Journal Papers

Journal: Energies, Volume 16, Issue 19

Authors: Sriraj Gokarakonda, Christoph Van Treeck, Rajan Rawal, Stefan Thomas

Abstract: 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.

Keywords: room air-conditioners; ceiling fans; set-point temperature; thermal comfort; user behaviour; sensors and monitoring

Journal: Energy and Built Environment, Volume 4, Issue 6

Authors: Sriraj Gokarakonda, Christoph Van Treeck, Rajan Rawal, Stefan Thomas

Abstract: Studies show that people can tolerate elevated temperatures in the presence of appreciable air movement (e.g., by using ceiling fans). This results space cooling energy savings by reducing the use of air-conditioners and extending their set point temperature (Tset). However, there is little empirical evidence from India on the energy savings from the use of ceiling fans with air-conditioners. To address this gap, we analysed the energy performance of room air-conditioners (RACs) with both fixed speed compressors and inverter technology at different set point temperatures (Tset) and ceiling fans at different Fan Speed Settings (FSSs) in relation to thermal comfort conditions according to the Indian Model for Adaptive Comfort-Residential (IMAC-R) in 15 residential mixed-mode buildings (MMBs). The study showed that using high FSSs with RACs resulted in unnecessary energy consumption. Compared with the mandatory default Tset of 24°C in the Indian RACs, the results showed that at all FSSs, Tset at 28 and 30°C maintained thermal comfort conditions, i.e., the indoor air temperature (Tin) was between the neutral operative temperature (Tneu) and lower 80% thermal comfort band according to IMAC-R and resulted in mean RAC energy savings 44 and 67%, respectively. Furthermore, at different Tset, RACs with inverter technology consumed 34-68% less energy than fixed speed compressors.

Keywords: Room air-conditioners; Ceiling fans; Set point temperature; Thermal comfort

Journal: Journal of Building Performance Simulation, Volume 15, Issue 6

Authors: Saranya Anbarasu, Wangada Zuo, Yangyang Fu, Yash Shukla, Rajan Rawal

Abstract: Direct evaporative coolers (DECs) are a low-energy cooling alternative to conventional air conditioning in hot-dry climates. The key component of DEC is the cooling pad, which evaporatively cools the air passing through it. While detailed numerical models of heat and mass transfer have been proposed for the cooling pad, these require many input parameters that are not readily accessible. Alternatively, simplified models lack accuracy and are confined to common types of cooling pad. To address these limitations, we developed and validated a physics-based model, that only needs the nominal data to compute the heat and mass transfer with considerable accuracy. The proposed model is implemented in Modelica, an equation-based object-oriented modeling language. For comparison, a basic lumped model from EnergyPlus based on the efficiency curve of the cooling pad is also implemented. The physics-based model exhibits <2% error from the experimental data and the lumped model exhibits a 12.3% error.

Keywords: direct evaporative cooler, modelica, physical-based model

Journal: Building and Environment. Volume 219

Authors: Rajan Rawal, Yash Shukla, Vishnu Vardhan, Sneha Asrani, Marcel Schweiker, Richard de Dear, Vishal Garg, Jyotirmay Mathur, Sanjay Prakash, Saurabh Diddi, Vikash Ranjan, Abdullah N. Siddiqui, Govinda Somani

Abstract: Indian residences are vulnerable to heat-driven discomfort amid the mounting prevalence of weather extremes, residential design and construction practices, and densifying urbanscapes. Therefore, it is vital to understand the thermal comfort characteristics of nationwide residences. This study proposes an adaptive thermal comfort model based on yearlong field surveys in eight cities located across five climate zones of India – the India Model for Adaptive Comfort - Residential (IMAC-R). The model prescribes the operative temperature bands for 80% and 90% thermal acceptability in correlation with the outdoor reference temperature, applicable to mixed-mode (MM) and naturally ventilated (NV) residences.

More than 80% of the Indian residential occupants experienced a neutral thermal sensation in the indoor operative range of 16.3–35 °C in response to a 5.5–33 °C variation in the 30-day outdoor running mean temperature. Comparing the proposed model with the PMV model revealed that the latter underpredicts the thermal adaptivity of Indian occupants. The model was also compared against its predecessor – India Model for Adaptive Comfort for Commercial Buildings (IMAC MM and NV), along with relevant global and regional thermal comfort models. On average, the neutral temperature prescribed by IMAC-R was warmer than the temperatures prescribed by IMAC MM and NV by 2.9 °C and 2.1 °C, respectively; it was also warmer than the temperature prescribed by the recent ASHRAE-55 and EN 16798-1 models by 2 °C and 0.3 °C, respectively. IMAC-R reserves the prospect of addressing the thermal comfort needs of the national population while paving the way for long-term energy savings and climate action.

