How this calculator works
Choose an independent moisture property at the entered dry-bulb temperature and absolute pressure. The tool converts it to vapour pressure and derives the remaining state. Wet-bulb calculations use the NWS ventilated liquid-water psychrometer equation, rather than the thermodynamic adiabatic-saturation definition. Enthalpy and volume use ASHRAE ideal-mixture engineering approximations per kilogram of dry air, referenced to 0 C. Cooling effectiveness estimates an outlet temperature approaching the ventilated wet bulb, without a full cooler energy balance. All bulb and dew-point temperatures remain inside the -40 through 60 C liquid-water range.
Formula
w = 0.621945 e/(p-e); w_s = 0.621945 e_s/(p-e_s); degree = w/w_s; v = R_d T(1+w/0.621945)/p. h = 1006 t+w(2501000+1860 t) J/kg dry air, t in C. e = e_s(Tw)-0.00066(1+0.00115 tw)p(T-Tw); T_out=T-effectiveness*(T-Tw).
Worked example
At 0 C, 100% RH and 101325 Pa, dew point and wet bulb are both 0 C. Humidity ratio is about 0.00377439 kg/kg dry air, with enthalpy about 9439.74 J/kg dry air.
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Frequently asked questions
Which two measurements define the state?
Here most modes pair dry bulb with one moisture property at known pressure. Separate modes recover dry bulb from ratio and enthalpy, or pressure from ratio and vapour pressure.
Is specific volume per kilogram of moist air?
No. It is per kilogram of dry air, matching the humidity ratio and enthalpy basis.
Can I mix natural and ventilated wet-bulb measurements?
They are different instrument conditions. This psychrometer relation assumes a ventilated wetted bulb and liquid-water saturation.