THEORETICAL ANALYSIS OF THERMAL PERFORMANCE OF CLAY AND CONCRETE MASONRY STRUCTURAL UNDER VARIOUS CONDITIONS Grabarz, Regina Candeloro 1 ; Souza, Léa Cristina Lucas 2 ; Parsekian, Guilherme Aris 3 1 MSc Candidate, Federal University of São Carlos, Civil Construction Graduated Program, regina.cg@hotmail.com 2 PhD, Professor, Federal University of São Carlos, Civil Engineering Department, leacrist@ufscar.br 3 PhD, Professor, Federal University of São Carlos, Civil Engineering Department, parsekian@ufscar.br Currently, construction system has been widely used in Brazilian housing construction as it offers significant advantages in relation to building execution time consumption and costs. Considering the wide use of this system, it is important to assess whether the commonly wall thickness, material and rendering meets the levels of minimum thermal comfort required by the Brazilian performance codes. Analyzing the thermal performance of concrete and clay structural walls, the thermal properties of these systems were calculated and its adequacy for different bioclimatic zones in Brazil has been verified. The results indicate that the structural clay has better performance than the concrete when compared to uncoated internal and external walls. As a conclusion, it is pointed out the regions in which clay and concrete walls built in accordance to the common construction standards are thermically adequated. Keywords: Low-Income Housing, Structural Masonry, Thermal Performance INTRODUCTION Among serious social problems faced by Brazilians, accessibility to housing is placed in focus. The Brazilian housing deficit in 2007 was 6.273 million households (BRASIL, 2009). Achieving a high demand for Social Housing - SH is not an impossible challenge. The adoption of industrialized building systems is a response to the promotion of this type of building. Mainly because the actual demand requires optimization of time and costs of execution. On this point, the structural construction system becomes a very advantageous solution. It can be applied to projects of SH, because it reduces the total project costs and it is easy to implement. It is conceived through rational calculation, having as its main characteristic, the multi-functional, functioning both as a seal and as a building structure. In order to attend the current needs, in July 2001 the Associação Brasileira de Cimento Portland (ABCP) launched a project called CASA 1.0. The main objective of this was to assist in reducing the housing deficit in Brazil.CASA 1.0 was developed with focus on the evolution of processes towards industrialization, seeking the optimization of project.. This optimization is based on several premisses, among which we highlight here the environmental projects aimed at user comfort, well ventilated and lit (ABCP, 2002).
Despite the need for user comfort, many builders, architects and engineers indiscriminately adopt the building system with structural, without any regard to the thermal performance of the building envelope. Studies conducted by various Brazilian researchers show that the achievement of users' thermal comfort in low-income housing is rare. The main reason of this is the adoption of projects without consideration to the climate region where they are constructed. Based on the above, this article seeks to theoretically study the adequacy of the application of clay building block and concrete - the most applied in Brazil - and their structural for different climatic regions in Brazil. In order to do so, we take into account the bioclimatic zones of Brazil established by NBR 15220-3:2005 and the minimum performance conditions determined by it. The theoretical approach initially establishes the key concepts involved in the thermal performance of residential buildings, then presents the methodological steps and finally points out the results, analysis, discussions and conclusions. FUNDAMENTS, CHARACTERISTICS, DEFINITIONS AND DELIMITATIONS The thermal performance of residential buildings depends on climatic conditions of the site and on construction features they present. While the climate and weather conditions are responsible for the amount of thermal energy available in the environment, the design characteristics influence the passage of