THE GREEN ROOF THERMAL PERFORMANCE EVALUATION IN

Angélica Felicidade Guião Marcato Costa, João Alexandre Paschoalin Filho, Tatiana Tucunduva Philipi Cortese, Brenda Chaves Coelho Leite. -- Archnet-IJAR, Volume 12 - Issue 3 - November 2018 - (288-307) – Regular Section

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Archnet-IJAR: International Journal of Architectural Research www.archnet-ijar.net/ -- https://archnet.org/collections/34

THE GREEN ROOF THERMAL PERFORMANCE EVALUATION IN COMPARISON TO ASBESTOS CEMENT TILES APPLIED TO LIGHT STEEL FRAME BRAZILIAN BUILDINGS DOI: http://dx.doi.org/10.26687/archnet-ijar.v12i3.1709

Angélica Felicidade Guião Marcato Costa; João Alexandre Paschoalin Filho; Tatiana Tucunduva Philipi Cortese; Brenda Chaves Coelho Leite

Keywords Abstract

thermal comfort; sustainable constructions; green roof

This research aimed at comparing the thermal performance provided in experimental modules, one of which was performed with conventional cover, made of asbestos cement tiles; an another with green cover. The structure of the studied modules was executed using Light Steel Frame technique. As an experimental research, modules were built in a wide place, without the interference of shading. Instruments were installed in the inner part of the modules to measure the following data: air temperature, relative humidity. From the collected data, representative episodes have been chosen for the studies that aimed to compare the comfort provided by both modules, built with different roofs. As result, it was verified that the module with green roof had better performance than the module covered with asbestos cement tile in all selected episodes. The module covered with green roof maintained lower internal temperature variation throughout the days, indicating that the green roof has characteristic thermal insulation, reducing the heat flow from the roof.

A.F.G.M. Costa: University Nine of July, Adolpho Pinto Avenue 109, São Paulo, 01156-050, Brazil; J.A.Paschoalin Filho*: University Nine of July, Adolpho Pinto Avenue 109, São Paulo, 01156-050, Brazil T.T.P.Cortese: University Nine of July, Adolpho Pinto Avenue 109, São Paulo, 01156-050, Brazil; B.C.C.Leite: University of São Paulo, São Paulo, Brazil *Corresponding Author’s email address: [email protected]

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International Journal of Architectural Research



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INTRODUCTION

Discussions about sustainability have been taken great relevance. In this context, the urbanization and civil construction industry are the main players responsible by environmental impacts. There are many effects caused by the modern urbanization model in last decades, such as hygrothermal discomfort and heat islands. The thermal discomfort inside the buildings increases considerably in the face of this phenomenon. In this situation, Mascaró and Mascaró (2009), comment that vegetation has an important role to improve the urban ambience. Tan et. al (2017) highlights the phenomenon of Urban Heat Island (UHI) as one of the most significant impacts of urbanization, which is defined as the observation of significantly higher air temperature in densely built environments to their surrounding rural areas. Tam et. al (2017) comment that many studies have observed temperatures increases up to 4oC arising from UHI in many cities all over the world. To Tan et. al (2010), Urban Heat Island has negative consequences on human health, human outdoor comfort and energy consumption for regulating indoor temperatures inside the buildings.

