Many works had been studied by several institutes, but the study by CTI is most acceptable for the tower designs. The recirculation in the cooling towers is defined as an adulteration of the atmosphere entering the tower by a portion of the atmosphere leaving the tower. This adulteration by the exhaust air raises the wet bulb temperature of the entering air above that of the ambient air, reducing the tower overall performance.

The recirculation phenomenon arises primarily because of the negative pressure produced on the leeward side of the cooling tower by the wind blowing across the structure. Thus, any factors which enhances this lee-side negative pressure will increase recirculation. At the same time, those elements of tower design or meteorological phenomena which increase the amount of ambient air which mixes with the exhaust air before entering the lee-side air inlets will reduce the magnitude of recirculation. Recirculation is therefore a complex result of factors which affect the lee-side negative pressure and the amount of exhaust air dilution.

From the mathematical standpoint recirculation can be expressed as the percent of the exhaust air which reenters the tower at the air inlets. Thus, considering a heat balance on the air around the tower:

Heat (Q) = G h₁ = G (1 - R_c/100) h_a + G (R_c /100) h₂ 

This equation could be written as below:

G h₁ = G h_a - G R_c h_a / 100 + G R_c h₂ / 100 
G (h₁ - h_a) = G R_c /100 (h₂ - h_a) 

Solving for R_c, 
R_c = (h₁ - h_a) / (h₂ - h_a) x 100