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A review on energy consumption in the residential and commercial buildings located in tropical regions
of Indian Ocean- A case of Madagascar island
M. Kameni Nematchoua 1* , Y. Andrianaharison 2 E.J.R. Sambatra 3, C.G. Ralijaona 4, R. Mamiharijaona 5
J.N. Razafinjaka 6 and T. Raoelivololona 7
1Fluid and Energy Laboratory, Higher Polytechnic School University of Antsiranana, Madagascar
2Department of Electrical Engineering,
National Higher Polytechnic School of Antananarivo, Madagascar
3Higher Institute of Technology Antsiranana Department of Industrial Engineering, Madagascar
4Ministry of Education Higher and Scientific Research General Secretariat, Madagascar
5Material Science Laboratory, Higher Polytechnic School University of Antsiranana, Madagascar
6Automatic Laboratory, Department of Electricity Higher Polytechnic School, University of Antsiranana, Madagascar.
7Department of Technology’s science of Information and Communication, Higher Polytechnic School
University of Antsiranana, Madagascar
(reçu le 15 Décembre 2018 - accepté le 25 Décembre 2018)
Abstract - The aim of this research is to review the status and current trends on energy consumption, but also to assess the cooling energy in some buildings in Madagascar. To achieve this objective, but due to a lack of data regarding energy consumption in buildings in this region, experimental and subjective studies were carried out in 1272 residential buildings and 51 commercial buildings, distributed in 12 cities in the tropical region of Madagascar. A specific questionnaire was designed to collect these data. A total of 1323 questionnaires were distributed during dry and rainy seasons. The results showed that energy consumption varied by both function of design and occupants' behaviors.
Cooling energy demand was the highest in modern buildings, while 60 % of occupants found their environment uncomfortable. Good indoor air and optimal worker’s performance were watched in buildings with local materials. Although Madagascar has an important source of renewable energy, electricity production remains heavily dependent on more than 80 % of fossil fuel sources.
Résumé - L'objectif de cette recherche est de faire le point sur l'état et l'évolution actuelle de la consommation d'énergie, mais aussi d'évaluer l'énergie de refroidissement dans certains bâtiments à Madagascar. Pour atteindre cet objectif, mais en raison d'un manque de données sur la consommation d'énergie dans les bâtiments de cette région, des études expérimentales et subjectives ont été réalisées dans 1272 bâtiments résidentiels et 51 bâtiments commerciaux, répartis dans 12 villes de la région tropicale de Madagascar. Un questionnaire spécifique a été conçu pour recueillir ces données. Au total, 1323 questionnaires ont été distribués pendant la saison sèche et la saison des pluies. Les résultats ont montré que la consommation d'énergie variait en fonction de la conception et du comportement des occupants. La demande d'énergie de refroidissement était la plus élevée dans les bâtiments modernes, tandis que 60 % des occupants trouvaient leur environnement inconfortable. La qualité de l'air intérieur et la performance optimale des travailleurs ont été observées dans les bâtiments construits avec des matériaux locaux.
Bien que Madagascar dispose d'une importante source d'énergie renouvelable, la production d'électricité reste fortement dépendante à plus de 80 % des énergies fossiles.
*kameni.modeste@yahoo.fr
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Keywords: Energy consumption - Review - Residential and commercial buildings - Tropical regions - Madagascar island.
1. INTRODUCTION
Nowadays, some people preferred to live in old historical buildings. They enjoy the craftsmanship they represent and the robustness of their construction [1, 2]. However, sometimes there is a perception that old buildings are comfortable [3]. With the strong increase of the world's population, it has been noticed that energy is the foremost requirement of all nations for development [4, 5]. A good energy policy can therefore facilitate the rapid development of a country [6].
Environmental sustainability is the challenge for future long-term success. Today, the transition between renewable and fossil energy is extremely slow, despite several state summits summoned for this purpose [7, 8]. The services connected with energy contribute in a most meaningful manner to the impetus in the economic sector and in social development, as well as to all human activities in their endeavor for better conditions in life [9]. Energy is an irreplaceable resource that controls every aspect of life and supports human welfare [10]. Following new technology, it is interesting to note that several techniques are proposed to produce energy efficiently [11].
In developed countries, this is seen by several measures being taken in different energy consuming sectors to achieve climate protection objectives [12, 13]. Politicians and leaders of poor and emerging countries are slow to develop good energy policies in their countries. As a result, it is difficult to install energy-intensive industries in these countries. For specialists in development, energy consumption is an indicator of the level of development in the dynamism of economy of a country [14-16].
Thus, each country develops its own energy policy by ensuring the availability of energy resources in sufficient quantities corresponding to the needs of its users in terms of quality, efficiency and safety. In recent decades, it has been shown that the building sectors responsible for 40 % of the total energy consumption and for 34 % of CO2
emissions in Europe [17].
Residential building energy consumption is still dominated by some domestic and international complex factors [18]. To provide the correct guidelines for energy efficiency by analysis and study of energy demands, it is important for us to understand the characteristics of each area of residential building energy consumption [19-21].
Current prediction shows that energy use in emerging economies countries is expected to be 3.2% higher than developed countries by 2020 [22].
In 2040, oil and natural gas will likely be nearly 60 % of global supplies, while nuclear and renewable will be approaching a 25% share [23]. A number of empirical and numerical research has been carried out to investigate the energy demand in several residential places; after a study carried out in 376 new-build dwellings in the UK, Pan et al. [24], found that there exists a complex system of factors which affected energy- regulation compliance regarding a wide range of stakeholders. These conclusions and suggestions should improve the energy-efficiency building regulations and policy in the future.
Alnaser [25] showed that in all the countries, the increase of electricity consumption for domestic use is always the function of strong population growth. To estimate energy-efficiency performance of a production, Zhou et al. [26] used the stochastic frontier analysis technique, and found that this approach has higher discriminating power in energy efficiency performance measurement compared to other. In Korea, Chung et al. [27] reported that in this last decade, around 47.5 % of the total non- industry usage energy was consumed by the building sector.
547 Therefore, building-energy consumption can be assessed by statistical models or physical. Perez et al. [28], after some investigation in Mexico, found that natural ventilation can be considered as an interesting potential to reduce cooling energy in the households located in warm climates. Henze et al. [29], used a tool allowed to distinguish normal and abnormal energy use in some building of the USA. One of its objectives was to assess whole building energy Signal accuracy in the presence of uncertainty and faults at the sub-metered level.
The results showed that uncertainty in energy use could be quantized by a Monte Carlo exploration. Some complex science methods for knowing energy systems and system change were analyzed by Bale et al. [30]. They found that sometimes, complex science is not well understood by practitioners in the energy domain. Good models can be adopted allowing decision-making. Proskuryakova et al. [31] reported that the introduction of thermodynamic indicators can completed insufficiency of energy intensity indicators.
Invidiata et al. [32], showed that it's possible to reduce up to 50 % of the future annual cooling and heating energy demand in houses in Brazil by the use of passive design strategies. Buontempo et al. [33], found that local climate forces will be a significant driver of the regional response to climate change over Africa.
Asimakopoulos et al. [34], showed that the energy demand for cooling could increase by as much as 248 %, while the heating energy demand could decrease by about 50 %, until 2100. Some other interesting research in this field is given in [35, 40].
The different techniques of energy savings however remain unknown in most dwellings in Africa. In the majority of countries located in this continent, residential buildings sectors used more than 40 % of total energy consumed. Currently, charcoal and electricity are the main energy sources in the modern residences, however, oil and coal are the most used in traditional habitats.
The Indian Ocean is essentially made up of five islands: the Comoros, Madagascar, Mauritius, Reunion and the Seychelles. The closest ones are 200 km apart and the farthest ones are 1.800 km apart. The choice of Madagascar as the place for this study was not made randomly. It is the biggest island in the Indian Ocean and the 4th largest in the world. It also has the largest population. This country has an important potential in renewable energy which no again exploited at more than 30 %. Moreover, no investigations on building-energy demand have been carried out yet in Madagascar and some other Indian Ocean countries.
Madagascar is ranked among those countries that are rich in solar energy, with an estimated potential of around 2000 kWh/m2.year. Its hydraulic potential was around 8 GW, and 2000 MW for windmill potential. Madagascar’s largely rural population mainly depends on subsistence agricultural activities, which contribute to habitat degradation, particularly deforestation [41, 42].
In this country, energy is obtained either from the development of natural resources, such as biomass, forest residues, crop residues, water, sun and wind, or through the import of petroleum products [43, 44]. The country does not produce oil, despite the numerous prospecting work carried out there [43].
The main purpose of this research is firstly, to make a review on energy consumption in residential buildings of Madagascar to help this country in its new energy policy and create a comprehensive database on energy demands in sub-Sahara Africa.
The second goal of this study is to understand, and analyse the cooling energy demand in some buildings with different micro-climate.
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2. AN OVERVIEW ON ENERGY IN THE WORLD 2.1 According to International Energy Agency (report-2015) [45]
Energy demand worldwide is expected to grow up to 34 % by 2040 in some regions in China, India, Africa, and Southeast Asia. Coal has increased its share of the global energy mix between 23 % in 2000 and 29 % currently. It’s found that energy efficiency plays an important role in limiting world energy demand growth to 34 % by 2040, while the global economy grows by 150 %.
Nowadays, 1.2 billion people in the world live without electricity, and 2.7 billion people depend on traditional biomass for cooking. By 2030, it is expected that the number of people without electricity will decrease to 800 million and the number without access to clean cooking fuel will decline up to 2.3 billion.
2.2 According to U.S. Energy Information Administration (report-2016) [46]
Between 2012 and 2040, world population will increase 25 %, from 7.2 to 9 billion and total world energy consumption will increase 48 % from 549 to 815 quadrillion Btu.
The majority of the world’s energy growth will occur in the non-OECD nations due to strong population growth [46]. Figure 1a shows that renewable energy consumption will increase by an average 2.6 %/year between 2012 and 2040.
Nuclear power consumption is expected to increase by 2.3 %/year over that period.
Global natural gas consumption will increase by 1.9 %/year.
Globally, fossil fuels will account for 78 % of energy use in 2040. World energy consumption by country is shown in figure1b. Between 2012 and 2020, world use of petroleum and other liquid fuels will increase from 90 to 100 million barrels per day. In 2040, it is expected consumption will be 121 million barrels per day [46].
Fig. 1: World energy consumption by country grouping, 2012–2040 (left a), Total world energy consumption by energy source, 1990–2040 (quadrillion Btu) (right b) [46]
Natural gas consumption is projected to increase from 120 trillion cubic feet (Tcf) in 2012 to 203 (Tcf) in 2040; while coal will rise by an average 0.6 %/year: 153 quadrillion Btu in 2012 and 180 quadrillion Btu in 2040 [46].
2.3 According to other sources of information on energy in the world [47-59]
Global energy consumption has almost doubled in the last century. In 2004, about 77.8 % of the primary energy consumption was from fossil fuels (32.8 % oil, 21.1 % natural gas, 24.1 % coal); 5.4 % from nuclear fuels; 16.5 % from renewable resources,
549 of which the main one was hydroelectric, 5.5 %; whereas the remaining 11 % consists of non-commercial biomasses, such as wood, hay, etc. [56-59].
Uranium and Nuclear- Global uranium production increased more than 30 % between 2000 and 2015 [47]. In 2015, 65 nuclear reactors were under construction with a total capacity of 64 GW. All of these constructions were located mainly in China, India and Russia [49].
Hydropower- The global hydropower capacity increased by more than 35 % between 2000 and 2015, with a total of 1 209 GW was registered in 2015 [50].
Oil- Accounting for 33 % of global energy, oil remained the world’s leading fuel.
Nowadays, around 60 % of oil consumption is from the transport sector [47].
Unconventional oil recovery accounts for at least 25 % of the global recoverable oil reserves.
Coal- Research has shown that Asia presents the biggest market for coal and currently accounts for more than 65 % of global coal consumption [51]. Coal still provides around 40 % of the world’s electricity, with production decreasing to 0.6 % in 2014 and 2.8 % in 2015 [49].
Wind- Global wind power generation reached 432 GW in 2015 [53].
Bio-energy- Bio-energy is the largest renewable energy source in Africa and several other countries in development. It supplies 10% of global energy [49].
Geothermal- Today, geothermal global production is estimated to be 75 TWh [52].
This kind of technology is most known in developed countries (USA, China, etc.).
All these examples [45-55] showed that energy demand increases every year in all the sectors and almost in all the countries. This can be due to increase of population.
But, the two biggest are population and economic growth. In the future, we may see more use of renewable energy sources, such as geothermal and solar energy, to heat and cool our homes and workspaces.
2.4 An overview on building energy consumption
Energy use is directly oriented to our well-being. Indeed, it gives us good domestic comforts [63]. Population and construction material play an important role in residential energy use [55]. With the strong energy demand in residential buildings over these last years, some projections have shown that the building sector should play a key role in effective climate policy [50].
In 2015, the report of IEA [46] explained that the building sector regroups residential and commercial sectors. Any place where people live is considered a residential building. Commercial buildings include offices, stores, hospitals, restaurants, and schools.
Residential and commercial buildings are often grouped together because they use energy in the same ways - for heating and cooling, lighting, heating water, and operating appliances. Except transportation use, energy consumption in the residential sector includes all energy consumed by households [68].
*Residential sector
Bin et al. [67], reported that energy consumption in the residential sector includes all energy consumed by households. In 2015, according to Bank word [69], energy consumption in the residential sector is affected by income levels, location, weather, efficiency , energy prices, etc. However, the amount of energy consumed by households varied significantly with some requirements of each country [68].
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In 2012, Safrova et al. [72], showed that residential energy consumption in the non- OECD countries accounted for less than 50 % of the world’s total residential energy usage. In addition, Wang [73], reported that the OECD share of the world’s residential energy consumption should decline from 50 % to 40 % between 2013 and 2040.
Figure 2 showed the average annual change in OECD. The average annual increase in residential sector energy consumption will be 1.9 in Mexico and 0.1 in the United states. It’s interesting to notice that total OECD between 2012 and 2040 is expected to be 0.6 %. After 27 years, China and India will account for 27 % of the world’s residential energy consumption.
Fig. 2: Average annual change in OECD residential sector energy consumption, 2012–2040 (percent per year) [46]
*Commercial sector
Electricity and natural gas are the most common energy sources used in commercial buildings [49]. EIA [46] reported that in commercial sector, energy consumption will grow by an average of 1.6 %/year from 2012 to 2040.
In figure 3, it's shown that electricity is increasingly the preferred energy source in the commercial sector between 2012 and 2040, while renewable energy is weakly consumed. The energy produced by coal stays stable during this period.
Fig. 3: World commercial sector delivered energy consumption by energy source, 2012–2040 (quadrillion Btu) [46]
In 2012, OECD commercial energy use was 116 % greater than non-OECD use [74- 76]. Table 1 gives some percentages of energy consumption in buildings in some regions.
551 Table 1: Frequency of energy consumption in building according to regions
Both (residential and commercial) 2.4.1 Building and energy use
Some governments have set a target of cutting CO2 emission by 34 % of 1990 levels by 2020 [62-64]. It is important to find some methods for improving energy use in habitats. Indeed, according to Tao Zhang et al. [60], energy consumption in a modern building is a very complex organizational issue involving four important elements as represented in figure 4. While most energy is consumed by developed nations, developing nations are using more energy as their economies grow [65-66].
In a recent study in 2009, Steemers et al. [70], showed that the energy consumption in buildings was influenced by several factors. In 2011, Yu et al. [71], in further experimental studies reported that these elements can be classified in six categories:
Building orientation; climate (outdoor air temperature, wind speed, etc...); building operation and maintenance; occupants' activities and behavior; building services and energy systems; and indoor environmental quality [80]. This section evaluated the effects of these elements on building energy use.
