Cooling Tower Module Guide
Cooling Tower Selection & Lifecycle Cost
A practical guide to cooling tower selection: open vs closed circuit, counterflow vs crossflow, fan and approach selection, and how to model lifecycle cost including water and water-treatment expenses.
Technology Overview
Cooling towers are the unsung component of every water-cooled chiller plant. A poorly-selected tower forces the chiller to work harder, drives up plant-wide energy cost for the building’s entire life, and adds water and chemical costs that often exceed the tower’s own electric consumption. Done right, the tower lets a water-cooled chiller plant outperform any air-cooled alternative on lifecycle cost.
The selection problem decomposes into a few choices: open-circuit (evaporative) or closed-circuit (fluid cooler), counterflow or crossflow, axial or centrifugal fan, number of cells, and the design approach (the gap between leaving water and ambient wet bulb at peak conditions). Each choice trades CAPEX, footprint, water consumption, fan energy, and pump head against the chiller’s annual efficiency.
The CogenS™ Cooling Tower Module uses industry-standard CoolTools and YorkCalc performance coefficients to model tower performance hour-by-hour against TMY wet-bulb data, then ties the result to the paired chiller TEA. Output includes annual fan energy, water consumption (drift + evaporation + blowdown), chemical treatment cost, and lifecycle financial metrics.
Module Specs at a Glance
Tower Types
Open circuit (evaporative) and closed circuit (fluid cooler / dry cooler). Counterflow and crossflow configurations.
Fan Types
Axial (lower fan energy, larger footprint) and centrifugal (higher fan energy, ducted, indoor-capable).
Capacity Range
From 50-ton single-cell units through 5,000+ ton multi-cell installations. Modular cell-and-fan combinations for redundancy.
Performance Modeling
CoolTools and YorkCalc performance coefficients. Range, approach, and L/G ratio drive performance against wet-bulb temperature.
Water Consumption
Evaporation, drift, and blowdown modeled hour-by-hour. Cycles of concentration governed by water-treatment program.
Output
TEA report with NPV, IRR, fan/pump energy, water cost, chemical treatment cost, and multi-vendor comparison.
How to Design a Project
A high-level workflow that mirrors how the CogenS™ platform structures the analysis end-to-end.
Define plant cooling load and approach
Pull the tower load directly from the chiller TEA — typically 1.25 × chiller capacity. Choose a design approach (5-7°F at design wet bulb is typical) — tighter approach means a bigger and more expensive tower but better chiller efficiency year-round.
Pick open-circuit vs closed-circuit
Open circuit (cooling tower) is cheaper, smaller, and more efficient — but the process water is exposed to air and contaminants. Closed circuit (fluid cooler) keeps the process loop clean at the cost of an intermediate heat exchanger and additional fan/pump energy. Use closed circuit when contamination risk is high or freeze protection matters.
Pick counterflow vs crossflow
Counterflow towers have better thermal performance per square foot — the air and water move in opposite directions for maximum heat-transfer driving force. Crossflow towers are easier to maintain and have lower pump head, but require more fill volume for the same performance.
Pick a fan type
Axial (propeller) fans use less fan energy per CFM but require open-air installation. Centrifugal fans handle ductwork and indoor installation but burn more fan energy. Use VFDs on either to capture significant part-load fan-energy savings.
Size cells for redundancy and turn-down
A multi-cell tower with VFD fans gives excellent part-load efficiency — at low load, run one cell at low fan speed instead of one cell at full speed. Single-cell towers can't do this and pay efficiency tax all year.
Model water and chemical treatment
Annual water cost = (evaporation + drift + blowdown) × water rate. Cycles of concentration governed by treatment chemistry — higher cycles reduce makeup but increase scaling/corrosion risk and chemical cost. Model both at 8,760-hour resolution against the actual cooling load and ambient wet-bulb.
Run TEA and feed back to chiller
The tower's leaving water temp drives the chiller's entering condenser water temp, which drives chiller efficiency. Run the tower TEA, feed the result back to the chiller module, and iterate until the plant-wide answer converges.
Related Guides
Commercial Chiller Design Guide
The chiller-tower pairing — both decisions interact and must be designed together.
Thermal Systems TEA Guide
Suite-level overview tying cooling into the rest of the thermal stack.
CHP System Design Guide
CHP with absorption cooling needs a cooling tower for heat rejection — design them together.
Ready to run a real analysis?
Sign up free and run a complete technoeconomic analysis in your browser — pre-loaded weather, tariffs, equipment specs, and financials for 340+ cities.