Cooling tower selection matches the heat rejection load, entering wet-bulb temperature, and available footprint to a tower type that keeps the condenser water at 30 to 37 °C. A typical 1,000 kW chiller rejects about 1,200 to 1,300 kW of heat, needing a tower that evaporates roughly 0.5 to 0.7 kg/s of water to hold the design approach of 3 to 5 °C above the 25 to 30 °C wet bulb. Undersize the tower and the chiller loses COP; oversize it and you waste concrete, fan power, and water-treatment capacity.
How a Cooling Tower Works
Warm condenser water (35 to 40 °C) is sprayed over fill while fans draw ambient air upward. A portion evaporates, removing latent heat at about 2,400 kJ/kg, which cools the remaining water toward the wet-bulb temperature. The colder the wet bulb, the lower the leaving water temperature and the better the chiller COP. The rest of the water falls to the basin and is pumped back, so only the evaporated fraction is truly lost from the loop.
Tower Types Compared
The table contrasts the three common arrangements on the criteria that drive selection.
| Type | Airflow | Typical Range | Best Use |
|---|---|---|---|
| Counterflow induced-draft | Up, fan on top | 100 kW – 10 MW | Space-limited sites |
| Crossflow | Across, fan on top | 200 kW – 15 MW | Easy maintenance |
| Open vs closed circuit | Direct / indirect | 50 kW – 20 MW | Process vs clean loop |
Key Selection Parameters
Four numbers define the duty: the heat load (kW), the wet-bulb design temperature (often 25 to 30 °C), the approach (leaving water temperature minus wet bulb, usually 3 to 5 °C), and the range (entering minus leaving water temperature, commonly 5 to 10 °C). Raising the approach by just 1 °C can shrink the tower by 10% to 15% but raises chiller condenser pressure, so the trade must be evaluated on total plant energy, not tower first cost alone.
Water and Treatment
A tower evaporates 1% to 3% of circulation and drifts a tiny fraction, so a 1,000 kW plant may lose 0.5 to 1.0 kg/s of water. Make-up water must be treated for scale and biologically, with continuous dosing keeping total dissolved solids under 3 to 5 times the make-up concentration via bleed-off. Without bleed-off, mineral concentration can climb past 6 times make-up and scale the fill within a single season, cutting heat transfer and raising fan power.
Fan Power and Sizing
Tower fan power scales with airflow, typically 0.01 to 0.03 kW per kW of heat rejected, so a 1,200 kW tower may draw 15 to 35 kW of fan power. Two-speed or variable-speed fans let the tower track load, cutting fan energy 30% to 60% at part load. Matching the fan to the design wet bulb rather than the absolute summer peak avoids a permanently oversized, noisy installation that wastes electricity most of the year.
When to Choose Each Type
- Choose a counterflow induced-draft tower when footprint is tight and you can accept slightly harder fill access.
- Choose a crossflow tower when you want easy internal access for cleaning and can spare the larger plan area.
- Choose a closed-circuit tower when the process fluid must stay separate from ambient air to avoid fouling or freezing of a clean loop.
Keruite manufactures this equipment at an 80,000 m² facility in Dezhou, China, with an in-house AMCA-210-style test laboratory; every unit is balanced to G2.5 and performance-tested before shipment.
Noise and Plume
Induced-draft fans emit 70 to 85 dBA at 1 m, so towers near offices need low-noise fans or acoustic baffles. Plume (visible vapor) is harmless but can annoy neighbors; in cold climates a hybrid tower blending dry and wet sections cuts plume and saves water during winter by 20% to 40%. Siting the tower upwind of intakes and away from windows resolves most complaints before they start.
Water Treatment in Practice
Because a tower concentrates everything dissolved in the make-up water, a routine program holds total dissolved solids to 3 to 5 times the make-up level using automatic bleed-off keyed to conductivity, and doses a scale inhibitor plus an oxidizer to keep biofilm below the limit that fouls fill. Legionella control targets less than 1 CFU per 100 mL in most jurisdictions, checked monthly during the cooling season, and a spike above that triggers a shock oxidizer dose and a supersized bleed-off until the count returns.
A neglected tower can scale its fill so that heat transfer drops 10% to 20% and fan power rises to compensate, quietly eroding the efficiency advantage the tower exists to provide. Winter downtime should include a full drain and disinfection, because stagnant warm water is exactly the condition where colonies establish before the next startup. The make-up meter is the cheapest insurance: tracking make-up against evaporation tells you when drift eliminators are failing, since a sudden rise from 1% to 3% of circulation points to a damaged eliminator throwing 0.5 to 1.0 kg/s of water out the fan stack rather than a leak you would otherwise chase for weeks.
Fan Stack and Motor Selection
The fan is the tower's only moving part and its largest auxiliary load, typically 0.01 to 0.03 kW per kW rejected, so a 1,200 kW tower draws 15 to 35 kW of fan power. Specify a two-speed or variable-speed motor so the fan tracks load and cuts energy 30% to 60% at part load, and protect the stack inlet with a bird screen that is cleaned each season, because a 30% blocked inlet raises static pressure and steals 10% to 15% of airflow. Belt drives are cheaper to service than direct drives but need tension checks every 3 to 6 months, while direct drives remove that task at the price of a larger motor replacement when it fails.
Hybrid and Air-Cooled Alternatives
Where water or plume is a concern, a hybrid tower blends a dry coil with the wet section so that during cool months it runs dry, cutting water use 20% to 40% and eliminating most plume, then switches to evaporative mode only in summer peaks above 25 °C wet bulb. A once-through or dry cooler is an option where even drift is unacceptable, though it needs 3 to 5 times the fan power of a wet tower for the same heat rejection, so the hybrid remains the usual compromise between water saving and energy cost.
FAQ
What size cooling tower do I need for a 1,000 kW chiller?
A 1,000 kW chiller rejects about 1,200 to 1,300 kW of heat, so the tower must handle that load at the local design wet bulb of 25 to 30 °C. It will evaporate roughly 0.5 to 0.7 kg/s of water to hold a 3 to 5 °C approach, and the selection also depends on the allowable footprint and noise limit.
What is approach and range in a cooling tower?
Approach is the leaving water temperature minus the wet-bulb temperature, normally 3 to 5 °C, while range is the entering minus leaving water temperature, usually 5 to 10 °C. A smaller approach gives colder water and better chiller efficiency but demands a larger, costlier tower shell and fill.
Open or closed-circuit tower: which to pick?
Pick an open tower for general chiller condenser loops where direct contact is acceptable and cheapest. Pick a closed-circuit tower when the process fluid must stay isolated from ambient air, such as a clean loop or a fluid that could freeze or foul the fill.
How much water does a cooling tower use?
A tower evaporates about 1% to 3% of its circulating flow and drifts a small additional fraction, so a 1,000 kW plant may lose 0.5 to 1.0 kg/s. Make-up water requires scale and biological treatment, with bleed-off holding dissolved solids to 3 to 5 times the make-up concentration.