Light Steel Frame construction tops test

A recent research project by the Built Environment Division of the Council for Scientific Industrial Research (CSIR) confirmed that a light steel frame (LSF) dwelling, built to SANS 517, will result in significant savings of electricity used for heating and cooling of the building, compared with a conventionally built heavy masonry building. Johan Schronen, representing International Metalworking News – Middle East & Africa (IMNE), spoke to South African Light Steel Frame Association Director John Barnard, to find out how the two building types stood up against each other.

IMNE: What prompted this research project?

JB: In order to obtain an objective prediction of the thermal performance of a light steel frame dwelling compared with a masonry building in the different South African climate zones, SASFA approached the CSIR to carry out the analyses. A typical 120m2 single storey house was used for the comparison. The Light Steel Frame (LSF) and the masonry houses were specified to be geometrically identical, with identical orientation. The LSF house complies in all respects to SANS 517 Light Steel Frame Building. A typical masonry house with double leaf external clay brick walls, without any insulation in the walls and ceilings, was used as the base case. The effects of adding 40mm insulation in the ceilings, and similar ceiling insulation as used for LSF buildings (140mm) and 50mm insulation in external walls, were also evaluated.

IMNE: How did the CSIR ensure that the findings were reliable?

JB: The Built Environment Division of the CSIR decided to use the Ecotect TM V 5.6 software to carry out the computer analyses. In order to eliminate the effect of user input data which could influence the outcome, it was decided to use a passive analysis, i.e. without making assumptions regarding the occupancy and usage patterns of the house. The heating effect of lights and appliances was also not taken into account. The analyses were firstly aimed at determining the number of hours of uncomfortably high or low temperatures in each of the buildings.

The buildings were considered to be naturally ventilated and the thermal comfort temperature range for naturally ventilated buildings in Pretoria is 17.8°C – 28.3°C. The adaptive model was used in calculating the levels of thermal comfort in the two houses. The electricity needed for heating and cooling for each of the buildings to thermal comfort levels (ranging from 20°C to 24°C, as recommended by SANS 204) was also determined.

IMNE: What were the important differences between the structures?

JB: The major differences between the two types of building are the thermal insulation and the thermal mass. The walls in a LSF building have better thermal insulation, but lower thermal mass than masonry buildings. The higher thermal mass in the walls of brick buildings reduces the diurnal internal temperature swings towards the average temperature, which could be too high or too low for comfort. It should be noted that the concrete floor in both building types contribute to the thermal mass of the building.

IMNE: What was the outcome of the tests?

JB: It was found that the LSF house will be warmer than a base case masonry building in winter, as well as in summer. If the hours of discomfort due to too high and too low temperatures are added together, the LSF house performs better than the masonry alternative in all locations but Durban.

As example, the indoor temperature of the LSFB was within the thermal comfort range for 74% of the time in Pretoria’s climate, compared with 71% for the masonry base case – a relatively small advantage.

IMNE: So does this small difference mean that energy consumption for heNike Air Max 97