Buildings.HeatTransfer.Windows

Package with models for windows

Information

This package contains models for heat transfer in windows.

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

Package Content

Name	Description
BeamDepthInRoom	Depth of solar beam in the room
ExteriorHeatTransfer	Model for heat convection and radiation at the exterior surface of a window that may have a shading device
FixedShade	Model for exterior shade due to overhang and/or side fin
InteriorHeatTransferConvective	Model for heat convection at the interior surface of a window that may have a shading device
Overhang	For a window with an overhang, outputs the fraction of the window area exposed to the sun
SideFins	For a window with side fins, outputs the fraction of the window area exposed to the sun
Window	Model for a window
Functions	Functions used in window radiation model
Examples	Collection of models that illustrate model use and test models
Validation	Collection of validation models
BaseClasses	Package with base classes for Buildings.HeatTransfer.Windows

Buildings.HeatTransfer.Windows.BeamDepthInRoom

Depth of solar beam in the room

Information

This component computes the maximum distance at which a solar beam that enters the window hits the workplane. The distance is measured perpendicular to the wall.

The parameter azi is the azimuth of the window. For example, if the window faces south, set azi=Buildings.Types.Azimuth.S. The figure below explains the parameters.

For a definition of the parameters, see the User's Guide Buildings.BoundaryConditions.UsersGuide. The surface azimuth is defined in Buildings.Types.Azimuth.

The component requires as parameters the longitude, latitude and time zone. These can automatically be assigned by setting the parameter filNam to a weather data file, in which case these values are read from the weather data file.

Assumptions and approximations

The following assumptions and approximations are made:

1. If an overhang is present, then the corner of the overhang is the only object that casts a shade. In reality, for very shallow incidence angles, the top of the window frame may be sun exposed, but this model neglects any shade that is cast by the top of the window frame.
2. The overhang is assumed to have infinite length in the direction of the wall, as this allows neglecting any effects that the corner may have at shallow incidence angles.
3. The wall is vertical.

Extends from Modelica.Blocks.Icons.Block (Basic graphical layout of input/output block).

Parameters

Connectors

Modelica definition

Buildings.HeatTransfer.Windows.ExteriorHeatTransfer

Model for heat convection and radiation at the exterior surface of a window that may have a shading device

Information

Model for the convective heat transfer between a window shade, a window surface and the room air. This model is applicable for the outside-facing surface of a window system and can be used with the model Buildings.HeatTransfer.Windows.Window.

This model adds the convective heat transfer coefficient to its base model.

Extends from BaseClasses.PartialWindowBoundaryCondition (Partial model for heat convection or radiation between a possibly shaded window that can be outside or inside the room).

Parameters

Connectors

Modelica definition

Buildings.HeatTransfer.Windows.FixedShade

Model for exterior shade due to overhang and/or side fin

Information

This model outputs the fraction of the window area that is sun exposed for a window that may have an overhang and sidefins. Depending on the record with construction data conPar, an overhang, side fins or no external shade is modeled. The model allows having an overhang and side fins at the same time. In such a case, the overhang width should be measured from the window edge to the sidefin, because the overhang width beyond the sidefin will cast a shadow on the side fin and not on the window. Similarly, the side fin height should be measured from the upper window edge to the overhang, because the side fin height above the overhang will not cast a shadow on the window. The parameters for the dimensions of the overhang and side fins are as described in the models Buildings.HeatTransfer.Windows.Overhang and Buildings.HeatTransfer.Windows.SideFins.

Limitations

For overhangs, the model assumes that

• the overhang is at least as wide as the window, i.e., w_L ≥ 0 and w_R ≥ 0, and
• the overhang is horizontal.

For side fins, the model assumes that

• the side fins are placed symmetrically to the left and right of the window,
• the top of the side fins must be at an equal or greater height than the window, and
• the side fins extends at least to the lower edge of the window.

Implementation

The detailed calculation method is explained in Buildings.HeatTransfer.Windows.BaseClasses.SideFins and in Buildings.HeatTransfer.Windows.BaseClasses.Overhang.

Extends from HeatTransfer.Windows.BaseClasses.ShadeInterface_weatherBus (Base class for models of window shade and overhangs).

Parameters

Connectors

Modelica definition

Buildings.HeatTransfer.Windows.InteriorHeatTransferConvective

Model for heat convection at the interior surface of a window that may have a shading device

Information

Model for the convective heat transfer between a window shade, a window surface and the room air. This model is applicable for the room-facing surface of a window system and can be used with the model Buildings.HeatTransfer.Windows.Window.

This model adds the convective heat transfer coefficient to its base model.

Extends from BaseClasses.PartialWindowBoundaryCondition (Partial model for heat convection or radiation between a possibly shaded window that can be outside or inside the room).

Parameters

Connectors

Modelica definition

Buildings.HeatTransfer.Windows.Overhang

For a window with an overhang, outputs the fraction of the window area exposed to the sun

Information

For a window with an overhang, this model outputs the fraction of the area that is exposed to the sun. The models can also be used for doors with an overhang.

The overhang can be asymmetrical (i.e. wR ≠ wL is allowed) about the vertical centerline of the window. However, the overhang must completely cover the window, i.e., wL ≥ 0 and wR ≥ 0. wL and wR must be measured from the respective corner of the window.

The figure below shows the parameters.

The surface azimuth azi is as defined in Buildings.Types.Azimuth.

Limitations

The model assumes that

• the overhang is at least as wide as the window, i.e., w_L ≥ 0 and w_R ≥ 0, and
• the overhang is horizontal.

Implementation

The implementation is explained in Buildings.HeatTransfer.Windows.BaseClasses.Overhang.

