.Buildings.HeatTransfer.Convection.Exterior

Information

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:

  1. If conMod= Buildings.HeatTransfer.Types.ExteriorConvection.Fixed , then the convective heat transfer coefficient is set to the value specified by the parameter hFixed.

  2. 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 ht is the sum of the temperature-driven free convection coefficient hn and the wind-driven forced convection coefficient hf,

    ht = hn + hf

    The free convection coefficient hn is computed in the same way as in Buildings.HeatTransfer.Convection.Interior. The forced convection coefficient hf is computed based on a correlation by Sparrow, Ramsey, and Mass (1979), which is

    hf = 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

    hf = 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
    MediumSmooth1.13 Clear pine
    Smooth 1.11 Smooth plaster
    VerySmooth 1.00 Glass

References

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.

Revisions


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