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On 20 April, Expo 92, the greatest show on Earth, opens in Seville.
Spain has given over a large chunk of the island of La Cartuja in the Guadalquivir
river to a global village where the pavilions of more than 100 countries
jostle with others devoted to the theme of the event – Discovery – and still
more occupied by individual companies.

Up to 430 000 people will be able to cram into the exhibition every
day. If they were to spread out uniformly over the 215-hectare site, each
would have their own space 2.2 metres square. But visitors are unlikely
to be so obliging, and are more likely to swarm around the most popular
pavilions and events. In the Andalusian summer, when temperatures can exceed
45 °C, people are going to get hot.

Expo’s organisers had to take seriously the problem of how to keep visitors
cool and comfortable. They have banned any of the pavilions from ejecting
waste heat into the air, and commissioned a team of researchers, led by
the Department of Energy Engineering and Fluid Mechanics at the University
of Seville, to look for the most efficient and cost-effective ways of keeping
people cool while out in the open air.

From the outset, the researchers turned for inspiration to traditional
methods of cooling. Andalusian architecture makes much use of awnings, sails,
pergolas, fountains, ponds, trees and shrubs to counter the harshness of
the summer. Using a combination of computer modelling and experiment, the
team identified which of these features were truly effective and how they
might be implemented with modern materials.

Conditioning outdoor spaces presents quite different problems from conventional
air conditioning. The air inside an efficiently sealed building can be mechanically
cooled. Outdoors this is impossible, but a careful approach to architecture
and design can make people more comfortable. The researchers first considered
a ‘reference situation’: an average person standing in an uncovered open
space at 2 o’clock on a summer afternoon in Seville.

Under such conditions, 55 per cent of the heat gained by the person
comes as radiation from direct or reflected sunlight. So providing shade
is the most important factor in keeping people cool. Another 14 per cent
of heat gained comes from thermal radiation emitted by nearby objects such
as the pavement or walls. Heat transfer from the surrounding air, which
is governed by the air temperature, accounts for only 7 per cent. The remaining
heat comes from the person’s own metabolism. So, if people are to remain
comfortably in the open at Expo, they need shade and cool surfaces around
them; cooling the air is less important.

The research team built a full-scale experimental structure to test
a combination of cooling techniques and validate the results of their computer
models. Known as the bioclimatic rotunda, it was intended to typify the
stuctures that would appear at Expo. A sunken paved area 31 metres across
was covered with a pyramid-shaped canopy, open at the peak and made of white
PVC, which let through 13 per cent of the light falling on it.

The rotunda was equipped with a variety of cooling devices. A film of
running water flowed over the outside of the PVC covering to keep its inside
surface cool. An air handling unit sucked air from outside the rotunda,
cooled it by passing it through a damp packing material, and fed it through
underground ducts into the structure. Trees inside the rotunda were fitted
with nozzles called micronisers that emitted a fine spray of water to create
an artificial fog. As the droplets evaporated they cooled the air. Micronisers
above the entrances of the rotunda cooled the breezes that blew in. More
of these devices were fitted inside a tall, hollow tower in the centre of
the pyramid. Air blown down the tower by a fan emerged at the bottom as
a cool breeze.

To monitor conditions in the rotunda and the surrounding area, the researchers
installed 96 temperature and humidity sensors. With the area inside the
rotunda permanently shaded, they compared the benefits of cooling surrounding
surfaces – the PVC canopy – with cooling the air through use of micronisers
and the air handling unit. They assessed degrees of comfort by looking at
the rate people sweated, taking 90 grams of sweat per hour as the maximum
comfortable rate. On a typical summer day (38 °C and 30 per cent relative
humidity) they found a person would feel comfortable in the rotunda if the
air was cooled to 30 °C and the canopy cooled to 27 °C with water.
If, however, the canopy was left uncooled it reached a temperature of 48
°C, and it was then necessary to cool the air to less than 20 °C
to achieve the same degree of comfort.

