Thermal Comfort of residential buildings in Pilot Plan

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PLEA2005 - The 22 Conference on Passive and Low Energy Architecture. Beirut, Lebanon, 13-16 November 2005

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Thermal Comfort of residential buildings in Pilot Plan of Brasilia Darja Kos Braga1 and Claudia Naves David Amorim2 1, 2 Faculty of Architecture and Urbanism, University of Brasilia, Brasilia, Brazil Instituto Central de Ciências - ICC Norte - Gleba A - Subsolo, Campus Universitário Darcy Ribeiro, Asa Norte, Caixa postal 04431 - CEP:70910-900 - Brasília – DF - Brazil. Phone: (+55) (61) 3072454 / Fax: (+55) (61) 274-5444. E-mail:[email protected]

ABSTRACT: Brasilia, capital of Brazil, is a new city, planed and built between 1956 and 1960. The residential buildings, object of this study, were constructed from 1958 on. Most of those, built before 1980, follow the modernistic style, respecting the five points of Le Corbusier, among them the use of horizontal strip windows. This often implicates in facades with a high percentage of glazing. However, most of the buildings don’t have any kind of solar protection. For tropical climates this kind of approach isn’t appropriate. On clear days direct solar radiation enters in high quantity inside the apartments, raising the temperatures that frequently exceed limits of thermal comfort. Trying to solve the problem the residents handle, with their own criterion, awnings, solar control films, air conditioning etc. The result are visually polluted facades, which is a relevant question as the Pilot Plan of Brasilia is considered “National Patrimony” and as well “Cultural Heritage of Humankind” by UNESCO, due to the quality of its architecture and urbanism. This article exposes these problems and through simulations with the software Ecotect proposes some solutions in order to achieve environmental (thermal and luminous) comfort in the apartments, with minimum interventions in the original architecture. Conference Topic: Case Studies Keywords: thermal comfort, modern residential architecture

1. INTRODUCTION 2. CLIMATE IN BRASILIA The climate of Brasilia is classified as tropical of altitude and has two seasons well defined: hot humid (October to April) and dry (May to September). 35

90 80

30 DRY BULB TEMPERATURE [°C]

The lack of climatic adaptation of part of residential buildings in Pilot Plan of Brasilia causes three kinds of problems: thermal discomfort of dwellers, alterations of the facades and energy consumption by the air conditioning (that could be avoided). Thermal comfort is fundamental for the health and well being of people. Temperatures out of the limits of the comfort origin thermal stress and drop in work production [1]. On the other hand, the climate of Brasilia is known as very mild. An investigation of Goulart et al [2] showed that among 14 big Brazilian cities Brasilia has the biggest percentage of hours with thermal conditions in the limits of the comfort. Many of the local researches proved that in Brasilia is possible to obtain thermal comfort in residencial buildings with passive strategies, without air conditioning. However it’s important to have in mind the characteristics of the climate and the orientation while projecting. When this doesn’t happen a huge amount of energy must be spent to achieve comfort condition.

70 25 60 20

50

15

40 30

10 20 5

10

0

0 JAN

FEB

MAR

APR

MAI

JUN

JUL

DBT average of maximum values DBT average od medium values DBT average od minimum values

AGO

SEP

OCT

NOV

DEC

RH average (%)

Figure 1: Average values of dry bulb temperatures and relative humidity for Brasilia (19821997). Source: Adapted from [3]

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Some authors [3] suggest a distinction of the third period, inside the dry season, that could be classified as hot and dry, comprehending months of August and September. These two months are considered very unfavourable from the point of view of the thermal comfort, presenting high diurnal temperatures and low air humidity (see Figure 1). June and July present significant discomfort by low temperatures, occurring specially during the night period. The average air humidity is 70%. The driest month is August, with 56%. The minimum absolute humidity registered is 8% in September. The annual insolation is 2.400 hours. Direct solar radiation is very strong during the dry season and the diffuse radiation is more intense during the hot-humid season. 2.1 Bioclimatic analysis An extensive research about the climate in Brasilia [3] identified 1987 as the Test Reference Year (TRY) for the period 1982-1997. The temperature and humidity data of all 8.760 hours of TRY were plotted on the Bioclimatic Chart. Table I shows the percentages of comfort, discomfort and recommended bioclimatic strategies obtained from Bioclimatic Chart.

