What input is needed?

Geometry

Building body

With the IDA ICE geometry editor, a building geometry is composed of one or several “building bodies”. A building body is described by a right prism based on a polygon (see left picture below). Even with these restrictions, buildings like in the right picture below can be modelled.

In order to be able to model sloped roofs, the top faces of building bodies can be edited with the “roof editor”. The roof is splitted into polygonal “roof parts” that can be sloped in different directions (see left picture below). The roof editor helps to model rather classical building shapes like in the right picture below.

The IDA ICE geometry editor can still limit the user in describing complex geometry. Depending on the question to be answered, accurate geometry description can be relevant, e.g. when envelope area and/or orientation counts. For more complex building shapes, IDA ICE can import arbitrary geometry from many 3D CAD file formats or from IFC.

Clearly explained, a building body describes the geometric shape of the building(s). But strictly speaking, the only function of building bodies is, that they have the following effects on a building model, which is actually based on the zones with their surfaces:

• Zone surfaces that are close enough to a building body surface are regarded as inner surfaces of external walls, which means that they are exposed to ambient conditions on the other side. (even more precisely, building body surfaces must not be attached to surfaces of other building bodies in order to represent an external surface).
• Windows are regarded as extarnal as soon as they are inserted to walls that are regardes as external. Windows can alternatively be inserted to building body surfaces. In this case, they are only included to the model, if a zone wall is placed close to such a window.
• Building bodies are alsway shading objects that always shield windows from direct solar radiation.
• Beside windows, other objects can be inserted to building body surfaces, such as PV panels, facade shading objects or daylight measurig planes.

In IDA ICE the best modelling habit is to define building bodies in such way that their surfaces go along the internal surfaces of the external walls (red line in the picture below).

Shading objects

Shading objects can be inserted either related to

• the site (vertical, horizontal or imported CAD object)
• the building (building body or imprted CAD or BIM object)
• a facade (balcony, fixed shade = simple screen, fixed fins)
• a window (drop arm awning, markisolette, simple screen, side fins, marquee with sides)

During the invoke process, when the mathematical model is built, shading matrices are calculated for all windows and PV panels, considering all the shading objects at site and building levels as well as the affected facade and window. This shading matrix calculates a shading reduction factor depending on the position of the sun, that reduces the calculated solar radiation hitting the shaded object.

Imported 3D CAD or BIM objects can be selected to be shading or non-shading. If shading, they can have a transparency between 0 (fully shading) to 1 (fully transparent).

Zone Geometry

For the AHU systems, the presentations for the standard and advanced user interface levels are the same (for the distinction between standard and advanced levels, see Section 5). However, in the case of the zone models, the presentations are completely different. This section explains the principal features of the zone models, and also provides a brief overview of the advanced level in this context. Actually, most users will never have to deal with the advanced level, but it is useful to know it exists, and the physics are more easily explained from the point of view of the advanced level.