Energies, March 2022
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
Paper available on: https://www.mdpi.com/1996-1073/15/6/2259
Science and Technology for the Built Environment, June 2021
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.
Paper available on: https://www.tandfonline.com/doi/full/10.1080/23744731.2021.1941248
Energy and Buildings, Volume 216, June 2020
Stephanie Gauthier, Leonidas Bourikas, Farah Al‐Atrash, Chihye Bae, Chungyoon Chun, Richard de Dear, Runa T. Hellwig, Jungsoo Kim, Suhyun Kwon, Rodrigo Mora, Himani Pandya, Rajan Rawal, Federico Tartarini, Rohit Upadhyay, Andreas Wagner
Abstract: Thermal comfort research has been traditionally based on cross-sectional studies and spatial aggregation of individual surveys at building level. This research design is susceptible to compositional effects and may lead to error in identifying predictors to thermal comfort indices, in particular in relation to adaptive mechanisms. A relationship between comfort and different predictors can be true at an individual level but not evident at the building level. In addition, cross-sectional studies overlook temporal changes in individual thermal perception due to contextual factors. To address these limitations, this study applied a longitudinal research design over 8 to 21 months in eight buildings located in six countries around the world. The dataset comprises of 5,567 individual thermal comfort surveys from 258 participants. The analysis aggregated survey responses at participant level and clustered participants according to their thermal sensation votes (TSV). Four TSV clusters were introduced, representing four different thermal sensation traits. Further analysis reviewed the probability of cluster membership in relation to demographic characteristics and behavioural adaptation. Finally, the analysis at individual level enabled the introduction of a new metric, the thermal zone (Zt), which in this study ranges from 21.5 °C to 26.6 °C. The thermal sensation traits and person-centric thermal zone (Zt) are a first step into the development of new metrics incorporating individual perceived comfort into dynamic building controls for adaptive buildings.
Paper available on: https://www.sciencedirect.com/science/article/abs/pii/S0378778819315361?via%3Dihub
Energy and Buildings, Volume 214, 2020
Rajan Rawal, Marcel Schweiker, Ongun Berk Kazanci, Vishnu Vardhan, Quan Jin, Lin Duanmu
Abstract: Conventional heating, ventilation, and air-conditioning (HVAC) systems are designed to condition the entire building volume. In contrast, Personal Comfort Systems (PCS) target conditioning only the occupied zones of the space, while maintaining the remaining volume at a relatively under-conditioned state. PCS offer the occupants the choice of modulating their immediate thermal ambience with local controls. The individual-level control helps in improving the subjective thermal and air quality acceptability with the desired thermal sensation. This review paper details on the various types of heating, cooling, ventilation, heating with ventilation, and cooling with ventilation PCS devices. It summarises the thermal ambience created by the respective PCS devices and the resultant subjective responses of the occupants. This review also identifies the energy saving potential of various kinds of PCS devices, the power use of PCS devices, and discusses their economic viability.
Paper available on: https://www.sciencedirect.com/science/article/abs/pii/S0378778819316111
Energy and Buildings, Volume 205, December 2019
Runa T. Hellwig, Despoina Teli, Marcel Schweiker, Joon-Ho Choi, M.C. Jeffrey Lee, Rodrigo Mora, Rajan Rawal, Zhaojun Wang, FarahAl-Atrash
Abstract: The concept of adaptive thermal comfort was formulated many decades ago and has been validated in numerous field studies. As a result, wider acceptable indoor temperature ranges based on adaptive models have been included in international and national standards and the adaptive approach to thermal comfort is regarded as a significant contributor in achieving low energy building design and operation. Despite the ever-increasing scientific literature on adaptive comfort around the world, the overall understanding of how to translate the adaptive principles into design practice and concepts for operating buildings is still limited, which suggests a gap between the scientific outcomes and the real-world applications. This discussion paper identifies the challenges and gaps in using the principles of adaptive thermal comfort by design practitioners and discusses them in light of relevant research findings. More than 100 literature sources were reviewed in support of the discussion. The paper then proposes a framework that aims to facilitate the adoption of adaptive comfort principles in design and operation of buildings and describes the outline of an imminent guideline for low energy building design based on the concept of adaptive thermal comfort.
