This is a model for a convective heat transfer for exterior, outside-facing surfaces.
The parameter conMod
determines the model that is used to compute
the heat transfer coefficient:
If conMod=
Buildings.HeatTransfer.Types.ExteriorConvection.Fixed
, then
the convective heat transfer coefficient is set to the value specified by the parameter
hFixed
.
If conMod=
Buildings.HeatTransfer.Types.ExteriorConvection.TemperatureWind
,
then the convective heat transfer coefficient is
computed based on wind speed, wind direction and temperature difference.
The total convection coefficient h_{t} is the sum of the temperature-driven free convection coefficient h_{n} and the wind-driven forced convection coefficient h_{f},
h_{t} = h_{n} + h_{f}
The free convection coefficient h_{n} is computed in the same way as in Buildings.HeatTransfer.Convection.Interior. The forced convection coefficient h_{f} is computed based on a correlation by Sparrow, Ramsey, and Mass (1979), which ish_{f} = 2.537 W R √( P v ⁄ A )
where W=1 for windward surfaces and W=0.5 for leeward surfaces, with leeward defined as greater than 100 degrees from normal incidence, R is a surface roughness multiplier, P is the perimeter of the surface and A is the area of the surface. This is the same equation as implemented in EnergyPlus 6.0.
We make the simplified assumption that the surface is square, and hence we set
h_{f} = 2.537 W R √( 4 v ⁄ √(A) )
The surface roughness is specified by the parameter surfaceRoughness
which has to be set to a type of
Buildings.HeatTransfer.Types.SurfaceRoughness.The coefficients for the surface roughness are
Roughness index | R | Example material |
---|---|---|
VeryRough | 2.17 | Stucco |
Rough | 1.67 | Brick |
MediumRough | 1.52 | Concrete |
MediumSmooth | 1.13 | Clear pine |
Smooth | 1.11 | Smooth plaster |
VerySmooth | 1.00 | Glass |
Sparrow, E. M., J. W. Ramsey, and E. A. Mass. 1979. Effect of Finite Width on Heat Transfer and Fluid Flow about an Inclined Rectangular Plate. Journal of Heat Transfer, Vol. 101, p. 204.
Walton, G. N. 1981. Passive Solar Extension of the Building Loads Analysis and System Thermodynamics (BLAST) Program, Technical Report, United States Army Construction Engineering Research Laboratory, Champaign, IL.
isFloor
to is_floor
,
and isCeiling
to is_ceiling
,
for consistency with naming convention.