As stated by Squier and Davidson (2016), the urbanization of past century led to destruction increasing of natural environmental and great areas of waterproof cover. According to the authors, many ecosystems were destroyed and natural cycles were altered. Within this context, green roofs or vegetated roofs are often used by their ability to provide quasi-natural surfaces. Green roofs can help regulate thermal process, leading to reductions in building cooling and heating loads and decreases urban heat island phenomenon. Silva et. al (2011) comment that the hygrothermal discomfort generated by the cities could be softened with natural resources. In this way, green roofs became an important agent in urban microclimate transformation. According to Mahdavi and Orehounig (2008) new buildings must embodied intelligent design to adapt on local climatic conditions and social functions. To Cubukcu and Diktas (2013) only a limited number of studies considered the effect indoor environmental features, and physical characteristics such as complexity, roof type, window size, and amount of open space of a building. As specified by Shafique et. al (2018), green roofs built at the building rooftop are old techniques. At ancient time, people constructed green roofs on the rooftops as gardens to thermal insulating and to reduce the adverse effects of urbanization. According to the authors, one of the most famous ancient green roofs was the Hanging Gardens of Babylon, built around 500 before Christ. The modern green roofs started from Germany in the 1960s to reduce energy consumption in the building during the energy crisis. Nowadays Germany is known as the world leader of green roofs, because green roofs on the large scale are being developed, designed and implemented on commercial and residential buildings (Shafique et. al, 2018).

According to Dias (2013, p.1), “...among the components of a building, the roof is the most important considering the indoor heat increase”. To Righi et. al (2016) the green roof can influence on violet rays harmful effects, providing better thermal inner conditions in the buildings. Genko and Henkes (2013) comment that the green roofs can reduce heat island phenomena in the cities keeping a pleasant microclimate and helping carbon sequestration. According to Loiola et. al (2018) the green roof, or rooftop garden, consists of a vegetative layer grown on a rooftop, and since 1990s, installing green roofs has become an usual practice, especially in the urban areas of many cities in developed countries. Shafique et. al (2018) report that green roofs are also referred as vegetated roofs, cool roofs, eco roofs, and roof garden or living roofs. As stated by the authors, green roofs are designed to encourage the vegetation on the top of the buildings aiming to get environmental benefits, better thermal comfort and storm water retention. To Li and Yeung (2014), green roofs increase green spaces and the sense of wellness. According to Feng and Hewage (2014); Santamouris




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(2014) and Loiola et. al (2018), green roofs reduce the heat island effect on big cities, improve buildings thermal performance cooling internal environmental during summer, as well as promoting insulation during winter, providing energy savings and better management.

GREEN ROOFS: TECHNICAL ASPECTS

As stated by Speak et. al (2013), there are many technical aspects to be considered during green roof projects and installation, divided in three categories by planting density, vegetation type and roof structural capacity. These categories are: Extensive – characterized by low structural load capacity and low implantation costs, since it requires little fertilization and irrigation; Semi-Intensive – used for structures with higher load capacity and medium maintenance costs; Intensive – usually used for structures with higher load capacity (Shafique, et. al, 2018). This category requires constant fertilizing and irrigation. Silva Junior et. al (2012) comment the extensive green roofs are conceived of as being almost self-sustaining, that is, they need the minimum maintenance. However, green roofs require a reasonable depth of soil according to vegetation that will be used. According to Vacilikio and Fleishfreesser (2011), the intensive green roof requires soils with a thickness of more than 20 cm. According to the authors, the extensive green roofs are cheaper, formed by creeper species and can be installed on sloping surfaces. Rangel et. al (2015) highlight that each kind of green roof will demand a specific vegetation type.

Speak et. al (2013) and Shafique et. al (2018) carried out researches on the hydrological properties of green roofs that revealed a range of average rainwater retention efficiencies. According to De Nardo et. al (2005), Mentens et. al (2006) and Moran et. al (2003), for extensive green roofs there is a range between 45 to 60% of cumulative water retention. Mentens et. al (2006) states the direct relationship between green roof substrate depth and higher water volumes retention.

Nicks et. al (2016) consider that green roofs are able to provide a layer of vegetation and soil to offset the original loss of landscape in the cities. As specified by them, many green roof systems support shallow substrates, making possible to use green roofs on many pre-existing buildings with little or no additional structural support needed. Speak et. al (2013) recommend the use of rustic vegetation species, such as native plant and well adapted to local environmental conditions. According to Lopes (2007), the choice of plant species should take into account certain criteria, such as resistance to high solar radiation level, and regeneration capacity after prolonged droughts and torrential rains; horizontal root development; reduced growth time; adaptation to narrow substrates and with few nutrients; large leaf surface and do not loose many leaves. From the authors' considerations, it is observed that grasses are considered the most suitable plant species for extensive green coverings.

