The design relevant to this BIM modeling is a grocery store construction project that consists of two story-grocery store and three story-parking building. Since the owner of this project seeks to achieve LEED Platinum award, several sustainable features are included in its schematic design. The features include Photovoltaic Car Shading Canopy (PV CSC), Wind Turbine, Green Rooftop System, etc. As shown in figure 1 below, schematic design of the grocery store is completed using REVIT Architecture.
Figure 1. Rendering image from East view
Parametric Model Design
Among the sustainable features, Photovoltaic Car Shading Canopy was selected and designed using BIM parametric modeling techniques. This feature has been selected because of the benefit acquired by harvesting solar energy, providing shade to cars and customers, and because of the challenge to provide flexible angle of Photovoltaic panels for better energy absorption.
Modeling idea
Figure 2, 3 show possible PV CSC options for the project. Taking account the project conditions that PV canopy is going to cover partial area of parking building roof, solar panels’ angle and canopy location may vary depending on other design decisions, parametric characters of the PV CSC design are decided as follow:
Figure 2, 3. Different types of Photovoltaic Car Shading Canopy
· PV canopy family design includes both canopy and parking areas under the roof.· PV panel angle is changeable by changing type property.
Modeling process
Construction process for PV CSC parametric model is as following:
1. Design ‘h’ shaped truss that will be placed along the length of car parking area using array function to support PV panels above the cars.
2. Array the ‘h’ shaped trusses and parking spaces according to predefined reference planes.
3. Redefine removed constraints and define slope for the roof.
4. Draw a roof extrusion that covers parking area and overhangs.
Diagram and equation
Diagrams are described using screen shots, and equations for the parametric model are shown in Table 1. Constructed model has one sided roof while it was sketched to have roofs on both sides of truss in the early design sketch in Figure 4 and 5.
Figure 4. Early design sketch 1
Figure 5. Early design sketch 2
Figure 6. Reference Level diagram for parametric modeling
Figure 7. Front view diagram for parametric modeling
Figure 8. Right side view diagram for parametric modeling
Table 1. Equation used for modeling 50 length & 60 angle type
Designed parametric family by types
Once parametric family is designed, four family types are defined as shown in Figure 9 to 12.
Figure 9. 50’ Length and 60° Angle type of Movable Canopy family
Figure 10. 100’ Length and 45° Angle type of Movable Canopy family
Figure 11. 150’ Length and 35° Angle type of Movable Canopy family
Figure 12. 150’ Length and 65° Angle type of Movable Canopy family
Critics about modeling application
The most important thing learned was the ‘visibility’ which is a strength Building Information Modeling technique has above previous approaches. For very innovative challenges like this project, letting project participants understand what is being designed and bringing them to the designer’s view point is very hard without showing it. However, using BIM, communication among participants can take place more easily and can be more productive. In the beginning stage of design, I was not sure about aesthetic aspect of PV CSC. However, detailed design aspects could be determined and fixed while working on the model because overall project was visualized by the REVIT tool.
On the other hand, there are some disadvantages I experienced as a BIM modeling beginner. When there were some parts of design that should be changed, it took considerable amount of time when a complicated parametric model has to be modified or there is no proper existing model. Though the strength of parametric modeling of BIM exists in the usability of the past design works, very different kind of parameters can be defined for a similar family when the usage is different. In other words, designers can use same or similar design feature of buildings once parametric design is properly constructed. This leads to fast design process and enables non-experts to generate ‘good’ models. However, construction of parametric model needs considerable amount of time and certain level of BIM skills.
In order to facilitate better use of Building Information Modeling techniques, there are things to be improved according to the project experience:
· Design idea has to be exact and concise
· More efficient visualization of constraints: All along the parametric design process, it was hard to recognize constraints defined for components main because it is three-dimension tool. If constraints can be visualized in ways that enhance understanding movement of components, complexity of parametric design will be relieved.
Appendix
Appendix
Figure 13. Rendering image of interior space
Figure 14. Parking building entrance
Figure 15. Design view of PV canopy and parking area
Figure 16. Grocery store schematic design view from East