Keywords: Thermal adaptation; Adaptive comfort model; Indian residences; Mixed-mode ventilation; Natural ventilation; IMAC

Journal: Buildings and Cities, Volume 3, Issue 1

Authors: Brian Ford, Dejan Mumovic, Rajan Rawal

Abstract: Far from being a panacea, air-conditioning is shown to create social, environmental and economic problems. Alternatives to air-conditioning are identified as a key means of reducing energy demand and carbon emissions, improving resilience to heat, and providing a healthy indoor environment. These alternatives are more than a technological issue and help to reframe coolth as an attribute and not a commodity. This editorial introduces the themes and individual papers in this special issue. It explores the implications of these alternative solutions across a range of issues: health and wellbeing; air quality; heat stress; technical/design solutions; economics and equity; climate change; social expectations and practices; policy and regulation; supply chain and procurement; education and training. Recommendations for change involve policy and regulation, construction industry business models, redefining the design decision process, improving performance and feedback, and updating workforce skills and capabilities.

Keywords: Adaptation air-conditioning, climate change, cooling, design, energy demand,, environmental control, passive cooling, public policy, thermal comfort

Journal: Buildings & Cities, Volume 3, Issue 1

Authors: Mili Jain, Rajan Rawal

Abstract: This study quantifies the gap between net-zero energy and net-zero carbon through a life cycle assessment (LCA) of a net-zero energy building (NZEB) in Ahmedabad, Gujarat, India. The annual net-zero energy evaluations of a building do not account for the greenhouse gas (GHG) emissions released before the building operation phases. Nor does it account for the GHG emissions during the end-of-life processes. As a consequence, an NZEB may not be a net-zero emission building over its lifespan. Comprehensive carbon-based evaluations are necessary to ensure an overall reduction in emissions is in line with the goals of the United Nations Paris Agreement. The LCA frameworks of ISO 14040 and EN 15978 form the basis of analysis and a method is presented based on data collection, consistency checks, uncertainty evaluation, impact assessment and interpretation of the results. It also acknowledges the lack of a nationalised inventory for LCA in India. The results show that despite an annual net-zero operation status of a building, the building has a negative impact with 866 tCO2e across a calculated lifespan of 60 years. The case study reveals the sensitivities of the analysis towards the system boundary, data quality requirements and acceptable limits of uncertainty.

Keywords: Buildings; carbon footprint;embodied carbon; life cycleassessment; net-zero carbon;net-zero energy; India

Journal: Buildings and Cities, Volume 3, Issue 1

Authors: Malcolm Cook, Yash Shukla, Rajan Rawal, Charalampos Angelopoulos, Luciano Caruggi-De-Faria, Dennis Loveday, Eftychia Spentzou, Jayamin Patel

Abstract: Rapidly developing economies of countries in hot climates face the risk of a significant increase in CO2 emissions. This study developed strategies for low energy cooling and ventilation for Indian residences (LECaVIR). Ventilation and cooling techniques were developed and tested for India’s four climatic zones. The analysis shows that natural ventilation is possible in typical residential buildings for about 20–40% of the year. Using an enhanced natural ventilation mode with appropriately sized openable windows and controls, the total number of hours for which natural ventilation is able to offer satisfactory conditions for occupants can be extended by a further 13 percentage points, leading to a potential reduction of 46% in the mechanical cooling hours for residences. Dynamic thermal simulation models, coupled with control software, were used to test the most promising natural ventilation strategies as part of a mixed-mode approach to ensure year-round comfort at minimal energy cost. The simulation shows that energy savings of up to 55% are possible.

Keywords: control cooling, dwellings, energy, mixed mode, residential, thermal comfort, ventilation, India

Journal: Building and Environment, Volume 217

Authors: Rashmin Damle, Nikita Khatri, Rajan Rawal 

Abstract: Traditional buildings since many centuries have used lime as a binder and finishing material. However, in contemporary construction practices, lime mortar and lime plaster have been replaced by cement mortar and cement plaster. Lime is a sustainable and self-healing material whose strength increases with time. In addition to its pleasing appearance, lime has excellent moisture buffering properties. Buildings with lime mortar and lime plaster are also breathable due to moisture transfer across the envelope. The objective of this work is to compare the hygrothermal performance of lime and cement plaster. For this purpose, two identical test cells of 1 m3 volume were constructed with brick as masonry material. One of the test cells was built with cement mortar and cement plaster, while the other cell was made with lime mortar and lime plaster. Environmental variables such as indoor air temperature, indoor relative humidity, globe temperature, surface temperatures, surface moisture content were monitored for a period of 74 days. It was found that the lime test cell was cooler by 3–5 °C and the indoor conditions were comfortable for 40% more time. The moisture buffering capacity of lime also helped to moderate the indoor relative humidity. The above differences were observed when the test cells passively responded to the changing outdoor conditions without internal loads. Further investigation of real-sized spaces would be necessary to endorse the advantages of lime plaster found in this study.

