Improvement of cavity option in InternalWall

[hscheipe]

The IDEAS.Buildings.Components.InternalWall component has the option to add a a cavity by setting hasCavity to true. However, the surface area of the cavity is not automatically subtracted from the surface area of the wall (to calculate transmission etc). We (BFG UGent) would find it more intuitive if this would be the case. Due to compatibility reasons with previous models, it may not be desirable to subtract this automatically in all cases, but maybe the option can be included to subtract this automatically by means of a check box (or at least adjust the annotation to make clear that this area is not automatically subtracted to avoid mistakes)?

[LoneMeertens]

Thanks for raising this issue!

You are correct that in IDEAS.Buildings.Components.InternalWall the cavity area is not automatically subtracted from the wall surface area A. This is mentioned in the model documentation:

“Parameter hasCavity can be set to true to simulate heat transfer through a cavity such as an open door in a simplified way. The cavity height h and width w then have to be specified. We assume that the value of A excludes the surface area of the cavity.”

However, this can indeed be a bit unclear when configuring the component through the GUI.

Practical usage

Typically, IDEAS.Buildings.Components.InternalWall is used together with the IDEAS.Buildings.Components.Zone model when constructing custom zone geometries. In these cases, the surface areas of the walls are explicitly defined by the user.

A similar manual adjustment is also required when using windows (IDEAS.Buildings.Components.Window) in combination with external wall components (IDEAS.Buildings.Components.OuterWall). In that case as well, the wall surface area must be corrected manually so that the window area is not counted as opaque wall area.

These components are therefore mainly intended for building custom zone models, where the user has full control over the geometry.

Alternative: RectangularZoneTemplate

If you want to set up a rectangular zone geometry more quickly, you may want to use:

IDEAS.Buildings.Components.RectangularZoneTemplate

This model allows fast setup of a rectangular zone and internally consists of:

• one zone,
• four walls,
• a roof,
• a floor,
• and optional windows.

In this component, the limitation you pointed out is already handled:
when adding a window or cavity to a surface, the corresponding wall area is automatically adjusted.

Therefore, if the zone you want to represent fits within this template, using RectangularZoneTemplate may be a convenient alternative.

Possible improvement

We agree that the current behavior in InternalWall could be clearer. A possible improvement could therefore be to update the description of the wall area parameter A to make it more explicit that this area is expected to exclude any cavity or opening area.

It could also be useful to apply a similar clarification in other related wall components, such as OuterWall, where the wall area should likewise exclude the area occupied by windows (IDEAS.Buildings.Components.Window).

We will have a look into this and see how the documentation can be improved to make this clearer for users.
Thanks again for pointing this out!