Published April 22, 2008


Nuts and bolts of green buildings

A perfect orientation is best but architects can also use other means to reduce energy consumption, reports MATTHEW PHAN

IT IS hard to pin down exactly what green architecture entails. Each building is a case study in itself, with specific surroundings, usage patterns, client requirements and weather conditions. One might use a north-south alignment to block off the sun's heat. Another, forced by circumstance to face the rising or setting sun, might use glazing or shades to achieve the same. Light and temperature controls for a residential apartment block differ from those for retail malls or industrial facilities. Still, certain principles run throughout.

Going green: City Square Mall's glass facade uses double-glazed low-emission glass to mitigate excessive heat and glare, plus an automatic sun-screen that will come down in the afternoon and rise back up in the evening

Architects approach a design in two ways - passive and active. 'If you have the passive side right, half the battle is won. Then you actively use technology to manage the things you couldn't solve with the passive approach', says Tang Kok Thye, senior principal architect at ADDP Architects.

Passive refers to elements like site layout, the facing of a building and how it is structured to allow for natural lighting and ventilation. Active refers to add-ons, like special glass to keep out heat and glare, solar panels or green roofing and the building's mechanical and electrical (M&E) guts.

Because air-conditioning is typically the largest user of energy in a building, the biggest energy savings come from temperature control. In a local context, this means figuring out how to stop a building from getting too hot. The right orientation is critical. 'If a building is facing east-west, a lot of money is spent just to make it comfortable to live in', says Mr Tang. Site layout and surroundings are also important. A building next to the sea or a park is cooler than one standing next to another building that might reflect heat and light.

In the early stages of design, architects often simulate how the sunlight and wind might flow into a structure, using techniques known as Computational Fluid Dynamics.

Sun-path and wind analysis are the most common analyses. A third kind, which examines the amount of energy a building uses under varying conditions and people movements, is far more expensive and rare in Singapore.

But even the more basic analyses, due to cost, are not always done, says Mr Tang. In contrast, architectural firms in the US, where the green building movement is more advanced, often conduct environmental analysis as part of the design process.

If a building cannot have a perfect north-south orientation, which is often the case due to site constraints, architects can use other means to protect the main activity areas.

For example, Xilinx's Asia-Pacific Headquarters building - winner of the Building & Construction Authority's Green Mark Platinum award in 2007 - is diagonally oriented.

But its designer, RSP Architects Planners & Engineers, cleverly placed the stairwells and M&E rooms at the corners of the building facing the east and west, protecting the offices and chip-testing facilities at the centre of the building from the direct sun.

Xilinx also invested in doubled-glazed, low-emissive glass that helped it achieve an envelope thermal transfer value (ETTV) - a calculation how much heat a building gains through walls and windows - of 38.53 W per square metre.

This is remarkably low, said Vivien Heng, a director at RSP. There is a mandatory standard of 50 W/sq m, but most buildings don't achieve lower than 45 W/sq m, she said.

The wind flow simulation also showed up a 'dead space' with poor cross-ventilation at one portion of the building, said Ms Heng. The firm jigged the design by opening up external gaps in the facade, resulting in vastly improved wind movement through this part of the building and up and out through the central atrium. The building's internal courtyards and 'shallow' offices - no work space is more than 10 metres from the glass walls - allow wind and natural light to flow through the space, Ms Heng said.

Lend Lease Retail, the design consultant for City Square Mall, City Developments' eco-mall at Serangoon, faced similar challenges on that project. Because of the site's peculiar square shape and orientation, the mall has to contend with a main entrance facing the hot afternoon sun, though it is blocked from the rising sun by the adjacent City Square Residences, which were separately designed.

Malls are typically designed in a 'dumb-bell' layout, to maximise shop frontage, said Felix Lim, principal architect at Lend Lease Retail. This means that they are laid out in a linear strip, with speciality shops on both sides, and anchor tenants, like supermarkets or department stores, at the far ends.

The squarish site constrains an effective linear layout. So instead, Lend Lease Retail created an 'L-shape', with smaller speciality shops along the east and south sides of the square to achieve linearity, and large anchor tenants at the north-west corner.

Compared with speciality shops, anchor tenants need less 'transparency' or glass windows that allow passers-by to look in. Since the west side was largely occupied by anchor tenants, the layout meant that half or more of the mall's western front could be solid, rather than glass. This shields the mall from the western sun, and allows for advertising space on the external facade, Mr Lim explained.

For the rest of the facade - part was glass to make for an attractive entrance and allow natural light to flood the mall's large atrium - Lend Lease Retail used double-glazed low-emission glass to mitigate excessive heat and glare.

It also planned an automatic, timed sun-screen that will come down in the early afternoon and rise back up in the evening, to allow evening pedestrian traffic to look into the mall.

Both Xilinx's building and City Square Mall feature Pre-cooled Air-Handling Units (AHUs) to contain energy bills.

Air-conditioning is energy consuming because the air here is warm and humid. A Pre-cooled AHU system first brings in outside air, cools it via cooling coils and mixes it with treated return air in a separate chamber. The pre-cooled air is then further cooled in the AHU system proper and piped into the building.

The process is capital intensive upfront but results in long-term savings. Thanks to such measures, as well as other green innovations, City Square Mall, which won the Building and Construction Authority's Green Mark Platinum award last year, saves the equivalent of 11.4 million kWH per year or equivalent to the total consumption of nearly 2,400 four-room HDB flats.

ADDP Architects incorporated light screens, solar panels and rainwater harvesting into its design for Cliveden, a CDL condominium project and another 2007 Green Mark Platinum award winner.

On Cliveden's clubhouse, solar panels reduce energy dependence on the main grid, while a green roof not only helps to reduce heat inside the clubhouse but also the surrounding environment. The centre was planned as an educational centre for public awareness on using green power, said Mr Tang.

The condo collects rainwater from its roof and reuses it for landscaping, saving about 10 swimming pools of water a year. The total water and energy saved, about 30 per cent, is equivalent to saving 77,475 trees.

Another green building, from a water conservation point of view, is Temasek Polytechnic. The school installed a $1.6 million rainwater harvesting system when its 30 hectare campus was being built in the early 1990s, with the water used to for the school's extensive gardens.

Ultimately, though, the greenest of green architecture is conservation and restoration, because a lot of energy is required to knock down a building and erect a new one, architects say.

'Building is one of the most energy-intensive activities around', says Ms Heng. And ADDP's Mr Tang agrees. 'As an architect. you would like to preserve nature but it depends on the developers' needs,' he said. 'Buildings should be made to last more than 50 to 100 years.'