Background study
Southeastern coastal cities in India have hot humid climatic conditions with airborne salinity that are thermally uncomfortable to live in today without energy consuming heat and moisture regulation devices such as air conditioners and dehumidifiers. However, vernacular methods of the same region which was developed several centuries ago have successfully created indoor environments that prove otherwise. For my study, I chose the vernacular houses in Nagapattinam, Tamil Nadu to understand the techniques they use to passively attain thermal comfort conditions in the interiors of its spaces.
The climate of Nagapattinam is warm-humid with hot humid summers and warm or mild winters. The temperature during the summer (March to May) hovers between 28°C to 41°C whereas it is 21°C to 32°C during the winter (December to February). The monsoon period during June to September has moderate conditions with medium rainfall. The relative humidity (RH) conditions vary from 60% to 90% and will be 90% during most of the time of the year with wind velocity varying from 4m/s to 9m/s. Due to the presence of airborne salinity and high moisture in the atmosphere for most of the year, there is extreme sweating that are caused by less evaporation in the air. |
The research by Priya, R. Shanthi, M. C. Sundarraja, S. Radhakrishnan, and L. Vijayalakshmi shows the success in achieving indoor comfort heat levels in a 250-year-old vernacular house in Nagapattinam. The house has a rectilinear plan with a central courtyard that lets in light and air movement into the house surrounded by dwelling rooms with appropriate openings for cross ventilation. The house faces the coastline with the shorter sides aligned along the east west axis. The most important feature of these houses are their wind catchers, that are placed directly above the courtyard with its opening facing the windward direction. These wind catchers help to capture the wind and allow wind movement within the house during the day and night for a cooling effect. During the day, cool air moves in the dwelling through the wind catchers and during the night, hot air rises and moves out through the wind catcher to counteract the heat produced within the house.
Multiple experiments and research have been done to understand the success of these vernacular houses in creating a thermally comfortable environment. Most of them placed air temperature and relative humidity sensors in the interior and immediate exterior of selected vernacular houses for a prolonged period (three to four months) and documented the data. Sometimes the data was even compared and contrasted with data collected from a contemporary house in similar climatic conditions. Some experiments were also conducted in a virtually simulated environments with the aid of software to recreate particular conditions.
Multiple experiments and research have been done to understand the success of these vernacular houses in creating a thermally comfortable environment. Most of them placed air temperature and relative humidity sensors in the interior and immediate exterior of selected vernacular houses for a prolonged period (three to four months) and documented the data. Sometimes the data was even compared and contrasted with data collected from a contemporary house in similar climatic conditions. Some experiments were also conducted in a virtually simulated environments with the aid of software to recreate particular conditions.
In the research by Sharples, S., and R. J. S. E. Bensalem, models with different roof conditions that were constructed with perspex in 1:100 scale measuring 339×339×130mm were used to understand the wind movement in traditional wind catchers in the vernacular architecture of the Middle east and North Africa. Additionally, the models’ walls and roofs were perforated with 10mm dia holes to simulate the leakiness if the building.
The results of the on-site experiments proved in favor of the vernacular houses as they had lower heat fluctuation in the interiors when compared to the contemporary houses. As for the virtually simulated and scaled model experiments, certain limitations and difference in recorded values occur as these experiments could not successfully replicate the vernacular materiality of the original techniques in the study. However, they do achieve preliminary understanding of isolated aspects such as the heat value or wind velocity that were under experimentation.
Sources
Priya, R. Shanthi, M. C. Sundarraja, S. Radhakrishnan, and L. Vijayalakshmi. "Solar passive techniques in the vernacular buildings of coastal regions in Nagapattinam, TamilNadu-India–a qualitative and quantitative analysis." Energy and Buildings 49 (2012): 50-61.
Sharples, S., and R. J. S. E. Bensalem. "Airflow in courtyard and atrium buildings in the urban environment: A wind tunnel study." Solar Energy 70, no. 3 (2001): 237-244.
Rajapaksha, Indrika, H. Nagai, and M. Okumiya. "A ventilated courtyard as a passive cooling strategy in the warm humid tropics." Renewable energy 28, no. 11 (2003): 1755-1778.
Ghaffarianhoseini, Amirhosein, Umberto Berardi, and Ali Ghaffarianhoseini. "Thermal performance characteristics of unshaded courtyards in hot and humid climates." Building and Environment 87 (2015): 154-168.
Bensalem, Rafik. "Wind driven natural ventilation in courtyard and atrium-type buildings." PhD diss., University of Sheffield, 1991.
Sharples, S., and R. J. S. E. Bensalem. "Airflow in courtyard and atrium buildings in the urban environment: A wind tunnel study." Solar Energy 70, no. 3 (2001): 237-244.
Rajapaksha, Indrika, H. Nagai, and M. Okumiya. "A ventilated courtyard as a passive cooling strategy in the warm humid tropics." Renewable energy 28, no. 11 (2003): 1755-1778.
Ghaffarianhoseini, Amirhosein, Umberto Berardi, and Ali Ghaffarianhoseini. "Thermal performance characteristics of unshaded courtyards in hot and humid climates." Building and Environment 87 (2015): 154-168.
Bensalem, Rafik. "Wind driven natural ventilation in courtyard and atrium-type buildings." PhD diss., University of Sheffield, 1991.