Scholarly article on topic 'Assessing Impact of Material Transition and Thermal Comfort Models on Embodied and Operational Energy in Vernacular Dwellings (India)'

Assessing Impact of Material Transition and Thermal Comfort Models on Embodied and Operational Energy in Vernacular Dwellings (India) Academic research paper on "Materials engineering"

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Abstract of research paper on Materials engineering, author of scientific article — K.I. Praseeda, Monto Mani, B.V. Venkatarama Reddy

Abstract Vernacular dwellings are well-suited climate-responsive designs that adopt local materials and skills to support comfortable indoor environments in response to local climatic conditions. These naturally-ventilated passive dwellings have enabled civilizations to sustain even in extreme climatic conditions. The design and physiological resilience of the inhabitants have coevolved to be attuned to local climatic and environmental conditions. Such adaptations have perplexed modern theories in human thermal-comfort that have evolved in the era of electricity and air-conditioned buildings. Vernacular local building elements like rubble walls and mud roofs are given way to burnt brick walls and reinforced cement concrete tin roofs. Over 60% of Indian population is rural, and implications of such transitions on thermal comfort and energy in buildings are crucial to understand. Types of energy use associated with a buildings life cycle include its embodied energy, operational and maintenance energy, demolition and disposal energy. Embodied Energy (EE) represents total energy consumption for construction of building, i.e., embodied energy of building materials, material transportation energy and building construction energy. Embodied energy of building materials forms major contribution to embodied energy in buildings. Operational energy (OE) in buildings mainly contributed by space conditioning and lighting requirements, depends on the climatic conditions of the region and comfort requirements of the building occupants. Less energy intensive natural materials are used for traditional buildings and the EE of traditional buildings is low. Transition in use of materials causes significant impact on embodied energy of vernacular dwellings. Use of manufactured, energy intensive materials like brick, cement, steel, glass etc. contributes to high embodied energy in these dwellings. This paper studies the increase in EE of the dwelling attributed to change in wall materials. Climatic location significantly influences operational energy in dwellings. Buildings located in regions experiencing extreme climatic conditions would require more operational energy to satisfy the heating and cooling energy demands throughout the year. Traditional buildings adopt passive techniques or non-mechanical methods for space conditioning to overcome the vagaries of extreme climatic variations and hence less operational energy. This study assesses operational energy in traditional dwelling with regard to change in wall material and climatic location. OE in the dwellings has been assessed for hot-dry, warm – humid and moderate climatic zones. Choice of thermal comfort models is yet another factor which greatly influences operational energy assessment in buildings. The paper adopts two popular thermal-comfort models, viz., ASHRAE comfort standards and TSI by Sharma and Ali to investigate thermal comfort aspects and impact of these comfort models on OE assessment in traditional dwellings. A naturally ventilated vernacular dwelling in Sugganahalli, a village close to Bangalore (India), set in warm – humid climate is considered for present investigations on impact of transition in building materials, change in climatic location and choice of thermal comfort models on energy in buildings. The study includes a rigorous real –time monitoring of the thermal performance of the dwelling. Dynamic simulation models validated by measured data have also been adopted to determine the impact of the transition from vernacular to modern material-configurations. Results of the study and appraisal for appropriate thermal comfort standards for computing operational energy has been presented and discussed in this paper.

Academic research paper on topic "Assessing Impact of Material Transition and Thermal Comfort Models on Embodied and Operational Energy in Vernacular Dwellings (India)"

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Energy Procedía 54 (2014) 342 - 351

4th International Conference on Advances in Energy Research 2013, ICAER 2013

Assessing impact of material transition and thermal comfort models on embodied and operational energy in vernacular dwellings (India)

K. I. Praseedaa*, Monto Manib, B. V. Venkatarama Reddyc

aResearch Scholar, Department of Civil Engineering, Indian Institute of Science, Bangalore 560012, India bAssociate professor, Centre for Sustainable Technologies, Indian Institute of Science, Bangalore 560012, India cProfessor, Department of Civil Engineering, Indian Institute of Science, Bangalore 560012, India

Abstract

Vernacular dwellings are well-suited climate-responsive designs that adopt local materials and skills to support comfortable indoor environments in response to local climatic conditions. These naturally-ventilated passive dwellings have enabled civilizations to sustain even in extreme climatic conditions. The design and physiological resilience of the inhabitants have coevolved to be attuned to local climatic and environmental conditions. Such adaptations have perplexed modern theories in human thermal-comfort that have evolved in the era of electricity and air-conditioned buildings. Vernacular local building elements like rubble walls and mud roofs are given way to burnt brick walls and reinforced cement concrete tin roofs. Over 60% of Indian population is rural, and implications of such transitions on thermal comfort and energy in buildings are crucial to understand. Types of energy use associated with a buildings life cycle include its embodied energy, operational and maintenance energy, demolition and disposal energy. Embodied Energy (EE) represents total energy consumption for construction of building, i.e., embodied energy of building materials, material transportation energy and building construction energy. Embodied energy of building materials forms major contribution to embodied energy in buildings. Operational energy (OE) in buildings mainly contributed by space conditioning and lighting requirements, depends on the climatic conditions of the region and comfort requirements of the building occupants. Less energy intensive natural materials are used for traditional buildings and the EE of traditional buildings is low. Transition in use of materials causes significant impact on embodied energy of vernacular dwellings. Use of manufactured, energy intensive materials like brick, cement, steel, glass etc. contributes to high embodied energy in these dwellings. This paper studies the increase in EE of the dwelling attributed to change in wall materials. Climatic location significantly influences operational energy in dwellings. Buildings located in regions experiencing extreme climatic conditions would require more operational energy to satisfy the heating and cooling energy demands throughout the year. Traditional buildings adopt passive techniques or non-mechanical methods for space conditioning to overcome the vagaries of extreme climatic variations and hence less operational energy. This study assesses operational energy in traditional dwelling with regard to change in wall material and climatic location. OE in the dwellings has been assessed for hot-dry, warm - humid and moderate climatic zones. Choice of thermal comfort models is yet another factor which greatly influences operational energy assessment in buildings. The paper adopts two popular thermal-comfort models, viz., ASHRAE comfort standards and TSI by Sharma and Ali to investigate thermal comfort aspects and impact of these comfort models on OE assessment in traditional dwellings. A naturally ventilated vernacular dwelling in Sugganahalli, a village close to Bangalore (India), set in warm - humid climate is considered for present investigations on impact of transition in building materials, change in climatic location and choice of thermal comfort

1876-6102 © 2014 K.I. Praseeda. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/3.0/).

Selection and peer-review under responsibility of Organizing Committee of ICAER 2013 doi:10.1016/j.egypro.2014.07.277

models on energy in buildings. The study includes a rigorous real -time monitoring of the thermal performance of the dwelling. Dynamic simulation models validated by measured data have also been adopted to determine the impact of the transition from vernacular to modern material-configurations. Results of the study and appraisal for appropriate thermal comfort standards for computing operational energy has been presented and discussed in this paper.

© 2014 K.I. Praseeda. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

Selectionandpeer-reviewunderresponsibility ofOrganizingCommittee ofICAER2013 Keywords/Embodied energy;Operational energy; Buildings material, Thermal Comfort, models

