Publications

Abstract

Operational uncertainties play a critical role in determining potential pathways to reduce the building energy footprint in the Global South. This paper presents the application of a non-dominated sorting genetic (NSGA II) algorithm for multi-objective building design optimization under operational uncertainties. A residential building situated in a mid-latitude steppe and desert region (Köppen climate classification: BSh) in the Global South has been selected for our investigation. The annual building energy consumption and the total number of cooling setpoint unmet hours (h) were assessed over 13,122 different energy efficiency measures. Six Pareto optimal solutions were identified by the NSGA II algorithm. Robustness of Pareto solutions was evaluated by comparing their performance sensitivity over 162 uncertain operational scenarios. The final selection for the most optimal energy efficiency measure was achieved by formulating a robust multi-criteria decision function by incorporating performance, user preference, and reliability criteria. Results from this robust approach were compared with those obtained using a deterministic approach. The most optimal energy efficiency measure resulted in 9.24% lower annual energy consumption and a 45% lower number of cooling setpoint unmet h as compared to the base case.

Keywords: multi-objective building design optimization; robustness assessment; multi-criteria decision making

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1. Chaturvedi, S., Rajasekar, E., & Natarajan, S. (2020). Multi-objective Building Design Optimization under Operational Uncertainties Using the NSGA II Algorithm. Buildings, 10(5), 88.

Abstract

Heat waves are one of the deadliest of natural hazards and their frequency and intensity will likely increase as the climate continues to warm. A challenge in studying these phenomena is the lack of a universally accepted quantitative definition that captures both temperature anomalies and associated mortality. We test the hypothesis that social media mining can be used to identify heat wave mortality. Applying the approach to India, we find that the number of heat-related tweets correlates with heat-related mortality much better than traditional climate-based indicators, especially at larger scales, which identify many heat wave days that do not lead to excess mortality. We conclude that social media based heat wave identification can complement climatic data and can be used to: (1) study heat wave impacts at large scales or in developing countries, where mortality data are difficult to obtain and uncertain, and (2) to track dangerous heat wave events in real time.

Keywords: heatwave; heatwave definition; Twitter mining; social media

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2. Cecinati, F., Matthews, T., Natarajan, S., McCullen, N., & Coley, D. (2019). Mining social media to identify heat waves. International journal of environmental research and public health, 16(5), 762.

Abstract

Modern buildings are operationally classified as fully naturally ventilated (free running, FR), fully mechanically ventilated and conditioned (air-conditioned, AC) or intermediary (mixed mode, MM). Each strategy implies (i) the selection of different internal comfort models and controls, e.g. adaptive thermal comfort + operable windows in FR and static thermal comfort (Predicted Mean Vote - PMV) + non-operable windows in AC, and (ii) different energy consumption and carbon emissions with FR being the least (zero) and AC being the most. In each instance, the choice of strategy is dictated by the designer with little choice for the occupants. Here we ask the question: what operational mode would occupants select, given complete freedom? We examine this question using real concurrent data from three offices of similar size and use. In each, occupants have complete freedom in adopting FR, AC or a series of intervening MM strategies. We use monitored data on window and air-conditioning operation combined with internal and external thermal conditions to create validated computer models for each office. We discover the true operational mode of each office by comparing the computer model against 23 different scenarios using Dynamic Time Warping for binary (window open/close, AC on/off) and Euclidean distance for continuous operative temperature time series. Strikingly, results demonstrate that while each office used divergent strategies across the seasons, the indoor conditions were very similar and attainable through NV alone. This suggests that while a purely NV strategy is likely to deliver indoor thermal comfort, understanding occupant motivation and educating them on the impact of AC operation is needed to minimise energy use.

Original language: English, Pages (from-to): 1-18, Number of pages: 18, Journal: Energy for Sustainable Development, Volume: 56, Early online date: 10 Mar 2020, Publication status: Published - 1 Jun 2020

Keywords: Mixed-mode ventilationOccupant behaviourOffice buildingThermal comfort

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3. Neves, L. O., Hopes, A. P., Chung, W. J., & Natarajan, S. (2020). “Mind reading” building operation behaviour. Energy for Sustainable Development, 56, 1-18.

