Evaporative Cooling Tower Water Loss & Makeup Sizing

Determines condenser water circulating flow rate, thermal cooling range and approach to ambient wet-bulb, evaporation consumption, drift losses, blowdown bleed-off, and total daily makeup water volume per CTI STD-201 and ASHRAE 90.1.

✔ 1. Formula Verified → ⚡ 2. Engineering Screening → 📐 3. Standards Referenced (CTI STD-201 / IS 11504) → ⚖ 4. Engineer Review Required

⚙ Chiller & Hydronic Heat Rejection Inputs

Chiller Plant Cooling Capacity TR

Total rated refrigeration tonnage of water-cooled chillers connected to the tower.

Condenser Water Flow Rate GPM / TR

Design condenser flow rate (standard 3.0 GPM/TR for electric centrifugal/screw chillers; 3.6–4.0 GPM/TR for vapor absorption).

Cooling Tower Leaving Water Temp (CWS) °C

Cooled water temperature entering the chiller condenser (typically 29.5–32.0°C in Indian summer conditions).

Cooling Tower Entering Water Temp (CWR) °C

Hot condenser water returning from the chiller (typically 5°C higher than supply, i.e. 35°C).

Design Ambient Wet-Bulb Temp (WBT) °C

Local summer 1% peak design wet-bulb temperature (typically 27–29°C for Northern India).

Cycles of Concentration (COC) Ratio

Ratio of dissolved solids in circulating water to raw makeup water (typically 3.5 to 5.0 with chemical treatment).

📊 Tower Water Loss & Makeup Sheet

Preliminary Screening

Total Daily Makeup Water Required
56.6 kL / Day
Hourly Continuous Makeup Rate: 2.36 m³/hr (2,358 L/h)

Circulating Flow Rate

900 GPM (204.4 m³/h)

Thermal Range (ΔT)

5.0 °C (9.0 °F)

Approach to Wet-Bulb

2.0 °C (Approach)

Evaporation Loss

1.76 m³/h (74.7%)

Blowdown / Bleed-off

0.59 m³/h (24.9%)

Drift / Windage Loss

0.010 m³/h (0.4%)

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Governing Engineering Standards & Calculation Model

Governing Standards & References

CTI STD-201: Cooling Technology Institute Standard for Thermal Performance Certification.
ASHRAE Standard 90.1: Energy Standard for Buildings (Heat rejection efficiency & drift eliminator limits).
IS 11504: Code of practice for criteria for structural design of reinforced concrete natural draught cooling towers.

Engineering Equations & Derivations

Circulating Flow: GPM = Chiller_TR × Flow_per_TR (900 GPM = 56.78 kg/s = 204.4 m³/h)
Thermal Range (ΔT): CWR - CWS = 35.0°C - 30.0°C = 5.0°C (9.0°F)
Condenser Heat Rejection: Q_cond = m_dot × Cp × ΔT = 56.781 kg/s × 4.186 × 5.0 = 1,188.4 kW (337.9 TR)
Evaporation Rate: Evap = (Q_cond × 3600) / (h_fg × 1000) = (1,188.4 × 3600) / 2,430,000 = 1.76 m³/h
Drift Loss: Drift = Circ_Flow × Drift% = 204.4 × 0.005% = 0.010 m³/h
Blowdown Rate: Blowdown = Evap / (COC - 1) = 1.76 / (4 - 1) = 0.59 m³/h
Total Makeup Water: Makeup = Evap + Drift + Blowdown = 2.36 m³/h (56.6 kL/day)

First Law Thermodynamics Distinction: Condenser heat rejection (1,188.4 kW / 337.9 TR) strictly exceeds the nominal chiller cooling capacity (300 TR = 1,055.1 kW) because the cooling tower must reject both the building thermal load absorbed at the chiller evaporator and the electrical/shaft work of the compressor (Q_condenser = Q_evaporator + W_compressor).

⚖ Statutory Notice & Engineering Disclaimer (Tier D Integration)

Evaporation loss equation uses the industry standard empirical sensible/latent factor (0.00085/°F range) representing normal summer conditions. Actual water consumption varies dynamically with ambient psychrometric enthalpy, chiller partial loading, and seasonal wet-bulb fluctuations. Raw water quality (silica, calcium hardness, chloride levels) strictly dictates safe Cycles of Concentration (COC) to prevent calcium carbonate scale precipitation on chiller condenser tubes. Comprehensive water testing and chemical dosing are required.