Vacilikio and Fleishfreesser (2011) carried out a study where they compared the inner air temperatures of two experimental buildings. One building was covered by green roof, and asbestos cement tiles covered the other. According to the authors, the obtained data showed a significant reduction on thermal amplitude inside the building covered by green roof. The green roof reduced the temperatures along the day and kept the inner environment warm by night. Such behaviour was also identified in the work conducted by Lima et. al (2009), which obtained a reduction in the thermal amplitude around 5º C, comparing a module constructed with green roof, with another one endowed with waterproofed slab. According to Rosseti et. al (2013), this phenomenon occurs because green roofs increase thermal insulation layers




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that reduces the heat flux through the roof. Therefore, lower thermal energy is transferred from the exterior to the interior of the building. Carneiro et. al (2015) performed an experiment by a period of 70 days in the city of Recife, Brazil. The researchers built experimental models covered by four different kinds of roofs, such as: asbestos cement tile with 6mm thickness, recycled tile with 6mm thickness, green roof with Zoysia japônica grass and other green roof, however covered by Arachis repens grass. The authors concluded that the roofs covered by vegetation demonstrated better thermal performance comparing with the other kinds of roofs. Squier and Davidson (2016) carried out the study of the thermal properties of a green roof using field data gathered from an extensive 0.56 ha green roof in Syracuse, NY. Sensors were installed at five stations across the roof aiming to measure temperature at four depths within the roof layers. Data have been gathered from September 2013 to September 2015. Heat fluxes ranges from -5.75W/m-2 to 9.46 W/m-2 were observed. Negative (downward) heat flux is found during summer and early fall, and positive (upward) heat flux dominates during heating season. According to the authors, solar radiation can heat upper layers of the roof significantly above ambient air temperature during the summer. Barmparesos et. al (2018) studied six classrooms located under concrete roofs during warm and cold periods of school year.

The Experimental monitoring took place in a typical school building in Athens/Greek. The results show that, during summer, the green roof reduces indoor temperature of classrooms by about 2.8oC in comparison with the respective classroom covered under concrete roof. However, during cold season, the classrooms underneath green roof cover demonstrated higher values of indoor temperatures (19.7oC) than the classrooms under concrete roof (16.4oC). The author also report that the absolute air humidity showed a relatively stable for both classrooms during all of the experimental period. He et. al (2017) studied the effects of two important parameters on a green roof thermal performance; the thickness of soil layer and leaf area index of plant layer. The author simulated 18 cases with different combinations of soil thickness and leaf area index. The results show that the soil thickness has a significant effect on long term thermal performance of green roof in both summer and winter, while the effect of leaf area index is only significant in summer. Study carried out by Olivieri et. al (2013) in a Mediterranean climate show that the density of green roof plants affected the energy consumption of the studied building by up to 60% depending on specific conditions. Lee and Jim (2018) performed measurements using a wide range of precision sensors in order to study the thermal-cooling performance of an intensive green roof (0.5m of substrate thickness) in a building localized in Hong Kong. The green roof data were compared to a bare roof also monitored. The authors concluded that the green roof registered significant surface and air-cooling on sunny days. The vegetation served as an interceptor and filter of incoming solar radiation. However, the authors report that the solar irradiance imposed notable influence on surface temperature on the bare roof.

As stated by Khan and Assif (2017), beyond thermal performance increasing, the green roof also provides energy saving for the buildings. According to then, green roofs are a passive strategy that can be a useful solution in different climates in order to reduce building´s energy consumption. Green roofs provide energy saving and reduction in greenhouse gas emissions. Masseroni and Cislaghi (2016), using extensive and detailed green roof parameters, concluded that green roof attenuates flood events that can produce overflows in the large urban areas. However, the authors highlight that the green roofs effective can be influenced by their initial conditions in terms of volumetric water content of the substrate. Under field capacity of saturation, the effects of floods attenuation and water volume retention drastically decrease.