Abstract

The Global South, much of it in warm tropical latitudes, is expected to double its total energy demand by 2050. In addition to increased mean demand, greater demand for space cooling during external temperature peaks will exacerbate the strain on already fragile energy networks. Recent anecdotal evidence that a proportion of the increase in cooling demand is driven by cold—rather than warm—indoor thermal discomfort, suggests the imposition of an unnecessary cooling energy cost. Here, we investigate the impact of this cost on the expanding Global South using field data from four cities in India, Philippines, and Thailand. We observe that mean cold discomfort across the four cities is roughly 45 percentage points higher than warm discomfort, suggesting warmer indoor temperatures would not only lower overall discomfort but also reduce cooling energy demand. Computer simulations using a calibrated building model reveal that average savings of 10%/Kelvin and peak reductions of 3%–19%, would be feasible across the expected external temperature range in these cities. This suggests that more climatically appropriate indoor thermal comfort standards in the Global South would not only significantly counteract the expected rise in energy demand, but also produce more comfortable indoor conditions and reduce peak demand. View Full-Text

Keywords: building energy; thermal comfort; global south; cold thermal discomfort; building overcooling

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4. Alnuaimi, A. N., & Natarajan, S. (2020). The Energy Cost of Cold Thermal Discomfort in the Global South. Buildings, 10(5), 93.

Abstract

Optimization results for thermal interaction of a double U-tube borehole heat exchanger (BHE) used along with a 5 ton capacity ground source heat pump system (GSHP), are discussed in this paper. Heat transfer from the BHE is computed using thermal resistance concept for space cooling and heating mode operations. The main objective of optimization is to achieve maximum heat extraction during space heating and maximum heat rejection during space cooling operations. For the purpose of optimization, eight control variables consisting of geometric parameters, thermo-physical parameters and mass flow rate are considered at three levels for a series connected double U-tube BHE of 120 m depth. For Taguchi method L27 orthogonal array has been employed for the computation of heat transfer and S/N ratios for both modes of operations. Results obtained show that optimum values of 9270 W and 7210 W heat can be rejected to and extracted from the ground. Taguchi results are combined to obtain a single set of optimum levels of control variables using the utility concept. Mass flow rate of water in the BHE is found to be the most influential variable. For variation in the duration of cooling and heating mode operations, the optimum heat that could be rejected and absorbed becomes the same and equal to 6180 W for equal duration. It is observed that the heat transfer calculated from the utility concept is 11.11% and 42.86% less than those values calculated by Taguchi method for cooling and heating mode of operations respectively.

Keywords: Double U-tube borehole heat exchangerGround source heat pump systemOptimization of heat transferSpace cooling and heating applicationsTaguchi methodUtility concept

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5. Kumar, S., Murugesan, K., 2020. Optimization of geothermal interaction of a double U-tube borehole heat exchanger for space heating and cooling applications using Taguchi method and utility concept. Geothermics 83, 101723. doi.org/10.1016/j.geothermics.2019.101723.

Abstract

This article elucidates a real-time energy management strategy for a smart residential apartment building having nonidentical occupants at the dwelling units (DUs). The aim of the present article is to design a distributed energy management algorithm, which can optimize the real-time demand of the entire building against abruptly updated rooftop solar generation and real-time price (RTP) of energy. The proposed energy management strategy differentiates among the DUs by considering a new parameter named load criticality level, which is defined as the value imposed by the DU residents to their power consumption. The optimization portfolio is developed as a novel bilevel, stochastic, multiobjective optimization problem where the maximization of utility of the consumed power is considered simultaneously with the cost minimization. To this end, a virtual energy trading platform is designed in this article between central building management system and the DUs, where they interact with each other by following the directives of single-leader multifollower Stackelberg game. The solution strategy is proposed as a Lyapunov optimization, which needs only the current values of the uncertain parameters, such as load variation, renewable generation, and energy price, and do not require any knowledge about their probabilistic variation, to eliminate the complexities regarding time average stochastic equations. Strenuous simulation on real-time data of four DUs, it is proved that the proposed framework can track the abrupt change in RTP and solar generation efficiently. Comparing with two benchmark methods viz. centralized process and greedy algorithm, the superiority of the designed energy management portfolio is established.

