Cool roofs cut energy consumption, save money: study

Cooling down hot roofs by using reflective surfaces can not only beat the summer heat, but also help save money by cutting down your electricity bills, even in cities with colder climates, a new study has found.
As the summer heats up, so do cities. Regardless of latitude, urban temperatures are typically several degrees higher than those of nearby suburban and rural areas.
The resulting "heat islands" mean increased discomfort, higher air-conditioning bills and denser smog.
Cooling down hot roofs by using reflective surfaces may be a viable solution, researchers said.
Scientists from Concordia University in Canada confirm that, contrary to the belief that cool roofs would not work in colder climates, they actually provide net energy and monetary savings.

"Using a cool roof on a commercial building in cold climates is typically not suggested based on the presumption that the heating penalties may be higher than the cooling savings," said Hashem Akbari, professor at Concordia University.

"Our research shows that any improvement to a roof that limits the summertime solar heat gain actually results in energy-cost savings for the building owner, as well as a reduction in the building's overall environmental impact," said Akbari.
For the study, researchers used modelling software to simulate energy consumption for several prototype office and retail buildings in four cold-climate cities in North America: Anchorage, Milwaukee, Montreal and Toronto.

They found that cool roofs for the simulated buildings resulted in annual energy expenditure savings in all municipalities.
A cool roof on a new, medium-sized office building would save USD 4 per 100 square metres in Montreal, USD 10 per 100 square metres in Toronto and USD 14 per 100 square metres in Milwaukee and Anchorage.
The research also showed that cool roofs can reduce the peak electric demand of the retail buildings by up to five watts per square metre.
"Our study proves that cool roofs for commercial buildings are a net saver of energy in all climates that use air conditioning during the summer," said Akbari.

"In cooler climates, installing cool roofs may even prevent buying an air conditioner altogether. Even in non-air-conditioned buildings, cool roofs improve comfort during hot summer days, he said.
"In extreme cases, these roofs may even save lives by reducing the risk of heat stroke," he added.
Many municipalities already prescribe cool roofs in the construction of new buildings and for re-roofing existing buildings. This study proves that those rules should also apply in colder climates.
"On a large scale, cool roofs can moderate the air temperature surrounding a building, decrease greenhouse gas emissions and mitigate the urban heat island effect," he said.