Commercial HVAC Load Calculator
ANA›Life Services Authority›National Calculator Authority›Commercial HVAC Load Calculator
.calc-container { max-width: 640px; margin: 2rem 0; padding: 1.5rem; background: #fff; border: 1px solid #ddd; border-radius: 8px; box-shadow: 0 1px 3px rgba(0,0,0,0.06); font-family: system-ui, -apple-system, sans-serif; } .calc-container h3 { font-family: Georgia, serif; font-size: 1.15rem; color: #1a1a1a; margin-bottom: 1rem; padding-bottom: 0.5rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-row { display: flex; align-items: center; gap: 0.75rem; margin-bottom: 0.75rem; flex-wrap: wrap; } .calc-row label { min-width: 160px; font-size: 0.9rem; color: #333; font-weight: 500; } .calc-row input[type="number"], .calc-row select { flex: 1; min-width: 120px; max-width: 200px; padding: 0.5rem 0.6rem; border: 1px solid #ccc; border-radius: 4px; font-size: 0.9rem; font-family: system-ui, sans-serif; color: #1a1a1a; background: #fafaf8; } .calc-row input:focus, .calc-row select:focus { outline: none; border-color: var(--ac, #3d5a80); box-shadow: 0 0 0 2px rgba(26,74,138,0.12); } .calc-row .unit { font-size: 0.82rem; color: #888; min-width: 30px; } .calc-btn { display: inline-block; margin-top: 0.5rem; padding: 0.55rem 1.5rem; background: var(--ac, #3d5a80); color: #fff; border: none; border-radius: 4px; font-size: 0.9rem; font-weight: 600; cursor: pointer; font-family: system-ui, sans-serif; } .calc-btn:hover { opacity: 0.9; } .calc-result { margin-top: 1.25rem; padding: 1rem 1.25rem; background: #f0f6fc; border-left: 3px solid var(--ac, #3d5a80); border-radius: 0 6px 6px 0; display: none; } .calc-result.visible { display: block; } .calc-result-label { font-size: 0.78rem; text-transform: uppercase; letter-spacing: 0.06em; color: #666; margin-bottom: 0.25rem; } .calc-result-value { font-size: 1.6rem; font-weight: 700; color: var(--ac, #3d5a80); } .calc-result-detail { font-size: 0.85rem; color: #555; margin-top: 0.5rem; line-height: 1.5; } .calc-note { margin-top: 1rem; font-size: 0.8rem; color: #888; font-style: italic; } .calc-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 0.75rem; margin-top: 0.75rem; } .calc-grid-item { padding: 0.6rem 0.8rem; background: #f8f9fa; border-radius: 4px; border: 1px solid #eee; } .calc-grid-item .label { font-size: 0.75rem; color: #888; text-transform: uppercase; letter-spacing: 0.04em; } .calc-grid-item .value { font-size: 1.1rem; font-weight: 600; color: #1a1a1a; } @media (max-width: 720px) { .calc-row { flex-direction: column; align-items: flex-start; gap: 0.3rem; } .calc-row label { min-width: auto; } .calc-row input[type="number"], .calc-row select { max-width: 100%; width: 100%; } .calc-grid { grid-template-columns: 1fr; } } .calc-chart { margin: 1rem 0; text-align: center; } .calc-chart svg { max-width: 100%; height: auto; } .calc-chart-legend { display: flex; flex-wrap: wrap; justify-content: center; gap: 0.6rem 1.2rem; margin-top: 0.6rem; font-size: 0.8rem; color: #555; } .calc-chart-legend span { display: inline-flex; align-items: center; gap: 0.3rem; } .calc-chart-legend i { display: inline-block; width: 10px; height: 10px; border-radius: 2px; font-style: normal; } .calc-related { max-width: 640px; margin: 2rem 0 1rem; padding: 1.25rem 1.5rem; background: #f8f9fa; border: 1px solid #e8e8e8; border-radius: 8px; } .calc-related h3 { font-family: Georgia, serif; font-size: 1rem; color: #1a1a1a; margin: 0 0 0.75rem; padding-bottom: 0.4rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-related-list { list-style: none; padding: 0; margin: 0 0 0.75rem; display: grid; grid-template-columns: 1fr 1fr; gap: 0.4rem 1.5rem; } .calc-related-list li a { font-size: 0.88rem; color: var(--ac, #3d5a80); text-decoration: none; } .calc-related-list li a:hover { text-decoration: underline; } .calc-browse-all { margin: 0.5rem 0 0; font-size: 0.9rem; font-weight: 600; } .calc-browse-all a { color: var(--ac, #3d5a80); text-decoration: none; } .calc-browse-all a:hover { text-decoration: underline; } @media (max-width: 720px) { .calc-related-list { grid-template-columns: 1fr; } }
Commercial HVAC Load Calculator
Estimates commercial building heating and cooling loads based on ASHRAE simplified load calculation methods. Calculates sensible heat gain/loss through walls, roof, windows, infiltration, and internal loads.
