Every cooling tower loses water in two ways: evaporation and blowdown. Evaporation is the mechanism by which the tower actually cools — water evaporates and carries heat away with it. The minerals dissolved in that water do not evaporate; they stay behind and concentrate in the recirculating water. Blowdown is the deliberate discharge of a portion of that concentrated water to prevent dissolved solids from building up to levels that cause scale, corrosion, or biological problems. Make-up water is added to replace both the evaporation loss and the blowdown.
The relationship between the concentration of dissolved solids in the recirculating water and the concentration in the make-up water supply is the cycles of concentration. A system running at five cycles of concentration has circulating water that is five times more concentrated in dissolved solids than the incoming make-up supply. A system at ten cycles is ten times more concentrated.
Why Cycles of Concentration Matters for Water Efficiency
The higher the cycles of concentration, the less water is wasted through blowdown. At two cycles, for every litre of water evaporated, one litre is discarded as blowdown — a 50% efficiency. At five cycles, for every litre evaporated, only 0.25 litres is discarded. At ten cycles, only 0.11 litres per litre evaporated. The relationship is not linear, and the water savings from moving from two cycles to five are far larger than the savings from moving from five to ten.
Many cooling towers in Malaysia operate at low cycles of concentration not because of deliberate choice but because their blowdown is either manual, timer-based, or poorly controlled. The result is that they discharge more water than necessary, add more make-up water than necessary, and dose more chemical treatment than necessary — because chemical consumption scales with the volume of water discharged.
The Upper Limit: Why You Cannot Just Run Indefinitely High Cycles
Running at very high cycles of concentration is not without risk. As dissolved solids concentrate, the saturation indices for sparingly soluble salts — primarily calcium carbonate and calcium sulphate — increase. Above a certain cycles level for a given make-up water chemistry, the risk of scale precipitation on heat exchanger surfaces increases significantly. The Langelier Saturation Index and Ryznar Stability Index are the standard tools for calculating the scale tendency of the recirculating water at a given cycles level and temperature.
Biological risk also increases at higher cycles. Elevated conductivity and dissolved solids can affect the efficacy of some biocides. The optimal cycles level for a given system is therefore determined by the make-up water chemistry, the treatment programme chemistry, and the operational temperature of the system — not by a universal target.
Conductivity-Based Blowdown Control
The practical method for managing cycles of concentration is conductivity measurement. Conductivity in the recirculating water rises as dissolved solids concentrate and falls after blowdown dilutes the system. If you measure the conductivity of both the make-up water and the recirculating water, the ratio of the two gives you the cycles of concentration directly. Alternatively, if the make-up water conductivity is relatively stable, a single conductivity setpoint on the recirculating water serves as a reliable proxy for cycles level.
A conductivity-based controller measures circulating water conductivity continuously and opens the blowdown valve when conductivity exceeds a setpoint, discharging concentrated water until conductivity falls back within range. This replaces timer-based or manual blowdown with demand-responsive blowdown — the system discharges only when the water chemistry actually requires it, not on a fixed schedule that is almost always wrong for the actual operating conditions.
Automated Management with the Aquarius Ultima Controller
The Aquarius Ultima water treatment controller provides conductivity-based blowdown control as part of a broader cooling tower management platform. It measures recirculating water conductivity continuously, controls the blowdown valve automatically to maintain the target cycles setpoint, and logs conductivity and blowdown activity over time — providing a documented record of system water management that supports both operational optimisation and compliance reporting.
The controller can also integrate with dosing pumps to coordinate chemical treatment with blowdown events, ensuring that treatment chemical concentration is maintained correctly as water is discharged and replaced. This closes the loop between water management and chemical management, reducing both water waste and chemical overconsumption simultaneously.
For cooling tower operators in Malaysia looking to reduce water and chemical costs without compromising treatment programme performance, optimising cycles of concentration through automated conductivity control is one of the highest-return operational changes available. To discuss how the Aquarius Ultima can be configured for your system, contact us at info@autoflotechnology.com.