Refrigerant Charge Calculator — Superheat and Subcooling
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Refrigerant Charge Calculator — Superheat and Subcooling
Determine refrigerant charge status by calculating actual superheat and subcooling values, then comparing them to target ranges. Supports both TXV/EEV and fixed-orifice metering device systems.
### System Configuration
Metering Device Type
Fixed Orifice / Piston (use Superheat method) TXV / EEV (use Subcooling method)
Refrigerant Type
R-22 R-410A R-404A R-134a R-407C R-32
### Superheat Method (Fixed Orifice / Piston)
Suction Line Pressure (psig)
Suction Line Temperature at Service Valve (°F)
#### Target Superheat Inputs (Fixed Orifice Systems)
Outdoor Ambient Dry-Bulb Temperature (°F)
Indoor Return Air Wet-Bulb Temperature (°F)
### Subcooling Method (TXV / EEV)
Liquid Line Pressure (psig)
Liquid Line Temperature at Service Valve (°F)
Calculate Charge Status
// ── Saturation temperature lookup tables ────────────────────────────────────── // Format: { psig: sat_temp_F } — key data points, interpolated linearly // Sources: ASHRAE refrigerant property tables
const REF_SAT_TABLES = { R22: { // psig → sat temp °F (suction/low side range + liquid/high side range) 0: -41.4, 5: -28.0, 10: -17.0, 15: -7.6, 20: 0.5, 25: 7.7, 30: 14.2, 35: 20.1, 40: 25.6, 45: 30.6, 50: 35.3, 55: 39.7, 60: 43.8, 65: 47.7, 70: 51.4, 75: 54.9, 80: 58.2, 85: 61.4, 90: 64.4, 95: 67.3, 100: 70.1, 110: 75.4, 120: 80.4, 130: 85.1, 140: 89.5, 150: 93.7, 160: 97.7, 170: 101.5, 180: 105.1, 190: 108.6, 200: 111.9, 220: 118.2, 240: 124.1, 260: 129.7, 280: 135.0, 300: 140.1 }, R410A: { 0: -62.9, 5: -51.4, 10: -41.7, 15: -33.3, 20: -25.8, 25: -19.0, 30: -12.8, 35: -7.1, 40: -1.8, 45: 3.1, 50: 7.7, 55: 12.0, 60: 16.1, 65: 20.0, 70: 23.7, 75: 27.2, 80: 30.6, 85: 33.8, 90: 36.9, 95: 39.9, 100: 42.8, 110: 48.3, 120: 53.5, 130: 58.4, 140: 63.1, 150: 67.5, 160: 71.8, 170: 75.9, 180: 79.8, 190: 83.6, 200: 87.2, 220: 94.1, 240: 100.6, 260: 106.8, 280: 112.7, 300: 118.3, 320: 123.7, 340: 128.9, 360: 133.9, 380: 138.7, 400: 143.3, 420: 147.8, 440: 152.1 }, R404A: { 0: -62.0, 5: -51.0, 10: -41.5, 15: -33.2, 20: -25.8, 25: -19.1, 30: -13.0, 35: -7.3, 40: -2.1, 45: 2.8, 50: 7.4, 55: 11.7, 60: 15.8, 65: 19.7, 70: 23.4, 75: 26.9, 80: 30.3, 85: 33.5, 90: 36.6, 95: 39.6, 100: 42.4, 110: 47.8, 120: 52.9, 130: 57.7, 140: 62.3, 150: 66.6, 160: 70.8, 170: 74.8, 180: 78.6, 190: 82.3, 200: 85.8, 220: 92.5, 240: 98.8, 260: 104.8, 280: 110.5, 300: 115.9 }, R134a: { 0: -15.0, 5: -6.0, 10: 2.0, 15: 9.2, 20: 15.7, 25: 21.6, 30: 27.1, 35: 32.2, 40: 37.0, 45: 41.5, 50: 45.8, 55: 49.9, 60: 53.8, 65: 57.5, 70: 61.1, 75: 64.5, 80: 67.8, 85: 71.0, 90: 74.1, 95: 77.0, 100: 79.9, 110: 85.4, 120: 90.6, 130: 95.6, 140: 100.4, 150: 105.0, 160: 109.4, 170: 113.6, 180: 117.7, 190: 121.7, 200: 125.5, 220: 132.8, 240: 139.8 }, R407C: { // Uses bubble point (liquid line) for subcooling; dew point (suction) for superheat // Approximate midpoint values used here for simplicity 0: -45.0, 5: -33.0, 10: -22.5, 