This model provides a prescribed temperature boundary condition for buried objects, where the temperature is computed per the ASCE (1996) equation:
where:
T_{s,z} = ground temperature at depth z,
τ = annual period length (constant 365.25 days),
α = soil thermal diffusivity (assumed constant throughout the year),
t = time,
T_{ms} = mean annual surface temperature,
A_{s} = temperature amplitude throughout the year (max - min),
t_{lag} = phase lag of the surface temperature sinusoid
Without correction, this model assumes that the surface temperature (depth = 0) is
equal to the air temperature, which is acceptable for most design calculations.
For more accurate calculation, this model provides methods to compensate for
the convective thermal resistance and the impact of surface cover.
The convective thermal resistance can be modeled as a virtual equivalent soil layer
by setting the flag useCon to true
and specifying the
heat transfer coefficient hSur.
This correction would result in a larger delay and dampening of the
resulting sinusoid.
The impact of surface cover on soil temperature can be modeled using
n-factors by setting the flag useNFac to true
and
specifying the thawing and freezing n-factors at the surface.
More information about n-factors correction can be found in the documentation
for
Buildings.BoundaryConditions.GroundTemperature.BaseClasses.surfaceTemperature.
Since n-factors incorporate the effect of surface convection,
both corrections would typically not be applied simultaneously.
ASCE (1996). Cold Regions Utilities Monograph. D.W. Smith, Technical Editor.