R-value unpacked

by Darren
Rvalue unpacked

The R-value is not the be all and end all when it comes to energy efficiency in South African climates.

While wall thermal resistance (R-value) is directly correlated with energy efficiency in North America and many European countries, in South Africa the R-value is only one measurement to consider.

This is because locally, the aim is to keep homes cool for most of the year, rather than heating them. South African buildings require walling materials with a high thermal mass to achieve optimum warmth in winter as well as optimal cooling in summer.

The R-value measures a material’s resistance to conductive heat transfer, but it does not factor in the time taken for heat to traverse a layer of high mass. To account for both factors, the thermal diffusivity (CR-value) also needs to be measured.

Experiential research at the University of Newcastle in Australia into the thermal performance of various walling materials in a climate similar to South Africa, gives statistics under real world conditions. In the study, dwellings constructed of different walling materials yielded a wide range of thermal comfort levels, even though they all had the same R-values. They were also shown to need very different energy levels for heating and cooling.

“When calculating actual energy savings and thermal comfort, the R-value needs to be considered in conjunction with the density of the material,” says CBA executive director, Jonathan Prior.

“Clay brick is not only an extremely dense walling material, but is usually built as a double layer. A clay brick shell ensures that a brick house remains warm in winter, and in summer it stays cool and comfortable for longer – mitigating the need for expensive heating or air-conditioning. This is why clay brick outperforms the majority of alternative walling systems by lowering energy costs each year, every year.”

The Clay Brick Association of South Africa
Tel: 011 805 4205
Website: www.claybrick.org

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