Cooling Tower Efficiency Calculator
ANA›Life Services Authority›National Calculator Authority›Cooling Tower Efficiency Calculator
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Cooling Tower Efficiency Calculator
Calculate cooling tower efficiency (effectiveness), range, approach temperature, and heat rejection rate based on inlet/outlet water temperatures, wet-bulb temperature, and flow rate.
Hot Water Inlet Temperature (°F)
Cold Water Outlet Temperature (°F)
Ambient Wet-Bulb Temperature (°F)
Water Flow Rate (GPM)
Calculate
function cooCalc() { var resultDiv = document.getElementById('coo-result'); resultDiv.style.display = 'none'; resultDiv.innerHTML = '';
var T_hot = parseFloat(document.getElementById('coo-hot-water-temp').value); var T_cold = parseFloat(document.getElementById('coo-cold-water-temp').value); var T_wb = parseFloat(document.getElementById('coo-wet-bulb-temp').value); var gpm = parseFloat(document.getElementById('coo-flow-rate').value);
// --- Validation --- var errors = []; if (isNaN(T_hot)) errors.push('Hot water inlet temperature is required.'); if (isNaN(T_cold)) errors.push('Cold water outlet temperature is required.'); if (isNaN(T_wb)) errors.push('Wet-bulb temperature is required.'); if (isNaN(gpm)) errors.push('Water flow rate is required.');
if (errors.length === 0) { if (T_hot 200) errors.push('Hot water temperature seems unusually high (> 200 °F). Please verify.'); if (T_wb 100) errors.push('Wet-bulb temperature is outside a typical range (20–100 °F). Please verify.'); }
if (errors.length > 0) { resultDiv.innerHTML = 'Please fix the following:' + errors.map(function(e){ return ''; }).join('') + ''; resultDiv.style.display = 'block'; return; }
// --- Core Calculations ---
// Range = Hot inlet temp - Cold outlet temp (°F) var range = T_hot - T_cold;
// Approach = Cold outlet temp - Wet-bulb temp (°F) var approach = T_cold - T_wb;
// Efficiency (Effectiveness) = Range / (Range + Approach) × 100 // Equivalent to: (T_hot - T_cold) / (T_hot - T_wb) × 100 var efficiency = (range / (T_hot - T_wb)) * 100;
// Heat Rejection Rate (BTU/hr) // Q = GPM × 500.4 × ΔT // 500.4 = 8.34 lb/gal × 60 min/hr × 1 BTU/(lb·°F) var heatRejection_BTUhr = gpm * 500.4 * range;
// Convert to tons of refrigeration (1 ton = 12,000 BTU/hr) var heatRejection_tons = heatRejection_BTUhr / 12000;
// Convert to kW (1 BTU/hr = 0.000293071 kW) var heatRejection_kW = heatRejection_BTUhr * 0.000293071;
// NTU (Number of Transfer Units) — Merkel approximation for equal Cp // NTU = Range / Approach (simplified; valid when approach > 0) var ntu = range / approach;
// --- Format Output --- var html = '### Results '; html += 'ParameterValue'; html += 'Cooling Tower Efficiency (Effectiveness)' + efficiency.toFixed(1) + ' %'; html += 'Range (ΔT Hot − Cold)' + range.toFixed(2) + ' °F'; html += 'Approach (Cold − Wet-Bulb)' + approach.toFixed(2) + ' °F'; html += 'Heat Rejection Rate' + heatRejection_BTUhr.toLocaleString('en-US', {maximumFractionDigits:0}) + ' BTU/hr'; html += 'Heat Rejection Rate' + heatRejection_tons.toFixed(2) + ' Tons of Refrigeration'; html += 'Heat Rejection Rate' + heatRejection_kW.toFixed(2) + ' kW'; html += 'Number of Transfer Units (NTU)' + ntu.toFixed(3) + ''; html += '';
// Efficiency interpretation var interpretation = ''; if (efficiency >= 70) { interpretation = 'Excellent — the tower is performing very efficiently.'; } else if (efficiency >= 55) { interpretation = 'Good — typical for well-maintained industrial cooling towers.'; } else if (efficiency >= 40) { interpretation = 'Fair — consider inspecting fill media, drift eliminators, and water distribution.'; } else { interpretation = 'Poor — significant performance issues likely; maintenance or redesign recommended.'; } html += 'Interpretation: ' + interpretation + '
';
resultDiv.innerHTML = html; resultDiv.style.display = 'block'; }
#### Formulas Used
Range (°F):
Range = Thot,in − Tcold,out
Approach (°F):
Approach = Tcold,out − Twb
Cooling Tower Efficiency (Effectiveness):
η = Range / (Range + Approach) × 100 = (Thot,in − Tcold,out) / (Thot,in − Twb) × 100
Heat Rejection Rate:
Q (BTU/hr) = GPM × 500.4 × Range
where 500.4 = 8.34 lb/gal × 60 min/hr × 1 BTU/(lb·°F) (specific heat of water)
Q (Tons) = Q (BTU/hr) / 12,000 | Q (kW) = Q (BTU/hr) × 0.000293071
Number of Transfer Units (NTU) — Merkel simplified:
NTU = Range / Approach
(Valid approximation when the operating line and equilibrium line are approximately parallel.)
#### Assumptions & References
- Water is assumed to have a specific heat (Cp) of 1.0 BTU/(lb·°F) and a density of 8.34 lb/gal.
- References: ASHRAE Handbook — HVAC Systems and Equipment (Chapter: Cooling Towers); Cooling Technology Institute (CTI) Standard STD-201; Merkel, F. (1925). Verdunstungskühlung.
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