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Its project was chosen on the international concourse in 1957. The plan is based on two crossing axis, which constitute the two main roads: the Monumental and the Residential Axis (Figure 2). Along the Monumental Axis were placed institutional, public and commercial areas. Along the Residential Axis, as the name suggests, were located residential areas in the form of superquadras (also called “superblocks”).

Monumental Axis Residential Axis Superblocks of six floors Superblocks of three floors

Figure 2: Original project of Pilot Plan. Table I: Recommended bioclimatic strategies for Brasilia Comfort Discomfort COLD 36,6 %

Bioclimatic strategies [%] Thermal mass for heating

31,3

Solar passive heating

4,37

Artificial heating

0,99

Ventilation

21,2

Evaporative cooling

8,38

41,2 % HEAT 22,2 %

Thermal mass for cooling

8,29

Air conditioning

0,08

Superquadras are green areas with dimensions of circa 250m x 250m. The land is public, fences and walls are forbidden. Residential buildings can occupy only 15% of the area, which results in low population density and generous green area (Figure 3). 98% ob the buildings are implanted parallel or perpendicular to the limits of the superquadras.

OBS.: The percentage of discomfort by heat or cold doesn’t correspond to total of strategies, as the percentage of these consider also overlaid zones.

Source: Adapted from [3]. Accordingly to Table I, the conditions of temperature and humidity are in the limits of comfort during 41,2% of the hours per year. The percentage of the discomfort caused by cold is 36,6% and by heat only 22,2%. The main strategies recommended for the cold periods are: thermal mass and solar passive heating. In case of hot weather are suggested: ventilation, evaporative cooling and thermal mass. The use of artificial strategies is necessary in less then 2% of the hours per year. (Table I)

3. RESIDENTIAL ARQUITECTURE SUPERQUADRAS IN PILOT PLAN BRASILIA

OF OF

The Pilot Plan of Brasilia was conceived by Lucio Costa – Brazilian modernistic architect and urbanist.

Figure 3: An example of superquadra - SQN 202. Source: http://www.geocities.com Originally only three lines of superquadras where planned, all with residential buildings of six floors above the pilotis (Figure 2). Immediately after the concourse some changes were made in the plan, including the enlargement of residential areas. Therefore, one line of superquadras was added on the east side, adapted to receive residential buildings of three floors (above the pilotis) without elevators, thus considered economic dwelling.

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Residential buildings of the superquadras are very similar to each other. The main reasons are the strict norms and regulations that define the form and the height of the buildings.1 In many superquadras all the residential buildings follow the same architectural project, varying only the colours of the facades. 3.1 Modernistic and pos-modernistic architecture The residential buildings on superquadras can be roughly classified in two generations: - The first one are buildings constructed before 1980 and follow generally the modernistic style. The characteristics are: pure volumes, horizontal strip windows, free facade, pilotis, differences between the front and the back façade, presence of brise-soleil. (see Figure 4)

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4. INTERVENTIONS ON THE FACADES Flores [4] made a research estimating the quantity of alterations on the facades of the residential buildings implanted on superquadras. This work made a survey in all the 117 existing superquadras, with 1.392 residential buildings. The research demonstrated that a significant part the buildings suffers alterations on the facades. The most frequent are the addition of solar control films, air conditioning and awnings, elements aiming to control solar radiation (see Figures 4 and 6). Modernistic buildings 2 with strip windows and no solar protection are the most susceptible to this kind of interventions (see Figure 4). Table II shows the percentage of the interventions. Table II: Solar films, awnings and air conditioning on the facades of residential buildings3. Solar films [%]

Awnings [%]

Air cond. [%]

68

30

38

5. METHODOLOGY OF THE STUDY

Figure 4: Typical example of the first-generation residential building with modernist characteristics. Source: author The second generation, buildings built after 1980, presents usually irregular volumes, balconies and traditional windows. (Figure 5)

Based on this first studies, a metodology was stablished in order to investigate possible solutions for the improvement of environmental comfort in residential buildings, preserving the original façades and avoiding alleatory interventions. The methodology of the research can be summarized in the following steps [5] : 1. Choice of one representative typology for the case study; 2. Measurements of air temperature and relative humidity in two apartments of the chosen typology; 3. Thermal simulations of the original situation, with the software ECOTECT; 4. Proposals for improvement of environmental comfort, and new simulations; 5. Results analysis and conclusions.

