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Cooling Tower Evaporation & Blowdown Makeup Water Calculator

Open recirculating cooling towers reject condenser heat to the atmosphere through water evaporation, concentrating dissolved minerals in the basin basin water.

Total thermal heat rejected by the tower (1,000 tons refrigeration ≈ 3,517 kW + compressor power).

Temperature differential between hot entering condenser water and cold basin basin water (typically 5.5 °C / 10°F).

Ratio of dissolved solids in recirculating water to fresh makeup water (typically 3.0 to 6.0).

Drift mist droplets lost to windage (typically 0.005% to 0.02% of circulation flow).

Calculated Result
6.64 m³/hr

Total Required Makeup Water

Total Makeup Water Rate

6.64 m³/hr (159.3 m³/day)

Evaporative Loss Rate (E)

5.16 m³/hr

Blowdown Purge Rate (B)

1.42 m³/hr

Drift Droplet Loss (D)

0.055 m³/hr

Circulating Loop Flow Rate

547.3 m³/hr

Calculation Breakdown

  1. Condenser Water Circulation FlowQ_circ = Q_rej / (c_p × Range) = 3500 / (4.186 × 5.5) × 3.6 = 547.3 m³/hr
  2. Latent Heat Evaporation LossE = Q_rej / h_fg = 3500 / 2440 kJ/kg × 3.6 = 5.16 m³/hr
  3. Chemical Blowdown & Water BalanceB = E / (CoC - 1) = 5.16 / (4.5 - 1) = 1.42 m³/hr, Total Makeup M = 6.64 m³/hr

Cooling Tower Water Balance (m³/hr)

Interactive visualization based on your current inputs

Flow (m³/hr)
0.01.73.35.06.6Circulation (/100)EvaporationBlowdownDrift LossTotal MakeupStreamFlow (m³/hr)

What Is the Cooling Tower Evaporation & Blowdown Makeup Water Calculator?

The Cooling Tower Evaporation & Blowdown Makeup Water Calculator estimates water consumption and utility requirements for evaporative cooling plants.

How Does the Cooling Tower Evaporation & Blowdown Makeup Water Calculator Work?

It converts thermal rejection heat load into latent water evaporation, calculates required chemical bleed-off blowdown, and sums total daily makeup demands.

Cooling Tower Evaporation & Blowdown Makeup Water Calculator Formula & Variables

The core mathematical equation utilized by this calculator is expressed as:

E = \frac{Q_{rej}}{h_{fg}}, \quad B = \frac{E}{\text{CoC} - 1} - D, \quad M = E + B + D

Conservation of water and non-volatile mineral mass balance governing evaporative cooling tower chemistry.

How to Use the Cooling Tower Evaporation & Blowdown Makeup Water Calculator

  1. Enter total heat rejection load in kW or tons.
  2. Specify condenser water temperature range (ΔT).
  3. Input water treatment target Cycles of Concentration and drift percentage.

Step-by-Step Example Calculation

1,000-Ton Central Plant Cooling Tower

Input Values:

coolingHeatRejectionLoadKW:3500
waterRangeDeltaTC:5.5
cyclesOfConcentrationCoC:4.5
driftLossPercent:0.01
Worked Steps: Consumes 5.16 m³/hr evaporation and 1.42 m³/hr blowdown, demanding 6.64 m³/hr (159.4 m³/day) total fresh makeup water.

Understanding Your Result

Total Makeup Water: Hourly and daily fresh water volume consumed.

Evaporative Loss: Pure water vaporized to provide cooling.

Blowdown Rate: Water discharged to sewer to control mineral concentration.

Factors That Affect the Result

  • Increasing CoC from 2.0 to 4.0 cuts makeup water demand significantly; gains diminish past CoC = 5.0.
  • Higher thermal heat load directly scales evaporation requirements.

When Should You Use This Calculator?

  • Water utility billing estimates, environmental permitting, water treatment chemical sizing, and LEED water efficiency credits.

Assumptions & Limitations

  • Assumes steady-state thermal load and constant latent heat of vaporization (2440 kJ/kg).

Frequently Asked Questions

Calculation Accuracy & Reference Note

Conforms to Cooling Technology Institute (CTI) and ASHRAE Guideline 12.

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