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Design Optimization of Vernacular Building in Warm and Humid Climate of North-East India

Manoj Kumar Singh, PhDLocal Environment Management and

Analysis (LEMA), Université de Liège, Chemin des Chevreuils, 1 - 4000 Liège,

Belgium; Integrated Research andAction for Development (IRADe), C-80,

Shivalik, Malviya nagar, New Delhi 110017, India

Sadhan Mahapatra, M.Tech.Department of Energy,

Tezpur University,Tezpur, 784028, Assam, India

Jacques Teller, PhDFaculté des Sciences Appliquées,

Department ArGEnCo, Local Environment Management and

Analysis (LEMA), Université de Liège, Chemin des Chevreuils,1 - 4000 Liège, Belgium

ABSTRACT

Vernacular buildings are evolved through trial and error method over the period of time. These buildings are constructed more on ‘design-based approach’ suited to a particular climatic condition and socio-cultural setup rather than emphasizing technological solutions or prescriptive requirements. However, in recent times, due to quest for better thermal comfort, energy consumption is increasing in these naturally ventilated buildings. So, it is an urgent need to analyse the present level of thermal comfort and the occupant’s expectation in these buildings. In case of design based approach, passive solar design, ventilation, insulation on the building envelope, shading and glazing area, proper orientation of buildings etc. are the key parameters for optimization process. In this study, a vernacular building of warm and humid climatic zone of North-East India is considered. Thermal performance study has been done by carrying out year long measurements of environmental parameters both at indoor and outdoor of the building along with thermal comfort survey and interaction with the occupants. The comfort and neutral temperature for different seasons of the year have been evaluated in the study. Solar energy modular simulation tool TRNSYS 17 is used to carry out simulations of the building. Building 3D model is generated in TRNSYS and design optimization has been done by carrying out parametric simulations for different scenario such as wall thermo-physical properties and thickness, window to wall ratio, glazing type, orientation, shading, infiltration, ventilation and internal load. The objective of the simulations is to improve the indoor thermal environment close to the comfort temperatures obtained during comfort survey. Indoor temperature profile of the optimized building shows significant reduction in number of discomfort hours compared to the base case.

INTRODUCTION

Vernacular buildings are the structures that use the bioclimatic concepts and locally available building material to a large extent (Singh et al., 2011b). This provides an edge to vernacular buildings to withstand with the local climate constraints through adaptation. However, vernacular buildings are mainly constructed on design based approach and evolve over the period of time through trial and error method (Ruiz and Romero, 2011; Singh et al., 2010a; Singh et al., 2010b; Singh et al., 2011b). These buildings attract attention of researchers because these structures represent an excellent harmony between environment, available building material and resources, socio-economic status and socio-cultural need of occupants, climate pattern and comfort, thus putting forth a unique example of

30th INTERNATIONAL PLEA CONFERENCE16-18 December 2014, CEPT University, Ahmedabad

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sustainability (Kulkarni et al., 2011; Orehounig and Mahdavi, 2011; Singh et al., 2011b). In modern times, with the changing lifestyles, comfort standards and energy needs are increasing. Hence, it is important to look at the energy saving potential and sustainability presented by bioclimatic aspects of vernacular buildings (Singh et al., 2010a; Singh et al., 2010b). Vernacular buildings of North-East India are naturally ventilated and constructed using locally available building materials. Shape and form of these buildings are evolved over time to meet the socio-cultural and day to day requirements (Singh et al., 2010a; Singh et al., 2011b). These buildings are still favoured by people of the region and are still being widely constructed (Singh et al., 2010a; Singh et al., 2011b). However, in the present context of increasing comfort requirement and energy efficiency regulation and guidelines, it is an urgent necessityto carry out the thermal performance study of these vernacular buildings (Auliciems, 1981; Brager and Dear de, 1998). In this study, a vernacular house located in warm and humid climate (Tezpur, India) is considered. Selected house is modelled in TRNSYS 17 (Transient System Simulation), most widely used solar energy modular program to carry out the thermal performance study of buildings (Bansal and Bhandari, 1996; Beckman, 1994; Datta et al., 2001). It is a very powerful solar modeling and simulation tool (Bansal and Bhandari, 1996; Orehouning and Mahdavi, 2011). In this study, multi-zone building is integrated to simulation studio by Type 56. Number of studies has been carried out in different parts of the world on the thermal performance of modern buildings by using TRNSYS. However, no study has been done on the design aspect of the vernacular houses of North-East India. Thermal simulations are carried out to see the effect of different design features on indoor temperature. Based on the analysis of simulation data suggestions are made to improve the indoor temperature variation inside the house over the year.

