Form Finding with Solar Radiation Analysis

There's been a Solar Radiation "Technology Preview" plug-in for Revit available up on Autodesk Labs for a while now. I've been curious about it, but haven't had an idea to apply to it till now. So I mixed up a little form study of Foster and Partners' London City Hall to give it a test spin. Foster's design is a nice test case as the building form is directly driven by some relatively simple principles about passive solar design. In a temperate zone, maximize winter solar gain and minimize peak summer sun exposure. Through some clever geometric arrangements, the south face shades itself in the summer, and is basically fully exposed in the winter.

The idea of the Solar Radiation plug-in is that it allows Revit to "to understand and quantify solar radiation on various surfaces of your conceptual building model". There are a number of tutorials and demos about how to use it, so I won't cover that stuff. The thing that is particularly interesting to me about it is that the plug-in uses a new to r2011 API feature that allows the code to monitor and update the analysis model (also new to 2011) dynamically. That means that I can get the initial solar analysis up and running and then manipulate the model to get live feedback on the building's performance.

So my rough model of the building is based on an adaptive component. I won't go into detail here, but will mention that it is important to make the adaptive components category set to NOT "shared", that way, the adaptive component geometry will be subsumed in the mass into which it is nested. The solar radiation plug-in only works on mass category, so you need to expose the nested component geometry as mass. You can download the final file and dissect it if you like.

This component is nested into a partial ellipse with parameters to control the width and angle, as well as how tall the overall form is.

For this exercise, I only manipulate the angle, but you could play with all sorts of settings, including floor to floor height. I started off with the form loaded into an RVT environment, at a relatively upright 65 degree angle and ran the analysis

Units for the color gradient are displayed in the model space.

Now, if you want to monkey with the geometry, you need to keep the analysis dialog open, otherwise you get all sorts of out of sync data. (The plug-in actually creates "analysis results" geometry, which has an odd relationship to regular Revit elements. It is a temporary element that you can select and delete, and it disappears on save. Basically you need to save out images if you want to keep a record. Proceed with caution.)

With the dialog still active, I start incrementing the angle of the form downwards.

As I lower the angle, the form's self shading increases.

While it looks like I could probably get a little more shade out of the façade by tilting further, I'm already at 45 degrees, and the upper portions of the form are starting to increase their exposure (more yellow). And besides, my constraints start falling apart around 43. This is probably significantly steeper than the real thing in London, but it's interesting to see how far you could push the idea.

Now, if I change my view settings to Winter Solstice, I see a nice (perhaps blinding) exposure to the low angle sunlight.

So, this was quick and dirty, but you can get a sense for how the plug-in allows for interactive analysis of building form. What you choose to do with the results and how you interpret them is of course up to you.

You can download my rvt file from here. The plug-in is available here.

Here's a 2 minute realtime demonstration of making the manipulations and getting analysis results.