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Cooling Towers by the Numbers
Wet-bulb, range and approach, heat loads, performance, blowdown, water treatment, Legionella control, fans and siting, worked through one plant tower
Specify, run and check an industrial cooling tower with numbers: wet-bulb and approach, heat loads, Merkel performance, evaporation and blowdown, treatment, Legionella, fans, siting and tests.
Start readingAbout this book
A cooling tower rejects a plant’s waste heat to the atmosphere by evaporating a small fraction of the water passing through it. It is one of the most effective heat-rejection devices there is, able to cool water below the temperature of the air around it, and one of the most misunderstood: its performance depends on the air’s humidity, not its temperature; its water use depends on chemistry as much as on heat; and its water, warm, aerated and in contact with the air, can grow the bacteria that cause Legionnaires’ disease if it is not managed. Each of those can be understood with a few numbers.
This book works through a cooling tower in the order an engineer or operator meets it: what it does, the moist air it works with, the plant’s heat load and the water flow, the tower’s performance at different weather, evaporation, drift, blowdown and makeup, water treatment, Legionella control and the law, fans and energy, siting and recirculation, and testing and monitoring. Each chapter ends with an exercise and a worked answer.
It suits plant, facilities and maintenance engineers, operations managers and building owners. It assumes school algebra. Heat Exchangers by the Numbers covers the coolers that tower water serves; this book is about the tower.
The running case
Every chapter follows one fictional installation. This is an illustration. CT-250 is an open, induced-draught counterflow cooling tower serving a manufacturing plant: two hydraulic press oil coolers, two air compressors and a water-cooled chiller for its moulding machines, a total heat load of 250 kW. At a design wet-bulb temperature of 24 °C, it cools about 12 L/s of water from 34 °C to 29 °C. Its weather, loads, water chemistry and every number in the book are illustrations chosen to show the method.
The plant and its numbers are invented; none describes KEVOS® work or a real site. Prices, where they appear, are illustrations in Australian dollars, with GST stated.
Source limits and professional responsibility
This book is educational. Cooling towers are regulated in Australia for public health, and each state and territory sets its own requirements for registration, risk management, maintenance, testing and reporting; the requirements that apply to a real tower are those of its jurisdiction, administered by its health department or local council. Water treatment, Legionella risk management and testing must be carried out by qualified people as the law requires. Tower design and performance testing follow makers’ data and recognised codes. Nothing in this book replaces those obligations or that advice.
Who this book is for
Plant, facilities and maintenance engineers, operations managers and building owners who specify, operate or are responsible for open cooling towers serving industrial processes and buildings.
What you will learn
- Explain a cooling tower's performance in terms of wet-bulb temperature, range and approach, and why it can cool water below the air temperature.
- Build a tower's heat load from the plant it serves and work out its water flow, evaporation, blowdown and makeup.
- Predict a tower's cold water temperature at other wet-bulb temperatures from its characteristic.
- Set up water treatment and Legionella risk management within Australian state requirements and the AS/NZS 3666 series.
- Control fans for energy, site a tower to avoid recirculation, and test and monitor its performance.
Inside this book
Chapters
- 01What a cooling tower doesSee how a tower cools water by evaporating a little of it, what range, approach and wet-bulb mean, why it can cool below the air temperature, and catch a chiller nearly bought for a job a tower does.
- 02Moist air and the wet-bulb temperatureWork out the air a tower uses: humidity ratio, enthalpy, wet-bulb and dew point from temperature and humidity, why enthalpy drives a tower, and catch a 3 pm temperature paired with 9 am humidity.
- 03Heat loads, water flow and rangeBuild a tower's duty from its plant: each load's heat, chiller condensers, diversity, flow and range, and catch a list that counted a chiller's cooling, not its heat, and a diversity it never had.
- 04Tower performance and the Merkel methodModel a tower with the Merkel method: the air's operating line, the Merkel number, the characteristic and other wet-bulbs, and catch a tower specified at the annual-average wet-bulb.
- 05Evaporation, drift, blowdown and cyclesBalance a tower's water: evaporation, drift, blowdown and makeup, cycles of concentration and their cost, blowdown control, and catch a bleed left open that more than doubled the water bill.
- 06Water treatment: scale, corrosion, fouling and growthKeep tower water fit for the tower and its exchangers: scale, corrosion, fouling and growth, the treatment programme, monitoring and records, and catch a fouled probe that doubled the cycles.
- 07Legionella control and the lawManage a tower's public health risk: how Legionella grows and spreads, risk management plans, the NSW framework and AS/NZS 3666 as an example, and catch a restart without its procedure.
- 08Fans, control and energyControl a tower's fan for the cold water the plant needs: the fan laws, on–off, two-speed and variable-speed control, annual energy, and catch a drive left in hand at full speed all year.
- 09Siting, recirculation and plumePlace a tower where it breathes fresh air: recirculation, interference from other plant, clearances, plume and neighbours, and catch a courtyard site that raised the inlet wet-bulb by 1.5 K.
- 10Testing, monitoring and the tower's recordProve and track a tower's performance: the capability test and its conditions, routine monitoring against the model, inspections and the record, and catch a mild-day test that passed a 93% tower.
Apply This in Practice
Use these KEVOS® tools to try the method from this reading with your own numbers.
Explained in this book
Direct Evaporative Cooler Check (Wet-Bulb, Supply Temperature, Water Use, Cooling Capacity)
Uses the wet-bulb temperature this chapter calculates as the limit of a direct evaporative cooler.
Applies this method
Moist Air Dew Point and Surface Condensation Check (Humidity Ratio, Enthalpy, Dew-Point Margin)
Works out humidity ratio, enthalpy and dew point of air from temperature and relative humidity (not the wet-bulb).
Worked example
Adiabatic Mixing of Two Air Streams (Mixed Temperature, Humidity, Dew Point, Fog Risk)
Shows when two air streams make fog as they mix, as warm saturated tower exhaust does with cooler outside air to form the plume this chapter describes.
References and source notes
The manuscript and worked examples are original KEVOS® writing. References inform particular concepts; their authors do not endorse this book. Web references were consulted on 26 October 2026.
- U.S. Department of Energy. DOE Fundamentals Handbook: Thermodynamics, Heat Transfer, and Fluid Flow, Volume 2 of 3 (DOE-HDBK-1012/2-92) (1992). Supplied source, a public-domain United States government training handbook approved for public release. Used as a subject map of heat exchangers and cooling towers within plant heat rejection. Its treatment of cooling towers is brief; this book's methods, examples and figures are its own.
- NSW Health. Managing cooling water systems throughout their lifecycle (Current web page). Used for the New South Wales requirements described in Chapter 7: installation, operation and maintenance to the AS/NZS 3666 series, risk management plans, and monthly maintenance, chemical analysis and microbial testing by a duly qualified person. Other states and territories have their own laws.
- Standards Australia and Standards New Zealand. AS/NZS 3666.1, 3666.2 and 3666.3:2011 Air-handling and water systems of buildings — Microbial control (2011). Named by number and scope only: design, installation and commissioning; operation and maintenance; and performance-based maintenance of cooling water systems. No values or methods are quoted from them.
- Cooling Technology Institute. CTI ATC-105 Acceptance Test Code for Water Cooling Towers (Current edition). Named by number and scope only, as the code for testing a cooling tower's thermal capability, referred to in Chapter 10. No values or methods are quoted from it.