The effect of draught on performance, comfort and stress – a laboratory study

Thermal environment affects occupants’ work performance and well-being. Office workers’ complaints regarding thermal environment are often related to either too warm room temperature or draught. Efficiency demands have increased the heat loads in offices, and increased cooling is needed to control the room air temperature. Draught problems occurs typically in these situations when the workstation is located in the downfall area of the inlet jet. 
The aim of this study was to examine the effect of draught on work performance, comfort, and stress in an office laboratory simulating a draughty situation caused by downfall of colliding jets from the chilled beams. The study had a repeated measures design with two conditions: condition A (temperature T=23 °C, target air speed v<0.1m/s, supply airflow Q= 30 l/s) and condition B (temperature T=23 °C, target air speed v=0.4m/s, supply airflow Q= 70 l/s). Thirty-one volunteer university students participated in the experiment. The session lasted altogether 2.5 hours including practice phase and both test condition phases. Thermal comfort, perception of air movement, symptoms, self-estimated work performance and workload were assessed with questionnaires. Work performance was measured with the N-back task and stress effects were studied with heart rate variability. 
Condition had a significant effect on thermal comfort. Thermal sensation vote was cooler in condition B and more participants reported to be dissatisfied with the thermal environment in condition B. Majority of participants reported that air movement in condition B was unpleasant and 82% would have preferred less air movement. Draught also disturbed and annoyed more in condition B. No differences were found on self-estimated work performance, workload, symptoms, or perceived fatigue. The effects of draught were mainly seen in subjective responses. However, condition had also an effect on work performance and stress. Special attention should be given for reducing draught in offices