System and method for reducing windage losses in compressor motors

Abstract

A method and system for reducing windage losses in compressor motors is provided. The compressor motor is cooled by circulating refrigerant from a closed refrigerant loop incorporating the compressor. A pumping device coupled to a liquid expander in the closed refrigerant loop circulates refrigerant through the motor cavity and produces a motor cavity pressure lower than evaporating pressure. The lower pressure in the motor cavity reduces the density of the gasses in the motor cavity, resulting in reduced windage losses of the motor. Additionally, the pumping device is powered by the recovered liquid expansion energy between the condenser and the evaporator.

1 . A refrigeration system comprising:
 a compressor, an evaporator and a condenser connected in a refrigerant loop;   a motor connected to the compressor to power the compressor, the motor being disposed in a motor cavity;   a liquid expander connected in the refrigerant loop between the condenser and the evaporator; and   a motor coolant system, the motor coolant system comprising:
 a first connection with the refrigerant loop to receive refrigerant from the evaporator; 
 a second connection with the refrigerant loop to return refrigerant to the evaporator; 
 a pumping device to circulate refrigerant from the first connection through the motor cavity to the second connection, the pumping device being powered by operation of the liquid expander; and 
 wherein the pumping device lowers a pressure and gas density of the refrigerant in the motor cavity to reduce windage losses of the motor. 
   
   
   
       2 . The refrigeration system of  claim 1  wherein the liquid expander is configured to expand high-pressure refrigerant liquid from the condenser to low-pressure refrigerant liquid for the evaporator. 
   
   
       3 . The refrigeration system of  claim 2  wherein the liquid expander powers the pumping device by recovering energy from the expansion of refrigerant in the liquid expander. 
   
   
       4 . The refrigeration system of  claim 3  wherein the liquid expander comprises one of an eductor, a positive displacement expander or a turbine centrifugal expander. 
   
   
       5 . The refrigeration system of  claim 1  wherein the pumping device is a gas compressor. 
   
   
       6 . The refrigeration system of  claim 5  wherein the gas compressor comprises one of an aerodynamic compressor or a positive displacement compressor. 
   
   
       7 . The refrigeration system of  claim 6  wherein the gas compressor comprises one of a screw compressor, a reciprocating compressor, a scroll compressor, or a vane type compressor. 
   
   
       8 . The refrigeration system of  claim 7 , wherein the refrigeration system has as a 1000 ton capacity, the gas compressor has a swept volume of about 310 CFM and a volume ratio of about 3.3, and the liquid expander is configured for a flow of at least 300 GPM and has a volume ratio of about 13.8. 
   
   
       9 . The refrigeration system of  claim 1  wherein the liquid expander is coupled to the pumping device by one of a mechanical connection or an electrical connection. 
   
   
       10 . The refrigeration system of  claim 1  wherein the liquid expander and the pumping device are combined as a single unit. 
   
   
       11 . The refrigeration system of  claim 1  further comprising a heat exchanger connected between the pumping device and the evaporator, the heat exchanger being configured to de-superheat refrigerant discharged from the pumping device. 
   
   
       12 . The refrigeration system of  claim 11  wherein the heat exchanger is configured to de-superheat refrigerant from the pumping device with condenser cooling tower water. 
   
   
       13 . A motor coolant system for a chiller system having a compressor, an evaporator and a condenser connected in a closed refrigerant loop, the motor coolant system comprising:
 a motor housing for the motor;   a liquid expander connectable to the closed refrigerant loop between the condenser and the evaporator of the chiller system;   a first refrigerant connection connectable to the closed refrigerant loop to receive refrigerant from the evaporator and provide refrigerant to the motor housing;   a second refrigerant connection connectable to the closed refrigerant loop to return refrigerant to the evaporator; and   a pumping device disposed in the second refrigerant connection to circulate refrigerant from the first refrigerant connection through the motor housing to the second refrigerant connection to cool the motor and maintain a predetermined pressure in the motor housing, the pumping device being coupled to the liquid expander and powered by operation of the liquid expander.   
   
   
       14 . The motor coolant system of  claim 13  wherein the predetermined pressure in the motor housing is maintained at a predetermined level throughout the operation of the motor coolant system. 
   
   
       15 . The motor coolant system of  claim 13  wherein the coupled pumping device and liquid expander are connected by one of a mechanical connection or an electrical connection. 
   
   
       16 . The motor coolant system of  claim 13  wherein the coupled pumping device and liquid expander are connected as one unit. 
   
   
       17 . The motor coolant system of  claim 13  comprising a heat exchanger disposed in the second refrigerant connection between the pumping device and the evaporator, the heat exchanger lowering the temperature of the refrigerant in the second refrigerant connection. 
   
   
       18 . The motor coolant system of  claim 13  wherein the pumping device lowers the density of the refrigerant within the motor housing to reduce windage losses of the motor. 
   
   
       19 . The motor coolant system of  claim 13  wherein the pumping device comprises one of an aerodynamic compressor or a positive displacement compressor. 
   
   
       20 . The motor coolant system of  claim 19  wherein the pumping device comprises one of a screw compressor, a reciprocating compressor, a scroll compressor, or a vane type compressor. 
   
   
       21 . The motor coolant system of  claim 13  wherein the liquid expander comprises one of an eductor, positive displacement expander or a turbine centrifugal expander. 
   
   
       22 . A method for cooling a motor of a chiller system comprising the steps of:
 providing a first connection with a refrigerant loop, the first connection being configured to receive refrigerant from an evaporator;   providing a second connection with the refrigerant loop, the second connection being configured to return refrigerant to the evaporator;   providing a motor in a motor cavity, the motor cavity being connected to the first connection and the second connection;   circulating refrigerant from the first connection through the motor cavity to the second connection with a pumping device;   powering the pumping device with energy of expansion from a liquid expander, the liquid expander being configured to expand refrigerant in the refrigerant loop between a condenser and the evaporator; and   wherein the circulation of refrigerant in the motor cavity by the pumping device cools the motor and lowers a pressure and gas density of a refrigerant in the motor cavity thereby reducing windage losses of the motor.   
   
   
       23 . The method of  claim 23  further comprising the step of connecting the pumping device and the liquid expander by one of an electrical connection or a mechanical connection. 
   
   
       24 . The method of  claim 24  wherein the pumping device and liquid expander are combined as a single unit. 
   
   
       25 . The method of  claim 23  further comprising the step of cooling the refrigerant in the second connection with a heat exchanger. 
   
   
       26 . The method of  claim 26  wherein the heat exchanger uses a cooling liquid for the condenser to cool the refrigerant in the second connection.