In depth: Gardens By The Bay
Sustainability Report 2013
CIBSE International Project of the Year 2014
Three waterfront gardens that define Singapore as the world’s premier tropical garden city, Gardens by the Bay is a national and international exemplar of sustainable practice. There is no single strategy used in the Gardens by the Bay project that is completely unique in terms of sustainability and servicing approach. There are other buildings that, for instance, have biomass CHP systems implemented with varying degrees of success. There are many buildings that have automated shading systems. There are even some with liquid desiccant dehumidification with waste heat regeneration. It is the combination of multiple processes that makes this project truly exceptional in its engineering. This excellence has been acknowledged throughout the design and construction with multiple accolades including WAF World building of the year (2012), 3 design awards (2010-2012), Sustain magazine Award for International project of the year (2013), the prestigious British expertise award for Outstanding International Design (2013) and two awards from MIPIM, Best Innovative Green Building (2014) and Recognition of Excellence 2014: Special Jury Award.
An enlightened client
Through the competition briefing and the subsequent brief development stage, the Client actively encouraged the design team to consider innovative design solutions to minimise energy consumption and carbon emissions. In addition, Mah Bow Tan, then Minister for National Development, instructed that the team should endeavour to make the carbon emissions from the systems conditioning the buildings no worse than would be experienced in a modern Singapore office building of the same total floor area. This was a significant challenge, but one that was achieved and exceeded by the final design.
Background
As part of a team led by Grant Associates with Wilkinson Eyre Architects and Atelier One (structural engineers), we acted as the environmental and sustainable design consultant and building services engineer to help develop a holistic scheme based on first principles. Integrated solutions have been implemented for the demanding brief to create artificial interior environments enabling Mediterranean and mountain plants to grow in the tropical urban heat of downtown Singapore. Commissioned via an international competition in 2006, the project comprises 52 hectares of landscaped gardens on reclaimed ground in Marina Bay. It features a 20,000m² complex of cooled conservatories and 18 huge structures that support vertical gardens ranging in height from 25m to 50m known as ‘Supertrees’.
The conservatory complex is divided into two biomes creating two of the world’s largest conditioned conservatories. The Flower Dome re-creates a Mediterranean springtime with mild, dry days and cool nights. It is 170m long, 86m wide and 38m high, contained within a clear spanning double glazed gridshell structure. The Cloud Forest Dome emulates the conditions of mountainous tropical regions where the air temperature is relatively mild during the day, slightly cooler at night but with humidity levels that are approaching saturation throughout both day and night. The Cloud Forest Dome is 118m long, 77m wide and 58m high and has a large mountain in the centre with aerial walkways to take visitors through the tree-tops.
The conservatories and the gardens have been designed to be symbiotic, through the interaction of a number of energy and water processes. We developed innovative strategies for controlling conditions within the two biomes while minimising energy demand to exemplar levels. Materials and shading passively reduce cooling demand: the façade design is based on specifically selective glazing to control radiant transmission and surface temperatures while retractable external shades modulate internal daylight levels. The systems for environmental control include the use of a displacement air supply system. This involves introducing the conditioning air at low level within the occupied zone to limit the volume of the building that required conditioning reducing plant capacities and energy use. Displacement ventilation also allows for the conditioning supply air to be supplied to the space at around 18°C rather than at 12°C, which would be the norm for a conventional conditioning system, and this elevated supply temperature results in significant energy savings. We employ radiant cooling in pathways and pavements within the biomes to absorb and remove incident absorbed solar radiation. This reduces the amount of heat gain to be dealt with by the air systems and reduces mean radiant temperature for occupants thereby improving comfort. A desiccant dehumidification system is used removing the need for refrigeration-based dehumidification of air. The desiccant regeneration process also allows waste heat to be used as a regeneration source. To meet the humidity demands within the Cloud Forest Dome direct evaporative humidification (misting) is used. Significantly, the zero-carbon cooling and dehumidification system operates on horticultural waste diverted from landfill used as a source of fuel to generate energy.
Low carbon approach
Within the biomes, the zero-carbon cooling and dehumidification system operates on waste wood generated by a tree maintenance programme. This feeds a central energy centre that provides power, cooling and heat to the biomes. Within the energy centre, a biomass CHP plant is used to generate heat and power. This is fed into absorption and conventional chillers providing a variable temperature chilled water circuit to the biomes. The biomass is sourced as horticultural residue largely from urban street tree pruning operations throughout Singapore. The residue is chipped and burnt in a superheated steam biomass boiler. Before the project was developed, this horticultural residue waste was land filled and so this installation acts to turn a waste stream into an active energy supply that displaces the cost of imported utility energy. Absorption chillers act as an additional heat dump, while providing useful energy output. These work alongside conventional highly efficient centrifugal chillers to meet the cooling requirements of the biomes. Due to the way the biomass boiler combusts the fuel stock, there are two ash streams. One is a fine ash that is high in nitrates and other fertiliser compounds: this will be mixed with the waste plant matter from the gardens to create high-grade compost. The second contains heavier density particles and is taken off-site to be mixed into concrete or aggregates.
Managing sustainability
As part of the Masterplan development and implementation process we developed and utilised a number of sustainability implementation plans (SIPs). Tailored to each development stage of the project, these plans covered all areas of environmental sustainability potentially affected by the development, and aimed to finely weave holistic ideals of sustainability into the project. In this way, solutions, where waste streams can be actively processed to yield multiple resources through normal building operation, start to make triple bottom line sustainability savings. In the case of Gardens by the Bay, it is the use of a waste stream (horticultural cuttings) to create the primary conditioning energy for the site that in turn generate further bi-products in the form of fertiliser and industrial aggregate.
The Masterplan paid considerable attention to creating sustainable water cycles. Direct rainfall from within the site catchment is filtered and cleansed of the nitrogen, phosphorus and suspended solids arising from the gardens operation, prior to discharge into the Marina Reservoir. The intermittent and ‘peaky’ nature of tropical storms makes this a complex task of retention and release, and the solution uses aquatic landscapes to remediate the received water through a series of inter-connected lakes and filter ponds and planting troughs. The filter ponds leading into the lake are formed from a number of different layers of permeable substrate to allow the incoming water to be naturally filtered, without the need for mechanical filtration equipment. Water further treatment is undertaken in a sustainable manner through the use of aquatic plants within the water bodies.