Paper available on: https://www.sciencedirect.com/science/article/abs/pii/S0378778819316160
Building and Environment, Volume 151, 15 March 2019
Mona Doctor-Pingel, Vishnu Vardhan, Sanyogita Manu, Gail Brager, Rajan Rawal
Abstract: The ever-increasing demand for built spaces to cater to the needs of the tropical population compels for the adoption of sustainable building forms and passive design strategies. This research aims at studying the cases of six naturally ventilated occupied buildings constructed in the tropical ‘warm and humid’ climate of Pondicherry and Auroville, India. The buildings were subjected to long-term data logging and sporadic hand-held measurements. Indoor parameters of air temperature (Ta), surface temperature (Ts), and relative humidity (RH) across six living spaces, eight roof assemblies, and six passive design strategies were logged on an hourly basis and analysed for the hottest and coldest months. In order to estimate the thermal comfort, Ta readings of the most occupied zones were compared against ASHRAE-55 adaptive thermal comfort model and India Model for Adaptive Comfort (IMAC) temperature limits. This research showed that the hourly averaged Ta and RH in the six naturally ventilated spaces at the hottest summer hour (13:00) was between 31.0 and 33.2 °C and 56.0–69.0% while the outdoors were at 36.9 °C and 43.3% respectively. The hourly averaged rooftop and ceiling Ts for the unshaded roofs at 14:00 h during peak summer was between 53.0-43.4 °C and 36.6–31.0 °C respectively, while a shaded roof had a rooftop and ceiling Ts of 34.5 °C and 31.9 °C respectively. The passive design strategies of exposed cavity walls, night ventilation, and optimised building forms were found to be the most effective. The number of uncomfortable hours predicted by the ASHRAE model were found to be 93.4% higher than those by IMAC.
Paper available on: https://www.sciencedirect.com/science/article/abs/pii/S0360132319300344
Building and Environment, Volume 148, 15 January 2019
Sanyogita Manu, Gail Brager, Rajan Rawal, Angela Geronazzo and Devarsh Kumar
Abstract: India has a rich tradition of climate responsive architecture, incorporating several variations of passive design strategies that have been layered over time with the cultural, social and environmental context of the immediate geographical region. Designing climate responsive buildings is challenging, requiring an understanding of building physics, as well as the way buildings are designed, constructed and operated in a given cultural context. The process becomes more difficult with the ever-increasing comfort expectations. Unfortunately, it is easier to install air conditioners in a poorly designed building than to design a high-performing building to begin with. This paper is based on a study to evaluate the thermal performance of climate responsive buildings. We studied six modern institutional and office buildings in warm-humid, hot-dry and composite climate zones. Collectively, they incorporated a range of passive and hybrid design strategies, including various shading devices, courtyards, solar chimneys, cavity walls, various configurations of thermal mass, day and night-time ventilation, and evaporative cooling. We monitored each building for a period of one year and assessed their performance in terms of the behaviour of selected components, their overall response to the prevailing outdoor conditions. In addition to the measured variables, we compared performance using temperature gradients overlay on wall sections, heat maps and linear regression analysis to understand the relationship between the outdoor and indoor conditions to determine the nature of “climate responsiveness” of each building.
Paper available on: https://www.sciencedirect.com/science/article/abs/pii/S0360132318306887
Building Research & Information, Volume 47, 2019 - Issue 1
Peter Graham and Rajan Rawal
Abstract: India’s growth of energy demand in the building stock, and efforts to curb it, are placed into an international context by adapting the reporting criteria developed for the Global Alliance on Building & Construction's (GABC) Global Status Report (2017) on buildings and construction. A survey of state and non-state actor climate commitments submitted to the United Nations Framework Convention on Climate Change’s (UNFCCC) Non State Actors Zone for Climate Action (NAZCA) database and recent research on the status of building energy codes and standards globally are also presented. To contribute to a 2°C pathway, India must achieve a 50% reduction in building energy demand and related greenhouse gas (GHG) emissions by 2050. India is taking steps toward this goal through initiatives such as recent upgrades to the Energy Conservation Building Code (ECBC), encouraging green building rating and energy certification, and stimulating markets for low-carbon/high-efficiency technologies. However, despite improvements in building energy intensity, neither the global or the Indian building sectors are currently decarbonizing. The adoption of consistent national energy and GHG emission reduction goals could further align national, subnational and private-sector climate action commitments to facilitate a transition to a low-carbon emissions pathway and contribute to limiting global warming to well below 2°C.
