"However, the unpleasant heat and high humidity in the outdoor spaces, especially in summer, will deter people from leaving air-conditioned venues. Therefore, Foster proposed to use a canopy to create a microclimate so as to reduce the temperature in the outdoor space area."

According to the microclimate principle, hot air rises and leaves the sheltered area through the semi-permeable canopy while the surrounding cool air flows into the area, forming convection air currents and producing a cooling effect.

Partly equipped with adjustable louvres, the canopy will also help control the amount of sunlight in the area and prevent intense direct solar radiation.

Foster believed that such a design would reduce the temperature of the sheltered area by four to seven degrees Celsius.

The canopy can also reduce the exposure of sheltered buildings to sunlight, cutting down their cooling load demands and saving energy.

Other expected functions of the canopy include:

*sheltering the district from rain and adverse weather;

*screening out potential noise created in the district;

*providing structural supports for mounting stage lighting and stage engineering equipment; and

*providing a potential venue for organising artistic light shows, like the light shows in Les Vegas, to attract tourists.

Mr Kwan said there are a number of canopy-like structures in the world, for example, the canopy of the New Milan Trade Fair in Italy. The fully glazed canopy shelters the common area among buildings, offering a passage for both people and vehicles.

The Shenzhen Citizens' Centre, the new home of the Shenzhen Municipal Government, also has a canopy. The structure gives shade to facilities beneath it to achieve energy savings. Equipped with solar panels, it also helps collect solar energy to generate power for the buildings' lighting.

However, Mr Kwan stressed that these two structures are different from the cultural district's canopy. "The canopies in Milan and Shenzhen are not permeable while the cultural district's canopy is semi-permeable. Their designs and functions are just not the same. Ours is much more functional and architecturally more iconic." 

When asked whether the great span of the cultural district's canopy will create any technical problems, Mr Kwan said there are no particular problems for constructing this type of large roof structure.

"Many countries have overcome the spanning problem and succeeded in building even more complicated and larger roof structures. Stadium Australia in Sydney and Millennium Television & Entertainment Licensing Dome in London are some successful examples," he said.

According to Mr Kwan's initial estimate, the construction cost of the canopy in West Kowloon is between $2.5 billion and $4 billion.

"The three screened-in proponents have offered different solutions to the construction of the canopy. Their long-term maintenance proposals differ greatly because of the difference in design and use of material.

"As the proposals are being assessed, we think it is not the appropriate time to release their individual construction and maintenance cost at this early stage."

The Government is now studying the canopy-design proposals of the screened-in proponents and will assess their feasibility. After collecting public views, it will negotiate with the proponents, to try to make their canopy-design proposals comply with the overall requirements as much as possible.

Public encouraged to express their views

Mr Kwan invited the public to the upcoming exhibitions to express their views on the cultural district project, including the canopy's design and construction.

The main exhibition will first be staged at the Science Museum from December 16 to January 31, and continue at City Hall between February 5 and March 28.