# Do I need to use Brep for multi-objective optimization? or should I model every thing as parametric?

Hi. I am trying to assess energy consumption in a building with multi-objective optimization. Window-to-wall ratio is going to change for this optimization and my question is whether I need to set up the model completely in a grasshopper or should I draw it in Rhino and then use Brep?

Thank you guys!

Hi @Farzam,

If you want to analyse as multi-objective optimization, you will need to parameterized inputs for your optimization tool. You should create geometries in Grasshopper.

When you need to only static geometries, you can use Rhino Geometry definitions.

-Best
Oğuzhan

@oguzhankoral thank you very much for the information. May I ask you a few more questions, I am having a simple box with 3x4x3 m dimensions and I need the south-facing facade with 4 meters of length to have a relative parametric value. By saying that, I mean in the first scenario I need the window dimensions to change based on the wall (window to fall ratio) and in the second scenario, I need it to change based on the floor area (window to floor ratio). Could you please help me to find it out?

Also, it would be great if in both scenarios the longer length was horizontal.

Thank you!

You can easily use glazing ratio component.

You should define window size as floor area dependent using with geometrical definitions in Grasshopper. You can create this kind of logic:
FloorArea / WallArea(South) = c (constant) -----> c should define in any scope like 1 < c < 10 ;
_glzRatio = 0,c ;

Cheers,
Oğuzhan

@oguzhankoral wow; great, thank you very much. I will do my best for the second scenario! Thank you again!

@oguzhankoral Hi, I tried your solution and I achieved good results but I still have trouble. The window surpasses the wall boundaries at certain points. Do you know how I can solve it? I think it needs an If conditional statement that if the length of x is higher than 4, repeat choosing the numbers but I don’t know how to do it.

I can work with the file right now too but it will just take so much useless time for multi-objective optimization as many genes surpass the lengths and are useless scientifically.