heat through the building envelope (façades and roofs). The properties of building materials determine their behavior on admission, transfer, storage and heat emission. The main characteristics involved in this process are defined by the NBR 15220-1:2005, some of which are highlighted in Table 1. Table 1: Relevant Characteristics to the thermal performance of buildings (NBR 15220-1:2005) Characteristics Definition Symbol Unit Thermal Conductivity Physical property of a homogeneous and isotropic material, in which there is a constant heat flow, with a density of 1 W/m2, when W/(m.K) subjected to a uniform temperature gradient of one Kelvin per meter. Apparent mass density Ratio of mass to apparent volume of a body. kg/m³ Specific Heat or Specific Heat Capacity Ratio of heat capacity by mass. c J/(kg.K) Transmitance W/(m².K) Level of heat transfer corresponding to the layers of an element or component. U W/(m².K) Thermal lag (hours/s) Elapsed time between a thermal variation in a medium and its manifestation on the surface opposite to a constructive component subjected to a periodic regime of heat transfer. h Solar heat gain coefficient of opaque elements Ratio of the rate of solar radiation transmitted through an opaque component on the rate of total solar radiation incident on the outer surface of the same. FSo -
The NBR 15220-3:2005 provides recommendations and guidelines for climate adaptation of social interest houses. With regard to the, the standard classifies three types of walls (external seal): light, reflecting light and heavy. To each of these classes is assigned a minimum value required for the walls (Table 2), whose parameters are given through the thermal transmittance, thermal lag and the solar heat gain coefficient. In order to calculate the transmittance and the thermal lag, one should consider if the wall is composed of homogeneous layers (containing thermal resistances in series) or non-homogeneous and homogeneous layers (with thermal resistances in parallel). Table 2: Parameters of thermal transmittance, thermal lag and solar heat gain coefficient for eligible walls (NBR 15220-3:2005) External Building Envelope Thermal Thermal lag - transmittance - U Hours W/m².K Solar Factor- FSo Light U 3,0 4,3 FSo 5,0 Walls Light reflective U 3,6 4,3 FSo 4,0 Heavy U 2,2 6,5 FSo 3,5 For each of the 8 (eight) bioclimatic zones (Figure 1) established by the NBR 15220-3:2005, it is recommended a type of building envelope, as is summarized in Table 3. Figure 1: Brazilian bioclimatic zones (NBR 15220-3:2005) Table 3: Recommending building envelope wall for each of the eight Brazilian bioclimatic zones (NBR 15220-3:2005) Recommendation wall for each of the eight bioclimatic Brazilian zones WALLS ZONES Light 01 02 Light and Reflector 03 05 08 Heavy 04 06 07
METHODOLOGY The methodology was divided in two stages: consisted on a planning phase and then the processing and analysis. The planning stage allowed to raise the dimensional characteristics of the units, define the case study layout in structural, choose the software to be used and the sources of information. The stage of processing and analysis allowed the establishment of the performance of units studied for the selected project and verification of the adequacy of the building system to the Brazilian bioclimatic zones. An overview of the work steps is shown in Figure 2. Figure 2: General steps of the methodology CHARACTERISTICS OF MASONRY UNITS STUDIED AND DATA SOURCES Two types of units were studied: clay and concrete hollow blocks. The units studied were selected depending on the availability of the product in the Brazilian market, the degree of implementation and the cost. The criterion for choosing the size of the unit was taken from the publication of the file available electronically by the ABCP, (2001) entitled CASA 1.0. This project layout was developed specific for the use of concret structural. Among the available dimensions in the market, the 14 cm x 19 cm x 39 cm (width x height x length) block was selected. For a more comprehensive study, apart from the concrete block, suggested by the ABCP, the clay block of the same dimension was also investigated. Currently, both are the most widely used structural units in Brazil and are shown in Figure 3.