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The use of Light Steel Frame as construction methodology

According to the Brazilian Association of Technical Standards – ABNT: NBR 15.575/2013, the construction materials used in civil construction can influence the inner comfort conditions of a building, specially the roof. In this way, civil construction industry has been developing technologies in order to reduce the environmental impacts caused due its activities and improve the thermal comfort of new buildings. According to Lee et a. (2017) the use of light steel frame (LSF) in rapid constructions has grown significantly, especially concerning low and medium-rise buildings. Light steel frame can be considered a dry construction method.

Angelo and Serra (2014), Gorgolewski (2007) and Lawson et. al (2009) report that, in recent years, lightweight walls have become more used in Europe because of its’ advantages such as quick execution time, the integration of systems in walls thickness, the reduction and recyclability of wastes during the construction phase, the reduction of structural loads and low water consumption. However, according to Angelis and Serra (2014), the thermal characteristics of light steel frame materials are more heterogeneous than traditional wall, made with bricks and mortar. In fact, the thermal conductivity of insulation layer of these materials is about 0.04 W/mK while steel frames are about 1000-1500 times higher.

According to Gomes et. al (2013), LSF is new to Brazil, having been introduced in the late 1990s aiming construction of residential houses. Thus, LSF design practices needs some adjustments considering Brazilian climate conditions. As stated by Gomes et. al (2013), it occurs because LSF system was imported from United States and, therefore, implicitly includes assumptions about climate that may not apply to Brazilian conditions. In addition, according to the authors, steel structural systems have been recently considered by designers and construction contractors seeking innovative construction technologies. However, despite the great interest by designers and construction contractors, there are few academic researches about this issue yet.

RESEARCH GOALS

In this context, two experimental modules were built using LSF constructive technique in the city of São Paulo/Brazil. It can be said that LSF may be considered a sustainable constructive system because it generates low amounts of wastes and improve thermal conditions of the buildings. One of the modules was built with green roof, and the other with asbestos cement tile. Therefore, the main goal of this research is evaluate the thermal performance of each module built using LSF technique. As stated by Lundholm and Willians (2015), it is very important to carry out researches that focuses on quantifying thermal behaviour of green roofs. To Shafique et. al (2018), many researches are aiming to the performance of green roofs in different regions around the world. According to the authors of the research on the green roofs, there are numerous social, environmental and economic benefits. Significant evidence shows that green roofs can give different kind of benefits, such as storm water management, reduced urban heat island, enhance the air and water quality, decrease of water and energy consumption, decreased noise pollution and other benefits more.




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MATERIAL AND METHODS

Execution modules site

The modules were built in an area located in the Campus Vergueiro parking lot of Nove de Julho University, in the city of Sao Paulo/Brazil. The geographic coordinates of the chosen area are: 23,56°S 46,64°Wand 745m of altitude. According to Sao Paulo municipality (2017), the climate of the city is characterized as tropical altitude, with average annual temperatures between 19º C and 27º C. In summer, it is common to present rains in the late afternoon, which relieves the heat and in the winter usually presents dry and sunny days. Spring is hot and dry, and in autumn the temperature is mild.

For the adoption of climatological data used in this research, government agencies and monitoring institutes were consulted, with meteorological stations located near the area where the modules were built. In this way, the meteorological station closest to the area of the modules was Sé Meteorological Station, administered by the Center of Management of Emergencies (CGE).

The modules were built in a wide area with no shading incidence or any kind of interference, caused by other buildings or vegetation. According to Nicks et. al (2016), the spatial heterogeneity where the green roofs are built may influence its behavior in thermal conditions. For the authors, shaded areas promote small heat fluxes through the roof and reduce storm water retention. The modules were positioned with the same solar orientation, arranged side by side, at a distance of 2,0m from each other, with the doors directed towards the south orientation and the windows directed towards the east orientation, as shown in Figure 1.