15: -13.3, 20: -5.1, 25: 2.4, 30: 9.3, 35: 15.7, 40: 21.7, 45: 27.3, 50: 32.5, 55: 37.5, 60: 42.2, 65: 46.7, 70: 51.0, 75: 55.1, 80: 59.0, 85: 62.8, 90: 66.4, 95: 69.9, 100: 73.3, 110: 79.8, 120: 85.9, 130: 91.7, 140: 97.2, 150: 102.5, 160: 107.6, 170: 112.4, 180: 117.1, 190: 121.6, 200: 125.9, 220: 134.1, 240: 141.9, 260: 149.3, 280: 156.4 }, R32: { 0: -61.0, 5: -50.0, 10: -40.5, 15: -32.2, 20: -24.8, 25: -18.1, 30: -12.0, 35: -6.4, 40: -1.2, 45: 3.7, 50: 8.3, 55: 12.7, 60: 16.9, 65: 20.9, 70: 24.7, 75: 28.3, 80: 31.8, 85: 35.2, 90: 38.4, 95: 41.5, 100: 44.5, 110: 50.2, 120: 55.6, 130: 60.7, 140: 65.6, 150: 70.2, 160: 74.7, 170: 79.0, 180: 83.1, 190: 87.1, 200: 90.9, 220: 98.2, 240: 105.1, 260: 111.7, 280: 118.0, 300: 124.0 } };
// ── Target superheat table (AHRI / manufacturer standard) ───────────────────── // Rows = outdoor ambient dry-bulb (°F), Cols = indoor return wet-bulb (°F) // Values = target superheat (°F) for fixed-orifice systems // Source: AHRI Standard 210/240, typical manufacturer charging charts
const REF_TARGET_SH_TABLE = { // WB: 50 55 60 63 65 67 70 75 outdoorDB: [75, 80, 85, 90, 95, 100, 105, 110, 115], wetBulb: [50, 55, 60, 63, 65, 67, 70, 75], data: { // ODB → [SH at each WB above] 75: [57, 48, 39, 34, 31, 28, 23, 15], 80: [53, 44, 35, 30, 27, 24, 19, 11], 85: [49, 40, 31, 26, 23, 20, 15, 7], 90: [45, 36, 27, 22, 19, 16, 11, 3], 95: [41, 32, 23, 18, 15, 12, 7, 0], 100: [37, 28, 19, 14, 11, 8, 3, 0], 105: [33, 24, 15, 10, 7, 4, 0, 0], 110: [29, 20, 11, 6, 3, 0, 0, 0], 115: [25, 16, 7, 2, 0, 0, 0, 0] } };
// ── Target subcooling ranges by refrigerant ─────────────────────────────────── const REF_TARGET_SC = { R22: { min: 10, max: 15, typical: 12 }, R410A: { min: 10, max: 15, typical: 12 }, R404A: { min: 8, max: 12, typical: 10 }, R134a: { min: 10, max: 15, typical: 12 }, R407C: { min: 10, max: 15, typical: 12 }, R32: { min: 10, max: 15, typical: 12 } };
// ── Utility: linear interpolation from table ────────────────────────────────── function refInterpolateSatTemp(table, psig) { const keys = Object.keys(table).map(Number).sort((a, b) => a - b); if (psig = keys[keys.length - 1]) return table[keys[keys.length - 1]]; for (let i = 0; i = keys[i] && psig = dbKeys[i] && db = wbKeys[i] && wb db0) ? (db - db0) / (db1 - db0) : 0; const tWB = (wb1 > wb0) ? (wb - wb0) / (wb1 - wb0) : 0;
const data = REF_TARGET_SH_TABLE.data; const sh00 = data[db0][wb0i]; const sh01 = data[db0][wb1i]; const sh10 = data[db1][wb0i]; const sh11 = data[db1][wb1i];
// Bilinear interpolation return sh00 * (1 - tDB) * (1 - tWB) + sh10 * tDB * (1 - tWB) + sh01 * (1 - tDB) * tWB + sh11 * tDB * tWB; }
// ── Toggle UI sections ──────────────────────────────────────────────────────── function refToggleMethod() { const device = document.getElementById("ref-metering-device").value; document.getElementById("ref-superheat-section").style.display = (device === "fixed") ? "" : "none"; document.getElementById("ref-subcooling-section").style.display = (device === "txv") ? "" : "none"; document.getElementById("ref-result").innerHTML = ""; }
