This design is one of the first zero-net-energy (ZNE) public libraries in the U.S. The building minimizes its energy loads through extensive daylighting throughout, natural ventilation with night purging and a radiant floor slab for both heating and cooling. The building was modeled at a low energy load of 20 Btu/sf per year (EUI = 20), which is offset completely by the 50 kW renewable energy system of 120 435-watt solar photovoltaic panels, a solar thermal system for the hydronic heating and an air-air heat pump for the solar thermal backup and the small amount of cooling required in late summer peak weather events.
The principal low-energy design feature is also the most dramatic architecturally: large angled light-diffusing panels spanning the main space provide glare-free daylight throughout the year from the rows of skylight arrays on the roof. The limited roof area available in the tight urban site required careful balancing and optimization of solar harvesting by the photovoltaic arrays for power and the skylight system for daylighting the spaces below. Daylight analysis provided information for adjusting the large ceiling panel geometry to ensure continuously adequate light levels for browsing and reading across the space.
All spaces are passively ventilated for fresh air and cooling most of the year using the “ventilation chimney” feature. CFD analysis (computational fluid dynamics) confirmed the performance of this natural drafting effect for the prevailing breeze directions at the site.
The client for this project, Berkeley Public Library and the City of Berkeley, did not initially request or consider a ZNE design, but A/E team leader Edward Dean convinced them that this could be achieved through good design within the parameters established for the project, including the fixed cost budget determined as part of a public bond measure. The design successfully incorporates the cost of the photovoltaic system within the project budget of $5.5 million.
The building was opened to the public in December, 2013, with much celebration of the deep green design and the initial post-occupancy commissioning is underway. With power meters and flow meters in place, the data collection to verify the ZNE performance will start once the basic commissioning is completed.