Buildings.HeatTransfer.Convection

Package with models for convective heat transfer

Information




This package provides component models to compute heat convection.




Extends from Modelica.Icons.VariantsPackage (Icon for package containing variants).

Package Content




NameDescription


Buildings.HeatTransfer.Convection.Exterior Exterior
Model for a exterior (outside) convective heat transfer


Buildings.HeatTransfer.Convection.Interior Interior
Model for a interior (room-side) convective heat transfer


Buildings.HeatTransfer.Convection.Examples Examples
Collection of models that illustrate model use and test models


Buildings.HeatTransfer.Convection.Functions Functions
Functions for convective heat transfer


Buildings.HeatTransfer.Convection.BaseClasses BaseClasses
Package with base classes for Buildings.HeatTransfer.Convection








Buildings.HeatTransfer.Convection.Exterior
Buildings.HeatTransfer.Convection.Exterior

Model for a exterior (outside) convective heat transfer

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. 

  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
    


    

    

    3. 



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.




Extends from Buildings.HeatTransfer.Convection.BaseClasses.PartialConvection (Partial model for heat convection).

Parameters




TypeNameDefaultDescription


AreaA Heat transfer area [m2]


CoefficientOfHeatTransferhFixed3Constant convection coefficient [W/(m2.K)]


Angletil Surface tilt [rad]


ExteriorConvectionconModBuildings.HeatTransfer.Types...Convective heat transfer model


SurfaceRoughnessroughnessBuildings.HeatTransfer.Types...Surface roughness


Angleazi Surface azimuth [rad]


Initialization


TemperatureDifferencedT.start0= solid.T - fluid.T [K]




Connectors




TypeNameDescription


HeatPort_asolid 


HeatPort_bfluid 


input RealInputvWind speed [m/s]


input RealInputdirWind direction (0=wind from North) [rad]




Modelica definition


model Exterior 
  "Model for a exterior (outside) convective heat transfer"
  extends Buildings.HeatTransfer.Convection.BaseClasses.PartialConvection;

  parameter Buildings.HeatTransfer.Types.ExteriorConvection conMod=
    Buildings.HeatTransfer.Types.ExteriorConvection.TemperatureWind 
    "Convective heat transfer model";
  parameter Buildings.HeatTransfer.Types.SurfaceRoughness roughness=
    Buildings.HeatTransfer.Types.SurfaceRoughness.Medium "Surface roughness";
  parameter Modelica.SIunits.Angle azi "Surface azimuth";

  Modelica.Blocks.Interfaces.RealInput v(unit="m/s") "Wind speed";
  Modelica.Blocks.Interfaces.RealInput dir(unit="rad", displayUnit="deg",
     min=0, max=2*Modelica.Constants.pi) "Wind direction (0=wind from North)";
  Modelica.SIunits.CoefficientOfHeatTransfer hF 
    "Convective heat transfer coefficient due to forced convection";
  Modelica.SIunits.HeatFlux qN_flow 
    "Convective heat flux from solid -> fluid due to natural convection";
  Modelica.SIunits.HeatFlux qF_flow 
    "Convective heat flux from solid -> fluid due to forced convection";
protected 
   parameter Real R(fixed=false) "Surface roughness";
   Real W(min=0.5, max=1) "Wind direction modifier";
initial equation 
  if (conMod == Buildings.HeatTransfer.Types.SurfaceRoughness.VeryRough) then
    R=2.17;
  elseif (conMod == Buildings.HeatTransfer.Types.SurfaceRoughness.Rough) then
    R=1.67;
  elseif (conMod == Buildings.HeatTransfer.Types.SurfaceRoughness.Medium) then
    R=1.52;
  elseif (conMod == Buildings.HeatTransfer.Types.SurfaceRoughness.MediumSmooth) then
    R=1.13;
  elseif (conMod == Buildings.HeatTransfer.Types.SurfaceRoughness.Smooth) then
    R=1.11;
  elseif (conMod == Buildings.HeatTransfer.Types.SurfaceRoughness.VerySmooth) then
    R=1.00;
  else
    R=0;
  end if;
equation 
  if (conMod == Buildings.HeatTransfer.Types.ExteriorConvection.Fixed) then
    qN_flow = hFixed * dT;
    W = 1;
    hF = 0;
    qF_flow = 0;
  else
    // Even if hCon is a step function with a step at zero,
    // the product hCon*dT is differentiable at zero with
    // a continuous first derivative
    if isCeiling then
       qN_flow = Buildings.HeatTransfer.Convection.Functions.HeatFlux.ceiling(
                                                                             dT=dT);
    elseif isFloor then
       qN_flow = Buildings.HeatTransfer.Convection.Functions.HeatFlux.floor(
                                                                           dT=dT);
    else
       qN_flow = Buildings.HeatTransfer.Convection.Functions.HeatFlux.wall(
                                                                          dT=dT);
    end if;
    // Forced convection
    W = Buildings.HeatTransfer.Convection.Functions.windDirectionModifier(
                                                               azi=azi, dir=dir);
    hF = 2.537 * W * R * 2 / A^(0.25) *
         Buildings.Utilities.Math.Functions.regNonZeroPower(x=v, n=0.5, delta=0.5);
    qF_flow = hF*dT;
  end if;
  q_flow = qN_flow + qF_flow;

end Exterior;