Fig. 4: Some Elements in building Energy Consumption [61]
2.4.1.1 Energy and climate
In 2003, Qian et al. [81], after research carried out in China, showed that energy consumption in a country depending also of economic level. Energy is at the core of economic activity [82]. It is essential for the new industrial generation, commercial and societal wealth [83]. However, energy production and use place important pressure on the environment: greenhouse gas and air pollutant emissions as well as land use [84].
Today, climate has a great effect on energy consumption in buildings. Global warming has involved climate change, with the consequences varying according to the region. An increase of air temperature up to 2 °C in the next decade implicates a considerable cooling building energy demand [85]. According to IPCC [86, 87] and
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IEA [45], the world will require 35 % more energy in 2040 than it currently uses. Small buildings are more sensitive to global warming than large buildings, because the enveloped heat gain (loss) of small buildings is a larger portion of the cooling (heating) load than that of large buildings [111, 112].
Santamouris et al. [91], related that the climate influenced directly on building energy demand in every region, while Cartalis et al. [92] asserted that climate change will have some major consequences on the buildings no adapted with outdoor climate.
Conscious of this situation, Belcher et al. [94] developed proper climatic data for future constructions.
Invidiata et al. [89], investigated the impact of climate fluctuation on energy demand in dwellings in three cities in Brazil, with Scenario A2 associated to Energy plus software. Results showed that there will be an increase of energy demand ranging from 19 % - 65 % in 2020; 56 % - 112 % in 2050; and 112 % – 185 % in 2080. Amato et al.
[95], suggested the following formula for estimating the Heating Degree Days (HDDs) and Cooling Degree Days (CDDs) :
365
1 24 1
o b
24 ) T T HDD (
365
1 24 1
b o
24 ) T T CDD (
where Tb is the balance point temperature and To is the outdoor daily temperature.
For simulating energy consumption in residential and commercial buildings, Wang et al. [90], used the HadCM3 Global Circulation Model to generate weather data for future (2020, 2050, and 2080), for 15 cities in the U.S. The results showed that the heating and cooling energy varied versus outdoor climate in every city. Table 2 gives some climate impact and energy consumption.
Table 2: Summary on climate impact on building energy use [90]
2.4.1.2 Energy and building orientation
According to Selkowitz [103], building orientation refers to the way a building is located on an area and the space of rooflines, windows, and other features. After some investigation, Nematchoua et al. [5], found that the building orientation has a significant effect on energy demand for heating and cooling. Indeed, the habitats located in the northern hemisphere should be orientated differently to those in the southern hemisphere [101].
In a tropical region, with a Simulink model constructed from H-Tools, Wati et al.
[102], suggested a method for optimizing the thicknesses of insulation layers in the external walls of building. The results showed that energy savings varied (from 46.89 to 101.29 $/m2), while the payback periods was from 3.56 to 4.97 years, depending on
553 shade level and wall orientation. The first purpose of passive design is to increase solar gain while minimizing conductance [103].
Figure 3 shows that in the winter months, the tilt of the earth causes the sun to rise and set slightly south of east and west. However, in the summer months, the tilt of the earth causes the sun to rise and set slightly north always of east and west [104]. In general, cooling energy will increase and heating energy will decrease for all types of buildings [109]. The magnitude of changes varies among different types of buildings [110]. The orientation of building was given in figure 5.
Fig. 5: Building orientation [104]
The south and orth facing directions are found to be the most energy efficient [105].
Odunfa et al. [106], carried out a study at the University of Ibadan, Nigeria, with the aim to investigate the effect of building orientation on energy demand in buildings.
The results reported that an increase in energy demand of 7.96 and 4.29 kW was obtained with the east-west building orientation and north-south. These findings proved that energy efficiency is more guaranteed with north-south building orientation.
2.4.1.3 Energy systems and building services
An energy system is a system primarily designed to supply energy-services to end- users [114]. The concept of an energy system is evolving as new regulations, technologies, and practices enter into service – for example, emissions trading, development, respectively [115]. Building services are linked for the design, installation, operation and monitoring of the mechanical, electrical and public health systems required for the safe, comfortable and environmentally friendly operation of modern buildings. Household consumption and investment decisions may also be included within the ambit of an energy system [116].
Such considerations are not common because consumer behavior is difficult to characterize, but the trend is to include human factors in models. Household decision- taking may be represented using techniques from bounded rationality and agent-based behavior [117]. In 2005, Amato et al. [106], asserted that, generally, heating energy percentage reductions of small buildings are larger than that of big buildings. Indeed, small buildings are more sensitive to weather changes because of their low volume to surface area ratio [107, 108].
Globally, its noticed that, the more a modern society becomes increasingly dependent on electricity, the more the implications are apparent during grid disruptions
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such as extreme weather events etc. [102]. Integrated energy systems enable buildings to use and store energy from available resources efficiently [54].
Figure 6 shows a method to estimate energy consumption. It’s interesting to see from this figure that for calculating energy supply costs, it must first estimate the energy consumption.
Fig. 6: General structure for the estimation of the building energy consumption and the corresponding energy supply costs [54]
2.4.1.4 Energy and building operation maintenance
Maintenance is defined as the work that is done on a regular basis to keep your building in good working condition. It’s important to review all the energy systems for reducing energy consumption in the buildings (residences and commercials).
The maintenance management objective is to make sure that all technical equipment is working correctly and efficiently and if in any way some part of the building is defected, it can be restored to a good condition [99]. Individual tenants should taking responsibility for energy maintenance and repairs in their apartments [100].
Generally, it’s noticed three possible types of maintenance strategies: corrective maintenance, preventative maintenance and then predictive maintenance [118]. In households, preventative maintenance allows preservation of the originality of the building, the original fabric is kept in place as there is no extensive restoration work performed [117].
2.4.1.5 Energy and occupant’s behavior
The actions and behaviors in operating a building can significantly impact its performance [119, 120]. Often, in new buildings, the inhabitants focus their attention on operating to support occupants and meet varying demands of the facility, losing sight of the energy target that was so carefully engineered [121]. Some literature studies asserted that the impact of the occupants’ behavior is also important as the quality of the building envelope or the efficiency of technology [122, 124]. Indeed, the cognition of influences of occupant behavior is quite insufficient both in building systems design and energy retrofit nowadays, leading to limited understanding and inappropriate over- simplification.
In 2012, Deuble et al. [125] showed that there is a positive relationship between occupants' environmental concerns and their satisfaction level. However, a better understanding of occupants’ behavior seems to be crucial for the development of ambitious building concepts [126]. The need to integrate social science aspects into energy research has brought more awareness to the role of occupants in buildings [127, 128]. Hong et al. [128], provided some obstacles and advances in modeling occupant behavior and quantifying its impact on building energy use [129].
Figure 7, shows occupant energy behavior. According to Nicol [130], the effect of the occupant's behavior on building energy consumption can be described using four main components: drivers, needs, actions and systems.
Drivers: Stimulating factors that provoke an occupant into performing an energy;
Needs: are focused on the physical and non-physical requirements which ensure the satisfaction of the occupant with their environment;
555 Actions: show the activities which an occupant can conduct to achieve environmental comfort;
Systems: show the equipment or mechanisms regarding a building and occupant.
The actions which occupants can perform in order to satisfy their needs; and the building systems with which occupants can interact to affect the building energy performance [131].
Indeed, occupants’ activities and manners towards energy consumption is the major determining factor of residential building consumptions [153]. Occupant behavior may admit between expectations and reality [135]. Every architectural conception is based on assumptions about how it will be used; but when the fitting is realized, it may be used differently than its designer assumed, affecting results validity [136].
Fig. 7: Occupants’ types of activities affecting building energy consumption.
Adapted from [113].
2.4.1.6 Energy and Indoor environmental quality
In most cases, a considerable energy quantity is used for heating and cooling in the buildings as purpose for improving indoor air. Global warming has a significant effect on energy use in new buildings. In residential buildings, under natural ventilation, it's interesting to notice that indoor air is always more acceptable in traditional habitats than modern buildings. Nevertheless, modern designs are staying the most requesting.
The building orientation influences indoor environment and has several implications on energy consumption. Nowadays, the allocated cost for architecture respecting the international standards is still initially the highest, but it stays the most economic after some years. The occupant’s health and productivity depend on indoor air. However, the buildings where energy consumption is high are often very uncomfortable [5].
Thermal conditions inside buildings vary considerably with time [137]. Numerous studies reported that occupants who perceived their control opportunity as being insufficient were less satisfied of energy consumption in their residence [138, 139]. The acceptability of air quality decreased linearly with increasing indoor air enthalpy [140].
As an overview, indoor environmental quality can be improved by reducing the pollution load on the air by selecting low-polluting building and furnishing materials.
2.4.2 Building energy consumption model
Building Energy Model is a simulation instrument which calculates the energy and thermal load used in buildings [154]. In the literature, several works studied the relationship between the household energy consumption and climate change [141-145], little attention has been paid to explain the complex interrelationships that exist among the various variables involved. Motawa et al. [146] addressed the urgent need for
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exploring the interrelationship between the household, occupants and environment systems. For that, they suggested a system dynamics model using the soft data incorporated with variables that are involved in the mental judgment of the experts and industry practitioners.
In addition, according to other researchers [147-149], the socio-technical systems (STS) can be an approach capable of modeling the complexity involved in household energy consumption and CO2 emission (HECCE) systems. The main challenging problem of the building energy modeling is the lack of proper and comprehensive detail validation [155].
In some administration buildings at the University of Saõ Paulo, Hernandez et al.
[150], analyzed a simple model based on an artificial neural network (ANN) and a model that is based on physical principles (Energy Plus) as a predicting tool in order to forecast building energy consumption.
Results show that both models are suitable for energy consumption forecast. After an investigation carried out in 23 commercial buildings and 16 hotels, Yik et al. [151]
suggested a model to predict energy consumption. The results showed a very good correlation between detailed simulation programs and the proposed model.
Building energy models provide a simplified and efficient prototype for future forecasts on energy use in buildings [156]. Botsaris et al. [152] suggested a model regarding energy auditing based on index assessing all the information in a building.
2.5 Energy efficiency
Buildings should be treated as sophisticated, integrated, interrelated systems [47].
Energy use in buildings depends on a combination of good architecture and energy systems design [159]. Indeed, different climates probably require different designs and equipment [160]. Energy efficiency measures for buildings are approaches through which the energy consumption of a building can be reduced while maintaining or improving the level of comfort in the building [158].
