Research 

Doctoral Research

under  

Prime Ministers Research Fellowship (PMRF), Government of India

Under the joint guidance of Prof.Debapratim Pandit and Prof. Joy Sen at IIT-KGP

Micro-Zonal Occupant-Centric Control (MZOCC): A novel method to reduce air-conditioning energy consumption

Soaring global energy demands and an increase in carbon dioxide emissions have always been a threat to future development. The buildings and construction sectors together contribute to 41% of global energy consumption. Also, 80% of the energy cost is during the operational phase of the building. Air conditioning contributes to more than 50% of the operational energy consumption. More than 50% of building energy consumption is during non-working hours, which indicates energy wastage. The previous decade saw an increasing demand by users to improve comfort conditions, whilst reducing energy consumption and CO2 emissions. Occupant-centric control (OCC) is one method of smart conditioning. Currently, OCC is designed to function at thermal zones (spaces with uniform thermal conditions) and mostly the finest thermal zone is a room. The research aims at extending OCC to large spaces with multiple users, considering the spatial location and activity of the user.  The research developed MZOCC as a means to create virtual 'micro-zones' of comfort within large thermal zones. Working conditions of 40+ varieties of open-plan offices in India were studied, and airflow patterns were analysed using CFD to develop an IoT-based smart control to prioritise cooling around occupants, leading to 60% energy savings and enhanced thermal comfort. 

Highlights: 

1. Two patents on  MZOCC

2. Seven journal articles published in top journals

3. Presented at seven international conferences, including ASHRAE and ACM conferences

4. Selected among top 50 PMRF works

Journal Publications 

Journal Article 1

Jeslu Celine Jacob, Debapratim Pandit & Joy Sen (2022) An explorative study on transient cooling pattern and energy efficiency while using micro-zonal occupant-centric control, Architectural Engineering and Design Management, DOI: 10.1080/17452007.2022.2049439

Abstract: 

Virtually dividing thermal zones into micro-zones and conditioning them using occupant-centric control (OCC) has emerged as a significant method in reducing cooling energy. Hence, the need arises to study time-sensitive thermal behaviour within micro-zones under OCC as thermal coupling from adjacent micro-zones significantly influences cooling patterns. This will explain possible variations in cooling time and energy consumption under different occupancies and aid in analysing the feasibility of micro-zoning as an efficient strategy. This study aims at exploring the key parameters that influence cooling patterns under micro-zonal OCC. Effects of four factors, namely indoor ambient temperature, supply air velocity, thermostat location and occupancy are explored using validated transient state CFD simulations for a hypothetical open-plan office. Results indicate that compared to zone conditioning, micro-zonal OCC can reduce about 20%–70% overall cooling energy while maintaining setpoint conditions and show the following three patterns: rate of cooling in occupied micro-zones decreases as they start to cool unoccupied zones through thermal coupling; supply air velocity and ambient temperature impact thermal coupling and the size of a chosen micro-zone influences energy load. This study is the first attempt at transient exploration of thermal developments within micro-zones under the influence of relevant parameters and is a necessary precursor to experimental studies on micro-zonal OCC. 

Journal Article 2: 

J. C. Jacob, D. Pandit, and J. Sen, “Energy-saving potential in Indian open-plan offices using Micro-Zonal Occupant Centric Control (MZOCC),” Energy Build., vol. 282, p. 112799, Mar. 2023, doi: 10.1016/J.ENBUILD.2023.112799. 

Abstract: 

HVAC energy consumption can be reduced by air-conditioning only the regions which are occupied. Though occupancy-based smart controllers are common in this regard, they are mostly used for physically separated HVAC zones. Only limited studies have explored localized conditioning within HVAC zones. Micro-zonal occupant-centric control (MZOCC) aims at maintaining a target air temperature only in the virtual micro-zones where occupants are present, leaving other regions unconditioned. There is a need to understand the potential of MZOCC in terms of investment and energy savings and develop strategies for improving it. This study addresses these research gaps by exploring MZOCC in a typical Indian open-plan office using an experimentally validated CFD model. Cooling pattern, energy consumption and thermal contours for varying (1) diffuser arrangement, (2) airflow control, and (3) occupancy conditions are explored.

The study’s key findings are (1) MZOCC induces substantial energy savings at minimal additional investment; (2) Strategizing diffuser location and airflow control are required to avoid merging of air jets and heavy thermal gradients; (3) Using a low-velocity flow (setback-flow) or maintaining a higher setpoint temperature (setback-temperature) in unoccupied micro-zones improves the efficiency of MZOCC. This study extends the literature on MZOCC by addressing operational challenges in MZOCC.

Journal Article 3: 

Jacob, J. C., Pandit, D., & Sen, J. (2024). Developing a validated simulation model of micro-zonal air-conditioning to evaluate thermal comfort parameters. Architectural Engineering and Design Management, 1–26. https://doi.org/10.1080/17452007.2024.2319756 

Abstract: 

Micro-Zonal Occupant-Centric Control (MZOCC) helps in reducing building energy consumption by conditioning only the occupied regions in a room. For this, MZOCC divides a large room such as open-plan offices into virtual micro-zones to allow independent diffuser level control. But, unplanned MZOCC can lead to heavy thermal gradients and deflection of air jets, leading to thermal discomfort. To evaluate thermal comfort at different regions of a room under MZOCC, there is a need to accurately model parameters of thermal comfort. Field studies, exploring the transient variations in air temperature, humidity and velocity at different regions of the room due to MZOCC, are limited. At the same time, developing validated simulation models or digital twins using experimental data helps in exploring micro-zonal strategies to arrive at the best strategy. The aim of this study is to create a digital twin of an open-plan office and model the parameters required to estimate thermal comfort. This study senses transient variations in air temperature, velocity and humidity using a wireless sensor network and develops a computational fluid dynamic (CFD) model that can accurately model the sensed transient variations. Field data, constituting external surface temperatures captured using thermal images, variations in air-conditioning control strategy, dynamic occupancy and location, are periodically updated in the digital twin. The CFD model accurately predicts the trends in variations in indoor temperature, velocity and humidity at different regions of the room. The developed digital twin can be used in future studies to evaluate thermal comfort and plan MZOCC control strategies. 

Journal Article 4: 

Jeslu Celine Jacob, Debapratim Pandit, Joy Sen (2024), Investigating enhanced thermal comfort and energy efficiency through strategized airflow in Micro-Zonal Occupant-Centric Control (MZOCC), Energy and Buildings, Volume 318, 2024, 114497, ISSN 0378-7788, https://doi.org/10.1016/j.enbuild.2024.114497. 

Abstract: 

The potential of Micro-Zonal Occupant Centric Control (MZOCC) to save HVAC energy consumption in medium sized open-plan offices has been established in literature. This is done by virtually dividing a thermal zone into micro-zones and allowing independent diffuser-level control in each micro-zone when the micro-zone is occupied. In continuation, there is a need to ensure that thermal comfort is achieved within micro-zones under such localised control. This is important because several forms of discomfort such as draft, horizontal thermal asymmetry and vertical thermal gradients may arise in MZOCC. Further, the effect of MZOCC airflow control strategies, such as setback flow and setback temperature, which were proposed in previous studies on thermal comfort of occupants needs to be evaluated. In an attempt to address these research gaps, this study explores thermal comfort for different scenarios of diffuser arrangements, airflow control strategies and occupancy conditions and also explores the effect of varying supply velocities used in setback flow and setpoint temperatures used as setback temperatures on air distribution and thermal comfort.

