New Approach for Surface n Factors

Abstract

Air and surface freezing and thawing indexes and prediction of ground temperatures from air temperatures were investigated. A new method for applying n factors on a daily basis to capture localized temperature extremes is presented and compared to conventional seasonal n-factor analysis. Measured air temperatures from five locations and measured air and surface temperatures from one location were used. Freezing and thawing indexes were determined using daily and monthly average temperatures, different time frames, and seasonal and daily applications of n factors. Air and surface freezing indexes �I af and I sf � varied more than air and surface thawing indexes �I at and I st �. Significant variations were observed in air and surface indexes due to the length of the time period used �1, 10, and 30 years� and frequency of temperature data used �daily and monthly�. The surface indexes from seasonal n factors �using daily average temperatures� and daily n factors were similar �within 4%� and higher than the indexes from seasonal n factors �using monthly average temperatures�. The average surface temperatures were within 2°C, whereas the maximum and minimum surface temperatures were significantly different �up to 26°C� between the seasonal and daily n factors. Maximum variations between consecutive daily maximum and minimum temperatures were significantly higher using daily n factors �up to 52°C� than seasonal n factors �less than 1°C�. Surface indexes from seasonal �using daily average temperatures� and daily n factors can be used interchange ably. Daily n factors are recommended to obtain representative surface and near surface temperature variations, diurnal extremes, representative timing for tem perature change events, and localized freezing or thawing indexes during change over months.

Thermal Numerical Analysis of Vertical Heat Extraction Systems in Landfills

“…To determine the difference in temperature between the air and ground temperatures, relationships have been established using dimensionless surface n-factors (Labs 1981, Romanovsky and Osterkamp 1995, Smith and Riseborough 1996, Hanson et al 2010). The surface n-factor is a ratio of the air to ground freeze and thaw indices and is given by Equation 2.17 and Equation Phase lag represents the difference in timing of the peak and minimum air temperature and peak ground temperature (Andersland and Ladanyi 1994).…”