Calculation Methodology

Refrigerant P-T Charts

Saturated pressure-temperature data is sourced from ASHRAE Fundamentals Chapter 30 and manufacturer published data sheets. Values represent equilibrium saturation conditions at sea level. For temperatures between published data points, linear interpolation is used. All pressures are gauge pressure (PSIG).

Duct Sizing

Duct sizing uses the equal friction method per ASHRAE Fundamentals Chapter 21 and SMACNA standards. Friction factors assume galvanized steel duct with absolute roughness of 0.0003 ft. Noise velocity thresholds follow SMACNA Table 5-1: quiet (<500 FPM), moderate (500-700 FPM), loud (>700 FPM).

BTU Load Calculation

Load estimates use a simplified methodology based on ACCA Manual J (8th Edition) with per-square-foot multipliers by IECC climate zone. Factors include insulation quality, ceiling height, and window area percentage. For accurate equipment sizing, a full room-by-room Manual J calculation is recommended.

SEER Comparison

Annual energy cost is calculated as: (BTU x annual cooling hours) / (SEER x 1,000) x electricity rate ($/kWh). This follows AHRI Standard 210/240 methodology. CO2 reduction uses EPA eGRID US average emission factor.

Refrigerant Charge

Additional charge per foot of liquid line is based on averaged values from major manufacturer installation manuals (Carrier, Lennox, Trane, Goodman). Factory charge length assumes 25 feet for split systems unless specified.

Verification

All formulas are verified against published reference values. Refrigerant P-T data is cross-checked against manufacturer charts. Calculation results are compared with established HVAC engineering tools.