Table1 Properties of the selected vernacular houseHouse details Properties

Building type Vernacular house (Local common name : Assam type)Climatic zone Warm and humidBuild up area (m2) 94

Building materialBrick, cement, sand, plywood, asbestos sheet/wood, galvanized tin sheet

Ventilation type Naturally ventilated

Temperature rangeSummer temperature : Maximum : 30 – 35 0C; Minimum: 22 – 27 0C Winter temperature : Maximum : 25 – 30 0C; Minimum: 20 – 15 0C

Layout and orientation Open layout, NW-SERelative humidity (%) 75 - 90Altitude (m) 48Elevation of building 4.8 m (floor to eaves 3.8m and ceiling to roof top 1m)

North-East India is classified into three climatic zones (warm and humid, cool and humid and cold and cloudy) and vernacular houses in each climatic zone possess distinct climatic responsive features(Singh et al., 2007). Table 1 and 2 present the specific details and building materials of the selectedvernacular house in warm and humid climatic zone. Figure 1 presents the layout of the selected vernacular house in warm and humid climatic zone (numbers in the Figure 1 represent the zone number). It can be observed from Figure 1 that openings (windows and ventilators) are evenly distributed on the facade of the house. It is found that windows of the zone 2 and 3 are made up of wood with single glazing (30% of total window area). Ventilators are made up of wood with single glazing (35% of total ventilator area). It is found from the thermal performance study of the selected house that the maximum indoor temperature swing is 10 0C (Singh et al., 2010a). It is also found from thermal performance analysis that the house is more comfortable in pre-summer and summer season compared to pre-winter and winter season (Singh et al., 2009; Singh et al., 2010a). Figure 2 represent the 3D drawing created in Trnsys3D and Google SketchUp. In 3D model, window on exterior façade are constructed by adding all the windows on exterior wall of same zone (keeping the area same) to reduce the complexity of the model. Since the selected vernacular house is naturally ventilated so auxiliary heating, cooling and mechanical ventilation are kept off for all simulations. In case of naturally ventilated building indoor air temperature variation is the most important parameter so entire study is focussed on analysis of indoor temperature variation in different zones of the house. In this house zone 2 and zone 3 are occupied for maximum duration of time so due consideration is given to the temperature profile of these two zones.

30th INTERNATIONAL PLEA CONFERENCE 16-18 December 2014, CEPT University, Ahmedabad

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Indoor temperature variation of base case is also compared with the data collected during thermal monitoring work carried out in 2008 to judge the accuracy of the developed model.

Figure 1 Layout of the house with different zones

Figure 2 3D Drawing of the vernacular house

Figure 3 Methodology of the study

METHODOLOGY

Vernacular house in warm and humid climate is locally called Assam type in this region (Singh et al., 2011b). This build form is very popular and it has wide acceptance because it fits well into social-cultural setup, economical to construct, easy to maintain and above all meets the climatic constraints (Singh et al., 2011b). In modern times, with changing life style, demand for better comfort and energy use regulations is forcing occupants to explore different options that modify the indoor environment. Thus, it becomes necessary to study the design aspects of vernacular house for its energy efficiency. This enables us to understand the thermal behavior of the vernacular house with respect to design modification required in the building design. Figure 3 represents the methodology followed to carry out the present study. Parametric simulation studies are carried out by using TRNSYS and MATLAB simulation tool is also used to process the simulation data. Three different 3D models like without false ceiling, false ceiling with common attic space and false ceiling with individual attic space are made in


