Dry-Bulb from Enthalpy and Humidity Ratio
Dry-bulb temperature of an air state from its enthalpy and humidity ratio.
Example
You enter
- Enthalpy h (Btu/lb dry air) 31.48
- Humidity ratio W (lb water / lb dry air) 0.0112
You get
- Dry-bulb temperature 80.0 F
No published worked example is on file for this calculation. It is checked against a hand-worked derivation of its method and an independent reference test.
Details, formula, and sources
ScopeThe dry-bulb temperature of an air state from its enthalpy and humidity ratio - t = (h - 1061 W) / (0.240 + 0.444 W) deg F. An enthalpy of 31.48 Btu/lb at W 0.0112 recovers an 80 F dry-bulb. Use it to back out the dry-bulb of a coil's entering or leaving state when a psychrometric analysis gives the enthalpy and W but not the temperature. Sea-level ASHRAE coefficients; a design aid, not a substitute for a measured chart state.
Formula or tablet = (h - 1061 W) / (0.240 + 0.444 W) deg F (the moist-air enthalpy h = 0.240 t + W (1061 + 0.444 t) solved for t).
Source and editionThe I-P moist-air enthalpy relation from the ASHRAE Handbook - Fundamentals solved for the dry-bulb, the inverse of the moist-air-enthalpy tile, by name.
Free accessThe moist-air enthalpy relation and its sea-level coefficients are standard ASHRAE psychrometric results. A measured chart state and the equipment ratings govern.
What governsEstimate. AHJ and licensed professional govern.
API field namesenthalpy_btu, w_lb_lb, t_db_f
- Inverse relation t = (h - 1061 W) / (0.240 + 0.444 W)ASHRAE Fundamentals
- Sea-level coefficients 0.240 dry-air cp, 1061 the enthalpy of saturated vapor at 0 F (from liquid water at 32 F), 0.444 vapor cpASHRAE
- Humidity-ratio input W comes from the chart or RH; returns the dry-bulb, not the wet-bulb or dew pointscope of this tile