Expo’s designers applied the results from the experiments with the rotunda
in structures such as the Palenque, a white PVC canopy covering an area
of 8000 square metres. The Palenque houses a theatre space with seating
for 1500 people as well as restaurants and shops. The canopy is cooled by
a controllable film of water flowing over its surface. Inside, five air
handling units cool the air while on the perimeter a ring of water curtains
and microniser mists cools incoming breezes.

The Avenida de Europa has 12 cooling towers of the type used in the
rotunda. The towers are made of PVC wrapped around a metal frame and stand
30 metres high. Instead of fans they are topped by wind catchers that funnel
air into the tower. The wind catchers point towards the southwest, the source
of the prevailing wind in Seville. If the wind comes from another direction,
it blows over the top of the wind catchers and has the effect of drawing
air up the towers. When this happens, the water supply to the micronisers
in the towers is switched off by its computer control system. An automatic
weather station feeds information on wind direction to the computer. The
station also takes temperature readings so that the water is automatically
turned off when the ambient temperature drops. Below 35 °C, the water
spray in the towers does not evaporate completely and emerges at the bottom
as a fine rain.

All over the Expo site, vegetation is being used for shading because
it is very efficient at blocking out light and does not become overheated;
transpiration from the leaves absorbs the sun’s heat. Plants in portable
modules have been grown over an area of 50 000 square metres that will soon
be car parks. Before the exhibition starts, the plants will be moved to
parts of the site that require shade and hoisted up onto pergolas.

Even passengers in the cable cars that will glide gracefully above the
Expo site will be able to keep their cool. The cars, which will carry people
from one side of the site to the other, have cooling systems based on fine
sprays of mist from micronisers.

Many of the pavilions draw on traditional methods to cool their interiors,
though in many cases these are allied to more modern techniques. Part of
the British pavilion mimics the thick stone walls of Andalusian architecture
to absorb the heat of the sun. A section of its west wall is built from
steel freight containers lined with plastic and filled with water. The outer
surface is sprayed with a coat of insulating polymer, 50 millimetres thick.
This huge body of water, amounting to more than 600 cubic metres, acts as
a heat sink, and while the outside surface may reach temperatures as high
as 60 °C, the inner surface will remain below 32 °C.

Ten fabric-covered louvres prevent the roof becoming too hot. An array
of 1045 photovoltaic solar cells mounted on the louvres provide almost half
the power needed to pump water to the top of the east wall of the pavilion,
from where it cascades down 1134 square metres of glass. This water wall
is claimed to be the largest in the world and keeps the glass at a temperature
of 24 °C. Conventional air conditioning supplements the British pavilion’s
passive cooling techniques.

* * *

Sensitive screens for staying in touch

Even when sheltered from the ravages of summer, visitors to Expo risk
becoming hot under the collar if they cannot find the pavilion or event
they are looking for, or have lost contact with their companions, or simply
want to reserve a table at one of more than 100 restaurants on the site.
To console the distressed visitor and demonstrate multimedia techniques
that may be commonplace in a few years’ time, IBM has installed a network
of 33 electronic information points. At every information point there are
seven personal computers, each equipped with a touch-sensitive screen.

The system draws on a store of text and a library of 10 000 maps and
other images to provide visitors with information on pavilions, events and
restaurants that offer cuisines from all over the world. Visitors will select
the information they require by pointing at the screen. Text will be available
in Spanish, French or English; speakers of other languages will have to
rely on visual clues, music and sound effects.

Each screen also has a microphone and a video camera that takes still
pictures so that the network can double as a message service. To leave a
message for friends elsewhere on the site, visitors simply slide their entry
ticket into a card reader to identify themselves, and speak into the microphone
while the video camera takes their picture. By tapping into another information
point, a friend can hear the message and see the sender’s face. Visitors
can also use the system to reserve tables at restaurants, take part in opinion
polls, enter contests and browse through electronic newspapers.