Humidity & Ventilation Load Calculator
Account for West Virginia's variable humidity levels in HVAC system sizing. Calculates latent and sensible ventilation loads per ASHRAE 62.1 and Manual J principles.
Space & Occupancy
WV Climate Conditions
Indoor Design Conditions
Ventilation Parameters
Formulas Used
Humidity Ratio (W):
W = 0.62198 × (φ × Pws) / (Psite − φ × Pws) [lb water / lb dry air]
where Pws = saturation pressure (Magnus formula), φ = relative humidity fraction,
Psite = barometric pressure corrected for WV elevation.
Enthalpy of Moist Air:
h = 0.240·T + W·(1061 + 0.444·T) [BTU/lb dry air]
Sensible Ventilation Load:
Qs = 1.1 × CFM × ΔT [BTU/hr]
(1.1 = 60 min/hr × 0.075 lb/ft³ × 0.240 BTU/lb·°F)
Latent Ventilation Load:
Ql = 0.68 × CFM × ΔWgrains [BTU/hr]
(0.68 = 60 × 0.075 × 1076 / 7000; 1076 BTU/lb = latent heat of vaporization)
ASHRAE 62.1 Ventilation Rate:
CFM = (Occupants × Rp) + (Floor Area × Ra)
ERV/HRV Recovery:
Tsupply = Tout + εs·(Tin − Tout)
Wsupply = Wout + εl·(Win − Wout)
Altitude Correction (WV elevations 565–4,863 ft):
Psite = 14.696 × (1 − 6.8754×10⁻⁶ × elevation)5.2559 psia