Energy and Buildings 42 (2010) 917–927

Passive environment control system of Kerala vernacular residential architecturefor a comfortable indoor environment: A qualitative and quantitative analyses

A.S. Dili a,*, M.A. Naseer b, T. Zacharia Varghese a

a Department of Civil Engineering, National Institute of Technology Calicut, Kerala, Indiab Department of Architecture, National Institute of Technology Calicut, Kerala, India

A R T I C L E I N F O

Article history:

Received 18 March 2009

Received in revised form 4 January 2010

Accepted 4 January 2010

Keywords:

Kerala

Passive environment control system

Vernacular architecture

Thermal comfort

A B S T R A C T

The modern day practice does not give due respect to passive and natural environment control measures

in buildings. With modern materials and technology, the buildings of present architectural style results

in high energy consumption, in an attempt to provide thermal comfort indoors. The vernacular

architecture at any place on the other hand has evolved through ages by consistent and continuous effort

for more efficient and perfect solutions. The authors have conducted a qualitative analysis of the passive

environment control system of vernacular residential architecture of Kerala that is known for ages for its

use of natural and passive methods for a comfortable indoor environment. The orientation of building,

internal arrangement of spaces, the presence of internal courtyard, use of locally available materials and

special methods of construction, etc. have together created the indoor environment. A quantitative

analysis was also carried out based on field experiments by recording thermal comfort parameters in a

selected building. The study has provided positive results confirming that the passive environment

control system employed in Kerala vernacular architecture is highly effective in providing thermal

comfort indoors in all seasons.

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1. Introduction

Review of vernacular architecture in its ecological concernssuggests that human beings should adapt all their design activitiesto the natural order of the global system. In the light of this,environmental architecture can be the most appropriate disciplineto perform the role of stabilizing the ecological system. The term,environmental architecture, means the architecture adjusted to itssurroundings or in harmony with nature creating a healthyenvironment for human beings by maximizing the utilization ofnatural energies [1]. Environmental architecture is the one thatwould provide a comfortable indoor environment in response tothe seasonal variations of the climate. Irrespective of the extremeclimatic conditions that prevail outside, the building indoorsshould keep its occupants physiologically comfortable.

The strength of vernacular architecture is that it makesbuildings that are in natural harmony with climate, built formand people. Vernacular architecture has evolved through ageswhere among other factors, the climate has also played a veryimportant role [2–9]. However, the modern practice in architecturelacks conscious effort in using passive methods of controlling theindoor environment [10,11]. Excessive use of modern materials

* Corresponding author. Tel.: +91 9447303875; fax: +91 4952287250.

E-mail addresses: dili@nitc.ac.in, dili_as@yahoo.com (A.S. Dili).

0378-7788/$ – see front matter � 2010 Elsevier B.V. All rights reserved.

doi:10.1016/j.enbuild.2010.01.002

irrespective of their efficiency in regulating the indoor environ-ment has often resulted in high energy consumption, leading tomany environmental problems [12]. Also, energy intensivesolutions are required in such buildings to attain comfortconditions in terms of cooling and ventilation. Fortunately thereare conscious efforts now to design building that require lowenergy by utilizing the passive techniques to achieve comfortablecooler indoors.

Kerala has a characteristic warm–humid climate because of itsgeographic settings. The presence of high amount of moisture inthe atmosphere for major part of the year causes thermaldiscomfort as there is less evaporation, resulting in sweating.Prolonged exposure to such thermal discomfort conditions cancreate adverse effects including extensive loss of efficiency in workalong with physical strain [13,14].

The vernacular architecture of a region derived out of variousfactors, such as social, culture, etc. gives more importance to local-specific factors such as climate and topography. The principles ofvernacular architecture of Kerala are based on empirical observa-tions and experimental wisdoms acquired through generations[15]. The use of natural and passive methods in the vernacularKerala architecture is attributed to be highly effective in providingthermal comfort in all distinct seasons.

Although there have been attempts to analyze the vernaculararchitecture of Kerala, they were focused only on one or twoparameters and were qualitative in approach [7,13]. It is not

Fig. 1. Climatic zones of India [17].

