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Vital Signs
Project: Phoenix Central Library
Rising like a copper clad mesa, from out of the desert, the new Phoenix Central Library
is an imposing sight. This building was inspired by the awesome forms of Monument Valley.
Designed by Will Bruder, in collaboration with DWL Architects, it opened in May 1995.
Since its completion, this building has been receiving widespread acclaim for its
architectural style, and its energy efficiency. Currently 2500 people visit this
impressive facility every day. Designed to accomodate over one million volumes, this
library is double the size of the one it is replacing. The Great Reading Room, comprising
the whole fifth floor, is the largest room of its type in the nation. We chose this
building as the focus of our case study, because of its significance as a major new
building in Arizona, and because of its reputation for energy efficiency. The
concentration of our study was the conflict between the choice of elements for
architectural effect, and the solar requirements to maintain thermal comfort in the harsh
Phoenix climate. Our feeling was that this building was sculpted as a "box in the
Desert", and then had a complex solar control system applied to it. Fixed shading
devices and passive strategies would offer simplicity as well as similar results. Thus, we
have attempted to analyze the consequences of the architectural decisions made in this new
library. The Climate Located in the southwestern United States, in Phoenix, Arizona, this building
experiences the harsh climate of the Sonoran Desert. Summers are very hot and dry, while
winters are typically mild. Southern Arizona has the clearest skies in the U.S., receiving
over 85% of annual possible solar radiation. The clear skies and intense sun result in
extreme summer temperatures. The summer period begins in mid-April and continues into
September. In June, July and August the average daily temperature is over 100 degrees
Fahrenheit, but can reach as high as 120 degrees. Consequently, cooling is a concern for
over half the year. Extreme aridity is also characteristic of the desert, with the
introduction of humidity often being a welcome cooling strategy. The cold season lasts
between November and March. Average winter temperatures range from highs of 50-65 degrees,
to lows in the 30's. January and February are the coldest months, in which heating becomes
necessary. Due to the internal load domination in commercial and public buildings, cooling loads
may extend into other times of the year, even when outside temperatures are considered
comfortable. The priority, therefore, is to moderate the summer temperatures and control
solar radiation gain and interior sources of heat. The envelope is still important even in
an internal load dominated building; the building materials act as the buffer between the
natural and the man-made environment. The Building The building is composed of two main parts, a central section, or "box", which contains the library’s public spaces, culminating in the Great Reading Room on the fifth floor, and the “saddlebags”, which contain the service zones, mechanical equipment, some offices, group meeting rooms and the restrooms. The "box" has glazed facades to the North and South, and the East and West
walls are 12 inch thick precast concrete. The "saddlebags" are clad in
perforated copper sheeting and are steel framed and insulated where the adjacent space is
occupied. The structure consists of a central precast concrete box, with steel framed
"saddlebags" to the East and West. The suspended floors are precast T stems and
beams supported on precast columns. The impressive tensile roof structure of the Great
Reading Room was designed by Ove Arup & Partners. Steel caps bolted to the tapered
columns anchor tensile cables that support the steel struts, that then support the roof.
The "saddlebag" roofs are of a more conventional steel framed structure. The
roof over the second floor extension is a concrete deck. The most visible cladding
material is the perforated copper cladding used on the "saddlebags". The entries
are defined by a strip of stainless steel cladding. The precast concrete walls are unclad.
The "saddlebags" provide the lateral bracing for the structure. The mechanical equipment is state of the art. The chillers are two 400 ton gas fired
absorption chillers, that use bromide lithium salts to chill the water. This machinery was
chosen because the project receives a significant reduction on the purchase of gas. The
chillers are connected to two 600 ton cooling towers. There are four air handling units
per floor with the air movement being controlled via computer and v.a.v.'s (variable air
volume units), depending on the cooling requirements of the specific area. Heating in the
building is supplied by coil heaters located against the glass facades. Computers control all the mechanical solar protection devices, including the South
facade louvers, and the atrium skylight louvers. In the Great Reading Room, daylighting
has been used for dramatic effect. This room is a colossal 38 foot high space, and covers
the entire fifth floor. Twenty two circular skylights crown each of the candlestick
columns, and at the Summer Solstice, light penetrated and "lights" these
columns. There are also 2'6" wide strip skylights between the roof and the East and
West walls, which give the tensioned roof the appearance of floating. |
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Comments to
author: vitalsigns@ All contents copyright (C) 1998. Vital Signs Project. All rights reserved. Created: 03/19/96 |
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Figure 3: A diagram of the structure of the library shows
the main "box" with "saddlebag" at right.
Figure 4: An air handling unit at Phoenix Central Library.
There are four units on each floor.
Figure
5: A view to the exterior through the operable louvers in the library's reading room.
