This is the second in a series of blogs that explore Autodesk’s Energy Analysis solutions.
Using daylight in your building is a key strategy for passive design. Letting sun into your building impacts visual and thermal comfort. To determine the right balance, we need to consider the visual needs of the space & how we could efficiently use the Sun’s light to meet those needs.
Illuminance and Daylight Factor studies are a great way to determine if a space is achieving enough daylight throughout the day. Fortunately, Revit has a tool that will help us with this requirement. Autodesk Insight 360 Daylighting Analysis Plugin for Revit. Although this tool is heavily influenced by the American ‘LEED’ simulation standard we can use it here in the UK because we’re provided with custom settings that allow us to configure the software to provide results that we can use with BREEAM.
Firstly, you will require an Autodesk Account to gain access to the plugin, if you don’t already have one, you can register here. It’s free and provides many additional benefits.Once registered, sign in. The process of running an analysis is very simple:
- Set the Project Location.
- Prepare the model by setting the opaque and transparent materials.
- Create Rooms.
- Run the Analysis, select the analysis type required.
- Generate the results.
To start the process, use the ‘Location’ command and specify an address your then offered a range of nearby weather stations, the nearest weather station is automatically selected unless you select a different one from the list provided.
From the Analyze tab, select Lighting from within the Insight panel.
The first dialog that appears provides best practices for conducting a lighting analysis study. Following these guidelines will help you achieve more representative results.
Define surface and glazing materials.
To obtain accurate results we need to consider the transmittance (The percentage of visible light) of any glazing, commonly known as TVis. (Glass painted black =0%, an empty opening =100%) and the amount of light bouncing off any interior surfaces. (Reflectivity). Both variables are defined in Revit by assigning a Red, Green, Blue (RGB) custom colour value for the appropriate material.
To define the transparency of glazing –
Pick a Window – Edit family – Select the Glazing – Edit Material – APPEARANCE tab – Color = custom – provide a value for RGB.
IMPORTANT, only the RGB for custom colour value affect an illuminance simulation, any other property related to reflectivity is ignored. Three factors affect the reflectivity of glazing, the custom colour, the quantity of panes and the pane thickness, use the Table below to determine the appropriate RGB value.
For Example, 3mm thick glass, comprising two panes with a TVis value of 70% = R50, G50, B50. (The convention is to use the same value for all three colours)
As a comparison, values between 40% and 70% are typical, perfectly clear glass = 92%
Defining the Reflectivity of Opaque Materials
Accurate results depend on simulating light bouncing off interior surfaces.
To define the reflectivity of materials -
Pick a Wall – Edit Type – Select the Material – Edit Material – APPEARANCE tab – Color = custom – provide a value for RGB. Use the Table below to determine the appropriate RGB value.
Rooms are a mechanism for reporting results. The results (performance percentages) are organised and reported in the schedules by rooms. Graphically, the results are created on a surface derived from the rooms.
Run the Analysis.
Next, you run a new analysis type or recall previously saved results. Select
The Lighting Analysis in the Cloud dialog box will allow you to set your study settings. Select Illuminance Analysis as the Analysis type.
Select the date and time range for your study.
Selecting the icon highlighted above allows you to define custom properties for time, and weather data values for DHI (Diffused Solar Radiation) and DNI (Direct Solar Radiation) and GHI (GHI = DHI + DNI * cos (solar zenith angle)
Follow this Link to find out how to download these values.
Set the minimum Illuminance threshold and analysis plane height.
These are high and low threshold values that are used to as the basis for qualification of the results shown in the automatically created Room and Floor schedules. The analysis plane height defines the height (in inches) for the grid at which the results are analysed. Select Start Analysis to begin the simulation. Cloud credits will not be charged until the analysis is complete.
After selecting Start Analysis, the model geometry will be uploaded to the cloud rendering engine. Do not close the project or Revit during this process. Once the model is successfully uploaded to the cloud, it is okay to close the project or continue working in Revit. Note that any changes you make to the model geometry or material settings will not be reflected in your analysis results, as the model has already been uploaded for analysis.
Autodesk Revit will notify you once the results are ready. Accept or Decline the cloud credit charges at this point. It is recommended you also save the project, so you will be able to recall the lighting analysis results after exiting Revit.
What is a ‘grid’?
The analysis job is divided into parts based on floor objects and time/date settings to help parallelize the simulation. When you see the word ‘grid’ in the processing dialogues, these are simply parts of the building simulation. Autodesk report the status of the simulation by grids so you can see how much is done and how much is left to do. If any grid fails (this is very rare), the analysis completed on the successful grids is still valid. Since a grid is basically a floor object, this means any failed grids will be equivalent to missing floors in the analysis results.
Open the _Lighting Analysis Model View under 3D Views. Note that any “_Lighting ...” views are automatically created to easily access results in plan, 3D, and as a schedule. Analysis results will populate in whatever 3D view is currently active.
From the Insight panel select Lighting to access your analysis results. This time, select the results for the analysis that has been completed and select Go.
You’ll be prompted with a dialog box with a summary of your results.
You can use the Section Box to view the results in 3D or open the corresponding “_Lighting” floor plan.
You can toggle between different analysis visualizations by selecting the analysis plane, and changing the Analysis Configuration in the Properties
Use the results to change properties for model elements, perhaps the glazing transmittance value etc.
Two schedules are generated automatically. Both schedules have headers that show a summary of performance data and the analysis settings used in the simulation.
Open _Lighting Analysis Room Schedule. To get more detail for the rooms included in the analysis.
Two Room Parameters are used to define how to interpret the analysis results in the schedules and on the Floor Plan results views and are used for narrowing down the parts of the building that need further review.
Include in Daylighting: If this is checked, the results for this room are used in the floor plans and building threshold performance percentages. If not, results will not be shown for this area of the floor.
Automated Shades: If this is checked, the room is assumed to have shades that are automatically lowered to block high levels of direct solar and raised when not needed - this is theoretical not literal.
Any changes made in the schedule do not require you re-run the analysis. Simply select Lighting and access the study results to regenerate results considering the information updated in the schedule.
Lighting Analysis floor plan photometric views are automatically created for any level that has at least one Room with Include in Daylighting set to On. If you don’t see a floor plan that you expect to see, the reason is probably because it has no Rooms or Rooms are associated with a different level.
Note that the rendered results do not persist between Revit sessions. However, the view settings are saved, so simply click ‘Generate Results’ again, and the views will be regenerated as they were before you closed the project.
A very useful technique for reviewing daylighting results is to generate results in a 3d view, then cut a section of the building to view the results in the context of the building geometry. When doing this, some floor levels may obscure levels below. Results are organized by Level, so you can use the Analysis Results Settings to turn Visibility off for levels that are in the way.
If you'd like to get a quote or to know more about Autodesk Revit or Insight 360, please get in contact with us through the link below: