SDA 2. Overview of sDA Calculation

The sDA metric scores a space’s daylighting in conjunction with manual blind operation in a two-step simulation process, which we will briefly outline in this blog post and go over in more detail in following posts. The first determines the position of the blinds (whether they are open or closed) and the second measures daylight levels with the corresponding position of the blinds.

Blind positions are determined by how much direct sun gets into the windows. When a space receives too much direct sun, blinds close in groups until the amount is sufficiently decreased (Step 1).

sdaSouthFacing

Step 1. Blind Operations: Blinds, either electronically or manually controlled, contribute greatly to the quality and quantity of light. In the figure above, we see that as the sun’s position changes, different groups of blinds are used to maintain visual comfort in the space. Facades that use dynamic glass or redirect film to control for direct sun do not need blinds.

Realistic illuminance for the space is then calculated using a simulation of the blinds in their determined position from step 1 for each hour of the day. The sDA score is calculated using a formula that takes these raw illuminance values as input (Step 2). The score is the percent of points on the grid that meet the minimum thresholds.

SDAFullGrid1

Step 2. Scoring: Annual metrics like sDA determine the level of illumination at each point and at each hour after the blinds are in position., these metrics take thousands of time points of illuminance data comprising potentially millions of light readings and thousands of blind positions and compact them into a single value.

In the next several parts of the sDA series, we will cover blind operations and scoring in detail.

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