How To Calculate Cooling Tower Water Consumption

Introduction

In industrial cooling, HVAC, and process cooling systems, the use of cooling towers (such as those from Mach Cooling — https://www.machcooling.com/) inevitably leads to water consumption. Cooling tower water consumption mainly includes evaporation, drift loss (water droplets carried out by airflow), and blowdown (water discharge). Accurately calculating cooling tower water consumption is critical for system make-up water, water treatment, resource management, and operational cost control.

This article introduces the components of cooling tower water consumption, calculation methods, required parameters, examples, a table template, and how to reasonably estimate and manage water use with Mach Cooling towers.

Components of Cooling Tower Water Consumption — Evaporation / Drift / Blowdown

2.1 Three Major Water Loss Mechanisms

Cooling tower water consumption (or make-up water requirement) mainly comes from three mechanisms:

• Evaporation Loss (E) — water evaporates to remove heat and cool the remaining water.

• Drift Loss (D) — fine water droplets are carried out by airflow. Even with a drift eliminator, a small amount of water is lost.

• Blowdown Loss (B) — a portion of water is discharged to control dissolved solids (minerals, salts, etc.) and replaced with fresh water to maintain water quality and system stability.

The total make-up water (M) required equals the sum of these losses:

M = Evaporation (E) + Drift (D) + Blowdown (B)

Calculation Methods for Cooling Tower Water Consumption

2.2 Evaporation Loss

Evaporation loss is the largest portion of water consumption. A common empirical formula is:

E = 0.00085 × C × (T_in – T_out)   (when temperature in °F and C is the circulating water flow)

Or using the metric approximation: roughly, for every 10 °F drop (~5.5°C), evaporation is about 1% of circulating water flow.

The heat balance method can also calculate evaporation based on heat transfer and latent heat:

E = (C × Cp × ΔT) / λ

• C = Circulating water flow (kg/hr or m³/hr)

• Cp = Specific heat of water (~4.184 kJ/kg·°C)

• ΔT = Temperature difference between inlet and outlet

• λ = Latent heat of vaporization (~2260 kJ/kg)

2.4 Drift Loss

Drift loss depends on tower structure, drift eliminator efficiency, airflow, and environmental conditions. Typically estimated as a percentage of circulating water:

• Induced-draft towers: 0.1%–0.3%

• High-efficiency eliminators: 0.01% or lower

• Natural-draft or older towers: 0.3%–1%

D ≈ Drift Rate × C

Drift Rate depends on tower design and operational conditions.

2.5 Blowdown Loss

As water evaporates, the concentration of dissolved minerals and salts increases. Without blowdown and make-up water, scaling and corrosion can occur.

Blowdown is estimated as:

B = E / (COC – 1)   (COC = Cycle of Concentration)

COC is determined by make-up water quality, allowable concentration, and blowdown frequency, typically ranging from 3–7.

 Practical Operation — Required Data and Calculation Example

3.1 Required Parameters

• Circulating water flow C (m³/hr or GPM)

• Cooling tower inlet and outlet water temperatures (T_in, T_out) → ΔT

• Blowdown cycle and COC

• Drift eliminator status / drift rate estimate

• Make-up water quality and system water quality limits

3.2 Example Calculation

Assume a system with a Mach Cooling tower:

• C = 2000 m³/hr

• T_in = 45 °C, T_out = 35 °C → ΔT = 10 °C

• Drift rate = 0.2%

• COC = 4

Calculations:

1. Evaporation: E ≈ 0.00085 × 2000 × 18 ≈ 30.6 m³/hr

2. Drift: D ≈ 0.2% × 2000 = 4 m³/hr

3. Blowdown: B ≈ 30.6 / (4 – 1) ≈ 10.2 m³/hr

4. Total Make-up Water: M = E + D + B ≈ 30.6 + 4 + 10.2 = ≈ 44.8 m³/hr

So the tower requires approximately 44.8 m³ of make-up water per hour.

 Water Consumption Record and Management Table Template

Why Accurate Water Consumption Calculation Matters for Mach Cooling Towers

4.1 Large Flow / Heavy Load Systems

Mach Cooling towers are widely used in industrial and HVAC systems. Inaccurate estimation may cause:

• Insufficient water → system instability

• Excessive concentration → scaling / corrosion

• Frequent or inadequate make-up → increased cost or damage

4.2 Water Conservation and Environmental Compliance

Accurate calculation and optimization of drift and blowdown:

• Reduces make-up water

• Decreases blowdown volume

• Extends water treatment intervals

• Improves system stability and compliance

4.3 Maintenance and System Stability

Regular monitoring of:

• Evaporation losses

• Drift increase

• Blowdown efficiency

Helps adjust operations promptly and prevents performance degradation.

Notes and Common Mistakes

5.1 Consistency of Units

• Ensure temperature units (°F/°C) and flow units (m³/hr, GPM) match the formulas.

 5.2 Do Not Ignore Drift and Blowdown

Even small percentages accumulate to significant water loss; ignoring them underestimates make-up water needs.

5.3 Water Quality and System Design

Hard water or high mineral content may require lower COC, more blowdown, or more frequent make-up to prevent scaling and corrosion.

 Conclusion

Accurate calculation of cooling tower water consumption is essential for design and operation management. By understanding the components of water loss, formulas, examples, and record-keeping, combined with Mach Cooling tower operational features, you can:

• Accurately estimate make-up water demand

• Plan effective blowdown and drift control

• Save water and reduce operating costs

• Improve system stability and equipment lifespan