1. Introduction

Vernacular dwellings portray building design and construction practices evolved with centuries of traditional wisdom. These traditional buildings adopt material use and building design to suit local climate, environment and socio-economic pattern. They exhibit outstanding ability to mitigate extremities of local climatic conditions to achieve comfortable conditions indoor. Vernacular dwellings involve significant human effort and skill for construction and use of locally available natural materials. These dwellings exploit animate energy extensively rather than inanimate or mechanized energy. In India, traditional buildings illustrate variety of examples for vernacular building design suiting different climatic conditions experienced across the country. Houses with massive mud walls in desert regions, houses with sun dried brick or stone block walls in warm and humid, cold climate regions, use of natural materials such as thatch, mud, bamboo, slate stone for roofing are examples for use of locally available materials in buildings. A significant feature of India's climate responsive architecture is the courtyard which serves diverse functions based on the climate of the region. Use of natural, locally available materials and adoption of vernacular building design to create comfortable living space require less resource and energy consumption for construction and maintenance of traditional buildings. Recently, these traditional dwellings show trends of gradual transformation of material use from locally available natural materials to conventional building materials such as cement, steel, prefabricated roofing sheets etc. This has significant adverse impact on EE of dwellings. Also, such transition renders the buildings out of context with the climate and shifts the indoor conditions out of the comfort zone.

Study of thermal comfort conditions in vernacular dwellings attracted researchers across the world due to the wide spectrum of parameters involved in design or prediction of indoor thermal comfort in these naturally ventilated dwellings. Thermal comfort models are used to define indoor comfort conditions in buildings. These models estimate various comfort parameters such as temperature, relative humidity, mean radiant temperature etc. to determine whether the indoor environment is comfortable or not. Thermal comfort models are mostly developed based on subjective measurements on thermal sensations experienced by the occupants at different indoor temperature ranges. Hence, it becomes crucial that one adopt region specific thermal comfort models for building design. Choice of thermal comfort models have significant influence on operational energy assessment in buildings since that would eventually determine the different strategies required for combating discomfort.

The objective of this study is to explore the impact of transition in material use and adoption of different thermal comfort models on energy use in vernacular dwellings. A naturally ventilated vernacular dwelling in Sugganahalli, a village close to Bangalore (India), set in warm - humid climate is considered for present investigations on impact of transition in building materials, change in climatic location and choice of thermal comfort models on energy in buildings. The study includes a rigorous real -time monitoring of the thermal performance of the dwelling. Dynamic simulation models validated by measured data have also been adopted to determine the impact of the transition from vernacular to modern material-configurations.

Nomenclature

T Air temperature (°C)

RH relative Humidity (%)

TSI Tropical Summer Index EE Embodied energy OE Operational energy

2. Embodied and Operational Energy in Vernacular Dwellings

Embodied energy of a building includes total energy consumption associated with production of building materials, transportation of building materials and building construction. Embodied energy assessment generally takes into account only the inanimate energy components and omits the animate energy inputs due to the complexity involved in quantification. Energy consumption associated with building material production i.e., embodied energy of building materials represent nearly 90% of embodied energy of buildings [1]. Natural materials extracted manually have zero embodied energy while conventional building materials such as cement, steel, glass, aluminium etc., which are produced in industries, are energy intensive. Use of locally available natural materials and animate energy (manual labour) for construction makes EE of traditional dwelling insignificant. But replacement of natural materials with conventional building materials would result in high EE for these dwellings.

Operational energy of building implies energy consumption during building's operational phase. Operational energy of buildings mainly includes energy consumed for indoor lighting and space - conditioning to maintain indoor comfort conditions. Design philosophy of vernacular dwellings advocate natural light for indoor lighting and indoor space conditioning by regulating heat gain and air movement inside the dwelling. This design approach is called passive solar architecture, where the buildings are designed to keep the occupants comfortable by passively moderating external environmental conditions [2]. It is also observed that occupants in naturally ventilated dwellings follow adaptive approach for thermal comfort. In adaptive approach occupants develop behavioural modifications and mental resilience to deal with their surrounding environment [3].

The passive solar design and adaptive approach for indoor comfort yield negligible operational energy for vernacular dwellings. Recent developments of electricity have introduced use of light fixtures and ceiling fans in these dwellings. This results in some operational energy in these dwellings.

