The thermal analysis routines in ECOTECT require the construction of a model in a certain way. The following is a summary of the important points to note when constructing a model for thermal analysis.

Building Zones

Each building must be comprised of one or more fully enclosed thermal zones. The thermal zone is the basic geometry used in thermal calculations such as internal temperatures and heat loads.

Defining Thermal Zones

A thermal zone should represent a relatively homogeneous area of enclosed air. This could be a single room, a roof-space, or a specific precinct in the building (for example, a storeroom and two toilets on the south side). It may also be necessary to create multiple thermal zones within large spaces, in which case it is important to use a VOID object between adjacent zones within the same volume.

Geometrically Complete

All thermal zones must be geometrically complete, meaning that they have surfaces fully enclosing their entire volume. Imagine any thermal zone you create is full of water and that you pick it up and turn it all around and upside down. If any water can leak out, it is not a fully enclosed thermal zone.

Surface Normals Point Outwards In order for ECOTECT to know the orientation of each surface, especially in very complex thermal zones, the normals of all surface surrounding the zone must point outwards. This way ECOTECT can quickly calculate when they are facing the Sun and whether any point is inside or outside a zone. For more information, see the Surface Normals topic.

Adjacent Zones

Adjacent thermal zones must have their intervening walls, ceilings or floors coplanar and overlapping. ECOTECT is thus able to automatically detect adjacency and determine the extent of heat flow between them. If a thermal zone has an opening to the outside or when one large room is separated into two or more thermal zones, you must use a VOID object to indicate that a hole exists. Do NOT simply leave the surface out of the model as ECOTECT will have no idea that there is supposed to be a gap there (for more information, see the Double Counting and Inter-Zonal Adjacency topics). The model below shows how the adjacent walls from two thermal zones should overlap.

The main reason for this is that the model is intended as a conceptual design tool. If you completely enclose each zone, you can move them around or rearrange them completely and ECOTECT will still be able to accurately recalculate adjacencies.

Non-Thermal Zones

External shading devices and objects that do not form a thermal zone should be placed on the Outside zone or on a zone tagged as non-thermal (for more details see the Non-Thermal Zones topic).

Ground Effects and Earth Berms

Any exposed surface that is on or below the ground plane (Z=0) is assumed to be in direct contact with the ground. This will be obvious during an adjacency calculation when overlap dots appear on such objects. If any surface above the ground is found to be adjacent to another surface that belongs to the Outside Zone, it is assumed that the area of adjacency is actually an earth berm, in which case ground effects are calculated for that section of the object. (for more details see the Non-Thermal Zones topic).

Internal Partitions

PARTITION objects are assumed to be completely internal to a zone and therefore are not tested for incident solar radiation (any radiation that does hit them must have already passed through a window object and been calculated there) or for adjacency with other zones. They do, however, contribute to the internal thermal mass of a zone. Any furniture or completely internal walls should therefore be constructed as PARTITION elements.

Building a Thermal Model

Any building for thermal analysis must be formed from one or more fully enclosed thermal zones, with each such zone representing a room or precinct within the building. Being fully enclosed, the walls of adjacent thermal zones should be coplanar (or at least very close and parallel) and overlap each other - the west wall of Zone 1, for instance, and the east wall of Zone 2. This may seem like double-counting, however this way ECOTECT can work out for itself which thermal zones are adjacent, how much heat can pass between them and, ultimately, accurate internal temperatures and heat loads for each thermal zone. For more details on the construction of thermal zones this way, refer to the Double Counting and Inter-Zonal Adjacency topics.

It should be noted that shading and visualisation functions are not dependant on a building's zoning. Whilst a model created for thermal, lighting and acoustic simulation would be more than suitable for shading analysis, the reverse may not be true. For example, you may wish to add wall thickness or detailed window frames for more accurate sun penetration results as the design progresses. Such additions, however, are likely to significantly increase thermal and acoustic calculation times without any appreciable affect on their accuracy.

Geometric Detail Only When it is Needed

Much of the detail in a 3D CAD model is pretty well redundant in a thermal model. For example skirting boards, window frames, sills, architraves and other ornamental geometry will have a negligible affect on thermal performance but will significantly increase calculation times. The key to a good thermal model therefore is simplicity, getting rid of all the thermally redundant geometry. The image below provides an example of a model set up for both thermal (coloured zones and simple geometry) and lighting analysis (complex geometry and zones not too important).

It is possible to develop a single model that contains both a simplified set of zones for thermal calculations and all the complexity required for a realistic visualisation or lighting analysis. Simply generate your rooms first as simple thermal zones containing all the information required for the thermal analysis, which you are likely to do first anyway. Then add any of the more visual and thermally redundant geometry into non-thermal zones that can be quickly turned on and off as required.

Having just said that a thermal model should be stripped down and simplified as much as possible, a good passive solar design may be completely ruined by a few rugs or pieces of furniture obscuring the exposed thermal mass. Thus determining exactly what is thermally redundant geometry can be a bit of a judgement call.

Shading Devices and Non-Thermal Zones

All planar objects in ECOTECT except internal PARTITIONS are assumed to receive solar radiation. As the geometric modeller isn't particularly bright, it cannot tell if a surface is inside or outside a zone. Thus, if you create a number of large external shades on a zone, ECOTECT will simply add any incident radiation that falls on them to the overall indirect solar load of that zone. If you make them PARTITIONS, it will still add them to the overall internal thermal mass to that zone.

The exception to this is the Outside Zone and zones that have been defined as non-thermal. Everything on the Outside zone is assumed to be outside the building, either a site element or an adjacent building. Thus, it is usual to add external shading devices to the Outside zone or create a zone specifically for shades and tag it as non-thermal in the Zone Management dialog box.

Non-thermal zones do not appear in the thermal zone list and do not participate in temperature or heat load calculations. Their elements will provide shade for and reflect onto objects in other zones, but incident solar radiation and overshadowing calculations are not performed for them.