Paper available on: https://www.tandfonline.com/doi/abs/10.1080/09613218.2018.1495803?journalCode=rbri20
Building and Environment, Volume 148, 15 January 2019
Sriraj Gokarakonda, Christophvan Treeck, Rajan Rawal
Abstract: The potential of mixed-mode office buildings with varying design and control parameters is examined by using an uncertainty analysis in the three climate zones of India. The analysis is in terms of cooling energy consumption, thermal comfort conditions, and natural ventilation hours. Furthermore, influential parameters are identified using sensitivity analysis. In this study, opening the windows enables natural ventilation. Night-time ventilation through the windows is not enabled because these are mostly closed at night. A maximum natural ventilation of 10% of the total building occupancy hours are observed in warm and humid, and hot and dry climates; however, they are slightly higher in the composite climate. A further increase in the number of natural ventilation hours leads to an increase in the occupancy hours outside the Indian Model for Adaptive Comfort model for mixed-mode buildings with at least 90% of occupants are satisfied. There are no occupancy hours outside of 80% of occupants are satisfied. The choice of thermal comfort band is crucial for determining the potential of mixed-mode buildings. The cooling setpoint temperature, building size, window solar heat gain coefficient, and surface properties of exterior surfaces are identified as the more influential parameters than the thermophysical properties of building envelope constructions. Although the building envelope which is in compliance with the Energy Efficient Building Code of India increases energy efficiency during air-conditioning periods, whether it reduces natural ventilation hours, because of overheating during such period remains to be determined.
Paper available on: https://www.sciencedirect.com/science/article/abs/pii/S0360132318306681
Intelligent Buildings International, Volume 11, 2019 - Issue 2
Sam Babu Godithi, Enna Sachdeva, Vishal Garg, Richard Brown, Christian Kohler and Rajan Rawal
Abstract: The buildings are conventionally operated to maintain homogeneous indoor ambient conditions to maintain comfortable thermal and visual environments. However, maintaining these homogeneous conditions throughout the building leads to unnecessary energy consumption, and does not address the varying thermal and visual comfort needs of the individual occupants. This has led the building science community to pursue personal environmental control (PEC) systems that work in tandem with adaptive centralized ambient comfort systems. These PEC systems create favorable environmental conditions around each occupant, employing specialized equipment, such as a personal thermal conditioning system, task lighting, plug load monitoring and control, window shade control system, and similar systems. Coordinating among personal control systems and with centralized building management systems allows the optimal provision of services such as cooling, lighting, and other such services where they are needed, potentially leading to significant energy efficiency and improved occupant satisfaction.
This paper provides an overview of the state of research associated with personalized thermal conditioning and lighting systems. In addition, presents a survey of controls and communication systems that operate these devices. Finally, the paper considers the energy savings potential from a personal thermal comfort and lighting comfort.
Paper available on: https://doi.org/10.1080/17508975.2018.1543179
Journal of Facilities Management, Vol. 16, No. 2
Reshma Singh, Paul Mathew, Jessica Granderson, Yash Shukla, Amiya Ranjan Behera
Abstract: Purpose: Building Energy Information Systems (EIS) are performance monitoring software, data acquisition hardware, and communication systems used to store, analyze, and display building energy data. Some $60 billion is spent annually on wasted energy in U.S. buildings, and actions taken based on EIS data can enable operational energy savings of ~10 percent in the U.S. commercial sector (~2 quads of primary energy). However, EIS adoption is low due to various technical and market challenges. This paper provides technical specifications for standardized EIS packages that can help overcome barriers and accelerate scale.
Design/methodology/approach: A five-step approach was followed: 1. Identifying business drivers as key determinants for hotel sector-specific packages 2. Addressing heterogeneity to develop standardized, tiered packages 3. Determining performance metrics for key stakeholders 4. Recommending streamlined data architecture 5. Developing visualization enabling insights and actions
Findings: Technical specifications for two tiers (entry and advanced) of EIS packages for hotels have been developed. EIS vendor, integrator, and client organization’s facilities and IT staff have been considered as key stakeholders. Findings from six field demonstrations show benefits of (i) cost-effectiveness, through reduced transactional, first, and operational costs, (ii) scalability, by accommodating heterogeneity across the building sub-sector, (iii) simplicity, by integrating meters, gateways, and software in the package, and (iv) actionability in organizations, across various decision making levels.
Originality/value: Building owners and operators can use these specifications to ease procurement and installation of EIS in their facilities. EIS software vendors can use them to develop new product offerings for underserved sectors.
Building and Environment, Volume 142, September 2018, Pages 502-512
Veronika Földváry, Toby Cheung, Hui Zhang, Richard de Dear, Thomas Parkinson, Edward Arens, Chungyoon Chun, Stefano Schiavon, Maohui Luo, Gail Brager, Peixian Li, Soazig Kaam, Michael A Adebamowo, Mary M Andamon, Francesco Babich, Chiheb Bouden, Hana Bukovianska, Christhina Candido, Bin Cao, Salvatore Carlucci, David KW Cheong, Joon-Ho Choi, Malcolm Cook , Paul Cropper, Max Deuble, Shahin Heidari, Madhavi Indraganti, Quan Jin, Hyojin Kim, Jungsoo Kim, Kyle Konis, Manoj K Singh, Alison Kwok, Roberto Lamberts, Dennis Loveday, Jared Langevin, Sanyogita manu, Cornelia Moosmann, Fergus Nicol, Ryozo Ooka, Nigel A Oseland, Lorenzo Pagliano, Dušan Petráš, Rajan Rawal, Ramona Romero, Chandra Sekhar, Marcel Schweiker, Federico Tartarini, Shin-ichi Tanabe, Kwok Wai Tham, Despoina Teli, Jorn Toftum, Linda Toledo, Kazuyo Tsuzuki, Renata De Vecchi, Andreas Wagner, Zhaojun Wang, Holger Wallbaum, Lynda Webb, Liu Yang, Yingxin Zhu, Yongchao Zhai, Yufeng Zhang, Xiang Zhou
Abstract: Recognizing the value of open-source research databases in advancing the art and science of HVAC, in 2014 the ASHRAE Global Thermal Comfort Database II project was launched under the leadership of University of California at Berkeley's Center for the Built Environment and The University of Sydney's Indoor Environmental Quality (IEQ) Laboratory. The exercise began with a systematic collection and harmonization of raw data from the last two decades of thermal comfort field studies around the world. The ASHRAE Global Thermal Comfort Database II (Comfort Database), now an online, open-source database, includes approximately 81,846 complete sets of objective indoor climatic observations with accompanying “right-here-right-now” subjective evaluations by the building occupants who were exposed to them. The database is intended to support diverse inquiries about thermal comfort in field settings. A simple web-based interface to the database enables filtering on multiple criteria, including building typology, occupancy type, subjects' demographic variables, subjective thermal comfort states, indoor thermal environmental criteria, calculated comfort indices, environmental control criteria and outdoor meteorological information. Furthermore, a web-based interactive thermal comfort visualization tool has been developed that allows end-users to quickly and interactively explore the data.
Paper available on: https://www.sciencedirect.com/science/article/abs/pii/S0360132318303652
Applied Thermal Engineering, Volume 138, 25 June 2018, Pages 501-512
Kaushik Biswas, Yash Shukla, Andre Desjarlais, Rajan Rawal
Abstract: This article presents combined measurements of fatty acid-based organic PCM products and numerical simulations to evaluate the energy benefits of adding a PCM layer to an exterior wall. The thermal storage characteristics of the PCM were measured using a heat flow meter apparatus (HFMA). The PCM characterization is based on a recent ASTM International standard test method, ASTM C1784. The PCM samples were subjected to step changes in temperature and allowed to stabilize at each temperature. By measuring the heat absorbed or released by the PCM, the temperature-dependent enthalpy functions for melting and freezing were determined.
The simulations were done using a previously-validated two-dimensional (2D) wall model containing a PCM layer and incorporating the HFMA-measured enthalpy functions. The wall model was modified to include the hysteresis phenomenon observed in PCMs, which is reflected in different melting and freezing temperatures of the PCM. Simulations were done with a single enthalpy curve based on the PCM melting tests, both melting and freezing enthalpy curves, and with different degrees of hysteresis between the melting and freezing curves. Significant differences were observed between the thermal performances of the modeled wall with the PCM layer under the different scenarios.