Figure 1. Modules positioning – no Scale (Source: Authors).

Modules characterization

Light Steel Frame technique has been used in modules execution. These were supported on sill plate foundation with 15cm thickness. The modules have identical characteristics, except for the kind of the roof. One module was covered by green roof (1) and the other one was covered by asbestos cement roof (2). Both modules have the following inner dimensions: 1.90 x 2.35m and 2.55m of ceiling high, as show in Figures 2 and 3.




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Figure 2. Modules positioning – no Scale (Source: Authors).

Figure 3. Section AA – Modules 1 and 2 – no scale (dimensions in meters) (Source: Authors).

For each module was installed a window in white color with the dimensions of 1.20 x 1.0m, and also a wood door with the dimensions of 0.72 x 2.10m painted in white. For green roof waterproofing, was installed flexible bicomponent made with thermoplastics materials and cements with additives and incorporation of synthetic fibers (polypropylene). The module´s 1 draining layer was composed by recycled civil construction aggregate. To enable the rainwater flow, a drainage PVC tube was installed (Ø 2”). The green roof used was the extensive type with substrate of 15cm thickness. Figure 4 shows the details.




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Figure 4. Draining system used in green roof (module 1) (Source: Authors).

The vegetal species chosen to the green roof was “emerald grass” (Zoysia japônica). According to Lopes (2007), this kind of grass presents great resistance to weather and is appropriate to green roofs. The module 2 was covered with asbestos cement tiles with 6mm thickness and dimensions of 1.10 x 1.83m. This kind of tile was used in module 2 because it is very commonly used in Brazil. Figures 5 and 6 show the modules 1 and 2.

Figure 5. Studied Modules (Source: Authors). Figure 6. Studied Modules (Source: Authors).

Data Collection For the evaluation of the internal thermal comfort of the modules, these individually counted on a system for measuring the environmental variables, composed of a thermal stress measurement instrument with a globe thermometer to measure the variables: radiant temperature, air temperature, relative humidity and air velocity. The measuring instruments were fixed on a metal tripod, positioned at the center of each module. The fixing height is based on the recommendations of Fundacentro - Jorge Duprat Figueiredo Foundation of Labour Safety and Medicine (2002). Fundacentro (2012) recommends that the instruments have to be fixed 1.10m height. This value corresponds to the level of the thorax of a seated person.

To measure the inner environmental conditions of each module, the following equipment had been used: Thermal stress meter, globe thermometer and a data logger model HMTGD-1800 – Highmed. The obtained data were stored by means of continuous monitoring, with records every ten minutes. It was performed a total of 144 measurements per day.




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The CGE (Emergency Management Center) made available meteorological data from the Sé Meteorological Station. The measurement period occurred between March 2017 and February 2018. Table 1 presents the days that were performed the measurements.

Table 1. Data measurements dates (Source: Authors).

FINDINGS

Representative episodes For the characterization and thermal performance analysis of the modules 1 and 2, in front of the data of the Sé Meteorological Station, a representative episode was selected in each of the nine analysed periods. The episodes were selected considering the thermal peaks of the periods, being peaks of high or low air temperature, as show on Figure 7.

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Figure 7. Identification of the maximum and minimum values of air temperature (Source: Authors).

Table 2 presents the representative elected episodes; limiting date and schedule in order to make possible the individual analysis of each episode.

Table 2. Selected representative episodes (Source: Authors).

