Evaluator Node 1: Calculate Building’s Cost Per Square Feet
This node is inspired by the custom node in the example where the cost (by level and total) is calculated for the building. However, that total cost does not take into account the useable area size of the building. By dividing the total cost value by the total cross floor area in the new custom mode, we get a much meaningful data that shows construction value and helps compare how different building forms impact unit cost. The custom node takes in the mass floor areas (processed with the BuildingForm.MassFloors custom node provided in the example), gross floor area, value at lowest level ($500/sf at ground level), value at highest level ($1000/sf at 750 feet), height at highest level (750 feet for my building), and level to level height (10 feet for my building). The output returns a single value of the cost per square feet.
Evaluator Node 2: Calculate Building’s Surface to Volume Ratio
For the second custom node, I looked into known data we can obtain from the building Revit model (gross floor area, gross surface area, gross volume) and thought of potential metrics that could be useful. One important metric is the surface-to-volume ratio (SVR), which can measure a building’s compactness and heat efficiency. A lower SVR means a better energy efficiency due to less heat gain/loss per cubic foot of enclosed volume. For the custom node itself, it takes in gross surface area and gross volume and divides the two values to produce a single output. Although the calculation is simple, it is a crucial metric for the developer to know to understand the building’s energy performance and potential additional HVAC and lighting requirements.
Both custom nodes are called in a driver custom node called BuildingForm.EvaluateValueByFloorAreaForTwoInputs (the same one implemented in the lecture example). This custom node takes in all relevant inputs (parameters to test, parameters to report, costs and heights of the building) and returns a list of all output to be converted into Excel. Specifically, this custom node takes in all the inputs, unpacks the pairs of input values, set the input parameter values and update the Revit element, calls both of the custom evaluator nodes above, and returns a list of outputs.
The summary csv table showing the input value cases (combinations of top rotation and mid rotation both ranging from 0 to 140 degrees) and computed values (gross floor area, gross surface area, gross volume, cost per square feet, surface to volume ratio) is shown below.
Cost per square feet shows how the building’s overall cost and economic efficiency are impacted between building form alternatives. In this case, we can observe how the cost and gross floor areas are changed by adjusting the top and mid rotations of the building. Although in some testing cases the appearance of the building does not look very different, the cost per square feet drastically changes.
Surface-to-volume ratio captures the building’s thermal and energy performance. In this case, changing the rotation of the building affects how much surface is exposed to the outside air, which affects how much thermal energy can be gained/lost based on volume.
Point to Ponder: What other metrics would be useful to compute to help understand and make the case for which alternatives are truly better than others?
Some metrics I wish I could have more time to explore and implement are
- Solar potential for building surfaces: taking into account the geographical solar data and the building’s ability to take in solar energy can provide a more accurate overview of the building’s thermal efficiency and solar sustainbility performance.
- Line of Sight and Directness of Views: This is an important measurement of occupant experience and natural lighting of the building. An optimal balance between views and shading from the surrounding buildings can be achieved through Dynamo.
- Twist-angle vs. panels efficiency: Since the two parameters tested are both twists for my building, I believe tracking how increased twist affects the ratio of total panel area vs. gross floor area is important because it quantifies fabrication and installation, as well as providing a more detailed view of what type of panels will be required for each building form.