A major feature in cove.tool's arsenal is the Facade Guidance Tool for Daylight optimization. This feature allows users to rapidly prototype shading configurations for each orientation without requiring it to be modeled in a 3rd party platform, first.
The feature works best as the first step in a multi-step process. This rapid style analysis tool is key to testing dozens of strategies quickly and identifying where, when, and which strategy to carry forward in detailed model simulation such as the Full Floor Plate Daylight analysis.
This article covers how the facade guidance feature works, its relation to your full building geometry and energy results, and best practice tips on identifying the best facade configuration for your project.
How to get to the Facade Tool?
After starting a new project and entering geometry (manual or 3D model), a user can click on the facade button (window with overhang icon) to enter the facade tool. Each facade orientation (N,NE,E,SE,S,SW,W,NW) with glazing will create its own custom shoe-box model to begin with. This shoe-box model replicates your project's glazing percentage and sky domes. The façade guidance feature will calculate and display the sDA and ASE as the facade changes and new configurations are explored. To learn more about the technical assumptions for daylight calculation, check the section Determining sDA% at the end of this article. This tool also allows for control over the window sizes and placement, addition and customization of fins, overhangs, obstructions, and glazing's visual transmittance value. The interface and feature capabilities are broken down below. If you want to see the impact on your building's energy use (EUI), just make sure manual-mode is active and click the Save & Continue button. Energy results will appear on the Baseline page.
USING THE FACADE TOOL
- N, NE, E, SE, S, SW, W, NW Tabs: The Cardinal Direction tabs allow users to open and edit each facade configuration based on their orientation. Only facades that have glazing (As modeled in the Geometry page) will appear on the facade tool page.
- Daylight Model Viewer (3D Model): Users can use their mouse to move around the 3D analysis model, zoom in to see their overhang and fin strategy, and zoom out to see the resulting daylight map.
- WWR% (Window to Wall Ratio): This is auto-loaded based on your building geometry's glazing percentage. A user is able to modify glazing percentage, the shape and place of their window to test it's impact on daylight penetration and glare.
- sDA% (Spatial Daylight Autonomy): This is one of the most commonly used and robust metric for studying daylight (also used by LEED). It describes how much of the space receives sufficient daylight. This metric is calculated by measuring whether the space receives enough daylight (<300lux/50% year) during standard operating hours (8 a.m. to 6 p.m.) on an annual basis on the horizontal work plane (0.76 m (SI)/ 30 in (IP) above finished ground).
- ASE % (Annual Solar Exposure): This is one of the most commonly used and robust metric for studying Glare (also used by LEED) . This refers to the percentage of space that receives too much direct sunlight (1000 Lux or more for at least 250 occupied hours per year), which can cause glare or increased cooling loads.
- Visual Transmittance (VT%): Visible transmittance is the amount of light in the visible spectrum that passes through a glazing material.. This is a spec that can be typically found on the website of the glass product being utilized. Using the Visual Transmittance (VT%) slider, users can control the amount of daylight that passes through their windows. A higher VT% means more daylight penetrates the interior space which, can directly impact electric lighting and its associated cooling loads. NOTE: SHGC and U-Value for Glazing materials can be changed on the Baseline Energy Page.
- Overhangs (#of Overhangs and Depth): Using the Number of Overhangs slider, users can add up to 8 horizontal overhangs. With the Overhang depth slider users can specify their overhang's depth up to 2.5m (SI) / 6.5ft (IP).
- Fins (#of Fins and Depth): Using the Number of Fins slider, users can add up to 8 vertical fins per window. With the fin depth slider users can specify their fin's depth up to 2.5m (SI) / 6.5ft (IP).
- Daylight Diagram and Legend: Helpful graphics to interpret what is being shown.
- Add and Remove Windows (#of Windows): These two buttons allow users to add as many windows as they want, or remove all the glazing from their facade.
- Window Dimensions (Height and Depth): By using the height and depth sliders users can customize the size of their windows. Be sure to select the window first (highlight in red), then apply changes. The WWR (Window to Wall Ratio) should automatically update as you edit the size of the windows.
- Window Placement (Distance from Edge, and Window Sill): By moving these sliders, users can control the placement of their windows on each facade. To get an accurate sDA% make sure the sill height is accurately modeled in relation to the analysis grid. As a reminder, the facade guidance analysis model is an idealized analysis model that has scales the average strategy for the facade to fit a 8m x 2.7m (SI), 26.24ft x 8.85ft (IP) surface.