Nowadays, energy efficiency implies in dwellings a tend to focus upon improved envelope walls, floors, rooves; design and efficient mechanical equipment performance such as heating, cooling, domestic hot water, etc. [157, 158]. Energy efficiency contributes to sustainable development by limiting growth in energy demand in buildings.
One of the most important barriers for reaching the purpose of improving energy efficiency of buildings is the lack of information about the factors determining the real energy consumption [132]. Sometimes, there is a small similarity between the design and the real total energy consumption in buildings [133]. The explanations for these weak similarities are generally poorly understood between human behaviour and the building design [134].
It is necessary for us to understand the characteristics of each area of residential building energy consumption to provide the correct guidelines for building energy efficiency by analysis and study of residential building energy demands [6].
IEA [46] reported that energy efficiency measures have the potential to deliver more than 60 % of the energy-related CO2 emissions reductions needed to achieve climate protection.
The number of buildings in urban areas will increase after increasing urbanization, higher in developing countries, as consequently its noticed an increased demand for electricity and other forms of energy commonly used in buildings [78, 79]. The practice of energy efficiency in buildings can be categorized by [161]: reducing heating demand;
reducing cooling demand; reducing the energy requirements for ventilation; reducing
557 energy use for lighting; reducing energy used for heating water; reducing electricity consumption of office equipment and appliances, etc .
3. FIELD STUDY
3.1 Studied region
Located at the 20°00 latitude South and at the 47°00 longitude East, Madagascar lies almost entirely within the tropical region. It is an island in the Indian Ocean, covering an area of 5. 92 000 km2. It is the fourth largest island in the world, and it is separated from Africa by the Mozambique Channel by about 400 km. There are basically two seasons in Madagascar: dry, from May to October, and rainy, from November to April.
Two short seasons of approximately one-month duration separate these two seasons.
From May to October, the climate is conditioned by an anticyclone at the Indian Ocean level, which directs a wind regime of trade winds south–east on Madagascar.
During this season, the eastern part of the island experiences a humid climate “in the wind”, while the western part undergoes a drought-like climate termed “down wind”.
The study was conducted in twelve cities in Madagascar: Antananarivo, Antsirabé, and Fianarantsoa (dominated by altitude tropical climate); Antsiranana, Ambilobé, Vohémar, Andapa and Sambava (dominated by transition tropical climate); Nosy-bé, and Mahajunga (hot tropical climate); Toamasina (humid tropical climate); and Toliara (arid tropical climate). The location of all these cities is given on figure 8.
Fig. 8: Cities studied
Detailed characteristics of the study area are given in Table 3.
Table 3: Some climatic characteristics of cities (yearly data)
This table shows that outdoor air temperature is higher for the cities located near the sea than those in a high altitude. It's seen that temperature decreases with altitude. The minimum temperature is the lowest for the regions dominated by altitude tropical
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climate (Antananarivo, Antsirabé, Fianarantsoa), this implies a heating energy demand between June and August.
In 2016, Nematchoua et al. [8], carried out a study in (05) big hospitals, (50) small and big shopping centers, (67) traditional buildings, and (25) schools, which were distributed in 25 districts with different micro-climates of the urban communes in northern Madagascar. The results showed that the comfort zone varied between 22.9 and 27.2 °C.
3.2 Experimental campaign
In this study, the primary objective was to make a review on energy consumption in residential and commercial buildings of Madagascar for helping this country in its new energy policy and create a comprehensive database on energy demands in sub-Sahara Africa. A total of 15 students were selected and trained to conduct the survey.
The main research methods included a survey questionnaire about energy consumption, and interviews with those who could neither read nor write well.
An experimental campaign was carried out in 1272 residential buildings and 51 commercial buildings, located in 12 big cities of Madagascar. In total, 1323 people were questioned.
The sample sex ratio was essentially 1:1, with 815 males and 508 females being investigated, in 345 traditional buildings, 927 modern buildings, 14 offices, 5 hotels, 6 stores, 19 schools, 1 hospitals and 6 restaurants.
Most of the selected traditional habitats were older than 40 years; traditional houses were built using local materials, such as, dry bamboo, red earth, straw leaf, enamelled iron, sheet-metal and sometimes provisional materials. Their heights varied between 1.9 m and 4.5 m. Most of these buildings had a square or rectangular plan, and their roofs were formed of dry straw leaves, with more than 5 cm of thickness, a slope of 45°C, and sometimes covered with old rusted metal sheets.
They were mostly located in the peripheral quarters of the town and often grouped near the main road. Some of these habitats included sheet fences, with earth brick around them. Other habitats were open to the public, which facilitated the lighting of the indoor by the sunlight during the day. These buildings had small verandas on the main faҫade that were used for rest and protection against the sun and rain.
The height or the length of most of the doors was less than 1.77 m. The occupants were the most numerous (always more than five people), and with double beds in a room. The average age of occupants in this habitat was 26 years, and for the most case oriented towards East.
The construction time of modern buildings varied between 0 and 50 years. These habitats were built using some imported and local materials such as red and black earth, hard parpen, marble, etc. Their heights varied between 2.5 m and 6.0 m, with different geometry form (square, rectangular plan).
