Night and Day when it comes to Daylighting for LEED 2009
Posted: August 3, 2009 by Suzanne, Category:Building Regulations
Reviewing the new Green Building Design and Construction LEED Reference Guide (aka LEED 2009) I found it ‘interesting’ how EQc8.1 Daylight 75% of Spaces has been revamped. I’ve entered the arena of air quotes as I’m torn on whether this latest change will benefit the industry or create a roadblock. First, though, some context:
Back in the day when it was just LEED-NC (New Construction), there were three main options for meeting the requirements for EQc8.1, Daylight 75% of Spaces:
Option 1: Glazing Factor Calculations
Option 2: Daylight Simulation Model
Option 3: Daylight Measurement
I would hazard a guess that the majority of projects pursued Option 1. Although not so simple, it was still a glorified excel spreadsheet that you filled out, room by room, using the long equation provided that incorporated room and window areas, window properties and locations. It was something simple enough that anyone could learn.
However, I remember one lab building I worked on where we ended up trying out all three options. The daylight simulation (Option 2) and field measurement (Option 3) results were relatively similar but the glazing factor calculations (Option 1) was that strange outlier that started to reveal the gross limitations that occur when reducing a dynamic situation such as daylighting into a linear equation with only a few variables.
Then came along LEED-CS (Core and Shell) and a fourth option was added, geared mainly for the generic office building that would use the rating system – simple rectangular floor plate with a central core:
Option 4: Prescriptive
This was the simplest calculation that replicated the good old rule of thumb used in bygone days – i.e. for a building with floor depth X you need Y for window area.
Now fast forward to today and LEED 2009. There are really just three main options: Options 2 - 4 listed above. Say goodbye to the glazing factor calculations (Option 1). If you consider most buildings are not simple rectangles and project owners don’t want to gamble and wait to see if they qualify for the daylight credit, you’re really just left with one option – daylight simulation model.
For a public comfortable with a simple spreadsheet to show compliance, the thought of using a computer model is, well, like night and day. Most will initially think of daylight modeling as something outside their ability. The good news is that this isn’t the case. We’ve been seeing an increase in engagement with daylighting software to inform design, especially in the architectural field – be it through purchasing IES software to use directly or subbing it out and using our consultancy services.
Will this be seen as moving LEED away from streamlining and simplifying the process? Or will it be perceived as encouraging a more informed and iterative design process? One conclusion we can all agree on is that at least it’s one less long equation to memorize when studying for the AP exam!