A.S. Dili et al. / Energy and Buildings 42 (2010) 917–927918

possible to establish the effectiveness of any passive environmentcontrol system without a comprehensive analysis supported byfield measurements of all the comfort parameters conducted in allseasons. A quantitative study was thus initiated by the authors bycontinuously monitoring comfort parameters over a period oftime. The results of the investigation carried out during summerand winter seasons have already been reported [16].

This paper illustrates the vernacular architecture of Kerala, adetailed qualitative analysis of typical vernacular residentialbuildings and a quantitative analysis based on field experimentswith emphasis on indoor thermal comfort.

2. Kerala: topography and climate

2.1. Topography

India is a tropical country with diverse climatic conditionsresulting in diverse shelter forms. According to Bureau of IndianStandards [17], the country has been divided into five differentregions with distinct climates (Fig. 1).

Extending from 88180 to 12848’N latitude and 748520 to 72822’Elongitude, Kerala is on the South-West coast of India lying betweenthe Arabian Sea on the West and the Western Ghats on the East(Fig. 2) in the belt of monsoon zone, which occurs in large landmasses that are sufficiently far from the equator to experiencemarked seasonal changes in solar radiation and wind direction.Even though Kerala comes under warm–humid climatic zone,microlevel variations are observed due to its geographicalpeculiarities. Based on the altitude, Kerala has three distinctzones—high land (800–2700 m), mid land (300–700 m) and lowland (sea level to 150 m), as given in Fig. 2.

2.2. Climate

The warm–humid climate of Kerala is characterized by heavyrainfall and high relative humidity, and relatively moderatetemperature. In effect, Kerala has only two predominant sea-sons—rainy and non-rainy seasons. The rainy season lasts for abouthalf of the year where heavy rainfall occurs due to South-Westmonsoon (locally known as Edavapathi) from June to August and

Fig. 2. Map of Kerala—the identified region is shown.

Fig. 3. A typical layout of a vernacular Kerala house.

A.S. Dili et al. / Energy and Buildings 42 (2010) 917–927 919

North-East monsoon (locally known as Thulavarsham) fromOctober to November. Winter and summer comes under thenon-rainy season. The summer season (February–May) is with hotand humid days and nights and intense solar radiation during theday. The moisture in the atmosphere causes acute discomfortduring this period. The winter period (December–January) withwarm and relatively less humid days and cold nights is morecomfortable than summer. In the non-rainy days during the rainyseason also the atmospheric temperature is high with very highrelative humidity. The monthly normal climate of Kerala is given inTable 1 [18]. Temperature vary from 21 8C to 33 8C and relativehumidity (RH) varies from 65% and will be above 70% in most of theseasons.

3. Kerala vernacular architecture

Kerala vernacular architecture is ancient and elegant. Thebuildings are built according to the principles of Vaastushastra, theIndian discipline on architecture. Vaastushastra is believed to have

Table 1Monthly normal climate of Kerala [18].

Months January February March April May

Temperature (8C) Max 32 32 33 33 32

Min 21 22 24 25 25

Rainfall (mm) 14 15 31 108 247

No. of rainy days 1 1 2 6 11

Relative humidity (%) 65 70 75 80 77

evolved as a philosophy during the Vedic time, the basic concept ofwhich is to treat the site and building as complementary to eachother. Vaastushastra has developed into distinct regional styles indifferent parts of India. Although these regional styles underwentchanges during the last 500 years, it remained relatively pure inKerala [15].

3.1. The basic form

The basic module of vernacular residential building of Kerala isknown as nalukettu with four blocks built around an opencourtyard. They are generally rectangular or square in plan withblocks topped with a sloping roof on all four sides while thecourtyard is left open to the sky for letting air and light inside.There is an internal verandah around the courtyard for protectionfrom rain and sun. A typical layout of a vernacular Kerala house isshown in Fig. 3.

