In March 2001, the Eden
Project, a massive environmental center in Cornwall,
England, opened to the general public. The finished structure
is an unprecedented accomplishment -- a giant, multi-domed
greenhouse, containing plants from around the globe. The site
has already become a popular tourist destination, attracting
thousands of visitors every day.
Photo courtesy Apex
Photo Agency, Photographer Simon
Burt The large, connected
dome structures that house the Eden Project's many
plants and
exhibits
In this edition of HowStuffWorks,
we'll see how (and why) Eden's creators undertook such an
elaborate enterprise. We'll also explore the general concept
of a greenhouse, as well as the particular structures used in
Eden. Finally, we'll find out what the Eden team has in store
for the future.
What is the Eden Project? The Eden Project
is a sprawling structure built along the side of a deep pit.
The structure comprises three biomes, areas designed to
represent three distinct climates found around the world.
The Humid Tropics Biome, the most impressive
section, is a multi-domed greenhouse that recreates the
natural environment of a tropical
rainforest. The warm, humid enclosure houses hundreds of
trees and other plants from rainforests in South America,
Africa, Asia and Australia. The dome is 787 feet (240 m) long,
180 ft (55 m) high and measures 360 ft (110 m) across at its
widest point.
Photo courtesy Apex
Photo Agency, Photographer Simon
Burt An inside view of the
Humid Tropics Biome, the centerpiece of the Eden
Project
From the Humid Tropics Biome, visitors move on to the
Warm Temperate Biome. The Warm Temperate Biome, which
has the same multi-domed structure as the Humid Tropics Biome,
houses plants from temperate rainforests around the
world. Like tropical rainforests, temperate rainforests
receive a high volume of rain every year, making them an ideal
environment for varied plant life. But since they are farther
away from the equator than tropical rainforests, they do
experience distinct seasons (see How
Rainforests Work for details). The Warm Temperate Biome at
the Eden Project has varied plant life from temperate
rainforests in Southern Africa, the Mediterranean and
California.
The final stop in the Eden Project is the Roofless
Biome, an open area with varied plant life from the
temperate Cornwall area, as well as similar climates in Chile,
the Himalayas, Asia and Australia. Visitors can learn about
plants that have played an important role in human history by
following nature trails that wind over 30 acres (12 hectares)
of land.
The creators of the Eden Project see the site as far more
than a collection of greenhouses. Their mission statement is
to "promote the understanding and responsible management of
the vital relationship between plants, people and resources,
leading towards a sustainable future for all.” To this end,
they have included informational kiosks and artistic
installations throughout the biomes. They also hold a number
of workshops and special events, all designed to inform people
about environmental issues. To learn more about the Eden
Project's mission, as well as its upcoming activities, check
out the Eden
Project Web site.
From a technical viewpoint, the most amazing thing about
the Eden Project is its giant greenhouses. In the next few
sections, we'll find out how these monumental structures work
and how they were built.
Greenhouse Basics To understand how the Eden
Project's super greenhouses work, you first have to understand
the fundamental concept of a greenhouse. The most basic
greenhouse would be a simple box made out of solid,
transparent material, such as glass or clear plastic. When
sunlight shines through the transparent walls of the
greenhouse, it heats the material inside. Let's consider how
this works in a greenhouse with a dirt-covered floor.
Click on the button to see how a greenhouse heats
up.
Radiation energy from sunlight heats up the greenhouse
floor. The floor releases some of this thermal energy, which
heats the layer of air at the bottom of the greenhouse. Warmer
air is lighter than cooler air (that is, it has a lower
density), so the heated air rises to the top of the
greenhouse. When the heated air rises, cooler air replaces it
at the bottom of the greenhouse. This air becomes heated by
the floor and also begins to rise.
This process is going on in our atmosphere all the time.
When the sun shines on an area, it heats the ground, which
heats the air above it. The heated air rises through the
atmosphere, cooling down as it moves upward. This is why air
near the ground is warmer than air higher up -- the air near
the ground hasn't had as much time to cool.
Photo courtesy Apex
Photo Agency, Photographer Simon
Burt The giant dome structure
of Eden's greenhouse roof dwarfs a worker installing the
transparent
panels.
Then what makes the air in a greenhouse hotter than the
atmosphere outside? Simply put, there is a smaller quantity of
air that needs to be heated inside a greenhouse. In the
Earth's atmosphere, there is a mass of air that extends more
than a mile (1.6 km) above the ground (at most points). Even
giant greenhouses like the ones in the Eden Project contain
only a tiny fraction of this air mass. The greenhouse floor
can heat its smaller volume of air much more efficiently than
the ground outside can heat all of the air contained in the
Earth's atmosphere.