Results show that low PMV values, increased draft discomfort and heavy thermal gradients are observed for certain scenarios of MZOCC. Tuning airflow control by choosing appropriate setback flow or setback temperature helps in restoring thermal comfort. As different forms of discomfort are observed in different cases, it is important to plan micro-zones and control airflow, such that, MZOCC does not violate thermal comfort criteria while optimising energy efficiency. This study gives a framework for selecting appropriate airflow control strategies for a selected diffuser arrangement for a given occupancy condition. Comfort-based MZOCC that uses appropriate airflow control strategy saves about 60% energy when the zone is half occupied and about 85% energy when the zone is quarter occupied. Results also show that, improving the diffuser arrangement improves energy savings and increases the options of airflow control strategies that can be used. Also, different airflow control strategies behave differently for each diffuser arrangement and has to be chosen separately for given diffuser setting and occupancy condition.

Journal Article 5

Jacob, J.C., Pandit, D. & Sen, J. Protocols for planning micro-zones to facilitate occupant-centric control (OCC) to reduce HVAC energy consumption in Indian open-plan offices. Energy Efficiency 17, 92 (2024). https://doi.org/10.1007/s12053-024-10271-4 

Abstract 

Micro-Zonal Occupant-Centric Control (MZOCC) saves HVAC energy by creating comfortable virtual micro-zones around occupants and controlling diffusers using occupant centric control (OCC). This is needed in modern open-plan offices with flexible work schedules to avoid energy wasted in air-conditioning unoccupied regions. Despite this, there is no clarity yet on how micro-zones are to be planned within thermal zones. There exist knowledge gaps between established methods of thermal zoning for HVAC design and micro-zoning. Several temporal and spatial factors influence the transient thermal exchanges between virtual micro-zones which increases the complexity of micro-zoning. This study develops protocols for micro-zoning to simplify the process of MZOCC. The study first outlines factors critical in micro-zoning open-plan offices which are identified from literature and survey of Indian offices. Results indicate that Indian open-plan offices are diverse and caters to a variety of activities within each thermal zone. Occupancy survey shows that office spaces are partially occupied, most of the time. The second part delineates protocols for micro-zoning following assumptions derived from literature and survey data. In the third stage, these protocols are used to shortlist the best micro-zonal layouts for MZOCC from numerous possible layouts. The effectiveness of the protocols is confirmed using CFD simulations where it is observed that the shortlisted layouts perform better than others. These layouts act as a starting point, on which airflow control can be strategized to further improve MZOCC. Results also show that planned MZOCC saves 73% energy compared to zone level OCC.

Journal Article 6

Jeslu Celine Jacob, Debapratim Pandit & Joy Sen, A case study exploring the influence of diffuser arrangement on air-distribution using field experiments and CFD simulations, Journal of Architectural Engineering, ASCE, 10.1061/JAEIED/AEENG-1832 

Abstract: 

Air distribution design plays a critical role in reducing HVAC energy consumption. Previous studies have suggested that placing supply and return diffusers very close to each other in overhead air-conditioning systems can lead to the immediate loss of cool air through the return diffusers without conditioning the air of the occupied region. There is a research gap in experimentally validating the same. Therefore, we performed a case study in the conference room of an office building in India using sensor readings and computational fluid dynamics (CFD) simulations to explore how the relative distance between diffusers influenced the air distribution in a zone and to suggest methods for rearranging the diffusers to improve the air distribution. Our experimental results showed that the air temperature at the return diffusers was lower than in the occupied region, which highlights that cool air was exiting through the return vents before effectively cooling the occupied zone. A CFD model of the room was developed and validated using the experimental results. The CFD simulation results showed that the presence of ceiling lights between the supply and return diffusers can delay the escape of cool air by a few minutes, thus slightly improving the air distribution. However, installing ceiling lights between the diffusers cannot be used as a strategy to reduce the loss of cool air through the return diffusers. Placing the diffusers at distances beyond the extent of the dispersion of the air jets from the supply inlets was found to improve the air distribution, and this strategy can be used to reduce the immediate escape of cool air through the return diffusers.

