Enter the conductivity of the system water and the conductivity of the makeup into the calculator to determine the cycles of concentration.

Cooling Tower Cycles of Concentration Formula

The following equation is used to calculate the Cooling Tower Cycles of Concentration.

COC = Csystem / Cmakeup

  • Where C is the Cooling Tower Cycles of Concentration
  • Csystem is the conductivity of the system
  • Cmakeup is the conductivity of the makeup

Conductivity can be substituted for values of chloride or values of silica and the result will be the same.

What is a Cooling Tower Cycles of Concentration?


A cooling tower cycles of concentration is a method of calculating the amount of dissolved solids in the water that enters and leaves the cooling tower.

This is important because, if there are high levels of dissolved solids in the water, there will be scaling or fouling of the heat transfer surfaces which reduces efficiency.

A cooling tower cycle of concentration calculation is also known as a total dissolved solids (TDS) calculation. To carry out a complete TDS calculation, you need to measure the temperature and pressure you are collecting your samples, as these will affect your TDS readings.

There are two methods for measuring cooling tower cycles of concentration, gravimetric and volumetric.

The most accurate way to determine the cycles of concentration is by using a gravimetric method. Gravimetric measurements involve weighing the cooling tower water before it enters the system and then weighing it after it has been through the system. The difference between these two weights is a direct indication of how much water has been evaporated from the cooling tower.

The tower design is dependent on COC, with higher COCs generally resulting in greater efficiency and capacity. The more water goes through each tower section, the more saturated with salts and other impurities it becomes. This can reduce overall efficiency and power over time. A typical cooling tower will have multiple passes for each section to combat this problem.

For example, if there are three sections in a cooling tower and six passes for each team, there will only be 108 total passes instead of 216 total passes—a reduction of nearly 50%. This also reduces overall pressure drop (how much energy is lost moving through piping) by reducing the pipe size required to move the same volume of water.