Direct Calculation of Thermodynamic Wet-Bulb Temperature as a Function of Pressure and Elevation

Sayed-Hossein Sadeghi Washington State University, Prosser, Washington

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Troy R. Peters Washington State University, Prosser, Washington

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Douglas R. Cobos Decagon Devices, Pullman, Washington

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Henry W. Loescher National Ecological Observatory Network, and Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado

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Colin S. Campbell Decagon Devices, Pullman, Washington

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Abstract

A simple analytical method was developed for directly calculating the thermodynamic wet-bulb temperature from air temperature and the vapor pressure (or relative humidity) at elevations up to 4500 m above MSL was developed. This methodology was based on the fact that the wet-bulb temperature can be closely approximated by a second-order polynomial in both the positive and negative ranges in ambient air temperature. The method in this study builds upon this understanding and provides results for the negative range of air temperatures (−17° to 0°C), so that the maximum observed error in this area is equal to or smaller than −0.17°C. For temperatures ≥0°C, wet-bulb temperature accuracy was ±0.65°C, and larger errors corresponded to very high temperatures (Ta ≥ 39°C) and/or very high or low relative humidities (5% < RH < 10% or RH > 98%). The mean absolute error and the root-mean-square error were 0.15° and 0.2°C, respectively.

Corresponding author address: Troy Peters, Washington State University, 24106 N. Bunn Rd., Prosser, WA 99350. E-mail: troy_peters@wsu.edu

Abstract

A simple analytical method was developed for directly calculating the thermodynamic wet-bulb temperature from air temperature and the vapor pressure (or relative humidity) at elevations up to 4500 m above MSL was developed. This methodology was based on the fact that the wet-bulb temperature can be closely approximated by a second-order polynomial in both the positive and negative ranges in ambient air temperature. The method in this study builds upon this understanding and provides results for the negative range of air temperatures (−17° to 0°C), so that the maximum observed error in this area is equal to or smaller than −0.17°C. For temperatures ≥0°C, wet-bulb temperature accuracy was ±0.65°C, and larger errors corresponded to very high temperatures (Ta ≥ 39°C) and/or very high or low relative humidities (5% < RH < 10% or RH > 98%). The mean absolute error and the root-mean-square error were 0.15° and 0.2°C, respectively.

Corresponding author address: Troy Peters, Washington State University, 24106 N. Bunn Rd., Prosser, WA 99350. E-mail: troy_peters@wsu.edu
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  • Alves, I., Fontes J. C. , and Pereira L. S. , 2000: Evapotranspiration estimation from infrared surface temperature. II: The surface temperature as a wet bulb temperature. Trans. ASAE, 43, 591598.

    • Search Google Scholar
    • Export Citation
  • Angström, A., 1920: Studies of the frost problem I. Geogr. Ann.,2, 2–32.

  • ASABE, 2006: ASABE standards: Psychrometric data. American Society of Agriculture and Biological Engineers ASAE D271.2 APR1979 (R2005), 27 pp. [Available online at http://elibrary.asabe.org/standards.asp.]

  • ASHRAE, 1997: 1997 ASHRAE Handbook: Fundamentals. SI ed. ASHRAE, 1426 pp.

  • Balogun, A. A., Jegede O. O. , Foken T. , and Olaleye J. O. , 2002a: Comparison of two Bowen-ratio methods for the estimation of sensible and latent heat fluxes at Ile-Ife, Nigeria. J. Afr. Meteor. Soc., 5 (2), 6369.

    • Search Google Scholar
    • Export Citation
  • Balogun, A. A., Jegede O. O. , Foken T. , and Olaleye J. O. , 2002b: Estimation of sensible and latent heat fluxes over bare soil using bowen ratio energy balance method at a humid tropical site. J. Afr. Meteor. Soc., 5 (1), 6371.

    • Search Google Scholar
    • Export Citation
  • Brooker, D. B. 1967: Mathematical model of the psychrometric chart. Trans. ASAE.,10, 558–560.

