Page:Journal of the American Society of Mechanical Engineers, Volume 33.pdf/660

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41As already pointed out, it is possible to derive a rational psychrometric formula based on the fundamental principles, A, B and C.

42In considering the interchanges of heat occurring in psychrometric phenomena, it is essential to consider primarily the relative weights of dry air and of water vapor rather than the usual density temperature relationship; that is, it is necessary to express moisture content as weight of water vapor per pound of pure air, rather than as weight of water vapor per cubic foot of space. Moreover, this relationship is much more adaptable to all of the usual calculations in air conditioning and in meteorology. The author, accordingly, has constructed all his formulae and psychrometric charts upon this basis. In the deduction of the formulae and in the construction of the accompanying charts, the following fundamental data were employed: