On 5/20/07, Russell McMahon wrote: > This is both a request and a reference to resources: > > I'm looking for a set of algorithms which allow the characteristics of > moist air to be determined. > Lots of people seem keen to sell me books and programs on the subject > and there are numerous online calculators covering the core variables. > > The essential algorithms which I'm after are here, courtesy of the > ASHRAE handbook. > This rather messy set of algorithms will probably allow most requisite > calculations > > http://www.ageng.ndsu.nodak.edu/envr/PsycEqns.htm > > Not rocket-science but annoyingly fiddly. > > > > Question: has anyone got any useful comments on the subject and/or > practical useful algorithms for psychrometric or hygrometric > calculations. If it's only about calculation then I'm sure will be easy for you. If it's about practic implementation and calibration of the psyhometric algorithm, I have negative feelings about it. Mostly because I wasn't able to reproduce with a resonable accuracy a complete set of psychometric measurements using a climateric (calibrated) chamber. Every measurement depends on many variables and the ugliest of them is the "sucking" time required by the wet temperature sensor (if we are talking about the same methode). Also the air flow velocity and distribution on sensors is very important for getting the real dew point. http://en.wikipedia.org/wiki/Dew_point For hygrometric measurements I've tested with some success the SHT75 Sensirion sensor. http://www.sensirion.com/en/02_sensors/03_humidity/00_humidity_temperature_sensor/06_humidity_sensor_sht75.htm But with the most accurate sensor from Sensirion I don't think you'll be able to get a better accuracy than +/-3%RH (real world, real mesurements and telling truth), maybe with a complete calibration procedure in the measuring environement and not with saturated salt atmosphere... One after the other, accurate humidity measurement is a real challenge. greetings, Vasile -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist