SOLAR PASSIVE ARCHITECTURE FOR THERMAL COMFORT OF RESIDENTIAL BUILDINGS IN WARM-HUMID CLIMATE OF THANJAVUR REGION
Solar passive architecture concepts and principles are used in traditional buildings worldwide. Extensive research works have been done on the analysis of thermal performance of such traditional buildings and found they are well within the comfort range as prescribed by thermal comfort standards for naturally ventilated buildings. A novel attempt has been made in design of a residential building at Thanjavur, Tamilnadu, and South India with solar passive architecture concepts in warm humid climate condition. Thermal performance analysis was carried out with reference to solar passive architecture principles and in comparison with another contemporary house nearby in that region. In the solar passive case study building, ten solar passive architecture strategies are incorporated. The study on solar passive house indicates that solar passive techniques can bring indoor temperatures down enough for occupants of a building. The observations and analysis made suggests that we can achieve thermal comfort by designing buildings with solar passive architecture. Indoor air temperatures are comparatively much lower than the outdoor air temperatures in summer. Compared to other modern residential building, the solar passive building is more than 2 ºC to 3 ºC cooler in summer as in the traditional buildings. Thus design of the energy efficient building plays a major role to save energy which in turn will give an impact on national and global economy.
Keywords: Solar Passive Architecture building –planning and design- thermal performance analysis- modern constructions analysis- temperature and humidity- thermal comfort – warm humid climate- naturally ventilated buildings
Accelerated urbanization and rapid change in the living standard has imposed immense pressure on the dwindling energy sources, thus aggravating the already rampant process of environmental degradation because of excessive consumption of energy and other natural resources [1, 6]. The operations of buildings worldwide contribute up to 40 percent of total global energy consumption [2, 3, 4, 5].
The basic need of all buildings is to adapt regional climatic conditions that will provide conducive and comfortable environment to the dwellers.
Now building designers face challenges to provide buildings constructed with modern building materials that will be comfortable and suitable for the 21st century .
The traditional buildings are considered as prime examples for their environmental design in response to the regional climatic conditions and making it more energy efficient.
From several researches it is found that traditional houses perform better thermal environment than contemporary structures [8, 9, 10, 11, 12]. The indoor environmental conditions and thermal comfort in modern houses are unsatisfactory due to improper design [13, 14]. Minimum of 10 to 20 percent energy can be saved in the native architecture compared with contemporary structures to keep the indoor comfortable. Minimum 1 to 2 degree C cooler can also be achieved in summer with such traditional houses. In the contemporary buildings, the energy used for maintaining thermal comfort is expected to mount up over the coming days, which will move the situations worse due to an intermittent and unreliable status access to electricity supply in India [5, 12].
From various studies, it is also found the Engineers and Architects have greater flexibility in building design to make it more energy efficient by introducing solar passive architecture features. Indoor environment comfort level can be improved by doing certain modifications in the existing houses too. Climate oriented building design enhances thermal comfort conditions inside the house and also reduces both the embodied and operational energy consumption [15, 16].
As an adverse impact, Energy efficiency of the traditional buildings are affected by gradual change of locally available materials to modern new building materials while preserving such structures. It also renders buildings out of context with the climate and shifts the indoor conditions out of the comfort zone .
In the era of globalization, it is necessary to validate the importance and applicability of these ideas in the contemporary buildings to design buildings appropriate to the context and response to the regional climatic conditions to achieve the comfort. Solar passive architecture is the major tool to create building more energy efficient and achieve thermal comfort through climate responsive design principles.
On the implementation of such energy efficiency measures in new buildings, energy consumption can be reduced on an average of 20% to 50% . Operational energy in the building can be substantially reduced in the building by the use of solar passive strategies and to make it energy efficient.
An attempt has been made to design a residential building in the warm humid climate of Thanjavur, Tamilnadu, South India with solar passive architecture concepts and study the following objectives:
1. To evaluate thermal performance of the designed solar passive architecture building.
2. To validate and highlight the solar passive principles adopted towards thermal comfort.
3. To compare the thermal performance of designed house with another contemporary house nearby in that region.
The objective of the study is also to prove that by incorporating solar passive architecture principles in the modern style housing appropriate to the context, the required thermal comfort can be achieved as in traditional structures. The study and results will be an eye opener for Architects and Engineers to adopt solar passive architecture in modern constructions and also to incorporate in existing buildings to improve comfort and energy efficiency.
METHODOLOGY & INSTRUMENTATION
Thanjavur is a small city located in the southern part of India at 10º47’N latitude and 79º8’E longitude and has an elevation of 88m above MSL. Thanjavur is classified under warm humid climate region in the climate zone of India. North-east monsoon between October and December contributes 54% main monsoon out of mean annual rainfall of 945mm. Hot months of the region are April, May and June with maximum mean temperatures ranging from 35 ºC to 36ºC and cool months are November, December and January with minimum mean temperature ranging from 23 ºC to 24 ºC. At times maximum temperature goes up to 40 ºC in summer.
The study is aimed to evaluate the architectural design features and building forms used in the solar passive designed house and other present day house with respect to their thermal performance during summer months, in terms of providing indoor thermal comfort conditions for their occupants. A comparative study of thermal performance of the building during winter months will be presented in the future research work.
The thermal performance of solar passive residential building of Thanjavur, Tamilnadu which is experimented to improve thermal comfort has been tested. The experimental results examined the effectiveness of such solar passive designed building (SPDB) in comparison with another present day contemporary building. The parameters used for the analysis are the indoor air temperature and humidity of the living rooms. The readings were taken during hot summer on various days of June 2015.
Measuring instruments and devices include (i) A digital anemometer MASTECH MS6252B used to measure relative humidity, ambient temperature and wind velocity (ii) A solar power meter TES 1333 used to measure the solar radiations of the location (iii) Data logger for measuring air temperature and relative humidity continuously. HTC easy log Temperature and humidity data logger (iv) INFRARED DT 8380 thermometer.
Thermal comfort conditions and strategies
Thermal comfort analysis was conducted for the living cum dining room in particular, as most of the time the occupants spent in this zone. Comfort always does not occur at fixed temperature. ASHRAE standard 55-2004 states “thermal comfort as the condition of mind that expresses satisfaction with the thermal environment”. Internationally ASHRAE standards are commonly adopted for various thermal comfort studies. The comfortable indoor temperature for summer ranges from 22.22 ºC to 26.66 ºC. The comfortable indoor relative humidity ranges from 30% to 60%. Givoni B provided strategies for developing countries using bio-climatic charts and stated acceptable range of temperature in summer is between 20 ºC to 29 ºC for still air [17, 19, 20, 21].
Tropical summer Index (TSI) has been developed for hot-dry climate and warm humid climate in India. The thermal comfort conditions given in National Building Code of India are based on the study of the Tropical Summer Index (TSI). According to NBC 2005, the thermal comfort limit of a person ranges from 25 ºC to 30 ºC. The comfortable indoor relative humidity ranges from 30% to 70%. According to TSI, temperature above 30 ºC and up to 34 ºC is classified as comfortably warm which can be managed with sensible air movement of 1.5 m/s [22, 23].
Details of the houses selected for the present study
In the present study a house designed and constructed with solar passive design strategies and a house with regular market driven contemporary strategies are selected and the thermal comfort in the designed building is compared with the other. The houses selected for the study are in same locations in Thanjavur city, Tamilnadu, India.
Fig: 3 View of the modern building
The orientations of both the buildings are similar along North-South direction with east wall exposed to sun adjacent to living room undertaken for study. Both are individual houses with a plinth of around 1200 sq. ft. in Ground floor. Living cum dining room was considered for the study in both the houses as it is similar and occupants use it most of the time. Both the houses have similar wall type construction and plastering with 23 cm thick external walls & 11.5 cm thick internal walls in burnt bricks and conventional 12 cm- 15 cm thick reinforced cement concrete roof slab.
