Water Consumption of Closed-Loop Cooling Systems

Emily Green

Emily is a senior R & D engineer at Oasis Bingfeng Fluid Equipment Co., Ltd. With over 10 years of experience in the cooling equipment industry, she has played a key role in the development of the company's core products, including closed cooling towers and air coolers.

A closed-loop cooling system consists of two independent water circuits: a sealed internal process circulation circuit and an external spray circulation circuit. The water consumption and loss of the two circuits are completely separated.

Total water demand covers two parts: static system holding water volume and makeup water for daily operation. Compared with traditional open cooling towers, it delivers outstanding water-saving performance and serves as the mainstream cooling solution for new energy, chemical industry, precision manufacturing and data centers.

I. Total Static Holding Water Volume (One-Time Filling Volume)

Static water volume refers to the total water to be filled during initial commissioning or full draining after major overhaul, composed of internal process water and external spray water.

Sealed Internal Process Circulation Water

This circuit is fully enclosed within coils, pipelines, heat exchangers and buffer water tanks without exposure to air, resulting in negligible natural water loss during operation. Calculation Formula: Process Water Volume = Pipeline Volume + Coil Volume + Buffer Tank Volume Under standard industrial working conditions, the static holding volume reaches around 8–12 m³ per 100 m³/h of process circulation flow. Small units with flow below 50 m³/h hold 3–6 m³ of water.

Large closed-loop systems for energy storage and chemical processes with flow exceeding 1,000 m³/h require up to hundreds of cubic meters for one-time filling. Softened water, pure water or ethylene glycol aqueous solution are commonly adopted as the circulating medium. Only tiny amounts of medium need to be supplemented for leakage after initial filling, and large-scale medium replacement is unnecessary all year round.

External Spray Circulation Water

Spray water flows over the outer surface of sealed coils for evaporative heat exchange and is stored in the bottom water sump of the cooling tower. Its static volume only accounts for 20%–50% of the process circulation flow. Take a 500 m³/h closed-loop process cooling system as an example: the spray circulation flow ranges from 100 to 250 m³/h, while the static holding water in the sump is merely 5–15 m³, far less than hundreds of cubic meters stored in the water basin of open cooling towers of the same specification.

The total one-time filling volume of a complete closed-loop system is only 30%–50% of that of an open system with identical heat dissipation capacity, greatly cutting initial water usage.

II. Makeup Water Consumption in Daily Operation (Core Source of Continuous Water Loss)

Daily water loss of closed-loop systems only occurs in the external spray circuit, while loss of the internal circulation can be ignored. Total makeup water volume comprises evaporation loss, drift loss and blowdown loss. General Formula: Hourly Makeup Water Volume = Evaporation Loss + Drift Loss + Blowdown Loss

Evaporation Loss (70%–80% of total loss, primary water consumer)

Heat is removed via evaporation of spray water, and temperature difference directly determines evaporation capacity. Industrial empirical standard: when the temperature difference between inlet and outlet spray water is 5℃, evaporation loss equals 0.54% of total spray circulation flow.Precise Calculation Formula: WE=Δt×L×4.1868÷2520 Where Δt = temperature difference of spray water;

L = hourly spray flow rate. For instance, with a spray flow of 200 m³/h and 5℃ temperature difference, hourly evaporation loss hits approximately 1.08 m³.

In hot summer with rising wet-bulb temperature, evaporation loss slightly rises to 0.6%–0.8% of spray flow.

Drift Loss

High-efficiency water eliminators intercept water mist, leading to extremely low drift loss for closed-loop systems, merely 0.001%–0.1% of spray water volume. Premium equipment can control drift loss below 0.05%, creating almost no water burden, vastly superior to open towers with 2%–3% drift loss.

Blowdown Dilution Loss

Salts accumulate in spray water after long-term evaporation, so regular blowdown is required to control concentration cycles, with standard concentration cycles ranging from 3 to 5.

Calculation Formula: Blowdown Volume = Evaporation Loss ÷ (Concentration Cycle − 1) Closed-loop systems feature a small base volume of spray water, resulting in low blowdown frequency and limited discharge volume. Systems with rigorous water quality management can extend blowdown intervals and further reduce makeup water demand.

Combining all three types of loss, under standard working conditions, the total hourly makeup water of closed-loop systems only accounts for 0.5%–1.5% of spray circulation flow. Converted to main process circulation flow, overall water consumption is just 10%–20% of open cooling towers of equal specification.

Comparison based on a 500 m³/h closed-loop process cooling system: open towers require 10–15 m³ makeup water per hour, while closed-loop systems only consume 0.5–1.5 m³ per hour. For 20-hour continuous daily operation, over 170 tons of water can be saved, equivalent to more than 50,000 tons of annual water savings, significantly alleviating water quota pressure in water-scarce regions.

III. Key Variables Affecting Closed-Loop System Water Consumption

Heat load and ambient wet-bulb temperature: evaporation loss surges by 20%–30% under hot and humid summer conditions. In low-temperature winter, the dry cooling mode can be activated with spray shut down to achieve zero makeup water consumption.

Equipment structure: widely spaced coils and high-density water eliminators cut drift loss, while large-capacity sumps reduce frequent makeup refilling.

Water quality management: adopting softened spray water raises concentration cycles and lowers blowdown-related water waste.

System tightness: leakage of internal circulation pipelines and valves slightly increases pure water makeup volume. Regular inspections can limit leakage loss below 0.05%.

IV. Practical Water Consumption Cases in Industrial Applications

800 m³/h closed-loop cooling system for data centers and energy storage: total static filling volume around 90 m³; hourly makeup water of 1.2–1.8 m³ under high summer temperature, zero makeup water in winter dry cooling mode.

400 m³/h closed-loop unit for chemical crystallization cooling: static filling volume of 45 m³, average hourly makeup water of 0.6–1.0 m³ all year round.

During long-term operation, closed-loop cooling systems deliver dual water-saving merits: low one-time filling volume and minimal continuous makeup water demand. Meanwhile, the internal process circulation water remains clean for extended periods without frequent medium replacement, cutting water resource consumption and water treatment costs from the source, and complying with industrial water conservation and emission reduction policies.