Possibilities for improving the equivalent thermal transmittance of single-leaf walls for buildings

• Thermal transmittance of the wall has a linear dependency on clay conductivity.
• Adding a lightening additive to the clay is the best economical solution.
• Ueq of a wall may be decreased by up to 20%, if we decrease λclay by up to 50%.
• An equation has been obtained to estimate the improvement in Ueq of a wall.

Recent years have seen several studies on the factors influencing heat transfer in single-leaf walls made of large lightweight clay blocks, the aim being to reduce energy losses and moderate the use of heating and air conditioning.Those factors are the geometry of the block (internal voids and vertical joint), the execution of the wall (horizontal joint) and the thermal conductivity of clay.This paper provides a comprehensive analysis of the various factors by making a comparative study of the equivalent thermal transmittance of the wall obtained with different geometries and different executions of the wall, depending on clay conductivity. Note that this parameter is the one on which it is easiest to act, by adding appropriate amounts of lightening additive in the manufacturing process.Our findings reveal that a percentage decrease in clay conductivity produces a linear percentage reduction in the thermal transmittance of the wall, regardless of the type of block and wall mounting. In particular, a 50% decrease in the thermal conductivity of the clay leads to a 20% reduction in the equivalent thermal transmittance of the wall.An equation has been obtained that enables the decrease in the equivalent thermal transmittance of a wall when the thermal conductivity of the clay is decreased to be estimated with an error of less than 3%.

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