Clean And Cool

Clean COLORBOND steel by Bluescope Steel used to roof Hotel Verde

Clean COLORBOND™ steel at the Hotel Verde

Popular roofing material, Clean COLORBOND™ steel with Thermatech™ solar reflectance technology coating, was used in the construction of Africa’s Greenest Hotel which is also one of the most sustainable designs in the world.

The Hotel Verde, near Cape Town International Airport, has achieved platinum certification across all categories of LEED Platinum Design and Construction Certification. It is the first hotel in Africa to have achieved this status across all categories and is among only about six hotels worldwide to have achieved it for the same category. It is also a first for a South African building to receive platinum certification for design and construction.

According to engineer André Harms, of Ecolution Consulting, the lead sustainability consultant on the project since the design stage, the hotel boasts a high SRI roof which contributes in no small way to its very low heating and cooling energy usage. Harms is a trained electro-mechanical engineer who provided the expertise behind many of the high tech aspects of the building.

Having spent 15 months at the South African Research Centre in Antarctica, Harms knows what it is to value everyday resources and is applying this dedication to each facet of the project. “We had the opportunity to change
the status quo there,” he says. “We looked at different ways of doing everything, right from the word go.” He collaborated closely with the project architects, Heinrich Gerstner Harding Architects.

The crowning glory of the Hotel Verde, its roof, consists of 1 510m2 of exposed sheet metal roofing plus a further 255m2 which is covered by PV panels. The roofing material is Clean COLORBOND™ Ultra steel with Thermatech™ solar reflectance technology coating to specification AZ200 (TCT 0.53 mm) and colour Enduring White. The SRI of this superbly efficient product is 85. This is one of the coolest operating roofing materials available and is complemented by an outstanding dirt-resistance property and long life which ensures the roof stays cooler for longer. The roof was installed in profile Brownbuilt Klip-Lok 406 by roofing contractor, Scheltema.

The Solar Reflectance Index (SRI) is widely used by green building rating tools to mitigate the Urban Heat Island (UHI) effect. SRI is a value that incorporates both solar reflectance and thermal emittance in a single value to represent a material’s temperature in the sun. SRI quantifies how hot a surface would get relative to standard black and standard white surfaces. In hot tropical climates, low thermal mass materials such as steel with light coloured roofs and walls can be used to reduce energy demand for internal cooling.

According to Wayne Miller, General Manager for BlueScope Steel in Southern Africa, the solar reflectance technology found in Clean COLORBOND™ steel lowers the surface temperature by absorbing less heat from the sun. “Thermatech™ optimises the thermal performance of every colour in the standard Clean COLORBOND™ steel and Clean COLORBOND™ Ultra steel palettes, without changing their appearance. This provides greater thermal comfort all year round whilst using less energy for air-conditioning and hence mitigating the UHI effect, he says. “In addition, our product’s outstanding dirt resistance property ensures the roof looks newer for longer. This also assists in cooling.”

In a comparison between a Clean COLORBOND™ and a conventional steel roof, both uninsulated, the positive effect of dirt resistance technology is illustrated.

Tests show that after two years’ exposure, assuming an irradiance of 1000W/m2, exterior temperature of 36°C and a high thermal emittance value of 0.86, typical of pre-painted steels, the Clean COLORBOND™ steel roof’s temperature is almost 10° cooler than the conventional steel roof and it radiates more than 40W/m2 less heat down into the building. This is a considerable easing of the HVAC load for any building, regardless of size.

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