India is a country of varying climates. It is usually associated with warm weather. But there are other climates in India including cold, dry, humid, and composite. The rise in buildings to shelter the growing Indian population using concrete along with great demands for air-conditioning leaves a carbon footprint that is worrying.
Thus the search is on to find environment-friendly materials for construction of buildings. The use of insulation materials is a simple passive thermal management technique to reduce energy consumption in buildings. Straw is an agricultural residue that is produced in large quantities. India produces nearly 500 million tonnes of straw yearly and approximately 80 percent of the straw is burnt which causes massive air pollution. This can be avoided. Straw is considered to be a good source of fuel. But it can also be used as an eco-friendly insulating material for buildings, and it is also hygroscopic (absorbs moisture from the air).
The climatic zones of India can be divided into five categories, namely:
1. Warm and Humid (Chennai)
2. Composite (Jaipur)
3. Cold (Shimla)
4. Hot and Dry (Ahmedabad)
5. Temperate/Moderate (Bengaluru)
Dr. Karthik A. Sabapathy and Prof. Sateesh Gedupudi from the Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai, India, studied the thermal performance of straw insulation retrofitted envelope (with concrete wall and plaster coating) with the help of CFD simulations, for both conditioned and ventilated rooms, and for the five climatic zones of India. The thermo-physical properties of straw used in the simulations were based on their previous experimental work.
Dr. Karthik A. Sabapathy 
Prof. Sateesh Gedupudi
From the simulations carried out for a conditioned space, straw was found to be a good insulation material. Maximum cooling load was obtained for the summer day of the hot and dry climate of Ahmedabad, while the maximum heating load was obtained for the winter day of the cold climate of Shimla. The regions experiencing extreme climate conditions were found to be ideally suited for the inclusion of straw insulation in buildings. Straw is an inexpensive material and found in abundance in India so that the increasing demand would not be a problem for its cost. The estimated energy savings were in the range of 67%- 96% for a 10 cm thick straw across different climate zones, and the estimated monthly electricity cost savings on using straw insulation in building envelope were between Rs 35 and Rs 44 per square metre of envelope area over the thickness range of 10 to 40 centimetres considering a typical Indian electricity price of Rs 4.5 per kWh.
The 3-D simulations carried out for a naturally ventilated room showed that for hot summer, the straw-based envelope with the temporary closing of the inlet vent during the day improved the thermal comfort (reducing the peak indoor temperature by 3-4 °C). For the winter conditions of composite and hot and dry climate zones, the insulated envelope with the temporary closing of the inlet vent during the night improved the indoor conditions, and for the winter condition of cold climate zone, the insulated envelope with the inlet vent always closed significantly reduced the additional active heating needed for thermal comfort. It was found that the occupant adaptation strategies can play a key role in ensuring optimized use of straw insulation in buildings in different climate conditions. Control of air entry to the indoor space was found to be an easily adoptable occupant strategy. With straw-insulation-based envelope, some of the strategies explored through simulation analyses proved to be beneficial in mitigating the peak indoor temperature.
The current research work makes a strong point for bringing straw based insulation panels/boards (as retrofit) into the commercial market as a viable alternative for synthetic insulations for conditioned spaces. Nonetheless, more research is required, both experimental and theoretical, to investigate the additional complexities which can lead to a better understanding of thermal comfort in naturally ventilated buildings and the role of cost-effective insulations such as straw in achieving it.
Dr. Andrew Shea, Associate Professor of Building Physics in the Department of Architecture and Civil Engineering at the University of Bath, U.K., made the comments on the two papers as follows:
1. On the influence of concrete-straw-plaster envelope thermal mass on the cooling and heating loads for different climatic zones of India:
“The ability to achieve acceptable occupant thermal comfort for minimal operational energy expenditure whilst reducing embodied energy through application of natural, low impact, building materials is a global challenge. This article evaluates the potential of straw, an agricultural residue, as a route to the reducing costs and energy use associated with the heating and cooling of buildings located in the five climatic zones of India. In addition to identifying significant energy saving potential in the use of straw insulation, the authors investigate the effect of thermal inertia on energy consumption and report recommendations for optimum envelope configuration.”
2. On the thermal performance of naturally ventilated room with straw insulation retrofitted envelope for different climatic zones of India:
“This article focusses on the insulation potential of straw, an agricultural residue, as part of the thermal envelope of a naturally ventilated building. The authors’ use of computational fluid dynamics (CFD) simulation software enables detailed analysis of local variations in temperature and air flow. The parametric evaluation of the transient thermal performance of the naturally ventilated room and comparison of indoor air temperatures under five climate zones provides useful insight to occupant comfort and the energy saving potential of straw insulation under varied hygrothermal conditions.”
Article by Akshay Anantharaman
Here is the original link to the paper:
1.On the influence of concrete-straw-plaster envelope thermal mass on the cooling and heating loads for different climatic zones of India:
https://www.sciencedirect.com/science/article/abs/pii/S0959652620331620
2. On the thermal performance of naturally ventilated room with straw insulation retrofitted envelope for different climatic zones of India:
https://www.sciencedirect.com/science/article/abs/pii/S0959652622003043