The courtyard and the blocks around it are laid out strictlyfollowing the rules of dimensions, scale and proportions.Depending on the size and importance of the household, thebuildings may have one or two upper storeys or further moduleswith enclosed courtyards. In the case of repeated modules, thenalukettu becomes ettukettu (eight blocks building) or a group ofsuch courtyards. The enclosed courtyard is usually sunken. Theverandahs opening to the courtyards prevent the intense solarradiation entering the rooms.

The roofs have steep slopes up to almost 458 and the gables(mughappu) are provided at the ends of roof to enhance ventilationand to allow the warm air to escape. Further, decorative jalli

June July August September October November December

29 28 28 29 30 31 32

24 23 23 23 23 23 21

556 502 304 208 277 172 49

21 20 16 11 12 8 3

85 90 90 86 83 80 65

A.S. Dili et al. / Energy and Buildings 42 (2010) 917–927920

(ventilators) are provided for the ventilation of attic spaces that areformed by the wooden false ceiling (tattu) provided for the roomspaces. This roof encloses a large insulated air space keeping thelower areas cooler. Walls in the upper floors comprises of ranks ofstruts connected by spaced slats thus becoming a part offenestration design for good air flow, thus keeping the roomscool and gently lit.

3.2. Materials of construction

The common building materials used for vernacular construc-tion in Kerala are mud, laterite and granite stone blocks, limemortar, wood, bamboo, clay roofing tile and coconut palm leaves.Though granite stone is a strong and durable building material, dueto its limited availability mostly to the highlands, the use of graniteis limited to the foundation of buildings.

Laterite, seen in shallow depth, is the most commonly usedbuilding material in Kerala, which can be easily cut, dressed andused as building blocks. It is strong and durable with exposure toatmospheric air. Laterite blocks are usually bonded in limemortar, the classic binding material in vernacular buildings. Limemortar, improved in its strength and performance, by addition ofvegetable juices is used for plastering the walls. The exterior ofthe laterite walls are either exposed or plastered with limemortar.

Wood is another building material used for construction inKerala. A wide variety of species, from bamboo (Bambusa Oldhamii)to teak (Tectona Grandis) are used. The skilful selection of wood,perfect joinery, artful assembly and subtle carving for columns,walls and roof frames are the unique characteristics of Keralaresidential architecture. Mud is also used in many forms intraditional buildings which include mud walling, bricks, clay tiles(both roofing and flooring), mud mortar for laterite masonry and asfiller for timber floors. Locally available mud is usually kneadedand treated with natural admixtures. Coconut leaves and palmleaves are also used for thatching the roofs and for makingprotection to walls at times.

3.3. Activity areas

A typical Kerala vernacular house consists of two major livingareas, inner spaces around the courtyard and the outer verandahsincluding the portico (poomukham). The house form offer flexibilityfor the inhabitants to shift their activities from one place to other indifferent climatic conditions. The important aspect of the Keralaarchitecture is the usage of courtyards. They are major activityspaces where bathing, cooking, sleeping and socializing takes placeat different periods of time. The front verandah is used for sitting inthe afternoon while the back verandah is used as a work area andalso as a chatting space for the women. The two side verandahs areused for either sleeping or as storage space. In dry season the innercourtyard is used for drying, cleaning and preparing cereals, food,etc. [19]. The courtyard also functions as a major functionalelement in the house with most of the internal movement confinedto this. The circulation of people is defined by the verandahsaround the courtyard, as the major rooms are entered from thisverandah.

4. Qualitative analysis

The traditional houses of Kerala are generally designed for thefollowing major problems caused by the characteristic warm–humid climate.

� E

xcess of moisture in the atmosphere. � H eavy rainfall.

� In

tense solar radiation and, � E ffect of high temperature.

Excess of moisture in the atmosphere make the indoors veryhumid preventing evaporation. The orientation of building to takeadvantage of the prevailing wind, the presence of internalcourtyard and the internal arrangement of spaces helps tomaintain the required air movement inside the building. Penetra-tion of water to the interiors through the roof due to heavy rain,prevalent in the climate, is prevented by pitched roofs coveredwith burnt clay roofing tiles, thatch, etc. Dampness is eliminatedup to a higher extent by building on elevated lands with highplinths. Large roof overhangs protecting the walls from the sun andshaded verandahs, prevents high intensity radiation. The use ofwalls with jalli while preventing the entry of direct sunlight, allowsnecessary air movement. Use of insulative materials like laterite forexternal walls, timber for ceiling and roof protects interior fromexcessive heat.

