ASAE D271.2 DEC94
Psychrometric Data273.16<T<338.72 Brooker (1967)
V
sa
Air specific volume, m /kg dry air or ft /lb dry air
24 ASAE STANDARDS 1998Reviewed by ASAE’s Structures and Environment Division and the Food
Engineering Division Standards Committees; approved by the Electric
Power and Processing Division Standards Committee; adopted by ASAE
December 1963; reconfirmed December 1968; revised April 1974, April
1979; reconfirmed December 1983; reconfirmed by the Food and
Process Engineering Institute Standards Committee December 1988,
December 1989, December 1990, December 1991; reaffirmed December
1992, December 1993, December 1994.
1 Purpose and scope
1.1 The purpose of this Data is to assemble psychrometric data in chart
and equation form in both SI and English units.
1.2 Psychrometric charts are presented that give data for dry bulb
temperature ranges of 35 to 600 F in English units and 10 to 120 C
in SI units.
1.3 Many analyses of psychrometric data are made on computers. The
equations given in Sections 2 and 3 enable the calculation of all
psychrometric data if any two independent psychrometric properties of an
air-water vapor mixture are known in addition to the atmospheric
pressure. In some cases, iteration procedures are necessary. In some
instances, the range of data covered by the equation has been extended
beyond that given in the original source. The equations yield results that
agree closely with values given by Keenan and Keyes (1936) and
existing psychrometric charts.
2 Psychrometric data in SI units
2.1 Psychrometric charts; two presented. One for a temperature range of
10 to 55 C and one for a temperature range of 20 to 120 C.
2.2 Psychrometric equations, SI units. Symbols are defined in Table 1.
2.2.1 Saturation line. P
s
as a function of T
Table 1 – Symbols
h
Enthalpy of air-vapor mixture, J/kg dry air or Btu/lb dry air
h
fg
Latent heat of vaporization of water at saturation, J/kg or
Btu/lb
h
fg
8 Latent heat of vaporization of water at T
wb
, J/kg or Btu/lb
h
fg
9 Latent heat vaporization of water at T
dp
, J/kg or Btu/lb
h
ig
Heat of sublimation of ice, J/kg or Btu/lb
h
ig
8 Heat of sublimation of ice at T
wb
, J/kg or Btu/lb
h
ig
9 Heat of sublimation of ice at T
dp
, J/kg or Btu/lb
H
Humidity ratio, kg water/kg dry air or lb water/lb dry air
ln
Natural logarithm (base e)
P
atm
Atmospheric pressure, Pa or psi
P
s
Saturation vapor pressure at T,Paorpsi
P
swb
Saturation vapor pressure at T
wb
,Paorpsi
P
v
Vapor pressure, Pa or psi
rh
Relative humidity, decimal
T
Dry-bulb temperature, kelvin or rankine
T
dp
Dew-point temperature, kelvin or rankine
T
wb
Wet-bulb temperature, kelvin or rankine
3 3ln P
s
531.96022
6270.3605
T
20.46057 ln T
Brooker (1967)
255.38<T<273.16
and
ln~P
s
/R !5
A1BT1CT
2
1DT
3
1ET
4
FT2GT
2
Adapted from Keenan and Keyes (1936)
273.16<T<533.16
where
R522,105,649.25 D50.12558310
23
A5227,405.526 E520.48502310
27
B597.5413 F54.34903
C520.146244 G50.39381310
22
2.2.2 Saturation line. T as a function of P
s
T2255.385
(
i50
i58
A
i
@ ln~0.00145P
s
!#
i
620.52,P
s
,4,688,396.00 Steltz and Silvestri (1958)
A
0
519.5322
A
1
513.6626
A
2
51.17678
A
3
520.189693
A
4
50.087453
A
5
520.0174053
A
6
50.00214768
A
7
520.138343310
23
A
8
50.38310
25
2.2.3 Latent heat of sublimation at saturation
h
ig
52,839,683.1442212.56384 ~T2255.38!
255.38<T<273.16 Brooker (1967)
2.2.4 Latent heat of vaporization at saturation
h
fg
52,502,535.25922,385.76424 ~T2273.16!