2.1. Case study - vernacular dwellings in Sugganahalli village, Karnataka

The present study is a continuation of an on-going study into climate responsive performance of vernacular dwellings [4]. The study examined vernacular dwellings in a village called Sugganahalli; an agricultural settlement situated 90 kilometres North West of Bangalore, Karnataka, India. This region is classified as warm-humid climatic zone [5] with temperature extremes ranging from 36°C in summer (March-May) to 14°C in winter (December-February). In summer, daily temperatures can range between 28 and 34°C during the day and 22 and 26°C during the night. Humidity level averages around 72% RH in summer and 50% RH in winter. In winter, daily temperature can range from 25 to 30°C during the day and 18 to 22°C during the night.

The dwellings adopt local building materials such as stones and boulders for walls, mud flooring and timber to span the mud and/or clay-tile roofs. From a preliminary survey, one typical courtyard house was identified based on the commonality in the floor plan, design features and living habits. The dwelling has a built up area of 400m2 comprising four bedrooms, three kitchens, a common open bathroom and a central open courtyard (50 m2) with Mangalore (clay) tiled corridor (100 m2) on three sides for rearing livestock. Fig. 1 shows the floor plan of the studied dwelling. The main entrance faces north and opens out onto the road. Two families currently occupy the house -three females, two males and a boy. Table 1 lists the traditional materials and construction details adopted in the dwelling under study.

Table 1 Traditional materials and construction details Walls Rubble masonry with mud mortar - 450mm thick, mud plastering on interior walls

Roof type Mud roof: Wooden plank stone slab compacted mud - 300mm thick

Pitched roof: Standard Mangalore tiles on wooden rafters Flooring Rammed earthen flooring with a screed of cow dung/cement

2.2. Present day scenario

Burnt clay bricks and cement transported from nearby towns have replaced the free, locally available stone chips and mud mortar. The heavy (450 mm thick) rubble masonry walls have slimmed down to slender (230 mm thick) brick masonry which has much lesser heat storing capacity. Citing the issue of maintenance (re -applying a layer of soil) during rainy season, the thick mud roofs that provide the necessary thermal mass have made way for standard Reinforced Cement Concrete (RCC) slabs. Cement flooring in place of cool earthen floors and thin tin sheets in place of clay tiles are few other changes. Owing to the recent availability of electricity, transport facilities, improving education facilities in villages and job opportunities in the cities, the urban influence on the current generation is increasingly evident in the lifestyles of people. The slow disappearance of the community of builders who specialized in traditional construction methods has also contributed towards such a transformation. Similar concerns are expressed by Indraganti et al., Upadhyay et al. and Hanaoka et al. [6-8], and such a trend poses a threat to the vernacular traditions that help define the cultural make-up of a community [9].

2.3. Impact of material transition on EE

For the present study, increase in EE of vernacular dwellings with regard to change in wall material is examined for two alternative wall materials. As recently observed, burnt clay bricks have been increasingly adopted for masonry walls in these dwellings. As a second alternative, cement stabilized soil blocks were also considered for the current study.

Cement stabilized soil blocks (CSSB) are being used for masonry construction since the last 4 - 5 decades.

Stabilized soil blocks are manufactured by compacting the processed soil at Optimum Moisture Content (OMC) manually or in a machine to a desired density. Basic materials consumed in SSB include soil, sand, stabilizer (cement, lime etc.) and water. It is observed from the literature [10] that EE value of stabilized soil blocks (0.35 MJ/kg) is very low when compared to burnt clay bricks (2.42 MJ/kg). Stabilized soil blocks are considered as an alternative for burnt clay bricks from the perspective of limiting EE in buildings.

Table 2 provides the summary of embodied energy calculation for the dwelling with different wall materials and existing roofing configurations.

Table 2 EE of traditional dwelling for three different wall configurations

Type of wall EE of the dwelling MJ GJ/m2

1 Rubble stone masonry 66347.51 0.17

2 Naturally compacted soil block (Adobe) 66347.51 0.17

3 Burnt clay brick masonry 658753.8 1.65

4 Cement stabilized soil block masonry 190313 0.48

The result shows that replacing rubble stone masonry with burnt clay brick masonry and stabilized soil block masonry would increase the EE of the dwelling by 9.7 times (870%) and 2.8 times (182%) respectively. This shows that the transition of material used in walls from stone to burnt clay bricks has significant impact on EE of the dwelling. Projecting this impact for the entire group of vernacular dwellings in the country, this transition would cause huge implication on energy demand of the country.