4.1. Orientation of building

Kerala vernacular buildings are oriented strictly according tothe cardinal directions as per vasthusasthra. This makes thebuilding more perfect to control its environment with maximumcomfort in different seasons. The cardinal directions are deter-mined correctly using traditional techniques based on solar pathand shadows [15]. The entry to the building is provided from Southor East. The spaces that are used during the day time are mostlyplaced on the North and South sides while those used during thenights are on the West.

4.2. Internal arrangement of spaces

The positioning of spaces is very much important in spatialplanning. The living spaces which are semi-open are on theSouthern side with optimum number of openings for ventilation.The kitchen is positioned at the North-East corner of the buildingas the wind is mostly from South-West direction. This avoids thespreading of hot air from kitchen to other spaces. All other spacesincluding bedrooms are arranged around the courtyard in such away as to permit adequate air movement in all seasons.

4.3. Internal courtyard

Internal courtyard and patio are quite common in warm humidclimate where the building encloses an open space fully or partly.Such spaces are commonly referred to as microclimate modifiers.They enjoy better microclimatic conditions than the surroundingopen areas, and are supposed to have a positive effect on the indoorcomfort conditions of the enclosing building volume. This is trueunder certain conditions, by allowing solar access to all parts of thebuilding, and by enabling better ventilation of internal spaces [20].

In the courtyard a pool of cool air is retained as this is heavierthan the surrounding warm air [21]. The courtyard is an excellentthermal regulator in many ways. The heat gain from the sun will bemore in the upper part of the courtyard. This makes the air in theupper part of courtyard warmer and lighter, causing the air tomove upwards. Thus a low pressure develops in the courtyard andit induces an air movement from outside, through the surroundingspaces (Fig. 4). After sunset also the phenomenon continues till theair in the courtyard cools fully by convective flow.

A smoke study was conducted to understand the characteristicsof air movement due to the effect of courtyard under still aircondition or when the external wind was absent. Smoke wasgenerated outside the building and was allowed to pass throughthe building. The flow through the building and courtyard was then

Fig. 4. Concept of air movement in nalukettu.

A.S. Dili et al. / Energy and Buildings 42 (2010) 917–927 921

observed. The smoke entered through the semi-open space andmoved upwards through the courtyard (Fig. 5). It was observedthat when the smoke was put off, it disappeared from the buildingwithin seconds. This clearly establishes that there exists aconvective flow through the building as explained above.

4.4. Openings and use of natural ventilation

Most of the houses are set amidst large parcels of land.Buildings are hence opened up for better air movement. Openplanning and free spaces between buildings help to capture windand achieve good ventilation.

Buildings usually have large number of openings in the form ofwindows and ventilators. Provision of open or semi-enclosedspaces also give ample scope for air movement. Anotherremarkable feature in the Kerala vernacular architecture is the

Fig. 5. Images of smoke study.

provision of open gables (mughappu) in the roof and the provisionof wooden jalli (azhi) in the external walls at appropriatepositions. The wooden jalli (azhi) in the external walls inappropriate positions helps to draw external air with the effectof courtyards.

4.5. Thermal protection

The thermal insulation in buildings is achieved by the effectiveuse of materials and the techniques used in the construction ofwalls and roof. The external walls of vernacular buildings areusually very thick up to a maximum of 750 mm with double layerof laterite masonry with a gap in between that is filled with finesand. This makes the external wall highly insulative.

In order to achieve thermal insulation, wooden ceiling (tattu) isalso provided beneath the roof. This provides a large air space atthe attic which acts as an insulation layer against the conduction ofexternal heat through the roof. This air space is well ventilatedwith openings (jalli) on both sides to permit maximum cross-ventilation. The breathing space between the clay tiles, that areused for roofing, further helps in ventilating the under side of theroof reducing the temperature.

