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By Robert S. Ross Ph.D.
Originally published in Properties,
November 2002
Young engineers in training are told that a good
engineer can improve any product.
This is true, but the cost for the improvement may
not be worth it.
This can be compared to squeezing an orange. The
first squeeze of a new orange yields much juice. The
second squeeze is harder and yields less and it
finally gets to the point that the effort is not
worth the result.
There is a way to break this typical cycle, which
consists of looking at a different technology.
A good example of this is the combining of the
movement of a Swiss watch with an electronic timing
system to produce the current low cost wrist watches
with clock faces and fantastic accuracy.
In developing the esi system, GOODYEAR combined tire
technology with aerospace technology to produce a
structural concept that contributes much to the
construction field. Original tire technology
contained air in a “tube” and the structure was
a high strength “casing”. In this “pressure
stabilized cable structure” GOODYEAR developed,
steel cables in the seams of the film or fabric
carry the design loads. This means the air container
is not under load and can be a wide variety of
materials, temporary to long-life, window-clear to
opaque. The structure size, therefore, can be as
wide as a cable can span and being modular in
concept, it can be any length.
As a new structural concept, it opened the doors to
many applications. One of the first was a giant
greenhouse. Previous air supported structures merely
simulated rooms, which were dark and only used
sufficient air to support them. The greenhouse
required high ventilation, uniform temperature and
all the sunlight it could get.
With the structure utilizing cables spaced about
every 5 feet, standard width for vinyl rolls, and
the air at a low pressure, no obstructions from
interior columns, a maximum amount of sunlight was
available depending on the clarity of the vinyl.
This essentially simulated the outdoors. For
greenhouses, it was found that a ventilation rate of
about an air change a minute was require, about 10
times what one normally considers, in “people”
buildings.
This was obtained economically by using propeller
fans, which operate at very low pressures. Studies
showed that most of the time that was adequate for
normal structural requirements. Storm conditions
required higher pressures, so at those times, two
fans in tandem were used. This increased the
pressure without increasing the volume, and is
essentially what happens in a jet engine where
multiple fans are used in tandem. To operate
efficiently, air was brought in on one side and
exhausted on the other and the internal pressure was
automatically adjusted according to the wind
velocity. Once this was accomplished, the outdoors
was essentially simulated with its sunshine and
fresh air, but without the wind, rain and snow. This
concept was then applied to a variety of
applications.
Early clear vinyls were only good for about a year
before they started to get brown and brittle like
the old rear windows of convertibles. However, esi,
working with DuPont developed a material they
trademarked “ESIFILM,” which raised the expected
life to 15-20 years. Since the new materials are
polymers, a new and growing field, further increases
in life span can be expected with continued
developments. A roof made using this system, in many
cases, can be changed in a day.
Since 1971, when esi was formed, this concept has
been used in over 30 different kinds of applications
in 26 states and nine foreign countries. Each was
custom designed to fit the requirements, showing
that the concept is merely a tool for architects to
apply wherever it proves beneficial.
Typical examples in the Cleveland area are a
temporary enclosure for a pool at the CLUB ULTIMATE
in Eastlake and an electronics laboratory in
Middlefield. The pool cover is made of woven poly,
which is light in weight and is easily installed for
winder operations. Being highly translucent, it
gives the pool an “outdoor” environment. The
laboratory, built in 1995, used ESIFILM: and as a
result part of the floor was planted with geraniums
and the structure was even used once for a wedding
reception.
Over recent years, conventional construction with
its high insulation and tight construction
requirements has become so effective that it is now
causing problems. The most energy efficient
structures are windowless, air tight and
conditioned. To make the structures more people
friendly, giant atriums of glass are being added.
Recirculating the conditioned air in many cases is
causing sickness due to the emissions from the
carpets and furniture that cannot get out.
Ventilation is needed. Older buildings “leaked”
so much that they were automating ventilated by
infiltration. The added sunlight of the atriums is
welcome, but the extra initial and continued
maintenance costs are not.
In many cases, the esi concept of simulating the
outdoors with its fresh air and sunlight and use of
self-cleaning maintenance-free materials, can be
attractive. Applying this concept is not a cure-all
for every situation. For instance, in small sizes it
may not be economical. As clear spans increase,
conventional construction goes up in cost per square
foot, while esi costs stay relatively constant.
Applying this concept to large structures brings
lots of improvements, while lowering costs. The
“outdoor” environment makes it more pleasant to
be “inside” regardless of the weather. Operating
costs, as well as initial costs, are reduced by
utilizing solar benefits. Comfort is enhanced and
interior landscaping is possible.
In sports facilities, like a stadium, natural grass
playing fields are a reality. There are no “rain
out days”, with ideal weather inside at all times.
If desired, a shadow-free cover material is used.
Architects with vision love it, because it gives
them a proven new tool that opens doors to giant
structures never before considered practical.
It has been used as stand alone structures or as a
roof combined with conventional construction; as a
greenhouse, construction site cover, remedial
clean-up enclosure, child care center, factory,
warehouse, laboratory, multipurpose room, indoor
sports complex with natural grass playing field,
etc. and is being considered for enclosing an entire
18 hold golf course in Canada, a world’s first!
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