• A-Z
• Directory
• myUVM

### Contact

Chris Callahan
310 Main St, Po Box 559
Bennington, VT 05201
802-447-7582 x256
chris.callahan@uvm.edu

Andrew Chamberlin
140 Kennedy Rd, Suite 201
S. Burlington, VT 05403
802-651-8343 x512
andrew.chamberlin@uvm.edu

## UVM Extension AgEngineering Blog

### Psychrocalc

Posted: August 16th, 2015 by Chris Callahan

Psychrocalc is a free Excel(TM) add-in that makes psychrometric calculations easier. Currently the following calculations are supported with Excel(TM) friendly functions:

• RH_TDB_TWB (TDB, TWB, P) – Calculates relative humidity (RH, %) for a known dry-bulb (TDB, F) and wet-bulb (TWB, F) temperature at a given pressure (P, PSIA)
• RH_TDB_W (TDB, W, P) – Calculates relative humidity (RH, %) for a known drybulb (TDB, F) and humidity ratio (W, lbw/lbda) at a given pressure (P, PSIA).
• TDB_RH_W (RH, W, P) – Calculates drybulb (TDB, F) for a known relative humidity (RH, %) and humidity ratio (W, lbw/lbda) at a given pressure (P, PSIA).
• TWB_TDB_RH (TDB, RH, P) – Calculates wet-bulb temperature (TWB, F) for a known dry-bulb (TDB, F) and relative humidity (RH, %) at a given pressure (P, psia).
• TDP_TDB_RH (TDB, RH, P) – Calculates dew-point temperature (TDP, F) for a known dry-bulb temperature (TDB, F) and relative humidity (RH, %) at a given pressure (psia)
• W_TDB_TWB (TDB, TWB, P) – Calculates humidity ratio (w, lbw/lbda) for known dry-bulb temperature (TDB, F) and wet-bulb (TWB, F) at a given pressure (P, psia)
• T_Wsat (Wsat) – Calculates the temperature (Tsat, F) corresponding to a given saturation humidity ratio (w, lbw/lbda)
• Wsat_T (T) – Calculates the saturation humidity ratio (w, lbw/lbda) for a given temperature (Tsat, F)
• Tsat_P (P) – Calculates the saturation temperature (Tsat, F) of water vapor for a given pressure (Psat, PSIA)
• Psat_T (T) – Calculates the saturation pressure (Psat, psia) of water vapor for a given temperature (Tsat, F)
• Pvap_TDB_RH (TDB, RH, P) – Calculates the vapor pressure of water (Pvap, psia) in air for a given dry bulb temperature (TDB, degF), RH (%) and total pressure (P, psia) as inputs.
• hfg_T (T) – Calculates the specific enthalpy of evaporation at a given temperature (T, degF).
• Interpolate (x, x1, x2, y1, y2) – Calculates y (unknown) given x and four known table lookup values (x1, x2, y1, y2) using a linear interpolation.
• hda_T (T) – Calculates specific enthalpy of dry air (BTU/lb) at a specified temperature (T, degF).
• hsa_T (T) – Calculates specific enthalpy of saturated air (BTU/lb) at a specified temperature (T, degF).
• ha_T_RH (T,RH) – Calculates specific enthalpy of a air water mixture (BTU/lb) at a specified temperature (T, degF) and relative humidity (RH).
• Tda (h) – Calculates a specific temperature for dry air of a specific enthalpy.
• vda_T (T) – Calculates specific volume of dry air (ft3/lb) at a specified temperature (T, degF).
• vsa_T (T) – Calculates specific volume of saturated air (ft3/lb) at a specified temperature (T, degF).
• va_T_RH (T,RH) – Calculates specific volume of a air water mixture (ft3/lb) at a specified temperature (T, degF) and relative humidity (RH).

The calculations follow ASHRAE Handbook – Fundamentals. 2005. Chapter 6.