With the plans in their possession the engineer will go about the task of defining by floor each unique space. This is done in the following way. This phase of model construction is similar to what the EAM expects of the CAD tool.
1. Identify the origin to be used for all measurements on the plan. Determine the location of the building including its zip code.
2. Identify unconditioned spaces versus conditioned spaces. This is done by the descriptions of the spaces and the mechanical drawings.
3. Identify space types (office, hallway, conf. room) by space descriptions or layouts.
4. Group similar small spaces by similar external envelope thermal loads and HVAC schedules into simulated spaces. Similar external envelope thermal loads are determined by wall constructions and orientation. On a large floor with windows on each side, there are typically zones for each perimeter orientation and a core zone. Perimeter zones are typically about 15 feet deep.
5. If there is a large space that has large interior openings separating the space into smaller spaces use these openings as virtual walls (air walls) to cut the larger space into smaller spaces. This is done when a large space has either of the following.
Exterior walls that have multiple and unique exposures to different Cartesian directions. Clearly defined unique mechanical HVAC
needs to separate parts of the space often indicated by multiple thermostats in the
large space. An airport gate area is a good example of this.
6. For each space or grouped spaces, use the end- point vertices at the floor of each space’s enclosing walls to develop the floor polygon of the space. Exterior walls are measured on their exterior plane and interior walls are measured on their centerline plane. Interior walls are extended to an exterior wall’s exterior plane for their connecting coordinate and to an interiors center plane. Do the same at the ceiling/roof to develop the ceiling/roof polygon. 7. Calculate the actual area of the space based on the
area of the floor polygon developed in the previous step.
8. Spaces with multi-levels will need to be simplified by making them into a single floor (eg. a theatre with a stage) that spans several levels, if the difference in height between each level is
equivalent to a new floor (eg. a mezzanine), that section of the floor will be divided into two spaces, one over the other, and with an air-type interior wall separating them. This stacked space approach is required in a CAD tool if its space object can not accommodate spanning multiple floors.
9. For unspecified volumes the engineer will assume it is a large unconditioned space by deciding whether the space can be occupied based on height. If it is too low for people to stand in then it is most likely an unconditioned space. If the height is less than approximately two feet then it is assumed to be a thick construction and will be modeled in its entirety as a surface.
10. The floor and the ceiling planar polygon surfaces will need to be divided depending on what is adjacent to them. For instance, the floor may cantilever over an exterior walkway as well as two spaces below it. The floor polygon will then be divided into three floor polygons, one for the cantilever portion, and two for each space the floor is over. The rules for dividing space surfaces are described in the EAM Object Rules section above. 11. Determine the average height of the ceiling for the
space and use this height along with the space area to calculate the estimated space volume. The simulation results are not highly sensitive to variations in the volume of spaces; so do not be concerned with the errors introduced by averaging the height of the ceiling.
12. For each wall enclosing the space define the surface width, height, azimuth, and the planar polygon of each wall’s surface representation. Divide the wall up for unique orientations and constructions. Also, apply the rules mentioned above for floors and ceiling for adjacent spaces. For example, in Figure 2, Room C has a skylight well with walls adjacent to Plenum B. These walls will need surfaces defined for them that are adjacent to Room C and Plenum B.
13. Determine the openings for all surfaces enclosing the space including windows, doors, and skylights. Measure the height and width as well as the polygons for each of these openings.
14. For exterior walls and windows where there exists any exterior shading surfaces that are attached to the wall or window and are unique to that wall or window, define these surfaces as shading surfaces with their height, width and polygon.
15. Determine surfaces that shade more large portions of the building that are not unique to any one space wall or window. Define those surfaces as shading surfaces with their height, width and polygon. 16. Determine if an adjacent structure or vegetation will
shade the building and construct a planar surface that simulates that shading structure. Define the polygon for the planar structure and give it a name. Note that most energy analysis for code
compliance require that these types of shades should be ignored.
17. Determine the thermal and optical properties of all surfaces and build material and construction “libraries” that will be assigned to each wall, floor, ceiling and roof in the building. Do the same with windows, doors, and skylights.