Page 26 - Designing for Zero Carbon - Case Studies of All-Electric Buildings

CASE STUDY NO. 1
SANTA MONICA CITY HALL EAST
(Right) View of new City Hall East building from the south, with the curtain wall visible on the south and east elevations (Photo: Randall Howard)
Building Envelope
The City’s Landmarks Committee had ruled that the new addition was required to be strongly differentiated from the historic City Hall through the choice of material for the building’s enve- lope. The Committee approved the proposal for an all-glass curtain wall, which provided both the desired strong architectural contrast as well as some reflective characteristics of the historic facades within the enclosed green space. This choice of building envelope material, however, created design issues related to energy performance. The issues are control of solar heat gain, insulating value and daylighting.
The “plain glass box” design concept required the absence of exterior sun shading devices of any kind. Given the roughly east-west orientation of the building, exterior shading design would have been challenging and expensive. The result is that these three design issues are neces- sarily addressed entirely by the curtain wall characteristics, which are optimized to reduce the energy loads caused by the building envelope. (See the typical wall section in the figure on the opposite page.)
The design team chose an advanced type of glass6 with a neutral-silver appearance, incorporat- ing it into a double-glazed curtain wall system. The modern glass coating provides high daylight transmission with a low solar heat gain factor. A variable frit pattern is applied to the glass to further reduce the solar heat gain and to eliminate the visual glare produced at the interior space by the direct sun incident on the curtain wall. The frit pattern is minimal (30%) when the glass is in the optimal location for daylighting (above desk height) and maximum density (80%) when the glass is not in a vision-outward location. (See the typical curtain wall elevation with frit patterns on page 14.)
The building envelope does not have a low U-value since it is almost entirely glass curtain wall, but the building utilizes other energy efficient design strategies as described in the following sec- tions to achieve zero-net-energy performance.
6 Viracon low-iron glass with VN-53 coating for both high visible light transmission and low solar heat gain factor. The base specification is Solar Heat Gain Coefficient = 0.23, Summer U-Value = 0.25, Visible Light Transmittance (VLT) = 52%.
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Designing for Zero Carbon: Volume 1