2.4. Thermal comfort models and operational energy

Thermal comfort and operational energy assessment strategy included real-time monitoring of the selected courtyard dwelling's thermal performance and a community-based thermal sensation survey, along with the concurrent development of a dynamic simulation model of the dwelling. The real-time monitoring included measurements of indoor thermal environment factors (temperature, humidity and wind velocity) and external climatic factors including temperature and humidity. Solar intensity and wind speed were however manually recorded intermittently. The building simulation includes a detailed model of the monitored dwelling, integrating thermal performance values for building materials and adopting climate-files for the region. The monitored data enabled a real-time validation for the simulation model.

The selected house was monitored by installing calibrated resistance temperature detector (RTD) based dataloggers (temperature at 0.05°C resolution and ± 1°C accuracy; RH at 0.1% resolution and ± 2% accuracy) to measure temperature, dew-point and humidity every 30 minutes at five locations. Three of these were installed at regions of maximum occupancy at a height of 1.8m from the ground, one just above the courtyard and one outside. The external data-loggers were housed in a Stevenson screen to protect the instrument from direct rain and solar radiation. No restrictions were imposed on the occupants. For verifying consistency in data-logger performance, dry and wet-bulb measurements were also periodically taken using a whirling psychrometer.

A computer-based building simulation model was developed in DesignBuilder (v 2.2.5), a Computational Fluid Dynamics (CFD) based simulation package built over the successfully adopted EnergyPlus [11, 12]. Hourly weather files were generated using METEONORM v6.0. Construction details, occupancy and activity patterns including general door-window opening/closing schedule and heat gain from cooking, cattle, etc., were input based on observation and survey. The neighbouring houses have also been integrated into the simulation model (Fig. 2) to enable a more realistic representation and performance of the dwelling under study. The building model was validated with existing dwelling by comparison of measured and simulated indoor temperature values. Since the simulation model responds to climate files (statistical data) and the real-time thermal monitoring responds to actual climatic conditions, one cannot expect an exact one-to-one temperature correlation. However, a comparison of the simulated and observed indoor temperatures corresponding to the external temperatures showed good correlations. The daily minimum, maximum and mean temperatures were nearly the same; however, a slight parallax existed in terms of an average 15-min delayed thermal response (or lag) in the simulated output and 0.2-1°C momentary

variation in temperate in the Central Living. The observed delay/lag can be attributed to the fact that the thicknesses of stone and earthen walls are actually not uniform (as in the simulation model) but vary by 20 to 50mm depending on the size of stone used. Also, the stone masonry adopting mud mortar comprises numerous crevices wherein the mud mortar has either fallen/ washed off. This detailing has been difficult to incorporate in the simulation model.

Fig. 2 Block-model view of the dwelling.

Operational energy in the dwelling for three different wall materials; rubble stone masonry, burnt clay brick masonry and stabilized soil blocks, for three different thermal comfort models in two different climate zones have been assessed using the building simulation model. Operational energy of the dwellings includes energy for thermal comfort and lighting. Lighting energy is directly obtained as a result of the building simulation. Thermal comfort energy in the dwellings is assessed for three different wall materials and for two different thermal comfort models.

