Raycasting in Ecotect
In this workshop, we will look at using Ecotect's raycasting capabilities, in the context of both lighting and acoustic performance simulation. Raycasting is used to "sample" geometry - oftentimes it is done in reverse order. Rays are cast from geometry out towards the sky, sometimes hitting other objects. This is known as "occlusion". Raycasting usually asks the user to determine how many rays are used to describe the characteristics of each piece of geometry. More rays = more accuracy, but longer calculation times.
Import Your File
Ecotect can import 3D geometry from other programs. This pathway is necessary but somewhat buggy - Ecotect will often display a model correctly even though it has misunderstood it. This will show up later as missing geometry in calculations and results. To successfully work with imported geometry, you need to follow a few principles:
- The most useful formats for us are OBJ and DXF.
- Download OBJ samples here
- Its preferable that you import DXF - it is less likely to introduce errors into your model. If one does not work for you, try the other.
- Models must be polygons. Ideally, they are triangulated (no quads). If you want multiple readings across a surface, you must further tessellate your model.
- Polygons must be relatively low-complexity. Try not to import anything that has more than 10,000 faces. Preferably a model is less than 1000 faces.
- Be careful about scale. Ecotect units are in "mm". Accuracy degrades if your model is incredibly small. Some tests require models to be at 1:1 scale (preferable in all cases anyways). A scale factor is entered when you import the model.
- Useful commands to fix models within Ecotect:
- Modify... Surface Subdivision > Rectangular Tiles
- Modify... Merge Coincident Triangles
Relative to one piece of geometry, generate a shading graph. See Sky Subdivision and Why do Shading Calculations Take So Long? on naturalfrequency.com - these go into more depth on what is being calculated in Ecotect when doing solar analysis.
- Establish Geometry
- Import weather data file...
- Under Model select Date/Time/Location
- Click load climate data and select new york new york
- Allow Ecotect to change the global position to match climate file
- Go to Calculate and click Sun Path Diagram
- Select a surface from your geometry. All data displayed will be relevant to this surface. You should notice that certain parts of the graph are shadowed.
- Select Calculate Shading... and make sure Overshadowing Percentage is selected under Displayed data and press OK
Solar Access Analysis
See the degree to which each unit of geometry is exposed to incident solar radiation. There are multiple ways to filter the question of incident energy. Incident solar radiation is also called insolation and is measured in W/m2 (Watts of energy per Square Meter) note that this is an average over an area. This is also called irradiance. We can look more specifically at different ranges of energy, for instance we can isolate the "photosynthetically active" radiation, or PAR, to quantify the energy that is useful to plant life.
- Download the example model DXF Geometry File
- Load Weather File
- Calculate... Solar Access Analysis
- Select Incident Solar Radiation...
- For Current Day...
- Cumulative Values...
- Objects in Model...
- Perform Detailing Shading Calculations
- If your simulation is taking too long, try turning down the "number of sky segments". You can also turn down Overshadowing accuracy, but you probably want this at least at medium. If the options are gray, reselect 'perform detailed shading calculations'
- Click 'OK' and run the simulation
- You can view the result by...
- Go to Display Settings (the red surface icon)
- At the bottom of the menu, click 'display attributes' and also toggle 'show colors'
A note on units
- A watt (W) is a measure of power. Power is the rate at which energy is generated and consumed. It is equivalent to 1 joule per second.
- Irradiance, or insolation, is expressed in watts per square meter (W·m2)
- Ecotect returns cumulative energy in Wh/m2, or watt hours per square meter. Knowing the surface area that receives this value, you can easily calculte the watt hour, which is total incident energy on that face. Solar panels convert energy at efficiencies between 10 and 20%. Other technologies, including solar towers which have a conversion rate of 2-3%, have lower efficiencies.
Solar Shading Potential
By examining the energy striking a particular geometric feature or arbitrary plane, we can analyze how a surface might participate as a screen. In this case, we will use this Ecotect example file. The file depicts a small gallery between two existing buildings. We will project "solar potential" from a series of points of interest onto the roof plane.
- Establish geometry
- Setup the analysis grid to see solar gains
- Display Analysis Grid
- Fit to Model Extents...
- Adjust sizing of cell in "Grid Management..."
- Do a Solar Access Calculation ("Calculate"... "Solar Access")
- Copy off the results so that we can compare later
- Visualize Solar Gains directly above the window (in the plane of the shading device)
- select the window
- Fit the analysis grid to it
- We might also expand the analysis grid manually, by clicking "Adjust Grid Extents" under the Analysis Grid tab. We can manually drag its extents to get a larger surface area to test.
- Calculate... Shading and Shadows... Shading Design Wizard
- We will use the "Project Solar Shading Potential" Wizard
- We need to have our window selected
- In step 4, we need to set it to work with the analysis grid
- We can use the generated contours to draw our own shading device ("Draw"... "Plane")
- Test the shading device by re-analyzing the building volume, as in step 1
Ecotect can do lighting analysis in 3D, using the analysis grid. Think of it as getting a light meter reading at a series of points in space.
- Establish geometry
- To fit the analysis grid to your geometry...
- Select all of your geometry
- Under the analysis grid tab, select fit to selected objects and fit grid extents in all axis - you should see your analysis grid (if its turned on) fitted to the extents of your geometry. It should only display a 2-dimensional representation.
- To adjust analysis grid density...
- the density of your analysis grid will determine both the fineness and accuracy of your simulation.
- select grid management under the analysis grid tab...
- under management type in the number of cells for each axis (x,y and z)
- Run calculation with proper settings
- Now that we have setup the grid properly, we can run the simulation. At the bottom of the tab, make sure lighting levels is toggled and click perform calculation
- In the dialogue box that opens up, select Full-daylighting Analysis under Calculation settings and make sure Full 3D Grid Calculation is toggled. You may want to set the precision to low or medium to allow the calculation to run faster.
- To re-adjust the analysis range...
- Change Minimum under Grid data & scale to 0 and Maximum to 100
- To adjust the sectional view of the analysis grid...
- See Grid Data & Scale... and adjust the offset
- Note that you can adjust the section plane by changing the axis
- To adjust how our data is displayed...
- See the Grid Settings at the top of the tab and try toggling the Show values in 3D or Show contour lines
Here are the steps to setting up an acoustic simulation:
- Establish interior model. Acoustic simulation assumes an interior condition. If youre speaker object is not contained within some geometric volume, it will not cast rays in a uniform fashion.
- To create a speaker object...
- In the Draw menu select Sound Source
- Place your speaker object in the XY plane with the first click. To have it face upward, keep your mouse on the same spot, hold down the CTRL key and move your mouse, then click.
- To change the volume of the speaker, select the speaker and go to the Material Assignments tab to the right, and double click the speaker object that shows up in the tab. Change the Sound Level(dB) to the desired number in the model view properties tab, and press Apply Changes
- To setup a ray calculation...
- Go to the particles tab to the far right. Under Generate Rays select Spherical random and max out the azimuth and altitude.
- Select Generate Rays
- Depending on how many rays you have allowed for and how many bounces, you will wait either a short or long time for ecotect to perform the simulation. More than 10 bounces is probably unnecessary and more than 10000 rays is probably excessive.
- Under display settings, change to Animated particles - you can now use the animation menu to stop and start the animation.
- You might want to adjust the time-step of the animation. Do this by typing a smaller number in the frame step increment box.