// ── Main calculation ────────────────────────────────────────────────────────── function refCalc() { const resultDiv = document.getElementById("ref-result"); const device = document.getElementById("ref-metering-device").value; const refType = document.getElementById("ref-refrigerant").value; const satTable = REF_SAT_TABLES[refType];
let html = "";
// ── SUPERHEAT METHOD ────────────────────────────────────────────────────── if (device === "fixed") { const suctionP = parseFloat(document.getElementById("ref-suction-pressure").value); const suctionT = parseFloat(document.getElementById("ref-suction-temp").value); const outdoorDB = parseFloat(document.getElementById("ref-outdoor-db").value); const indoorWB = parseFloat(document.getElementById("ref-indoor-wb").value);
// Validation if (isNaN(suctionP) || isNaN(suctionT) || isNaN(outdoorDB) || isNaN(indoorWB)) { resultDiv.innerHTML = 'Please fill in all Superheat Method fields.
'; return; } if (suctionP 500) { resultDiv.innerHTML = 'Suction pressure must be between 0 and 500 psig.
'; return; } if (outdoorDB 115) { resultDiv.innerHTML = 'Outdoor ambient must be between 75°F and 115°F for target SH lookup.
'; return; } if (indoorWB 75) { resultDiv.innerHTML = 'Indoor wet-bulb must be between 50°F and 75°F for target SH lookup.
'; return; }
// Saturation temperature at suction pressure const satTempSuction = refInterpolateSatTemp(satTable, suctionP);
// Actual Superheat = Suction Line Temp − Saturation Temp at Suction Pressure const actualSH = suctionT - satTempSuction;
// Target Superheat from AHRI charging chart (bilinear interpolation) const targetSH = refInterpolateTargetSH(outdoorDB, indoorWB);
// Deviation const deviation = actualSH - targetSH;
// Charge status let status = "", statusClass = "", recommendation = ""; if (Math.abs(deviation) 3 && deviation 10) { status = "🔴 Significantly Undercharged"; statusClass = "calc-error"; recommendation = "Actual superheat is " + deviation.toFixed(1) + "°F above target. System is significantly undercharged. Check for leaks before adding refrigerant."; } else if (deviation = -10) { status = "⚠️ Slightly Overcharged"; statusClass = "calc-warn"; recommendation = "Actual superheat is " + Math.abs(deviation).toFixed(1) + "°F below target. System may be slightly overcharged. Recover refrigerant in small increments and recheck."; } else { status = "🔴 Significantly Overcharged"; statusClass = "calc-error"; recommendation = "Actual superheat is " + Math.abs(deviation).toFixed(1) + "°F below target. System is significantly overcharged. Recover refrigerant carefully."; }
html = ` ### Superheat Results — ${refType} (Fixed Orifice)
ParameterValue Suction Pressure${suctionP.toFixed(1)} psig Saturation Temperature at Suction Pressure${satTempSuction.toFixed(1)} °F Measured Suction Line Temperature${suctionT.toFixed(1)} °F Actual Superheat${actualSH.toFixed(1)} °F Outdoor Ambient Dry-Bulb${outdoorDB.toFixed(0)} °F Indoor Return Wet-Bulb${indoorWB.toFixed(0)} °F Target Superheat (AHRI Chart)${targetSH.toFixed(1)} °F Deviation (Actual − Target)${deviation >= 0 ? "+" : ""}${deviation.toFixed(1)} °F
