Precision Ventilation in an Open-Plan Office: A New Application of Active Chilled Beam (ACB) with a JetCone Feature

Abstract

Mixing ventilation systems effectively improves thermal comfort in open-spaces due to adequate turbulent mixing of the cold stream with ambient air. This study introduces the concept of precision ventilation for achieving local thermal comfort in a mixing ventilation system. This precision ventilation system provides asymmetrical airflows from an active chilled beam (ACB) to each of the office occupants. These ACBs provide air velocities with different magnitudes and directions. To achieve different magnitudes and directions, JetCones are used to vary the airflow in different parts of the ACB. The performance of the precision ventilation system was analyzed using full-scale laboratory experiments and computational fluid dynamic (CFD) simulations. The full-scale laboratory experiments were conducted in a 4.2 m × 3 m × 2.8 m (L × W × H) thermal isolated room with an open-plan dual desk-chair setup. The jet-cones in the ACB unit were adjusted to throw the required amount of flow to the occupants. The occupants had different metabolic rates of 1.2, 1.4, and 1.6 in a warm office space. The room set point temperatures varied between 23 and 26 °C. The experimental and CFD results show that occupants facing symmetrical airflow distribution and with a constant 1.2 metabolic rate had a similar PMV index. The occupants with 1.2, 1.4, and 1.6 metabolic rate were exposed to asymmetrical airflows, i.e., 30%, 58%, and 70% of the total airflow. Occupants with higher metabolic rates were kept thermally neutral, in the −0.5 to +0.5 PMV range, by increasing the air velocity and room temperature to 0.4 m/s and 25 °C, respectively.

Precision Ventilation for an Open-Plan Office: A Study of Variable Jet Interaction between Two Active Chilled Beams

“…Previous studies have shown that a local air velocity range up to 1.2 m/s is considered acceptable by raising room temperatures up to 28 • C during experiments [43,45]. In the previous study on precision ventilation [30], single ACBs established high velocity zones by pushing more airflow towards the targeted zones. The airflow along the ceiling and walls reached the occupied zone for creating micro-climate zones in the dual desk-chair setup.…”

“…The grid independence test was carried out and tetrahedral meshes were generated in the entire computational domain with a 3.67 million element size (see Appendix A). The RNG k-ε turbulence model along with a similar setup (solver, boundary conditions, and numerical algorithm) was applied according to previous studies on precision ventilation [30,[34][35][36]. In simulations, the geometry of the ACBs was made circular in order to have radial flow and 50 L/s airflow (sum of primary and secondary airflows) produced from each ACB unit.…”

“…Precision ventilation [30] involves advantages of both mixing ventilation and personalized ventilation to achieve individual thermal comfort. Precision ventilation is achieved by using ACBs (with JetCones) which can direct airflow in different directions along the ceiling.…”

“…This use of ACBs eliminates the need for multiple air terminal devices around a single workstation in order to achieve individual thermal comfort [23]. In our previous study [30], precision ventilation achieved individual thermal comfort for a dual desk-chair setup by directing more airflow towards occupants with higher air velocity needs (metabolic rates). This paper expands the previous work by including an experimental and a CFD study in order to achieve precision ventilation by using the variable jet interaction between two ACBs as part of larger open plan offices, i.e., four-desk-chair setup.…”

Precision Ventilation in Open-Plan Offices: A Study of Variable Jet Interaction Between Active Chilled Beams

“…Figure 12: ACBs with a JetCone feature showing asymmetrical airflow distribution (adapted from [214], [215])…”