- Adding Obstructions (Distance and Height of Obstruction): User can model site context adding obstructions. Users can specify the distance from their facade the obstruction will be located and the obstruction's height. Height should be calculated by finding the average angle to the horizon, learn more about calculating height in the Context tab of the manual settings (gear icon) page.
- Gear Icon (manual settings): Users can continue to manually input their facade details in the manual facade and context tool. Once inside users can specify overhang, fin, and context details. Once complete users can return to the facade guidance model, too see their sDA% and WWR. Below is an overview of the manual input page.
Determining sDA% and ASE%: Assumptions and Methodologies
Cove.tool uses user-defined Envelope Geometry, the ASHRAE Standard 140, LEED v4 Reference Guide, and the IES LM-83 to determine the daylight calculations and methodology. See below to learn more about each facade analysis assumption and calculation method.
- Idealized Room Model: a recreation of the ASHRAE Standard 140 – Base Case 600 Model using the 5.1.2 Geometry Convention.
- Room dimensions: 6 × 8 × 2.7 m = 129.6 m3 (SI), 19.68 x 26.24 x 8.85 = 4570.16 ft3 (IP). Read as room depth x width x height = volume
- Analysis plane height: 0.76 m, or 30 inches above the floor
- Analysis grid size: 0.25 m2 (SI), 9.84 sq. in. (IP)
- Analysis period: 6am-8pm
- Meteorological year data: .epw from DOE, based on building location
- Glass transmittance: User-defined value, or 0.65 VT% (default)
- Surface reluctance: 0.2, or 20% reflectivity
- Illuminance threshold: 300 lux/50% year (sDA) & 1000lux/250hrs (ASE)
- Calculation Method: Taken from "LEED v4.0 - IEQ c7 Daylight, Option 1. Simulations: Spatial Daylight Autonomy" and "IES LM-83: Approved Method: IES Spatial Daylight Autonomy (sDA%) and Annual Sunlight Exposure (ASE)" with few modifications*.
- Rendering Tool: Ray-tracing for heat map visuals
- What are the benefits of using a facade guidance tool?
A well-designed day-lit building is crucial for occupant health and happiness, and also helps reduce energy use by lower electric lighting. Sufficient daylight has been shown to increase healing times in hospitals, improve students’ performance, increase productivity in the workplace, fight depression and lethargy, and even increase sales in retail environments. The facade guidance tool allows teams to explore a range of strategies before spending time to model it on the project 3D model.
- What is the margin of error between a High-level Facade Analysis (cove.tool's facade feature) vs. a Detailed Full-Building Model for Daylight ?
For Daylight, the average percent difference [of sDA or ASE] between an average shoe box and a whole building simulation is not an apple-to-apple comparison, since one looks at the whole building and the other, looks at just a sample shoe box room.
- Why is there a small room model, with fixed dimensions, and not my geometry?
The shoe box model is generated with reference of your building design. Collected from the geometry inputs, Window-to-Wall ratios (WWR%) of each cardinal direction are recorded and reconfigured for the small room models.
The facade guidance tool is a prototyping feature designed to save a user's time by providing the ability to quickly mock-up a facade 'idea' [using the overhangs, fins, obstructions, or window management sliders] and immediately generate feedback on the design's daylight (sDA and ASE) performance by orientation, and whole building EUI results. The dimensions of the small room, also known as the Base Case 600 model, comes from the ASHRAE Standard 140 – 5.1.2 Geometry Convention for Facade Analysis. The ASHRAE Standard 140 ("Standard Method of Test for Building Energy Simulation Computer Programs”) is the most-recognized, nationally accepted, and industry-approved software evaluation test. The Base Case 600 room is the foundation and benchmark of all US daylighting and energy simulation methodologies.
- My facade is very unique and the room model cannot recreate it, what should I do? The facade tool is an optional analysis, supplied among the many capabilities which are available to the cove.tool user. This analysis is higher-level and designed to provide a quick turn-over for teams seeking feedback on their shading strategies. The primary benefit of this tool is that it does not require the facade to be first modeled in Revit, SketchUp, or any other BIM Tool. However, If you already have the configuration modeled, and are seeking for a detailed 1:1 translation of your building conditions, users can utilize the Full Floor Plate Daylight Analysis. The whole building daylight simulation will accept any level of detailed modeling, but will only generate feedback for the information it has received via a 3rd party plugin.
If you would like additional modeling tips to recreate a specific configuration, try this reference table below. Angle fins and unique window shapes may not be directly possible in the facade tool, but there are ways to reconstruct the same impact with an equivalent strategy. If you have a strategy that is not included below, please contact the live-chat support team for further guidance. Also, check out this case study which used the facade tool to shading strategies.