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Views: 0 Author: Site Editor Publish Time: 2025-12-15 Origin: Site
In any water cooling tower application, understanding and controlling cooling tower make up water is essential for efficient operation, cost control, and water conservation. Make-up water replaces losses caused by evaporation, blowdown, and drift, ensuring stable operation of the water cooling tower system.
This article provides a complete and practical guide on how to calculate cooling tower make up water, with clear formulas, tables, and engineering explanations. It applies to both water cooled tower and closed loop cooling tower designs and reflects common practices used by professional manufacturers such as Mach Cooling (https://www.machcooling.com/).
Cooling tower make up water is the fresh water supplied to a cooling tower to compensate for water losses during operation. These losses occur as part of the heat rejection process and water quality control strategy.
In a typical water cooling tower system, make-up water is automatically added to maintain a stable basin water level and consistent thermal performance.
Accurate cooling tower make up water calculation helps to:
Ensure sufficient cooling tower water supply
Reduce unnecessary water consumption
Control chemical treatment costs
Support sustainable cooling tower water use
Incorrect estimates can lead to system instability, overflow, or excessive blowdown.
Evaporation is the primary cooling mechanism. As water evaporates, heat is removed, but pure water vapor leaves the system.
A common engineering approximation is:
Blowdown is the intentional discharge of water to control dissolved solids and maintain acceptable water quality.
Blowdown depends on the Cycle of Concentration (COC):
Blowdown is directly influenced by cooling tower water testing and the cooling tower water treatment system.
Drift is water lost as fine droplets carried out with exhaust air. Modern towers with drift eliminators typically limit drift to:
0.005%–0.02% of circulating water flow
The total make-up water requirement is calculated as:
M = E + B + D
Where:
(M) = make-up water
(E) = evaporation loss
(B) = blowdown loss
(D) = drift loss
This formula applies to all water cooled tower configurations.
| Parameter | Value |
|---|---|
| Circulating water flow | 800 m³/h |
| Cooling range | 5 °C |
| Cycle of concentration | 4 |
| Drift rate | 0.01% |
E=0.001×800×5=4 m³/h
D=800×0.0001=0.08 m³/h
M=4+1.33+0.08=5.41 m³/h
This is the required cooling tower makeup water to maintain stable operation.
Cooling tower makeup water per ton refers to the amount of make-up water required for each ton of refrigeration (TR).
A typical engineering estimate is:
| Operating Condition | Makeup Water per Ton |
|---|---|
| Low COC (2–3) | 5–7 L/h·TR |
| Medium COC (4–5) | 3–5 L/h·TR |
| High COC (6–7) | 2–4 L/h·TR |
Higher COC reduces water consumption but requires stronger cooling tower water treatment system control.
In a closed loop cooling tower, process water circulates inside a coil, while spray water evaporates externally. Make-up water calculation still follows the same principles but applies only to the spray water circuit.
Although closed loop systems reduce contamination risk, cooling tower water testing remains essential to control spray water quality and prevent fouling of heat exchange surfaces.
A cooling tower makeup water float valve is a mechanical device that maintains basin water level by opening or closing based on water height.
Advantages:
Simple structure
Low cost
Reliable for small to medium systems
Cooling tower electronic water level control systems use sensors and solenoid valves to regulate make-up water more precisely.
Benefits:
Accurate water level control
Reduced overflow risk
Better integration with automation systems
| Parameter | Recommended Range |
|---|---|
| pH | 6.5 – 8.5 |
| Conductivity | Project-specific |
| Total hardness | < 300 mg/L |
| Suspended solids | < 50 mg/L |
Maintaining cooling tower makeup water quality standards protects equipment and allows higher cycles of concentration.
A well-designed cooling tower water treatment system enables:
Reduced blowdown
Lower cooling tower water use
Stable long-term operation
Chemical dosing, filtration, and monitoring are key components.
Accurate make-up water calculation helps operators:
Reduce fresh water consumption
Control wastewater discharge
Improve system sustainability
Manufacturers like Mach Cooling (https://www.machcooling.com/) design cooling towers and accessories that support precise water balance control and efficient make-up water management.
Understanding how to calculate cooling tower make up water is essential for efficient operation of any water cooling tower system. By accurately estimating evaporation, blowdown, and drift losses, operators can determine the correct cooling tower makeup water requirement and optimize overall water usage.
Proper make-up water control improves:
Thermal performance
Water efficiency
Chemical treatment effectiveness
Reliability of both water cooled tower and closed loop cooling tower systems
With professional design support and proven solutions from Mach Cooling, cooling towers can achieve long-term efficiency while minimizing operating costs and environmental impact.
