Research on application and thermal performance of raw earth material in building envelope

Abstract

Mainstream green has recently swept the construction industry throughout the world. Building envelope and material are two important aspects of green building evaluation. As the growing development of new green building concept “human-orientation design”, raw earth, as a natural, locally sourced, minimally processed, and recyclable material that is very different from concrete, becomes one of the most attractive options. Most architects pay attention to the aesthetic design of the raw earth wall, while other researchers like civil engineers focus on the physical properties of raw earth material itself. Few studies discussed the effect of the raw earth wall in building a thermal environment. This paper firstly conducts a parametric study on the thermal performance of raw earth wall with the consideration of thermophysical properties of materials, application of thermal insulation layer in the wall, and design parameters, i.e. thickness, of each layer of the wall. A naturally ventilated public building in Shanghai is then simulated to discuss the feasibility and the most optimum strategy of raw earth wall applications as building envelope in the sub-tropical high-density cities. Based on comprehensive data analysis, four findings are identified: (1) Compared with common building materials like concrete, raw earth materials have significant advantages in two thermophysical parameters - thermal transmittance and thermal effusivity which directly influence the indoor air temperature; (2) Thickness and structure of both raw earth layer and insulation layer are two important design parameters to meet the requirements of the indoor thermal environment; (3) Raw earth wall performs better than the standardized “Green Wall” based on local green building standards; (4) In terms of thermal performance, “Raw Earth Wall with External Insulation” is more suitable in subtropics. However, “Raw Earth Wall with Sandwich Insulation” is more recommended if pursuing the beauty of raw earth materials, because the thermal performances of “Raw Earth Wall with Sandwich Insulation” and Raw Earth Wall with External Insulation” are almost the same in summer, and very close in winter.