Thermal insulation can have reverse effect, when for somereason the indoor temperature is even higher than outdoor and thebuildings insulation obstructs a quick heat loss [20]. In Keralavernacular architecture, the above problem is overcome with theconstant air exchange between outdoor and indoor with the help ofopenings provided on the external wall.

5. Quantitative analysis

5.1. Building selection criteria

In Kerala, a number of vernacular residential buildings havebeen demolished/modified, due to the change in the social setup,when joint families changed into nuclear families. However, a goodnumber of buildings still exists with their original use or as holidayhomes for tourist preserved in their original form and functionaluse. Residents as well as visitors prefer to stay in such buildingsbecause they are very comfortable to live in for the former while itis a real experience for the visitors.

Since the design of vernacular residential building is based on amodular concept with four blocks built around an open courtyardstrictly adhering to the ancient rules of geometrical grids,proportions and scale [15], the investigation is confined to atypical traditional building which is remaining in its original formwithout any alterations or modifications in a selected region ofKerala.

A region with more temperature fluctuation was identified bycomparing the climatic data of Kerala. The comparison of identifiedregion (Fig. 2) with normal temperature of Kerala is shown in Fig. 6.

5.2. Building description

The residential building selected for the study is located atNilambur in the Malappuram district of the Northern part ofKerala. The building (Puthiya Kovilakam) is nearly 300 years old.

The building has three courtyards of rectangular shape in whichone courtyard is surrounded by a double storeyed structure. Theother two courtyards are surrounded by single storeyed structures.The internal space taken for the investigation is around thecourtyard of 1.83 m � 3.66 m. The courtyard has an inward lookingverandah of 1 m width. The two sides of the courtyard are semi-open spaces used for living and prayer. The other two sides areadjoined with rooms having windows opening to the courtyard(Fig. 7).

Fig. 6. Comparison of temperature between the selected region and Kerala normal.

A.S. Dili et al. / Energy and Buildings 42 (2010) 917–927922

5.3. Experimentation setup

The authors have conceptualized an instrumentation setupcalled architectural evaluation system (AES) to continuouslyrecord the comfort parameters over a period of time. AES is acombination of electronic sensors to record temperature, relativehumidity and air movement, a data logger, a high speed datalogger, a memory module to record data from the various sensorsand computer interface to view and download data to thecomputer (Fig. 8). The air movement sensors are connected tothe high speed data logger to record the air movement in everysecond.

The instrumentation setup (AES) has been calibrated andcertified by India meteorological department (IMD) which is theauthority to certify instruments related to climatic measurementsin India.

Fig. 7. Plan and section of Nilambur Kovilakam—selected area for investigation is

marked in rectangle [16].

5.4. Field measurements

Temperature sensors were fixed at the outside verandah, thebottom and top of courtyard, the semi-open space around thecourtyard and a bedroom adjacent to the courtyard. Ambientoutdoor temperature was measured using a sensor enclosed inwooden Stevenson’s screen located outside the building. Relativehumidity sensors were fixed outside the building, in the courtyard,

Fig. 8. A schematic diagram of AES.

Fig. 9. Installation of AES in the selected locations of Nilambur Kovilakam.

A.S. Dili et al. / Energy and Buildings 42 (2010) 917–927 923

in the semi-open space and in the bedroom adjacent to thecourtyard (Fig. 9). An air movement sensor was located inside thebuilding to record the air movement in the semi-open spacearound the courtyard. Outdoor wind velocity was also recordedsimultaneously. Continuous data were collected for a period fromJune 2009 to October 2009. The data from various sensors weretaken at an interval of 15 min with the windows kept open forunobstructed air flow through the courtyard while the airmovement was recorded at every second using high speed datalogger.

Fig. 10. Temperat

6. Results and analysis

6.1. Results

It is observed that the outdoor temperature has a diurnalvariation of 12 8C i.e., from 22 8C to 34 8C. But the simultaneousindoor temperature was varying from 26 8C to 30 8C showing adiurnal variation of just about 4 8C only (Fig. 10). The lower partof the court yard is found to be cooler by about 5 8C from themaximum outdoor temperature while the upper part of the

ure vs. time.

