As has been mentioned in a number of previous posts we recently renovated our office here in Seattle. Over the next few weeks we will be highlighting some of the more interesting aspects of the renovation, beginning with our use of daylighting to achieve better overall lighting quality and energy reduction. LMN’s offices are housed on the 4th and 5th floor of the Norton Building, a 1950’s International Style tower designed by SOM, in downtown Seattle. The building is blessed with ample glazing and narrow floor plates, but that also provides some significant challenges.
As part of the initial discovery process for the renovation we interviewed and surveyed the staff on a wealth of different topics. One of the most obvious outcomes of that effort was an almost universal desire for improved lighting quality and control. This led to a concerted effort,early in the design process, to prioritize the use and control of both our artificial light sources and daylighting. On top of the functional benefits we were also set a goal of 60% lighting energy reduction.
The initial daylighting simulations were done with Diva and focused on Useful Daylight Illuminance. The first false color image below shows the UDI without a light shelf the second with a light shelf. To see the full results of the simulations see the downloadable white paper at the bottom of this post.
The immediate realization from these studies was that the light shelf was offering benefit in shading at the perimeter and reducing glare. To augment these virtual simulations we created a real world mock-up incorporating a roller shade and a light sensor to control its movement.
The mock-up was helpful in a number of ways. The shelf at certain heights, within the zone we were considering, blocked a significant portion of the view. It was much more obstructive than we had anticipated. The sensor controlling the shade movement was a switch that was activated when the lighting level reached a certain threshold. Though this did the job, the constant reaction to light level changes was distracting (for more on the fabrication of the mock-up see this earlier blog post.) We realized that a more complex control system was needed if we were to go this route. The observed reflected light and shading followed the simulations very closely.
Our findings from these studies showed that given the narrow floor plate of our building the increased light penetration typical of a light shelf was not a demonstrable improvement. Where the light shelf did provide benefit was in shading at the perimeter which helped to reduce glare and increase UDI by 12.5%. This finding was not altogether a surprise but it did help to solidify our final approach.
Since the light shelf obscured the view and was only giving us benefit in shading we decided to pull the worksurfaces away from the perimeter where the glare was the worst and to implement a sophisticated automatic shading system from Lutron without a light shelf. This allowed us very fine grained control of the natural light coming into the space while preserving uninterrupted views. The system is also tied to our artificial lighting controls so the two systems work in concert to save energy while keeping lighting levels constant.
Since commissioning the lights we are now achieving a lighting power density of .55 watts/square foot vs. our initial 1.3 watts/square foot, a total reduction of 58%. We are still tweaking some settings and working out some kinks and believe that the target of 60% is well within reach. We have also taken light measurements throughout the office in varying day lighting conditions from dark to clear skies, and are achieving consistent target light levels throughout. Finally, we took a post occupancy survey and it shows overwhelming approval of the new lighting control system and the general quality of the lighting, which is very important because quantitative data and occupant perception do not always correlate.
The next blog post will follow up on the occupancy comfort sensor deployment now that we are moved in. Stay tuned…
Please find below a more detailed whitepaper including the initial interviews, survey, and post occupancy survey.