Compact indirect evaporative cooler

Abstract

An indirect evaporative cooling system with a core greatly reduced in size compared to conventional evaporative cooling systems The system has a heat exchanger core having heat exchange plates defining a plurality of wet air flow passages and a plurality of dry air flow passages. At least one fan drives air through the passages. The dry air passages have a small height and a short length, configured so that a substantially laminar airflow having a raised shear rate arises in the dry air passages, and so that a back pressure across a length of the dry air passages remains low.

1 . An indirect evaporative cooler comprising
 a heat exchanger core having heat exchange plates defining alternating wet and dry air flow passages, wherein the relationship between the passage height, measured as space between plates defining at least the dry air flow passages, and the length of the air flow passages falls within an area on a graph defined by the following points, wherein passage length is plotted on one axis and passage height, measured as distance between plates, is plotted on another axis:   
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                   Passage 
                   Passage 
                 
                     
                   Length (mm) 
                   Height (mm) 
                 
                     
                     
                 
                     
                 
                 
                 
                 
               
                     
                   500 
                    1.9-7.5 
                 
                     
                   400 
                    1.7-5.5 
                 
                     
                   300 
                   1.55-4.5 
                 
                     
                   200 
                    1.3-3.5 
                 
                     
                   100 
                    0.9-2.7 
                 
                     
                   75 
                    0.8-2.3  
                 
                     
                   50 
                    0.7-1.7 
                 
                     
                   25 
                    0.6-1.1 
                 
                     
                     
                 
             
                
                
                
                
               
               
                
               
            
             
                
                
                
                
                
                
                
                
                
               
            
           
         
       
     
     
         2 . The indirect evaporative cooler as claimed in  claim 1 , wherein the relationship between the passage height of at least the dry air flow passages and the length of the passages falls within an area on a graph defined by the following points, wherein passage length is plotted on one axis and passage height is plotted on another axis: 
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                   Passage 
                   Passage 
                 
                     
                   Length(mm) 
                   Height (mm) 
                 
                     
                     
                 
                     
                 
                 
                 
                 
               
                     
                   500 
                    2.8-4.5 
                 
                     
                   400 
                    2.5-3.7 
                 
                     
                   300 
                    2.2-3.3 
                 
                     
                   200 
                    1.8-2.5 
                 
                     
                   100 
                    1.5-2.2 
                 
                     
                   75 
                    1.1-1.7 
                 
                     
                   50 
                    0.9-1.1 
                 
                     
                   25 
                   0.65-0.7 
                 
                     
                     
                 
             
                
                
                
                
               
               
                
               
            
             
                
                
                
                
                
                
                
                
                
               
            
           
         
       
     
     
         3 . The indirect evaporative cooler as claimed in  claim 1 , wherein passage length is from 80 to 200 mm. 
     
     
         4 . The indirect evaporative cooler as claimed in  claim 1 , wherein the space between plates defining dry passage height is from 0.6 mm to 2.5 mm. 
     
     
         5 . The indirect evaporative cooler as claimed in  claim 4 , wherein the space between plates defining dry passage height is from 0.7 mm to 1.4 mm. 
     
     
         6 . The indirect evaporative cooler as claimed in  claim 5 , wherein the space between plates defining dry passage height is from 0.8 mm to 1.2 mm. 
     
     
         7 . The indirect evaporative cooler as claimed in  claim 1 , wherein the space between plates defining wet passage height is from 0.6 mm to 2.5 mm. 
     
     
         8 . The indirect evaporative cooler as claimed in  claim 7 , wherein the space between plates defining wet passage height is from 0.7 mm to 1.4 mm. 
     
     
         9 . The indirect evaporative cooler as claimed in  claim 8 , wherein the space between plates defining wet passage height is from 0.8 mm to 1.2 mm. 
     
     
         10 . A method of indirect evaporative cooling, the method comprising
 directing a laminar flow of air at a flow rate of 2.5-7.0 m/s through at least dry air passages of a heat exchanger having heat exchange plates defining alternating wet and dry air flow passages, the plates having a separation of from 0.6 mm to 2.0 mm and defining air passages having a length of from 25 to 300 mm,   dividing the air after passing through the dry passages into first and second air streams,   directing the first air stream into the wet air flow passages in counter-current flow to the airflow in the dry passages, and   directing the second air stream to a space to be cooled.   
     
     
         11 . The method of indirect evaporative cooling as claimed in  claim 10 , wherein air is flowed through the dry air flow passages at 3.0-7.0 m/s. 
     
     
         12 . The method of indirect evaporative cooling as claimed in  claim 10  Of  claim 11 , wherein air is flowed through the wet air flow passages at 2.5-4.0 m/s. 
     
     
         13 . An indirect evaporative cooler comprising:
 a heat exchanger core having heat exchange plates defining a plurality of wet air flow passages and a plurality of dry air flow passages; and   at least one fan configured to drive air through the dry air passages,   the dry air passages being configured so that a substantially laminar airflow having a raised shear rate arises in the dry air passages, and so that a back pressure across a length of the dry air passages remains acceptably low.