The establishment of design criteria for precision ventilation in open-plan offices

Precision ventilation is used in open-plan offices to establish micro-climate zones according to the metabolic requirements of its occupants. The aim of this study is to determine design criteria and highlight the opportunities and limitations for precision ventilation in large-scale offices. The simulations and experiments were conducted under steady state conditions with fixed airflow from all active chilled beams (ACBs) and constant room temperatures. A temperature difference of 3.5K was maintained between supply and room air in all cases with and without occupants. Results showed that precision ventilation can simultaneously establish low-level (<0.15 m/s), medium-level (<0.45 m/s), and high-level (<0.65 m/s) air velocity zones in the same shared office space such that occupants with different metabolic rates had Predicted Mean Vote (PMV) values maintained within the acceptable limit. The establishment of a single air velocity zone in an open-plan office layout without influencing air velocities of other zones was achieved by lowering the airflow rates of two ACBs by 35%. The vertical and horizontal temperature uniformity was maintained with this precision ventilation system with draught rates of less than 20% for occupants with normal metabolic rates. Comparative analysis using precision ventilation with and without occupants showed that targeted air velocity distribution in the room can be negatively influenced by the absence of any heat sources in any zone. An annual energy saving of up to 15% was achieved by raising the cooling setpoint temperature from 23 °C to 25 °C.