🌡 Tower Approach
⚡ Estimated Fan Power
Sizing Breakdown
Full Calculation Table
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How to Use the Cooling Tower Calculator
Choose open circuit for direct condenser water contact with outdoor air, or closed circuit for indirect heat exchange that keeps the condenser loop separate.
Enter chiller cooling capacity from the chiller plant calculator and its design efficiency to calculate total heat rejection.
Choose the Canadian city closest to your project for design wet-bulb temperature, or enter a custom value from local weather data.
Click Calculate Cooling Tower Sizing to see condenser water flow, tower approach, estimated fan power, and blowdown water requirements.
Understanding Cooling Tower Sizing
A cooling tower rejects heat from a water-cooled chiller's condenser into the outdoor atmosphere, primarily through evaporative cooling rather than simple sensible heat exchange. Sizing a tower correctly starts with total heat rejection from the chiller, then works through condenser water flow, tower approach to outdoor wet-bulb temperature, and finally fan power and water consumption.
Heat Rejection Includes Compressor Power
Total heat rejected through the tower is not just the chiller's cooling capacity. It also includes the compressor's electrical input power, since that energy ultimately converts to heat and gets rejected through the condenser along with the heat removed from the building. A chiller with lower kW per ton efficiency rejects proportionally more heat relative to its cooling capacity than a more efficient chiller, a gap worth checking with the compressor efficiency calculator when comparing two chiller options for tower sizing purposes.
Why Wet-Bulb Temperature, Not Dry-Bulb
Cooling towers work by evaporating a small fraction of circulating water, and the heat carried away by that evaporation depends on outdoor wet-bulb temperature rather than dry-bulb. Wet-bulb represents the coldest temperature achievable through evaporative cooling at a given outdoor condition, setting a physical limit on how cold the tower can bring water regardless of dry-bulb temperature. This is why cooling tower selection always references design wet-bulb data specific to your location, which the wet-bulb calculator can work out from local dry-bulb and relative humidity readings, rather than the dry-bulb design temperatures used for building load calculations.
Approach and Range: The Two Key Temperature Differences
Range is simply the temperature drop of condenser water through the tower, matching the temperature difference set at the chiller condenser. Approach is the gap between the tower's leaving water temperature and outdoor wet-bulb temperature, representing how close the tower brings water toward the theoretical evaporative limit. A tighter approach, meaning colder leaving water relative to wet-bulb, requires a larger and more expensive tower for the same heat rejection load, since getting closer to the physical limit takes more heat transfer surface area and airflow, the same thermal performance basis the Cooling Technology Institute uses to certify manufacturer-rated tower capacity.
Open vs. Closed Circuit Towers
Open circuit towers spray condenser water directly into contact with outdoor air, which is simple and cost-effective but exposes the condenser water loop to atmospheric contamination, requiring more aggressive water treatment. Closed circuit towers keep the condenser water loop sealed inside coils, with a separate spray water circuit doing the evaporative cooling against those coils, protecting the condenser loop from contamination at the cost of somewhat higher capital cost and slightly reduced heat transfer efficiency.
Water Treatment and Blowdown
As water evaporates continuously, dissolved minerals concentrate in the remaining circulating water. Blowdown periodically discharges some of this concentrated water, replaced by fresh makeup water, to control mineral concentration and prevent scale formation that would otherwise foul the tower and condenser over time. All cooling tower operation in Canada falls under CSA B52 for the associated mechanical refrigeration system and provincial requirements for cooling tower water management and Legionella control, so confirm current local requirements before finalizing a water treatment program.
Frequently Asked Questions
Heat rejection equals the chiller cooling capacity plus the compressor motor power, since both the heat removed from the building and the energy used to run the compressor end up rejected through the condenser. As a simplified estimate, heat rejection in kW is roughly the chiller tonnage times 3.517, plus the chiller's electrical input power at design conditions. See the chiller plant calculator for chiller sizing.
Range is the temperature drop of condenser water as it passes through the tower, typically the chiller's condenser water temperature difference. Approach is the temperature difference between the tower's leaving water temperature and the outdoor design wet-bulb temperature, representing how close the tower can bring water toward ambient wet-bulb conditions. A smaller approach requires a larger, more expensive tower for the same heat rejection.
Cooling towers reject heat primarily through evaporative cooling, where a small fraction of the circulating water evaporates and carries heat away with it. Wet-bulb temperature represents the lowest temperature achievable through evaporation at a given outdoor condition, which sets the theoretical limit for how cold the tower can cool water, regardless of dry-bulb temperature.
As water evaporates in a cooling tower, dissolved minerals in the remaining water become more concentrated over time. Blowdown intentionally discharges a portion of concentrated water and replaces it with fresh makeup water, preventing scale buildup and corrosion inside the tower and condenser. Blowdown rate depends on makeup water quality and the target cycles of concentration for the specific water treatment program.
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