🌡️ HVAC

Cooling Tower Sizing Calculator

Size cooling towers for central chiller plants. Calculate condenser water flow, range, approach, and fan power per CTI ATC-105 and ASHRAE guidelines.

📐 Standard: CTI ATC-105 / ASHRAE
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ℹ️ About This Calculator

The cooling tower rejects heat from the chiller condenser to the atmosphere through evaporative cooling. Correct sizing ensures the condenser water temperature meets chiller requirements. The key parameters are range (temperature drop across the tower), approach (difference between leaving water temperature and wet-bulb temperature), and flow rate. Per CTI ATC-105 and ASHRAE Handbook.

Cooling towers in India are designed for wet-bulb temperatures of 27–32°C depending on location (Mumbai: 28°C; Delhi: 26°C; Chennai: 30°C; Bangalore: 23°C). Tower sizing and selection from manufacturer curves (e.g., PAHARPUR, BALTIMORE AIRCOIL, SPX). Water treatment is critical: scale, corrosion, and biological (Legionella) control. CPCB regulations apply to cooling tower water discharge. Annual cleaning and inspection required. ASHRAE Guideline 12 covers Legionella risk management in cooling towers.

📐 Cooling Tower Sizing

CTI ATC-105 / ASHRAE

Condenser Water Flow:
  Q_cw = Q_condenser / (ρ × Cp × Range)
  Q_condenser = Q_cooling × (1 + 1/COP)  [heat rejection]
  Range = T_in − T_out (typical: 5–6°C; 29°C in / 35°C out)

Approach Temperature:
  Approach = T_out_cold − T_wb  (≥ 3°C minimum, 5°C typical)
  Smaller approach = larger tower (more difficult to achieve)

Evaporation Rate:
  E = 0.00085 × Q_cw × Range  (m³/hr make-up water)
  Blowdown: B = E / (cycles of concentration − 1)  [cycles=3–5]
  Total make-up = E + B + drift (≈ E × 1.5 for practical estimate)

❓ Frequently Asked Questions

What wet-bulb temperature should I use for cooling tower design? +
Use ASHRAE 1% WB design condition for your city: Mumbai 28°C WB; Delhi 26°C; Chennai 30°C; Bangalore 23°C; Hyderabad 24°C; Kolkata 30°C; Pune 24°C. Design at 1% WB means the tower meets its rated performance for 99% of operating hours. For critical applications (hospitals, 24×7 data centres): use 0.4% WB (slightly higher, more conservative).
How much make-up water does a cooling tower use? +
Approximately 2.0–2.5 L per kWh of heat rejected (1.5–2.0% of condenser flow). For a 1000 kW (280 ton) cooling tower: approximately 2.0–2.5 m³/hr make-up water. This is a significant water consumption – for a 250-day, 10-hour operating season: 5,000–6,250 m³/year per 1000 kW. Water-scarce locations: consider air-cooled chillers (higher energy, no water) or water-efficient tower designs.
What is cycles of concentration and why does it matter? +
As water evaporates, dissolved minerals concentrate in the basin. Cycles of concentration (CoC) = mineral concentration in basin / mineral concentration in make-up water. Typical target: CoC = 3–5. Higher CoC = less blowdown water wasted, but higher risk of scale formation. Water treatment (scale inhibitor, pH control, conductivity blowdown control) maintains CoC at the target level. Poor treatment at CoC > 6: scale coats condenser tubes, reducing chiller efficiency.
Is Legionella a concern in cooling towers? +
Yes. Cooling tower warm water (30–40°C) is ideal for Legionella growth, and drift water droplets can infect people who breathe them in. Requirements: quarterly water testing for Legionella (recommended); annual physical cleaning; continuous disinfection (chlorination, UV, or bromine); drift eliminators to minimise water droplets leaving the tower. ASHRAE Guideline 12 and BIS guidelines on cooling tower water treatment should be followed.
Can I use a single cooling tower for multiple chillers? +
Yes. A common condenser water header with multiple cooling tower cells serves multiple chillers. The advantage: flexibility to operate fewer cells at part load, saving fan energy. The design must ensure each chiller gets its rated condenser water flow even when other chillers are off. Individual cell isolation valves, bypass lines, and condenser water header pressure control are required. This is the standard approach for large chiller plants.

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⚠️ Disclaimer: For preliminary engineering design only. Verify all results with a licensed engineer before use. Full disclaimer →

🌡️ Cooling Tower Sizing Calculator
Reference: CTI ATC-105 / ASHRAE