Period- Episode

Air temperature Since To Date time Date Time

1 Maximum temperature 03/24/2017 1:00 PM 03/24/2017 8:30 PM 2 Minimum temperature 04/11/2017 1:00 PM 04/11/2017 11:00 PM 3 Minimum temperature 05/13/2017 8:00 AM 05/13/2017 3:00 PM 4 Minimum temperature 09/25/2017 3:00 PM 06/26/2017 3:00 PM 5 Minimum temperature 10/21/2017 6:00 AM 10/24/2017 3:00 PM 6 Minimum temperature 11/13/2017 4:00 PM 11/14/2017 4:00 PM 7 Maximum temperature 12/17/2017 7:00 AM 12/18/2017 5:00 AM 8 Maximum temperature 01/24/2018 6:00 AM 01/25/2018 6:00 AM 9 Maximum temperature 02/09/2018 7:00 AM 02/10/2018 7:00 AM

The nine episodes selected were isolated and generated graphs that demonstrate the variation of the air temperature. These graphs also compare the data obtained for both modules and Meteorological Station, as shown below (Graphics 1 to 9).

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12:2

0 A

M

1:00

AM

1:

40 A

M

2:20

AM

3:

00 A

M

3:40

AM

4:

20 A

M

5:00

AM

17-Dec-17 18-Dec-17

Tem

pera

ture

(°C

)

Episode 7- Air Temperature

Modue 1 Module 2 Sé Metereological Station

27.7

30.6 33.5

13

18

23

28

33

38

6:00

AM

6:

40 A

M

7:20

AM

8:

00 A

M

8:40

AM

9:

20 A

M

10:0

0 A

M

10:4

0 A

M

11:2

0 A

M

12:0

0 PM

12

:40

PM

1:20

PM

2:

00 P

M

2:40

PM

3:

20 P

M

4:00

PM

4:

40 P

M

5:20

PM

6:

00 P

M

6:40

PM

7:

20 P

M

8:00

PM

8:

40 P

M

9:20

PM

10

:00

PM

10:4

0 PM

11

:20

PM

12:0

0 A

M

12:4

0 A

M

1:20

AM

2:

00 A

M

2:40

AM

3:

20 A

M

4:00

AM

4:

40 A

M

5:20

AM

6:

00 A

M

24-Jan-18 25-Jan-18

Tem

pera

ture

(°C

)

Episode 8- Air Temperature





302


From the results, the initial, peak and final temperature measurements of module 1, module 2 and the Meteorological Station are shown in Table 3.

Table 3. Air Temperature – Episode measurements – Initial/Peak/Final (Source: Authors).

Epi

sode

Initial Peak Final

Date

Sche

dule

Temperature (°C)

Sche

dule

Tem

p. (°

C)

Sche

dule

Tem

p. (°

C)

Sche

dule

Tem

p. (°

C)

Date Sc

hedu

le

Temperature (°C)