Journal Article 7 

Jeslu Celine Jacob, Debapratim Pandit & Joy Sen, Evaluation of thermal comfort and age of air on employing micro-zonal air-conditioning in an existing open-plan office in India, Science and Technology for the Built Environment. 31(4), 429–465. https://doi.org/10.1080/23744731.2024.2433387 

Abstract

Micro-Zonal Occupant-Centric Control (MZOCC) is an emerging strategy to facilitate localized air-conditioning within large thermal zones. While energy-saving potential of MZOCC is extensively studied, adequate studies have not explored its impact on thermal comfort. Localized air-conditioning can lead to discomfort due thermal gradients, draft, and poor ventilation. This study evaluates thermal comfort, air of age, and ventilation effectiveness in an Indian open-plan office, offering quantitative insights into the effects of MZOCC on thermal comfort. Results indicate that thermal comfort is achieved in micro-zones before reaching setpoint temperature and using setpoint-based control causes over-conditioning. PMV values near the diffusers fall below 0.5; while further away, they exceed 0.5. Percentage of people dissatisfied due draft exceeds 20% in most of the experimented scenarios. In few scenarios, temperature differences between head and ankle reach 5 °C, indicating discomfort from thermal gradients. Cool air jets from diffusers are concentrated at specific regions around the diffusers, causing discomfort from horizontal gradients. Though breathing level has relatively fresh air, air-conditioning the entire zone using only two cassette diffusers results in air stagnation. These findings underscore the difficulty in maintaining thermal comfort under localized cooling methods like MZOCC, suggesting the need for improved air distribution and airflow control

Conferences Publications

1. J.C. Jacob, D. Pandit, J. Sen; Sen, Joy. Reducing HVAC Energy Consumption Through Optimal Sub-Zoning Considering Occupant-Centric Control (OCC). Paper ID: 2141. ASHRAE Beirut 2022 Conference on Efficient Building Design, Beirut, Lebanon October 20-21, 2022 

2. J.C. Jacob, D. Pandit, J. Sen, Reimagining Energy-Efficient Cooling Through Comfort-Based Occupant-centric Micro-zonal Control, ASHRAE Transactions, Volume 129, Part 2, June 2023

3. Jacob, J. C., Pandit, D., Sen, J. (2024). Re-imagining Energy Efficiency in Open-Plan Offices Using Micro-Zonal Occupant Centric Control: Protocols to be Considered. In Proceedings of Energise 2023- Lifestyle, Energy Efficiency, and Climate Action, pp 44–56, Alliance for an Energy Efficient Economy.

4. J.C. Jacob, D. Pandit, J. Sen, A case study exploring micro-zonal occupant centric control (MZOCC) for HVAC energy efficiency, ASHRAE conference papers. Published:2023 November, Number of Pages:12, Product Code(s):D-2023ICERD8-C18.

5. J.C. Jacob, D. Pandit, J. Sen, Micro-zonal Occupant Centric Control: Protocols for Improving Air Distribution, Thermal Comfort and Energy Efficiency in Open-Plan Offices, ASHRAE Transactions, January 2024

6. J.C. Jacob, D. Pandit, J. Sen. 2024. A Machine Learning Approach to Benchmark Thermal Comfort. In Proceedings of the 11th ACM International Conference on Systems for Energy-Efficient Buildings, Cities, and Transportation (BuildSys '24). Association for Computing Machinery, New York, NY, USA, 363–368. https://doi.org/10.1145/3671127.3699676

7. J.C. Jacob, D. Pandit, J. Sen, 2025. Customising Micro-Zonal Occupant-Centric Control (MZOCC) Using Digital Twins to Reduce Energy Consumption: A Case Study in a Working Office in India, ASHRAE Transactions. (Annual conference 2025, Phoenix) 

Patents 

1. A process for Micro-Zonal Occupant-Centric Control (MZOCC) of air conditioning systems in large spaces to reduce building energy consumption. Patent Application No. 202431073728 dated 30-09-2024

2. Smart air conditioning system for air-conditioning only the occupied regions in a thermal zone using advanced airflow control strategies with Micro-Zonal Occupant-Centric Control to reduce air conditioning energy consumption without compromising thermal comfort. Patent Application No. 202431073646 dated 30-09-2024