Publication Link

6. S. Paul and N. P. Padhy, "Real-Time Bilevel Energy Management of Smart Residential Apartment Building," in IEEE Transactions on Industrial Informatics, vol. 16, no. 6, pp. 3708-3720, June 2020.

Abstract

Conjoint participation of wind generation with conventional power plant, necessitate wind-farms to participate in automatic generation control(AGC) for frequency regulation. This implicates wind farms operator to monitor commands received from the transmission system operator(TSO). Consequently, advanced control techniques are deployed, which assuredly helps in power tracking, but increases pitch angle controller dynamics. This has resulted in mechanical stress on equipment involved. In order to improve wind-farms response, a synergistic frequency regulation control mechanism(SFRCM) is proposed by the authors. The scheme considers the response time and reserve availability depending on forecasted wind data and also examine load curve pattern to obtain the reference signal for the wind-farm controllers. The work provides a distinct solution to address the following: 1) Optimal pitch dynamics regulated operating point tracking with revised-pitch angle control(R-PAC), 2) Maximization of rotational kinetic energy viz attuned-rotor speed control(A-RSC), to increase stored kinetic energy in the rotor. Case studies at constant and variable wind speed are presented to show the effectiveness of proposed algorithm. To test robustness of the technique, transient operation is also conducted. The simulations, performed in the real time environment, depict the fulfillment of the above objective in an efficient manner compared with other conventional approaches.

Keywords: Rotors, Wind forecasting, Frequency control, Wind speed, Wind farms, Wind turbines, StressPublication Link

7. R. Prasad and N. P. Padhy, "Synergistic Frequency Regulation Control Mechanism for DFIG Wind Turbines with Optimal Pitch Dynamics," in IEEE Transactions on Power Systems.

Abstract

An increase in the utilization of renewable energy has called for a cost-effective and reliable solutions to overcome their intermittency. With this regard, this paper offers a unique way of interfacing dc microgrid (DCMG) to the doubly fed induction generator (DFIG) wind system during grid-connected, fault, and isolated working conditions making it economical. The control flow strategy proposed here uses the grid-side converter (GSC) of the DFIG system to serve multiple purposes; first, the GSC is used to regulate the DCMG voltage during the grid-connected mode and avoids the need for an additional converter for the DCMG to connect it to the grid. Second, the GSC is allowed to function as a simple diode bridge rectifier thereby allowing the DFIG machine to feed DCMG during isolated conditions hence avoiding the need for replacing the converter. This paper also improves the fault ride through performance of the DFIG wind system without any additional investment. This is possible due to the usage of already available ultracapacitor in the DCMG. Hence, the DFIG wind system need not have to finance separately to protect its dc link during the fault. Furthermore, a small-signal-based stability analysis performed also indicates the robustness of the proposed control strategy. A 2.2-kW hardware prototype has been developed and the results obtained from the elaborate experimentation justify that this paper is economical, efficient, reliable, and offers better power quality compared to the existing work.

Publication Link

8. M. V. Gururaj and N. P. Padhy, "A Cost-Effective Single Architecture to Operate DC Microgrid Interfaced DFIG Wind System During Grid-Connected, Fault, and Isolated Conditions," in IEEE Transactions on Industrial Informatics, vol. 16, no. 2, pp. 922-934, Feb. 2020.

