Research of Design Features that Influence Energy Consumption in Office Buildings in Belo Horizonte, Brazil

Available online at www.sciencedirect.com

ScienceDirect Energy Procedia 111 (2017) 101 – 110

8th International Conference on Sustainability in Energy and Buildings, SEB-16, 11-13 September 2016, Turin, ITALY

Research of design features that influence energy consumption in office buildings in Belo Horizonte, Brazil Ana Carolina de Oliveira Velosoa*, Roberta Vieira Gonçalves de Souzab, Ricardo Nicolau Nassar Kourya a

Mechanical Engineering Department, Federal University of Minas Gerais, Avenida Antonio Carlos 6627, Belo Horizonte 31270-901, Brazil b Laboratory of Environmental Comfort (LABCON), School of Architecture, Federal University of Minas Gerais, Rua Paraiba, 697, Belo Horizonte 30130-140, Brazil

Abstract Buildings in Brazil in the residential, commercial and public sectors represent, according to the National Energy Balance in 2015, 50% of the total electricity consumption of the country. According to the National Energy Plan 2030, buildings energy consumption is projected to grow 3.7% per year by 2030. Thus, understanding of the architectural variables that influence the consumption of buildings has significant importance to contribute to the reduction of the expected energy demand for these buildings. The aim of this work is, therefore, the analysis of the architectural variables in the 102 office buildings of medium and large electricity consumption in the city of Belo Horizonte for which the monthly consumption per square meter was obtained. Then, the sample was segmented considering the following parameters: air conditioning system type, window-to-wall ratio, existence of glass facades, average absorptance of the walls, type of glass, existence of solar protection and construction decade. This segmentation was statistically treated using the frequency of occurrence of the listed building features and their influence on consumption of the sample was analyzed. The results indicate that naturally conditioned or mixed-mode air conditioned system buildings consume up to 58.7% less electricity per area in comparison with buildings with central conditioning systems in the city. This is explained by the fact that Belo Horizonte is a city with a mild climate with high percentage of comfort hours when natural ventilation is used. This discussion becomes important once it is believed that the analysis of such data can contribute to presenting guidelines to designers and legislative bodies to improve the building design decisions in order to achieve lower electricity consumption in buildings. © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of KES International. Keywords:energy consumption; benchmarking; building design

* Corresponding author. Tel.: +55-31-3409-8825 E-mail address: [email protected]

1876-6102 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of KES International. doi:10.1016/j.egypro.2017.03.012

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1.
Introduction According to the Energy Demand Study [1], the world population is estimated to increase from 6 billion people in 2000 to around 9 billion by the year 2050. This expected growth, in addition to the increase in power consumption of the population, impacts in a direct way the overall energy consumption framework, creating the need to consider alternatives able to reduce this growth impacts. According to Perez-Lombard et al [2], in the commercial sector, office and retail buildings have the highest electricity consumption and CO2 emissions. Office buildings in the US account for 18.0% of electricity consumption and 3.2% of total energy consumption. In Spain, the office buildings account for a third of the commercial building sector energy consumption and are responsible for the consumption of 2.7% of the total energy consumed in the country. In the UK commercial buildings consume 17.0% of electricity and 2.0% of total energy consumption. In Brazil the buildings in the commercial sectors and public services represent 14.5% of total electricity consumption in the country [3]. Therefore, in Brazil as in other countries, the construction, operation and use of the buildings mean a significant share of electricity available of the country and therefore represent a great potential for energy conservation. Thus, it is of fundamental importance to ensure that the quality of life offered by the building and its facilities are compatible with the minimum standards of habitability and consumption and besides, they are considered ways and means to implement energy conservation programs are considered [4]. Energy consumption in buildings is related to gains or heat gains or loss through the building envelope which, in addition to the internal loads generated by the occupation, the equipment use of equipment and by artificial lighting, result in the consumption of air conditioning systems, plus the own lighting equipment and systems [5]. The implementation of energy efficiency strategies in buildings not only reduces peak energy demand, but also reduces the use of energy in general and the impact that buildings have on the environment. A good architectural design should include analyses of their energy performance, as each decision taken during the design process can influence the thermal and light performance of the building [6]. The project interactions and decision-making must be set correctly allowing the array of architectural responses of the various problems to produce integrated results. Passive buildings, with low energy consumption, that have climate control strategies will provide a greater opportunity to adapt to climate change [7]. The various parameters that influence the building's consumption should be investigated and checked for the possibility of design change so that the building becomes more efficient. The architecture should assume the role of minimizing the climatic effects and not to intensify them or aggravate them [4,8]. Assess the energy efficiency of a building is a more difficult task than in equipment in general, because the efficiency covers an interplay of factors such as architecture and environmental variables like external temperature and humidity, systems, among others [9]. Studies of the impact on some architectural features such as the shape of the building [10,11], opening percentage in facades, colors and shading devices [12,13], showed that there was significant variation on total consumption and energy costs by altering constructive variables. Climate characteristics may also influence the energy consumption in buildings and to minimize these influences, the architecture must be able to offer thermal conditions compatible with human thermal comfort inside it, regardless of external weather conditions. Thus, the architecture should assume the role of minimizing the climatic effects and not intensify them or aggravate them [4,8]. In countries where energy efficiency regulations already consolidated or in consolidation, an important parameter to be raised is the power consumption according to the typology of buildings. These surveys are called benchmarks, which are an important tool to promote the efficient use of energy in commercial buildings [14,15]. Having a large database created is the starting point to proposing new criteria for construction, for performing evaluation of existing criteria and improve the management of buildings of different performances. When it comes to the Brazilian reality, according to the National Energy Plan 2030[16], the energy consumption of buildings is projected to grow 3.7% annually through 2030, which would represent an increase of 55.5% in electricity demand over the next 14 years. In this sector are the commercial buildings that consume 14.5%of the electricity in the country and several studies have significant potential to improve efficiency in energy consumption. According to Dornelles [17], the most efficient mean for the designer to control the amount of heat that reaches

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the interior of a building is carefully considering how the constructive envelope both absorbs as reflected solar radiation. Moreover, argue that the use of external shading devices is an important strategy for buildings in Brazil, since they block direct solar radiation before they can penetrate the glass and this can lead to a reduction in air conditioning energy consumption and total consumption [18,19]. However, it is observed that this strategy is under explored in office buildings in Brazil [20]. In tests done to Florianopolis - Brazil office buildings, the greater the percentage opening, the lower tends to be the level of the envelope efficiency [20]. The increase in the percentage opening on the facade reached a variation of 41.6% of the total energy consumption tests in office buildings located in Florianopolis [21]. Thinking about a future scenario, the National Energy Plan Brazilian-PNE 2030 [16] foresees that with the energy-efficiency measures, the trend of increase in consumer demand in Brazil may decrease if you continue having government policies in this sector. Currently, regulations, studies and procedures in order to minimize consumption and seeking alternative energy sources have been developed. These standards establish parameters that describe the minimum efficiency of the building, avoiding the practice of building energy-inefficient ones. Therefore, this article will evaluate the energy consumption in office buildings in the city of Belo Horizonte, according to their construction features. This analysis is important for better understanding of how the construction variable affects the consumption of buildings and to promote the development of a benchmarking methodology for office buildings in Brazil. Nomenclature PNE IPTU CEMIG CC CS CN EUI

National Energy Plan Urban Building and Land Tax Energy Company of Minas Gerais Office building with central conditioned system Office building conditioned by split or window systems. Unconditioned office building Energy Use Intensity

2.
Methodology 2.1.
Climate characterization According to Köppen's climate classification, the city of Belo Horizonte is classified as having a temperate climate with mild winter and with average temperatures of 18° C in winter and 22°C in summer. The average normal temperature varies during the year from 17° to 27°C. The normal annual relative humidity is 72.2 % and the average annual total precipitation is 1,473.4mm. The dominant sky is partly cloudy with an average global solar radiation of 5,254 W/m² and the period of thermal gain is from 7am-18pm, with the peak between 12pm-15pm. The analysis of hours of comfort from 8am to 6pm (operational hours of office buildings in Belo Horizonte) given by the ASHRAE Adaptive Comfort model 55, based on the weather data base of a SWERA TRY file, was done through the use of Climate Consultant software [28]. From that, it is indicated that in 71% of the hours of use it would be possible to obtain the Adaptative Comfort Ventilation indoors. 2.2.
Typology definition This paper is part of an ongoing PhD study of the electricity consumption in office buildings in Belo Horizonte and it will demonstrate the pre-test carried out to check the constructive characteristics of buildings influence on the electricity consumption of office buildings. This initial analysis will support a future sensitivity analysis. This paper gathered 3-years monthly electricity consumption and building feature data of 102 buildings in the city. An energy end use survey (cooling, lighting, plug load, etc.) was not conducted for each building. Thus, the data used is referred to the total electricity consumption in the buildings. The buildings taken into account in this paper were

