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drops ISSN 2175-6716


Faz-se aqui uma reflexão sobre o desempenho térmico e energético do edifício “caixa de vidro”, em climas quente, com base em fenômenos da física aplicada. Ao final, retoma-se a necessidade de revisão do uso generalizado do vidro sem proteção externa.

A reflexion about the thermal and energy performance of the glass-box building in warm climates is put forwarded here, based on the phenomena of the applied physics.

Se hace aqui una refleccion sobre el rendimiento térmico y energético del edifício “caja de vidrio” en climas calientes, basada en fenômenos de la física aplicada.

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GONÇALVES, Joana; et. al. The poor environmental performance of offices behind the glass-box. Thermal comfort and energy demand (chapter 02/08). Drops, São Paulo, year 21, n. 160.02, Vitruvius, jan. 2021 <>.

Collage-Manifest 2
Colagem de Eduardo Pizarro / Collage by Eduardo Pizarro [Acervo pessoal / Personal collection]

The glass-box building is the one of a artificially controlled environment for 100% of the time, with the use air conditioning systems and artificial light, corresponding to a concept of environmental comfort from the 70s, proposed by P. O. Fanger (1) and characterized by a narrow thermal zone, of supposed comfort temperatures that oscillate around 22oC, with serious implications from the point of view and well-being of the occupants and to the associated energy demand. To a great extent, due to this approach, in the years 2000 the global commercial and residential building stock was already responsible for approximately 60% of all electricity produced globally (2).

Nowadays, 50 years after the popularization of the glass-box building, hermetically sealed, the market sector of office buildings has available types of glass which are commercialized as efficient alternatives to control solar radiation, encompassing different types of coloured glass and reflective glass with various treatment to diffuse radiation (“milky” aspect), which is applicable to single or double glazed facades and even in triple and quadruple glass façades. However, the question about the influence of these types of glass on the holistic environmental performance of the building remains, considering the specific climatic conditions of a city like Sao Paulo.

The high degree of thermal insulation, natural of glass facades with two or more layers is not an adequate feature to the envelop of buildings in warm places (even for those artificially climatized for 100% of the time), where solar radiation is the climatic variable with the potential biggest impact on internal thermal environments and not the external air temperatures, as it happens in colder climates (3). Looking at the example of São Paulo, the maximum global radiation can supersede the mark of the 1.000 W/m² on an unobstructed horizontal plane, whilst maximum mean temperatures for the warmest month in the year stays around 27,5oC, being this value significantly lower than in other cities of warm climates, such as Rio de Janeiro, where the maximum daily average temperature between December and March figures above the mark of 30°C (4).

The thermal insulation of double glazed facades can be four times bigger than the single glazed one. In the single glazed scenario, the heat generated internally, a part from being partially removed by the air conditioning system, is also lost to the exterior via the glass conduction during those hours when the internal temperatures are smaller than the external, which is frequently the case in Sao Paulo during the first hours of the morning and late hours of the day, including the summer period. In the meantime, a great deal of solar radiation enters the building via the transparency of the glass, to a certain extent even in those cases of reflective and coloured glass, because some degree of transparency is kept, despite being reduced by the referred treatment.

In this respect, the reflective glass types are the worse, as they allow the transmittance of a portion of solar radiation associated merely with heat associated with the long wave radiation, at the same time that block the radiation spectrum associated with daylight and, consequently, make the interior darker, given a false impression that “the heat was left in the outside”.

About the glass types with the “milky”/diffuse effect, such as the new U-glass (a type of glass-brick with two sets of double glazing and an internal cavity, which has recently arrived in the Brazilian market of commercial architecture), the hypothesis is that its performance has a positive impact in controlling glare caused by the incident solar radiation, resulting in quite homogenous daylight conditions, however with the same risks and implications of internal overheating as in the case of the glazed types different from the single glaze solution, furthermore, compromising the visual communication between interior and exterior.

On the contrary, the use of external shading continues to have a more important role to a better environmental and energetic building performance rather than the thermal insulation of the facade, in some cases making viable the adoption of natural ventilation in those times of the day when external temperatures are more mild, since a great portion of global radiation on the outside of the building’s envelop and, therefore, contributing to the achievement of more mild internal temperatures.

The accumulation of heat inside a glass-box building due to solar gains alone (which is added to the heat generated by the occupation) leads to high amounts of thermal loads, which need to be removed by the air conditioning system, in order to make the space occupyable. Simplified calculations of solar gains for a typical glass-box building in Sao Paulo, carried out by students of Architecture and Urbanism undergraduate course of FAU USP, showed that if such thermal load was not removed, internal temperatures would go above the 40oC, whilst external temperatures are around 24oC.