6. CASE STUDY

Figure 5: Typical example of the second-generation building. Source: author

For the case study one typical typology of the first generation buildings was choosen. This typology was projected by the architect Helio Ferreira Pinto and constructed in the 70’s. The criteria for the choice were considerable quantity of the buildings (there are 33 buildings of the same typology in Brasília) and the evidence of thermal comfort problems. The characteristics of the selected typology are: horizontal strip windows (Window Wall Ratio –WWR75%), free facade and a clear distinction between the front and the back facades (Figure 6). The

2

1

The basic dimensions of the residential buildings are 12,5m x 85m, and the height is limited by 6 floors above the pilotis.

Approximately 30% of all residential buildings on the superquadras have these characteristics. 3 To be considered, each element had to appear in at least two apartments of the building.

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apartments have three bedrooms, dinning room, kitchen and bathroom.

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(Figure 8). On the other hand, the north-facing room receives considerable solar gains in the winter and autumn.

Figure 6: Front and back facades of the case study building. (Source: author)

Temperatura

5.1 Measurements The aim of the measurements was to confirm the existence of thermal comfort problems. Two apartments of this typology were selected, with two diferent orientations. This way was possible to evaluate thermal comfort conditions in rooms with four different orientations (the measurements were done in two opposite rooms in each apartment). In each apartment the equipment4 was placed in the living room (front facade) and in the bedroom that faces back facade. Measurements of air temperatures and humidity were taken every 15 minutes during 4 days in September, 4 days in December and 4 days in March (near equinox and the solstice dates). The measurements were compared, using the graphics (Figure 7), with the external temperatures and humidity obtained in the local weather station (INMET).

Figure 8: Case study buildings overlaid to the solar chart. 5.3 Simulations For thermal simulations was used software Ecotect v. 5.2. The software combines a 3-D design interface with a set of performance analysis functions and interactive information displays. Several analyses are possible (solar, thermal, natural and artificial light, acoustics, cost and environmental impact). In this article only thermal simulations are presented. The first step was the construction of the 3D model. It was modeled only one apartment and one zone above, below and at each side, representing the neighboring apartments (Figure 9).

35 30 SALA

25

SUÍTE

20

EXTERNA

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Figure 9: 3D model of the apartment 24. Dez. 2003 4:00 8:00 12:00 16:00 20:00 25. Dez. 2003 4:00 8:00 12:00 16:00 20:00 26. Dez. 2003 4:00 8:00 12:00 16:00 20:00 27. Dez. 2003 4:00 8:00 12:00 16:00 20:00

10

Data/Hora

Figure 7: An example of the graphic that compares internal and the external temperatures The results show that all four orientations present high temperatures (above 29° C) in at least one period of the year. The temperatures were higher in the apartment facing east and west, but also the north-south apartment presented temperatures above the comfort level especially during the hot days of September and December. 5.2 Insolation analysis East and west-orientated rooms receive a huge amount of solar radiation all over the year. The room orientated to the south gains significant direct radiation only during the summer and spring mornings

4

Gemmini Data Loggers

The next step was the specification of the materials and the zone attributes: type of HVAC system and schedule, occupancy (nº of people, activity and schedule), internal heat gains and air infiltration rates. The zone attributes were specified considering the occupation of the apartment by one family of four persons in a routine day. The weather file5 of Brasilia was downloaded from 6 the electronic pages of EERE (Energy Efficiency and Renewable Energy). Four strategies were simulated, aiming the optimization of thermal comfort with minimum interference in the facades: 1. Windows with reflective solar control film7;

5

Ecotect recognizes weather data in WEA format. http://www.eere.energy.gov/buildings/energyplus/cfm/weath er_data.cfm 7 2 Original glazing: 6 mm transparent (U= 6W/m K, Shading coefficent=0.95, T=0,88); Proposed strategy: glazing with 2 reflective incolor film (U=6 W/m K, Shading coefficent=0.55, T=0,55). Data extracted from the ECOTECT’s database. 6

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2. External wall with 113% higher thermal mass8; 3. Reduction of window wall ratio (WWR) to 50%; 4. The combination of the three alternatives. The output of the software considered for the research was: hourly air temperature profile, hourly heat gains and losses, mean radiant temperature (MRT). To evaluate thermal comfort, the indices Predicted Mean Vote (PMV) and Percentual of People Dissatisfied (PPD) were used9 (also output of the software). Simulations were made for the 24th of nd September (hot dry period), 22 of December (hot umid) and 21st of June (cold).

