     
     
         5 . The multi-compressor refrigeration system as recited in  claim 3 , 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 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. 
     
     
         6 . The multi-compressor refrigeration system as recited in  claim 3 ,
 wherein the compressor for which a low oil level situation has been detected is in one of the first and second groups, and the balancing action includes operating the oil pumping device and the at least one valve to transfer oil from the oil sump of at least one compressor in the other of the first and second groups for which a low oil level situation has not been detected to the oil sump of the of the compressor having the low oil level situation; or   wherein one of the first and second groups includes at least one first compressor for which a low oil level situation has been detected and at least one second compressor for which a low oil level situation has not been detected, and the balancing action includes operating the oil pumping device and the at least one valve to transfer oil from the oil sump of the at least one second compressor through a temporary oil vessel to the oil sump of the at least one second compressor, wherein the temporary oil vessel is constituted by the oil sump of at one compressor in the other of the first and second groups.   
     
     
         7 . The multi-compressor refrigeration system as recited in  claim 3 , wherein 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. 
     
     
         8 . The multi-compressor refrigeration system as recited in  claim 1 , wherein 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 that calculation. 
     
     
         9 . The multi-compressor refrigeration system as recited in  claim 8 , wherein the controller is configured to control the oil pumping device and the at least one valve 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 block the transfer of oil from a compressor that has a high risk of a low oil level occurrence. 
     
     
         10 . The multi-compressor refrigeration system as recited in  claim 1 , wherein the at least one oil pump includes a volumetric oil pump configured to measure and output an amount of pumped oil. 
     
     
         11 . The multi-compressor refrigeration system as recited in  claim 1 , wherein the at least one oil pump includes two one-way oil pumps which are connected in parallel. 
     
     
         12 . The multi-compressor refrigeration system as recited in  claim 1 , wherein the at least one oil pump includes a bidirectional oil pump. 
     
     
         13 . The multi-compressor refrigeration system as recited in  claim 1 , wherein the at least one valve includes a normally closed solenoid valve. 
     
     
         14 . The multi-compressor refrigeration system as recited in  claim 1 , wherein 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. 
     
     
         15 . The multi-compressor refrigeration system as recited in  claim 1 , wherein 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. 
     
     
         16 . The multi-compressor refrigeration system as recited in  claim 1 , wherein at least one compressor of the multi-compressor device comprises at least two oil level detection devices. 
     
     
         17 . 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 coupled in parallel, each compressor 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 the compressors fluidly connected through a common oil equalization line and the suction fittings that are fluidly connected through a common suction line, the method including:
 dividing the compressors into a first group including at least one compressor and a second group including at least two compressors;   providing an oil pumping device in the common oil equalization line and between the first group and the second group, the oil pumping device including 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 the second group 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 second group,   monitoring an oil level in the oil sump of each compressor ( 8 ) through the respective oil level detection device,   detecting a low oil level situation in a compressor based on the oil level in said compressor reaching a predetermined low oil level condition,   performing an oil balancing action in response to a low oil level situation in the compressor, the oil balancing action including controlling operation of the oil pumping device and the at least one valve to transfer oil from the oil sump of at least one compressor 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.   
     
     
         18 . The method according to  claim 17 ,
 wherein the compressor for which a low oil level situation has been detected is in one of the first and second groups, and the balancing action includes operating the oil pumping device and the at least one valve to transfer oil from the oil sump of at least one compressor in the other of the first and second groups for which a low oil level situation has not been detected to the oil sump of the of the compressor having the low oil level situation; or   wherein one of the first and second groups includes at least one first compressor for which a low oil level situation has been detected and at least one second compressor for which a low oil level situation has not been detected, and the balancing action includes operating the oil pumping device and the at least one valve to transfer oil from the oil sump of the at least one second compressor through a temporary oil vessel to the oil sump of the at least one second compressor, wherein the temporary oil vessel is constituted by the oil sump of at one compressor in the other of the first and second groups.   
     
     
         19 . The method according to  claim 18 , further comprising 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. 
     
     
         20 . The method according to  claim 19 , 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.