The heated air in a greenhouse rises to the ceiling, is
replaced by even warmer air and gradually sinks back to the
floor. The circulation path is short enough that the sinking
air is still relatively warm when it reaches the floor, and so
can be heated to an even higher temperature than before. The
ground and air absorb enough heat during the day to keep the
greenhouse relatively warm all night.
This is the basic idea behind any greenhouse, no matter its
size. Most greenhouses function as a controllable environment
for plant life. The plants get all the sunlight they need to
survive, but they are not fully exposed to the natural
elements.
Photo courtesy Apex
Photo Agency, Photographer Simon
Burt Workers finishing Eden's
largest dome, in June
2000
You can't really control air temperature with a simple
glass box, because the amount of sunlight varies a good deal
from day to day. To maintain the same optimal conditions
year-round, a greenhouse needs additional climate-control
features. A typical greenhouse will have some sort of venting
system, so air can be released when the temperature rises too
high, and some sort of heating system, so the air can be
warmed when there isn't enough sunlight. Additionally, a
greenhouse needs a plumbing system to keep the ground and the
air moist.
As you can see, there are a number of elements that go into
constructing a greenhouse. In the next few sections, we'll see
how the people who built the Eden Project dealt with these
issues.
The Domes In the last section, we looked at
the most basic greenhouse, a simple box made of transparent
glass or plastic. Eden's designers decided not to use these
traditional materials in their greenhouses -- they went with
glazed ethyl tetra fluoro ethylene (ETFE) foil instead.
ETFE foil is a perfect covering for a greenhouse because it is
strong, transparent and lightweight. A piece of ETFE weighs
less than 1 percent of a piece of glass with the same volume.
It is also a better insulator than glass, and it is much more
resistant to the weathering effects of sunlight.
Photo courtesy Apex
Photo Agency, Photographer Marc Hill Workers installing ETFE foil panels in the
dome
ceiling
The Eden Project designers formed this ETFE material into
extremely sturdy pillows, each made from three sheets
of ETFE foil welded together along the sides, one on top of
the other, with layers of air pumped in between them. The air
layers provide increased insulation without decreasing the
amount of sunlight that shines through. The coolest thing
about these pillows is that they are adjustable: On a colder
day, they can be pumped up with more air to provide better
insulation; on a hotter day, they can be partially deflated to
allow more cooling.
Eden's designers attached pillows together to form
geodesic domes. In this sort of structure, many flat
panels, formed into triangles, pentagons, hexagons or other
polygons, are pieced together to form a curved surface. This
design is remarkable because none of the individual pieces are
curved at all, but they come together to form a rounded
structure.
Photo courtesy Apex
Photo Agency, Photographer Simon
Burt Each ETFE pillow is
secured in the steel
framework.
In the Eden Project domes, these geometric panels are the
ETFE pillows. Each pillow is attached to a web of interlocking
steel
tubes. Each dome actually has two web layers, one with
hexagonal and pentagonal panels and one with triangular
panels. The total Eden structure uses 625 hexagons, 16
pentagons and 190 triangles.
Like the steel grid in a skyscraper,
the steel frame of the geodesic dome is incredibly strong
relative to its weight. This weight (667 tons) is dispersed
evenly throughout the entire structure so that the dome only
needs support around its base, leaving lots of room for the
plants inside. The edges of the dome rest on a sturdy
foundation necklace, an underground concrete wall
around the perimeter of the structure.
Photo courtesy Apex
Photo Agency, Photographer Simon
Burt Workers assemble the
steel framework of the greenhouses. The Eden Project
crew broke the world record for largest free-standing
scaffold.
Designing these sorts of domes is a mind-boggling exercise
in geometry. You have to figure out exactly which shapes to
use and how to fit them all together to form a perfectly
curved structure. Eden's designers figured everything out
using sophisticated computer software. The software generated
precise 3-D
computer models of the different domes, which the
designers fed into an automated production-line
computer. Using the 3-D models, this computer determined
which pieces the construction crew would need and directed
machines to cut steel beams to those exact specifications.
When it came time to build the domes, the crew simply followed
the instructions and put all of the pieces together.
One advantage of the geodesic dome shape is that it adapts
easily to most ground surfaces. Eden's designers describe the
domes as giant bubbles that can be set down just about
anywhere. The designers built the domes along the side of the
pit that faces south, since the Sun is in the southern part of
the sky in Cornwall (click
here to find out why). The slanted ground is perfectly
positioned to absorb thermal energy all day long, heating the
air even after the sun has gone down.