(a) (b) Figure 3: Illustration of structural units, (a) concrete and (b) clay The source of information used as a database to calculate the characteristics of the units was the Manual Técnico de Alvenaria, (CHICHIERCHIO, 1990) which provides data of specific density (ρ) and thermal conductivity coefficient (λ). For information on specific heat (c), the reference was NBR 15220-2:2005, Table B.3. Thus, the characteristics of each unit type studied here are presented in Table 4 and Table 5. Table 4: Characteristics of concrete blocks, specific density (ρ), thermal conductivity coefficient (λ) and specific heat (c) BLOCK A BLOCK B BLOCK C Specific density (kg/m³) 2.300 2.100 2.200 Thermal conductivity coefficient (W/mºC) 1.81 1.80 1.70 Specific heat (kj/kg.k) 1.00 1.00 1.00 Table 5: Characteristics of clay blocks: specific density (ρ), thermal conductivity coefficient (λ) and specific heat (c) BLOCK A BLOCK B BLOCK C Specific density (kg/m³) 1.800 1.800 1.800 Thermal conductivity coefficient (W/mºC) 1.00 1.00 1.00 Specific heat (kj/kg.k) 0.92 0.92 0.92 MASONRY STRUCTURAL CHARACTERISTICS AND DATA SOURCES The ABCP model CASA 1.0 is a model of Social Housing applied throughout Brazil. This study considered the elements described in CASA 1.0 report as the reference for calculations of the around the unit (block). The report describes that external walls have acrylic paint applied directly on the blocks, and the inner walls (dry areas) are covered with industrialized plaster mortar, 0.5-cm thick. A brief survey of colors indicated that yellow (or variations of this color) is one of the most common color applied in external walls of Brazilian social houses and also that few houses are painted white. Therefore, this was considered in calculating the solar heat gain coefficient. SOFTWARE USED IN CALCULATION OF THERMAL PROPERTIES Transmitância 1.0, developed by the Laboratório de Eficiência Energética em Edificações LabEEE, Universidade Federal de Santa Catarina UFSC, were the software used to apply the method for calculating the thermal performance of ISO 15220. The input data of this software are: heat flux, external surface, data of section (height x length x thickness), thermal conductivity coefficient (λ), specific density (ρ) and specific heat (c). The outputs of the
software are: thermal transmittance (W/m².K); thermal resistance (m².k/w); heat capacity (kj/m².k); solar heat gain coefficient and thermal lag (hours). Thus, the input data of the program are related to the element or component data and sections and layers data. The elements or components data area related to flow direction, external and internal superficial resistance, characteristics of external surface, absortance and emissivity. The section data referring to the layers finishing are the height and length, while the data corresponding to the layer itself are the thermal conductivity, the density, the specific heat and the thickness. The flows were considered horizontal, as they were walls, and the sections used for calculation are described in Table 6 and Figure 4. Table 6: Sections used for calculation of thermal properties Concrete block 14 cm x 19 cm x 39 cm Clay block (width x height x length) Mortar 1 cm in thickness between blocks Plaster 0.5 cm thick (inner wall) (a) (b) Figure 4: (a) single element and (b) wall element According to the standards, the thermal resistance of external surfaces is 0,04 (m 2.K)/W, while the resistance of internal surfaces is 0.13 (m 2.K)/W, The absortances and emissivities were made available by the software. Their values are 0.30 for yellow paint absortance and 0.90 for yellow paint emissivity. For the concrete blocks and clay blocks these values were in both cases 0.65 e 0.85. SUITABILITY FOR BIOCLIMATIC REGIONS In order to analyze the performance of structural clay and concrete, the recommendations described in NBR 15220-3:2005 were adopted. The suitability of them for each of the eight bioclimatic Brazilian zones was verified. The calculated values were compared with the parameters of Tables 2 and 3. Then it was possible to point out the climate regions where the building systems studied have adequate thermal performance.
