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Most air-conditioned buildings in India operate as Mixed-Mode Buildings (MMBs), either fully air-conditioned or with natural ventilation depending on the weather. Energy consumption for space cooling is a vital end-use service in buildings. Air-conditioning is expected to increase significantly due to high growth estimates in building construction, sales of Room Air-Conditioners (RACs), and real income growth. Therefore, this thesis examines the most influential design and control parameters that influence the potential of MMBs in India in relation to their thermal and energy performance. The primary features of MMBs analysed in the research project are as follows: shutting windows at night makes night ventilation redundant; natural ventilation through ceiling fans and windows is utilised to maintain optimal thermal conditions in naturally-ventilated mode and RACs are employed in air-conditioned mode. This thesis poses three research questions and aims to answer them. Firstly, what are the research gaps in assessing thermal and energy performance in mixed-mode buildings in India? Secondly, what is their potential concerning key operating conditions, and which parameters affect this potential? Lastly, how can these influential parameters be optimised? To answer these questions, three research methods were employed: 1) literature review; 2) large-scale simulation of building energy performance combined with uncertainty and sensitivity analysis; and 3) field studies of user behaviour with regards to RACs and the impact of ceiling fans and RACs on indoor conditions and energy consumption. The study identifies the cooling set point temperature as the most influential control parameter. In general, input parameters related to building design, shape and geometry were considered more important than those related to construction parameters. Furthermore, the study highlights that a set point temperature of 28 or 30°C is sufficient to maintain indoor comfort according to the Indian Model for Adaptive Comfort (IMAC) for residential buildings. If a specific airflow is required, it would use the least energy to run the ceiling fan at a low speed, usually set at 1.
Studies show that people can tolerate elevated temperatures in the presence of appreciable air movement (e.g., from using ceiling fans). This minimises the use of air-conditioners and extends their set-point temperature (Tset), resulting in energy savings in space cooling. However, there is little empirical evidence on the energy savings from using ceiling fans with Room Air-Conditioners (RACs). To address this gap, we analysed the energy performance of RACs with both fixed-speed compressors and inverter technology at different set-point temperatures and ceiling fan speed settings in 15 residential Mixed-Mode Buildings (MMBs) in India. Thermal comfort conditions (as predicted by the Indian Model for Adaptive Comfort-Residential (IMAC-R)) with minimum energy consumption were maintained at a set-point temperature (𝑇set) of 28 and 30 C and a fan speed setting of one. Compared with a Tset of 24 °C, a 𝑇set of 28 and 30 °C resulted in energy savings of 44 and 67%, respectively. With the use of RACs, a configuration with a minimum fan speed was satisfactory for an optimal use of energy and for maintaining the conditions of thermal comfort. In addition, RACs with inverter technology used 34-68% less energy than fixed-speed compressors. With the rising use of RACs, particularly in tropical regions, the study's outcomes offer a significant potential for reducing space-cooling energy consumption and the resultant greenhouse gas (GHG) emissions.