Multi-stage heat exchanger

Abstract

A refrigeration system that utilizes both an air-cooled heat exchanger and a cooling tower to cool refrigerant prior to the refrigerant being provided to the evaporator. This multi-stage cooling permits the refrigeration system to operate with improved efficiency, while reducing the amount of water lost to evaporative cooling in the cooling tower, since the thermal load handled by the cooling tower is reduced by the air-cooled heat exchanger. This in turn means less water is required to replace water lost to evaporative cooling. In arid regions or regions of low water quality, both efficiency increase and reduction of water lost to evaporative cooling are important improvements.

1 . A multi-stage cooling system for use in a refrigeration system having a condenser, a subcooler, an evaporator and a compressor circulating refrigerant in a closed system, comprising:
 an air-cooled heat exchanger in heat exchange communication with the condenser, the air-cooled heat exchanger cooling the refrigerant to a first temperature before exiting the condenser and circulating the refrigerant to the subcooler;   a cooling tower having an open water loop in heat exchange communication with the subcooler, the water-cooled cooling tower cooling the refrigerant from the first temperature to a second temperature before circulating the refrigerant to the evaporator; and   wherein a thermal load on the cooling tower from cooling the refrigerant from the first temperature to the second temperature is reduced, resulting in a reduced consumption of water by the cooling tower.   
     
     
         2 . The system of  claim 1  wherein the air-cooled heat exchanger includes a closed water loop having a first heat exchanger in communication with the condenser and a second heat exchanger in communication with the air. 
     
     
         3 . The system of  claim 2  wherein the cooling tower is sized to accommodate the thermal load required to cool the refrigerant from the condenser exit temperature to the second temperature. 
     
     
         4 . The system of  claim 1  wherein the refrigeration system further includes a plurality of compressors operating in series. 
     
     
         5 . The system of  claim 1  wherein the refrigeration system further includes a plurality of compressors operating in parallel. 
     
     
         6 . A refrigeration system that includes a compressor, a condenser, an evaporator, an expansion valve, refrigerant in a refrigerant loop cycled from the compressor, to the condenser and to the evaporator, the improvement comprising;
 an air-cooled heat exchanger that includes
 a fan, 
 an outdoor heat exchanger, and 
 a first closed water loop that cycles water from the condenser to the outdoor heat exchanger, wherein the water removes heat from a refrigerant gas in the condenser, condensing the refrigerant gas to a liquid at a first temperature, and wherein the outdoor heat exchanger removes heat from the water by circulating air over the outdoor heat exchanger with a fan; 
 a subcooler unit comprising 
 a subcooler heat exchanger, 
 a cooling tower, 
 a cooling tower supply water line, and 
 a cooling tower return water line, 
 wherein the subcooler unit receives the refrigerant liquid from the condenser and cools the refrigerant liquid to a second temperature lower than the first temperature using cooling water, the cooling water supply line providing heated water from the subcooler to the cooling tower, the cooling tower cooling the water, the cooling water return line providing cooled water from the cooling tower to the subcooler, and the cooling tower return water replenishment line providing additional water to the cooling water return line to replenish water evaporated in the cooling tower; 
   wherein refrigerant is provided to the evaporator at the second temperature; and   wherein a thermal load on the subcooler unit resulting from cooling the refrigerant from the first temperature to the second temperature is reduced due to cooling by the air-cooled heat exchanger.   
     
     
         7 . The refrigeration system of  claim 6  wherein the subcooler heat exchanger includes a refrigerant side and a water side, the water side of the subcooler heat exchanger, the cooling tower supply water line, the cooling tower and the cooling tower return water line forming an open loop system. 
     
     
         8 . The refrigeration system of  claim 7  wherein evaporative cooling in the open loop system results in evaporation of water, which evaporation is reduced due to the reduced thermal load. 
     
     
         9 . The refrigeration system of  claim 8 , wherein the open loop system further includes a cooling tower return water replenishment line, wherein the cooling tower return water replenishment line that replaces water lost to evaporation, which replacement is reduced due to reduced evaporation from the reduced thermal load. 
     
     
         10 . The refrigeration system of  claim 8  further including a body of water in fluid communication with the cooling tower return water replenishment line. 
     
     
         11 . The refrigeration system of  claim 10  wherein the body of water in fluid communication with the cooling tower is a river, a stream or a lake. 
     
     
         12 . The refrigeration system of  claim 10  wherein water from the body of water is first treated and purified prior to entering the cooling water return line. 
     
     
         13 . The system of  claim 1  wherein the refrigeration system further includes a plurality of compressors operating in series. 
     
     
         14 . The system of  claim 1  wherein the refrigeration system further includes a plurality of compressors operating in parallel.