No more than four people by house and individual room. Their main faҫade was always dominated by a green garden, with a great enclosure which protected the inhabitants; and often oriented towards the south-east. Rooves were constructed with sheet material and double windows.
The offices area varied from 14 to160 m2, with average height of 4.5 m. For multi- storey buildings, the offices selected were those that supported a greater number of concerning solar radiation which influences the quality of indoor air, buildings with the same orientation were selected. The choice of offices corresponds to several criteria, concerning structure, typology as well as external environment. But the essential criteria
559 was the availability and the desire of people to participate to the investigation. Also the inertia of the building. In each office, one person had the right to vote. In each office it was at less three bulbs of more than 40 W everyone.
The five hotels studied were among the more visited in the city. The questionnaire was completed by the manager or hotel’s founder. There were more the fifty rooms and all with air conditioning under high security system. The majority were built using materials such as marble, glass and pane, with several floors.
The five hotels studied were among the more visited in the city. The questionnaire was completed by the manager or hotel’s founder. There were more the fifty rooms and all with air conditioning under high security system. The majority were built using materials such as marble, glass and pane, with several floors.
In addition, stores were located in the center city, near big crossroads. The façades of their main walls were for the most part covered with clear glass, which allowed passers to admire the goods from ten meters. The majority oriented North-East.
On the other hand, the schools were mostly located in densely populated neighbourhoods and close to roads. Most of these establishments were built between 10 and 50 years ago, with plastered and painted walls, and sometimes, with earth brick. All these schools were protected and surrounded by large barriers and walls that prevented students from going home during study break. During this study, only the naturally ventilated conditions were investigated.
Finally, only cheap-restaurant was selected, attainable to all the people. Always with local and particularly provisional materials such as sheet-metal, old plank, etc. It had a small area around 10 meter per square. The study was conducted during the periods reported in Table 4.
Table 4: Periods of study
3.3 Survey questionnaire
The subjective approach was necessary in this study. The questionnaires received the subjective answers of director (hospitals), manager (store, hotel and restaurant), administrator (schools), worker (office), and occupants (traditional and modern buildings), The opinions of individuals were obtained by a careful analysis of these questionnaires.
A total of 1323 questionnaires were collected during both seasons: One person for each of the 1323 studied building. To encourage some people who could neither read nor write, to participate in the study, oral questions were posed and their answers collected.
3.3.1 Background information
Questionnaires were written in the French and Malagasy languages, which are the country’s official languages. The language preferences of the occupants were
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considered while distributing questionnaires. The questionnaire was subdivided into three parts:
-Part 1: General data: age, gender, height, area, type of habitat, city, time, building duration, orientation etc.);
-Part 2: Different sources of supply energy;
-Part 3: Energy consumption and monthly cost.
The questionnaires were given randomly, without any physical constraint.
3.3.2 Characteristics of the voters and activity
The average age of participants was 26 years in all the studied places. Their weights ranged between 33 kg and 95 kg. Their activities varied according to seasons.
Meanwhile, the activities were more intense in the restaurant compared to other studied places. All the selected participants were those who had a good knowledge on energy consumption in their environment. Table 5 shows the number of building’s occupant according to the period.
Table 5: Occupant’s and study period
Regarding this table, it's seen that the number of occupant varied versus daytime.
Commercial sector was weakness visited between 08:00 pm and 6:00 am. In the residential sector, energy demand increased between 14:00 - 20:00, and particularly from 8:00 am, to 6:00 am, while in commercial buildings (schools, stores, restaurants, etc.), it's interesting to see that energy consumption increased between 6:00 and 12:00, then, from 2:00 pm to 8:00 pm, may be because of the occupant’s variation.
4. RESULTS AND DISCUSSIONS
4.1 Analysis of building energy source
Figure 9 shows the different energy sources used for application in the buildings.
More than 55 % of residential and commercial energy used was electricity. Between 2015 and 2025, it's expected a decrease up to 5.5 % of energy supplied by electricity benefic to energy coming from solar panels. Approximately 20 % of total energy consumption depended on charcoal.
From 1995 to 2025, energy supplied by solar panels should increase to 21.1 %, while the energy produce by charcoal will decrease to 23.2 %. The data analysis showed that only 21.6 % of studied buildings depended of other habitats regarding energy supply.
It's interesting to notice that between 1995 and 2015, the majority of the energy service supply by a building at other buildings was 'electricity'. 78.4 % of building energy source directly comes from a connection with a national electricity distribution company (figure 10).
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Fig. 9: Percentage of used energy for supplying both (residential and commercial buildings) in pass (1995 and 2005) present (2015) and future (2025) in Madagascar
Fig. 10: Distribution of energy services supply by a building at other buildings in Madagascar
As shown on figure 11, it is seen that, in both buildings, the main electricity production source was other than hydraulic and thermal. In the commercial buildings, 25 % and 21 % of electricity comes from generating set and solar panels, respectively.
In some developed countries like the USA, buildings use more than 38 % of all energy and 76 % of electricity [46].
The energy consumption quantity being the most important in residential building in Madagascar, these results show that, nowadays, in this island, more than 95 % of energy consumption in both building types comes from fossil energy. This can be due to bad government energy policy, but also the lack of available funds for large scale projects.