From the energy perspective, data raised in loco in a sample of office buildings in Rio de Janeiro and Sao Paulo pointed out the consumption values up to 268 kWh/m²/year, where space cooling accounts for typically 50% of the total (5). On the other hand, analytical studies performed by Julia Galves (6) demonstrated the possibility of reducing cooling loads of a hypothetical building model in São Paulo, from 130 kWh/m2to 72 kWh/m2, approximately, as a function of adequate shading, associated with other strategies for the thermal and energy building´s performance, including the exposure of the internal concrete structure acting as a heat-sink to the heat generated internally by the occupation.

It is worth mentioning that the same studies pointed out to a likely increase of 20% in the cooling demand of glass-box office buildings without external shading by 2050, because of climate change and the consequent warm-up of urban climate.

Besides the problem of cooling energy demand in this specific building type, there i salso the risk of discomfort, particularly for those who are positioned near the glass façade, due to the heat which is emitted by the internal surface of the glass facade. These occupants are exposed to the contrast created between the internal mean temperature (usually between 22 and 24oC) and the cool air pushed into the space by the air conditioning system, close to the facade area (around 14oC or lower) and is necessary to counter act the heat irradiated by the glass which has been heated-up from the outside up by the sun, because of the lack of external shading.

The attempt to block radiation by applying a shading factor to the glass (with colour), or any kind of reflective treatment, ends up creating darker spaces in which the artificial light becomes a constant necessity, different from what happens in the case of diffuse-effect glass types, as already mentioned. This is because of the access of sun rays into the space (even with the coloured and/or reflective glass), occupants are driven to introduce various types of internal devices for solar control, such as blinds and curtains, which tend to darken the space and isolate the visual communication between interior and exterior.

As a result, the classic “promise” of visual communication provided by the glass facade technology “goes out of the window”. The translucent rolo blinds type, that filter the solar radiation rather than blocking it, is an option available in the Brazilian market today, that allows the necessary daylight inside. Nevertheless, the external solar heat is still passing through. For this reason, the solutions for facades of better environmental performance in cities of warm climates like São Paulo, is related to the revision of the generalized use of glass and the development of external shading strategies, including the reinvention of the classic brise-solei, an icon of the Brazilian Bioclimatic Modernism.


NE – This is the second in a series of eight articles on the topic of “environmental performance”. The complete series is as follows:

GONÇALVES, Joana; et. al. The poor environmental performance of offices behind the glass-box. An overview (chapter 01/08). Drops, São Paulo, year 21, n. 158.08, Vitruvius, nov. 2020 <>.

GONÇALVES, Joana; et. al. The poor environmental performance of offices behind the glass-box. Thermal comfort and energy demand (chapter 02/08). Drops, São Paulo, year 21, n. 160.02, Vitruvius, jan. 2021 <>.

GONÇALVES, Joana; et. al. The poor environmental performance of offices behind the glass-box. The control of the thermal environment and air quality in times of pandemic (chapter 03/08). Drops, São Paulo, year 21, n. 161.02, Vitruvius, feb. 2021 <>.

GONÇALVES, Joana; et. al. The poor environmental performance of offices behind the glass-box. Daylight and artificial light. Drops, São Paulo, year 21, n. 162.08, Vitruvius, mar. 2021 <>.

MICHALSKI, Ranny; et. al. The poor environmental performance of offices behind the glass-box. Acoustic comfort. Drops, São Paulo, year 21, n. 163.02, Vitruvius, apr. 2021 <>.

GONÇALVES, Joana; et. al. The poor environmental performance of offices behind the glass-box. The transformation force of architectural strategies. Drops, São Paulo, year 21, n. 164.08, Vitruvius, may 2021 <>.

MICHALSKI, Ranny; et. al. The poor environmental performance of offices behind the glass-box. The myth of green certifications (chapter 07/08). Drops, São Paulo, year 21, n. 165.07, Vitruvius, jul. 2021 <>.

GONÇALVES, Joana; et. al. The poor environmental performance of offices behind the glass-box. Future perspectives (chapter 08/08). Drops, São Paulo, year 21, n. 166.09, Vitruvius, jul. 2021 <>.

FANGER, P. O. Thermal comfort: analysis and application in environment engineering. Nova York, McGraw Hill, 1972.

IEA – International Energy Agency. World Energy Outlook 2009 <http://www.iea/electricity>.

FROTA, Anésia Barros; SCHIFFER, Sueli Ramos. Manual de conforto térmico. 7ª edição. São Paulo, Nobel, 2005.

INMET – Instituto Nacional de Meteorologia. Arquivos Climáticos 2018. 2019 <>.

