## DERIVATION OF A RATIONAL PSYCHROMETRIC FORMULA

59The need of an accurate rational psychrometric formula for vapor pressures using modern data is therefore apparent. The required values could be obtained indirectly from the formula already given, but computation is facilitated by another derivation giving directly the vapor pressure .

38This method consists, ﬁrst, in bringing a continuous supply of air close to saturation, where its moisture content can be determined with great accuracy by means of a wet and dry-bulb thermometer and applying the rational psychrometric formula [3] assuming an approximate value for the speciﬁc heat; second, in heating this current of air of known moisture content to any desired amount andtaking the wet and dry-bulb readings as in experiment No. 2, Appendix No. 2. By applying the rational psychrometic formula derived in Pars. 58-67, we have

## DERIVATION OF A RATIONAL PSYCHROMETRIC FORMULA

Willis Carrier's Rational Psychrometric Formulae brought science to what had been the often hit-or-miss design of air-conditioning systems, and in the process made Carrier an international name. The chart would be updated and reprinted regularly, serving as an essential tool to generations of engineers.

1911 - Willis Carrier's Rational Psychrometric Formulae brought science to what had been the often hit-or-miss design of air-conditioning systems, and in the process made Carrier an international name. The chart would be updated and reprinted regularly, serving as an essential tool to generations of engineers. Psychrometric chart:Where did it come from? On December 3, 1911, a young engineer by the named of Willis Carrier, presented the most significant documents ever prepared on air conditioning – his "Rational Psychrometric Formulae" – at the annual meeting of the American Society of Mechanical Engineers. It became known as the "Magna-Carta of Psychrometrics."