Fig. 11: Distribution of different main electricity sources used in both buildings during this ten last years
This problem is common to all developing countries and especially to sub-Saharan Africa. It is important to develop mechanisms to preserve the destruction of the
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environment. Some research shows that less than 20 % of potential resources (hydraulic, solar, wind, biomass etc.), exploited in Madagascar will be able to supply all the five countries of the Indian Ocean with electricity [44].
4.2 Analysis of building energy consumption
In the different building studied, it's noticed that the average annual energy consumption varied from 74.5 kW/h by 2014, to 84.8 kW/h by 2016 (figure 12). A statistical analysis of data revealed that the energy demand increased to 14 % during these last three years in the studied buildings.
Energy use was highest between June and August for the residences located in the central region, because of cooling degree very important during this time. In the residential buildings, this energy was used for cooling, lighting, water cooling, and consumer products.
Fig. 12: Monthly energy uses in both buildings during three years
These findings confirmed the results explained by IEA [48]. In these regions, transmission heat losses played an important role for the energy performance of buildings.
Given the country's vulnerability to climate change, and mushroom-like constructions in all cities across the country, with no respect for design standards, we can expect higher demand of energy in the new buildings.
4.3 Analysis of building energy expenditure cost
As shown on figure 13, in both buildings, the majority of occupants preferred 'to use economical lighting fixtures' for reducing energy consumption. In the commercial buildings, 22.5 % wanted' to reduce the power of consumption, while in household buildings, the least would like 'to limit the use of cooling apparatus'.
These results are almost similar at those found by Nematchoua et al. [7] who showed that in residential building, more than 80 % of occupants preferred to use 'economical lighting fixtures' as the main technical for reducing energy consumption.
Figure 14, shows the average expenditure cost in residential and commercial buildings during these last three years in studied places. The mean energy consumption cost varied from 230 to 257 €/year. In 2014 and 2015, the consumption cost was the highest in May (with a mean 22.7 €), but, in 2016, the demand cost increased up to 21
% in December.
This difference can be due to strong activities in the buildings during this month. It’s important to notice that energy expenditure cost was the weakest in October (around to 18.5 €). This may be because October is the transition month between dry and rainy season.
563 During this month, the weather is slightly better. In Madagascar, the new energy policy planed by the government has five qualitative goals: universal access to modern energy; affordability of price; quality and service reliability; energy security; and sustainability. Each of these objectives is to be achieved at the least cost, taking into account the economic and social benefits of the country [165].
Fig. 13: Distribution of some methods to reduce energy consumption in buildings
Fig. 14: Average expenditure cost per month in both buildings 4.4 Analysis of occupant’s thermal satisfaction
According to results shown on figure 15, it's easy to deduce that the satisfaction of occupants varied regarding the kind of building. In both buildings, the majority of voters (more than 30 %) were satisfied with the energy consumption in their environment.
24.9 % of voters were unsatisfied in residential buildings, while 29 % of workers were 'indifferent' about energy consumption in their environment in commercial buildings. These findings confirmed the research carried out by Nematchoua et al. [8]
which found that thermal satisfaction varied according to building type. Another conclusion is that residential buildings are less comfortable than commercial.
The building performance also depends on the techniques used to reduce energy consumption. The optimal comfort in a building does not necessarily imply a high- energy consumption [2]. The Malagasy government in its new energy policy would like free access and lower electricity costs for all households [164].
Several reforms in the electricity sector on the island include: - The 98-032 Law of 20 January 1999, relating to the Electricity Sector Reform; - The Political Declaration of 1999 which confirms the principles of liberalization of the sub sectors of electricity and hydrocarbons; The law 2002-001 of 7 October, 2002: Relating to the creation of the National Electricity Fund etc. [162, 163].
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In 2025, electricity use, propane gas, and charcoal demand in building of Madagascar will decrease to 1.8 %, 0.76 %, and 9.8 %, respectively, while energy production by natural gas, solar panels and bio-fuel will increase to 1.5 %, 12 %, and 1.1 %, respectively. These results testify to the variability of different energy production sources in residential and commercial buildings in Madagascar
.
Despite sophisticated technologies used in new buildings, energy consumption always remains higher than traditional habitats.
It's important to use local materials for sustainable construction. These kind of materials are adapted to the local climate [5]
.
Fig. 15: Occupant’s thermal satisfaction in buildings 5. CONCLUSION AND POLICY IMPLICATIONS
The present statistical study of questionnaires provided the subjective answers with regard to energy consumption of the occupants in 1323 residential and commercial buildings located in 12 cities with different micro-climates in Madagascar during dry and rainy season.
Data analysis revealed that energy consumption is the highest in the commercial sector, but nevertheless, cooling energy demand increases the most in the residential sector. With implementation of new technology, some inhabitants trended to adapt solar panels for producing electricity in their environment.
In this recent decade, the average energy consumption was estimated around 247 € in residential buildings. With the strong increase of the population, and a lot of new designs , it is noticed that in the world, more than 40 % of energy produced is consumed in building. Electricity and natural gas are two main fuels used in commercial buildings.
80 % of energy produced in traditional buildings of Madagascar come from charcoal. In residential buildings, the majority of occupants preferred to use 'economical lighting fixtures' as the main technique for reducing energy consumption.
These results can help the Malagasy government in its new energy policy and also served of guide at all the tourists, investors and new researchers who are interested in building energy uses in Madagascar.
Acknowledgment - The authors acknowledge the PAFROID Project for their support in this work, and the 15 students who have conducted the survey in the different cities.
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