M1 M2 EM M1 M2 EM M1 M2 EM

1 05/24/2017 1:00 AM 24.0 24.9 24.15 3:50

PM 26.1 3:50 PM 27.8 5:30

PM 29.06 03/24/2017 8:30 PM 24.1 24.4 23.5

2 04/11/2017 1:00 AM 24.1 24.1 24.32 3:30

PM 27.0 4:30 PM 29.5 6:00

PM 30.97 04/11/2017 11:00 PM 25.0 25.1 25.37

3 05/13/2017 8:00 AM 17.6 17.4 15.69 10:10

AM 17.2 10:00 AM 17.0 11:20

AM 14.55 05/13/2017 3:00 PM 21.2 22.7 22.63

4 09/25/2017 3:00 PM 23.7 25.3 23.97 7:00

AM 18.7 6:10 AM 18.0 8:00

AM 15.25 09/26/2017 3:00 PM 23.9 26.0 25.08

5 10/23/2017 6:00 AM 19.8 20.1 18.14 00:50

AM 17.4 10:10 PM 17.0 10:30

PM 13.87 10/24/2017 3:00 PM 20.2 21.2 18.82

6 11/13/2017 4:00 PM 23.6 25.7 26.6 6:30

AM 17.7 6:00 AM 17.0 7:10

AM 14.44 11/14/2017 4:00 PM 23.9 25.5 28.19

7 12/17/2017 7:00 AM 22.7 22.0 22.45 3:30

PM 28.6 3:20 PM 31.2 6:20

PM 33.29 12/18/2017 5:00 AM 23.0 22.3 21.34

8 01/24/2018 6:00 AM 22.7 23.0 20.92 3:00

PM 27.7 2:50 PM 30.6 4:00

PM 33.5 01/25/2018 6:00 AM 23.6 23.5 21.88

9 02/09/2018 7:00 AM 22.2 21.7 21.1 3:50

PM 29.1 4:00 PM 32.0 5:50

PM 33.72 02/15/2018 7:00 AM 24.2 24.0 23.61

M1- module 1; M2-module 2; MS-Meteorological Station. In Table 3 it is possible to visualize the temperature variations between the episodes. In order to compare the thermal comfort between the modules, it was necessary to group the episodes of minimum and maximum peaks separately. Table 4 presents the data of Episodes 1, 2, 7, 8 and 9, which corresponds to the maximum peaks of temperature, and

29.1

32 33.72

13

18

23

28

33

38

7:00

AM

7:

50 A

M

8:40

AM

9:

30 A

M

10:2

0 A

M

11:1

0 A

M

12:0

0 PM

12

:50

PM

1:40

PM

2:

30 P

M

3:20

PM

4:

10 P

M

5:00

PM

5:

50 P

M

6:40

PM

7:

30 P

M

8:20

PM

9:

10 P

M

10:0

0 PM

10

:50

PM

11:4

0 PM

12

:30

AM

1:

20 A

M

2:10

AM

3:

00 A

M

3:50

AM

4:

40 A

M

5:30

AM

6:

20 A

M

9-Feb-18 10-Feb-18

Tem

pera

ture

(°C

) Episode 9 - Air Temperature





303

Table 5 presents the data of Episodes 3, 4, 5 and 6, which corresponds to the minimum temperature peaks.

Table 4. Air temperature variation – Initial/maximum peak /Final (Source: Authors).

Epi

sode

Module 1 (M1) Module 2 (M2) Meteorological Station (MS)

Initial (°C)

Variation(°C)

Peak (°C)

Variation (°C)

Final (°C)

Initial (°C)

Variation (°C)

Peak (°C)

Variation (°C)

Final (°C)

Initial (°C)

Variation (°C)

Peak (°C)

Variation (°C)

Final (°C)

1 24.0 +2.1 26.1 -2.0 24.1 24.9 +2.9 27.8 -3.4 24.4 24.15 +4.91 29.06 -5.56 23.5

2 24.1 +2.9 27.0 -2.0 25.0 24.1 +5.4 29.5 -4.4 25.1 24.32 +6.65 30.97 -5.6 25.37

7 22.7 +5.9 28.6 -5.6 23.0 22.0 +9.2 31.2 -8.9 22.3 22.45 +10.84 33.29 -11.95 21.34

8 22.7 +5.0 27.7 -4.1 23.6 23.0 +7.6 30.6 -7.1 23.5 20.92 +12.58 33.5 -11.62 21.88

9 22.2 +6.9 29.1 -4.9 24.2 21.7 +10.3 32.0 -8.0 24.0 21.1 +12.62 33.72 -10.11 23.61

Table 5. Air temperature variation – Initial/minimum peak/Final (Source: Authors).

