Wilkinson Eyre’s Gardens by the Bay, Singapore

When faced with the task of sustainably cooling two massive conservatories, which form part of the highly complex Gardens by the Bay scheme in Singapore, the design team found their usual palette of tools rapidly whittled down when dealing with the country’s sultry climate.

“It’s a unique project,” says Patrick Bellew, principal at environmental engineer Atelier Ten. “We have never done anything of this scale before, of such complexity and at such speed. We were all inspired by the depth of vision of the Eden Project [in Cornwall], but the one thing we wanted to do differently with this scheme was to conceal the services and make them as invisible as possible”.

Atelier Ten is part of a design team led by landscape architect Grant Associates working with Wilkinson Eyre Architects, which won the competition for the Marina Bay South regeneration scheme in 2006.

The project, which started on site in July 2007, is the largest of three waterfront public gardens and involves 54ha of reclaimed land south of the city’s central business district.

The development will include an intricate level of themed gardens, featuring 18 concrete and steel “super trees” (the tallest being 55m) housing exhaust air ducts and solar panels, together with a concert arena and shops, as well as the two scallop-shaped steel and glass conservatories.

The attraction of the conservatories will not only be the cooler temperatures experienced within but the breadth of the coloured flowers on show. The conservatories will be replicating environments alien to the tropics: the 183m x 130m x 38m cool-dry biome will recreate the conditions of a Mediterranean spring; while the 123m x 95m x 58m cool-moist biome will recreate the cool, misty environment of a mountain “cloud forest”.

One of the most striking features of the cool-moist conservatory will be a 40m-tall man-made mountain and waterfall, believed to be the world’s highest indoor waterfall.

To create and maintain these cool internal environments sustainably has presented the design team with one of its greatest challenges ever.

“It is the agglomeration of multiple little steps that makes this project truly exceptional in its aspirations,” says Meredith Davey, associate director at Atelier Ten.

Cooling the conservatories

Working out how to cool the conservatories was a two-fold process says Atelier Ten’s Patrick Bellew.

The first step involved managing the solar gain coming into the glass roof and balancing the requirements for the horticulture. This led to the development of a retractable shading device for the glass and steel arched grid-shells, combined with high-performance selective glazing, which lets in more light than heat, and without which the cooling loads in the structures would have been too great.

The second step was working out how to use huge amounts of fresh air to cool the conservatories and how to do so without wasting energy.

The innovative solution that emerged came in the form of vast quantities of liquid desiccant, which helps to dehumidify the air in the biomes. The process absorbs moisture from the air, which is then evaporated outside the conservatories, so regenerating the desiccant. The primary heat source used to evaporate the water comes from a 20m-long x 15m-tall, 7.2MW superheated steam biomass boiler, with a capacity eight to ten times greater than the one used for the entire BedZed housing development. This will drive the combined heat and power system. The primary energy source for the entire development will be waste wood, about 5,000 tonnes per month, which will come from the 3 million trees the client is responsible for in Singapore’s streets and parks.

Using the Eden Project as the benchmark for minimum light, it was determined that the light levels in the conservatories must be in excess of 45,000 lux for more hours than at Eden in order for the plants to flourish. In comparison, a typical office requires about 500 lux.

“Singapore might be incredibly humid, but it’s often very overcast and when not overcast, it’s very bright and allows almost too much light in,” says Atelier Ten’s Meredith Davey.

The facades will use double glazed units with a low-e coating on the inner face of the outer pane, which will allow 65% of the incidental daylight through to the interior, but only 35% of the solar heat. The automated external shading system that has been developed with structural engineer Atelier One to restrict the amount of direct sunlight into the interior comprises of an engineered shading fabric of a triangular shape that varies in size, the maximum span being 7m x 10m.

“It’s a responsive skin and will be like a series of sails unfurling from the primary supporting structure of the conservatory,” says Paul Baker, director at Wilkinson Eyre.

Each triangle unfurls from one arch to another and, when completely rolled out, the shading system will resemble a giant pinecone.

When complete, the project is hoping for platinum accreditation — Singapore’s equivalent to Breeam.

Exploring the sustainable landscaping

The themed gardens, designed by Grant Associates, are arranged in three main parts: Plants & People, which runs along a ridge into the cool-dry conservatory; Plants & Planet, which extends from the cool-moist conservatory, and Nature in Balance, or the Lion Grove, which nestles between the other two gardens.

The Lion Grove will be defined by a cluster of 12 giant Supertrees; the other six are located near the conservatories, and will rise above the rain trees surrounding the grove.

These fantastical structures will have a flue embedded in the steel lattice trunk to expel waste water from the desiccant circuit. The trunks will also support ferns, orchids, climbers and other plants up to a height of 30m, and will be topped by a series of canopies providing shelter and shade.

Some of the steel lattice branches will support solar hot water collectors (the hot water will be used, along with waste heat from the CHP, to help regenerate the desiccant); others will support PV panels; two will contain lifts to carry visitors up to an aerial walkway; and the tallest, at 55m, will house a treetop café. Some of the Supertrees will also harvest rainwater for irrigation, reducing demand for potable water.