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Vital Signs
Project: Phoenix Central Library
(Background) (Site Visits & Objectives) (Strategies &
Results) (Conclusion) (References)
After creating a reliable computer model of the library, we began to investigate our questions about the building. Our initial reason for choosing this building was that we doubted the effectiveness and appropriateness of the energy strategies. In particular, we wanted answers to the following questions: how much were the computer controlled louvers saving in energy consumption and how effective were the elaborate skylight systems at modulating light and heat? Even though this building is internal load dominated, due to the harsh climatic
situation the envelope has to be considered. During an un-structured interview with
maintenance staff we were told that the computer system for the louvers went down
approximately once a month. A fixed system of horizontal louvers would be more reliable
and could include light-shelves for more even light distribution. An accepted strategy for
the design of daylighting is to improve ambient light and to use artificial light for task
lighting. Another aspect of the lighting system, the blue-glazed skylights over the
columns in the reading room, provide a soft glow near the top of the room. However, due to
the 38 foot ceiling height, the light is mostly decorative, adding little to the ambient
light levels at floor level. Although the skylights are located above the book stacks, the
light fixtures directly above the books are turned on even in the middle of the day. One
simple way to reduce the need for lighting in the stacks would be to orient them
perpendicular to the windows, so that light could travel down the rows. As it is, the
first stack shades the ones behind it. The vertical sails on the north side of the building help control solar gain in the
early and late hours of the summer, when the sun rises and sets approximately fifteen
degrees north of the east-west line. Due to the extension of the buildings side-elements,
the "saddlebags", only a small portion of the north glazed wall is exposed to
direct gain. Acting as vertical fins, the translucent acrylic sails diffuse any direct
light as well as reflected light, which can be quite significant in desert climes. This
reduces glare, allowing visitors to enjoy the sweeping view. After this review of the system we chose several strategies that would help us
understand how the building would perform had different design decisions been made. We
looked at three alternative strategies, the first two: fixed shading on the south facade
and reduced solar access on the roof, focus on the envelope; the third deals with a zoned
evaporative cooling strategy.
When studying the south facade, we investigated the impact of replacing all the
computer controlled louvers on the South Facade with fixed overhangs. Currently the South
Facade is all glass, being made up of a double glazed window with external solar tracking
louvers. These operable louvers are an expensive, often unreliable mechanical system. Over
the last three months the louvers have been non-operational on a number of occassions, due
to a malfunction of either hardware or software. The initial computer model simulated the
effect of these louvers by admitting 100% of solar radiation through the months of October
to March, and 10% of solar radiation for the remainder. This 10% is due to the fact that
the louvers do not completely block sunlight, even when fully shut. This actually was a
very conservative figure, as light levels would be too low if 90% of daylight was
excluded. Predictably, the computer simulation results showed an overall increase of 2.7%
in space conditioning loads, with a 1.2% increase in cooling and a 4.7% decrease in
heating. The fixed overhangs were sized to omit solar access between March 21 and Sept 21.
The large fifth floor window was split into three vertical parts. It was obvious shading
was necessary due to the high amounts of solar radiation received on the South Facade.
Control of this radiation is of the utmost importance to preserve thermal comfort. But we
maintain that the system could have been much simpler. In addition to concern about solar gain from the south facade, there were questions
about alternatives for the skylights on the roof. We decided to experiment with removing
the twenty-two, 6' diameter skylights. These are the skylights that crown the columns of
the Great Reading Room. The glazing system for these skylights consists of two layers of
1/4" laminated glass, a pair of 1/4" layers of glass surrounding one 1/8"
layer of laminated glass that encloses a blue interlayer in which a 4" hole has been
cut. They are an architectural feature; at the Summer Solstice sunlight passes through the
clear opening and appears to “light” the candlestick columns. Removal of the
skylights decreased the energy consumption by only 0.57%. This was comprised of a 0.94%
increase in heating and a 1.7% decrease in cooling. Although these skylights have a
combined area of 622 sq. ft., this is not a large area in relation to the volume of the
building. The resistant construction and the blue tint of these skylights also combine to
minimize direct gain. This is one example of the trade-offs in working with issues of
energy conservation, daylighting and architectural aesthetics. Compromises are often made
in favor of form. Next we experimented with the two strip skylights, located against the East and West
walls. These skylights amount to an area of about 1260 sq. ft. They have been used to
maximum effect, allowing light to enter and wash the East and West concrete walls, and
they visually separate the roof from these walls, thus increasing the tensioned
roofs’ appearance of floating. These skylights allow direct solar gain to enter the
building. Removing them resulted in a 0.92% saving in energy consumption. There was a
1.19% increase in the heating component, offset by a 2.4% decrease in the cooling
component. The loss of these skylights would be to the detriment of the architecture, they
have a fundamental part to play in creating the effect in the Great Reading Room. The use
of a more controlled system, however, would be beneficial. Therefore in our next
investigation, we modeled vertical light monitors. By utilizing vertical glazing with a
12" overhang, greater control is achieved. Less light is admitted during the hot
summer days when the light is directly overhead. The softer light of morning and evening
will still be admitted as will light reflected off the roof. The aesthetic effect can be
maintained and there is a total 0.13% consumption saving compared to the existing case. The last strategy was the most radical concept we investigated. In library buildings
there is a zone containing the books that requires a carefully controlled humidity level,
and there is a zone containing areas such as rest rooms, meeting rooms and other
activities, requiring cooling, but not necessarily a low humidity level. In this strategy
the building was separated into two zones. The central “box” zone was air
conditioned as previously, the “saddlebags” were evaporatively cooled.
Evaporative cooling is a very energy-efficient way of cooling in a desert climate, due to
the extreme aridity. The “saddlebags” therefore are acting as a buffer for the
main air conditioned space. This strategy resulted in a 5.7% saving in energy consumption.
This was made up of an 11% reduction in consumption for cooling, and a 1.56% increase in
consumption for heating. |
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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 14: Library stacks with skylights above. (52K JPEG)
Figure 15: Fixed vertical sails as sunscreens on the library's north
elevation.
Figure 16: At the south facade, horizontal louvers are
computer controlled. 
Figure 17: An exterior view of one of the circular
skylights placed atop columns in the reading room.
