Cooling Tower Performance & Water Balancev1.0.0Method: Cooling Tower

Cooling Tower Performance & Water Balance Calculator

Thermal performance evaluation (Range, Approach, Effectiveness), Heat Rejection Duty, Evaporation, Blowdown, and Make-up Water Balance per CTI ATC-105.

Operating Temperatures & Water Treatment

Circulating Water Flow (L)

m³/h

Design Wet-Bulb (T_wb)

°C

Hot Water Inlet (T_in)

°C

Cold Water Basin (T_out)

°C

Range 5.0 °C · Approach 5.0 °C

Cycles of Concentration (COC)

Drift Loss Allowance

Tower Water Balance

CTI ATC-105 · M = E + B + D

Results

Ready to calculate

Enter values and press Calculate to see results.

Reference Codes & Standards

CTI STD-201Governing Code

Thermal Certification of Cooling Tower Performance

Scope:Range, approach to wet bulb, and thermal rating procedures.

ASHRAE Systems & Equipment Ch. 40Governing Code

Cooling Towers

Scope:Water balance, evaporation loss, and cycles of concentration guidelines.

Literature & Further Reading

[1]CTI STD-201 — Thermal Certification of Cooling Towers.
[2]ASHRAE Handbook — HVAC Systems and Equipment (Cooling Towers).
[3]Hensley, J.C. — Cooling Tower Fundamentals.

Engineering Tips

Practical checks before using the result

Core Formulas

Thermal effectiveness

η = (T_in − T_out) / (T_in − T_wb) = Range / (Range + Approach)

CTI measure of cooling achieved relative to the wet-bulb limit

Evaporation loss

E = 0.00153 · L · Range (L in m³/h, Range in °C)

Latent heat rule of thumb: ≈ 0.85 % of circulating flow per 5.6 °C (10 °F) range

Blowdown

B = E / (COC − 1) − D

Cycles-of-concentration mass balance

Tower size is driven by the approach: the closer the cold water gets to the wet-bulb, the larger the fill and fan power.

Good practice

Raising COC from 2 to 4 cuts blowdown by about two thirds (B ∝ 1 / (COC − 1)) and with it chemical use.
Select the design wet-bulb as the ASHRAE 0.4 % or 1 % non-exceedance value for the plant location.

Watch out

Approaches below 3–4 °C (5–7 °F) grow tower footprint and fan power steeply.
Do not run high COC (> 6–7) without effective scale and corrosion treatment of the condenser.

Not covered

Evaporation uses a rule of thumb; it does not solve the Merkel / psychrometric tower model or predict off-design performance.
Does not size fans, fill, basin or make-up piping, and does not check plume or Legionella control.