Abstract

Currently, in the literature, the slow responding device like on-load tap changer transformer (OLTC) is better operated by introducing the time delay in the operation of fast-acting converters. Although the literature also indicates an improvement in the transient condition, it keeps the converters idle during the waiting period. Henceforth, there is a lot of scope for improving the reactive power reserve. In this article, we propose a coordinated voltage control (CVC) scheme that employs a unique approach where the converters are allowed to absorb reactive power (of a specific voltage range from the grid) during the waiting period. A modified IEEE 33-bus distribution system is modeled in the real-time digital simulator platform and the simulation results are compared with the existing and without CVC schemes. The simulation results justify the effectiveness of the proposed CVC scheme in terms of improving the reactive power reserve and voltage profile up to 100%/164% and 0.0093 pu/0.014 pu against existing/without CVC scheme, respectively. Furthermore, the postfault voltage recovery time in the case of proposed CVC is decreased by 20 ms/28 ms with respect to the existing/without CVC schemes. These results imply that the proposed CVC scheme performs better in all the operating conditions of the grid.

Publication Link

9. M. V. Gururaj and N. P. Padhy, "An Improvized Coordinated Voltage Control Scheme for Better Utilization of Regulating Devices During Various Operating Conditions of a Distribution System," in IEEE Systems Journal (Accepted for publication)

Abstract

In the literature, the fault ride through (FRT) studies of the doubly fed induction generator (DFIG)-based wind system consider fault to occur after the fault current limiter (FCL) with respect to the DFIG system. In this article, the fault is considered before FCL and the power hardware in the loop (PHIL) experimentation is performed. Results demonstrate that the occurrence of the fault before FCL can worsen the FRT of the DFIG system. To address this, a novel arrangement of FCL with four power electronic switches in a particular fashion has been suggested. This arrangement allows the perception of fault occurring before FCL as after FCL due to the alternate path of power flow thereby improving the FRT of the DFIG. Furthermore, a quick fault detection and switching technique has been developed which is able to detect the fault by comparing the instantaneous value of the phase current with the threshold. Thereby, it is possible to achieve on/off of the switches upon the fault occurrence with negligible time delay. In order to validate the effectiveness of the proposed technique, the PHIL experimentation is performed at sub/supersynchronous mode of operations (±0.1 slip), different fault resistances (6, 20 Ω), delay time (40 ms), and various fault perception instants (negative, zero, positive). The results justify the effectiveness of the proposed arrangement in improving FRT of the DFIG when a fault occurs before the FCL with respect to the DFIG in comparison to the existing literature and in the absence of FCL in the system.

Publication Link

10. M.V Gururaj and N. P. Padhy, "PHIL Experimentation on Fault Ride Through Behavior of Doubly Fed Induction Generator Based Wind System in the Presence of Fault Current Limiter," in IEEE Transactions on Industry Applications (Accepted for publication).

Abstract

Globally climate change driven thermal severity has resulted in increased demand for comfort conditioning. Buildings which are designed to the present day scenarios are subject to performance variations in such contexts. It is essential to establish the impact of climate change severity on building energy demand not only in terms of its amplitude but also the periodicity. This study investigates the impact of climate severity on a mid-size office building located in a composite climate of India (New Delhi). The study has the following objectives (a) to map the impact of climate change based on the magnitude and temporal variations of climate variables (b) to establish the effect of climate change on the energy use of a mid-size office building and (c) to delineate design strategies for climate change resilient building envelope. The weather data used in the simulations is made available by ISHRAE for the year 1990 and is morphed for the years 2020 and 2050 using the climate change world weather file generator. This tool uses IPCC TAR model summary data of the HadCM3 A2 experiment ensemble. A statistical analysis of climate variables is carried out to map the magnitude and temporal variation between the years 1990, 2020 and 2050. An energy model of the building was developed for simulations and the results are validated with the actual energy data of the building. The building was found to experience reduction in heating load and increased cooling load in a climate change scenario. Further analysis of periodicity reveals that there is significant increase in cooling demand in the pre-summer and post-summer durations. The study concludes with a set of interventions so as to maintain the current-day energy demand in the future scenario.