Fig: 4 Plan of the modern building
RESULTS AND DISCUSSION
Solar passive design strategies:
In the solar passive case study building ten solar passive architecture strategies are incorporated. This can enhance the comfort of the occupants in the designed solar passive building. The strategies are:
1. Orientation and Planning
North – South orientation is adopted with minimum exposure to habitable rooms. The aspect ratio of the house is 1 : 1.6 (55′ x 33′) which is in ‘golden proportion’. This is designed by linear arrangement of two rows of rooms, front row being shaded by portico. Shaded area avoids heat radiations and allows cool air to flow in.
Fig: 2 Plan of the SPDB
2. Courtyard and Planning
Compactness in planning allows light but not heat radiations through the buffer courtyard with dry garden adjacent to living cum dining room. Compactness in overall planning also avoids unwanted exposure of habitable rooms to solar radiations. The buffer courtyard creates good air flow by density difference creating a draft pulling air either upwards or downwards.
3. Light coloured painting
White or lighter shades have higher emissivity which is an ideal situation for warm humid climate . The designed building is completely painted in white colour to improve thermal performance by reducing heat gain through less absorption and maximum reflection through light coloured walls.
Fig: 1 View of the SPDB
4. White roofing tiles
In residential buildings, heat transmission across the building roof is about 50 – 70% of the total rooms below the exposed roof. Covering roof top with white tiles with highly reflective coatings having more solar reflectance is found to reduce 20 – 70 percent heat transmission through the roof [25 – 27]. Solar reflectance is increased by increased by white roofing tiles on the roof, which has high solar reflective index . This significantly reduce inside building temperature and provides better indoor thermal comfort.
5. Shading elements
All the fenestrations have shading elements to block solar radiation incident on the exposed surfaces of a building, consequently reducing heat gain. such shading elements can significantly improve the performance the building . Apart from shading elements for fenestrations the sunshade is projected four feet on southern direction casting complete shadow on the walls facing south. Such overhang projection is made on northern direction which allows cool air and cuts heat radiation. Toilet spaces are very well located in plan along the western direction which provides a buffer and also casts mutual shading along the west side. The long wave radiations on the western side are cut to the maximum by locating such buffer rooms.
6. Solar chimney and Sky light
Passive cooling by induced ventilation can be most effective in warm and humid climate. This method involves heating of air in a restricted area through solar radiation, thus creating a temperature difference and causing air movements. The draft causes hot air to rise and escape to the ambient, drawing in cooler air and thereby increasing cooling effect. A solar chimney is created to give continuous air circulation . A combination of central courtyard with a solar chimney of size 3′ x 6′ is provided with a transparent roofing sheet. This acts as a light well or sky light as well as an air shaft, bringing both day light and air circulation in the living space and rooms around. Like the courtyard principle, warm air rises up creating an upward draft and is exhausted through the openings at the top. The pressure difference thus created pulls the air from the living space and the rooms around, creating continuous air flow to keep the indoor temperature down. Adequate day lighting is provided throughout the day in all the areas of the designed house resulting in zero energy consumption for artificial lighting.
Fig. 7 Solar chimney cum wind shaft
7. Planning and cross ventilation
Cross ventilation is prime importance in warm and humid tropical climates with protection of roof to avoid heat gain. As per the solar passive concept of architectural design, the alignment of openings, window placement in all the rooms, front and back door along the central axis, courtyard at the centre part and a buffer courtyard promotes good airflow. Optimum number of openings on exterior wall, inward looking plan and open plan without much internal wall provides good privacy, comfortable indoor temperature and required lighting everywhere inside the house.
8. Landscaping around the building
Planting of trees at strategic locations and shadow casted will improve the indoor thermal comfort of buildings . Evergreen trees are used on the southern direction to shade the building and avoid heat radiations falling on the wall.
Fig. 8 Buffer courtyard with dry garden
9. Roof level ventilators
Outlets at higher levels and roof level ventilators will serve to vent hot air [29, 30]. The form of the roof is designed in such a way that vents at the roof top effectively induce air flow and also draw hot air-out. The solar chimney design of living room also adds to the upward draft to vent hot air out.