Paper available on: https://www.sciencedirect.com/science/article/abs/pii/S1359431118306495
Science and Technology for the Built Environment, Volume 24, 2018 - Issue 8
Malcolm Cook and Rajan Rawal
Paper available on: https://www.tandfonline.com/doi/full/10.1080/23744731.2018.1522144
Energy, Volume 140, Part 1, December 2017, Pages 952-965
Amit Garg, Jyoti Maheshwari, P.R. Shukla and Rajan Rawal
Abstract: The total electricity consumption from commercial sector was about 9% during 2013–14 in India. Load research survey was carried out to study the usage patterns for all types of electric appliances used in commercial establishments at income, appliance and end-use levels in Gujarat state of India – one of the most progressive states. Penetration level of efficient appliances, electricity load curves and Energy Performance Index (EPI) were estimated. The mean EPI was 98 kWh/m2/year (SD = 105.5) for surveyed small commercial establishments (low income) while mean EPI was 181 kWh/m2/year (SD = 68) for surveyed large commercial establishments (Malls). Electricity saving potentials was estimated if electric appliances at these commercial establishments were replaced with efficient appliances. Four alternate scenarios were analyzed using cost of conserved energy (CCE) curves with various efficiency enhancement options – following at least commercial sub-category level median EPIs, following average EU equivalent EPI levels, following average EPI levels of equivalent US commercial establishments, and following the best available technologies (BAT). The average energy savings ranged between 14% and 25% across buildings and scenarios. Energy efficient air-conditioner and LED lights offer the highest energy savings potential among appliances.
Paper available on: https://www.sciencedirect.com/science/article/abs/pii/S0360544217315104
Building and Environment, Volume 123, October 2017, Pages 37–49 Francesco Babich, Malcolm Cook, Dennis Loveday, Rajan Rawal, Yash Shukla Abstract: Ceiling fans have been used for decades as a means of providing thermal comfort in tropical countries such as India. However, recent years have witnessed a significant increase in the use of air conditioning as a means to achieve comfort, and therefore in the total energy consumption and related CO2 emissions. Ceiling fans are still viable options to limit use of air conditioners or in combination with air conditioners without compromising on thermal comfort and still achieving energy savings. Ceiling fans generate non-uniform velocity profiles, and therefore relatively non-uniform thermal environments, whose characteristics may be tough to analyse with simple modelling methods. This issue can be investigated using CFD. However, to date, there are few works on ceiling fans, CFD and thermal comfort. More accurate models are therefore required to predict their performance. The research presented in this paper aimed to develop and validate a three-dimensional transient implicit CFD model of a typical ceiling fan available in India by comparing simulation results obtained using different URANS turbulence models with measured data collected in controlled environment. The results highlight that this ceiling fan model is able to replicate the predominant characteristics of the air flow generated by the fan such as the meandering plume and the local fine free shear layers. The best results are achieved when the SST k-ω turbulence model is used, with 83% of the simulated values being within the error bars of the respective measured value. Keywords: Ceiling fan, Thermal comfort, CFD validation, Turbulence modelling, India, Environmental chamber Download Paper
Building and Environment, Volume 106, September 2016, Pages 422-426 Sanyogita Manu, Yash Shukla, Rajan Rawal, Leena E.Thomas, Richard de Dear Abstract: India is witnessing unprecedented growth trends in building construction, particularly office spaces. Indian offices are designed to operate at 22.5 ± 1 °C all year round to meet the stringent “Class A” specifications outlined by international standards in the absence of an India-specific comfort standard. This paper proposes an India Model for Adaptive Comfort – IMAC – based on the field surveys administered in 16 buildings in three seasons and five cities, representative of five Indian climate zones. A total of 6330 responses were gathered from naturally ventilated, mixed mode and air-conditioned office buildings using instantaneous thermal comfort surveys. Occupants in naturally ventilated Indian offices were found to be more adaptive than the prevailing ASHRAE and EN models would suggest. According to the IMAC model, neutral temperature in naturally ventilated buildings varies from 19.6 to 28.5 °C for 30-day outdoor running mean air temperatures ranging from 12.5 to 31 °C. This is the first instance where a study proposes a single adaptive model for mixed mode buildings asserting its validity for both naturally ventilated and air-conditioned modes of operation in the building, with neutral temperature varying from 21.5 to 28.7 °C for 13–38.5 °C range of outdoor temperatures. For air-conditioned buildings, Fanger's static PMV model was found to consistently over-predict the sensation on the warmer side of the 7-point sensation scale. Keywords: Indian office buildings, Fanger PMV, Adaptive thermal comfort, Adaptive model, Neutral temperature, Comfort standards Download Paper
Journal of Habitat Engineering, Vol3-2, pp 209-218 Jalpa Gandhi, Rajan Rawal