Cooling Tower Calculator Formula

Understand the math behind the cooling tower calculator. Each variable explained with a worked example.

Use the Cooling Tower Calculator

Formulas Used

Heat Rejected

heat_rejected = circ_flow * 4.18 * temp_range

Evaporation Rate

evaporation = evap_rate

Blowdown Rate

blowdown = evap_rate / (cycles - 1)

Total Makeup Water

makeup = evap_rate + evap_rate / (cycles - 1)

Variables

VariableDescriptionDefault
circ_flowCirculation Flow Rate(L/s)50
temp_rangeCooling Range (inlet-outlet)(deg C)8
cyclesCycles of Concentration4
circ_m3hDerived value= circ_flow * 3.6calculated
evap_rateDerived value= circ_m3h * temp_range * 0.00085calculated

How It Works

Cooling Tower Water Balance

Cooling towers reject heat through evaporation, requiring continuous makeup water.

Formulas

Heat rejected = m_dot cp delta_T

Evaporation rate = 0.00085 x Circulation (m^3/h) x Range (deg C)

The 0.00085 factor is an approximation for the fraction evaporated per degree of cooling. Blowdown removes concentrated water to limit mineral buildup: Blowdown = Evaporation / (Cycles - 1)

Makeup = Evaporation + Blowdown

Worked Example

50 L/s circulation, 8 deg C range, 4 cycles of concentration.

circ_flow = 50temp_range = 8cycles = 4
  1. 01Heat rejected = 50 x 4.18 x 8 = 1672 kW
  2. 02Circulation = 50 x 3.6 = 180 m^3/h
  3. 03Evaporation = 180 x 8 x 0.00085 = 1.224 m^3/h
  4. 04Blowdown = 1.224 / (4-1) = 0.408 m^3/h
  5. 05Makeup = 1.224 + 0.408 = 1.632 m^3/h

Ready to run the numbers?

Open Cooling Tower Calculator