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ASAE D271.2 DEC94
Psychrometric Data
Reviewed by ASAEs Structures and Environment Division and the FoodEngineering Division Standards Committees; approved by the ElectricPower and Processing Division Standards Committee; adopted by ASAEDecember 1963; reconfirmed December 1968; revised April 1974, April1979; reconfirmed December 1983; reconfirmed by the Food and
Process Engineering Institute Standards Committee December 1988,December 1989, December 1990, December 1991; reaffirmed December1992, December 1993, December 1994.
1 Purpose and scope1.1 The purpose of this Data is to assemble psychrometric data in chartand equation form in both SI and English units.
1.2 Psychrometric charts are presented that give data for dry bulbtemperature ranges of 35 to 600 F in English units and 10 to 120 Cin SI units.
1.3 Many analyses of psychrometric data are made on computers. Theequations given in Sections 2 and 3 enable the calculation of allpsychrometric data if any two independent psychrometric properties of an
air-water vapor mixture are known in addition to the atmosphericpressure. In some cases, iteration procedures are necessary. In someinstances, the range of data covered by the equation has been extendedbeyond that given in the original source. The equations yield results thatagree closely with values given by Keenan and Keyes (1936) andexisting psychrometric charts.
2 Psychrometric data in SI units2.1 Psychrometric charts; two presented. One for a temperature range of10 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. Ps as a function of T
ln Ps31.96026270.3605
T0.46057 ln T
Brooker (1967)
255.38T273.16and
ln Ps /R ABTCT2DT3ET4
FTGT2
Adapted from Keenan and Keyes (1936)
273.16T533.16
where
R22,105,649.25 D0.12558103
A27,405.526 E0.48502107
B
97.5413 F
4.34903C0.146244 G0.39381102
2.2.2 Saturation line. T as a function of Ps
T255.38i0
i8
A i ln 0.00145Psi
620.52Ps4,688,396.00 Steltz and Silvestri (1958)
A019.5322
A113.6626
A21.17678
A30.189693
A40.087453
A50.0174053
A60.00214768
A70.138343103
A80.38105
2.2.3 Latent heat of sublimation at saturation
hig2,839,683.144212.56384 T255.38
255.38T273.16 Brooker (1967)
2.2.4 Latent heat of vaporization at saturation
hfg2,502,535.2592,385.76424 T273.16
273.16T338.72 Brooker (1967)
Table 1 Symbols
h Enthalpy of air-vapor mixture, J/kg dry air or Btu/lb dry air
hfg Latent heat of vaporization of water at saturation, J/kg orBtu/lb
hfg Latent heat of vaporization of water at Twb , J/kg or Btu/lb
hfg Latent heat vaporization of water at Tdp , J/kg or Btu/lb
hig Heat of sublimation of ice, J/kg or Btu/lb
hig Heat of sublimation of ice at Twb , J/kg or Btu/lb
hig Heat of sublimation of ice at Tdp , J/kg or Btu/lb
H Humidity ratio, kg water/kg dry air or lb water/lb dry air
ln Natural logarithm (base e)
Patm Atmospheric pressure, Pa or psi
Ps Saturation vapor pressure at T, Pa or psi
Psw b Saturation vapor pressure at Twb , Pa or psi
Pv Vapor pressure, Pa or psi
rh Relative humidity, decimal
T Dry-bulb temperature, kelvin or rankine
Tdp Dew-point temperature, kelvin or rankine
Twb Wet-bulb temperature, kelvin or rankine
Vsa Air specific volume, m3/kg dry air or ft3/lb dry air
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hfg 7,329,155,978,00015,995,964.08 T2 1/2
338.72T533.16 Brooker (Unpublished)
2.2.5 Wet bulb line
Psw bPvB TwbT Brunt (1941)
where
B
1006.9254( Psw bPat m) 10.15577Pv
Pat m
0.62194 hfg
Substitute hig for hfg where Twb 273.16
255.38T533.16
2.2.6 Humidity ratio
H0.6219 Pv
Pat mPv
255.38T533.16
PvPat m
2.2.7 Specific volume
Vsa287 T
Pat mPv
255.38T533.16
PvPat m
2.2.8 Enthalpy
Enthalpy=enthalpy of air+enthalpy of water (or ice) at dew-pointtemperature+enthalpy of evaporation (or sublimation) at dew-pointtemperature+enthalpy added to the water vapor (super-heat) aftervaporization.
h1006.92540 T273.16
H 333,432.12030.5980 273.16Tdp hig H
1875.6864H TTdp
255.38Tdp273.16
and
h1006.92540 T273.16
4186.8 H Tdp273.16 hfg H1875.6864 H TTdp
273.16Tdp373.16
2.2.9 Relative humidity
rhPv /Ps
3 Psychrometric data in English Units3.1 Three psychrometric charts are presented with temperature rangesof 35 to 50 F, 32 to 120 F and 32 to 600 F, respectively.
3.2 Psychrometric equations, English Units. Symbols are defined inTable 1.
3.2.1 Saturation line. Ps as a function of T
ln Ps23.392411286.6489
T0.46057 ln T
Brooker (1967)
459.69T491.69
ln Ps /R ABTCT2DT3ET4
FTGT2
Adapted from Keenan and Keyes (1936)
491.69T959.69
where
R3206.18
A27405.5
B54.1896
C0.045137
D0.215321104
E0.462027108
F2.41613
G0.00121547
3.2.2 Saturation line. T as a function of Ps
T459.69
i0
i8
A i ln 10Psi Steltz and Silvestri (1958)
0.09Ps680
where
A035.1579
A124.5926
A2
2.11821A30.341447
A40.157416
A50.0313296
A60.00386583
A70.249018103
A80.684016105
3.2.3 Latent heat of sublimation at saturation
hig1220.8440.05077 T459.69
459.69T491.69 Brooker (1967)
3.2.4 Latent heat of vaporization at saturation
hfg1075.89650.56983 T491.69 Brooker (1967)
491.69T609.69
hfg 1354673.2140.9125275587 T2 1/2 Brooker (Unpublished)
609.69T959.69
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3.2.5 Wet bulb line
Psw bPvB TwbT Brunt (1941)
where
B0.2405 Psw bPat m 10.15577Pv /Pat m
0.62194 hfg
Substitute hig for hfg when Twb 491.69
459.69T959.69
3.2.6 Absolute humidity (humidity ratio)
H0.6219 Pv
Pat mPv
459.69T959.69
PvPat m
3.2.7 Specific volume
Vsa53.35T
144 Pat mPv
459.69T959.69
PvPat m
3.2.8 Enthalpy
Enthalpy=enthalpy of air+enthalpy of water (or ice) at dew-pointtemperature+enthalpy of evaporation (or sublimation) at dew-pointtemperature+enthalpy added to the water vapor (super-heat) aftervaporization.
h0.2405 T459.69 H 143.350.485 491.69Tdp
hig H0.448H TTdp
459.69Tdp491.69
h0.2405 T459.69 H Tdp491.69
hfg H0.448H TTdp
491.69Tdp671.69
3.2.9 Relative humidity
rhPv /Ps
Note: Psychrometric charts are printed with permission from theAmerican Society of Heating, Refrigerating and AirconditioningEngineers, Inc., 345 E. 47th St., New York, NY; Proctor & Schwartz,Inc., 7th St. and Tabor Rd., Philadelphia, PA; and Carrier Corp.,Carrier Parkway, Syracuse, NY.
ReferencesLast printed in 1981 AGRICULTURAL ENGINEERS YEARBOOK; list available
from ASAE Headquarters.
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