Fig. 11. Temperature and RH vs. time.

A.S. Dili et al. / Energy and Buildings 42 (2010) 917–927924

courtyard with a temperature 1.5 8C lower than the maximumoutdoor temperature. The temperature of the verandah is varyingin synchronization with the upper part of the courtyard duringthe day time. The temperature of the bedroom is varying insynchronization with the upper part of the courtyard and thesemi-open space during night. The temperature recorded insidethe room is found to be lower by about 4 8C than that of semi-open space around the courtyard during day time. In the night, itis observed that the indoor air temperature is maintained at 26 8Ceven when the outdoor temperature is as low as 22 8C. It isobserved that there is no time lag between the indoor andoutdoor peak temperature and the decrement factor is 0.33.

Fig. 11 shows the variation in temperature and relativehumidity corresponding to the outdoor and bedroom. It is obviousfrom the figure that both temperature and RH have an inverserelationship. The outdoor RH is fluctuating more during day timeand it reaches its minimum i.e., 58% when the temperature ismaximum. The indoor RH is minimum around 77% when thetemperature reaches the maximum of 30 8C during day time. Whilethe outdoor RH reaches its maximum (97–100%) during the night,the indoor (bedroom) RH is fluctuating between 84% and 88% only.

Fig. 12. Relative hum

When the diurnal variation of outdoor RH is about 40%, that ofindoor RH is only about 10%.

The variation of RH at different locations (outdoor, courtyard,semi-open space and bedroom) is shown in Fig. 12. The RH of thebedroom is varying almost in synchronization with the semi-openspace throughout. RH of the courtyard is the most fluctuating oneamong the interiors, but during night, it has only a variation ofaround 3% with that of bedroom and semi-open space. During theday time, RH of the courtyard reaches its minimum i.e., around66%.

The air movement recorded at an interval of 5 min for acontinuous period of 3 days is shown in Fig. 13. While the outdoorwind velocity is highly fluctuating and reaches its maximumaround 3.5 m/s, the indoor air movement is maintained around0.5 m/s. Inorder to analyze the air movement over a longer periodof time, the recording interval was set to 5 min. Hence the graphshows a discontinuous plot of otherwise a continuous airmovement. The air movement recorded by high speed data logger(records in every second) is given in Fig. 14. This shows acontinuous plot of air flow and the same is useful for criticalanalysis.

idity vs. time.

Fig. 13. Wind velocity vs. time (recorded in 5 min).

A.S. Dili et al. / Energy and Buildings 42 (2010) 917–927 925

6.2. Analysis of results

The indoor temperature shows a very low diurnal variation(Fig. 10) due to high thermal insulation property of the buildingenvelope. Infact there is no conductive heat gain through thebuilding envelope. The absence of time lag between outdoor andindoor air temperatures proves the thermal insulation property ofthe materials and the high degree of natural ventilation main-tained through the building. That is, when outdoor is very hot,those heat scalars are only transmitted into indoor by wind, whichreduces the intensity of heat.

The outdoor air which is at a higher temperature looses the heatas it reaches the interior space of the building. This is due to thecontinuous heat exchange with the cooler surfaces and then thecooler air of the courtyard, as the air moves from outside to inside.The lower part of the courtyard is the coolest part inside thebuilding (Fig. 13). This is because the cooler air settles at thebottom as explained in the qualitative analysis.

Fig. 12 shows control over the RH within the building system.While the outdoor RH reaches its saturation point, the indoor RH ismaintained around 85%. This is achieved due to the presence of airvolume indoors, maintained at optimum temperature.

Fig. 14. Wind velocity vs. time (

Figs. 13 and 14 clearly show that the building system ismaintaining a continuous and controlled air flow indoors. Thisactually helps to accelerate the evaporative cooling by continuousexchange of air that is in contact with the occupant’s bodyespecially when the RH is higher along with high temperature.