Energy assessment for space conditioning require proper choice of thermal comfort models and data with regard to the strategies adopted to overcome any discomfort conditions inside the building. OE is assessed using two different thermal comfort models, ASHRAE 55 [13] combined with strategies from Givoni (1996) [14] and TSI model by Sharma and Ali (1986) [15]. ASHRAE standards are commonly adopted internationally for thermal comfort studies. Design Builder simulation tool uses ASHRAE standards for estimation of discomfort hours. According to ASHRAE standards,

Range of comfortable indoor temperature - 20°C to 23.33°C (68F to 74F) (winter)

22.22°C to 26.66°C (72F to 80F) (summer) Range of comfortable indoor relative humidity - 30% to 60%

TSI has been developed for warm-humid and hot-dry conditions in India. According to TSI,

• T< 19-Cold

• 19 - 25 - Comfortably cold

• 25 - 30 - Comfortable

• 30 - 34 - Comfortably warm

• T > 34 - Hot

For thermal comfort energy assessment, number of discomfort hours within each room, based on both the models, is calculated using output data from the simulation on hourly temperature and relative humidity for different rooms (zones). The strategies to fight discomfort depend on the thermal sensation at different temperature levels. Along with ASHRAE thermal comfort model, strategies to combat discomfort due to high, low temperature and relative humidity are adopted from the bio-climatic charts in Givoni B. (1996). Givoni B provides strategies for developing countries. According to Givoni B., acceptable range of temperature for still air is between 18°C and 27°C in winter and between 20°C and 29°C in summer. Hence, no strategy is considered for temperature range

between 18°C and 29°C. For temperature beyond this comfort range, occupants would resort to some measures to restore the comfort conditions.

• For T < 18°C - Use of room heaters

• For 29°C< T < 32°C - Use of ceiling fans

• For T > 32°C - Use of room coolers

• For 20°C< T < 26.66°C but RH < 30% and RH > 60% (comfortable temperature but uncomfortable relative humidity) - Use of ceiling fans

• For 29°C < T < 32°C and for 20°C < T < 26.66°C but RH < 30% and RH > 60% in Kitchen area - Use of exhaust fans

For TSI model, following strategies are adopted.

• For T < 19°C - Use of room heaters

• For T > 34°C - Use of room coolers

• For 19°C< T < 34°C but RH < 30% and RH > 60% (comfortable temperature but uncomfortable relative humidity) - Use of ceiling fans

• For 19°C < T < 34°C and for 20°C < T < 26.66°C but RH < 30% and RH > 60% in Kitchen area - Use of exhaust fans

Assessment of thermal comfort energy involved estimation of number of discomfort hours in the different cases. The thermal comfort energy is estimated as the product of number of discomfort hours, power rating of the appliances and an average power factor of 0.9. Total operational energy (sum of thermal comfort energy and lighting energy) of the dwelling for different scenarios is then expressed in terms of GJ/m2/year. Table 3 summarizes the seasonal OE estimates for the traditional dwelling based on the ASHRAE model, for various wall configurations and climatic zones. Energy for indoor lighting was estimated at 1706.31 kWh/year for all the cases. Figure 3 provides a comparison of annual air-conditioning energy for the above configurations.

Table 3 Operational energy for traditional dwelling in different climate zones

AC energy (kWh/year) Total energy

Location (Climate zone) Type of masonry Summer Winter Rest of the year (AC+ Lighting) (kWh/year) MJ/year GJ/m2/ year

Rubble stone 3018.05 88.67 411.74 5224.77 18809.16 0.05

Ahmedabad (Hot-Dry) Burnt clay brick 1415.75 224.28 400.82 3747.16 13489.79 0.03

Stabilized Mud Block 2944.90 413.72 592.10 5657.02 20365.28 0.05

Rubble stone 304.11 555.66 581.98 3148.06 11333.00 0.03

Sugganahalli (Warm-Humid) Burnt clay brick 358.94 586.04 613.12 3264.41 11751.88 0.03

Stabilized Mud Block 336.78 544.77 573.40 3161.27 11380.56 0.03

Rubble stone 276.09 386.10 637.74 3006.24 10822.46 0.03

Bangalore (Moderate) Burnt clay brick 328.46 345.51 643.56 3023.84 10885.82 0.03

Stabilized Mud Block 310.95 311.84 623.61 2952.71 10629.74 0.03

Fig. 3 Comparison of annual air-conditioning energy for the traditional dwelling with varying wall configurations and climatic zones, with