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selected because they were commercial facilities that housed offices as a primary activity. After a survey conducted via Google Maps buildings were classified in three typologies: •
Typology 1: office building with central air conditioning (CC); •
Typology 2: office building with split or window air conditioning (CS); •
Typology 3: unconditioned office building (CN). By consulting the City Hall data bank, it was possible to access the total gross area of the buildings and their construction year. The electricity consumption data of these buildings was obtained from the Energy Company of Minas Gerais (CEMIG). Monthly data of 36 months between the years of 2012 and 2014 were obtained. In order to create a comparative basis of consumption between the buildings, an Energy Use Intensity (EUI) analysis was used and the consumption is presented as a mean kWh/m²/month.

2.3.
Office building data An adequate description of the buildings is the key to better forecasting energy consumption. In the case of the studied buildings, it was not possible to obtain architectural design plants or detailed systems information so it was necessary to create a classification range for parametric analysis of the buildings taking into consideration features such as window-to-wall ratio (WWR), glass solar heat gain coefficient (SHGC), solar absorptance of walls, construction decade and the presence of frontal glass facades and solar shading. The choice of variables was based on previous literature case studies that took into account the constructive features that significantly influenced the energy consumption of buildings. Limit ranges for these features were defined from the literature which presents range values as shown in Table 1. Table 1. Tested variables and ranges for similar jobs Paper
[13]
[24]
[21]
[25]
[26]


Window-to-Wall Ratio (%) 17 – 55 10; 50; 90 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 20; 80 29; 60

[18]


-

[27]


2 - 90

Solar Heat Gain Coefficient 0,47 - 0,66 0.69; 0.83; 0.95

Solar absorptance of walls 0.2; 0.55; 0.9

Construction decade -

Glass Facade -

Solar Shading 0%; 50%; 100%

0,22; 0,61; 0,87

0.2; 0.4; 0.6; 0.8

-

-

45°

0.2; 0.87 0.14; 0.15; 0.23; 0.48; 0.95 0.2 – 0.6

0.3; 0.7 0.6

-

-

29%; 100% 0°; 30°; 35°

-

-

-

-

-

-

-

5% - 100%

From Table 1 it can be noticed that in none of the above studies the decade of construction and the existence of glass facades in buildings were analyzed. However, the data sample indicated that it was essential to take these building characteristics into account. As it was previously said, the construction decade was obtained from data provided by Belo Horizonte's local authority. The presence of glass facades in buildings was investigated via Google Maps. The works presented in Table 1 have shown a wide variation in the range for the Window-to-Wall Ratio. Then to specify the range limits of the present work WWR values of ten buildings evaluated by the Environmental Comfort and Energy Efficiency Laboratory of the Federal University of Minas Gerais (LABCON-UFMG) to obtain the National Energy Conservation Label (ENCE) for Commercial Buildings were raised. By this sample four WWR ranges: 1-10%, 11-20%, 21-35% and 36-50% were defined. It is important to reinforce that this sample showed that even buildings with glass facades do not present WWR superior to 50%. Also from the building analysis of LABCON-UFMG sample, glass SHGC and solar wall absorptance ranges were defined. Three glass types were established to define the SHGC ranges: clear glass, with SHGC equivalent to 0.87; blue reflective glass with SHGC equal to 0.41; and green reflective glass, with SHGC equivalent

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to 0.33. For the analysis of the absorptances of the external walls, three values were established: 0.25, equivalent to the light walls; 0.5, equivalent to the average wall; and 0.7, equivalent to the dark walls. The analysis of the influence of solar shading presence was made in a simplified way, because it was not possible to specify in detail the performance of these solar protections in this phase of the study as the survey was conducted via Google Maps. The range values adopted in the present study are presented in Table 2. Table 2. Building properties and assumed values describing the existing building stock for Belo Horizonte, Brazil. Variable Window-to-wall ratio (%) Solar Heat Gain Coefficient (SHGC) Solar absorptance of external walls Construction decade Glass Facade Solar Shading

Categories 1-10, 11-20, 21-35 e 36-50 0.33 (green); 0.41 (blue); 0.87 (colorless) 0,25; 0,5; 0,7 1940, 1950, 1960, 1970; 1980; 1990; 2000 Yes, No Yes, No