### Building Envelope
Floor Area (sq ft)
Number of Stories
Floor-to-Ceiling Height (ft)
Wall U-Value (BTU/hr·ft²·°F)
Roof U-Value (BTU/hr·ft²·°F)
Window-to-Wall Ratio (%)
Window U-Value (BTU/hr·ft²·°F)
Window SHGC (Solar Heat Gain Coefficient)
### Climate & Occupancy
Outdoor Summer Design Temp (°F)
Outdoor Winter Design Temp (°F)
Indoor Design Temp (°F)
Number of Occupants
Lighting Power Density (W/sq ft)
Equipment Power Density (W/sq ft)
Infiltration Rate (ACH)
Ventilation Rate (CFM/person)
Calculate HVAC Loads
### ☃ Heating Load Results
Component Load (BTU/hr) % of Total
Total Heating Load
100%
### ☀ Cooling Load Results
Component Load (BTU/hr) % of Total
Total Cooling Load
100%
Heating Capacity
Tons / kW
Cooling Capacity
Tons / kW
Load Intensity
BTU/hr·ft² (cooling)
function comCalc() { const err = document.getElementById('com-error'); const res = document.getElementById('com-result'); err.style.display = 'none'; res.style.display = 'none';
// --- Parse inputs --- const floorArea = parseFloat(document.getElementById('com-floor-area').value); const stories = parseFloat(document.getElementById('com-stories').value); const ceilHeight = parseFloat(document.getElementById('com-ceiling-height').value); const wallU = parseFloat(document.getElementById('com-wall-uval').value); const roofU = parseFloat(document.getElementById('com-roof-uval').value); const winPct = parseFloat(document.getElementById('com-window-pct').value) / 100; const winU = parseFloat(document.getElementById('com-window-uval').value); const winSHGC = parseFloat(document.getElementById('com-window-shgc').value); const tOutSummer = parseFloat(document.getElementById('com-outdoor-summer').value); const tOutWinter = parseFloat(document.getElementById('com-outdoor-winter').value); const tIndoor = parseFloat(document.getElementById('com-indoor-temp').value); const occupants = parseFloat(document.getElementById('com-occupants').value); const lightingDens = parseFloat(document.getElementById('com-lighting-density').value); const equipDens = parseFloat(document.getElementById('com-equipment-density').value); const infiltACH = parseFloat(document.getElementById('com-infiltration').value); const ventCFM = parseFloat(document.getElementById('com-ventilation').value);
// --- Validation --- const inputs = {floorArea, stories, ceilHeight, wallU, roofU, winPct, winU, winSHGC, tOutSummer, tOutWinter, tIndoor, occupants, lightingDens, equipDens, infiltACH, ventCFM}; for (const [k, v] of Object.entries(inputs)) { if (isNaN(v)) { err.textContent = 'All fields are required and must be numeric.'; err.style.display = 'block'; return; } } if (tOutSummer = tIndoor) { err.textContent = 'Winter outdoor design temp must be less than indoor temp.'; err.style.display = 'block'; return; }
// ============================================================ // GEOMETRY // ============================================================ // Footprint = floorArea / stories (assume square building) const footprint = floorArea / stories; const sideLength = Math.sqrt(footprint); const perimeter = 4 * sideLength; const totalHeight = stories * ceilHeight;
// Gross wall area (all four sides, full building height) const grossWallArea = perimeter * totalHeight; const windowArea = grossWallArea * winPct; const netWallArea = grossWallArea - windowArea; const roofArea = footprint; // only top floor roof
// Volume for infiltration (total building) const buildingVolume = floorArea * ceilHeight; // ft³
// ============================================================ // TEMPERATURE DIFFERENCES // ============================================================ const deltaTCool = tOutSummer - tIndoor; // °F, cooling const deltaTHeat = tIndoor - tOutWinter; // °F, heating
// ============================================================ // SOLAR RADIATION (ASHRAE simplified peak) // Average peak solar on vertical surface ~200 BTU/hr·ft² // Apply orientation diversity factor 0.5 (not all walls face sun simultaneously) // ============================================================ const peakSolar = 200; // BTU/hr·ft² on sunlit glass const orientFactor = 0.5; // diversity for multiple orientations
// ============================================================ // INTERNAL GAINS // Occupant sensible heat: 250 BTU/hr/person (office activity, ASHRAE 62.1) // Occupant latent heat: 200 BTU/hr/person // Lighting: 1 W = 3.412 BTU/hr (100% to sensible) // Equipment: 1 W = 3.412 BTU/hr (75% sensible, 25% latent) // ============================================================ const occSensible = occupants * 250; // BTU/hr const occLatent = occupants * 200; // BTU/hr const lightingLoad = lightingDens * floorArea * 3.412; // BTU/hr const equipSens = equipDens * floorArea * 3.412 * 0.75; // BTU/hr const equipLatent = equipDens * floorArea * 3.412 * 0.25; // BTU/hr
