What Should the Minimum Ventilation Rate Be in a Demand-Controlled Ventilation Strategy?

Abstract

Demand-Controlled Ventilation is emerging as a dominant ventilation strategy in non-residential buildings in Norway. The ventilation airflow rate is controlled between pre-set minimum (Vmin) and maximum (Vmax) values, based on the signal from room-sensors. The choice of Vmax is based on current knowledge about necessary airflow rate to reach an acceptable IAQ (indoor air quality) with maximum likely personal load and emission load from building materials. The choice of Vmin has an obvious impact on energy use, but there are few studies about its impact on IAQ. Vmin varies typically from 0.7 to above 2 (l/s)/m2 in Norway. In several buildings, Vmin is set to the upper range of this interval due to technical limitations of the specific equipment used. We have performed blind cross over intervention-studies with an untrained test panel to evaluate PAQ (perceived air quality) when entering 20 PAQ-rooms. All the rooms have low-emitting building materials, but extra pollution sources were introduced in some of the rooms for this study. Supplementary, intervention studies were performed in a dedicated test room to assess the impact of airflow rate on PAQ, performance and well-being during the first 20 min of occupation. We found that increasing Vmin has a significant positive impact on PAQ in rooms with extra pollution sources. This effect was not consistently present in the low-emitting rooms. Airflow rates did not noticeably affect PAQ, performance and well-being during the first 20 min of occupation. This indicates that Vmin above 1 (l/s)/m2 has limited benefit to IAQ in low emitting rooms.