CBCS – Conselho Brasileiro de Construção Sustentável. DEO – Desempenho Energético Operacional em Edificações. Benchmarking de escritórios corporativos e recomendações para certificação DEO no Brasil. Relatório Final, 2015 <>

GALVES, Julia. Contemporary Translucent Buildings in São Paulo. Dissertação (Architecture and Environmental Design – AED, University of Westminster, 2019.

about the authors

Joana Carla Soares Gonçalves é arquiteta e urbanista pela UFRJ, mestre em Environment and Energy pela AA School of Architecture, doutora e livre-docente pela FAU USP. Orientadora dos programas de pós-graduação Arquitetura e Urbanismo da FAU USP e Architecture and Environmental Design, School of Architecture and Cities, University of Westminster, Londres. Profa. da AA School of Architecture, Londres. Diretora da Associação PLEA.

Roberta C. Kronka Mülfarth é arquiteta e urbanista pela FAU USP, mestre pelo Programa Interdisciplinar de Pós-Graduação em Energia da USP, doutora e livre-docente pela FAU USP. Orientadora de pós-graduação em Arquitetura e Urbanismo da FAU USP e no Programa de Educação Continuada – PECE, no curso de especialização de Gestão em Cidades, junto a POLI USP. Vice-coordenadora do USP Cidades. Chefe do Departamento de Tecnologia da FAU USP.

Marcelo de Andrade Roméro é professor titular da FAU USP. Arquiteto e urbanista pela UBC, mestre, doutor e livre docente pela FAU USP, Pós-Doc pela CUNY (USA). Orientador e professor dos programas de pós-graduação da USP, do Instituto de Pesquisas Tecnológicas do Estado de São Paulo – IPT, da Universidade de Brasília, do Centro Universitário Belas Artes de São Paulo e da Peter the Great St. Petersburg Polytechnic University.

Ranny Loureiro Xavier Nascimento Michalskié engenheira mecânica pela UFRJ, mestre e doutora em engenharia mecânica pela COPPE-UFRJ. Professora doutora da FAU USP, onde atua como docente no ensino e na pesquisa, na graduação e na pós-graduação. Coordenadora da Regional São Paulo da Sociedade Brasileira de Acústica – Sobrac. Participa da elaboração de normas técnicas brasileiras em acústica da Associação Brasileira de Normas Técnicas – ABNT.

Alessandra Rodrigues Prata Shimomura é arquiteta e urbanista pela PUC-Campinas, mestre pela Unicamp e doutora pela FAU USP. Professora pela Faculdade de Arquitetura e Urbanismo e Orientadora do programa de pós-graduação em Arquitetura e Urbanismo da FAUUSP. Advisor no Student Branch ArchTech Labaut da ASHRAE e Membro do Comitê PLEA (Passive and Low Energy Architecture) Chapter Latin America and the Caribbean (PLEA-LAC).

Eduardo Pimentel Pizarro é arquiteto e urbanista, mestre e doutor pela FAU USP. Professor da Universidade São Judas. É embaixador do LafargeHolcim Awards e já desenvolveu pesquisa na Architectural Association Graduate School, em Londres, e na ETH, em Zurique. Ganhador de prêmios como o Jovem Cientista (Brasília, 2012) e o LafargeHolcim Forum Student Poster Competition (Detroit, 2016).

Monica Marcondes-Cavaleri é arquiteta e urbanista, doutora e pós-doutora pela FAU USP. mestre pela AA Graduate School, Londres. Há 15 anos é consultora e pesquisadora em desempenho ambiental e eficiência energética da arquitetura. Especialista no uso de ferramentas avançadas de simulação computacional em avaliações dinâmicas e integradas de desempenho ambiental e eficiência energética. Auditora AQUA-HQE.

Marcelo Mello é engenheiro civil pela Politécnica USP, arquiteto e urbanista pela FAU Mackenzie, Mestre em Sustainable Environmental Design pela Architectural Association School of Architecture, Londres, e doutor pela FAU USP. Trabalhou com consultoria em sustentabilidade no Centro de Tecnologia de Edificações – CTE, e hoje atua como Diretor na Arqio Arquitetura e Consultoria.

João Pinto de Oliveira Cottaé arquiteto pela PUC-Campinas, mestre em Sustainable Environmental Design pela AA School of Architecture, Londres, e doutorando pela FAU USP. Sócio do escritório Oliveira Cotta Arquitetura. Em seu portfólio destacam-se o novo centro de P&D da empresa Siemens na Ilha do fundão, no Rio de Janeiro e a ampliação da estação de metrô Santo Amaro.

Juliana Pellegrini L. Trigo é arquiteta e urbanista pela FAU Mackenzie, pós-graduanda no programa de Arquitetura e Urbanismo da FAU USP, com foco em processo de projeto de edifício de alta desempenho. President Elect ASHRAE Brasil Chapter 2021/2022 e diretora do escritório Studio Symbios. Com mais de 20 anos de atuação, obteve publicações e premiações em concursos nacionais e internacionais.



160.02 desempenho ambiental
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