  • Buck, A. L., 1981: New equations for computing vapor pressure and enhancement factor. J. Appl. Meteor., 20, 15271532.

  • Campbell, G. S., and Norman J. M. , 1998: An Introduction to Environmental Biophysics. 2nd ed. Springer-Verlag, 286 pp.

  • Chappell, C. F., Magaziner E. L. , and Fritsch J. M. , 1974: On the computation of isobaric wet-bulb temperature and saturation temperature over ice. J. Appl. Meteor., 13, 726728.

    • Search Google Scholar
    • Export Citation
  • Chau, K. V., 1980: Some new empirical equations for properties of moist air. Trans. ASAE, 23, 12661271.

  • Dunin, F. X., and Greenwood E. A. N. , 1986: Evaluation of the ventilated chamber for measuring evaporation from a forest. Hydrol. Processes, 1, 4762.

    • Search Google Scholar
    • Export Citation
  • Gan, G., and Riffat S. B. , 1999: Numerical simulation of closed wet cooling towers for chilled ceiling systems. Appl. Therm. Eng., 19, 12791296.

    • Search Google Scholar
    • Export Citation
  • Loescher, H. W., Law B. E. , Mahrt L. , Hollinger D. Y. , Campbell J. L. , and Wofsy S. C. , 2006: Uncertainties in, and interpretation of, carbon flux estimates using the eddy covariance technique. J. Geophys. Res., 111, D21S90, doi:10.1029/2005JD006932.

    • Search Google Scholar
    • Export Citation
  • Loescher, H. W., Hanson C. V. , and Ocheltree T. W. , 2009: The psychrometric constant is not constant: A novel approach to enhance the accuracy and precision of latent energy fluxes through automated water vapor calibrations. J. Hydrometeor., 10, 12711284.

    • Search Google Scholar
    • Export Citation
  • Monteith, J. L., 1965: Evaporation and environment. Proceedings of the 19th Symposium of the Society for Experimental Biology, Cambridge University Press, 205–234.

  • Murray, F. W., 1967: On the computation of saturation vapor pressure. J. Appl. Meteor., 6, 203204.

  • Schmidt, J. L., and Waite P. J. , 1962: Summaries of wet-bulb temperature and wet-bulb depression for grain drier design. Trans. ASAE, 5, 186189.

    • Search Google Scholar
    • Export Citation
  • Schurer, K., 1981: Confirmation of a lower psychrometer constant. J. Phys., 14E, 1153.

  • Simões-Moreira, J. R., 1999: A thermodynamic formulation of the psychrometer constant. Meas. Sci. Technol., 10, 302311.

  • Slatyer, R. O., and McIlroy I. C. , 1961: Practical Microclimatology. UNESCO, 297 pp.

  • Smith, J. W., 1920: Predicting minimum temperatures from the previous afternoon wet-bulb temperature. Mon. Wea. Rev.,48, 640–641.

  • Sreekanth, S., Ramaswamy H. S. , and Sablani S. , 1998: Prediction of psychrometric parameters using neural networks. Drying Technol., 16, 825837.

    • Search Google Scholar
    • Export Citation
  • Stull, R., 2000: Meteorology for Scientists and Engineers. 3rd ed. Discount Textbooks, 924 pp.

  • Stull, R., 2011: Wet-bulb temperature from relative humidity and air temperature. J. Appl. Meteor. Climatol., 50, 22672269.

  • Tejeda-Martínez, A., 1994: On the evaluation of the wet bulb temperature as a function of dry bulb temperature and relative humidity. Atmósfera, 7, 179184.

    • Search Google Scholar
    • Export Citation
  • Wai, M.-K., and Smith E. A. , 1998: Linking boundary layer circulations and surface processes during FIFE 89. Part II: Maintenance of secondary circulation. J. Atmos. Sci., 55, 12601276.

    • Search Google Scholar
    • Export Citation
  • Wexler, A., 1976: Vapor pressure formulation for water in range 0 to 100°C. A revision. J. Res. Natl. Bur. Stand., 80, 775785.

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