Date of Award
Spring 2024
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Forestry and Environmental Studies
First Advisor
Rao, Narasimha
Abstract
The buildings sector plays a key role in influencing global demand for energy and materials, and the emission of Greenhouse Gases (GHGs). 80% of future population growth is expected to take place in the Global South, primarily populated with low-and-middle income (LMI) countries, making these countries hotspots for growth in the buildings sector, especially the residential sector. India, the most populated low-and-middle income country, is expected to lead the world in energy growth from the residential sector in the next decades. However, previous global reports often do not represent the diversity in building types from these countries, especially excluding the low-income housing types. Residents in low-income homes face disproportionately severe heat stress, health issues and other adverse effects of climate change, as these homes are poorly constructed, and unable to provide durable, safe comfortable shelter. In this dissertation, I focus on the role that is played by the uniquely diverse building stock in low-and-middle income countries, specifically India, on the future resource demand and GHG emissions from their residential sector.Population growth, urbanization and development are the drivers behind the rapid residential sector emissions growth in India in the coming decades. As of 2019, 19 million houses in urban India did not meet decent living standards. India expected to see 20 billion square meters of new residential floorspace constructed between 2015-2040. As this construction growth begins to materialize, it presents a short window of opportunity to improve the construction methods, and introduce long-lasting solutions to provide durable, comfortable shelter to future generations. The largest source of energy demand and emissions growth in the future in the Indian residential sector is expected to stem from growth in cooling energy demand. This is due to increasing heat stress, characterized by high temperature and humidity in the Indian subcontinent, leading to increased ownership of air conditioners as affluence grows. In this dissertation, I evaluate the impact of representing realistic building types, thermal comfort choices, urban context and other unique characteristics in the urban Indian landscape on our understanding of the future resource demand and emissions from the sector. Previously, there has been incomplete representation of the diversity of building types in India or other LMI countries in future scenarios. I first examined the differences in the building stock in LMI countries and characterized the major building types unique to the 135 LMI countries. I classified the buildings sector in the LMI countries into three major types: formal, semi-formal and informal. Of these, the semi-formal building type was previously uncharacterized in literature, and covers a wide range of building types that house low-income residents. Only the formal building type has been documented and studied. I then used this characterization to create a highly specific and representative model of urban Indian residential buildings. This model helped provide detailed insight into the thermal comfort provided by each building type in major urban regions spanning across different climate zones in India. Thermal comfort was determined using a combination of temperature and humidity, in a metric named the heat index. Humidity has rarely been considered in previous literature, even though high humidity and high temperature are characteristic of the weather in many low-and-middle income countries like India, and both contribute to the high levels of discomfort experienced. The thermal comfort threshold in this dissertation is conservative and corresponds to the highest temperature and humidity levels previously considered in India. The inclusion of humidity was found to increase measures of thermal discomfort in India by a factor between five to ten. Formal buildings provided more thermal comfort than the other two low-income building types. Higher floors in multi-story buildings experienced less thermal comfort, and rooms with more exposure to the outside had better thermal comfort. Between the three largest metropolitan cities in India, Delhi, Mumbai and Bengaluru, Delhi ranked as the most uncomfortable when both duration and intensity of discomfort were considered, and Mumbai was uncomfortable for the longest. Decreasing density of urban buildings, achieved by increasing the distance between adjoining buildings increase thermal discomfort due to reduced shading and air flow between buildings. An increase of 5-7m between adjoining buildings can cause the thermal discomfort experienced to increase by 8%, and top floors can experience up to 50 times more discomfort than the lowest floors. Once insights into the thermal comfort gap, that is the gap to attaining complete thermal comfort, were gained on a building type and city level, I employed different ventilation and cooling strategies to determine the energy and emissions cost of filling the thermal comfort gap. Air-conditioning is a method to achieve thermal comfort, but I also included ventilation that precedes and supplements the usage of air-conditioners in urban India. Previous studies have modeled a simplified and constant form of ventilation, which does not fully consider the temporal changes in air flow due to diurnal temperature variations, air pressure, air speed and cross ventilation in rooms. I created an updated form of modeling ventilation which captures more of this intricacy and the several factors influencing the air flowing through open windows. Improving upon previous models of ventilation in this way showed that discomfort had previously been overestimated, and the improved model reduced the calculated discomfort by 60-80%. Changing the masonry materials from Burnt Clay Bricks (BCBs) to Hollow Concrete Blocks (HCBs) was found to reduce the annualized life-cycle energy demand by up to 20%. Additionally, in this dissertation, I included economic usage of air-conditioners with a higher set point than previous national level models have considered for India. This higher set-point corresponds to the set-point required to completely eliminate discomfort to meet the conservative thermal comfort standards defined in our previous study. The combination of ventilation, ceiling fans and air-conditioners was found to reduce the cooling energy demand projections for the Indian urban sector by up to 60% in 2050 compared to using air conditioning alone. This dissertation finds that imbuing realism in energy models for LMI countries like India by representing the uniquely diverse building types along with the local economical cooling practices and preferences can significantly reduce the energy demand projection to meet thermal comfort demands in India. It highlights the importance of representing low-income homes, as they can often be the most heat-stressed and require cooling intensities that might be unaffordable for their residents. It finds that reducing distance between buildings causes improvement in thermal comfort due to shading and air-flow dynamics, an effect that might have tradeoffs with other microclimate phenomena. It creates a framework to represent buildings and capture unique features of the urban landscape in contemporary energy models for LMI countries.
Recommended Citation
Iyer, Aishwarya V, "Implications for Energy Demand and Emissions by Mitigating Heat Stress in Heterogeneous Urban Building Types in India" (2024). Yale Graduate School of Arts and Sciences Dissertations. 1261.
https://elischolar.library.yale.edu/gsas_dissertations/1261