RESULTS AND ANALYSIS The results obtained for the concrete blocks and clay are shown in Table 7 and Table 8. For consideration of the possible variations according to different manufacturers, the mean values were also calculated and compared with each other and are presented in Table 9. Table 7: Characteristics of concrete blocks: Transmittance W/(m².K), Thermal lag (hour/s) and Solar Factor BLOCK A BLOCK B BLOCK C AVERAGE Transmittance W/(m².K) 4.04 4.04 3.96 4.01 Thermal lag (hour/s) 3.1 3.0 3.2 3.10 Solar Factor 10.5 10.5 10.3 10.4 Table 8: Characteristics of clay blocks: Transmittance W/(m².K), Thermal lag (hour/s) and Solar Factor BLOCK A BLOCK B BLOCK C AVERAGE Transmittance W/(m².K) 3.23 3.23 3.23 3.23 Thermal lag (hour/s) 3.6 3.6 3.6 3.60 Solar Factor 8.4 8.4 8.4 8.40 Table 9: Thermal characteristics of concrete blocks and clay: Transmittance W/(m².K), Thermal lag (hour/s) and Solar Factor CONCRETE CLAY Transmittance W/(m².K) 4.01 3.23 Thermal lag (hour/s) 3.10 3.60 Solar Factor 10.4 8.40 ANALYSIS OF THE RESULTS OF THERMAL PROPERTIES Regarding the thermal analysis of the unit, the survey found that the clay block has better thermal performance than concrete blocks. While clay blocks have a thermal transmittance of 3.23 W / (m². K), the concrete blocks have to 4.01 W/(m².K). The clay thermal lag is 3.6 (hour/s), whilst the concrete one is 3.10 (hour/s). Solar heat gain coefficient for clay block is 8.40 and for concrete block is 10.4. With the data obtained it is possible to compare the thermal performance of both as shown in Table 10. The structural clay under the same conditions of structural concrete, presented the best thermal performance among the systems, because it transmits 0.71 W/(m².K) less than the other, it has a thermal lag with a gain of 0.3 hours/s and solar heat gain coefficient of 0.9 less than concrete. Table 10: Thermal performance of the blocks, and their difference: Transmittance W/(m².K), Thermal lag (hour/s) and Solar Heat Gain Factor CONCRETE CLAY Block Masonry Relative Relative Block Masonry Difference Difference Transmittance W/(m².K) 4.01 3.91 2.5% 3.23 3.2 0.93% Thermal lag (hour/s) 3.1 3.3 6.5% 3.6 3.6 - Solar Factor 10.4 4.7 54.8% 8.4 3.8 54.8%
By adding elements of painting, plaster and mortar, there was a significant difference in the thermal performance of the construction elements (blocks) and components (), especially with regard to the Solar Factor, which dropped 54.8% to block, in both cases. The clay block is more stable to the new elements that made up the than concrete block. CLIMATE ANALYSIS OF SUITABILITY IN BRAZIL Initially, considering the bioclimatic zones for which the light walls are recommended by NBR 15220-3:2005, Table 11 highlights the values of some parameters disposing of the study zones 01 and 02 compared with the concrete and clay, according to the memorial of the ABCP CASA 1.0 (outside wall with yellow paint on the and the inside wall with 0.5 cm of plaster), which were highlighted (bold and underlined) values according. It can be seen that both walls have an adequate response as to the thermal lag and solar factor, but with regard to the thermal transmittance, none of them reached the recommended amount, so none of the should be assigned to these regions. Table 11: Study of Bioclimatic Zones 01 and 02 WALLS Transmittance - U W/ (m².k) Thermal lag - (hour/s) Solar Factor - FSo Light U 3.00 4.3 FSo 5.0 Structural CONCRETE 3.91 3.3 4.7 Structural CLAY 3.20 3.6 3.8 For light reflective walls, Table 12 allows the study of bioclimatic zones 03, 05 and 08 (on the same conditions as the previous study). Leading the recommended values for the building envelope, light and reflective wall, it is clear that the structural concrete has adapted itself only in relation to the thermal lag. Thus it fits the minimum recommended by the standard.the structural clay falls in all the values recommended by the standard and may be indicated for zones 03, 05 and 08 as light and reflective wall type. It is noteworthy that this statement meets the requirements of the study - building block of 14 cm x 19 cm x 39 cm (width x height x length), outer paint directly onto the surface of the and plaster cover of 0.5 cm. Table 12: Study of Bioclimatic Zones 03, 05 and 08 WALLS Transmittance - U W/ (m².k) Thermal lag - (hour/s) Solar Factor - FSo Light and Reflector U 3.60 4.3 FSo 4.0 Structural CONCRETE 3.91 3.3 4.7 Structural CLAY 3.20 3.6 3.8
