Oil management system for multiple compressors

Abstract

A HVAC system refrigeration circuit is configured to balance the oil carryover between multiple compressors using a single refrigeration circuit. Embodiments of the HVAC system allow for the use of one or more inverter compressors and one or more fixed speed compressors. Embodiments of the HVAC system utilize capillary tubes or other flow control methods to balance the oil carryover between multiple compressors.

1 . An HVAC system comprising:
 one or more inverter compressors in fluid communication with a first oil separator;   one or more fixed speed compressors in fluid communication with a second oil separator;   a suction line having a first side and second side, wherein the first side of the suction line is configured to supply refrigerant to the one or more inverter compressors and the second side of the suction line is configured to supply refrigerant to the one or more fixed speed compressors;   a first oil return line configured to transfer oil from the first oil separator to the second side of the suction line; and   a second oil return line wherein the second oil return line is divided to transfer oil from the second oil separator to both the first and second sides of the suction line.   
     
     
         2 . The HVAC system of  claim 1 , wherein the second oil return line comprises a first branch configured to transfer oil from the second oil return line to the first side of the suction line and a second branch configured to transfer oil from the second oil return line to the second side of the suction line. 
     
     
         3 . The HVAC system of  claim 2 , further comprising a first capillary tube in fluid communication with the first branch of the second oil return line, a second capillary tube in fluid communication with the first oil return line, and a third capillary tube in fluid communication with the second branch of the second oil return line. 
     
     
         4 . The HVAC system of  claim 3 , wherein the first capillary tube and the second capillary tube are configured to allow a substantially similar flow of oil to pass through. 
     
     
         5 . The HVAC system of  claim 3  wherein the third capillary tube is configured to allow a greater flow of oil to pass through compared to the first or second capillary tubes. 
     
     
         6 . The HVAC system of  claim 1 , further comprising a chiller system configured to supply chilled water to a building. 
     
     
         7 . The HVAC system of  claim 1 , comprising at least two fixed speed compressors in fluid communication with a single second oil separator. 
     
     
         8 . The HVAC system of  claim 1 , comprising exactly one inverter compressor. 
     
     
         9 . The HVAC system of  claim 1 , wherein the one or more inverter compressors have a lower oil carryover than the one or more fixed speed compressors. 
     
     
         10 . The HVAC system of  claim 1 , further comprising a compressor oil selected from the group consisting of Polyalkylene Glycol (PAG), Polyolester (POE), Mineral Oil, Alkylbenzene (AB), Polyvinyl Ether (PVE), and R-1234yf Oil. 
     
     
         11 . A compression mechanism for an HVAC system comprising:
 a first compressor in fluid communication with a first branch of a refrigerant suction line having the first branch and a second branch, the first compressor also being in fluid communication with a first oil discharge pipe; and   a second compressor in fluid communication with the second branch of the refrigerant suction line and in fluid communication with a second oil discharge pipe wherein the second oil discharge pipe is configured to transfer oil from the second compressor to the first and second branches of the refrigerant suction line and wherein the first oil discharge pipe is configured to transfer oil from the first compressor to the second branch of the refrigerant suction line.   
     
     
         12 . The compression mechanism of  claim 11 , wherein the first compressor is an inverter compressor and wherein the second compressor is a fixed speed compressor. 
     
     
         13 . The compression mechanism of  claim 11 , wherein first compressor has a lower oil carryover than the second compressor. 
     
     
         14 . The compression mechanism of  claim 11 , further comprising a compressor oil selected from the group consisting of Polyalkylene Glycol (PAG), Polyolester (POE), Mineral Oil, Alkylbenzene (AB), Polyvinyl Ether (PVE), and R-1234yf Oil. 
     
     
         15 . An oil return system for a plurality of HVAC compressors comprising:
 a low-pressure refrigerant line having a first portion and a second portion, the first and second portions of the low-pressure refrigerant line extending in different directions from a refrigerant inlet point;   a first oil discharge line fluidly connecting a first compressor to a first oil separator;   a first oil return line connecting the first oil separator to the second portion of the low-pressure refrigerant line through a second capillary tube;   a second oil discharge line fluidly connecting a second compressor to a second oil separator, wherein the second oil compressor has a larger oil carryover than the first oil compressor; and   a second oil return line connecting the second oil separator to the first portion of the low-pressure refrigerant line through a first capillary tube and connecting the second oil separator to the second portion of the low-pressure refrigerant line through a third capillary tube, wherein the first and second capillary tubes are configured to allow substantially equal amounts of oil to flow through and wherein the third capillary tube is configured to allow more oil to flow through with respect to the first or second capillary tubes.   
     
     
         16 . The oil return system of  claim 15 , further comprising a chiller system configured to supply chilled water to a building. 
     
     
         17 . The oil return system of  claim 15 , wherein the first compressor comprises an inverter compressor and the second compressor comprises at least two fixed speed compressors in fluid communication with a single second oil separator. 
     
     
         18 . The oil return system of  claim 15 , wherein the first compressor has a lower oil carryover than the second compressor. 
     
     
         19 . The oil return system of  claim 15 , further comprising a compressor oil selected from the group consisting of Polyalkylene Glycol (PAG), Polyolester (POE), Mineral Oil, Alkylbenzene (AB), Polyvinyl Ether (PVE), and R-1234yf Oil.