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combination of all the proposed solutions is as expected the most efficient. Watts

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5.4 Results and discussion In the weather file of Brasilia used by the software th Ecotect, the 24 of September is one of the hottest days of the year. The external temperature reaches 33°C at 3 pm. The direct insolation is very intense, especially in the morning (see Figure 10). On 22nd of December, outside thermal conditions are more favorable than on 24th of September. External temperatures vary from 18°C at dawn to 29°C at the beginning of the afternoon. The diffuse solar radiation is more intense. East/west apartment On the 24th of September in the east orientated living room (original situation), air temperatures raise quickly in the morning reaching the maximum of 30°C at 9 am (Figure 10). The analyses of hourly heat gains and losses indicated as the only cause direct solar radiation, (2.400 kW per hour). The gains by conduction occur from 10 am on and are much smaller (400 kW per hour).

Original

Solar Film

Ther. Mass

Conduction gains

WWR 50%

Combinat.

Direct solar gains

Figure 11: Direct solar and conduction gains in original living room (east) and with proposed strategies (24th of September). The analysis of PMV and PPD show that thermal conditions achieve the peak of discomfort at 9 am. In the original situation PMV on the 24th of September reaches 1,87 and the PPI comes to 70,5% (Table III), which overcomes the ISO 7730 recommendations. Table III: Extreme values of PMV and PPD for east/west apartment.

Original

Living room – EAST PPD PMV [%] 1.87 70.5

Bedroom – WEST PPD PMV [%] 1.67 60.3

Solar film

1.34

42.4

1.41

Ther. Mass

1.82

68.1

1.64

58.6

2.0k

WWR 50%

1.62

57.6

1.59

55.8

1.6k

Combinat.

1.22

36

1.34

42.4

1.2k

22

10

0.8k

Original

-0.88

21.2

-0.57

11.8

0

0.4k

Solar film

-0.82

19.1

-0.55

11.4

0.0k

Ther. Mass

-0.87

20.9

-0.56

11.7

WWR 50%

-0.74

16.5

-0.45

9.3

Combinat.

-0.69

14.9

-0.42

8.7

°C

HOURLY TEMPERATURES - All Visible Thermal Zones

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Monday 24th September (267) - BRASILIA, BRA W/m²

Outside

Living room

30 20

Bedroom

-10 0

2

4

Outside Temp. Beam Solar

6

8 Diffuse Solar

10

12

Wind Speed

14

16

Zone Temp.

18

20

22

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24 Sept.

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45.8

Dec.

Selected Zone

Figure 10: External and internal hourly temperatures in the original living room (east) and bedroom (west) - 24th of September. The graph of the Figure 11 compares direct solar and conduction gains in the living room of original and modified situations. With solar control film direct solar gains are reduced about 50%. The increase of thermal mass has inexpressive effect due to the small opaque surface of external wall (25%). Smaller window reduces significantly direct solar gains. The

8

Data/ Strategy

Original wall: perforated blocks, 13 cm thickness (U=1,8 2 W/m K); Proposed Strategy: adittional layer of massive 2 blocks, thickness 24 cm (U= 1,56W/m K). 9 The Internacional Organization for Standardization ISO7730 (1984) recommends for optimal thermal comfort condition a PPD less than 10%, which means PMV values between the -0,5 and +0,5.

With the addition of solar control film, we have an effective improvement (PPD goes to 42,4%). Combining the three strategies we have the most significant improvement (PPD 36%), even if not reaching the optimal comfort conditions. In the west orientated bedroom thermal conditions th are slightly better. On the 24 of September PPD reaches 60,3% (Table III – original situation). The maximum air temperatures occur between 3 pm and 4 pm, arriving to 29,6°C (Figure 10). Using the strategies with bigger thermal mass and reduction of WWR have modest effect. The combination of all the strategies decreases the PPD to 44,2%. It’s important to note that the software doesn’t allow effective simulations with ventilation, so this strategy was not considered. Ventilation, combined with the other proposed strategies, would improve thermal conditions significantly.

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On the 22nd of December the sky is overcast during the most time of the day. The most uncomfortable conditions are achieved at 6 am due to discomfort by cold (table III). In the original living room, for example, the PPD reaches 21,2%, while in the situation with combination of strategies it comes to 14,9%.

in both hot and cold seasons. The reduction of this percentual (WWR) have improved thermal condition in hot and cold period, but it's not enough to solve the problems, especially in cold period, where the percentual of dissatisfied people – PPD – is still very high (73,4%).

