Análise de transferência de calor em prisma composto por blocos de concreto com revestimento interno de gesso: subsídios para construções sustentáveis

Abstract

Environmental issues and sustainable development have guided the growth of cities. Sustainability in civil construction has major challenges in the industrial construction sector. One of the biggest is related to energy efficiency, that is, the industrial sector needs to efficiently reduce the environmental impact by seeking to use sustainable practices to reduce the use of fossil resources, allowing full recyclability, compliance with quality standards, energy efficiency combined with approaches aimed at technological evolution, economic and social development. The vertical fence along with the floor and roof are responsible for the interaction between the internal and external environments of the building to which it is inserted. Among these elements, the facade has fundamental importance and relevance in the constructive system, mainly because it is a great receiver of solar insolation. The objective of this work is to evaluate the heat transfer in prisms composed of concrete blocks (structural and solid cellular) with plaster internal coatings. The methodology of this research consists of making 02 prisms of blocks built from structural concrete blocks and solid blocks of cellular concrete. The composites received an external render with industrialized mortar 2.5 cm thick. In addition, new layers of plaster were added to the inside of the walls with different configurations of thicknesses of 1, 1.5 and 2.0 cm. Thus, prisms with different apparent mass densities were made for the study of heat transfer. For this to be possible, an active artificial condition was used as a source of study with continuous heat flow on the outside of the prism with temperature variations around 65 ± 2°C, focusing on the walls to evaluate the temperature conditions during 4 h of tests and later, determine the heat flux. In this way, the heat transfer values that were obtained in the tests of the prisms with and without coatings point to a greater thermal flux in the composition of the prism formed by structural concrete blocks - BCE without coating and a smaller thermal flux in the composite formed by blocks of cellular concrete - BCC with external coating composed of 0.5 cm of roughcast plus 2.0 cm of plaster. In the evaluations of the prisms with internal coating, the results showed that the heat transfer decreases when there was an increase in the thickness of the internal plaster coatings. The BCC prism with 2.0 cm thick internal plaster coating presented a lower thermal flux, when compared to the BCC prism with plaster coatings with thicknesses of 1.0 and 1.5 cm respectively. When the BCE prism had a smaller internal coating thickness, it obtained a higher heat flux value. Experimental studies have shown a significant reduction the internal temperature of the BCE prism around 2.82 °C, when a layer of 1.0 cm of plaster was added. In another expressive result, there was an excellent reduction of 3.13 °C in relation to the internal thickness of 2.0 cm of plaster and of 4.33 °C, the best result obtained, when there was an increment of the external ceramic coating plus 2, 0 cm of internal plaster. The BCC prisms showed a good reduction in the internal temperature, an average of 1.4 °C between the plaster layers with thicknesses of 1, 1.5 and 2.0 cm, however the best result occurred in the comparison between the BCC prism with 1, 0 cm related to the prism with a thickness of 2.0 cm of plaster plus external ceramic coating, there was a difference of 3.6 °C, obtaining a very relevant and satisfactory value for the research. Finally, the main thermal performance parameters were calculated: resistance, transmittance, capacity and thermal delay, according to NBR 15220 (ABNT, 2005). The thermal capacity found in the BCE and BCC prisms was compatible with the value suggested by the thermal performance standard, except for the uncoated BCC prism, which presented a lower value. The tests with infrared thermography allowed the qualitative analysis of heat transfer and temperature variations