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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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