Daylighting study of a LEED platinum laboratory building: a post-occupancy evaluation comparing performance in use to design intent

Daylighting is a common goal for sustainability-focused projects looking to achieve energy efficiency and occupant comfort and well-being. However, it is less common to evaluate the outcomes of these designs once the building is constructed and occupied; there is currently no established feedback loop to inform designers which strategies are most and least effective in meeting daylighting goals. ❧ In 2010, a university laboratory building in Southern California underwent a major renovation, most noticeable of which was a retrofit of the façade. One of the major goals of the renovation was to design for maximum daylight utilization. The major strategies used for daylighting included the construction of a highly-glazed curtainwall and placement of the laboratories and office spaces at the perimeter of the building. The renovated building earned a LEED Platinum rating under LEED v2009. ❧ In order to evaluate the daylighting design outcomes in this laboratory building a methodology was employed that consisted of two major parts: physical data collection in laboratories and office spaces and occupant surveys. The data collection consisted of observation of interior shade positioning and usage, and measurements off illuminance, glare, and spectral power distribution. The survey of building occupants was completed in two ways. The first was through a repeated-measures survey which polled occupants about their visual comfort at defined intervals over a two-week period by means of a smartphone application. The second survey method was a traditional one-time survey which asked occupants about their satisfaction with daylight, glare, and views in their workspaces. Through these methods, five research questions were evaluated in three categories: ❧ 1) Façade: Does the achieved visible light transmittance (VLT) of the façade and components in use match what was intended by the designer? ❧ 2) Physical Light Properties: a. Are the horizontal daylight illuminance levels intended by the designer being achieved? b. Is there a high potential for glare discomfort? c. Is the spectral power distribution from daylight sufficient for human health and well-being, specifically in regards to melatonin suppression? ❧ 3) Human Comfort: What percentage of occupants are satisfied with daylight and views in their workspaces? ❧ The results found that the VLT of the façade is greatly reduced from the intended design due to high occlusion by interior shades. The illuminance in the laboratories only met the intended design levels in the morning hours. Glare (measured by daylight glare probability) was effectively mitigated in most of the measured areas of the building. Despite reduced daylight penetration caused by interior shades, spectral power distribution was sufficient for adequate melatonin suppression in most measured areas. Occupant satisfaction with daylight was 79% in offices and 85% in laboratories, although a number of occupants also reported that daylight levels were low, but not low enough to cause discomfort. Occupant satisfaction with views was only 25% in offices and 63% in laboratories, likely due to the high occlusion of the façade by the interior shades. ❧ Most of the results are a product of shades usage of lack thereof. The effectiveness of the building’s daylighting design is heavily dependent upon an adaptive building. In the case, the ability of the building to adapt to the daylight conditions is dependent upon the occupants to adjust interior shades and artificial lighting. Optimal adjustment of the indoor environment by the occupants is not occurring, meaning that the building is not meeting its full daylighting potential.