The Constructions folder stores construction types for walls, floors, etc. built up from layers composed of materials.
Warning: Ceilings and walls must have a thickness applied in the Building Element table within Tas 3D Modeller in order that the correct volumes and floor areas are calculated for the spaces in a model. The thicknesses of constructions applied from the constructions database do not affect zone volumes or surface areas.
For details on how to apply a 'Construction' to a Building Element, please read the section: Constructions Table.
For both Opaque and Transparent constructions there is a group of parameters displayed near the top of the screen which cannot be entered by the user, since they are calculated automatically from the data supplied in the construction's constituent layers. The derived parameters are always calculated when a material is applied to them. If these parameters have a '-' in them the construction is illegal and any model using them will give an error when simulating.
The constructions profile has the following parameters:
Type
Each construction belongs to one of the following types;
Opaque (for example a brick and plaster wall)
Transparent (for example a double glazing unit)
A different set of construction parameters is entered for each material type. To switch between construction types when editing a construction, select the desired Construction Type from the drop down list. Note that an Opaque construction may contain only Opaque materials and Gas Layers, and a Transparent construction may contain only Transparent
Name
The name given to the construction when it was added to the database
Description
Details about the construction.
Parameters for Opaque Constructions:
External Solar Absorptance
The fraction of external solar radiation which is absorbed by the construction.
Internal Solar Absorptance
The fraction of internal solar radiation which is absorbed by the construction.
External Emissivity
The fraction of external long-wave radiation which is absorbed by the construction.
Internal Emissivity
The fraction of internal long-wave radiation which is absorbed by the construction.
Conductance
The heat flux per unit temperature difference applied across the construction in the steady state. Note that the conductance applies to the construction alone and does not include the effects of surface heat transfer (unlike the more commonly used U value).
Time constant
The approximate time taken for the construction to regain thermal equilibrium following a sudden change in either of its surface temperatures. This gives a measure of the thermal mass (thermal inertia) of the construction. A lightweight construction such as a plasterboard partition has a time constant less than 1 hour. A construction consisting of 1 metre of concrete has a time constant of about 50 hours.
There is also a table which has the following columns:
Layer number
By convention the layers are numbered from the inside to the outside.
M-Code
The material code identifying the material of which the layer is composed.
Width
The width of the layer. This need only be entered in the case of an Opaque Material. To edit it double click on the material layer and a dialog box will appear, enter a value for the width and then click OK. For an Opaque Layer or a Gas Layer the width is a material attribute and may not be edited.
<Other parameters>
As in the parameters section . These material attributes may not be edited.
There are also two buttons, they are described in the following sections: U-Value and Condensation.
Solar Transmittance
The fraction of solar radiation at normal incidence which is transmitted by the construction.
External Solar Absorptance (ext. surf.)
The fraction of external solar radiation at normal incidence which is absorbed by the construction and which may be considered to be effectively absorbed on its external surface, in so far as the interaction of the construction with its environment is concerned. The validity of this concept is a consequence of the assumed linearity of heat transfer in the construction. In the analysis of solar transmission, reflection and absorption in the construction (performed when a new material is added to the construction), the absorption within each layer of the construction is determined, taking into account all inter-reflections, and the various absorptions are then divided between the external and internal surfaces using a variant of Thevenin's theorem.
External Solar Absorptance (int. surf.)
The fraction of external solar radiation at normal incidence which is absorbed by the construction and which may be considered to be effectively absorbed on its internal surface.
Internal Solar Absorptance (int. surf.)
The fraction of internal solar radiation at normal incidence which is absorbed by the construction and which may be considered to be effectively absorbed on its internal surface.
Internal Solar Absorptance (ext. surf.)
The fraction of internal solar radiation at normal incidence which is absorbed by the construction and which may be considered to be effectively absorbed on its external surface.
Light Transmittance
The fraction of visible radiation which is transmitted by the construction.
External Emissivity
The fraction of external long-wave radiation which is absorbed by the construction.
Internal Emissivity
The fraction of internal long-wave radiation which is absorbed by the construction.
Conductance
The heat flux per unit temperature difference applied across the construction in the steady state. Note that the conductance applies to the construction alone and does not include the effects of surface heat transfer (unlike the more commonly used U value).
Time constant
The approximate time taken for the construction to regain thermal equilibrium following a sudden change in either of its surface temperatures. This gives a measure of the thermal mass (thermal inertia) of the construction. This value will be zero for transparent constructions as they are considered massless by Tas.
External Blind?
This box contains 'Yes' for constructions whose external layer is a blind, and 'No' otherwise. This affects the treatment of convection from this surface.
Internal Blind?
This box contains 'Yes' for constructions whose internal layer is a blind, and 'No' otherwise. This affects the treatment of convection from this surface
There is also a table listing the layers of the construction:
Layer number
By convention the layers are numbered from the inside to the outside.
M-Code
The material code identifying the material of which the layer is composed.
Width
The width of the layer. For material types permitted in Transparent Constructions the width is a material attribute and may not be edited.
<Other parameters>
As in the parameters section. These material attributes may not be edited.
There are also three buttons, they are described in the sections: U-Value, Glazing Parameters and Condensation.
Another way of viewing the materials used in this construction is to left click on the '+' by the construction icon in the Tree View. This will display each material used in this construction. To view the details of the material, left click on its icon in the Tree View.