ASHRAE 55 as the reference model

From the results it is evident that for the traditional dwelling in warm-humid and moderate climatic zones there is negligible variation (less than 1 kWh/m2 per year) in OE for varying wall configurations. Similarly, the OE for these dwelling in different climate zones, but with identical wall configuration, reveals negligible variation (less than 1 kWh/m2 per year). However, for the hot-dry climatic condition, the variation in OE for the three wall configurations is relatively significant (nearly 4 kWh/m2 per year). Similarly, for identical wall configuration there is significantly higher OE for the traditional dwelling in hot-dry zone when compared with warm-humid and moderate climate zones (2~6 kWh/m2 per year) respectively. These observations are concurrent with indoor temperature variations. Based on thermal comfort strategies recommended by Givoni (1996), indoor temperature ranges between 29~32°C generally require the use of ceiling fans (with a power consumption of 55 W). Indoor temperatures above 32°C and below 18°C generally warrant the use of room heaters or coolers (with much higher power consumption 1000 W). Based on the simulation results, dwellings in warm-humid and moderate climate zones, for the wall configurations tested, the indoor temperature ranges from 20.44~32.83°C and 19.42~31.32°C in summer and winter respectively. This does not compel the use of heaters or coolers. For the warm-humid zone, there is a rise of 0.8°C in indoor temperature beyond 32°C which can be alleviated with the use of ceiling fans. However, in the hot-dry climatic zone, for the indoor temperature range from 16.93~35.75°C, there is a 1.07°C below 18°C and a 3.75°C rise above 32°C. Both these conditions would compel the use/dependence on room coolers or heaters respectively.

Fig. 4 shows the comparison of operational energy assessed for different scenarios adopting ASHRAE and TSI comfort models. From the simulation results, annual operational energy in the dwellings range between 8 to 13 kWh/m2 for ASHRAE comfort model and it range between 7 to 9 kWh/m2 for TSI comfort model. Adopting TSI, use of coolers is considered for temperature above 34°C instead of 32°C and use of heaters for temperature less than 19°C instead of 18°C as in for OE assessment using ASHRAE standards. This has resulted in 6 to 93% change in operational energy when compared to OE assessed using ASHRAE. The results show that for the present traditional dwelling ASHRAE standards underestimate the operational energy consumption for the dwellings in warm - humid zone and overestimate operational energy consumption for dwellings in hot - dry zone.

Fig. 4 Operational energy in the traditional dwelling for different scenarios

Further, the present study estimated Life Cycle Energy as the sum of EE and OE (based on ASHRAE model) over a building's life (50 years), excluding demolition and disposal energy. The LCE ranged from 1.67~3.48 GJ/m2 for the various scenarios considered. Rubble stone masonry and stabilized soil block masonry based traditional dwelling revealed much lower LCE when compared with burnt clay brick, despite their OE component being comparatively higher. The EE component of burnt bricks seems to outweigh the reduction in OE.

3. Conclusions

Studies have observed transitions in vernacular dwellings with regard to materials used for walls and roof. It is highlighted that such transitions have adverse impact on embodied and operational energy consumption in dwellings. The present study examined impact of change in wall material of a traditional dwelling on its embodied and operational energy. The study also addressed proper choice of thermal comfort models by estimating operational energy in dwellings using two different thermal comfort models; ASHRAE and TSI thermal comfort models. The result shows that replacing rubble stone masonry with burnt clay brick masonry and stabilized soil block masonry would increase the EE of the dwelling by 9.7 times (870%) and 2.8 times (182%) respectively. Operational energy assessment using two different thermal comfort models; ASHRAE 55 and TSI comfort model, showed that for the present traditional dwelling ASHRAE standards underestimate the operational energy consumption for the dwellings in warm - humid zone and overestimate operational energy consumption for dwellings in hot - dry zone.

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