For the bioclimatic zones 04, 06 and 07 (on the same terms as the previous study), the recommendations correspond to heavy walls. None of the walls studied fulfilled the minimum established by standards. This statement can be verified on the values shown in Table 13. Table 13: Study of Bioclimatic Zones 04, 06 and 07 WALLS Transmittance - U W/ (m².k) Thermal lag - (hour/s) Solar Factor - FSo Heavy U 2.20 6.5 FSo 3.5 Structural CONCRETE 3.91 3.3 4.7 Structural CLAY 3.20 3.6 3.8 DISCUSSION AND CONCLUSIONS The structural clay block as an isolated element has presented a better thermal performance than the structural concrete block. Covering the study within the, it was possible to verify that the addition of elements such as painting and internal plastering within the standards specified in the survey, structural clay still stands out with a better thermal performance than concrete structural. Analyzing the structural as a function of adaptation to Brazilian bioclimatic zones, and according to recommendations of NBR 15220-3:2005, it was established that both, concrete and clay, are not suitable for two types of building envelopes, light and especially the heavy. Therefore they are not suitable for zones 01, 02, 04, 06 and 07. With regard to the zones 03, 05 and 08, only the structural clay fits the minimum values indicated for building envelopes, because they can be considered light and reflective. These results indicate the need for specific analysis of the various s units and structural systems before its indiscriminate application. They cause thermal performance below the minimum required. Considering that many buildings are already being developed with these solutions, there is a urgency of taking effective measurements for the achievement of a better quality of life for users. REFERENCES ASSOCIAÇÃO BRASILEIRA DE CIMENTO PORTLAND (ABCP). Manual Técnico para Implementação Habitação 1.0 Bairro Saudável. População Saudável. São Paulo, 2002. 88 p. ASSOCIAÇÃO BRASILEIRA DE CIMENTO PORTLAND (ABCP). Casa Modulada em Blocos de Concreto: Sugestão de Projeto. 2001. Available at: <http://www.abcp.org.br/conteudo/wpcontent/uploads/2010/01/ae_planta_kit_sugestao.pdf>. Accessed: 01 set. 2010. ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS (ABNT). NBR 15220-1: Desempenho térmico de edificações Parte 1: Definições, símbolos e unidades. Rio de Janeiro, 2005.
ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS (ABNT). NBR 15220-2: Desempenho térmico de edificações Parte 2: Métodos de cálculo da transmitância térmica, da capacidade térmica, do atraso térmico e do fator solar de elementos e componentes de edificações. Rio de Janeiro, 2005. ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS (ABNT). NBR 15220-3: Desempenho térmico de edificações Parte 3: Zoneamento bioclimático brasileiro e diretrizes construtivas para habitações unifamiliares de interesse social. Rio de Janeiro, 2005. CHICHIERCHIO, L. C. Conforto Ambiental: Desempenho térmico e acústico e proteção contra fogo. In: ASSOCIAÇÃO BRASILEIRA DA CONSTRUÇÃO INDUSTRIALIZASA. Manual técnico de Alvenaria. São Paulo: ABCI/PROJETO, 1990. p 119-141. Laboratório de Eficiência Energética em Edificações (LabEEE). Universidade Federal de Santa Catarina (UFSC). Transmitância versão 1.0 (beta). [20--?]. Available at: <http://www.labeee.ufsc.br/software/transmitancia.html>. Accessed: 24 nov. 2010. MINISTÉRIO DAS CIDADES, SECRETARIA NACIONAL DE HABITAÇÃO. Déficit Habitacional no Brasil 2007. Belo Horizonte, 2009. 128 p.