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Solar Angle Impact on High-Rise Buildings
The sun is the life force of this planet. Without it the planet would
not be here, or exist in it’s current form in many different relationships
between the two. This essay looks to examine the affects on a building by
the sun, and the strategies used in High-Rises to deal with those affects.
The advantages to considering the sun are many and important.
Sustainable design demands that the sun be considered and dealt with.
Many of the strategies in dealing with the sun are free, such as the
orientation of the building.
It plays a role in site usage, as well as skin
development. The success of the building can not be without dealing with
the effects of the sun. z
Man learned long ago the effects of the sun on the built environment.
The Romans employed various techniques the most famous of which is
perhaps the velarium on the Coliseum. This was a retractable awning that
shaded the masses from the sun.
sun completely is the goal.
That is not to say that blocking out the
Day lighting is important too.
The industrial
revolution saw the most horrible of conditions in the slums, talked about
by the likes of Engels of English cities.
The overcrowding in the slums
made it so that ventilation, both of light and air, were impossible.
positive
effects
of
the
sun
on
a
person’s
psychology
are
not
The
to be
underestimated. People will actually become sick if they are in absence of
the sun for too long. All of these things by the time the twentieth century
came about had been perfected and honed by the architect.
When researching the sun and different ways to deal with it, some
questions came up, especially in regards to the Three Arts program and site.
The first is that there is an inherent conflict between the view to the west
and the sun’s properties when in the west.
One wants the building to be
open and transparent towards the south, the other wants the exact opposite.
How will that be worked out? Also, when dealing with the sun, I learned
that the south façade wants to be the smallest to minimize building
exposure from that direction, at least in the Northern Hemisphere. The site,
however, wants the longest façade to be on the north and south.
That is
another polar conflict where the solution is unclear. These questions seem
to me to be a source of ponderance and perhaps frustration.
Other things
that I noticed was that most concepts that have been shown by the class
seem to do little for shading of the public area in between One and Three
Arts.
Also, no one as addressed the south façade in the orientation of the
building. These are things that should be considered!
The first thing I think about is one of the most amazing examples of
sustainable design in a building, let alone a high-rise.
Lake Flato
designed the Health Science Center for the University of Texas in Houston.
This case study is excellent to look at for much more than strategies for the
sun, it provides an excellent president on how to reduce heated and cooled
space, how to condition the space that must, and how to reuse materials, or
use materials with a low financial and environmental cost.
Most of the
strategies I will discuss will come directly from this president study.
The
information about this building I’ve learned both from direct observation
and from a lecture by one of the architects of the building.
The first thing to design is the building’s orientation.
This is the
easiest to do in that it’s free. It won’t cost anymore to place a building this
way or than on a site…usually.
The sun, in the Northern Hemisphere, is
always to the south of the building, except during the very early morning
and very late evening during and around a solstice. The south façade, as a
general rule of thumb, should be the shortest in dimension.
warm climates.
This is for
In cold climates, like Canada, exposure to the south is
desirable, as heating is a concern for most of the year.
In the Southern
Hemisphere, the directions are opposite. North is the worst sun, and people
in places like Australia want to avoid the northern sun as much as
possible.
As in our site, The UT HSC had a site that wanted the long
dimension to be on the southward side.
The
second
thing
that is important in sun
mediation
is
day
lighting. For many years
buildings have kept to a
certain depth of 25’ per
side,
with
a
general
maximum of 50’.
is
because,
This
especially
before electric lighting,
that was as deep as the daylight would go in a normal height room. While
electric lighting has changed that as an absolute necessity, having natural
day lighting is still extremely important. Besides the psychological benefits
of day lighting, it can save money as well.
This is even more true in a
high-rise office building where the day use far exceeds the night use. By
reducing the amount of lights needed to illuminate a space, the energy that
it would take to power the lights as well as the energy it took to remove the
extra heat introduced by the unneeded lights is saved. This need conflicts,
however, with the next obstacle the sun provides. One way to increase the
day lighting in a building is through a skylight, especially in conjunction
with an atrium.
In warm climates, such as Dallas, blocking the sun becomes a smart
idea to save on heat gain during the day. There are several strategies, and
each cardinal direction should be treated differently. Lake Flato used light
shelves on the south of the HSC.
These are shading devices that protrude
out a few feet, two per floor, and light is reflected and diffused before
hitting the glass, reducing the radiated heating but maintaining a usable,
desirable day lighting standard.
The East used window shaders that
blocked the sun from about 9am on.
The west façade used a strategy that
will prove useless for most for Three Arts. They used an asymmetrical core,
placed on the west side of the building, and put exterior vertical
circulation on the west façade.
This easily acted as a barrier because the
late evening sun hit little window, and had to go through a shading device
enclosed stair well before it reached the window.
On the north, vertical
sails were used so that the early morning sun or late evening sun during
the solstices would not produce any heat gain on that façade.
In the
skylight above the atrium, the firm implemented light diffusers on the
exterior and interior of the glass, so that the skylight overall saved the
building’s cost on money and energy due to the reduced need for lighting.
Other ways to block the sun from hitting the building is through the use of
roof gardens. They will absorb light, and prevent most sun from hitting the
roof, as well as create great spaces for the building’s users. Buildings can be
used in positioning the building to block the sunlight during certain times
of the day, such as One Arts relation to the site of Three Arts. One Arts will
largely block the western sun on the first 30 floors of Three Arts.
Second
skins are also great ways to block the radiating effects of the sun.
Lastly,
photovoltaics can be used in the place of shaders, as is discussed in the
Energy Production paper.
The presidents of the UT HSC, as well as the other strategies are us for
consideration of possible strategies for the Three Arts building. The Winter
solstice occurs on Dec 21. At noon on
this day, the angle of the sun above
the
horizon
approximately
September
or
in
35
Dallas
degrees.
March
is
On
21,
the
equinoxes, at noon, the sun’s angle
above
the
horizon
is
55
degrees.
Finally on June 21 at noon, the sun’s
angle is 80 degrees. The relationship
between
these
three
angles
is
important. The summer solstice has a
much higher angle than the winter
solstice or either of the equinoxes. By
providing a shader that blocks the sun during the warm part of the year,
but allows it to hit the façade during the cool part of the year, heat gain
can be optimized for both extremes. Since Dallas is warm for the most part
of the year, the sun should be blocked for most of the year.
In more even
climates, like Lubbock, the time of year blocked should be less because it
gets cooler sooner and warmer later. A ratio between Depth: Height can be
established for a place. Dallas, by drawing a diagram, has a ratio of 7:10.
That means for every ten feet of building height, a seven foot shader should
be provided.
Each number increases as the other.
For a typical building
height of 15 feet, a 10.5 foot shading device should be at the slab of each
floor.
This is an extreme height to cantilever out, however, so it is
recommended that smaller heights be used, like a five foot module.
This
would allow the 15 feet to be divided into three equal parts, and the
shading devices would only be 3.5 feet deep, which for a high-rise is not
unusual at all.
References:
Abley, Ian; and James Heartfield.
Sustaining Architecture in the Anti-
Machine Age. Wiley-Academy, New York. 2001. 164-169.
Humm, Othmar; and Peter Toggweiler.
Photovoltaics in Architecture.
Birkhäuser Verlag, Boston. 1993.
Jones, David Lloyd.
Architecture and the Environment: Bioclimatic
Building Design. The Overlook Press, New York. 1998.
Stitt, Fred A. Ecological Design Handbook. McGraw-Hill, New York. 1999.
91-164.
Thomas, Rendall, ed.
Urban
Sustainable
Design:
Environmental
An
Approach.
Spon Press, New York.
46-88.
2003.