Cooling Tower Capacity Calculator

Enter Project Inputs

Calculation Method *

Choose how you want to define the duty.

Water Flow Rate (m³/h) *

Heat Load (kW)

Used only when Heat Load method is selected.

Water Temperature Unit

Hot Water Temperature *

Cold Water Temperature *

Wet-Bulb Temperature Unit

Entering Wet-Bulb Temperature

Used to compute approach (cold minus wet-bulb).

Water Density (kg/m³)

Specific Heat (kJ/kg·°C)

Heat Rejection Factor

Use 1.00 for process duty; higher for condenser systems.

Results appear above after submission

Flow (m³/h)	Hot (°C)	Cold (°C)	Wet-Bulb (°C)	HRF	Heat Rejection (kW)	Capacity (TR)
120	40	32	27	1.00	1,112.9	316.4
180	42	33	28	1.00	1,878.0	534.0
90	38	30	26	1.10	918.2	261.1
150	45	35	29	1.00	1,738.9	494.4
210	41	31	27	1.05	2,556.2	726.8

Examples assume typical water properties near ambient conditions.

Cooling range: Range = T_hot − T_cold

Mass flow: ṁ = (Flow × ρ) / 3600 (kg/s)

Heat rejected: Q = ṁ × C_p × Range × HRF (kW)

Tower capacity: TR = Q / 3.517

Approach: Approach = T_cold − T_wetbulb

Notes: C_p uses kJ/kg·°C, so kJ/s equals kW.

HRF is a multiplier for systems that reject more than the base duty.

Choose Flow & Temperatures for measured condenser or process data.
Enter water flow, hot and cold temperatures, and wet-bulb temperature.
Keep default water properties unless your project requires adjustments.
Set Heat Rejection Factor to match your system duty.
Press Calculate Capacity to show results above the form.
Download CSV or PDF to attach to design submittals.

Design Duty and Heat Rejection

Cooling tower sizing starts with rejected heat, not equipment nameplate. This calculator converts water flow and temperature drop into heat rejection in kilowatts, then into tons of refrigeration. A heat rejection factor lets you represent condenser heat, motor heat, and piping gains during peak conditions. Compare results against vendor ratings.

Range, Approach, and Weather Sensitivity

Range is the hot-to-cold water temperature difference. Approach is cold water temperature minus entering wet-bulb temperature. Smaller approach values demand more airflow and larger fill area. Use a realistic design wet-bulb for your site, because each degree change directly shifts the achievable cold water setpoint. When local humidity spikes, the same tower may deliver warmer cold water, affecting chiller lift and energy.

Water Flow, Pumping, and Pipework Impacts

Mass flow is derived from volumetric flow and density. If flow is increased while duty stays fixed, range decreases and tower control becomes more sensitive. Higher flow also raises pump energy and velocity losses. Keep flow units consistent and verify metering points match the condenser or process header. For variable-speed fans, duty tracking improves when range is maintained with stable flow control and balanced distribution.

Capacity Units and Selection Margins

The calculator reports both kW and TR so mechanical and electrical teams can align. One TR equals 3.517 kW of heat rejection. Apply selection margins to cover fouling, drift eliminator pressure drop, and fan performance at elevation. Document whether capacity is “at rating” or “at site” conditions. Consider standby cell redundancy and future load additions during expansion projects.

Commissioning Checks and Documentation

During commissioning, confirm hot and cold temperatures stabilize, and wet-bulb readings are taken in the inlet air stream. Compare calculated duty against design duty, then trend approach over time. Persistently rising approach often indicates scaling, insufficient airflow, or bypass mixing. Record basin level, drift, and makeup rates to validate operating cycles and water treatment. Export the CSV and PDF outputs to include in submittals, startup reports, and operator handover packages.

What is Heat Rejection Factor used for?

It scales the calculated duty to reflect system realities, such as condenser heat plus compressor power, or additional gains in piping. Use 1.00 for direct process duty, and a higher value when your specifications require it.

What approach should I target for selection?

Lower approach improves cold water temperature but requires a larger tower and more fan power. Many projects rate towers around 3–5°C approach at design wet-bulb. Confirm your vendor rating point and performance guarantees.

Why does a small range change capacity so much?

Duty is proportional to range. If the temperature drop falls, the rejected heat falls at the same flow. Small range also makes control more sensitive, so verify sensor accuracy and confirm bypass valves are not mixing warm water.

Can I use the Heat Load method if temperatures are unknown?

Yes. Enter the heat load in kW and a reasonable flow rate to estimate an implied range. You can also enter hot and cold temperatures later to refine the range and confirm the duty against measured site data.

Should I change water density and specific heat values?

Defaults suit typical fresh water near ambient conditions. Adjust if your process fluid differs, water temperature is extreme, or glycol content is significant. Consistent properties improve estimates when comparing alternative designs and operating scenarios.

How should I use the exports during construction?

Save the CSV for quick checks and trend logs. Use the PDF in submittals, commissioning reports, and handover packages. Keep notes on wet-bulb measurement location, flow meter points, and any correction factors applied.