Has there been any improvement in calculating ground temperatures since the 1973 Kusuda study?

asked 2018-01-25 13:19:08 -0600

Joe Huang
2772 ●5 ●14

updated 2018-01-25 13:29:53 -0600

There's been an ongoing thread about the reliability of ground temperatures in EPW files, with the common lament that these temperatures are based on an old study by Kusuda and Achenbach from more than 50 years ago (1965 as an ASHRAE paper, 1973 as a NBS report). The Kusuda/Achenbach model is a one-harmonic model, i.e., sine curve, with the coefficients for amplitude and lag based on data for 28 locations in the US. As used in all the simulation programs and weather files, this is reduced to a sine curve with amplitude and lag based solely on the annual air temperature profile (also reduced to a sine curve) and the depth below the surface, with the soil diffusivity held constant.

I was just at the ASHRAE Conference in Chicago (Jan 21-24, 2018) and happened to see a technical paper that describes a much improved two-harmonic model that also varies the soil conditions depending on the Koppen-Geiger climate classification. I thought such a breakthrough warrants starting a new thread instead of merely adding it as a comment to the ongoing thread.

answered 2018-01-25 13:30:02 -0600

Joe Huang
2772 ●5 ●14

updated 2018-01-25 13:37:14 -0600

Lu Xing and Jeff Spitler have developed a two-harmonic analytical model for the estimation of undisturbed ground temperatures for engineering applications that is described in three companion papers:

Xing and Spitler 2017. Prediction of undisturbed ground temperature using analytical and numerical modeling. Part I: Model development and experimental validation. Science and Technology for Built Environment 23:787-808.
Xing and Spitler 2017. Prediction of undisturbed ground temperature using analytical and numerical modeling. Part II: Methodology for developing a world-wide dataset. Science and Technology for Built Environment 23:809-825.
Xing, Spitler, and Bandyopadhyay 2017. Prediction of undisturbed ground temperature using analytical and numerical modeling, Part III: Experimental validation of a world-wide dataset. Science and Technology for Built Environment 23:826-842.

(excerpt from the abstract for Paper 2): "... a two-harmonic analytical model which is used for the estimations of undisturbed ground temperatures for engineering applications has been developed. This model relies on a second-order harmonic relationship and five weather-related constants - annual average ground temperature, two temperature amplitudes, and two phase lags to predict the ground temperatures. These parameters are estimated using temperature results calculated from the numerical method developed by Xing and Spilter (2017). The two -harmonic model is validated using measured ground temperature data at 19 sites in the US... in three different climates - arid, warm, and snow... The model... relies on inputs such as soil diffisivity, vegetation density, and snow depth to estimate the ground temperatures...