Deciduous Trees in ClimateStudio

by Jon Sargent | 30 August 2024

Deciduous trees have a significant impact on daylight, visual and thermal comfort, and solar loading of building façades. They are often an important part of a project’s existing context. And, when scope allows, they can be strategically placed to offer passive design benefits.

Until now, however, deciduous trees have been difficult or impossible to model in annual simulations. Partial states of leaf growth in the spring and the disappearance of leaves in winter are not behaviors these methods were designed to handle. As a result, the arboreally curious have been relegated to analyzing moments in time, or jumping through hoops to compose annual results (e.g. by running separate simulations and stitching them together).

ClimateStudio 2.0 solves these problems with its new multiversal engine. Instead of looking at one condition at a time, the engine assesses all deciduous leaf states in a single ray trace.

Figure 1: ClimateStudio's engine analyzes changing leaf states during annual simulations.

For each time step, the software switches between leaf colors and sizes using a weather-based schedule. The resulting simulation accounts for the presence of leaves in summer, their absence in winter, color changes in the fall, and partial states of leaf growth and loss.

Why is this useful? Well, if you are in the position of advocating for the preservation or planting of trees as part of a site or urban design strategy, you can now use the software to properly study their impact. A common argument in favor of deciduous plantings is their seasonal shading effect – casting shade in summer when it’s most needed, while allowing solar transmission in winter, when gains are potentially thermally useful. To evaluate this effect, users can deploy ClimateStudio’s tree assets in a radiation analysis. The figure below shows the annual and hourly radiation falling on a South façade in Washington, DC, with and without a row of deciduous trees.

Figure 2: Deciduous trees shade a South façade in summer.

The addition of trees reduces annual insolation by 63%. More importantly, using ClimateStudio’s built-in temperature filters, one can see that the bulk of this reduction (67%) occurs during warm hours, when the outdoor temperature is above a balance point of 15˚ C. Comparatively little occurs during cold hours, when the temperature is below 15˚ C. In other words, the trees preferentially preserve insolation when gains are thermally useful, while blocking the sun when the building is likely to be in cooling mode.

The lighting-based case for trees is less straightforward. With their large canopies and dark leaves, trees generally reduce daylight levels in buildings. For this reason, some standards committees have avoided requiring the modeling of trees in compliance simulations, fearing it would motivate developers to cut them down. But there are more nuanced effects to consider, and a sophisticated analysis often finds trees to be beneficial from a purely visual perspective.

Consider the same Washington, DC façade above, with an office space interior to the South glazing. Although the tree canopies block daylight in the summer, they also mitigate glare, reducing the amount of time occupants must close the blinds (from 51% to 23% of occupied hours, assuming an LM-83 control schedule). Keeping the blinds open increases light transmission, counteracting the dimming effect of the trees and – in this case – increasing the room’s spatial daylight autonomy (sDA) from 35% to 65%.  Open blinds also preserve the view to the outside – a view that now includes a strong connection to nature. Even if the trees reduced daylight access, their positive impact on visual comfort, view openness and view quality might be regarded as a net benefit.

Figure 3: Deciduous trees increase daylight in a South-facing office by reducing blinds use.

For many projects, the addition or removal of trees is not within the scope of design. In these cases, if trees are part of the extant context, they are at least worth considering, regardless of what the standards require. Given their influence on daylight and insolation at lower floors, they may suggest different façade strategies (e.g. more glazing or less static shading) than higher in a building.

To study these and other tree-based effects, simply place ClimateStudio tree assets in your Rhino model, as described here. The assets cover a basic range of tree shapes (squat, round, tall) and canopy densities (sparse, medium, thick), and come prepopulated with dynamic leaf materials that change with the seasons. The dynamic effects are picked up by radiation, daylight and annual glare simulations. They also appear in time-point illuminance calculations and renderings, which automatically instantiate the correct leaf state based on the day of year.

Figure 4: Dynamic leaves respond to day of year in point-in-time simulations.

In addition to using ClimateStudio’s tree assets, you can also create your own deciduous vegetation by assigning a dynamic leaf material to any Rhino layer you like. If your geometry is quite detailed, the simulation may be slow to load, but it will run eventually! The layer will exhibit all the behaviors described above: color changes, disappearance in winter, and growth/shrinkage in spring and fall (achieved by scaling the layer’s mesh faces).

Deciduous leaf materials and tree assets are part of the ClimateStudio version 2.0 release candidate. The installer is available for commercial and educational users with a license key. Prospective customers can request a trial key and pricing information here, and a representative from Solemma will reach out to you.

For help with ClimateStudio visit climatestudiodocs.com or contact support@solemma.com.