Method of managing oil in a multi-compressor refrigeration system using oil level detection devices

Abstract

A method for managing oil in a running multi-compressor refrigeration system including a controller and a multi-compressor device, includes monitoring an oil level in the oil sump of each compressor through the respective oil level detection device; detecting that a lack of oil situation occurs in a running compressor, if the oil level in said running compressor reaches a predetermined threshold condition; performing an oil managing action if a lack of oil situation is detected for a running compressor, the oil managing action being based on a changing of ON/OFF configurations of the compressors in the multi-compressor device and including performing an oil balancing action, if more than a half of the total number of compressors are running, or performing an oil returning action, if a half or less of the total number of compressors are running.

1 . 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:
 monitoring an oil level in the oil sump of each compressor through the respective oil level detection device,   detecting that a lack of oil situation occurs in a running compressor, if the oil level in said running compressor reaches a predetermined threshold condition,   performing an oil managing action if a lack of oil situation is detected for a running compressor, the oil managing action being based on a changing of ON/OFF configurations of the compressors in the multi-compressor device and including:   if the total number of compressors in the multi-compressor device is from 2 to 4:
 performing an oil balancing action, if more than a half of the total number of compressors are running, wherein the oil balancing action includes balancing oil between the compressors, 
 performing an oil returning action, if a half or less of the total number of compressors are running, wherein the oil returning action includes retrieving oil from the multi-compressor refrigeration system to the multi-compressor device, 
   if the total number of compressors in the multi-compressor device is 5 or above:
 performing the oil balancing action, if more than a half of the total number of compressors are running, 
 performing the oil balancing action and/or the oil returning action, if a half or less of the total number of compressors are running and at least two compressors are running, 
 performing the oil returning action, if only one compressor is running. 
   
     
     
         2 . The method according to  claim 1 , further including:
 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.   
     
     
         3 . The method according to  claim 2 , wherein the predetermined threshold condition is reached if:
 the low oil level warning signal outputted from an oil level detection device is continuously outputted for a first predetermined time, or   the low oil level warning signal outputted from an oil level detection device has switched more than a predetermined number of times within a second predetermined time.   
     
     
         4 . The method according to  claim 1 , wherein 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. 
     
     
         5 . The method according to  claim 1 , wherein 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 in order to maintain substantially identical the workload of the multi-compressor refrigeration system. 
     
     
         6 . The method according to  claim 1 , wherein the oil balancing action includes stopping the operation of all compressors. 
     
     
         7 . The method according to  claim 1 , wherein the oil returning action includes increasing the workload of the multi-compressor refrigeration system. 
     
     
         8 . The method according to  claim 1 , wherein, 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. 
     
     
         9 . The method according to  claim 1 , wherein, 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. 
     
     
         10 . The method according to  claim 8 , wherein 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. 
     
     
         11 . The method according to  claim 1 , wherein 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. 
     
     
         12 . The method according to  claim 1 , further including:
 stopping the operation of all compressors, if, after lapse of a third predetermined time period 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.   
     
     
         13 . The method according to  claim 1 , wherein the oil level detection device of each compressor includes an oil level sensor or an oil level switch. 
     
     
         14 . The method according to  claim 1 , further including providing a low oil level warning, if a lack of oil situation is detected for a running compressor. 
     
     
         15 . The method according to  claim 1 , wherein, 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:
 performing the oil balancing action if a total piping length of the multi-compressor refrigeration system is below a predetermined length,   performing the oil returning action if the total piping length of the multi-compressor refrigeration system is above the predetermined length.   
     
     
         16 . A multi-compressor refrigeration system comprising:
 a controller configured to control operation of the multi-compressor refrigeration system,   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,   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, based on a signal outputted from a respective oil level detection device, that a lack of oil situation occurs in a running compressor, if the oil level in said running compressor reaches a predetermined threshold condition,   perform an oil managing action if a lack of oil situation is detected for a running compressor, the oil managing action being based on a changing of ON/OFF configurations of the compressors in the multi-compressor device and including:   if the total number of compressors in the multi-compressor device is from 2 to 4:
 performing an oil balancing action, if more than a half of the total number of compressors are running, wherein the oil balancing action includes balancing oil between the compressors, 
 performing an oil returning action, if a half or less of the total number of compressors are running, wherein the oil returning action includes retrieving oil from the multi-compressor refrigeration system to the multi-compressor device, 
   if the total number of compressors in the multi-compressor device is 5 or above:
 performing the oil balancing action, if more than a half of the total number of compressors are running, 
 performing the oil balancing action and/or the oil returning action, if a half or less of the total number of compressors are running and at least two compressors are running, 
 performing the oil returning action, if only one compressor is running.