2.4.
Data analysis To analyze the data of this study, it was necessary to calculate the average building monthly electricity consumption by the total area of the building. The average consumption per square meter of each building was then obtained from the average electricity consumption of 36 months between the years 2012 and 2014 divided by the total area of the building. The frequency of occurrence of the defined features was determined in each of the established ranges. Thus, it was calculated according to the number of buildings with the analyzed characteristic by the equation: %fo=(Ni/N)x100; where% fo= frequency of occurrence of a particular item; Ni = number of buildings with presence of the feature; N = total number of analyzed buildings. For the analysis of each variable, the buildings were split by typology 1, 2 and 3 and the results were compared between them and also between the typologies. 3.
Results 3.1.
Consumption by typology According to ASHRAE 55 [22], the comfort conditions of Belo Horizonte show a mild climate with an average maximum temperature of 27 °C and only 29% probability of discomfort during work hours. According to Fig. 1, 64.7% of the buildings have Split or window (typology 2) as an air conditioning system and 7.8% of the buildings are considered naturally conditioned (typology 3). The typology 3 generally category also presents few rooms with Split/Window systems. It is considered that both typology 2 and 3 present a mixed-mode system of air conditioning, using artificial air conditioning only at times when temperatures are above 27°C. What can be seen in Figure 1 is that the average monthly consumption of electricity per area in the CC building twice higher than in CS buildings; and 142% greater than the naturally conditioned buildings. Moreover, it is noted that the consumption difference per area between the CS buildings is 15.5% higher than in the CN buildings. Those buildings that do not use air conditioning systems are the minority of the sample, about 7.8%. It is important to say that only the existence or not of the air conditioning system was assessed, not taking into counting the effectiveness of relative indoor environmental quality.

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Fig. 1. (a) graph of the average energy consumption by typology of building; (b) frequency of occurrence of each building typology.

3.2.
Building Decade Most buildings, about 50%, were built on the decade of 1990's and most of them present some air conditioning system being the oldest buildings of the sample about 75 years old. It is noticed that the CC buildings begun to emerge in the 1980's and over the following decades their electricity consumption tended to decay. This is probably due to improved technology. Still, the consumption of this typology of building is higher than the Split / window and naturally ventilated buildings systems. It can also be seen in Fig. 2, that the electricity consumption of CS buildings remains within an average of 3.51 kWh/m²/month regardless of the time of construction.













Fig. 2. (a) graph of average energy consumption per decade of construction; (b) frequency of occurrence of each building typology.

3.3.
Window-to-wall ratio The increase in the percentage of opening in the facades generates an increase in the annual electricity consumption. This happens because being of simple glass (in Brazil double glass facades are not used because climates are mild) large areas of opening allow more intense heat gains or losses and, consequently, there is an increase in the use of air conditioning systems in buildings. In the CC buildings, the higher the percentage of opening, the greater the average monthly energy consumption of the building, reaching an 82.5% difference between the buildings with 1-10% and 35-50% WWR. In the CS buildings, the consumption also has increased proportionally, except that for the range of 36-50% it had present a small decrease but from the lowest range to the highest, this increase in consumption was of 46.8%. In CN buildings typology, there are no buildings with 35-50% opening percentages, but electricity consumption per square meter almost doubles from the lowest to the highest range. In all ranges the largest consumers are the CC building, followed by CS and CN. All of these observations are shown in Fig. 3. Regarding the frequency of occurrence of buildings in each range, it is clear that most of the buildings focus on opening percentages between 11-20%, followed by 21-35 %.

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Fig. 3. (a) graph of average energy consumption by typology of building and the percentage of openings in the facades; (b) frequency of occurrence of each building typology.

3.4.
Presence of glass facades According to the survey, it can be seen that buildings having at least one of its facades fully glazed is not a recurring characteristic of the sampled buildings. It is noted that in all of the building typologies that present this characteristic the energy consumption is higher than those which do not. According to Fig. 4, the biggest differences can be observed in the CC buildings, with electricity consumptions 37% higher when the buildings have a glass facade compared with buildings with no glass facade. Regarding the frequency of occurrence of buildings in this characteristic, it is possible to observe that only 40% of the sample has a glass facade, but these have the highest electricity consumption.













Fig. 4. (a) graph of average of energy consumption by typology of buildings with glass facade; (b) frequency of occurrence of each building typology.