Journal: Energies, Volume 15, Issue 6

Authors: Sriraj Gokarakonda, Christoph van Treeck, Rajan Rawal

Abstract: In warm and hot climates, ceiling fans and/or air conditioners (ACs) are used to maintain thermal comfort. Ceiling fans provide air movement near the skin, which enhances the evaporation of sweat, reduces heat stress, and enhances thermal comfort. This is also called the cooling effect. However, AC usage behaviour and the effects of elevated air speed through the use of ceiling fans on indoor operative temperature during AC usage are not widely studied. This study investigated the optimum AC (cooling) set point temperature and air velocity necessary for maintaining thermal comfort while achieving energy conservation, in mixed-mode buildings in India, through field studies by using used custom-built Internet of Things (IOT) devices. In the current study, the results indicate a 79% probability that comfort conditions can be maintained by achieving a temperature drop of 3K. If this drop can be achieved, as much as possible, through passive measures, the duration of AC operation and its energy consumption are reduced, at least by 67.5 and 58.4%, respectively. During the air-conditioned period, there is a possibility that the cooing effect is reduced because of increase in operative temperature due to ceiling fan operation. Therefore, the optimum solution is to maintain the highest AC set point and minimum fan speed setting that are acceptable.

Keywords: elevated air speed; thermal comfort; mixed-mode buildings; set point temperature; energy consumption in buildings

Journal: The Journal of Engineering Research (TJER), Volume 18, Issue 2

Authors: Sneha Asrani, Rajan Rawal, Yash Shukla, Peter Graham, Priyanka Bhanushali, Arjun Desai

Abstract: On an average, India has more than 3000 Cooling Degree Days (CDD). The multifamily public housing being constructed under India’s Prime Minister Awas Yojana (PMAY) is aimed at providing formal housing to the society’s Economic Weaker Section (EWS). It is essential that this housing delivers thermally comfortable in-doors to the occupants. This study mapped the design and construction practices followed under PMAY Urban (PMAY-U) against India’s Residential Energy Building Code, Eco Niwas Samhita (ENS). The metric prescribed in ENS is Residential Envelope Transmittance Value (RETV). For 80 PMAY-U projects, information related to spatial design, and walling assemblies was collated. 30 projects were short-listed for detailed analysis. The RETV for selected projects was calculated. The analysis demonstrated that walling assemblies and technologies having a lower thermal transmittance value (U-value) resulted in meeting the ENS prescribed RETV numbers, hence, code compliance. The study further extended to assess the energy performance of the housing unit by exploring the change in walling assemblies. The change in thermally comfortable hours were reported in the range of 4145 and 6034, and Energy Performance Index (EPI) of the dwelling units were reported between 64 and 68 kWh/m2/year for the various walling assemblies.

Journal: Science and Technology for the Built Environment

Authors: Anmol Mathur, Pamela Fennell, Rajan Rawal, Ivan Korolija

Abstract: Urban building energy models (UBEM) are driving sustainable design and operations of cities by combining urban datasets with energy simulations. UBEMs are developed from a range of inputs on the spatial and semantic details of the buildings, and the systems affecting their energy performance. Large geographical scales with finer spatio-temporal details increase the challenges of data processing for a reliable UBEM. Thus, it is essential to understand the impact of increasing the resolution of model inputs on the outputs to balance the efforts spent on model development, filling data gaps and maintaining the reliability of the results. This research introduces a Fit-for-Purpose modelling strategy and extends the concept of Levels of Detail (LoD) used for 3D models, to UBEM characteristics including occupancy, geometry, context, modelling methodology, and calibration with the proposed model characterisation framework. A case study based on a 0.3km2 area of Ahmedabad, India, is presented to demonstrate the framework. The results highlight a need for a higher LoD in occupancy modelling for the residential and educational buildings, whereas a higher LoD is more important for the commercial buildings’ envelope characteristics. These insights will enable a highly targeted supplementary data collection approach for the UBEM of the entire city.

Journal: Building and Cities, Volume 2, Issue 1

Authors: Nidhi Rai Jain, Rajan Rawal, Vishnu Vardhan, Shubhashis Dey

Abstract: India’s current standards and labels for room air-conditioners (RACs) account for energy efficiency, but omit other important criteria that could influence product development and consumer choice: thermal comfort and environmental impact. This study proposes comprehensive RAC evaluation criteria by accounting for the operational energy, thermal comfort and environmental impact through the metrics of the Indian seasonal energy efficiency ratio (ISEER), cooling seasonal energy consumption (CSEC) and total equivalent warming impact (TEWI), respectively. It uses five RAC product cases based on the Indian RAC market to demonstrate the enhanced evaluation criteria across the climatic conditions of 55 Indian cities subject to static and adaptive (air-conditioned, AC; and mixed-mode, MM) thermal setpoints. The analysis yields a significant difference in the number of RAC operational hours between the static and adaptive (AC and MM) methods, resulting in a difference in the overall performance of RACs across varied climatic contexts.

Journal: Building and Environment, Volume 123