Because of efficient fixtures, photosensors that turn off unneeded lights, and increased daylighting, Chatterjee was able to document a drop in the lighting power density (LPD, or watts per square foot) from 1.11, on par with a minimally code-compliant building, down to 0.86. While the electricity consumed went down, the quality of light went up.

A CFD analysis enabled Syska Hennessy Group to recommend a slotted lightshelf that would improve distribution of both air and daylight. Images courtesy Syska Hennessy Group

 

Chatterjee used Lawrence Berkeley National Laboratory's program Window to obtain data for the overall glazing system. "Manufacturers usually just provide a U-value and solar heat-gain coefficient (SHGC) for glass," Chatterjee explains. "We run that together with the frame type to get the overall U-value. Output from Window went into eQUEST."

Then, based on solar-radiation and cloud-cover information from historical weather data for Oakland, eQUEST calculated the amount of daylight the building would receive and lowered the predicted lighting energy use accordingly. Chatterjee notes "There's a lot of interaction between daylighting and electrical lighting, and it affects the loads and the mechanical system. It's all connected."

The choice of mechanical system was influenced by the super insulated shell. They chose a packaged rooftop variable air-volume (VAV) unit with a gas furnace and no reheat. "No reheat is unusual in California," Chatterjee points out. "We put more insulation in the walls, so the perimeter areas wouldn't need the reheat. That's where we think the energy conservation lies." The mechanical system was also less expensive than a conventional one would have been, and it supports natural ventilation when conditions permit. Calculations predict the building will outperform Title 24−2005, California's already stringent energy code, by 40 percent.