.Buildings.BoundaryConditions.GroundTemperature.BaseClasses.surfaceTemperature

Information

This function corrects the surface temperature climatic constants by applying n-factors with the methodology prescribed in the District Cooling Guide (ASHRAE, 2013).

n-factors corresponds to the ratio of freezing (/thawing) degree days or index between the air and the ground surface and can be used to couple the air and ground surface temperatures.
For example, a freezing n-factor of 1.35 means that during the freezing season, the daily average ground surface temperature is on average 1.35 times colder than the air (using the freezing temperature of water as a reference).
In its guide, ASHRAE suggests to first apply the n-factors to the uncorrected ground temperature at zero burial depth, and to fit a new sinusoidal curve to the result.
In this function, the freezing n-factor is applied to days where the daily mean air temperature is below the freezing temperature (0degC), whereas the thawing n-factor is applied to the remaining days.

T_ground - T_freezing = η_freezing * (T_air - T_freezing)   if T_air <= T_freezing
T_ground - T_freezing = η_thawing * (T_air - T_freezing)   if T_air > T_freezing

The sinusoidal curve is then fitted using the analytical solution proposed in Appendix B of the District Heating Guide.

n-factors are specific to a climate and surface cover, and should be extrapolated from other sites with caution. As a first approximation, tabulated values of n-factors are available in Lunardini (1981) and Freitag and McFadden (1997).

References

ASHRAE (2013). District Cooling Guide. ASHRAE, Atlanta, GA.
ASHRAE (2013). District Heating Guide. ASHRAE, Atlanta, GA.
D.W. Riseborough (2003). Thawing and freezing indices in the active layer. Proceedings of the 8th International Conference on Permafrost, Swets & Zeitlinger.
V.J. Lunardini (1981). Heat Transfer in Cold Climates. Van Nostrand Reinhold Company.
D.R. Freitag and T. McFadden (1997). Introduction to Cold Regions Engineering. American Society of Civil Engineers.

Interface

function surfaceTemperature
  extends Modelica.Icons.Function;
  input ClimaticConstants.Generic cliCon "Surface temperature climatic conditions";
  input Real nFacTha "Thawing n-factor (TAir > 0degC)";
  input Real nFacFre "Freezing n-factor (TAir <= 0degC)";
  output ClimaticConstants.Generic corCliCon "Corrected surface temperature climatic conditions";
end surfaceTemperature;

Revisions

• October 17, 2021, by Baptiste Ravache:
  Declare record parameters to avoid translation error in OpenModelica.
  This is for issue 2698.
• May 19, 2021, by Baptiste Ravache:
  First implementation.