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Google SketchUp. All these models are used to carry out the simulation for all eight possible building orientations. It has been tried to find out the best model by analyzing the simulation data which provides close result to thermal comfort survey data (Singh et al., 2010a; Singh et al., 2011a). This house is being selected as ‘base case’ for further simulations with design modifications. Figure 3 also shows the seven cases for which the base case model simulation is carried out with design modifications. Table 3 presents the specific details of seven cases for which the simulations are carried out. The different scenario for thesimulation are (i) applying different insulation to the walls of base case house (ii) replacing windows and ventilators with double glazing of base case (iii) increase and decrease the windows and ventilators area to base case (Table 2) (iv) replace the increased windows and ventilators area with double glazing to base case. The house considered for this study is naturally ventilated so the zone temperature is considered as the main output parameter along with zone heat gain due to infiltration. The infiltration iskept at 3 ACH (air changes per hour) for this naturally ventilated house for all simulation cases.

Table 2 Input parameters for base case building

Building materialsThermal conductivity

(W/m-K)Density(kg/m3)

Specific heat(kJ/kg-K)

Plaster 0.721 1762 0.84Brick 0.811 1820 0.88Tin sheet 61.06 7520 0.50Asbestos sheet 0.245 1520 0.84Wood(window, doors and ventilators) 0.17 900 1.7Foam insulation (10cm) U1 0.144 1.4 10Wooden wool (10 cm) U2 0.33 0.025 400Mineral wool (10 cm) U3 0.16 0.90 80

Table 3 Wall construction and thermo-physical properties of materials with thickness

Case Wall configuration Over all heat transfer coefficient (W/m2 K)

External wall Internal wall External wall

Internal wall

Base case+single glazing window with wooden frame

Plaster (1.5cm) + brick (23cm) + plaster (1.5cm)

Plaster (1.5cm) + brick (11cm) + plaster (1.5)

2.103 3.056

Base case + double glazing window


Plaster (1.5cm) + brick (11cm) + plaster(1.5)

2.103 3.056

Base case + wall with insulation 1

Plaster (1.5cm) + brick (23cm) + plaster (1.5cm) + insulation U1 (10cm)

Plaster (1.5cm) + brick (11cm) + plaster (1.5) + insulation U1 (10cm)

0.316 0.331




0.568 0.621




0.343 0.304

Base case + decreased window area


Plaster (1.5cm) + brick (11cm)+ plaster (1.5)

2.103 3.056

Base case + increased window area


Plaster (1.5cm) + brick (11cm) + plaster (1.5)

2.103 3.056

Base case + increased window area + double glazing

Plaster (1.5cm) +brick (23cm) + plaster (1.5cm)

Plaster (1.5cm) + brick (11cm) + plaster(1.5)

2.103 3.056

BUILDING MODEL GENERATION AND SIMULATION

TRNSYS 17 simulation tool is used to model the selected vernacular house to study the energy flow in the house as well as in between the zones of the house. TRNSYS is a quasi-state simulation tool (Bansal and Bhandari, 1996; Beckman, 1994). Its modular structure provides a tremendous flexibility and facility to users to customise the generated model (Singh et al., 2009; Beckman et al., 1994). It runs through hourly values but user can reduce the time step according to the system requirement (Beckman et al., 1994; Singh et al., 2011b). A systematic approach has been adopted to develop a multi-zone model


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of the selected vernacular house in TRNSYS using TYPE 56. Type 56 in the simulation tool also provides a provision to give 3D geometric surface information as input for detailed radiation calculation. This increases the accuracy of the calculations. Using Trnsys3D and Google SketchUp 3D model, vernacular house specifying zones is created. Once the building is defined properly the building variable needs to be updated and linked to TYPE 56.

RESULTS AND DISCUSSION

The vernacular house in warm and humid zone is generally constructed in three different pattern such as (a) without false ceiling (room air is in direct contact with roof), (b) with ceiling and attic space is common (most common type of construction) and (c) with ceiling but individual attic space above each room (walls of the houses are load bearing). 3D models for above three types of construction of vernacular house is generated in Google SketchUp and TRNBuild and imported to simulation studio as Type 56 (multi zone building). The simulations are carried out for all 8 possible orientations (00 due North, 450, 900, 1350, 1800, 2250, 2700, 3150). The build up area of the selected vernacular house is 94 m2. Figure 1 presents the configuration (numbers in the Figure 1 represent the zone number) of the house viz. zone 1: veranda, zone 2: living room/bed room, zone 3: bed room, zone 4: kitchen and zone 5: store room. Based on the functionality and specific requirements of rooms in a vernacular house, zone numbering is done in the selected vernacular house. Subsequently analysis of the simulation data has been carried out keeping in mind the requirement of the zones. In this study, due consideration has given to the temperature profile of zone 2 (living room/bed room) and zone 3 (bed room). Detailed thermal comfort model is applied by defining the geo-position. Thermal comfort, operative temperature and mean radiant temperature are calculated at the centre of each zone to analyse the thermal comfort. Since the selected house is naturally ventilated, heat gain/loss due to infiltration over 24 hours for entire year is also studied.