North/south apartment In the north-south orientated apartment, in September, the living room (south) receives small amount of direct insolation only until 9 am (Figure 8). The principal thermal gains proceed from conduction and convection, internal sources and ventilation. For this reason the differences between original and modified situations are insignificant (Table IV). On the other hand the north-facing bedroom is in this time of the year exposed to the direct sunlight from 9 am to 6 pm. On the 24th of September the original situation evidences 50,5% of dissatisfied (2 pm), and with the proposed modifications the PPD goes down to 39,6% - slightly better but still far from the optimal situation (Table IV).

FINAL CONSIDERATIONS

Table IV: Extreme values of PMV and PPD for north/south apartment. Data/ Strategy

Original

Living room – SOUTH PPD PMV [%] 1.27 39

Bedroom – NORTH PPD PMV [%] 1.49 50.5

Solar film

1.28

39.1

1.33

41.8

Ther. Mass

1.27

38.5

1.46

48.7

WWR 50%

1.29

40

1.46

48.9

Combinat.

1.26

38.1

1.29

39.6

th

24 Sept.

22

nd

Dec.

Original

-0.38

19.4

-0.53

10.8

Solar film

-0.78

17.9

-0.53

10.8

Ther. Mass

-0.82

19.3

-0.52

10.6

WWR 50%

-0.7

15.4

-0.42

8.7

Combinat.

-0.66

14.2

-0.4

8.3

Original

-2.23

85.8

-2.14

82.7

Solar film

-2.23

85.8

-2.06

79.3

Ther. mass

-2.22

85.5

-2.14

82.7

WWR 50%

-2.16

83.6

-1.98

75.9

Combinat.

-2.14

82.7

-1.93

73.4

22

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June

In December thermal conditions achieve the peak of discomfort at 6 am owed to discomfort by coldness (Table IV) - as in north/south orientated apartment. The simulations for the cold period (June) show a high percentual of dissatisfied people due to the coldness. In the original situation PPD comes to 85,8% in living room and to 82,7% in bedroom (Table IV). These extremes occur at the sunrise – 7 am. The proposed modifications slightly improve the situation but don’t solve the problems. In any case, the high percentual of glazing in the façades is one of the main reasons for the discomfort

The work shows the possibilities of solutions to achieve more thermal comfort in the residential buildings of the superquadras. The main problem in these buildings is the high percentual of glazing on the façades without any kind of solar protection. The proposed solutions were not enough to solve the problems. The best performances have the strategies with the reduction of glazing percentual and the addiction of solar control films. More simulations should be performed, with other alternatives for thermal improvement, considering also ventilation, which was not possible, due to few sensibility of the software regarding this strategy. It’s important to avoid alleatory interventions in this kind of buildings, creating visually polluted facades. The local administration should suggest the best solutions for each kind of building, stimulating architects and dwellers to use these strategies, studied to optimize thermal comfort with minimum interventions in the original architecture.

ACKNOWLEDGEMENTS We would like to thank the Programa Nacional de Conservação de Energia Elétrica (PROCEL) from Eletrobrás and the Fundo Setorial de Energia (CTEnerg), by means of CNPq (CT-Energ/CNPq), for the support of this research.

REFERENCES [1] A. B. Frota e S. R., Manual de Conforto Térmico. 5th edition, Studio Nobel, São Paulo, 2001. [2] S. Goulart, R. Lamberts e S. Firmino, Dados climáticos para projeto e avaliação energética de edificações para 14 cidades Brasileiras, PW ed., São Paulo, 1997. [3] A. Maciel, Projeto Bioclimático em Brasília: Estudo de Caso em Edifício de Escritórios. Master Thesis in Civil Engineering, Federal University of Santa Catarina, Florianopolis, 2002. [4] A. L. Flores. Conforto ambiental e eficiência energética em edifícios residenciais: preservação da arquitetura nas superquadras do Plano Piloto – Brasília. Final Report, Convênio FUB/Eletrobrás, Programa PROCEL Edifica, FAU - UnB, Brasília, 2005. [5] D. K. Braga, Arquitetura Residencial das Superquadras do Plano Piloto de Brasília: aspectos de conforto térmico. Master Thesis in Architecture and Urbanism, University of Brasilia, Brasilia, 2005.