// ============================================================ // INFILTRATION // Q_infil = (ACH × Volume / 60) × 1.1 × ΔT (sensible, BTU/hr) // CFM_infil = ACH × Volume / 60 // ============================================================ const cfmInfil = (infiltACH * buildingVolume) / 60; // CFM const heatInfil = 1.1 * cfmInfil * deltaTHeat; // BTU/hr heating const coolInfil = 1.1 * cfmInfil * deltaTCool; // BTU/hr cooling
// ============================================================ // VENTILATION LOAD // Q_vent = 1.1 × CFM_vent × ΔT (sensible) // ============================================================ const cfmVent = occupants * ventCFM; // CFM const heatVent = 1.1 * cfmVent * deltaTHeat; // BTU/hr const coolVent = 1.1 * cfmVent * deltaTCool; // BTU/hr
// ============================================================ // CONDUCTION LOADS // Q = U × A × ΔT // ============================================================ // HEATING const heatWall = wallU * netWallArea * deltaTHeat; const heatRoof = roofU * roofArea * deltaTHeat; const heatWindow = winU * windowArea * deltaTHeat;
// COOLING (conduction only — solar handled separately) const coolWall = wallU * netWallArea * deltaTCool; const coolRoof = roofU * roofArea * deltaTCool; const coolWindowCond = winU * windowArea * deltaTCool;
// ============================================================ // SOLAR GAIN (cooling only) // Q_solar = SHGC × A_window × Peak_Solar × OrientFactor // ============================================================ const solarGain = winSHGC * windowArea * peakSolar * orientFactor;
// ============================================================ // TOTALS // ============================================================ // Heating: envelope conduction + infiltration + ventilation // (internal gains offset heating but conservatively ignored for peak sizing) const totalHeat = heatWall + heatRoof + heatWindow + heatInfil + heatVent;
// Cooling: envelope conduction + solar + internal gains + infiltration + ventilation const totalCool = coolWall + coolRoof + coolWindowCond + solarGain + occSensible + lightingLoad + equipSens + coolInfil + coolVent;
// ============================================================ // UNIT CONVERSIONS // 1 ton = 12,000 BTU/hr; 1 kW = 3,412 BTU/hr // ============================================================ const heatTons = totalHeat / 12000; const heatKW = totalHeat / 3412; const coolTons = totalCool / 12000; const coolKW = totalCool / 3412; const intensity = totalCool / floorArea;
// ============================================================ // RENDER HEATING TABLE // ============================================================ const fmt = n => Math.round(n).toLocaleString(); const pct = (n, tot) => (tot > 0 ? (n/tot*100).toFixed(1) : '0.0') + '%';
const heatRows = [ ['Wall Conduction', heatWall], ['Roof Conduction', heatRoof], ['Window Conduction', heatWindow], ['Infiltration', heatInfil], ['Ventilation', heatVent], ]; const coolRows = [ ['Wall Conduction', coolWall], ['Roof Conduction', coolRoof], ['Window Conduction', coolWindowCond], ['Solar Gain (Glass)', solarGain], ['Occupants (Sensible)', occSensible], ['Lighting', lightingLoad], ['Equipment (Sensible)', equipSens], ['Infiltration', coolInfil], ['Ventilation', coolVent], ];
const buildRows = (rows, total, tbodyId) => {
const tbody = document.getElementById(tbodyId);
tbody.innerHTML = '';
rows.forEach(([label, val]) => {
const tr = document.createElement('tr');
tr.innerHTML = ${label}
${fmt(val)}
${pct(val,total)};
tbody.appendChild(tr);
});
};
buildRows(heatRows, totalHeat, 'com-heat-tbody'); buildRows(coolRows, totalCool, 'com-cool-tbody');
document.getElementById('com-heat-total').textContent = fmt(totalHeat) + ' BTU/hr'; document.getElementById('com-cool-total').textContent = fmt(totalCool) + ' BTU/hr'; document.getElementById('com-heat-tons').textContent = heatTons.toFixed(1) + ' T / ' + heatKW.toFixed(1) + ' kW'; document.getElementById('com-cool-tons').textContent = coolTons.toFixed(1) + ' T / ' + coolKW.toFixed(1) + ' kW'; document.getElementById('com-intensity').textContent = intensity.toFixed(1);
res.style.display = 'block'; }
#### Formulas Used
Conduction (Walls, Roof, Windows): Qcond = U × A × ΔT [BTU/hr] where U = U-value [BTU/hr·ft²·°F], A = area [ft²], ΔT = design temperature difference [°F]
Solar Heat Gain: Qsolar = SHGC × Awindow × Ipeak × forient where SHGC = Solar Heat Gain Coefficient, Ipeak = 200 BTU/hr·ft² (ASHRAE peak vertical surface), forient = 0.5 (orientation diversity factor)
Infiltration & Ventilation (Sensible): Q = 1.1 × CFM × ΔT [BTU/hr] CFMinfil = ACH × Volume / 60 | CFMvent = Occupants × CFM/person
Internal Gains: Occupants: 250 BTU/hr·person (sensible) + 200 BTU/hr·person (latent) Lighting: W/ft² × Area × 3.412 BTU/W Equipment: W/ft² × Area × 3.412 × 0.75 (sensible) / 0.25 (latent)
Unit Conversions: 1 Ton = 12,000 BTU/hr | 1 kW = 3,412 BTU/hr
#### Assumptions & References
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