Epi

sode

Module 1 (M1) Module 2 (M2) Meteorological Station (EM)

Initial (°C)

Variation (°C)

Peak (°C)

Variation (°C)

Final (°C)

Initial (°C)

Variation (°C)

Peak (°C)

Variation (°C)

Final (°C)

Initial (°C)

Variation (°C)

Peak (°C)

Variation (°C)

Final (°C)

3 17.6 -0.4 17.2 +4.0 21.2 17.4 -0.4 17.0 +5.7 22.7 15.69 -1.14 14.55 +8.08 22.63

4 23.7 -5.0 18.7 +5.2 23.9 25.3 -7.3 18.0 +8.0 26.0 23.97 -8.72 15.25 +9.83 25.08

5 19.8 -2.4 17.4 +2.8 20.2 20.1 -3.1 17.0 +4.2 21.2 18.14 -4.27 13.87 +4.95 18.82

6 23.6 -5.9 17.7 +6.2 23.9 25.7 -8.7 17.0 +8.5 25.5 26.6 -12.16 14.44 +13.7 28.19

Based on the collected data, it was found that module 1, compared to module 2, presented lower air temperature fluctuation in all episodes. Module 1 presented, lower peaks temperature than the module 2, in the order of 1.7 ° C to 2.9 ° C, proving the reduction of the heat flux of the green roof, which leads to the improvement of the thermal performance provided by the surveyed coverage system. The results were demonstrated as already observed by Getter et.al (2011) and Barmparesos et. al (2018). According to the authors, reduction of surface temperature and thermal comfort are two important functions of green roofs. Green roof vegetation and substrate absorbs fewer solar radiations than other type of roofs or any kind of tile. Yan (2011) carried out a research in Japan and the data revealed that the green roof reduced the surface temperature in order of 3oC comparing it to another kind of roof. Bevilacqua et. al (2016) show an experimental analysis of an extensive green roof installed on a building of University of Calabria. The analyses showed that the green roof was able to reduce the temperature at the interface with the structural roof, on average, by 12oC with respect to a black bituminous roof in summer and to maintain, on average, a value that is 4oC higher in winter.




304

In Singapore, Quin et. al (2012) measured the surface temperature from green roof and bare roof. When the results were compared with other, the green roof showed results in decreasing the surface temperature as compared do the bare roof. The author highlights that green roofs have the ability to decrease the surface temperature and hence improving the internal environment of a building. To Jim and Tsang (2011), the selection of vegetation influences the rates of evapotranspiration and the albedo of the roof, but also contributes of solar gain relative to a traditional roof due to vegetative surface shading. The greater thermal mass of a green roof aids in stabilizing temperatures throughout the year.

CONCLUSIONS

In the present work, the thermal behaviour of two modules was constructed, analysed and compared, being one with green roof and the other with conventional cover asbestos tile, denominated module 1 and module 2, respectively. Light steel frame methodology was chosen for its sustainable characteristics.

The module 1, covered with green roof, presented better thermal performance than module 2, covered with asbestos tile in all selected episodes. Module 1 also demonstrated less inner air temperature variation when compared to module 2. However, considering the lower air temperature peaks (Episodes 3, 4, 5 and 6) it was found that the lower the external temperature, the lower the temperature difference between both modules.

Considering higher temperatures peaks, which were Episodes 1, 2, 7, 8 and 9, the module 1 has lower temperatures than that of module 2, in the order of 2.0° C in average. This fact proves that the module covered by green roof provides the heat flow leading to the inner part of the module. Also, it can be affirmed that thermal performance of modules 1 and 2 met the expected behaviour, even both modules built with LFS construction method.

Thus, the usage of green roof and the light steel frame system (LSF) in building construction can be considered to reach the concept of sustainable architecture, because they represent a passive bioclimatic construction technique, once adopt technology that optimize the building performance and minimize harmful impacts to the environment. The LSF has aroused great interest in the market, being used in various types of housing, both small and large, as well as in apartment buildings (four floors), commercial buildings, schools, hospitals and retrofit of existing buildings.

Therefore, it can be concluded that the module equipped with green roof and executed by means of LSF technique consists of an environmentally efficient construction, since it provides interior thermal comfort, presents potential to improve the climatic conditions of the cities and is constructed using dry executive method with low demand for natural materials, high dimensional accuracy, low energy consumption and minimization of waste generation.

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