Glass tint link to AC bill

(The glass facade at Calcutta airport )

A team of Indian engineers has identified a combination of reflective bronze-tinted glass and mud-brick walls as among the best options to reduce the air-conditioning loads for modern buildings with outer glass facades.

The engineers, from the National Institute of Technology in Surathkal and the Vellore Institute of Technology, examined through computer simulations how multiple combinations of various building materials and glasses respond to heat and sunlight on a set of 80 building designs.

They say their findings are intended to guide building designers on what materials to use to minimise the heat trapped within buildings with glass façades, particularly during summer.

Commercial buildings with glass facades have become popular, a trend some industry insiders attribute to the lighter weight of glass and the area saved: glass façades take about eight per cent less space than brick wall faces, according to a glass-making company.

“We find that dense concrete walls and clear glass windows on the outer façade is the worst combination,” said Shaikh Saboor, a senior assistant professor of thermal and energy engineering at the VIT, who led the study. This combination is associated with the highest heat gain inside the building.

Saboor and his NIT colleagues G. Kiran Kumar and T.P. Ashok Babu measured how various combinations of four building materials (laterite stone, burnt bricks, dense concrete and mud bricks) and four kinds of glasses (clear glass, bronze glass, green glass and reflective bronze glass) influence heat gain inside buildings.

They simulated sunlight exposure conditions on their buildings in five cities -Ahmedabad, Bangalore, Chennai, Delhi and Guwahati – each representing a specific climate zone. They found that in every city, the combination of mud-brick walls with reflective bronze glass trapped less heat than dense concrete with clear glass.

The findings, published on Sunday in the journal Energy Procedia, show that reflective bronze glass windows combined with mud-brick walls reduce the heat gain by an average six per cent compared with clear glass and mud-brick walls.

“These findings should encourage builders to look at the most environment-friendly options, particularly for commercial buildings. The less the heat trapped in a building, the less the air-conditioning needed,” Saboor said.

“The ideal glass façade should deliver ideal thermal comfort and ideal visual comfort,” he added, saying that too much bright light inside was unnecessary.

Walls in a building serve primarily to partition it and are not the main load-bearing structures, the engineers explained. “The columns in the building are the main load-bearing structures. Mud-brick walls could easily meet the standard strength requirements for partitioning structures,” Saboor said.

However, specialists in energy efficiency point out that the energy efficiency of a building is not determined only by walls and glass. “Even with concrete walls and clear glass windows, there are other ways to achieve efficiency,” said a counselor with the Indian Green Buildings Council, a unit of the Confederation of Indian Industry. “The design, insulation gaps, lighting, and even seating of personnel in a commercial building can contribute to achieving lower energy consumption,” the official said.


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