In the event there are several users which needed to be cooled down and the needs for cooling water flow and cooling capacity can change through time, a dual-circuit cooling circulation system is the optimum solution.

The pumps which ensure water circulation in the circuit of users, also called primary circuit, pump cold water from the cold water pool and supply it to the users. Heated water from the users is directed to the heated water pool. The pumps which ensure water circulation in the circuit of cooling towers, also known as secondary circuit, pump cold water from the heated water pool and supply it to cooling towers where it cools down. Cooled water is directed to the cold water pool.

In open cooling system one part of energy is released by means of heat transfer from water into the air, another part of energy is released through evaporation. Such cooling systems are used when cooled water temperature is a few degrees higher than wet thermometer temperature. Theoretically, cooling water temperature is approaching to the wet thermometer temperature.

Due to a steady evaporation of water steam from the system, the concentration of other substances is rising, which is called thickening of the water system. When thickening becomes too strong or too high, this will overcome the solubility of some sorts of salt which could cause the appearance of lining or sediments, and corrosion on elements of cooling system. For this reason a part of the water system is released and replaced by fresh water with a lower concentration of dissolved substances. This is the way how we maintain a balanced quality of water system, where the problems of sediments, lining and corrosion can be manageable. Such water release is called total dissolved solids (TDS). In modernised systems this process is carried out automatically.

For regular functioning of the system we must take care of adequate preparation of intake water and water system treatment.