10. High ceiling roof
The thermal inertia of indoor environment is directly proportional to the volume of that environment according to thermodynamics and heat transfer principles. for tropical countries with hot weather locations during most of the period, if ceiling heights are increased it causes a small decrease in indoor temperature of environment . the ceiling height of the living room is increased incorporating roof level ventilators and solar chimney on other side of the room. This contributes to the reduction in the indoor air temperature at human occupancy level as heated air rises up towards vent above.
The impact of incorporating solar passive architecture design in turn can help in reducing the electricity consumption which is the need of the hour. The effects of the ambient temperature in comparison with the indoor temperature of both the buildings are studied.
Findings during the field study:
The field measurements were taken during the summer during June 2015, for a week’s time, in the predominant summer season of Thanjavur. From the readings it was observed that the ambient outdoor temperature has a temperature swing of 15.80C, i.e. from 22.40C to 38.20C, while the indoor room temperature of the solar passive designed building was varying from 25.60C to 30.20C showing a diurnal saving of about 4.60C (Fig ).
Fig: 5 graph showing temperature variations
The relative humidity of indoors varies from 45.8% to 70.1% (Fig ). It is observed that the indoor temperature falls within the comfort zone when the values are compared with ASHRAE standards.
Fig: 5 graph showing relative humidity
In the other modern building selected for study, the indoor room temperature was varying from 290C – 34.50C showing the diurnal variation of 5.50C (Fig. ). The maximum air temperature measured for the living room was about 34.50C when compared with ASHRAE standards it was found that the indoor temperature does not fall in the comfort zone
From the (Fig. ) comparison of Air temperature in SPDB and another modern building it can be observed the maximum temperature recorded in the living room of SPDB is 30.2 and in the modern building is 34.5. It is found that the maximum temperature in modern building is increased by 4.30C. The minimum temperature is lower by 3.40C in the SPDB.
This is attributed due to the Solar passive design features such as orientation and planning, courtyard and planning, light coloured painting, white roofing tiles, shading elements, solar chimney and sky light, planning and cross ventilation, landscaping around the building, roof level ventilators, high ceiling roof, etc.,. But the other modern building has similar construction materials without consideration of solar passive cooling features. The reason for the thermal discomfort in the other modern buildings of Thanjavur is due to the increase in temperature and humidity. From (Fig. ) it can be observed that the indoor air temperature in the SPDB is maintained in the range of 25.00C – 300C during summer with RH 45% – 70% which falls in the range within the comfort zone as prescribed by ASHRAE standards. In modern building (Fig. ) the indoor temperature is in the range of 290C – 34.50C. During this time the outdoor temperature is varying between 230C – 380C with RH of 35% and 90% which does not fall within the comfort zone as per ASHRAE standards. Hence it can be concluded that if no fan or Air conditioning systems are used, the SPDB is more comfortable for longer period than modern buildings designed without consideration of solar passive architecture.
The studies on solar passive designed house indicate that solar passive techniques can bring indoor temperatures down enough for thermal comfort of occupants of a residential building in Thanjavur region. The observations and analysis made suggests that with solar passive architecture, we can achieve comfort. The above findings should be presented to all the designers that would be useful and appropriate for architects to design climate sensitive residential buildings that will provide comfort for the future days to come.
The field study focused on the measurement of thermal performance with monitoring thermal environment for summer. This paper has presented the data from thermal measurement in the field regarding the indoor and outdoor thermal environment of solar passive building in Thanjavur. The research findings has identified that solar passive building has its own merit in maintaining thermal comfort. Compared to modern residential building, the solar passive building has better thermal performance during the study period.
1. It is evident from the field study that solar passive designed building maintains a comfort temperature (250C to 300C) during summer season which lies well within the comfort temperature of the region as per ASHRAE & TSI.
2. Indoor air temperatures are comparatively much lower than the outdoor air temperatures in hot summer.
3. Compared to other modern residential building, the solar passive building is 20C to 30C cooler in summer as observed in the traditional buildings.
4. Thermal comfort is a basic requirement of any building which is achieved through solar passive design strategies. Hence the design of such energy efficient buildings plays a major role to save energy which in turn gives an impact on national economy.
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