Screw chiller economizer system

Abstract

Screw chillers have economizer systems that include a low pressure economizer and a high pressure economizer. According to certain embodiments, the low pressure economizer includes a flash tank, an expansion device and a flow control valve while the high pressure economizer includes a heat exchanger and an expansion device. The screw chillers also include a screw compressor that compresses refrigerant. The screw compressor includes a low pressure economizer port designed to receive lower pressure refrigerant from the flash tank within the low pressure economizer and a high pressure economizer port designed to receive higher pressure refrigerant from the heat exchanger within the higher pressure economizer. The screw compressor is designed to compress the refrigerant received from the evaporator, the refrigerant received through the low pressure economizer port, and the refrigerant received through the high pressure economizer port and to discharge the refrigerant through a common discharge.

1 . A refrigeration system, comprising:
 a condenser configured to condense refrigerant;   a first economizer system comprising a first expansion device configured to expand a first portion of the condensed refrigerant and a heat exchanger configured to subcool a second portion of the condensed refrigerant with the first portion;   a second economizer system comprising a second expansion device configured to expand the refrigerant and a flash tank configured to separate the refrigerant into vapor phase refrigerant and liquid phase refrigerant;   an expansion device configured to receive the refrigerant from the first economizer system or the second economizer system and to expand the refrigerant;   an evaporator configured to evaporate the expanded refrigerant; and   a screw compressor comprising a suction port configured to receive the evaporated refrigerant, a first economizer port configured to receive the first portion of the refrigerant, a second economizer port configured to receive the vapor phase refrigerant, and a discharge port, wherein the screw compressor is configured to compress the evaporated refrigerant, the first portion of the refrigerant, and the vapor phase refrigerant and to discharge the compressed refrigerant through the discharge port.   
     
     
         2 . The refrigeration system of  claim 1 , wherein the first economizer system is disposed upstream from the second economizer system and downstream of the condenser. 
     
     
         3 . The refrigeration system of  claim 1 , wherein the second economizer system is disposed upstream from the first economizer system and downstream of the condenser. 
     
     
         4 . The refrigeration system of  claim 1 , wherein the first economizer port comprises a lower pressure port relative to the second economizer port. 
     
     
         5 . The refrigeration system of  claim 1 , wherein the first economizer port comprises a higher pressure port relative to the second economizer port. 
     
     
         6 . The refrigeration system of  claim 1 , wherein the condenser comprises an air cooled condenser. 
     
     
         7 . The refrigeration system of  claim 1 , wherein the first economizer system comprises a flow control valve configured to control flow of the first portion of the refrigerant to the first economizer port. 
     
     
         8 . The refrigeration system of  claim 1 , wherein the second economizer system comprises a flow control valve configured to control flow of the vapor phase refrigerant to the second economizer port. 
     
     
         9 . A refrigeration system, comprising:
 a condenser configured to condense refrigerant;   a high pressure economizer system comprising a high pressure expansion device configured to expand the condensed refrigerant and a high pressure flash tank configured to separate the expanded refrigerant into a high pressure vapor phase refrigerant and a high pressure liquid phase refrigerant;   a low pressure economizer system comprising a lower pressure expansion device configured to expand the high pressure liquid refrigerant and a lower pressure flash tank configured to separate the expanded refrigerant into lower pressure vapor phase refrigerant and lower pressure liquid phase refrigerant;   a third expansion device configured to receive and to expand the lower pressure liquid phase refrigerant;   an evaporator configured to evaporate the expanded refrigerant from the third expansion device; and   a screw compressor comprising a suction port configured to receive the evaporated refrigerant, a first economizer port configured to receive the high pressure vapor phase refrigerant, a second economizer port configured to receive the lower pressure vapor phase refrigerant, and a discharge port, wherein the screw compressor is configured to compress the evaporated refrigerant, the high pressure vapor phase refrigerant, and the lower pressure vapor phase refrigerant and to discharge the compressed refrigerant through the discharge port.   
     
     
         10 . The refrigeration system of  claim 9 , wherein the screw compressor is configured to draw the vapor phase refrigerant into the screw compressor based on a pressure difference between a pressure of the vapor phase refrigerant and a pressure in a compression area of the screw compressor coupled to the low pressure economizer port. 
     
     
         11 . The refrigeration system of  claim 9 , wherein the high pressure economizer system comprises a first flow control valve disposed downstream of the high pressure flash tank, wherein the first flow control valve is configured to control flow of the high pressure vapor phase refrigerant to the first economizer port, wherein the low pressure economizer system comprises a second flow control valve disposed downstream of the lower pressure flash tank, and wherein the second flow control valve is configured to control flow of the lower pressure vapor phase refrigerant to the second economizer port. 
     
     
         12 . The refrigeration system of  claim 11 , comprising a controller operably coupled to the first and second flow control valves and configured to govern operation of the first control valve to enable and disable operation of the high pressure economizer system, and to govern operation of the second control valve to enable and disable operation of the lower pressure economizer system. 
     
     
         13 . The refrigeration system of  claim 9 , comprising a controller configured to operate the high pressure expansion device to limit a level of liquid refrigerant in the high pressure flash tank, and to operate the low pressure expansion device to limit a level of liquid refrigerant in the low pressure flash tank. 
     
     
         14 . The refrigeration system of  claim 9 , wherein the condenser comprises an air cooled multichannel heat exchanger. 
     
     
         15 . A refrigeration system, comprising:
 a condenser configured to condense refrigerant;   a high pressure economizer system comprising a first expansion device configured to expand a first portion of the condensed refrigerant and a heat exchanger configured to subcool a second portion of the condensed refrigerant with the first portion;   a low pressure economizer system comprising a low pressure expansion device configured to expand the subcooled second portion and a flash tank configured to separate the expanded second portion into vapor phase refrigerant and liquid phase refrigerant;   a third expansion device configured to expand the liquid phase refrigerant;   an evaporator configured to evaporate the expanded refrigerant; and   a screw compressor comprising a suction port configured to receive the expanded refrigerant, a low pressure economizer port configured to receive the vapor phase refrigerant, a high pressure economizer port configured to receive the first portion of the refrigerant, and a discharge port, wherein the screw compressor is configured to compress the refrigerant received through the suction port, the low pressure economizer port, and the high pressure economizer port and to discharge the compressed refrigerant through the discharge port.   
     
     
         16 . The refrigeration system of  claim 15 , wherein the condensed refrigerant is separated into the first portion of the condensed refrigerant and the second portion of the condensed refrigerant upstream of the heat exchanger. 
     
     
         17 . The refrigeration system of  claim 15 , wherein the first and second portions of the condensed refrigerant both flow through the heat exchanger. 
     
     
         18 . The refrigeration system of  claim 15 , wherein the screw compressor is configured to mix the first portion of the refrigerant received through the high pressure economizer port with existing refrigerant in the screw compressor, and wherein the screw compressor is configured to mix the vapor phase refrigerant received through the low pressure economizer port with existing refrigerant in the screw compressor. 
     
     
         19 . The refrigeration system of  claim 15 , wherein the high pressure economizer system comprises a first flow control valve disposed upstream of the first expansion device, wherein the flow control valve is configured to control flow of the first portion of the condensed refrigerant to the high pressure economizer port, wherein the low pressure economizer system comprises a second flow control valve disposed downstream of the flash tank, and wherein the second flow control valve is configured to control flow of the vapor phase refrigerant to the low pressure economizer port 
     
     
         20 . The refrigeration system of  claim 19 , comprising a controller operably coupled to the first and second flow control valves and configured to govern operation of the first and second flow control valves based on an ambient air temperature, or a temperature of the refrigerant, or both.