3.5.
Average Solar Absorptance of external facades Regarding the mean solar absorptance of the external facades, three representative values were established: absorptances of 0.25, 0.5 and 0.7. What we can see in Fig. 5a, is that energy consumption increases due to the increase of the solar absorptance of the walls and that in the sample that no building had solar absorptance averages above 70% in CN buildings. It can also be seen in Fig. 5 that the greater consumption per square meter difference from the average solar absorptance of the facades happens in the CS buildings with 59% difference in consumption between the solar absorptance of 0.7 and 0.5. The highest numbers of buildings in this sample, about 77%, have solar absorptances of 0.5. Nonetheless, the minority of them, about 9%, that have high solar absorptance of external walls, are those that have higher electricity consumption.

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Fig. 5. (a) graph of average energy consumption per average absorptance of facades; (b) frequency of occurrence of each building typology.

3.6.
Glass Type Regarding the glass type used in buildings, three types were observed and thus determined the following solar factors: clear glass with SHFC equivalent to 0.87; blue reflective glass with SHGC equal to 0.41; and green reflective glass, with SHGC equivalent to 0.33. According to Fig. 6b, there are no samples of buildings with glass with solar factor to 0.33 for CN and 0.87 for CC. The highest numbers of samples, about 41% use glass with solar factor of 0.87 and are of CS typology. It can also be noted that the CC buildings utilize glass with lower solar heat gain coefficients. In this typology of buildings, glasses with a lower solar factor consume about 7.6% less electricity.













Fig. 6. (a) graph of average energy consumption by typology of glass; (b) frequency of occurrence for each type of glass.

3.7.
Solar shading presence The use of solar shading provides reduced thermal loads through the windows and therefore a decrease in the electricity consumption of buildings. According to the sample, only 15% of buildings present solar shading systems. According to Fig. 7, among the three typologies of buildings, there was a significant reduction in electricity consumption when sun protection devices are present in the building facades. The differences in electricity consumption found in the sample buildings with sunscreen compared to those without sunscreen is of 21% in CC buildings, 32% in CS buildings and 6% in CN buildings. The largest number of sample buildings with solar protection comes in CS buildings. It is noteworthy that the effectiveness of solar shading was not assessed, but only their existence or not.

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Fig. 7. (a) graph of average energy consumption by the presence of sun protection in the openings; (b) frequency of occurrence of each building typology.

4.
Discussion By analyzing the results found in this paper, it was noted that the architectural features of office buildings in Belo Horizonte behave similarly to the ones studied on the previous research on their influence on total consumption and energy costs reported on the literature review found at the Introduction section [4, 8-13]. The main founds of this research about the electricity consumption of 102 office buildings was that the decision of the air conditioning system type can lead to electricity per square meter consumptions more than twice higher when central conditioning systems are used in comparison to window/split systems or with naturally conditioned buildings. Another important result found was that high window-to-wall ratio, the presence of glass facades, high solar absorptance on external walls and high values of glass solar heat gain coefficient can definitively contribute to increase the energy consumption in buildings. On the other hand, the existence of solar protection can help to reduce this consumption. The perception of the impact of architectural features on electricity consumption, as reported in this work, may contribute to the debate and practice on zero energy buildings. The analysis of the results presented in this paper was made by the statistic treatment of frequency of occurrence. In order to reach more accurate information about the energy consumption of office buildings in Belo Horizonte, the methodology of data analysis may be enhanced by the use of a statistical sensitivity analysis. This will be done by using the data presented in this paper as groundwork within a more detailed future research.

5.
Conclusions With the forecast growth in the energy and electricity consumption of buildings, the major challenge for designers is to understand which constructive characteristics influence more in this consumption. The design interactions and decision-making must be set correctly allowing the array of architectural responses of the various problems to produce integrated results. This article demonstrates the influence of architectural features in the electricity consumption of office buildings in the city of Belo Horizonte, Brazil. In this paper, some important features for the energy consumption in buildings were determined in accordance with previous researches and from LABCON-UFMG data. The sample was analyzed according to the type of air conditioning and the following constructive features: window-to-wall ratio; existence of glass facades; average absorptance of facades; glass type; presence of sun protection devices and decade of construction. The main contribution of this research is that the decision of the air conditioning system type is the most influential factor on the electricity consumption. The understanding of the energy consumption of buildings due to variations of technological availability, use of building systems, construction period and project assumptions is important. With this, it is possible to develop guidelines so designers can create low energy buildings with a more efficient use of electricity.

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Acknowledgements The work reported in this paper was supported by The Brazilian Federal Agency for Support and Evaluation of Graduate Indication – CAPES.

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