June 9, 2015
Newcastle University’s engineering faculty recently did a study into the thermal properties of rammed earth. Earth Dwellings constructed a unstabilised rammed earth wall and Hillary Wong, under the guidance of Dr Michael Netherton, tested the wall in a hot box to determine the thermal properties of rammed earth. Rammed earth is often classified in terms of it’s R value, which is it’s steady state, or how it responds to a singular temperature change. In real life, the daily temperature changes dynamically, hot in the day, and cold at night. So test were conducted using a dynamic thermal analysis which gives a T value.
Hillary’s investigations showed that “Earthen materials are ideal substitutes for small to medium scale constructions, reducing carbon emissions and prolonging the use of non-renewable materials like steel and cement. Earth building materials require negligible embodied energy and also require low operational energy due to their superior thermal performance. Rammed earth possesses good thermal performance characteristics, however the steady state thermal resistance or R-values required by Australian energy efficiency schemes are not in accordance with the materials actual thermal superiority when tested dynamically. There is speculation about the inaccuracy of steady state analysis and the need for dynamic thermal analysis to determine the true thermal performances of materials. These current energy efficiency schemes (using only steady state parameters) are holding back earthen materials from being classified as a complete sustainable material.”
“A steady state and dynamic thermal analysis of a 300mm thick rammed earth wall was conducted to establish a full understanding on its thermal behaviour. As expected, the steady state and dynamic tests demonstrate contradictory results with steady state R-values showing poor thermal performance and dynamic T-values showing good thermal performance. A comparison between this rammed earth wall specimen and concrete panels proved that even though two materials can both be seen as poor thermal performers when steady state conditions are considered, the dynamic analysis can prove which material is truly a better thermal performer. This comparison proved that rammed earth is a good thermal performer, whilst the concrete panels were considered poor performers for both steady state and dynamic analysis. Rammed earth was also compared against an insulated cavity brick wall. Rammed earth’s thermal performance was found to surpass the performance of insulated cavity brick wall.”
“This proves that rammed earth has superior thermal performance. It clarifies that the dynamic thermal response of materials should be taken into account when analysing the thermal performance for energy efficiency schemes. Dynamic thermal analysis shows an accurate depiction of thermal behaviour and should be considered as a more appropriate test method as structures are exposed to dynamic diurnal conditions throughout their lifespan. The conclusion that rammed earth is a superior thermal performer proves that building with this earthen material can significantly reduce the operational energy of the structure. The near stable temperatures achieved inside the building decreases the need for additional heating and cooling, which is the main contributor to energy consumption in structures. This low operational energy combined with low embodied energy presents rammed earth as an ideal sustainable material for future construction.”
This shows the true value of rammed earth especially when used with good solar passive design !