Simulation data of zone 2 and 3 of the house with no ceiling, ceiling with common attic and ceiling with individual attic is analysed. It is found that the house with no ceiling show higher daily indoor temperature swing. Also roof of all the house is made up of galvanised tin sheet, so it gain and loose heat quickly. This happens because indoor air in this house is in direct contact with roof and in day time it gains heat inside quickly and loose heat quickly in the night time. It is also observed that temperature fluctuation remains high for most part of the year except for the last three months when daily temperature swing is less. This can be explained by observing the local wind velocity profile. Low wind velocity greatly affects the infiltration and natural ventilation. Again looking at the indoor temperature swing of house having ceiling with common attic and ceiling with individual attic, it can be found that difference is very less. Hence, it can be concluded that the house with individual ceiling shows slightly better thermal performance but considering the complexity of construction and safety this can be neglected (Assam lies in seismic zone V). Hence the house having ceiling with common attic has been considered for further study.

Table 4 Indoor temperature range from field measurements and simulation of zone 2

Climatic zone

(place)

Month Range of indoor temperature (°C)Field measurement and comfort survey

Simulation

Warm and humid(Tezpur)

January 13 - 23 13 - 22 April 22 - 28 22 - 29July 27 - 34 27 - 33 October 22 - 28 23 - 29

Figure 4 and 5 presents the daily maximum and minimum temperature variation for zone 2 of the simulated vernacular house for all orientations. Similar kind profiles are also obtained for zone 3 of the selected house. It is observed from these figures that in pre-summer and summer the orientations has no effect on the indoor maximum and minimum temperature profile of the selected vernacular house. This is because in naturally ventilated vernacular house infiltration is very high. However, in pre-winter and winter months, it is found that that zone 2 and 3 of the house show some variation in the indoor temperature depending on the orientation of the house. The effect is more visible in the minimum temperature profile of zone 2 and 3. The reason of this behaviour can be attributed to the change in solar


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altitude angle and exposure of different zone of the house at different orientation. The orientation of real house at Tezpur is 3150N (i.e. - 45 0N if the building is rotated anti clock wise). It is found that at this orientation, zone 3 (bed room) is showing better thermal performance than zone 2 (living room/bedroom). Hence, it can be concluded that the orientation of the vernacular house is wisely selected. The maximum duration of wind direction in this climatic zone is from south, south-east and south-west. Hence, zone 2 and 3 of the selected house are in the line of the wind in summer months. It can also be concluded from Table 1 that in this climatic zone summer season will be uncomfortable due to persisting high temperature and high relative humidity. Natural wind direction is used wisely in this case to minimise the discomfort due to high relative humidity. Large openings in the form of window and ventilators on the external façade of the house is also promoting cross ventilation. Table 4 shows the comparison of indoor temperatures range between the field measurements and simulation of zone 2 of the building for base case.

Figure 4 Daily maximum temperature profile of zone 2 of the selected house with common attic

Figure 5 Daily minimum temperature profile of zone 2 of the selected house with common attic

Figure 6 Daily total heat gains due to infiltration in zone 2 of the selected house with common attic

Figure 7 Daily maximum temperature in zone 2 of the selected house with different cases

