Central Chiller Plant Condenser Water, CTI Evaporative Cooling Towers & Wet-Bulb Approach
Cooling Tower Range, Wet-Bulb Approach & Effectiveness Formula
Calculate Condenser-Water Cooling Range T_hot - T_cold (°C), Wet-Bulb Approach T_cold - T_wb (°C), Cooling Tower Thermal Effectiveness (%), and Total Heat Rejection Rate (kW).
Cooling tower RANGE is set by chiller load—only WET-BULB APPROACH measures actual cooling-tower fill and fan performance!
Plant operators frequently confuse **Cooling Range `R_ct = T_hot - T_cold`** (°C) with **Wet-Bulb Approach `A_ct = T_cold - T_wb`** (°C)! Because `Q_rej = dot_m_w * c_p * (T_hot - T_cold)`, Range is dictated purely by chiller heat load divided by condenser-pump water flow—NOT by how big or clean the cooling tower is! Conversely, an evaporative tower cools water toward the thermodynamic limit of **Ambient Wet-Bulb Temperature `T_wb`** (never dry-bulb!), so **Approach `T_cold - T_wb`** (`>= 2.5–3.0 °C` economic CTI limit) directly reveals PVC fill fouling, broken spray nozzles, or slipping fan belts! Combining the two defines **Cooling Tower Thermal Effectiveness `eta_ct = (Range / (Range + Approach)) * 100 = ((T_hot - T_cold) / (T_hot - T_wb)) * 100%`**!
Verify on a 420 m³/h Induced-Draft Chiller Condenser Tower—Entering_Hot_Condenser_Water `T_hot` = 37.00 °C (B2), Leaving_Cold_Basin_Sump `T_cold` = 29.00 °C (B3 -> Range = `8.00 °C` in E2), Ambient_Outdoor_Wet-Bulb `T_wb` = 25.00 °C (B4 -> Approach = `4.00 °C` in E3), and Condenser_Water_Flow `Q_w` = 420.0 m³/h (`rho ≈ 995` kg/m³, `c_p = 4.184` kJ/(kg·K), B5): Thermal Effectiveness hits `66.67%` (E4), rejecting `3,885.5` kW (`~1,105` refrigeration tons) to atmosphere (E5)!
| CTI Cooling Tower Thermal KPI (Thot=37°C, Tcold=29°C, Twb=25°C, Qw=420 m³/h) | Formula | Verified Output |
|---|---|---|
| Cooling Range (Thot - Tcold) | Entering_Hot_C - Leaving_Cold_C | 8.00 °C (5.50 °C @ scaled fill 31.5 °C) |
| Wet-Bulb Approach (Tcold - Twb) | Leaving_Cold_C - Ambient_Wet_Bulb_C | 4.00 °C (6.50 °C @ scaled fill!) |
| Tower Thermal Effectiveness (%) | ((Thot - Tcold) / (Thot - Twb)) * 100 | 66.67% (45.83% @ scaled fill!) |
| Condenser Heat Rejection (kW) | ((Qw_m3_hr * 995) / 3600) * 4.184 * Range | 3,885.5 kW (2,671.3 kW @ scaled fill) |
Thermodynamic Wet-Bulb Approach, Tower Effectiveness & Heat Rejection Formula
Validate `T_wb < T_cold < T_hot <= 80` °C (leaving sump water CANNOT physically cool below entering ambient wet-bulb `T_wb` in a purely evaporative tower!) and `Water_Flow > 0` m³/h!
=LET(th_c, B2, tc_c, B3, tw_c, B4, qw_h, B5, IF(OR(tc_c <= tw_c, th_c <= tc_c, th_c > 80, qw_h <= 0), "Invalid Tower Temps (Tcold must exceed Twb)", ROUND(((qw_h * 995) / 3600) * 4.184 * (th_c - tc_c), 1)))Scaled PVC Fill & Clogged Spray-Nozzle Approach Degradation Check (Set T_cold B3 = 31.50 °C)
Let calcium carbonate scale foul the PVC fill so Basin Water `T_cold` B3 creeps up `+2.5 °C` to `31.50 °C` at `37.0 °C` inlet cap: Wet-Bulb Approach E3 degrades from `4.00 °C` to `6.50 °C`, Tower Effectiveness E4 drops from `66.67%` down to `45.83%`, and Heat Rejection Capacity at `37 °C` cap falls to `2,671.3` kW (E5)—forcing the centrifugal chiller compressor head pressure and kW/ton up!
=IF(ISTEXT(E5), E5, ROUND(((B2 - B3) / (B2 - B4)) * 100, 2))Try the example
Use the original values or change them to test your understanding.