${status}${recommendation} `;
// ── SUBCOOLING METHOD ───────────────────────────────────────────────────── } else { const liquidP = parseFloat(document.getElementById("ref-liquid-pressure").value); const liquidT = parseFloat(document.getElementById("ref-liquid-temp").value);
// Validation if (isNaN(liquidP) || isNaN(liquidT)) { resultDiv.innerHTML = 'Please fill in all Subcooling Method fields.
'; return; } if (liquidP 700) { resultDiv.innerHTML = 'Liquid line pressure must be between 0 and 700 psig.
'; return; }
// Saturation temperature at liquid line pressure (condensing temp) const satTempLiquid = refInterpolateSatTemp(satTable, liquidP);
// Actual Subcooling = Saturation Temp at Liquid Pressure − Liquid Line Temp const actualSC = satTempLiquid - liquidT;
// Target subcooling range const target = REF_TARGET_SC[refType];
// Charge status
let status = "", statusClass = "", recommendation = "";
if (actualSC >= target.min && actualSC = 0) {
status = "⚠️ Low Subcooling — Likely Undercharged";
statusClass = "calc-warn";
recommendation = Subcooling of ${actualSC.toFixed(1)}°F is below the target minimum of ${target.min}°F. Add refrigerant in small increments and recheck. Also check for restrictions.;
} else if (actualSC target.max && actualSC
ParameterValue
Liquid Line Pressure${liquidP.toFixed(1)} psig
Saturation Temperature at Liquid Pressure (Condensing Temp)${satTempLiquid.toFixed(1)} °F
Measured Liquid Line Temperature${liquidT.toFixed(1)} °F
Actual Subcooling${actualSC.toFixed(1)} °F
Target Subcooling Range${target.min}–${target.max} °F
Deviation from Target Midpoint${(actualSC - target.typical) >= 0 ? "+" : ""}${(actualSC - target.typical).toFixed(1)} °F
${status}${recommendation} `; }
resultDiv.innerHTML = html; }
#### Formulas
Actual Superheat (Fixed Orifice Systems):
Superheat (°F) = Tsuction line − Tsat @ suction pressure
Where Tsat @ suction pressure is the saturation (boiling) temperature of the refrigerant at the measured suction line gauge pressure, obtained from refrigerant pressure-temperature tables.
Target Superheat (Fixed Orifice Systems):
Determined by bilinear interpolation of the AHRI/manufacturer superheat charging chart using: outdoor ambient dry-bulb temperature and indoor return air wet-bulb temperature. The chart encodes the relationship between heat load, airflow, and required evaporator performance.
Actual Subcooling (TXV / EEV Systems):
Subcooling (°F) = Tsat @ liquid line pressure − Tliquid line
Where Tsat @ liquid line pressure is the condensing saturation temperature at the measured liquid line gauge pressure. Subcooling confirms all refrigerant has condensed to liquid before the metering device.
Saturation Temperature Interpolation:
Tsat(P) = T0 + (P − P0) × (T1 − T0) / (P1 − P0)
Linear interpolation between adjacent data points in the refrigerant P-T table.
#### Assumptions & References
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