Figure 6 represent the heat gain/loss due to infiltration in zone 2 for different orientations. It is observed from this figure that the present orientation of the selected house is the best option because in winter heat loss due to infiltration is less compared to other orientations. It is found that in summer there is a large heat gain due to infiltration and this may be one of the reasons for high indoor temperature and subsequently discomfort. In summer, it is expected to minimise the heat gain by operating windows and ventilators during day time and increase heat loss in night (night ventilation). Night ventilation can be enhanced naturally by opening windows and ventilators fully thus allowing maximum infiltration of outside air. This can also be achieved by using mechanical ventilation at night. This will reduce the discomfort duration in summer considerably. To avoid discomfort due to heat loss in winter, the main activity should be to increase the heat gain and minimise the heat loss. Here also if opening and closing of windows and ventilators are regulated intelligently then discomfort due to cold can be minimized to a large extent. So, it is found that large window to wall area ratio in existing vernacular houses can be used


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intelligently to overcome the climatic constraint and consequently increase comfort duration in this vernacular house.

Based on the above analysis, vernacular house of base case is selected (with common attic space and orientation 315 0N) for further simulations. The various scenarios considered for the simulation are listed in Table 3. Figure 7 and 8 represents the daily maximum and daily minimum temperature profile of zone 2 respectively. Similar profiles are also obtained for zone 3. It is observed from these figures that increase of insulation has minimum effect on the indoor air temperature profile of zone 2 in summer season. This happened due to high infiltration minimises the effect of increase in insulation. It is also observed from Figure 7 and 8 that increase in window area with double glazing leads to increase in daily maximum and minimum temperature in summer and winter season. However, the increase is more prominent in winter season. This happened due to low altitude of sun in winter helping sunlight enters directly inside the rooms through window glazing leading to increase in indoor temperature supported by better insulation properties of double glazing. Figure 9 represent the daily temperature swing in zone 2 for different cases. It is observed from Figure 9 that when insulation is applied to the inside wall of the building, the indoor temperature swing becomes high compared to base case. The reason for this can be attributed to the low inertia of the insulation and also insulation is not allowing energy stored in the external wall to radiate to indoors. Low thermal inertia and high infiltration is responsible for large temperature swing. This situation may lead to discomfort in indoors if insulation is applied to naturally ventilated buildings. Hence, it can be concluded that the base case is the best option with respect to the daily indoor temperature swing of zone 2. Similar results are also obtained for zone 3.

Figure 8 Daily minimum temperature in zone 2 of the selected house with different cases

Figure 9 Daily temperature swings in zone 2 of the selected house with different cases

It is also observed from Figure 9, that decrease in window area case is showing lowest swing in daily indoor temperature profile. However, this cannot be suggested as best design option, as it will also drastically reduce the day lighting level and natural ventilation which will lead to discomfort. In all the cases, high indoor temperature swing is observed from January to June months as during this period wind velocity is high, which enhanced the heat gain and loss due to high infiltration. It is found from the Predicted Mean Vote (PMV) and thermal model analysis, that these houses show low thermal comfort in winter and summer months (Singh et al., 2010a; Singh et al., 2011a; Singh et al., 2015). However, they show acceptable thermal comfort in pre-summer and pre-winter months. Simulation results also show that zone operative temperature is always lower than zone air temperature by 1 – 1.8 0C and zone meant radiant temperature is always lower than zone operative temperature by 1.2 – 1.8 0C throughout the year. Similar trend is also observed for all other cases also.

CONCLUSIONS

In this study, vernacular building of warm and humid climate zone of North East India is considered for design based thermal optimization by using the simulation tool TRNSYS. It can be concluded based on the analysis that the house having ceiling with common attic is showing acceptable daily indoor temperature swing. It is also found that the vernacular houses of this zone must have ceiling to minimize


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the daily indoor temperature swing. It is found from the analysis that due to high infiltration in naturally ventilated building, insulation has almost negligible effect on the daily indoor temperature swing. However, it is found that increase and decrease of window and ventilator area has significant effect on the daily indoor temperature swing (window and ventilator area is most sensitive building design parameter). It also can be concluded from this study that increase and decrease of glazing area has maximum effect in the winter season when the sun altitude is less. Hence, it can be recommended that if the window be replaced with double glazing with proper shading mechanism then the indoor thermal conditions will be significantly improved. Thermal comfort analysis shows that buildings are thermally more comfortable in pre-summer and pre-winter season. However, this study needs to be further carried out by integration of airflow model with thermal model to obtain better results.

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