INTERNATIONAL CASE STUDY BIOMES COOLING
skins to enable the alien blooms to flourish at a latitude just 1.4 deg north of the equator, where the temperature is a constant 24C to 30C for 95% of the year. The challenge of cooling the domes is
The real challenge of this building is trying to balance the light levels and heat with the comfort of the visitors
made all the more difficult by the need to simulate seasonal fluctuations in air temperature. This is achieved by dropping the temperature at night in the Flower Dome by an additional 4C and in the Cloud Forest dome by an additional 1C. This temperature reduction takes place every night of every third month to simulate an end-of-winter condition to encourage the plants to bloom. ‘The system has to be capable of going down to these very low temperatures at night because we cannot fight the solar gain during the day,’ says Atelier Ten’s Patrick Bellew, a member of the design team.
Below and main picture on facing page: the ‘supertrees’ are made of steel filigree surrounding a concrete core. Smaller images opposite: the roofing structure of the biomes
Balancing act The first task facing the design team in developing a solution was to establish the relationship between the horticultural lighting requirements, solar gain and cooling load. The brief from the client, the National Parks Board of Singapore, was to achieve a level of 45,000 lux for the same number of hours as the domes at Cornwall’s Eden Project, where similar plant species had flourished. ‘The real challenge of this building is trying to balance the light levels and heat with the comfort of the visitors,’ says Bellew. Achieving optimum daylight levels while minimising the heat gains for the glazed
structures required extensive daylight modelling. The domes were positioned adjacent to the river estuary to avoid being shaded by the tall buildings planned for the surrounding area. However, in addition to buildings, daylight analysis of the initial designs highlighted a problem of shadows cast in the mornings and afternoons by the proposed structural solution. Conversely the structure was also found to provide insufficient shading from the intense midday sun. ‘Being close to the equator means direct solar radiation is intense when the sky is clear. However, Singapore can also be quite cloudy for long periods and the luminance levels under these conditions can be lower than in a Mediterranean summer,’ says Bellew. As a result of the modelling, the initial structural solution of a fin-shaped truss gave way to a self-supporting structural gridshell with additional lateral stability provided externally by a series of giant steel arches. The advantage of this solution is that the elements of the grid shell are relatively slender to enable sufficient daylight to reach the plants. ‘It gave us the best overall transparency to daylight so when there is no sunlight we still get very high light levels,’ Bellew says. Glazing selection was also critical to the scheme’s success. It needed to have a high degree of transparency to meet the target daylight requirements for times of high cloud cover but it also needed to be able to filter out the infrared frequencies to minimise heat gains from the intense tropical sun on cloud- free days. ‘When the sun does come out it is 1,100 W/
sq m, so it is pretty toasty,’ says Bellew. The team modelled a variety of options including ETFE pillows and single glazing, but these were unable to filter out sufficient infrared. In addition, the single glazing would also have been prone to condensation when not in direct sunlight. Double-glazing with a low-e coating
applied to the inner face of the units’ outer pane was found to provide the best solution. It allows 65% of daylight frequencies to pass through with only 35% of solar heat transferred. ‘We wanted sufficient light but no heat’ explains Bellew. In addition, a series of 7m x 10m retractable, cable-tensioned, triangular blinds have been incorporated into the supporting structure outside the domes for use on sunny days. The blinds also provide added resilience in case of system failure.
22 CIBSE Journal August 2012
www.cibsejournal.com
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60