Extends from Buildings.ThermalZones.Detailed.BaseClasses.Overhang (Record for window overhang), Buildings.HeatTransfer.Windows.BaseClasses.PartialShade_weatherBus (Partial model to implement overhang and side fins with weather bus connector).

Parameters

Connectors

Modelica definition

Buildings.HeatTransfer.Windows.SideFins

For a window with side fins, outputs the fraction of the window area exposed to the sun

Information

For a window with side fins, this model outputs the fraction of the area that is exposed to the sun. The model calculates the fraction of the window area that is exposed to the sun. The side fins are symmetrically placed above the vertical window centerline, and its height must be equal or greater than the window height. This models can also be used for doors with side fins. The figure below shows the parameters. The parameter h is measured from the top of the window to the top of the side fins. Side fins are assumed to extend at least to the lower edge of the window. (Any portion of the side fin below the window edge does not cast as shadow on the window anyway.)

The parameter h is measured from the top of the window to the top of the side fins. The side fin must extend at least to the bottom of the window.

Limitations

• the side fins are placed symmetrically to the left and right of the window,
• the top of the side fins must be at an equal or greater height than the window, and
• the bottom of the side fins must be at an equal or lower height than the bottom of the window.

Implementation

The detailed calculation method is explained in Buildings.HeatTransfer.Windows.BaseClasses.SideFins.

Extends from Buildings.ThermalZones.Detailed.BaseClasses.SideFins (Record for window side fins), Buildings.HeatTransfer.Windows.BaseClasses.PartialShade_weatherBus (Partial model to implement overhang and side fins with weather bus connector).

Parameters

Connectors

Modelica definition

Buildings.HeatTransfer.Windows.Window

Model for a window

Information

Overview

This is a model for a window system. The equations are similar to the equations used in the Window 5 model and described in TARCOG 2006. The model computes the heat balance from the exterior surface to the room-facing surface for a window system. The window system can have an exterior or an interior shade, but not both, or it can have no shade. The convective heat transfer between the window system and the outside air or the room is not computed by this model. They can be computed using the models Buildings.HeatTransfer.Windows.ExteriorHeatTransfer, Buildings.HeatTransfer.Windows.InteriorHeatTransferConvective and Buildings.HeatTransfer.Windows.BaseClasses.ShadeRadiation.

Limitations

To calculate the angular transmittance, reflectance and absorptance of a glazing system, Window 5 model first calculates the value for each wave length, then calculate the weighted value over entire wave lengths. Current window model in Buildings library only uses the weighted value of each glass. As a result, there are some differences in prediciton between the current Modelica window model and WINDOW 5. The difference is small for single layer window or multi-layer window with the same glasses. But it can be large for multi-layer window with different glasses.

Parameters

This model takes as the parameter glaSys a data record from the package Buildings.HeatTransfer.Data.GlazingSystems. This data record specifies the properties of the glasses, the gas fills, the frame and of the shades, if any shade is present. Whether a shade is present or not is determined by the parameters glaSys.haveExteriorShade and glaSys.haveInteriorShade.

The parameter linearize can be used to linearize the model equations.

If the parameter steadyState is set to false then state variables are added at the heat ports that face the room side. For simulation of Buildings.ThermalZones.Detailed.MixedAir, adding states avoids large nonlinear system of equations, and generally leads to faster simulation. Default values are used for the states.

Ports

If a shade is present, then the input port u is used to determine the shade position. Set u=0 to have the window in the unshaded mode, and set u=1 to have the window shade completely deployed. Any intermediate value is possible. If no shade is present, then this port will be removed.

For the heat ports, the suffix _a is used for the exterior, outside-facing side of the window, and the suffix _b is used for the interior, room-facing surface of the window. Each side has heat ports that connect to the glass, to the frame, and, optionally, to the shade. If no shade is present, then the heat port to the shade will be removed.

Description of the Physics

The model has three main submodels that implement the relevant heat balances:

1. The model frame computes heat conduction through the frame.
2. The model glaUns computes the heat balance of the part of the window that is unshaded. For example, if u=0.2, then this model accounts for the 80% of the window that is not behind the shade or blind.
3. The model glaSha computes the heat balance of the part of the window that is shaded. For example, if u=0.2, then this model accounts for the 20% of the window that is behind the shade or blind. If the parameter glaSys specifies that the window has no exterior and no interior shade, then the model glaSha will be removed.

The models glaUns and glaSha compute the solar radiation that is absorbed by each glass pane and the solar radiation that is transitted through the window as a function of the solar incidence angle. They then compute a heat balance that takes into account heat conduction through the glass, heat convection through the gas layer, and infrared radiation from the exterior and the room through the glass and gas layers. The infrared radiative heat exchange is computed using a radiosity balance. Heat conduction through the frame is computed using a heat flow path that is parallel to the glazing system, i.e., there is no heat exchange between the frame and the glazing layer.

Validation

The window model has been validated by using measurement data at LBNL's Test Cell 71T and by using a comparative model validation with the WINDOW 6 program. These validations are described in Nouidui et al. (2012). The window model has also been validated as part of the BESTEST validations that are implemented in Buildings.ThermalZones.Detailed.Examples.BESTEST.

References

TARCOG 2006: Carli, Inc., TARCOG: Mathematical models for calculation of thermal performance of glazing systems with or without shading devices, Technical Report, Oct. 17, 2006.

Thierry Stephane Nouidui, Michael Wetter, and Wangda Zuo. Validation of the window model of the Modelica Buildings library. Proc. of the 5th SimBuild Conference, Madison, WI, USA, August 2012.

Parameters

Connectors

Modelica definition