what are cooling tower calculations?

Cooling Tower Calculations

Azerbaijan Edition (AZ) – Baku / Sumgait / Desert-Coastal All formulas, examples, and data tailored for AZ climate (WB = 25 °C, 0.4% ASHRAE)

1. Core 4 Cooling Tower Calculations

(Every engineer in Baku must know these)

    # Calculation Formula Unit 1 Cooling Load (Heat Rejection) Q = m × Cp × ΔT kW 2 Evaporation Rate E = (Q × 0.0018) / h_fg m³/h 3 Makeup Water M = E + D + B m³/h 4 Approach & Range Approach = LWT – WB Range = HWT – LWT °C   2. Step-by-Step Example (Baku 1,000-ton Chiller Plant)     Given (AZ Summer Design) Value Chiller capacity 1,000 tons = 3,517 kW Heat rejection (1.2 × cooling) 4,220 kW Hot Water Temp (HWT) 35 °C Leaving Water Temp (LWT) 30 °C Range 5 °C Wet Bulb (WB) – Baku 0.4% 25 °C Approach 5 °C   Calculation 1: Cooling Load (Q) latex   Q = m_{water} \times C_p \times \Delta T    

→ 4,220 = m × 4.18 × 5 → m = 4,220 / (4.18 × 5) = **202.4 kg/s** = **730 m³/h**

Water flow rate = 730 m³/h

Calculation 2: Evaporation Rate (E) latex   E = \frac{Q \times 0.0018}{h_{fg}}    

• h_fg at 32 °C ≈ 2,430 kJ/kg → E = (4,220 × 0.0018) / 2.43 = **3.13 kg/s** = **11.3 m³/h**

Evaporates 11.3 m³/h → ~1.5% of circulation

Calculation 3: Makeup Water (M) latex   M = E + D + B         Component % of flow m³/h E (Evaporation) 1.5% 11.3 D (Drift) 0.1–0.2% 1.5 B (Blowdown) E / (COC – 1) —  

→ Assume COC = 4 (common in AZ hard water) → B = 11.3 / (4 – 1) = **3.8 m³/h**

Total Makeup = 11.3 + 1.5 + 3.8 = 16.6 m³/h ≈ 2.3%

Cooling Towers design depend on the calculation of the following:

1.  Evaporation.
2. Temperature Drop.
3. Recirculation Rate
4. Concentration Ratio or Cycles of Concentration.
5. Make Up Water.
6. Holding Capacity or System Volume.
7. Blowdown Rate.

It's too long and need to the explain of each step, you can found in Process calculation handbook or any thermal engineering books.

would you be able to provide a detailed expalnation on this issue with some mathematical expressions?

 

Evaporation loss, drift loss & blow down loss.
Based on the heat rejection from the chiller, %age of drift loss and number of COC one could derive the total losses through the cooling towers.