Keywords: Climate change, energy demand, Thermal severity, Energy efficiency

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11. Chinmay Jhaa, Shweta Lalla, E. Rajasekar, Impact of Climate Change on Energy Demand of a Mid-Rise Office Building

Abstract

Abstract: The case study deals with outdoor thermal comfort assessment focusing on metabolic rates of pedestrians and its impact on walkability. The objectives of the paper are to (a) evaluate the impact of metabolic rates on outdoor thermal comfort of pedestrians, (b) establish the impact of thermal comfort on walkability. The paper is based on experimental field measurements of thermal comfort and subjective surveys with pedestrians in a multi-modal hub in Delhi, India which represents a humid subtropical climate. Resting metabolic rate test and cardiorespiratory fitness test is performed on subjects followed by measurement of oxygen consumption and heart rate for a designated set of pedestrian routes. Metabolic rates are estimated as per ISO: 8996-2004. A total of 18 subjects volunteered for the experiments. The subjects wore the portable metabolic analyser and registered sequential thermal responses at designated locations as well as time intervals during the survey. The paper presents the distribution of metabolic rates through the walking sequence and highlights the variation between standard metabolic rates in published literature. The change in comfort response with respect to various walking sequences and speeds are discussed. The paper summarizes the allowable walking distances for a given threshold of thermal comfort.

Keywords: Walkability, Metabolic rate, Indirect calorimetry, Outdoor environments

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12. Anand, V., Devi, S., & Rajasekar, E. (2020). Effect of metabolic rates on walkability in outdoor environments: A case study. In S. Roaf, F. Nicol, & W. Finlayson (Eds.), Proceedings of 11th Windsor Conference: Resilient Comfort (pp. 401–410).

Abstract

This paper deals with the effect of intra-climate diversity of composite climatic zone of India on the thermal performance of the naturally ventilated public housing buildings. This study is an attempt to improve the accuracy of the existing prescriptive benchmarks.The study has two objectives (a) to analyse the thermal severity variation within the composite climate of India and develop a tiered stratification of locations (b) analyse the impact of the thermal severity variation on the performance of representative public housing projects. The scope of the studyis limited to naturally ventilated residential typology.Data for 162 locations were obtained from the IndianMeteorological Department(IMD) and statistically analysed in order to classify them based on thermal severities. A review of housing designs of low-incomegroup housing being implemented by governmental agencies was reviewed and three representative designsare selected. A short-term thermal performance monitoring is conducted in these residences. The data is used to compare the thermal performance variations as well as to face validate the virtual models developed in Energy Plus software tool. The buildings are simulated for their performance at locations with high, moderate and low thermal severities within a compositeclimate zone. A comparative analysis is carried out with that of NBC prescribed thermal performance guidelines. A set of scaling factors isdetermined after performing local thermal optimizations at representative locations. The factors are validated with location-specificsimulations performed for other locations.

Keywords: Climate diversity, Composite Climate, ThermalPerformance Index, Thermal Damping, Tropical Summer Index.

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13. Gupta, V., Upadhyay, K., Rajasekar, E. & Kumar A. (2018). Effect of Intra-climatic Variation in Thermal Performance of Public Housing in a Composite Climate of India . In Edward Ng, Square Fong, Chao Ren (Eds.), Proceedings of 34th International Conference on Passive and Low Energy Architecture (pp. 439–444).

Abstract

This study deals with the effect of physiological thermoregulation of the human body at extreme cold thermal condition. It consists of effect of metabolic activity on thermoregulation of the human body, Effect of environmental parameters on the human body. Study focused on extreme cold climate where metabolic activity done on treadmill is analysed. For this Climate chamber have been used where any controlled environment can be created. Project consist of subjective and objective analysis. Effect of cold temperature on the human body was analysed and found hand and foot are cooler than other body parts in an extreme cold environment. Effect of activity on human body was investigated and found during running foot, and hand temperature decreases. Subjective responses were analysed based on individual thermal sensation voted of the subjects. Regression line is drawn between thermal sensation votes and different set point temperature and found neutral temperature.

Publication Link

14. Das S., Upadhyay, K., Subudhi S. & Rajasekar, E. (2019). Study of Physiological Thermoregulation of the Human Body at Extreme Temperature . ISBN: 978-1-56700-496-0 (Eds.), Proceedings of 25th National and 3rd International Conference ISHMT-ASFTE Heat and Mass Transfer (IHMTC-2019) (pp. 931–936).