CH-24-C047 - Micro-Zonal Occupant Centric Control: Protocols for Improving Air Distribution, Thermal Comfort and Energy Efficiency in Open-Plan Offices

Air-conditioning systems consume the maximum energy in buildings. This can be reduced by air-conditioning only the occupied regions. Though occupancybased smart controllers are available, they are mostly employed for physically separated HVAC zones. With surge in open-plan offices with flexible seat allocation and work hours, there is a need to improve zone level control of HVAC systems to allow diffuser level control. Micro-zonal occupant centric control (MZOCC), that conditions only the occupied virtual zones save energy, improves air distribution and thermal comfort, and requires only 5%-6% additional investment. Nonetheless, unplanned MZOCC can lead to poor air distribution, heavy thermal gradients, and draft discomfort. This can be addressed by developing a set of protocols or rules for employing MZOCC. Previous studies discuss the need for a bi-level framework for MZOCC, where the first level optimizes micro-zonal planning and second optimizes airflow control. The aim of this study is to explore considerations in framing the second level of protocols which focus on airflow control. Important factors affecting air movement under MZOCC are gathered from literature. Further, 30 office staff are surveyed to understand their occupant behavior and duration of absence from assigned workspaces. Airflow control for each micro-zone is to be planned by analyzing the thermal interaction between micro-zones. This requires detailed analysis of air distribution and is performed using CFD. Results indicate that parameters that influence choice of airflow control are static parameters such as (1) size and design of diffusers (2) air supply temperature and velocity, (3) distance between diffusers, (4) distance between diffusers and walls, (5) nature and location of heat sources, (6) size and shape of objects such as furniture, partitions etc. and transient parameters such as (1) occupancy schedule, (2) weather conditions and (3) inter-micro-zonal interactions. Unoccupied micro-zones are to be maintained with a setback temperature (high setpoint temperature) and a setback flow (low velocity airflow) to avoid thermal discomfort. The study identifies three rules that can be included in the protocols for airflow control. The study also demonstrates how micro-zones earlier designed using first level of protocols can be improved using rules developed for the second level. A simulation-based case-study is performed in an open-plan office to analyze energy savings and it is observed that planned MZOCC can reduce about 60% energy compared to zone level conditioning. Thus, the study establishes the effectiveness of protocols for MZOCC and shows the advantages for employing airflow control in MZOCC to improve air distribution, thermal comfort, and energy efficiency.