Photo courtesy Apex
Photo Agency, Photographer Simon
Burt Putting all the pieces
of the dome together, in April
2000
Capturing light is only one part of maintaining a
greenhouse, of course. For the plants to thrive, you also need
to provide good soil and adequate water. In the next section,
we'll see how this is done in the Eden Project biomes.
Plumbing and Climate Control The site chosen
for the Eden Project is ideal in many ways -- it receives
plenty of sunlight, has a south-facing slope and is relatively
accessible -- but in the beginning, it did have a few
problems. One of the first obstacles was the ground material.
The pit was composed mostly of clay, which does not have the
necessary nutrients to support extensive plant life. Before
the crew could begin constructing the greenhouses, they had to
build up a level of nutrient-rich soil.
Photo courtesy Apex
Photo Agency, Photographer Simon
Burt The site of the Eden
Project, before construction
began
They produced this richer soil by mixing clay waste
from the area with composted green waste. Composting
breaks waste material down to produce a nutrient-rich
fertilizer. By combining this fertilizing material with the
available dirt, the Eden crew was able to build a rich soil
that would have taken hundreds of years to develop through
normal geologic processes. In all, the crew produced some
85,000 tons of revitalized soil, more than enough to support
the biomes' varied plant life. (See How Composting
Works to learn more about the biochemical processes
involved.)
In the early days of construction, the Eden Project was hit
with another major obstacle: flooding. After two months of
heavy rain, some 43-million gallons (nearly 163-million L) of
water had drained into the bottom of the pit. In order to
build a solid base for the structure, the designers had to
find a way to channel the water so it wouldn't erode the
ground below. And as long as they were channeling the water,
the designers figured, they might as well put it to work.
Photo courtesy Apex
Photo Agency, Photographer Simon
Burt The domes were built
along the north side of the pit, so they would get
maximum sunlight from the
south.
The first step was to build a sump, a
water-collecting pool under the rich soil. Then they laid a
buried layer of matting to channel rain water and any runoff
water into this sump. The mat also filtered out most
sediments, generating a constant source of clean, filtered
water. This water is pumped out of the sump up into Eden's
structure, where it is used to irrigate the plants, as well as
drive the building's plumbing. This system collects, on
average, almost 6 gallons (22.71 L) of water every second --
about 20,000 bathtubs of water every day. The greenhouse
ceilings also collect rainwater, sending it to the sprinklers
that keep the air saturated.
With the plants, domes, soil and plumbing all in place,
Eden is now a fully functioning greenhouse. But its creators
still consider it a work in progress. In the next section,
we'll find out about some of the additions that are in the
works and about the long-term goals of the Eden team.
Long-term Goals The main goal of the Eden
Project is to educate the public about the natural world.
Specifically, Eden's creators want to expose visitors to the
issue of sustainable development -- using natural
resources conscientiously so they will continue to be
available for human use in the future. The facility is
intended to be an entertaining attraction to tourists, but the
Eden team also wants to further environmental research and
education.
Photo courtesy Apex
Photo Agency, Photographer Nick
Gregory An aerial view of the
finished
structure
To this end, the Eden Project will open its doors to a wide
variety of companies and organizations interested in
sustainable development, ecological science and many related
areas of study. As the project evolves, its creators hope the
site will become a meeting place for anybody interested in
these issues. The idea is to bring researchers, writers,
students and others together to advance the progress of
science and society.
The Eden team is already developing many new programs for
younger students. Some exhibits will incorporate elements from
popular children's books, such as the "Harry Potter" series
and classics by Roald Dahl, in order to give kids a
comfortable way of accessing the world of science. The Eden
educational division is also setting up a program that would
link schools from around the world. In this way, kids could
learn about the natural environments in other parts of the
world, as well as the cultures that interact with them.
Photo courtesy Apex
Photo Agency, Photographer Simon
Burt One of the tropical
butterflies released into the Humid Tropics
Biome
The Eden team will also keep working on the greenhouses
themselves, of course. New plants are added all the time, and
in spring 2001, butterfly expert Christopher Wood began
introducing exotic butterfly species to the enclosed biomes.
To avoid a population boom that could disturb the plants, the
plan is to introduce only male butterflies. If the butterfly
project goes well, the Eden team may introduce other animal
species in the future.
At this point, Eden's creators have left everything wide
open -- they want Eden to evolve naturally. The building is
even designed so that it can change over time. The ETFE
pillows are built to detach easily from the steel frame, so
they can be replaced should a more efficient material come
along. If the Eden Project is a success, it will continue to
expand and develop in the decades to come.
To learn more about Eden Project activities, check out the
official site. See the links section on the next page for
related information.
