Lubricant management in an HVACR system
A heating, ventilation, air conditioning, and refrigeration (HVACR) system is disclosed. The HVACR system includes a compressor, a condenser, and an evaporator fluidly connected to form a refrigerant circuit. A lubricant return line is fluidly connected to the compressor and to the evaporator. A pressure difference between the compressor and the evaporator induces a fluid flow of lubricant from the evaporator to the compressor.
1 . A heating, ventilation, air conditioning, and refrigeration (HVACR) system, comprising:
a screw compressor including a lubricant inlet port, a condenser, and an evaporator fluidly connected to form a refrigerant circuit, the screw compressor including a compression mechanism having a first helical rotor and a second helical rotor; and
a lubricant return line that is connected on an outlet end to the screw compressor at the lubricant inlet port and connected on an inlet end to a liquid level in the evaporator such that a pressure difference between the screw compressor and the evaporator induces a fluid flow of lubricant from the evaporator to the screw compressor,
wherein the lubricant return line is connected to the lubricant inlet port disposed between a suction inlet of the compression mechanism for receiving a working fluid and a discharge outlet of the of the compression mechanism for outputting the working fluid,
wherein the lubricant inlet port is disposed after the suction inlet on a portion of a housing of the screw compressor that is nearer the suction inlet than the discharge outlet and that is in direct fluid communication with a rotor pocket formed between the first helical rotor and the second helical rotor that is a trapped volume pocket for a suction phase of a compression process of the screw compressor configured such that as a volume of the rotor pocket expands, a pressure at a beginning of the suction phase is lower than a suction pressure at the suction inlet to pull the fluid flow of lubricant to the rotor pocket of the screw compressor, and
wherein the housing of the screw compressor includes material added to rotor bore surfaces in the housing, the screw compressor is configured to limit a duration of a pressure drop at the beginning of the suction phase and to cause the pressure drop being focused at an opening of the trapped volume pocket.
2 . The HVACR system of claim 1 , wherein the pressure difference between the screw compressor and the evaporator is at least 1 PSI.
3 . The HVACR system of claim 1 , wherein the pressure at the beginning of the suction phase is 0.6 psi below the suction pressure at the suction inlet of the screw compressor.
4 . The screw compressor of claim 1 , wherein an actual pressure drop across the screw compressor is the pressure at the beginning of the suction phase that is lower than the suction pressure at the suction inlet plus the pressure difference between the screw compressor and the evaporator.
5 . A lubricant management method for a screw compressor in a heating, ventilation, air conditioning, and refrigeration (HVACR) system, comprising:
forming a lubricant inlet port in a location of a screw compressor of the HVACR system, the location being disposed between a suction inlet of a compression mechanism of the screw compressor for receiving a working fluid and a discharge outlet of the compression mechanism of the screw compressor for outputting the working fluid, the compression mechanism including a first helical rotor and a second helical rotor;
fluidly connecting an outlet end of the lubricant inlet port to the screw compressor and an inlet end to a liquid level in an evaporator in the HVACR system,
wherein the lubricant inlet port is formed by disposing the lubricant inlet port after the suction inlet on a portion of a housing of the screw compressor that is nearer the suction inlet than the discharge outlet and that is in direct fluid communication with a rotor pocket formed between the first helical rotor and the second helical rotor that is a trapped volume pocket for a suction phase of a compression process of the screw compressor configured such that as a volume of the rotor pocket expands, a pressure at a beginning of the suction phase is lower than a suction pressure at the suction inlet to pull the fluid flow of lubricant to the rotor pocket of the screw compressor; and
to limit a duration of a pressure drop at the beginning of the suction phase, adding a material to rotor bore surfaces in the housing to cause the pressure drop being focused at an opening of the trapped volume pocket.
6 . The method of claim 5 , wherein the pressure difference between the screw compressor and the evaporator is at least 1 PSI.
7 . The method of claim 5 , wherein the pressure at the beginning of the suction phase is 0.6 psi below the suction pressure at the suction inlet of the screw compressor.
8 . The method of claim 5 , wherein the trapped volume pocket is defined between spiral lobes of the first helical rotor and spiral grooves of the second helical rotor.
9 . The method of claim 5 , wherein the material is added in an area surrounding the lubricant inlet port.
10 . A positive displacement compressor for a heating, ventilation, air conditioning, and refrigeration (HVACR) system, comprising:
a suction inlet that receives a working fluid to be compressed;
a compression mechanism fluidly connected to the suction inlet that compresses the working fluid;
a discharge outlet fluidly connected to the compression mechanism that outputs the working fluid following compression by the compression mechanism; and
a lubricant inlet port disposed between the suction inlet and the discharge outlet at a location that is after the suction inlet and closer to the suction inlet than the discharge outlet, the lubricant inlet port having an outlet end connected to the positive displacement compressor and an inlet end connected to a liquid level in an evaporator, wherein a pressure difference between the positive displacement compressor and the evaporator is configured to induce a fluid flow of lubricant from the evaporator to the positive displacement compressor,
wherein the lubricant inlet port is disposed after the suction inlet in a portion of a housing of the positive displacement compressor that is in direct fluid communication with a trapped volume pocket of the positive displacement compressor, the trapped volume pocket being for a suction phase of a compression process and configured such that as a volume of the trapped volume pocket expands, a pressure at the beginning of the suction phase is lower than a suction pressure at the suction inlet to pull the fluid flow of lubricant to the trapped volume pocket of the positive displacement compressor, and
wherein the housing of the positive displacement compressor is configured to limit a duration of a pressure drop at the beginning of the suction phase and to cause the pressure drop being focused at an opening of the trapped volume pocket.
11 . The positive displacement compressor of claim 10 , wherein the pressure difference between the positive displacement compressor and the evaporator is at least 1 PSI.
12 . The positive displacement compressor of claim 10 , wherein the pressure at the beginning of the suction phase is 0.6 psi below the suction pressure at the suction inlet of the positive displacement compressor.