7. Discussion

Thermal comfort of the interiors determines the energyconsumption by the environmental systems of a building andthey play a vital role in building sustainability. Thermal comforthas been defined as the condition of mind which expressessatisfaction with the environment related to air temperature,humidity and wind speed [22]. Hence the indoor environmentshould be designed and controlled in a passive manner so thatoccupants’ comfort and health can be assured with least amount ofexternal energy.

From Fig. 10, it is clear that the diurnal variation of indoor airtemperature is less compared to that of outdoor ambient airtemperature. This diurnal variation of indoor air temperature isless compared to that during winter and summer seasons and thedecrement factors are 0.22 and 0.28 respectively [16]. It is

recorded in every second).

Fig. 15. Bioclimatic chart (Koenigsberger et al. [21]).

A.S. Dili et al. / Energy and Buildings 42 (2010) 917–927926

observed that the decrement factor during the monsoon periodslightly increases i.e., 0.33, compared to the other two seasons.Comparing the diurnal variations and decrement factors oftemperature in all the three seasons, it can be observed that thebuilding system effectively controls the indoor temperature andmaintain its required level suitable to each season.

Natural ventilation has the potential to save energy use inbuildings. Hence it is recommended to improve the indoorenvironmental quality by natural ventilation to reduce energyconsumption [23]. From Figs. 13 and 14, it is clear that a controlledand continuous air flow is maintained inside the building and inmost of the time it is around 0.5 m/s. This has been re-affirmed bythe observations from the smoke study (Fig. 5). The smoke studyclearly shows that a gentle air movement is maintained inside thebuilding even when the outside air is still. This is achieved due tothe influence of internal courtyard as explained in the qualitativeanalysis. Also, experimental and numerical studies reported that acontrolled airflow in and around a building by utilizing cross-ventilation is helpful in order to improve indoor thermal comfort[24,25,26].

Fig. 11 shows that during the day time when the indoortemperature is high up to 30 8C, the relative humidity is as low as77%. This falls well within the comfort region of the bioclimaticchart constructed by Olgyay [21] since the wind velocitymaintained inside the building is around 0.5 m/s and it is verynear to the comfort zone (Fig. 15). During the night, sincetemperature is about 26 8C, the increase in humidity (up to 88%)does not really affect the indoor comfort condition.

8. Conclusion

The vernacular architecture gives solutions that are in perfectharmony with nature. Control of the indoor environment isalways an important aspect of vernacular architecture. Now, theresearchers in the field of energy efficient and sustainable designin various parts of the world are extracting the time testedpassive control techniques embedded in the vernacular archi-tecture. The vernacular architecture of Kerala has evolvedthrough ages by consistent and continuous effort for moreefficient and perfect solutions. Kerala with its rich heritage callsfor a comprehensive and quantitative research in the area ofpassive environmental control system of vernacular architec-ture.

The qualitative analysis reveals that, the presence of internalcourtyard within the living spaces and optimum window openingsprovided for a continuous air movement, highly insulative buildingenvelop for thermal protection, provision of verandahs forprotection of external walls from solar radiation and the pitchedroof for protection from heavy rain together contribute to a passive

environment control system in Kerala vernacular residentialarchitecture.

The findings from the quantitative analysis are very much inagreement with the inferences drawn from the qualitativeanalysis. So it can be concluded from investigation that thepassive environment control system of Kerala vernaculararchitecture is very effective in providing thermal comfort tothe occupants. A judicious use of appropriate materials andadoption of suitable traditional techniques in architecture isrequired for a sustainable, energy efficient and comfortablehuman life. Hence the methods and techniques adopted in theKerala vernacular residential architecture can be effectivelyused in the contemporary architecture for warm–humid regions.

Acknowledgement

The authors are grateful to Mr. Ravi Varma of NilamburKovilakam, Dr. Ziaudeen, principal and Mr. Nizar S.A., assistantprofessor of TKM College of Engineering, Kerala, Mr. Sreejith T.S. ofEMCON Cochin for providing necessary help for conducting thestudy and to the Meteorological Centre at Thiruvananthapuramfor providing the meteorological data required for the researchwork.

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