Buildings.HeatTransfer.Convection.Interior
Buildings.HeatTransfer.Convection.Interior

Model for a interior (room-side) convective heat transfer

Buildings.HeatTransfer.Convection.Interior

Information



This is a model for a convective heat transfer for interior, room-facing surfaces.
The parameter conMod determines the model that is used to compute
the heat transfer coefficient:





    

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

    

    2. 


    
If conMod=
Buildings.HeatTransfer.Types.InteriorConvection.Temperature, then
the convective heat tranfer coefficient is a function of the temperature difference.
The convective heat flux is computed using

    

      

    1. 
for floors the function 

Buildings.HeatTransfer.Functions.Convection.ConvectiveHeatFlux.floor

      2. 

    2. 
for ceilings the function

Buildings.HeatTransfer.Functions.Convection.ConvectiveHeatFlux.ceiling

      3. 

    3. 
for walls the function

Buildings.HeatTransfer.Functions.Convection.ConvectiveHeatFlux.wall

      4. 

    


    
Extends from Buildings.HeatTransfer.Convection.BaseClasses.PartialConvection (Partial model for heat convection).

    Parameters
    

    

    TypeNameDefaultDescription
    

    AreaA Heat transfer area [m2]
    

    CoefficientOfHeatTransferhFixed3Constant convection coefficient [W/(m2.K)]
    

    Angletil Surface tilt [rad]
    

    InteriorConvectionconModBuildings.HeatTransfer.Types...Convective heat transfer model
    

    Initialization
    

    TemperatureDifferencedT.start0= solid.T - fluid.T [K]
    

    Advanced
    

    BooleanhomotopyInitializationtrue= true, use homotopy method
    

    

    Connectors
    

    

    TypeNameDescription
    

    HeatPort_asolid 
    

    HeatPort_bfluid 
    

    

    Modelica definition
    

    model Interior 
  "Model for a interior (room-side) convective heat transfer"
  extends Buildings.HeatTransfer.Convection.BaseClasses.PartialConvection;

  parameter Buildings.HeatTransfer.Types.InteriorConvection conMod=
    Buildings.HeatTransfer.Types.InteriorConvection.Fixed 
    "Convective heat transfer model";
  parameter Boolean homotopyInitialization = true "= true, use homotopy method";
protected 
  constant Modelica.SIunits.Temperature dT0 = 2 
    "Initial temperature used in homotopy method";
equation 
  if (conMod == Buildings.HeatTransfer.Types.InteriorConvection.Fixed) then
    q_flow = hFixed * dT;
  else
    // Even if hCon is a step function with a step at zero,
    // the product hCon*dT is differentiable at zero with
    // a continuous first derivative
    if homotopyInitialization then
      if isCeiling then
         q_flow = homotopy(actual=Buildings.HeatTransfer.Convection.Functions.HeatFlux.ceiling(dT=dT),
                    simplified=dT/dT0*Buildings.HeatTransfer.Convection.Functions.HeatFlux.ceiling(dT=dT0));
      elseif isFloor then
         q_flow = homotopy(actual=Buildings.HeatTransfer.Convection.Functions.HeatFlux.floor(dT=dT),
                    simplified=dT/dT0*Buildings.HeatTransfer.Convection.Functions.HeatFlux.floor(dT=dT0));
      else
         q_flow = homotopy(actual=Buildings.HeatTransfer.Convection.Functions.HeatFlux.wall(dT=dT),
                    simplified=dT/dT0*Buildings.HeatTransfer.Convection.Functions.HeatFlux.wall(dT=dT0));
      end if;
    else
      if isCeiling then
         q_flow = Buildings.HeatTransfer.Convection.Functions.HeatFlux.ceiling(dT=dT);
      elseif isFloor then
         q_flow = Buildings.HeatTransfer.Convection.Functions.HeatFlux.floor(dT=dT);
      else
         q_flow = Buildings.HeatTransfer.Convection.Functions.HeatFlux.wall(dT=dT);
      end if;
    end if;

  end if;

end Interior;

    

    

    Automatically generated Fri May 06 14:13:02 2011.